RECENT STRATOSPHERIC TEMPERATURE TRENDS USING AMSU AND GPS RADIO OCCULTATIONS OBSERVATIONS
Authors: P. Keckhut(LATMOS, UVSQ, Guyancourt France), S.M. Khaykin (LATMOS, UVSQ, Guyancourt France), B. Funatsu (LETG-Rennes-COSTEL,CNRS, Rennes France), C. Claud (LMD,CNRS, Palaiseau France), A. Hauchecorne (LATMOS, CNRS, Guyancourt France)
A variety of observations and model simulations indicate that the stratosphere has cooled in most of the layers since 1979. Different analyses of the SSU series reveal large differences due to the complex challenge of combining successive experiments and trends seems to disappear from 1995 to 2015. Evaluation of stratospheric trends using recent temperature series from Aqua AMSU-A instrument benefits from the fixed orbit of Aqua satellite, which eliminates the tidal effect on the trends due to orbital drift. In addition, AMSU has a more distinct weighting functions (vertical half-width of ~10 km) compared to those of SS. GPS-RO is also a well established technique, providing stratospheric temperature profiles at ~1 km vertical resolution with global geographical and full diurnal coverage. We combine the observations from various RO missions processed using EUMETSAT ROM SAF facility - CHAMP, GRACE, COSMIC and Metop A/B - altogether covering 2002-2016 period.
AMSU and GPS-RO temperature trends the RO profiles ranging between the tropopause and 35 km were convoluted using AMSU weighting functions (channels 9-13). The altitude, latitudes and seasonal patterns of temperature trends from AMSU and RO appear in good agreement, providing confidence in our estimates.
Analysis of both AMSU and RO datasets are in good agreement showing a clear global cooling. A remarkable inter-hemispheric asymmetry with larger cooling trend throughout the Southern hemisphere’s mid-stratosphere and a quasi-null change at the Northern mid-latitudes is reported. In contrast to that, the (sub-)tropical lower stratosphere is shown to be warming in SH during all seasons and cooling in NH from April through December..