# User:Lacunae/2

Satellite picture of a European windstorm located near Iceland

European windstorm is a name given to the strongest Extratropical cyclones[1] forming in the Atlantic basin.[2]

are an extreme class of rapidly deepening Extratropical cyclone that produces a disproportionately large social and economic impact as a result of severe surface winds.[3]

there are no definitions set, although 40 metres per second (140 km/h) recurs in the European literature.[4][dubious ]

Has been defined variously as a weather-related air movement of at least force 8 on the Beaufort Scale min. 63 kilometres per hour (39 mph).[5]

They are most common in the winter months however, they can and do form outside this time,[6] some as tropical storms transitioning into extratropical storms. sometimes starting as nor'easters off the New England coast. Storms occur, in general, in north or north-western Europe all year, but in central Europe mainly between November and February.[7]

and frequently track past the north coasts of the British Isles where they typically reach their maximum intensity.[8] . However, when they veer south they can affect almost any country in Europe. Commonly-affected countries include Britain, Ireland, Norway, the Faroe Islands and France, but any country in central, northern and especially western Europe is occasionally struck by such a storm system.

perhaps defined by sting jet.[citation needed]

Deep low pressure areas are relatively common over the North Atlantic, approximately 180 areas of low pressure a year form over the North Atlantic.[9] Typically 70 storms per year form,[10] however most are steered into the Norwegian Sea without hitting populated areas/land.[citation needed]

cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. On average, a winter season sees 2 to 3 major winter storms impact Europe. Average storm lifetime/duration is 2-5 days and duration of storm typically 2 to 6 hours."[9] On average, the month when most windstorms form is January. The seasonal average is 4.6 windstorms.[11]

Since 1970 there have been 70 severe wind storm events resulting in total insured losses of approximately 50 bn USD. The thirteen most severe storm events alone account for nearly 80% (or 40 bn USD, in 2006 prices) of total insured winter storm losses in this period.[12]

"Gales are the most common cause of damage and disruption in the UK. Between 1962 and 1995, 184 deaths alone were caused by building failures resulting from wind. The majority of damage reports come from domestic dwellings. The average cost of damage each year is at least £300 million. Source Windstorms The Facts — report for ABI 2000 " http://www.metoffice.gov.uk/weather/uk/advice/storm.html

These storms cause economic damage of €1.9 billion per year, and insurance losses of €1.4 billion per year (1990–1998). They rank as the second highest cause of global natural catastrophe insurance loss (after U.S. hurricanes).[13]

• (i) windstorms account for more than one-third of all natural disasters;
• (ii) they also cause more than one-third of all fatalities;
• (iii) they are responsible for one-third of the overall economic loss;
• (iv) their share in insured losses is very high, with an average of more than two-thirds.-http://rsta.royalsocietypublishing.org/content/363/1831/1431.full.pdf

## Nomenclature

### Naming of Individual Storms

Deal between DMI and SMHI about naming storms, Swedes will use Danish name is storm hits Denmark first and vice versa.[14]

### Name of Phenomena

##### ==

Like many other severe weather conditions, windstorms are forecast in the UK by the Met Office. It is worth noting that the highest gust measured during the Great Storm of 1987 was 54.6m/s.[15]

Dutch/Flemish Kanaalrat (channel rat) http://www.weer.nl/weer-in-het-nieuws/weernieuws/ch/84d047ff14a213993fa5412995c9945f/article/kanaalrat.html rapidly deepening low (bomb) from Biscay up Channel to Netherlands. smaller in size... but

Unlike tropical cylcones there are no Regional Specialized Meteorological Centers devoted to these storms by the World Meterological Organisation who are responsible for tracking and issuing bulletins, warnings, and advisories about (extra(tropical)) cyclones. and as such no central authority who provides information about the http://www.wunderground.com/hurricane/subtropical.asp http://www.people.fas.harvard.edu/~pkatai/tropical_midlat_cyclone.htm#summary

The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from huracán, the Spanish word for the Carib/Taino storm god, Juracán. This god is believed by scholars to have been at least partially derived from the Mayan creator god, Huracan. Huracan was believed by the Maya to have created dry land out of the turbulent waters. The god was also credited with later destroying the "wooden people", the precursors to the "maize people", with an immense storm and flood.[16][17] Huracan is also the source of the word orcan, another word for a particularly strong European windstorm.[17]

## Cyclogenesis

A fictitious synoptic chart of an extratropical cyclone affecting Great Britain & Ireland. The blue and red arrows between isobars indicate the direction of the wind and its relative temperature, while the "L" symbol denotes the center of the "low". Note the occluded cold and warm frontal boundaries.

"derive their energy from horizontal temperature contrasts between cold, polar air masses and warm, subtropical air masses. Because the temperature contrasts between these air masses are greatest during winter, the frequency and intensity of European windstorms peak during this season as well." [2] association with jet stream, typically form in winter, however some form when tropical storms become extratropical

The development of extratropical cyclones takes place along the weather fronts where we find a shear vertical winds important. They are classified as cyclones baroclinic . The shear created in altitude jet stream around which we find areas of subsidence and of descent from the air. Indeed, the winds at the heart of the jet stream is stronger than around it. It moves, it was an accumulation of air in the area from which he comes in and lost the one he abandons. In quadrants of divergence, there is a loss of upper air which creates a suction effect of the lower layers and generates a surface convergence to compensate. This process provides two things: a reduction in pressure at the surface because the mass of the air column at this location is smaller, and the cyclonic rotation of the air, because of the deviation by the Coriolis force . The passage of the jet stream over an area more or less stationary front is the initiator of this type of weather depressions.

### The role of latent heat in some windstorms

For Xynthia, Klaus and Lothar diabatic processes contribute more to the observed surface pressure fall than horizontal temperature advection during their respective explosive deepening phases, while Kyrill and Martin appear to be more baroclinically driven storms.[18]

Large-scale environmental conditions conducive to their development include an unusually strong baroclinic zone associated with an intense jet stream over an extensive longitudinal sector of the North Atlantic [Pinto et al., 2009]. This is particularly true for extreme cyclones, which typically originate off the east coast of North America and propagate towards northern Europe, while secondary developments over the south-eastern North Atlantic are often more “low-level” forced [Dacre and Gray, 2009]. The latter suggests a more important contribution from latent heating to rapid cyclogenesis in line with ideas of so called diabatic Rossby waves or vortices [Parker and Thorpe, 1995; Wernli et al., 2002; Moore and Montgomery, 2005]. In fact, latent heat release and moisture advection from the subtropics apparently played a significant role in the development of storm Klaus in January 2009 [Knippertz and Wernli, 2010; Liberato et al., 2011]. Ulbrich et al. [2001] and Pinto et al. [2009] have shown that strong extratropical cyclones over the Atlantic Ocean are often flanked at their equatorward side with extreme values of the equivalent potential temperature, θe, at 850 hPa. This has commonly been interpreted as an indicator of important contributions from latent heat release to cyclone intensification. The quantification of the relative roles of dry baroclinic vs. moist diabatic processes on the development of the most destructive cyclones is a long standing issue [Chang et al., 1984; Sanders, 1986; Wernli et al., 2002]. While sensitivity studies using numerical weather prediction (NWP) models can give helpful indications for single cases, a diagnostic framework is needed that can be applied to a wide range of observational and modeling data in various spatial and temporal resolutions.[18]

#### North Atlantic Oscillation

Gross synoptic conditions

Some studies indicate that the NAO index alone is not sufficient to describe the variability in North Atlantic cyclones, NAO with latitudinal changed in storm tracks.[19]

East Atlantic pattern "southward shifted" NAO.[20]

Icelandic low also known as an Greenland lee-low http://www.map.meteoswiss.ch/map-doc/icam2005/pdf/poster-sesion-d/D42.pdf Azores_High North_Atlantic_oscillation

The strongest storms are mostly formed during high NAO, and may be a product of this.[21]

The role of sudden stratospheric warming in blocking westerly flow, even reversing it,[22] producing lower activity of strongest storms.

