Sudden stratospheric warming

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A sudden stratospheric warming (SSW) is an event in which the polar stratospheric temperature rises by several tens of kelvins (up to increases of about 50 °C (90 °F)) over the course of a few days.[1] The warming is preceded by a slowing then reversal of the westerly winds in the stratospheric polar vortex. SSWs occur about 6 times per decade in the northern hemisphere,[2] and only about once every 20-30 years in the southern hemisphere[3] (and two southern SSWs have been observed so far [4]).


The first continued measurements of the stratosphere were taken by Richard Scherhag in 1951 using radiosondes to take reliable temperature readings in the upper stratosphere (~40 km) and he became the first to observe stratospheric warming on 27 January 1952. After his discovery, he assembled a team of meteorologists specifically to study the stratosphere at the Free University of Berlin and this group continued to map the northern-hemisphere stratospheric temperature and geopotential height for many years using radiosondes and rocketsondes.

In 1979 when the satellite era began, meteorological measurements became far more frequent. Although satellites were primarily used for the troposphere they also recorded data for the stratosphere. Today both satellites and stratospheric radiosondes are used to take measurements of the stratosphere.

Classification and description[edit]

SSW is closely associated with polar vortex breakdown. Meteorologists typically classify vortex breakdown into three categories: major, minor, and final. No unambiguous standard definition of these has so far been adopted.[2] However, differences in the methodology to detect SSWs are not relevant as long as circulation in the polar stratosphere reverses.[5] "Major SSWs occur when the winter polar stratospheric westerlies reverse to easterlies. In minor warmings, the polar temperature gradient reverses but the circulation does not, and in final warmings, the vortex breaks down and remains easterly until the following boreal autumn".[2]

Sometimes a fourth category, the Canadian warming, is included because of its unique and distinguishing structure and evolution.

"There are two main types of SSW: displacement events in which the stratospheric polar vortex is displaced from the pole and split events in which the vortex splits into two or more vortices. Some SSWs are a combination of both types".[2]


These occur when the westerly winds at 60N and 10 hPa reverse, i.e. become easterly. A complete disruption of the polar vortex is observed and the vortex will either be split into daughter vortices, or displaced from its normal location over the pole.

According to the World Meteorological Organization's Commission for Atmospheric Sciences (Mclnturff, 1978)[who?]: a stratospheric warming can be said to be major if at 10 mb or below the latitudinal mean temperature increases poleward from 60 degree latitude and an associated circulation reversal is observed (that is, the prevailing mean westerly winds poleward of 60 latitude are succeeded by mean easterlies in the same area).


Minor warmings are similar to major warmings however they are less dramatic, the westerly winds are slowed, however do not reverse. Therefore, a breakdown of the vortex is never observed.

Mclnturff[who?] states: a stratospheric warming is called minor if a significant temperature increase is observed (that is, at least 25 degrees in a period of week or less) at any stratospheric level in any area of winter time hemisphere. The polar vortex is not broken down and the wind reversal from westerly to easterly is less extensive.


The radiative cycle in the stratosphere means that during winter the mean flow is westerly and during summer it is easterly (westward). A final warming occurs on this transition, so that the polar vortex winds change direction for the warming, however do not change back until the following winter. This is because the stratosphere has entered the summer easterly phase. It is final because another warming cannot occur over the summer, so it is the final warming of the current winter.


Canadian warmings occur in early winter in the stratosphere of the Northern Hemisphere, typically from mid November to early December. They have no counterpart in the southern hemisphere.


In a usual northern-hemisphere winter, several minor warming events occur, with a major event occurring roughly every two years. One reason for major stratospheric warmings to occur in the Northern hemisphere is because orography and land-sea temperature contrasts are responsible for the generation of long (wavenumber 1 or 2) Rossby waves in the troposphere. These waves travel upward to the stratosphere and are dissipated there, decelerating the westerly winds and warming the Arctic.[6] This is the reason that major warmings are only observed in the northern-hemisphere, with two exceptions. In 2002 and 2019, southern-hemisphere major warmings were observed.[7][8][9] These events are not fully understood.

