El Nino as a natural experiment for studying the tropical tropopause region

The interannual variability of the tropical tropopause region between 14 an d 18 km is examined using observations of convection, winds, and tropopause temperatures from reanalyses and water vapor from satellites. This variabi lity is compared to a simulation using the Community Climate Model version 3 (CCM3) general circulation model forced by observed sea surface temperatu res. A coherent picture of the effect of the El Nino-Southern Oscillation ( ENSO) on the tropopause region is presented in the NCEP-NCAR reanalyses and CCM3. ENSO modifies convection in the Tropics, and the temperature and cir culation of the tropical tropopause region, in agreement with idealized mod els of tropical heating. CCM3 reproduces most details of these changes, but not the zonal mean temperature variations present in the analysis fields, which are not related to ENSO. ENSO also forces significant changes in obse rved and simulated water vapor fields. In the upper troposphere water vapor is at maximum near convection, while in the tropopause region water vapor is at minimum in the regions of convection and surrounding it. Convection, cirrus clouds, temperatures, and transport are all linked to describe the w ater vapor distribution and highlight the role of transport in the tropopau se region.