The positive East Atlantic pattern means that winds and storms tend to come at north-west Europe from a long south-west track, bringing warmth and a lot of rain.-http://www.willisresearchnetwork.com/assets/templates/wrn/files/Willis%20Windstorm%20Kyrill%20Report%2001%20Feb%202007.pdf Westerlies

#### MJO teleconnection

Cassou C (2008) Intraseasonal interaction between the Madden– Julian Oscillation and the North Atlantic Oscillation. Nature 455:523–527.

Recent research has suggested that MJO-related convec- tion can also excite certain phases of the AO and the closely- related North Atlantic Oscillation (NAO), the leading modes of variability in the Northern Hemisphere and the North Atlantic sector, respectively. Studies have shown that the MJO significantly impacts the sign of the AO/NAO several weeks after Rossby wave trains are initiated in the Pacific sector (e.g., Cassou 2008; Lin et al. 2009; L’Heureux and Higgins 2008; Roundy et al. 2010; Zhou and Miller 2005). In contrast, no conclusive impact on the AO has been found from tropical convection anomalies associated with ENSO (L’Heureux and Thompson 2006). The mechanism by which the MJO affects the AO is not completely understood, but is possibly due to interactions between MJO-driven Rossby waves and wave breaking events downstream that impact the subtropical jet strength and position over the North Atlantic (Benedict et al. 2004; Cassou 2008).-http://www.meteo.psu.edu/~sbf1/papers/Riddle.etal.pdf

#### Clustering

Infra-red satellite image showing the position of Cyclone Lothar (L over Germany) and Cyclone Martin (M over the Atlantic) at 11:30 UTC 26 December 1999 (Meteosat)

#### Explosive cyclogenesis

Explosive cyclogenesis or bombogenesis, is vigorous or extreme cyclogenesis, often characterized by a barometric pressure drop of more than 24 millibars in a 24 hour period.

Much of the recent severe weather has been attributed to the phrase “Weather Bomb”, which is not a perfect meteorological term but is defined as an intense low pressure system with a central pressure that falls 24 millibars in a 24-hour period.-http://metofficenews.wordpress.com/tag/weather-bomb/

meteorological bomb

feature seen in many of the severe or damaging windstorms, though not a unique feature... "These happen frequently throughout the Atlantic, and several times a year, we see this happening pretty close to the UK."[23] rapid deepening of lows is part of the reason prediction of some windstorms is so difficult, even with computational modelling lows can rapidly deepen with little warning... example such as Fastnet, 1987 storm

### Tracks

Van Bebber (1891)- Map of cyclone tracks over Europe

Steered by the upper level jet.

Van Bebber (1891), classified cyclone tracks with relevance for Europe, identifying the well-known Meridional 'Vb-track" with a high potential for large summer floods in Europe."[8]and snow. The van Bebber classification, however, was based on observations from only a few years and station network of rather low density.To this date, track Vb of the latter group has remained in common use, unlike the large majority of van Bebber’s tracks.[24]

There is a great deal of natural variability in the extratropical storm tracks. Particularly in the Northern Hemisphere, there is a clear seasonal cycle in the location and intensity of the storm tracks. The North Atlantic and North Pacific storm tracks shift equatorward in the winter and poleward in the summer and are substantially stronger in the winter than in the summer (Chang et al., 2002; Eichler and Higgins, 2006).

Predominately move west to east, Van Bebber in 1891

• I Island-Faroes-North Norway (e.g. Berit)
• II Scotland-Scandianvia-Gulf of Finland (e.g. Gudrun, Dagmar)
• III Scotland-Denmark-East Europe (e.g. 1953 flood, Andrea)
• IV Galicia/S of Ireland, Biscay, Channel, German Bight, Sweden, Baltic (e.g. 1987, Xynthia)
• V France, Mediterranean- (e.g. Klaus)

difference in storm tracks between normal and warm winter, with tracks more central and penetrating into the continent during warm. Dronia 1991 -http://rsta.royalsocietypublishing.org/content/363/1831/1431.long

## Classification

"There is no universal real classification of storms to allow their intercomparison. According to the objective, we can use the financial cost and in human life, insurance premiums paid, the damage to forests and crops ... Lamb (1991) defined an index of severity of storms:

${\displaystyle I-Vmax.Amax.D}$

In this index, Vmax is the velocity maximum average surface wind reached on the affected area (kts), Amax is the surface of the area affected by destructive winds (in units of 10 5 km 2 ) And D is the duration of occurrence damaging wind (hours). This index is proportional to the energy recoverable wind (we could also imagine used to construct an indexing the square of the speed which would be proportional to the dynamic pressure wind over obstacles).

The Storm severity index is defined as V 3 AD , where V is the maximum storm wind speed, A the greatest max max area covered by the storm and D the duration of the storm. Lamb (1990) used damage reports to determine A and D , but these can also be determined by defining a wind speed threshold.http://www.knmi.nl/samenw/hydra/stormcatalogus/1204199-004-HYE-0002-r-Selection%20of%20historical%20storms%20for%20atmospheric%20modelvalidation_v1.pdf

Based on this index, the value record is approximately 20 000 for storms of 15/12/1986 and 10/01/1993 Braer Storm of January 1993 in the North Atlantic (both lowest observed low). It is then the order of 12 000 for storms that occurred in December 1792 and February 1825, from 9000 to "The Storm" of December 1703 Great Storm of 1703, to- approximately 8000 for the Great Storm of 1987 (at the time called "the storm of the century ", before the occurrence of Lothar and Martin, whose indices have not been evaluated here), about 6,000 for storm having broken Dutch levees at the end of January 1953 North Sea Flood of 1953.

The statistical analysis of long time series data of wind speed provides an estimate statistical frequency. The distribution generalized extreme value ("Generalized Extreme-Value Distribution ") is in widespread use for modeling the extreme values ​​of natural phenomena, whether meteorology or hydrology. It pre- has the advantage of combining in one unique form the three possible types of extreme value distribution described by Fisher and Tippett (1928). This distribution law depends on three coefficients, it is formulated to out below, with a distinction which is carried out according to the value the "shape factor":

${\displaystyle formula}$

ξ is called "coefficient of localized tion ", while α is the" coeffi- cient scale. " The special case k = 0 corresponds to the well-known law of Gumbel. The motivation tion first adjusting a sample of extreme values ​​by a law such as those mentioned here is determining the values ​​of the parameter that are exceeded by a predefined recurrence. Recall that we call "quantile return period of years, "the value the parameter in question is com- EBV on average once every years, that is to say the value of the parameter associated with the probability. The two possible formulations for such a quantile, which will be denoted as a function tion of the value of the parameter form, can be written as:

When Lothar and Martin, were identified, from the return period values extreme wind calculated for stations synoptic, three wind areas centenaux or more:

- A perimeter Strasbourg, Colmar, Mulhouse, Orleans, Rouen, Reims, Nancy, Strasbourg, where the majority of sometimes largely exceeded values values ​​cinquantenales hundred; - The foot of the Pyrenees; - Atlantic coast from Biscarosse to the Vendée. Maps of quantiles various return periods are regularly LY produced by Météo-France, for a zoning of risk associated with wind extreme. translated from[25]

definition of european windstorm... low eye pressure? kmph winds???any low pressure, ill defined...beaufort etc.. "

Metcheck At Metcheck, we class storms based on their current central pressure in millibars.

