Comparison of satellite limb-sounding humidity climatologies of the uppermost tropical troposphere

[摘要] Humidity climatologies of the tropical uppermost troposphere from satellitelimb emission measurements have been compared. Four instruments areconsidered; UARS-MLS, Odin-SMR, and Aura-MLS operating in the microwaveregion, and MIPAS in the infrared region. A reference for the comparison isobtained by MOZAIC in-situ measurements.

The upper tropospheric humidity products were compared on basis of theirempirical probability density functions and seasonally averaged horizontalfields at two altitude layers, 12 and 15 km. The probability densityfunctions of the microwave datasets were found to be in very good agreementwith each other, and were also consistent with MOZAIC. The average seasonalhumidities differ with less than 10%RHi between the instruments, indicatingthat stated measurement accuracies of 20–30% are conservative estimates.The systematic uncertainty in Odin-SMR data due to cloud correction was alsoindependently estimated to be 10%RHi. MIPAS humidity profiles were found tosuffer from cloud contamination, with only 30% of the measurements reachinginto the upper troposphere, but under clear-sky conditions there is a goodagreement between MIPAS, Odin-SMR and Aura-MLS.

Odin-SMR and the two MLS datasets can be treated as independent, being basedon different underlying spectroscopy and technology. The good agreementbetween the microwave limb-sounders, and MOZAIC, is therefore an importantstep towards understanding the upper tropospheric humidity. The foundaccuracy of 10%RHi is approaching the level required to validate climatemodelling of the upper troposphere humidity. The comparison of microwave andinfrared also stresses that microwave limb-sounding is necessary for a completeview of the upper troposphere.

[学科分类] 大气科学