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==Determination==
==Determination==
[[Satellite]]s do not measure temperature. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature.<ref name="NRC2000">{{cite book |chapter=Atmospheric Soundings |title=Issues in the Integration of Research and Operational Satellite Systems for Climate Research: Part I. Science and Design |author=National Research Council (U.S.). Committee on Earth Studies |coauthors= |year=2000 |publisher=National Academy Press |location=Washington, D.C. |isbn=0309515270 |pages=17–24 |chapterurl=http://books.nap.edu/openbook.php?record_id=9963&page=17 }}</ref><ref name="Uddstrom1988">{{cite journal |last=Uddstrom |first=Michael J. |authorlink= |coauthors= |year=1988 |month= |title=Retrieval of Atmospheric Profiles from Satellite Radiance Data by Typical Shape Function Maximum a Posteriori Simultaneous Retrieval Estimators |journal=Journal of Applied Meteorology |volume=27 |issue=5 |pages=515&ndash;549 |doi=10.1175/1520-0450(1988)027<0515:ROAPFS>2.0.CO;2 |url= |accessdate= }}</ref> The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. As a result, different groups that have analyzed the satellite data have obtained different temperature trends. Among these groups are [[Remote Sensing Systems]] (RSS) and the [[University of Alabama in Huntsville]] (UAH). Furthermore the satellite series is not fully homogeneous - it is constructed from a series of satellites with similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for satellite drift in orbit. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult.
[[Satellite]]s do not measure temperatura. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature.<ref name="NRC2000">{{cite book |chapter=Atmospheric Soundings |title=Issues in the Integration of Research and Operational Satellite Systems for Climate Research: Part I. Science and Design |author=National Research Council (U.S.). Committee on Earth Studies |coauthors= |year=2000 |publisher=National Academy Press |location=Washington, D.C. |isbn=0309515270 |pages=17–24 |chapterurl=http://books.nap.edu/openbook.php?record_id=9963&page=17 }}</ref><ref name="Uddstrom1988">{{cite journal |last=Uddstrom |first=Michael J. |authorlink= |coauthors= |year=1988 |month= |title=Retrieval of Atmospheric Profiles from Satellite Radiance Data by Typical Shape Function Maximum a Posteriori Simultaneous Retrieval Estimators |journal=Journal of Applied Meteorology |volume=27 |issue=5 |pages=515&ndash;549 |doi=10.1175/1520-0450(1988)027<0515:ROAPFS>2.0.CO;2 |url= |accessdate= }}</ref> The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. As a result, different groups that have analyzed the satellite data have obtained different temperature trends. Among these groups are [[Remote Sensing Systems]] (RSS) and the [[University of Alabama in Huntsville]] (UAH). Furthermore the satellite series is not fully homogeneous - it is constructed from a series of satellites with similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for satellite drift in orbit. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult.


===Surface measurements===
===Surface measurements===

Revision as of 13:09, 19 January 2011

Comparison of ground based measurements of surface temperature (blue) and satellite based records of mid-tropospheric temperature (red: UAH; green: RSS) since 1979. Trends plotted since January 1982.
Atmospheric temperature trends from 1979-2010 based on satellite measurements.

Satellite temperature measurements have been obtained from the sea surface since 1967 and from the troposphere since late 1978. By comparison, the usable balloon (radiosonde) record begins in 1958 but has less geographic coverage and is less uniform. Weather satellites measure radiances in various wavelength bands, which are then mathematically inverted to obtain indirect inferences of temperature. Surface measurements are derived from skin temperature, determined by thermal infrared imagery of weather satellites. These measurements can be used to locate weather fronts, monitor the El Niño-Southern Oscillation, determine the strength of tropical cyclones, and study urban heat islands. Microwave sounding units (MSUs) on National Oceanic and Atmospheric Administration polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen, which is proportional to the temperature of broad vertical layers of the atmosphere. Satellite datasets show there has been warming in the troposphere over the past few decades, and cooling within the stratosphere, both of which are supported by global warming research.

