Annual temperature cycle of the tropical tropopause: A simple model study

[1] A simple radiative-convective model is used to simulate the annual temperature cycle near the tropical tropopause and lower stratosphere (TTL) region. Seasonally varying residual vertical velocity and ozone variation are imposed, the latter derived from 7 a (1998-2004) of Southern Hemisphere additional ozonesonde (SHADOZ) data. Convection is treated only by eliminating lapse rates greater than 6.5 K/km. An upwelling rate proportional to the extratropical wave driving (midlatitude Eliassen-Palm (EP) flux) is sufficient to explain in detail the annual cycles of TTL temperature above 80 hPa and of tropopause pressure, each maximizing in northern summer and minimizing in northern winter. However, temperatures below 80 hPa lag those predicted, indicating either a delay in upwelling or the influence of tropospheric convection. The annual cycle of ozone in the TTL plays an important role in modulating that of temperature: Without ozone variations, the simulated temperature amplitude at 70 hPa falls from similar to 8 K to 5 K, and the maximum temperature occurs in July, 1 month earlier than observed. When the seasonal cycle of ozone is included in the calculation, the amplitude and phase of the temperature cycle come into close agreement with observations. These results support the high-latitude wave-driving hypothesis for explaining tropical upwelling but indicate complicating factors close to the tropopause and an important role for ozone in modulating temperature changes.