• Cyclone <940mb
• Storm 941-960mb
• Gale 961-980mb
• Depression 981-1013mb metcheck [26]

cf. with Saffir–Simpson Hurricane Scale

• cat 5 <920 (>70m/s)
• cat 4 920-944 (59-69m/s)
• cat 3 945-964 (50-58m/s)
• cat 2 965-979 (43-49m/s)
• cat 1 980-994 (33-42m/s)
• 12 Hurricane Force ≥ 118 km/h (≥ 32.8 m/s)
• 11 Violent Storm 103–117 km/h (28.6-32.5 m/s)
• 10 Storm 89–102 km/h (24.7-28.3 m/s)
• 9 Strong Gale 75–88 km/h (20.8-24.4 m/s)
• 8 Gale 62–74 km/h (17.2-20.6 m/s)

note on relative frequency of each, or marker of rarity of <940 Note that the wind speed used for distinguishing the hurricanes in the United States is measured as the average over 1 min whereas the 10-min average is used in Europe.[27]

Impression that the richest diversity of mesoscale sub-structures occurs in association with most intense cyclones.[28] http://www.weatheranswer.com/public/Snow_storm_index_Zielinski_.pdf-classification for nor'easters

Satellite picture of a European windstorm

Hanley and Caballero 2012[21]

## Hazards

"the size of an ETC (European Windstorm) can best be defined by the swath of its damaging winds. This is usually found to the right of the storm track and is typically 100-300 miles (150-500 km) wide." [29]

"The horizontal temperature gradient that powers an ETC can persist as the storm center moves over land. Thus wind speeds in these storms can occasionally remain high, or even increase, after landfall. Also, while a hurricane can sustain the same minimum central pressure for days, the energy that drives an ETC rapidly decays as the air masses within it intermix—a single cyclone typically exists independently for three to five days."[30]

Dry Slot [31]

### Winds

A depiction of warm conveyor belt precipitation during a wintertime extratropical cyclone

typically strongest to the SE of the low jet streak Maximum winds usually occur south of a cyclone core in Central Europe.[5] often the strongest winds in a mid-latitude system are located along its cold front[32] Two regions of strong low-level winds commonly occur during the passage of a cyclone.[1]The warm conveyor belt is a broad region of moderately strong surface winds that exists throughout most of the cyclone’s life cycle in the warm sector of the cyclone (to the south of the storm centre in the northern hemisphere). When the cyclone is mature the cold conveyor belt may also produce strong surface winds if it hooks around the cloud head that can be seen curving to the northwest around the storm centre. Additionally, a third localized region of strong winds, and especially strong gusts, which may be short lived (a few hours) can exist close to the ‘tail’ of the cloud head hook as it wraps around the cyclone centre. This has been dubbed the ‘sting at the end of the tail’, or ‘Sting jet’.[1] The sting jet seen in up to a third of the most intense windstorms.[1] http://www.hpa.org.uk/Topics/EmergencyResponse/ExtremeWeatherEventsAndNaturalDisasters/WindStorms/

#### fluid dynamics

inertial gravity waves, rossby waves etc....

text

### Derechos

Kyrill 2007, Emma 2008 [33]

convective rainbands

### Precipitation

#### Rain/Pluvial flooding

About 70-80% of the winter precipitation in continental Europe originates from about 15 frontal cyclones (Fraedrich et al 1986).[34]

autumn floods 2000, 2013

AIR explained that “extratropical cyclones, also known as winter storms, form when a warm, tropical air mass interacts with a cold, polar air mass, creating local atmospheric disruptions that can grow into powerful storms. The fronts that created this series of storms were exceptionally warm and cold.” According to AIR, this week’s clustered storms also showed a “characteristic alternation between wet and dry periods, whereby a warm, humid front dropping significant amounts of precipitation on an area is pushed by a “dry slot” containing powerful winds. Following that, a cold front arrives and lifts warm, moist air higher into the atmosphere where it cools and falls as precipitation. “Dirk drew a significant amount of warm, moist air from the south as it moved across the Atlantic. North of Scotland it slowed and became associated with a slow-moving cold front. That cold front lifted the warm, moist air higher into the atmosphere, where it cooled and is now falling as rain. This cold front was daisy-chained with the warm front of the next system coming across the Atlantic, Erich. “Systems with a southwest to northeast path, like the storm cluster that affected the UK this week, typically bring more rain to Europe than systems that travel from the northwest to southeast. Systems that originate in colder environments and move southeast into warmer regions (like Xaver earlier this December) generally have less moisture and less precipitation compared to storms that originate in warmer regions.”Windstorm Dirk also caused significant damage from falling trees that resulted in approximately 300,000 properties in the southeast and east of England losing power. AIR explained, however, that “while wind damage has been significant, most of the loss from this series of events has been from flooding.[35]

#### Snowfall/Avalanche

heavy snowfall in the Alps, and lead to increased Avalanche

the occurrence of large avalanches is not governed by general climatic trends but rather by short term weather events, such as particularly intense snow falls during a couple of days, possibly linked with strong winds or a rapid temperature increase with rainfall at high altitudes.[36]

alps 2011 andrea deadly avalanche near Galtür (Austria) which killed nine people.-http://www.absconsulting.com/resources/Catastrophe_Reports/Lothar-Martin%20Report.pdf

Galtür Avalanche of 23 February 1999??? Martin Lothar December 1999 9 feb 1999 Montroc

### Temperature

warm sector can bring unusually high temperatures rapid temperature changes can accompany frontal passages. effect of high temperatures can result in more storm damage as unfrozen soils can lead to more tree fall, landslides, and coastal flooding more common if sea ice not present around eastern baltic.

Flooding in Bremerhaven, note the modern buildings are not inhabited on the ground floor

### Storm surge

Storm surges in the north sea defined to an official scale.[37]

North Sea Hamburg
Storm surge 1.5 – 2.5 m above MHW 3.6 – 4.6 m above SL
Strong Storm Surge 2.5 – 3.5 m above MHW 4.6 – 5.6 m above SL
Very strong storm surge > 3.5 m above MHW > 5.6 m above SL

MHW = mean high water SL = sea level

Storm surges are unusually high water levels caused when high tide is accompanied by powerful storm winds. This happens when strong winds blow towards the coast over a period of many hours driving sea water landwards in addition to the astronomical tide. Which coastlines are affected depends on the path of the low pressure system causing the winds. The time required for an early warning prediction of the water levels of a coming storm surge is today usually 12 hours or more. The low pressure system responsible for the storm surge can already be predicted two to three days beforehand. The risk of storm surges is particularly high in the winter half-year, when Atlantic storm fronts approach from a west to north-westerly direction. Spring tides occur twice a month when the sun, moon and earth are lined up in a row behind each other. The resulting increased differences in gravitation lead to a higher tidal range. Storm surges rarely last for more than a day, as the low pressure systems usually sweep over the area relatively quickly. The peak period normally only lasts for a few hours; due to the astronomic tide cycle (the intertidal period between low tide and high tide lasts for six hours), the water level falls again quickly once high tide has reached its zenith. Along the shorelines of the North Sea, which with an average depth of 70 metres is a comparably shallow sea, the tidal range (mean difference between low tide and high tide) is approximately 0.5 m (Southern Norway) to 6.8 m (The Wash, England). Along the German North Sea Coast, the tidal range varies from two and four metres, in Hamburg it is 3.65 metres. The height of a storm surge is influenced significantly by geometrical factors such as the shape of the ocean bed and the coastline. Storm surges are particularly intense in funnel-shaped river estuaries such as on the Thames, Elbe and Weser, and in bays, whereas their strength is weakened by offshore islands.[37]