Determination

Satellites do not measure temperatura. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature.[1][2] The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. As a result, different groups that have analyzed the satellite data have obtained different temperature trends. Among these groups are Remote Sensing Systems (RSS) and the University of Alabama in Huntsville (UAH). Furthermore the satellite series is not fully homogeneous - it is constructed from a series of satellites with similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for satellite drift in orbit. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult.

Surface measurements

See also: Sea_surface_temperature § Weather_satellites

Satellites may also be used to retrieve surface temperatures in cloud-free conditions, generally via measurement of thermal infrared from AVHRR. Weather satellites have been available to infer sea surface temperature (SST) information since 1967, with the first global composites occurring during 1970.[3] Since 1982,[4] satellites have been increasingly utilized to measure SST and have allowed its spatial and temporal variation to be viewed more fully. For example, changes in SST monitored via satellite have been used to document the progression of the El Niño-Southern Oscillation since the 1970s.[5] Over the land the retrieval of temperature from radiances is harder, because of the inhomogeneities in the surface.[6] Studies have been conducted on the urban heat island effect via satellite imagery.[7] Use of advanced very high resolution infrared satellite imagery can be used, in the absence of cloudiness, to detect density discontinuities (weather fronts) such as cold fronts at ground level.[8] Using the Dvorak technique, infrared satellite imagery can used to determine the temperature difference between the eye and the cloud top temperature of the central dense overcast of mature tropical cyclones to estimate their maximum sustained winds and their minimum central pressures.[9]

Tropospheric and stratospheric measurements

See also: MSU temperature measurements

Since 1979, microwave sounding units (MSUs) on NOAA polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen. The intensity is proportional to the temperature of broad vertical layers of the atmosphere, as demonstrated by theory and direct comparisons with atmospheric temperatures from radiosonde (balloon) profiles. Upwelling radiance is measured at different frequencies; these different frequency bands sample a different weighted range of the atmosphere.[10] Channel 2 is broadly representative of the troposphere, albeit with a significant overlap with the lower stratosphere (the weighting function has its maximum at 350 hPa and half-power at about 40 and 800 hPa). In an attempt to remove the stratospheric influence, Spencer and Christy developed the synthetic "2LT" product by subtracting signals at different view angles; this has a maximum at about 650 hPa. However this amplifies noise,[11] increases inter-satellite calibration biases and enhances surface contamination.[12] The 2LT product has gone through numerous versions as various corrections have been applied.

See also: UAH satellite temperature dataset and MSU temperature measurements
Year UAH Trend
1991 0.087
1992 0.024
1993 -0.013
1994 -0.003
1995 0.033
1996 0.036
1997 0.040
1998 0.112
1999 0.105
2000 0.095
2001 0.103
2002 0.121
2003 0.129
2004 0.130
2005 0.139
2006 0.140
2007 0.143

Records have been created by merging data from nine different MSUs, each with peculiarities (e.g., time drift of the spacecraft relative to the local solar time) that must be calculated and removed because they can have substantial impacts on the resulting trend.[13] The satellite record is short, which means adding a few years on to the record or picking a particular time frame can change the trends considerably. The problems with the length of the MSU record is shown by the table to the right, which shows the UAH TLT (lower tropospheric) global trend (°C/decade) beginning with Dec 1978 and ending with December of the year shown.

The process of constructing a temperature record from a radiance record is difficult. The satellite temperature record comes from a succession of different satellites and problems with inter-calibration between the satellites are important, especially NOAA-9, which accounts for most of the difference between various analyses.[14] NOAA-11 played a significant role in a 2005 study by Mears et al. identifying an error in the diurnal correction that leads to the 40% jump in Spencer and Christy's trend from version 5.1 to 5.2.[15] There are ongoing efforts to resolve differences in satellite temperature datasets.