At an initial time a blocking-type circulation pattern establishes in the troposphere. This blocking pattern causes[clarification needed] Rossby waves with zonal wavenumber 1 and/or 2[clarification needed] to grow to unusually large amplitudes. The growing wave propagates into the stratosphere and decelerates the westerly mean zonal winds.[clarification needed] Thus the polar night jet weakens and simultaneously becomes distorted by the growing planetary waves. Because the wave amplitude increases with decreasing density this easterly acceleration process is not effective at fairly high levels.[why?] If the waves are sufficiently strong the mean zonal flow may decelerate sufficiently so that the winter westerlies turn easterly. At this point planetary waves may no longer penetrate into the stratosphere [10][clarification needed]). Hence further upward transfer of energy is completely blocked and a very rapid easterly acceleration and the polar warming occur at this critical level, which must then move downward until eventually the warming and zonal wind reversal affect the entire polar stratosphere. The upward propagation of planetary waves and their interaction with the stratospheric mean flow is traditionally diagnosed via so-called Eliassen-Palm fluxes.[11][12]

There exists a link between sudden stratospheric warmings and the quasi-biennial oscillation: If the QBO is in its easterly phase, the atmospheric waveguide is modified in such a way that upward-propagating Rossby waves are focused on the polar vortex, intensifying their interaction with the mean flow. Thus, there exists a statistically significant imbalance between the frequency of sudden stratospheric warmings if these events are grouped according to the QBO phase (easterly or westerly).

Weather effects[edit]

Although sudden stratospheric warmings are mainly forced by planetary scale waves which propagate up from the lower atmosphere, there is also a subsequent return effect of sudden stratospheric warmings on surface weather. Following a sudden stratospheric warming, the high altitude westerly winds reverse and are replaced by easterlies. The easterly winds progress down through the atmosphere, often leading to a weakening of the tropospheric westerly winds, resulting in dramatic reductions in temperature in Northern Europe.[13] This process can take a few days to a few weeks to occur.[1]

Table of Major mid-winter Sudden Stratospheric Warming Events in Reanalyses Products[14][edit]