A Historical Record of Coastal Floods in Britain: Frequencies and Associated Storm Tracks[38]When pressure decreases by one millibar, sea level rises by one centimetre. Therefore, a deep depression with a central pressure of about 960 mb causes sea level to rise half a metre above the level it would have been had pressure been about average (1013 mb).[39] Surges travel counter-clockwise around the North Sea - first southwards down the western half of the sea, then northwards up the western side. They take about 24 hours to progress most of the way around.[39]

low air pressure creates a dome of water + wind driven waves in shallow waters combined with the speed of the systems plus high tide

low lying coastal European Plain areas vulnerable especially close to the shallow southern North Sea German Bight

Characteristics of storm surges in German estuaries[40] storm surge levels in North sea and baltic defined (in German )http://www.bsh.de/de/Meeresdaten/Vorhersagen/Sturmfluten/index.jsp

storm surges have the power to profoundly change coastline as occurred during Grote Mandrenke and Buchardi Flood which destroyed the island of Strand. most powerful factor in European coastal geomorphology.[citation needed]

Major natural disasters have been caused by storm surge associated with European windstorms North Sea flood of 1953 North Sea flood of 1962 with North Sea flood being deadlier than Hurricane Katrina.

Major European construction works undertaken to protect against storm surges associated with windstorms include the Dutch Delta Works.The Thames Barrier to protect London, the St Petersburg Dam and the Belgian Sigma Plan.

Storm surge modelling is fundamental in protecting the London economy and is worth £94 million (2008) for each flood day.[41] A 5% fall in Foreign Direct Investment due to perceived flood risk would cost the London economy £2.1 billion per annum.[41] The value of human lives safeguarded from flooding in the Thames floodplain is £31.25 billion per year.[41]

North_Sea_flood_of_1953 2551 lives lost. North Sea flood of 1962 347 lives. massive dyke building and coastal safety measures surges of Gale of January 1976, January 1978 surge, 1994 surge, 2007 and 2011.

Surge events in the waters around Britain are caused by extratropical weather patterns, which produce a wide variety of dynamic responses. When considering tidal surges, attention is usually given to the extreme high water levels generated at the coast. However, fast flowing offshore currents are also generated during surge events that may have a significant impact on offshore structures as well as on sediment transport. negative surges can pose a significant threat to navigation...Surge events in the North Sea are notorious, not only for their severity and the frequency with which extreme events take place but for their unique features that are not observed at other locations (Heaps, 1983).-http://www.north-norfolk.gov.uk/files/Appendix_7_-_Discussion_paper_on_the_influence_of_storm_surges.pdf

#### Surge prediction]

After the North_Sea_flood_of_2007 the performance of the operational modelling system used for surge forecasting was examined. Significantly, this found that the modelling system provided accurate estimates of water levels at all east coast locations up to two days ahead of the event. The research compared predictions from the modelling system with quality-controlled data from several tide gauges and the key finding was that the surge was accurately forecast along the whole of the UK’s east coast.[41]

#### Seiches

Seiches noted from some storms in North Sea, Baltic Sea, also smaller scale in Rotterdam Harbour

"Seiches have been observed in seas such as the Adriatic Sea and the Baltic Sea/gulf of Finland, resulting in flooding of Venice and St. Petersburg respectively. The latter is constructed on drained marshlands at the mouth of the Neva river. Seiche-induced flooding is common along the Neva river in the autumn. The seiche is driven by a low pressure region in the North Atlantic moving onshore, giving rise to cyclonic lows on the Baltic Sea. The low pressure of the cyclone draws greater-than-normal quantities of water into the virtually land-locked Baltic. As the cyclone continues inland, long, low-frequency seiche waves with wavelengths up to several hundred kilometers are established in the Baltic. When the waves reach the narrow and shallow Neva Bay, they become much higher — ultimately flooding the Neva embankments.[13] Similar phenomena are observed at Venice, resulting in the MOSE Project, a system of 79 mobile barriers designed to protect the three entrances to the Venetian Lagoon." http://en.wikipedia.org/wiki/Seiche "the expected variation in sea level due to air pressure is between +63 cm and -37 cm around mean sea level" "Deep low pressure passages over the Bothnian Bay, combined with high pressure over the southern Baltic can create sea level differences of up to 2 m." [42] Wave conditions in the Baltic Sea during windstorm Gudrun[27]

#### Role in coastal morphology

Historic windstorm events have been documented as causing major changes to coast. Limfjord 1825, Dutch islands Strand island split in great Burchardi flood. Grote Mandrenke destroyed Ravenser Odd.

Lamb 1991 linked strong storms and Little Ice Age events Culbin sands Sands of Forvie text vis Estonia after gudrun, ec on lack of sea ice protection

Almost all erosion (95%) on sandy beaches on Saaremaa, Estonia is caused by rare extreme storms.[43] images of coastal defence failure methods[44]

Deepening of waterways to accommodate larger modern shipping, poses the risk of increased surge height.[citation needed] Since 1962 the Elbe has been extensively developed for navigation purposes. The outcome of this channelisation was that storm surges in Hamburg now run up higher than they did prior to 1962, as the water can no longer flow off into the Elbe marshlands.[37]

Low Oratia pulling warm, moist Mediterranean air over the Alps

### initiation of föhn

2000 autumn Low pressure traversing Northern Europe can induce warm humid Mediterranean air to migrate northwards, when this airmass reaches the (Pyrenees) Alps it undergoes Orographic lift and can lead to extreme flood events on the windward side (France/Italy/Slovenia 2000) and Foehn wind on the leeward side. http://www.bf.uni-lj.si/fileadmin/groups/2716/downloads/Članki_vaje/Brundl_Rickli_2002.pdf

### landslides

can bring warm air into usually cold areas, melting of snow and ground coupled with precipitation from storms themselves can lead to increased landslide risk. Perhaps additional from microseisms, noted during storms initiating slips and ground movement.[citation needed]

## Transport

### Shipping

MSC Napoli in 2007 increased use of post-panamax Maersk_Triple_E_class higher sides more vulnerable http://www.geograph.org.uk/photo/2754284

1987 Hengist ferry beached,

1979 Fastnet race

### Air

airports closed, large size of storms can affect large regions London Heathrow closed 1987

windstorm Emma, 2008 Hamburg airport landings http://www.youtube.com/watch?v=PWl0TygaeDw

### Rail

bridges close, roads crosswinds, scotland causeways closed,

## Characteristics

There are two main areas in the northern hemisphere whose climate is dominated by the influence of these synoptic-scale systems: the North Atlantic and European sector and the North Pacific.[34]

### Relative to tropical cyclones

http://www.wse.ie/articles/further-notes-on-extratropical-cyclones-05.php ? "The forward motion of an ETC, swept along by the jet stream, generally ranges from 20-45 mph, but can reach as high as 90 mph. Both these average and extreme values greatly exceed the forward speeds of low-latitude hurricanes. The storm’s windfield thus becomes highly asymmetrical, with damaging winds generally restricted to the south or right-hand side of the track"[45]

### Relative to other extratropical cyclones

studies of windstorms/extratrop in the UK have identified certain mesoscale features which tend to occur in the form of wave-trains or multiple circulations. these are:

• Multiple Rain bands
• stacked slantwise convection
• cloud top striations
• cloud heads with multiple substructure
• inertia-gravity waves[28]

#### Nor'easters

nor'easters and European windstorms are extratropical cyclones in each side of atlantic basin, no strict difference between, European windstorms differ chiefly from nor'easters as typified by strong winds rather than precipitation [citation needed]

In wintertime nor'easters, the strongest winds are often focused to the north of the center as it interacts with a cold high pressure system to the north.[46]

analogous to [Category:Pacific_Northwest_storms] North America extra tropical storms steered by jet

penetrate far overland, nor'easters tend to not given track, and pacific northwest storms meet rocky mountains

Baehr et al. (1999) showed that in the eastern North Atlantic the cyclones’ rapid-deepening phase occurs when the systems cross the jet axis even in the absence of additional upper-level features.http://onlinelibrary.wiley.com/store/10.1256/003590002321042036/asset/200212858001_ftp.pdf?v=1&t=h3of6vpa&s=c1326530d2a477bd5b8cb13b32b6dcde39e09650

##### Great lakes Witches

Witches of November great lakes lows.