Christy et al. (2007) find that the tropical temperature trends from radiosondes matches closest with his v5.2 UAH dataset.[16] Furthermore, they assert there is a growing discrepancy between RSS and sonde trends beginning in 1992, when the NOAA-12 satellite was launched.[citation needed] This research found that the tropics were warming, from the balloon data, +0.09 (corrected to UAH) or +0.12 (corrected to RSS) or 0.05 K (from UAH MSU; ±0.07 K room for error) a decade.

Using the T2 channel (which include significant contributions from the stratosphere, which has cooled), Mears et al. of Remote Sensing Systems (RSS) find (through December 2010) a trend of +0.099 °C/decade.[17] Spencer and Christy of the University of Alabama in Huntsville (UAH), find a smaller trend of +0.053 °C/decade.[18] A less regularly updated analysis is that of Vinnikov and Grody with +0.20°C per decade (1978–2005).[19] Another satellite temperature analysis is provided by NOAA/NESDIS STAR Center for Satellite Application and Research and use simultaneous nadir overpasses (SNO)[20] to remove satellite intercalibration biases yielding more accurate temperature trends. The SNO analysis finds a 1979-2010 trend of +0.140°C/decade for T2 channel.[21]

Lower stratospheric cooling is mainly caused by the effects of ozone depletion with a possible contribution from increased stratospheric water vapor and greenhouse gases increase.[22][23] There is a decline in stratospheric temperatures, interspersed by warmings related to volcanic eruptions. Global Warming theory suggests that the stratosphere should cool while the troposphere warms [24] The long term cooling in the lower stratosphere occurred in two downward steps in temperature both after the transient warming related to explosive volcanic eruptions of El Chichón and Mount Pinatubo, this behavior of the global stratospheric temperature has been attributed to global ozone concentration variation in the two years following volcanic eruptions.[25] Since 1996 the trend is slightly positive[26] due to ozone recover juxtaposed to a cooling trend of 0.1K/decade that is consistent with the predicted impact of increased greenhouse gases.[25]

Comparison to instrumental record

File:Radiosonde satellite surface temperature.png
1958-2009 radiosonde, satellite and surface temperature record.

The satellite records have the advantage of global coverage, whereas the radiosonde record is longer. There have been complaints of data problems with both records.

To compare to the trend from the surface temperature record (approximately +0.07 °C/decade over the past century and +0.17 °C/decade since 1979) it is most appropriate to derive trends for the part of the atmosphere nearest the surface, i.e., the lower troposphere. Doing this, through December 2010:

  • RSS v3.2 finds a trend of +0.163 °C/decade.[17]
  • UAH v5.4 finds a trend of +0.142°C/decade.[27]

An alternative adjustment introduced by Fu et al. (2004)[28] finds trends (1979–2001) of +0.19 °C/decade when applied to the RSS data set.[29]

Reconciliation with climate models

See also: Climate model and Global warming

Climate models predict that as the surface warms, so should the global troposphere. Globally, the troposphere should warm about 1.2 times more than the surface; in the tropics, the troposphere should warm about 1.5 times more than the surface. For some time the only available satellite record was the UAH version, which (with early versions of the processing algorithm) showed a global cooling trend for its first decade. Since then, a longer record and a number of corrections to the processing have revised this picture: the UAH dataset has shown an overall warming trend since 1998, though less than the RSS version. In 2001, an extensive comparison and discussion of trends from different data sources and periods was given in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (section 2.2.4).[30]

A detailed analysis produced by dozens of scientists as part of the US Climate Change Science Program (CCSP) identified and corrected errors in a variety of temperature observations, including the satellite data.[31][32] Neither regression models nor other related techniques were reconcilable with observed data. The use of fingerprinting techniques on data yielded that "Volcanic and human-caused fingerprints were not consistently identifiable in observed patterns of lapse rate change." As such, issues with reconciling data and models remain. A potentially serious inconsistency has been identified in the tropics, the area in which tropospheric amplification should be seen. Over multi-decadal time scales, while almost all model simulations show greater warming aloft, most observations show greater warming at the surface.[33] The lower troposphere trend derived from UAH satellites (+0.128 °C/decade) is currently lower than both the GISS and Hadley Centre surface station network trends (+0.161 and +0.160 °C/decade respectively), while the RSS trend (+0.158 °C/decade) is similar. However, the expected trend in the lower troposphere, given the surface data, would be around 0.194 °C/decade, making the UAH and RSS trends 66% and 81% of the expected value respectively.