Event Name NCEP-NCAR ERA40 ERA-Interim JRA-55 MERRA2 ENSO QBO 50mb
JAN 1958 30-Jan-58 31-Jan-58 30-Jan-58 El Niño West
NOV 1958 30-Nov-58 **** **** El Niño East
JAN 1960 16-Jan-60 17-Jan-60 17-Jan-60 Neutral West
JAN 1963 **** 28-Jan-63 30-Jan-63 Neutral East
MAR 1965 23-Mar-65 **** **** La Niña West
DEC 1965 8-Dec-65 16-Dec-65 18-Dec-65 El Niño East
FEB 1966 24-Feb-66 23-Feb-66 23-Feb-66 El Niño East
JAN 1968 **** 7-Jan-68 7-Jan-68 La Niña West
NOV 1968 27-Nov-68 28-Nov-68 29-Nov-68 El Niño East
MAR 1969 13-Mar-69 13-Mar-69 **** El Niño East
JAN 1970 2-Jan-70 2-Jan-70 2-Jan-70 El Niño West
JAN 1971 17-Jan-71 18-Jan-71 18-Jan-71 La Niña East
MAR 1971 20-Mar-71 20-Mar-71 20-Jan-71 La Niña East
JAN 1973 2-Feb-73 31-Jan-73 31-Jan-73 El Niño East
JAN 1977 **** 9-Jan-77 9-Jan-77 El Niño East
FEB 1979 22-Feb-79 22-Feb-79 22-Feb-79 22-Feb-79 Neutral West
FEB 1980 29-Feb-80 29-Feb-80 29-Feb-80 29-Feb-80 29-Feb-80 El Niño East
FEB 1981 **** **** **** 6-Feb-81 **** Neutral West
MAR 1981 **** 4-Mar-81 4-Mar-81 4-Mar-81 **** Neutral West
DEC 1981 4-Dec-81 4-Dec-81 4-Dec-81 4-Dec-81 4-Dec-81 Neutral East
FEB 1984 24-Feb-84 24-Feb-84 24-Feb-84 24-Feb-84 24-Feb-84 La Niña West
JAN 1985 2-Jan-85 1-Jan-85 1-Jan-85 1-Jan-85 1-Jan-85 La Niña East
JAN 1987 23-Jan-87 23-Jan-87 23-Jan-87 23-Jan-87 23-Jan-87 El Niño West
DEC 1987 8-Dec-87 8-Dec-87 8-Dec-87 8-Dec-87 8-Dec-87 El Niño West
MAR 1988 14-Mar-88 14-Mar-88 14-Mar-88 14-Mar-88 14-Mar-88 El Niño West
FEB 1989 22-Feb-89 21-Feb-89 21-Feb-89 21-Feb-89 21-Feb-89 La Niña West
DEC 1998 15-Dec-98 15-Dec-98 15-Dec-98 15-Dec-98 15-Dec-98 La Niña East
FEB 1999 25-Feb-99 26-Feb-99 26-Feb-99 26-Feb-99 26-Feb-99 La Niña East
MAR 2000 20-Mar-00 20-Mar-00 20-Mar-00 20-Mar-00 20-Mar-00 La Niña West
FEB 2001 11-Feb-01 11-Feb-01 11-Feb-01 11-Feb-01 11-Feb-01 La Niña West
DEC 2001 2-Jan-02 31-Dec-01 30-Dec-01 31-Dec-01 30-Dec-01 Neutral East
FEB 2002 **** 18-Feb-02 **** **** 17-Feb-02 Neutral East
JAN 2003 18-Jan-03 18-Jan-03 18-Jan-03 18-Jan-03 El Niño West
JAN 2004 7-Jan-04 5-Jan-04 5-Jan-04 5-Jan-04 Neutral East
JAN 2006 21-Jan-06 21-Jan-06 21-Jan-06 21-Jan-06 La Niña East
FEB 2007 24-Feb-07 24-Feb-07 24-Feb-07 24-Feb-07 El Niño West
FEB 2008 22-Feb-08 22-Feb-08 22-Feb-08 22-Feb-08 La Niña East
JAN 2009 24-Jan-09 24-Jan-09 24-Jan-09 24-Jan-09 La Niña West
FEB 2010 9-Feb-10 9-Feb-10 9-Feb-10 9-Feb-10 El Niño West
MAR 2010 24-Mar-10 24-Mar-10 24-Mar-10 24-Mar-10 El Niño West
JAN 2013 7-Jan-13 6-Jan-13 7-Jan-13 6-Jan-13 Neutral East
FEB 2018 12-Feb-18 12-Feb-18 12-Feb-18 12-Feb-18 La Niña West
JAN 2019 2-Jan-19 2-Jan-19 2-Jan-19 2-Jan-19 El Niño East
JAN 2021[15][16] La Niña[17] West[18]

See also[edit]