The Shapiro–Keyser cyclone model was developed for marine cyclones, not continental cyclones, and warm seclusions are not common in inland cyclones.[4]

#### Pacific Northwest windstorms

European windstorms These storms are similar to the ones that rake the U.S. Pacific Northwest the same time of year. However, the latitude of northwestern Europe is closer to that of the Canadian Pacific than the U.S. Pacific, and hence the low-pressure systems striking Europe tend to be more intense than those experienced in the U.S. Pacific states. The lowest pressure reading of 962 mb (28.40”) recorded along the Washington coast can hardly compare to Britain’s lowest reading of 925.6 mb (27.33”).[47]

"Pacific Northwest windstorms appear to have structural and synoptic similarities to the intense storms that make landfall on England and France; however, there is little evidence to date of the “sting jet” phenomenon, whereby mesoscale areas of enhanced wind and damage are caused by evaporatively cooled downdrafts."[48]

Climatology of 120 North Atlantic and North Pacific hurricane-force extratropical cyclones over a 2.5-year period yielded an estimate of roughly twenty events per basin per year, with a peak in frequency in December in the North Pacific and a January peak in the North Atlantic.[4][49]

The most intense storms in the North Atlantic occur in the winter, while in the North Pacific the most intense storms occur in the fall. The Southern Hemisphere displays much less variation between seasons.[50]

there is little evidence of clustering to the west of North America.[51]

Similarity of certain European windstorms to Pacific NW storms. For Xynthia, Klaus and Lothar diabatic processes contribute more to the observed surface pressure fall than horizontal temperature advection during 31 their respective explosive deepening phases, while Kyrill and Martin appear to be more baroclinically driven storms.[18] from subtropical south-east north atlantic, rather than from usa.

### NE Asian Extratropical

Seasonal distribution of extratropical cyclones is as follows: in northern East Asia, monthly mean count is 9.9 and the most frequent activity is mainly observed in May, while the lowest activity is in January. There is more extratropical cyclone activity in the warm season than the cold season. The highest cyclone frequency occurs in spring (MAM), which accounts for 31.2% for the entire year, while the fewest appear in winter (DJF), which accounts for 16.3% for the entire year. And the cyclone frequency is 29.2% in summer (JJA) and 23.3% in autumn (SON).Xinmin Wang and Panmao Zhai Variations in extratropical cyclone Variations in Extratropical Cyclone Activity in Northern East Asia Variations in Extratropical Cyclone Activity in Northern East Asia∗

## Forecasting

The formation of storms is finely balanced and needs a number of factors to come together in the right place at the right time. In order for a nasty storm to form, the fastest part of the jet stream at 30,000ft up needs to phase in time with the greatest zone of warmth, moisture and energy at the surface. If they are slightly out of phase, the path and intensity of a developing storm can be affected hugely. It is these subtleties that make it difficult to pin down the detail in the preceeding days before the storm and is why the situation will need to be closely monitored in the coming days.[52]

predicting the strong winds associated with these storms is difficult, as weather forecasters famously found out during the october Great Storm of 1987. Even within 2 hours of the 1999 French storms, forecasts were underestimating wind speeds by 25% - equivalent to a 6 to 8-fold underestimate of the amount of damage that they caused.[6] While larger-scale aspects of extratropical cyclones are generally forecast with reasonable skill, the occurrence, location, and severity of the local regions of major wind damage are not.[1]

Wind damage, and subsequently insured loss, is disproportionately related to the peak gust speed of a storm (Munich Re, 2002; Spence et al., 1998), with Hawker (2007) reporting that a 25% increase in peak gust speed can result in a 650% increase in damage.[53]

For example in December 1999, three consecutive intense storms hit central Europe claiming more than 130 lives and causing about 1.3 billion Euros of economic loss (Ulbrich et al., 2001). These storms were badly predicted by the majority of NWP systems across Europe (Saunders, 2000).-http://www.nerc-essc.ac.uk/~lsrf/Downloads/chapter1.pdf

differing mechanisms of formation, 87 storm and Anatol/Carola 99 "interaction between upper and lower-level potential vorticity anomalies (Hoskins and Berrisford 1988; Nielsen and Sass 2003) In contrast, the hypothesis for the explosive development of the “Lothar” storm was a bottom-up development induced by a diabatic Rossby wave below a straight and intense upper-level jet without a notable precursor disturbance at the tropopause level (Wernli et al. 2002). This subtle difference in the basic dynamical evolution is interesting and points to the existence of different mechanisms that lead to explosive cyclone development, and to potential forecast failures. The storms described above highlight also the challenge involved in the prediction of such systems, since their evolution depends crucially on mesoscale structures over the generally data sparse oceans, both at the level of the tropopause (wind, temperature) and in the lowest troposphere (also humidity)."[54]

not be able to forecast increased probability of windstorms, but... • ...potential for forecasting southward shift in storms-Seasonal to decadal climate forecasts in the context of European windstorm risk https://connect.innovateuk.org/c/document_library/get_file?p_l_id=4383230&folderId=4652967&name=DLFE-39396.pdf

https://connect.innovateuk.org/web/4383218

It seems therefore evident that positive NAO Index values correlate with increased storm activity. The question is then whether we can use this statistical insight to benefit the management of extra-tropical windstorm risk in the insur- ance industry? While forecasts of NAO conditions for entire winter seasons exist, their accuracy appears to be rather limited. Mid-term forecast, such as 14-day predictions of the NAO index, are more reliable, but are already factored into numerical weather predictions. It therefore appears that at present there is no silver bullet to enable us to predict the level of activity and intensity of future windstorm seasons. What seems certain, however, is that windstorm clustering exists and that it is cor- related with phases of a positive NAO Index. Further research into this phenomenon is, in our view, warranted and may one day help to better anticipate the seasonal storm activity to the benefit of both businesses and society.-perils newsletter #1 2012 refinement of NAO, as fixed locations, azores iceland, and poles of low and high pressure may be displaced, storms may in fact displace the icelandic low as they travel, more key could be large-scale westerly flow over Europe.[21] http://www.aon.com/attachments/reinsurance/070411_abr_newsletter_two.pdf http://thoughtleadership.aonbenfield.com/Documents/201011_ab_if_traditional_perils_new_challenges.pdf