References

  1. ^ National Research Council (U.S.). Committee on Earth Studies (2000). "Atmospheric Soundings". Issues in the Integration of Research and Operational Satellite Systems for Climate Research: Part I. Science and Design. Washington, D.C.: National Academy Press. pp. 17–24. ISBN 0309515270. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
  2. ^ Uddstrom, Michael J. (1988). "Retrieval of Atmospheric Profiles from Satellite Radiance Data by Typical Shape Function Maximum a Posteriori Simultaneous Retrieval Estimators". Journal of Applied Meteorology. 27 (5): 515–549. doi:10.1175/1520-0450(1988)027<0515:ROAPFS>2.0.CO;2. {{cite journal}}: Cite has empty unknown parameters: |month= and |coauthors= (help)
  3. ^ P. Krishna Rao, W. L. Smith, and R. Koffler (January 1972). "Global Sea-Surface Temperature Distribution Determined From an Environmental Satellite" (PDF). Monthly Weather Review. 100 (1): 10–14. Retrieved 2011-01-09.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ National Research Council (U.S.). NII 2000 Steering Committee (1997). The unpredictable certainty: information infrastructure through 2000; white papers. National Academies. p. 2. Retrieved 2011-01-09.{{cite book}}: CS1 maint: numeric names: authors list (link)
  5. ^ Cynthia Rosenzweig, Daniel Hillel (2008). Climate variability and the global harvest: impacts of El Niño and other oscillations on agroecosystems. Oxford University Press United States. p. 31. ISBN 9780195137637. Retrieved 2011-01-14.
  6. ^ Menglin Jin (April 2004). "Analysis of Land Skin Temperature Using AVHRR Observations" (PDF). Bulletin of the American Meteorological Society: 587. doi:10.1175/BAMS-85-4-587. Retrieved 2011-01-14.
  7. ^ Qihao Weng (May 2003). "Fractal Analysis of Satellite-Detected Urban Heat Island Effect" (PDF). Photogrammetric Engineering & Remote Sensing: 555. Retrieved 2011-01-14.
  8. ^ David M. Roth (2006-12-14). "Unified Surface Analysis Manual" (PDF). Hydrometeorological Prediction Center. p. 19. Retrieved 2011-01-14.
  9. ^ Chris Landsea (2010-06-08). "Subject: H1) What is the Dvorak technique and how is it used?". Atlantic Oceanographic and Meteorological Laboratory. Retrieved 2011-01-14.
  10. ^ Remote Sensing Systems
  11. ^ Christy, John R. (1998). "Analysis of the Merging Procedure for the MSU Daily Temperature Time Series". Journal of Climate. 11 (8): 2016–2041. doi:10.1175/1520-0442(1998)011<2016:AOTMPF>2.0.CO;2. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Fu, Qiang (2005). "Satellite-Derived Vertical Dependence Of Tropical Tropospheric Temperature Trends". Geophysical Research Letters. 32 (10): L10703. doi:10.1029/2004GL022266. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ The Satellite Temperature Records: Parts 1 and 2 May 1996
  14. ^ Remote Sensing Systems
  15. ^ Mears, Carl A. (2005). "The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature". Science. 309 (5740): 1548–1551. doi:10.1126/science.1114772. PMID 16141071. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  16. ^ Christy, J. R. (2007). "Tropospheric temperature change since 1979 from tropical radiosonde and satellite measurements". Journal of Geophysical Research. 112: D06102. doi:10.1029/2005JD006881. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  17. ^ a b "Remote Sensing Systems". Retrieved 2009-01-13.
  18. ^ "UAH". Retrieved 2011-01-07.
