| The tropical tropopause layer (TTL) is a transition region between the convectively dominated troposphere and the radiatively controlled stratosphere. The TTL plays an important role in radiative energy budget of our climate system, constituent entry to the stratosphere, and the photochemistry of ozone. However, many aspects of the TTL are not fully understood yet, for example, cloud feedback and water vapor exchange processes. The overall goal of this thesis is to understand how the TTL connects the stratosphere (i.e., the Brewer-Dobson circulation) and the troposphere (i.e., the tropical deep convection), especially on the seasonal time scale.;The connection between the seasonal thermal structure cycle in the TTL and the Brewer-Dobson circulation is investigated in Chapter 2. An upwelling rate proportional to the extratropical wave driving (mid-latitude EP flux) is sufficient to explain in detail the seasonal cycles of TTL temperature above 80 hPa. However, temperatures below 80 hPa lag those predicted, indicating either a delay in upwelling or the influence of by other more local influences (e.g., tropospheric convection and/or tropical waves). The annual cycle of ozone in the TTL amplifies the seasonal temperature cycle by 2.6 K at 70 hPa and 1 K at 100 hPa and delays the cycle by one month.;The connection between the TTL and the tropical deep convection is analyzed in Chapter 3 using Multi-angle Imaging SpectroRadiometer (MISR), focusing on the seasonal cycle, and simulated in Chapter 4 by the Weather Research and Forecasting (WRF) cloud resolving model. The tropical deep convection core (e.g., overshooting) height is explained by parcel theory represented by CAPE: The higher peak of thick-mod cloud-top height is observed in the higher CAPE season. However, the peak (near 13 km) of convective outflow (thin-mod clouds) shifts upward by 600 m in DJF over JJA regardless CAPE value. This shift is quantitatively reproduced by the cloud resolving model, which furthermore shows it to be entirely due to the different temperature structure (i.e., stability change) near and above 13 km.;This thesis shows that the tropical tropopause interacts with both the stratosphere and the troposphere: The stratospheric circulation modulates the thermodynamic structure up to 200 hPa, and the same time, the tropospheric physical features also affect it up to 80 hPa. The convective outflow height is controlled by thermal condition in the TTL. It is not explained by standard parcel theory, but is roughly consistent with predictions based on an overshooting+mixing process in the TTL. This indicates that mixing processes above the outflow level must be considered to predict where the outflow will occur, and gives new insight into the problem of cumulus cloud parameterization. This work also suggests that accounting for the thermal structure change of the TTL in future climate will be important in predicting cloud feedback and future water vapor in the stratosphere. |