During the late 1990s, extreme weather risk in Europe was modeled using an approach that combined historical storm track data and weather observations with simple statistical modeling of the shapes and intensities of storms. Since 2000, fundamental changes in the approach to windstorm modeling have significantly improved the ability to build realistic stochastic event sets of potential intense storms, like Anatol, Lothar, and Martin. The first of these advances concerns the use of constrained numerical models to model the full space-time structures of historical events. These methods, as used in the current generation of the RMS® Europe Windstorm Model, are similar to those used by meteorological agencies, but performed at a higher resolution. These reconstructions are then used as the basis for deriving the full range of storm characteristics, which are incorporated into the stochastic event set. Over the past five years, through the relentless reductions in the cost of hardware, supercomputers have become available to catastrophe modeling agencies. Modelers can now harness the power of hundreds of CPUs to conduct free-running numerical simulations capable of generating thousands of years of realistic storm data. Before the "raw" simulated data can be turned into the stochastic windstorm events in the model, it has to be corrected for its inherent biases. In the beginning, the size of the errors was prohibitive, but as modeling techniques have improved it became possible to remove the biases with aggressive calibration. Getting this calibration right is now one of the biggest challenges in windstorm modeling. However, the benefits of numerical models in producing more realistic storms outweigh the difficulties posed by the calibration. The corrected results of the numerical simulations can then be used to generate the underlying data for the event sets in a catastrophe model. Event sets generated by free-running numerical models are used in the current RMS® U.S. and Canada Winterstorm Models, and will be incorporated into the 2011 release of the RMS® Europe Windstorm Model. Significant advances have also occurred around the understanding and representation of windstorm clustering. Clustering reflects the tendency of storms, like Lothar and Martin, to occur closely together in time, and also have very similar tracks and intensities. Modeling clustering requires capturing both its temporal and spatial characteristics. While temporal clustering can be modeled statistically, the inclusion of spatial clustering or the similarity of storm characteristics in certain regions requires understanding the way in which sequences of storms are similar to one another. Both aspects of clustering were introduced into the RMS® Europe Windstorm Model via the RMS® Simulation Platform in 2008.The fundamentals of how to model windstorm risk, particularly the use of free-running numerical models and the representation of clustering, are now well established. What comes next? Future improvements in windstorm catastrophe models will come from using even higher resolution numerical models that simulate the strongest and smallest storm structure even more realistically. Model uncertainty will also become captured by the use of multiple numerical models. As the ability to define and calibrate the hazard becomes more advanced, modelers will next begin to focus on how to bring the vulnerability assessment of wind damage in Europe up to the same levels of sophistication.[55]

[56]

The large-scale energy budgets, called Lorenz energy cycle/Lorenz energetics. They found a strong energy signature that was virtually identical for 4 main geographical areas of explosive cyclogenesis/bomb meteorology. the fact that the energy signature of these bombs can be seen 48 hours before the actual storm takes shape. That suggests the method might be applied to lengthen forecast times.[57] -http://science.nbcnews.com/_news/2013/02/25/17088963-look-out-meteorological-bomb-is-on-the-way?lite

### Comunication

to the general public these storms are thought of as very rare, a view supported by the widely held belief that the

cultural phenomena of the Great storm of 1987 in the UK, as being the worst storm in 200 years since 1703, which has what has been termed a mytholigical status in the UK, coupled with the supposed mis-prediction of the Met Office to predict the ferocity of that storm. similarly severe storms in the UK such as Daria and Gale of January 1976. exacerbated by there being no central authority who produce information on the storms in a way comparable to the data produced for Hurricanes and tropical storms.

perceptions of the storms vary throughout europe,

[58]

## Economic Impact

There is no authoritative independent source of loss data for these storms in Europe...market loss data can be frustrating. Often, there are as many loss estimates as sources,and those estimates can vary alarmingly. In addition, there can be uncertainty about which lines of business are included in the loss figures, so it is clear why there can be so much confusion regarding the actual size of an event loss... the creation of PERILS AG by a group of insurers, reinsurers and a broker to aggregate and supply European catastrophe insurance data[59]

Windstorms can result in both direct losses to buildings and contents, vehicles, public infrastructure such as bridges and utilities, as well as indirect losses including business interruption costs, the provision of alternative accommodation for those made homeless, the cost of emergency services and other less tangible aspects such as consequent health and stress problems.[60]

Blue Banana

"Mid-latitude wind storms are the most loss-relevant natural hazard in central Europe, causing 53 (64) percent of economic (insured) losses in Germany (Munich Re, 1999; Munich Re, 2007)"-Donat Total insurance losses in Europe associated with these storms have averaged over 1 billion Euros (approximately \$1.5 billion) per year over this period (Browning 2004) "Windstorm facts: - Since 1950, nearly three- quarters of the UK’s insured losses due to natural catastrophes have been caused by windstorms. - Windstorm events of 1987 and 1990 alone saw property claims reach £1.4billion and £2.1 billion respectively. The smaller scale wind damage event of October last year resulted in insured losses in excess of £150 million "http://www.abi.org.uk/Media/Releases/2003/10/Its_an_ill_wind.aspx http://old.abi.org.uk/Display/File/Child/552/Windstorm_Report.pdf

"Windstorms are a class of extra-tropical cyclones that pose significant risk to insured assets across the continent. Recent historical events of note (and their estimated insured losses) include windstorms Daria and Vivian in 1990 (€3.98 billion and €1.64 billion respectively), Lothar, Martin, and Anatol in 1999 (€4.61 billion, €1.95 billion, and €1.87 billion respectively), Jeanette/Irina in 2002 (€1.33 billion), Erwin in 2005 (€2.03 billion), Kyrill in 2007 (€4.53 billion), and Klaus in 2009 (€2.34 billion). As evidenced recently in 2010 with windstorm Xynthia (€1.25 billion), damage may result from both high winds and resulting flooding from coastal storm surges.* Conversion rate: 1 USD = .7809 Euro

• Munich RE NatCatSERVICE, January 2010. Xynthia figure based on PERILS AG value, 12 April 2010"

http://www.eqecat.com/pdfs/eurowind-model-fact-sheet.pdf

### Insurance losses

--

Even if storms do not increase in frequency or severity, the potential for large insured losses is increasing...significant increase in insured values due to high levels of industrialisation along with the increased density of properties across Europe.“Prices are not where they should be. If you compare them to other cat exposures around the world they are too low. Maybe the buyer has a risk perception different from ours. Buyers do not buy cover up to the same return period as they do for other perils such as earthquake.” -http://www.insuranceinsight.com/insurance-insight/analysis/2135716/windstorm-insurance-market

Changes in the maximum wind speeds in these storms are important for insurance-oriented loss modelling, as they lead to exponential changes to losses.[61]

The prevalence of insurance against storm floods varies from country to country. Whereas a practically comprehensive insurance coverage for storm floods is customary in Great Britain, and enormous insured losses in the event of a catastrophic storm flood are consequently to be expected in this country, storm flood losses in other countries (including Germany) are only covered in the property insurance segments of Industry, Engineering Insurance, Transport, Marine and Comprehensive. In the Netherlands, probably practically nothing is insured in the private and commercial sector. Storm floods are often included in international industrial programmes only. The greatest value den- sity lies most likely in the port of Rotterdam. To estimate storm flood losses, the following insurance segments, which have very different levels of penetration, must be taken into consideration.Flood losses always are accompanied by wind losses so that the separation of the (in-sured) storm losses from the (usually uninsured) water losses can prove difficult. Why is there no coverage within the framework of elementary loss insurance? In Germany, over 70% of all households are not properly insured against the financial repercussions of elementary risks. To protect themselves against the financial conse- quences of such extreme weather events as torrential rains and floods or other natural disasters such as earthquakes, house owners and tenants require so-called elementary loss insurance. However, on national average, only just under 30% of households have taken out elementary loss insurance for their homes. And only 15% insure their personal household belongings against natural hazards. Without the inclusion of "further elemen- tary hazards", residential building and household effects insurance only covers damage caused by tap water, storm, hail and fire. Elementary loss insurance provides protection against the financial consequences of such natural events as floods, torrential rains, backwater, earthquakes, land subsidence, snow pressure, avalanches and volcano eruptions. It can be taken out as a supplementary component of the household effects and residential building policy. However, the risks of groundwater and storm floods cannot be insured within the frame- work of "further elementary hazards" coverage. Precisely the risk of storm floods in Germany is not representable in actuarial terms due to the high-level accumulation risk, the possibility of adverse selection and the lack of losses data required for calculation of the premiums. The most recent GDV conditions also specify these exclusions for retail business. At present, there no activities within the association or market trends advocat- ing the inclusion of these risks.[37]

[60]

### Building stock vulnerabilities

weighted roof, Arnol Blackhouse Isle of Lewis

Most traditional building stock resistant to the strong winds of these storms, with domestic buildings in northwest europe predominantly brick or stone construction.

