Long-term climatology of air mass transport through the TropicalTropopause Layer (TTL) during NH winter

[摘要] A long-term climatology of air mass transport through the tropicaltropopause layer (TTL) is presented, covering the period from1962–2005. The transport through the TTL is calculated with aLagrangian approach using radiative heating rates as verticalvelocities in an isentropic trajectory model. We demonstrate theimproved performance of such an approach compared to previousstudies using vertical winds from meteorological analyses. Withinthe upper part of the TTL, the averaged diabatic ascent is0.5 K/day during Northern Hemisphere (NH) winters 1992–2001.Climatological maps show a cooling and strengthening of this part ofthe residual circulation during the 1990s and early 2000s comparedto the long-term mean. Lagrangian cold point (LCP) fields showsystematic differences for varying time periods and natural forcingcomponents. The interannual variability of LCP temperature anddensity fields is found to be influenced by volcanic eruptions, ElNiño Southern Oscillation (ENSO), Quasi-Biennial Oscillation(QBO) and the solar cycle. The coldest and driest TTL is reachedduring QBO easterly phase and La Niña over the western Pacific,whereas during volcanic eruptions, El Niño and QBO westerlyphase it is warmer and less dry.

[学科分类] 大气科学