  1. ^ a b "Sudden Stratospheric Warming". Met Office.
  2. ^ a b c d Butler, Amy H.; Sjoberg, Jeremiah P.; Seidel, Dian J.; Rosenlof, Karen H. (9 February 2017). "A sudden stratospheric warming compendium". Earth System Science Data. 9 (1): 63–76. Bibcode:2017ESSD....9...63B. doi:10.5194/essd-9-63-2017.
  3. ^ Jucker, Martin; Reichler, Thomas; Waugh, Darryn (2021). "How frequent are Antarctic sudden stratospheric warmings in present and future climate?". Geophysical Research Letters. 48 (11). Bibcode:2021GeoRL..4893215J. doi:10.1029/2021GL093215.
  4. ^ Shen, Xiaocen; Wang, Lin; Osprey, Scott (2020). "The Southern Hemisphere sudden stratospheric warming of September 2019". Science Bulletin. 65 (21): 1800–1802. Bibcode:2020SciBu..65.1800S. doi:10.1016/j.scib.2020.06.028.
  5. ^ Palmeiro, Froila M; Barriopedro, David; Garcia-Herrera, Ricardo; Calvo, Natalia (2015). "Comparing Sudden Stratospheric Warming Definitions in Reanalysis Data" (PDF). Journal of Climate. 28 (17): 6823–6840. Bibcode:2015JCli...28.6823P. doi:10.1175/JCLI-D-15-0004.1. hdl:10261/122618.
  6. ^ Eliassen, A; Palm, T (1960). "On the transfer of energy in stationary mountain waves". Geofysiske Publikasjoner. 22: 1023.
  7. ^ Varotsos, C. (2002). "The southern hemisphere ozone hole split in 2002". Environmental Science and Pollution Research. 9 (6): 375–376. doi:10.1007/BF02987584. PMID 12515343. S2CID 45351011.
  8. ^ Manney, Gloria L.; Sabutis, Joseph L.; Allen, Douglas R.; Lahoz, William A.; Scaife, Adam A.; Randall, Cora E.; Pawson, Steven; Naujokat, Barbara; Swinbank, Richard (2005). "Simulations of Dynamics and Transport during the September 2002 Antarctic Major Warming". Journal of the Atmospheric Sciences. 62 (3): 690. Bibcode:2005JAtS...62..690M. doi:10.1175/JAS-3313.1. S2CID 119492652.
  9. ^ Lewis, Dyani (2019). "Rare warming over Antarctica reveals power of stratospheric models". Nature. 574 (7777): 160–161. Bibcode:2019Natur.574..160L. doi:10.1038/d41586-019-02985-8. PMID 31595070.
  10. ^ Charney, J. G.; Drazin, P. G. (1961). "Propagation of planetary-scale disturbances from the lower into the upper atmosphere". Journal of Geophysical Research. 66 (1): 83–109. Bibcode:1961JGR....66...83C. doi:10.1029/JZ066i001p00083. S2CID 129826760.
  11. ^ Andrews, D.G.; McIntyre, M.E. (1976). "Planetary waves in horizontal and vertical shear: the generalized Eliassen-Palm relation and the mean zonal acceleration". Journal of the Atmospheric Sciences. 33 (11): 2031–2048. Bibcode:1976JAtS...33.2031A. doi:10.1175/1520-0469(1976)033<2031:PWIHAV>2.0.CO;2.
  12. ^ Jucker, Martin (2021). "Scaling of Eliassen-Palm flux vectors". Atmospheric Science Letters. 22 (4). doi:10.1002/asl.1020.
  13. ^ King, A.D.; Butler, A.H.; Jucker, M.; Earl, N.O.; Rudeva, I. (2019). "Observed Relationships Between Sudden Stratospheric Warmings and European Climate Extremes". Journal of Geophysical Research: Atmospheres. 124 (24): 13943–13961. Bibcode:2019JGRD..12413943K. doi:10.1029/2019JD030480.
  14. ^ Laboratory (CSL), NOAA Chemical Sciences. "NOAA CSL: Chemistry & Climate Processes: SSWC". Retrieved 2022-11-23.
  15. ^ Lu, Qian; Rao, Jian; Liang, Zhuoqi; Guo, Dong; Luo, Jingjia; Liu, Siming; Wang, Chun; Wang, Tian (2021-07-28). "The sudden stratospheric warming in January 2021". Environmental Research Letters. 16 (8): 084029. doi:10.1088/1748-9326/ac12f4. ISSN 1748-9326.
  16. ^ "On the sudden stratospheric warming and polar vortex of early 2021 | NOAA". Retrieved 2022-11-23.
  17. ^ Center, NOAA's Climate Prediction. "NOAA's Climate Prediction Center". Retrieved 2022-11-23.
  18. ^ "Climate Prediction Center - Monitoring & Data: Current Monthly Atmospheric and Sea Surface Temperatures Index Values". Retrieved 2022-11-23.

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