Traditional buildings on exposed Scottish islands. The Lewis examples have clearly been modified to survive in the tough environment of the Outer Hebrides. Low rounded roofs, elaborately roped were developed to resist the strong Atlantic winds and thick walls to provide insulation and to support the sideways forces of the short driftwood roof timbers.[62][63]

changing architectural tastes, favouring less traditional styles, increasing use of cladding and large glazed panels, flat roofs may lead to increased risk in housing stock and commercial building.[citation needed] In terms of vulnerability, Erik Ruettener, head of catastrophe research at PartnerRe, commented on the big increase in glass in modern buildings and an increasing number of solar panels on roofs.[64]

Building codes superseded by the pan-european Eurocode building code that has superseded the older national building codes. Each country now has "country annexes" to localize the contents of the Eurocode. wind loading

Cities in western europe tended to only have few high buildings until the latter 20th century, flow of wind and deflection in high rise areas

coastal flooding,

surveys in towns in eastern France immediately after the passage of Lothar showed damage patterns that varied according to the age of the building. Broken roof tiles from very old houses were scattered throughout town centers. In addition, buildings constructed during the late 1980s and early 1990s were widely affected while housing of the 1960s and 1970s in the same locations suffered low levels of damage. A similar pattern was observed in eastern regions of Paris and new housing developments north of Paris.[65] Architectural elements: The tall, slender chimneys typical of older buildings in central Paris were particularly vulnerable to damage in the high winds, and many toppled over, causing additional damage to roofs. Buildings with modern high-pitched roofs also performed poorly.[65] Level of maintenance: Poorly maintained roofs showed higher levels of failure. This was particularly apparent among older buildings. For example, a row of mid-19th century Hausmann era buildings of the same age and style in western Paris showed varying levels of damage. Interviews with companies making repairs confirmed that the level of maintenance and renovation was a primary factor in the relative performance of the roofs.[65] Commercial properties sustained widespread damage to lightweight roofs commonly used for warehouses, causing water spoilage to stored goods and equipment. Warehouses and manufacturing facilities were hit hard in other regions as well, particularly around Paris. An RMS survey of a major auto manufacturing facility in Poissy south of Paris revealed that 40% of the total insured losses of €1.8 million (\$1.9 million) was from roofing damage. This is typical of industrial complexes in the path of the storm. Other commercial buildings suffered damage, particularly to glass curtain walls in office blocks. Buildings in most business parks around Paris were also affected.[65] Among public facilities of commercial construction, schools were the worst affected. The worst damage was found in schools built in the 1960s/70s and during the 1990s and was associated with the use of lightweight architectural elements of metal, plastic, and glass in walls and roofs.

### Clustering of Insurance losses

The volatility of losses is exacerbated by the clustering of severe storms, with four in 1990, and three in 1999.[12]

-Pinto et al 2012 -http://www.int-res.com/articles/cr_oa/c054p001.pdf

### Storm clustering vs Jet Stream Steering

windstorms occur throughout the year, more intense tend to form during the winter months but severe storms in summer are also relatively common...

Temporal clustering of windstorm events has also been noted, with 8 consecutive storms hitting Europe during the winter of 1989/90. Lothar and Martin in 1999 were separated only by 36 hours. Kyrill in 2007 following only four days after Hanno, and 2008 with Johanna, Kirsten and Emma. [66] [67]

European windstorms, an analysis of the clustering effect[68]

Mailier et al (2005)[51] "Mailier et al (2005) showed that storm clustering is statistically significant in northwestern Europe at the exit region of the typical North Atlantic storm track, but not at the entrance region near North America. His research suggests that storms form at regular intervals in the western North Atlantic, but that the variability in a number of large-scale climate patterns (including the North Atlantic Oscillation, the East Atlantic Pattern, and the Scandinavian Pattern) can influence their path and travel times over the Atlantic. These climate fluctuations ultimately lead to the clustered arrival of the storms in Europe. Further, consistent with anecdotal evidence, Vittolo et al. (2009) showed that storm clustering is positively correlated with the vorticity intensity of the cyclones, meaning that the stronger storms are more likely to cluster." http://www.air-worldwide.com/PublicationsItem.aspx?id=19693

"Storms are steered by the jet stream, so the position of the jet stream defines the storm track. The jet stream and storm track move from month to month and from year to year, but storms moving along the storm track tend to reinforce the jet, and keep it from shifting. This is called eddy feedback. By reinforcing the jet, eddy feedback helps the jet and storm track "remember" their position over weeks to months, and thus enhances the persistence and predictability of mid-latitude variability. It is also responsible for the tendency of European windstorms to occur in series (see Impacts). Eddy feedback is not, however, sufficiently robust to provide persistence from year to year."[69]

clustering may be artefact of jet stream steering of strong jets, along certain damaging pathways so applicable to insurance risks, but not the phenomena itsself.[70] http://www.air-worldwide.com/publicationsitem.aspx?id=14576 A cluster is a group of wind- storms occurring in a short time span: this may affect either the same geographical region or, from an insurer viewpoint, the same portfolio of insured properties.[71]

Clustering measures the tendency of storms to occur together over a short time in a particular region, rather than being randomly distributed.[72]

89/90 Daria Vivian/Wiebke 1999 Lothar Martin 2000 Nicole, Oratia, Rebekka 2007 Franz Hanno Kyrill 2008 Johanna Kirsten Emma 2009 Uk and Ireland floods, 2010 Wera, Xynthia 2011/12 Xaver and Yoda, Cato and Dagmar (and the finnish thing), Ulli and Andrea

-

## Climatological impact

Storm tracks interact with the Atlantic Ocean and can be affected by distant atmospheric events, like the El Nino in the tropical Pacific. Thus, climate variability and the variability of the intensity and location of the dominating storm tracks are closely linked.[34]

“We don’t have a good research basis for saying storms in the Atlantic are significantly influenced by the El Niño," said Richard Seager, a research professor at the Palisades Geophysical Institute at Columbia University's Lamont Doherty Observatory, in an interview with Mashable. While there is more "connectivity" between the North Pacific and North Atlantic storm track in El Niño years, Seager said, “The El Niño impact on storms over the Atlantic sector is not known to be very strong.”[73]

Historical records of European windstorms do exist, but data biases and inconsistencies hamper their use in climatic analyses and risk modeling.[2]

The number of such depressions crossing the UK in an average winter increases from about 5 for the present climate to 8 for the Medium-High emissions scenario by the 2080s. This is mainly due to a shifting southward of the depression tracks from their current position, resulting in a strengthening of the winter winds over the south of England. The probability of an individual low-pressure system being a ‘deep’ depression (below 970 hPa) does not change by the 2080s but, since there will be more depressions overall, there are more frequent depressions.[60]

