Stratospheric Temperature Trends Between 10 and 70 hPa During the Period 1948-2009

Abstract

Trends in zonal mean temperatures between 10 and 70 hPa have been assessed for the period 1948-2009 using zonal monthly mean temperature from the NCEP/NCAR reanalysis dataset. Monthly temperature linear trends were calculated for the Northern and Southern Hemisphere at a 5° step in latitude. The observed trend pattern agrees with a general cooling for every month. The area of negative trends, in the latitude-month grid, increases as we go down in the stratosphere. Positive trends are also observed, mainly at 10 hPa for equatorial zones and summer northern and southern latitudes, and also at southern high-latitudes during the months July-February for every height analyzed. The positive trends observed at 10 hPa at equatorial and mid-latitudes are due to a warming from the beginning of the record until the beginning of 1980s, coincident with the El Chichon eruption. In the case of high latitudes, also at 10 hPa, there seems to be a "step" in 1979. For lower altitudes the positive trends are smoother. In the case of 10 hPa we suggest as a hint, that the temperature behavior for the "warming" cases follows the 11-year running mean of the total solar irradiance.