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Data

The data used in this study are provided by the NOAA series polar satellites, which carry onboard the TIROS-N operational Vertical Sounder (TOVS). TOVS consists of three passive vertical sounding instruments (Smith et al, 1979): the High resolution Infrared Radiation Sounder (HIRS-2), a radiometer with 19 channels in the infrared and one in the visible band, the Microwave Sounding Unit (MSU) with 4 channels operating at 55 GHz, and the Stratospheric Sounding Unit (SSU) with 3 channels near to 15 micron. HIRS-2 and MSU data for the period ranging from January 1987 until June 1995 have been reanalyzed using the 3I algorithm (e.g. Chedin et al., 1985; Scott et al., 1999) to derive in particular the vertical temperature profile from the surface up to 10 hPa. Our study makes only use of monthly mean temperatures of four atmospheric layers: 100-70, 70-50, 50-30 and 30-10 hPa. The temperatures are gridded on a regular 1deg latitude per 1 deg longitude grid.

The 8.5 year measurement period covers about 3 QBO oscillations, 2 strong ENSO events ('87 and '92, refer) and the Pinatubo eruption (June '91). It covers a maximum in the solar cycle ('88-'92); but not an entire cycle