Storm severity is more sensitive to a changing climate than the frequency.[64] the relative importance also varies by geographical region. In the UK, for example, the increase in losses is predicted to be substantially smaller than, for instance, in Germany.[64]

### Long term trends

No upward trend in normalised windstorm losses in Europe: 1970–2008[74]

the 5 year European Commission funded ENSEMBLES Project models show windstorms in the 21st century will show

• a decrease in the total number of extra-tropical cyclones
• an increase in the number of severe cyclones[75]

variation, / The late 16th century, and especially 1588, was marked by unusually strong North Atlantic storms, perhaps associated with a high accumulation of polar ice off the coast of Greenland, a characteristic phenomenon of the "Little Ice Age."[76]

Poleward displacement of tracks, frequency reduced, intensity increased. via Krienkamp

WASA report NAO link to frequency and models of possible climate change scenarios[77]

Studies in conjunction with future emission scenarios have been published, e.g. by Lambert (1995), Carnell et al. (1996) or Schubert et al. (1998).[24]

Bengtsson et al. (2006) conclude in a comprehensive study that the Northern Atlantic and Scandinavia in particular will be subjected to a future increase in cyclone activity.[24]

Microseism Microseismological evidence for a changing wave climate in the Northeast Atlantic Ocean Nature 408, 349 - 352 (2000) © Macmillan Publishers Ltd. (Nov. 16, 2000) Microseismological evidence for a changing wave climate in the northeast Atlantic Ocean I. GREVEMEYER*, R. HERBER† & H.-H. ESSEN‡ http://www.heatisonline.org/contentserver/objecthandlers/index.cfm?id=3573&method=full

The Arctic is warming faster than the rest of the Northern Hemisphere; this could be increasing the likelihood of extreme weather events in mid-latitude regions by altering the circulation of air currents in the upper atmosphere. -http://www.nature.com/nature/journal/v484/n7395/full/484419f.html

Quantifying the impact of historical and future climate change on windstorm insured loss in Great Britain-http://engweb.swan.ac.uk/~hewstonr/Richard%20Hewston%20Thesis.pdf

Their gale frequency ( Jenkinson and Collison 1977) time series developed for the North Sea indicates a declining trend in annual storminess from the 1880s to the 1930s and an increase thereafter. A tentative conclusion presented in ‘Historic Storms’ was that the increase in storminess throughout the 1940–1950s, although significant, remained below the level witnessed during the 1570–1840 period, during which significant peaks occurred in the 1690s, as described above, and the 1790s. [78]

"The anti-correlation between hurricane frequency and European windstorm activity during the following winter provides a potential opportunity for insurers looking to diversify their portfolios geographically." [79] -http://www.bios.edu/rpi/public/pubs/pre2000/euwindsum/eurowindsum.html http://adsabs.harvard.edu/abs/2016EGUGA..18.4308B

With respect to North Atlantic/European climate statistically significant correlations have been found between summer and autumn snow cover on the northern hemisphere and the NAO in the following winter.[80]

cold water wake

judging by the Southern Oscillation Index Archives from Australia's Bureau of Meteorology. It is well-know that during an El Niño event, an atmospheric circulation that brings strong upper-level west-to-east winds over the tropical Atlantic typically sets up, and these winds tend to create high wind shear, discouraging tropical storm formation.- http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2737

### AO

Positive and negative phases of the Arctic Oscillation

the East Coast has experienced much higher flood frequencies than other sectors. Overlying the inter-decadal variability, the flood history of the East Coast can be divided into four phases. Firstly, the 1780s to 1840s saw a steady increase in flood frequency (Figure 3), followed by the second phase, the 1850s to 1900s, when flood frequencies fluctuated. These two phases coincided with the generally cool conditions during the late 18th and early 19th centuries (e.g. Jones and Bradley, 1992). There is a mark increase in flood frequency from the 1910s to 1930s. Such an increase seems to correspond to a rise in atmospheric temperature of the Northern Hemisphere (e.g. Fu et al., 1999; Parker et al., 2000) and strong positive NAO indexes (e.g. Hurrell, 1995), i.e. a warmer climate and stronger westerly airflow over the Northern Atlantic and Europe. The final phase, i.e. since the 1940s, saw relatively low numbers of floods except the 1950s and 1980s. This generally declining trend in flood frequency is associated with a small decrease in temperature and a negative NAO indexes between the 1940s and 1970s. However, it is noted that the slightly high flood frequency in the 1980s seem to coincide with the rise in temperature and the positive NAO indexes. But the low number of floods in the 1990s does not fit with the climate trend.Relatively lower numbers of floods were recorded for the South and Southwest Coasts for the 19th century. From the 1890s to 1940s, flood frequencies increased steadily, apparently coincided with the rise of temperature and positive NAO indexes. The declining flood frequencies during the 1950s and 1960s are associated with the small decrease of temperature and evidently negative NAO indexes. However, the relatively high number of floods in the 1970s does not correlate well with the relatively low temperature (e.g. Parker et al., 2000). Further decline in flood frequency since the 1970s contradict with the fact that temperature rose and the NAO indexes appeared strongly positive during this period. On the West Coast, the number of flood incidents was relatively consistent for the period between 1780s and 1860s, after which flood frequency rose to its highest in the 1890s. Such a trend seems to contradict the changes in temperature and there is no correlation with the NAO indexes. Since the 1890s, there has been a general decline in flood frequency, with the one exception of higher number recorded for the 1920s and associated with a rise in temperature. The slight increase in flood frequency in the last three decades seems to coincide with the rising temperature and positive NAO indexes.The above analyses suggest that the variability of flood frequencies recorded since the 1780s from the three coastal sectors (Figure 3) seems to a certain extent related to climate change, particularly the temperature of the Northern Hemisphere and the NAO index.[38]

http://onlinelibrary.wiley.com/doi/10.1002/joc.1601/abstract

ENSO can also impact cold season rainfall in Europe.[81]

#### Solar Variability

Relation of solar activity and storminess, inverse? Lamb, H.H. 1985. 'The Little Ice Age period and the great storms within it', in Tooley, M.J. and Sheail, G.M. (eds) The Climatic Ssene, George Allen and Unwin, London, 104- 131. the increasing frequency and intensity of Atlantic storms during the Little Ice Age.[82] but, http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1460.html

Link Between Solar Activity and the UK's Cold Winters[83]

...'there's enough evidence to suspect that jet stream behaviour is being modulated by the Sun...and it's certainly a headache for computer models that predict our future climate based on increasing levels of man-made greenhouse gases. They are unable to model the impact of weak solar activity, simply because the precise mechanism of how this affects climate patterns is unknown. These climate projections suggesting that winters will become milder and wetter, with summers drier and warmer, have been of little use to the water authorities in the south and east of the UK who are trying to cope with successive dry winters.-http://www.bbc.co.uk/blogs/paulhudson/2012/05/weakest-solar-cycle-in-100yrs.shtml

## investigate

Quasi-biennial_oscillation

## Notable Storms

see list_of_European_windstorms for more complete windstorm list

--

### Notable Storms since 1900

--

[84]

http://www.bios.edu/rpi/public/pubs/pre2000/euwindsum/EuropeanWindSum.pdf European Windstorms and the North Atlantic Oscillation: Impacts, Characteristics, and Predictability

## References

1. Cite error: The named reference `Martinez-Alvarado` was invoked but never defined (see the help page).
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