Regional and seasonal stratospheric temperature trends in the last decade (2002–2014) from AMSU observations

Abstract : Stratospheric temperature trends for the period 2002-2014 have been estimated using NOAA's Integrated Microwave Inter-Calibration Approach (IMICA) version of AMSU on AQUA satellite. In this period the stratosphere continued cooling over most of the globe with a rate ranging from -0.4±0.3 to -0.5±0.4 K/decade above 25 km. Considering specific latitude bands, trends are highly variable with height. In the Tropical region, trends vary from -0.5±0.3 K/decade for channel 12 (∼30 km) to -0.7±0.3 K/decade for higher channels, and present small seasonal variability in the intensity of cooling. In the polar regions and in the mid-latitudes, trends for all channels are negative but not significant; uncertainties are large due to the high dynamical variability particularly in high latitudes. There is also large seasonal variability, with Southern mid-latitudes seasonal trends significant during summer (DJF) and autumn (MAM) above ∼25 km, with values ranging from -1.0±0.5 to -0.6±0.5 K/decade. Regional trends estimated with AMSU and long-term lidar measurements (over 2 decades) confirm stratospheric cooling in the Northern mid-latitudes and Tropical regions. The effect of the length of the short series on trends was found to be small outside polar regions. It was found to be large in polar regions with about 1 K changes in trend depending on start dates of the time series.