UTLS water vapour from SCIAMACHY limbmeasurementsV3.01 (2002–2012)

[摘要] The SCanning Imaging Absorption spectroMeter for AtmosphericCHartographY (SCIAMACHY) aboard the Envisat satellite providedmeasurements from August 2002 until April 2012. SCIAMACHY measuredthe scattered or direct sunlight using different observationgeometries. The limb viewing geometry allows the retrieval of watervapour at about 10–25 km height from the near-infraredspectral range (1353–1410 nm). These data cover the uppertroposphere and lower stratosphere (UTLS), a region in theatmosphere which is of special interest for a variety of dynamicaland chemical processes as well as for the radiative forcing.Here,the latest data version of water vapour (V3.01) from SCIAMACHY limbmeasurements is presented and validated by comparisons with datasets from other satellite and in situ measurements. Consideringretrieval tests and the results of these comparisons, the V3.01 dataare reliable from about 11 to 23 km and the best results are foundin the middle of the profiles between about 14 and 20 km.Above20 km in the extra tropics V3.01 is drier than all other datasets. Additionally, for altitudes above about 19 km, the verticalresolution of the retrieved profile is not sufficient to resolvesignals with a short vertical structure like the tape recorder.Below 14 km, SCIAMACHY water vapour V3.01 is wetter than mostcollocated data sets, but the high variability of water vapour inthe troposphere complicates the comparison. For 14–20 kmheight, the expected errors from the retrieval and simulations andthe mean differences to collocated data sets are usually smallerthan 10 % when the resolution of the SCIAMACHY data is takeninto account. In general, the temporal changes agree well withcollocated data sets except for the Northern Hemisphereextratropical stratosphere, where larger differences are observed.This indicates a possible drift in V3.01 most probably caused by theincomplete treatment of volcanic aerosols in the retrieval. In allother regions a good temporal stability is shown. In the tropicalstratosphere an increase in water vapour is found between 2002 and2012, which is in agreement with other satellite data sets foroverlapping time periods.

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