  19. ^ Vinnikov, Konstantin Y.; Grody, Norman C.; Robock, Alan; Stouffer, Ronald J.; Jones, Philip D.; Goldberg, Mitchell D. (2006). "Temperature trends at the surface and in the troposphere" (PDF). Journal of Geophysical Research. 111: D03106. doi:10.1029/2005JD006392. {{cite journal}}: Cite has empty unknown parameters: |month= and |coauthors= (help)
  20. ^ Zou, C. (2006). "Recalibration of Microwave Sounding Unit for climate studies using simultaneous nadir overpasses". Journal of Geophysical Research. 111: D19114. doi:10.1029/2005JD006798. Retrieved 2010-10-07. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  21. ^ National Environmental Satellite, Data, and Information Service (December 2010). "Microwave Sounding Calibration and Trend". National Oceanic and Atmospheric Administration. Retrieved 2011-01-14.{{cite web}}: CS1 maint: multiple names: authors list (link)
  22. ^ Shine, Keith (2003). "A comparison of model-simulated trends in stratospheric temperatures" (PDF). Q. J. Royal Meteorol. Soc. 129: 1565–1588. doi:10.1256/qj.02.186. Retrieved 2010-02-15. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  23. ^ United Nations Environment Programme
  24. ^ Clough, S.A. (1995). "Line-by-line calculation of atmospheric fluxes and cooling rates 2. Application to carbon dioxide, ozone, methane, nitrous oxide and the halocarbons". Geophysical Research Letters. 16: 519–535. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  25. ^ a b Thompson, David W. J. (2009). "Understanding Recent Stratospheric Climate Change". Journal of Climate. 22 (8): 1934–1943. doi:10.1175/2008JCLI2482.1. Retrieved 2010-02-15. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  26. ^ Liu, Quanhua (2009). "Recent Stratospheric Temperature Observed from Satellite Measurements". SOLA. 5: 53–56. doi:10.2151/sola.2009-014. Retrieved 2010-02-15. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  27. ^ "UAH". Retrieved 2011-01-14.
  28. ^ Fu, Qiang (2004). "Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends" (PDF). Nature. 429 (6987): 55–58. doi:10.1038/nature02524. PMID 15129277. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  29. ^ "Climate of 2004 Annual Review: Temperature Trend". National Oceanic and Atmospheric Administration. 2005-01-13. Retrieved 2008-06-23.
  30. ^ United Nations Environment Programme
  31. ^ Tom M. L. Wigley, V. Ramaswamy, J. R. Christy, J. R. Lanzante, C. A. Mears, B. D. Santer, C. K. Folland (2006-05-02). "Executive Summary: Temperature Trends in the Lower Atmosphere - Understanding and Reconciling Differences" (PDF). United States Global Climate Change Research Program. Retrieved 2011-01-14.{{cite web}}: CS1 maint: multiple names: authors list (link)
  32. ^ Intergovernmental Panel on Climate Change (2007). "IPCC Fourth Assessment Report Summary for Policymakers" (PDF). Cambridge University Press. Retrieved 2011-01-14.
  33. ^ Benjamin D. Santer, J. E. Penner, P. W. Thorne, W. Collins, K. Dixon, T. L. Delworth, C. Doutriaux, C. K. Folland, C. E. Forest, J. E. Hansen, J. R. Lanzante, G. A. Meehl, V. Ramaswamy, D. J. Seidel, M. F. Wehner, T. M. L. Wigley (2006-05-02). "Temperature Trends in the Lower Atmosphere - Understanding and Reconciling Differences: Chapter 5" (PDF). U.S. Climate Change Science Program. Retrieved 2011-01-14.{{cite web}}: CS1 maint: multiple names: authors list (link)

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