Fine-scale structure of the tropical cold-point tropopause as derived from the COSMIC/FORMOSAT-3 GPS RO system

The characteristics of the tropical cold-point tropopause (CPT) are investigated using high-resolution temperature profiles from 2006 to 2010, with the COSMIC/FORMOSAT-3 GPS RO observations. The climatology and the seasonal/intraseasonal variabilities of the CPT temperature (T-CPT) and pressure (P-CPT) are examined in details. The climatological P-CPT shows zonally uniform structure over the tropics, whereas the T-CPT shows distinct local minima at the regions which correspond to the regions of deep convection. Both of them show a strong seasonality. Regardless of longitudinal location, the CPT is cold in temperature and low in pressure during boreal winter but is warm and high during boreal summer. This seasonality is associated with the stratospheric circulation as evident from the seasonal variation of the temperature on the lower-stratosphere. The seasonal cycle is strongest over the Western Pacific warm pool sector but weakest over the westerly duct region. This regionality indicates that the tropospheric processes such as convection and large-scale circulation can modulate the seasonality of the CPT. The intraseasonal variability of the CPT shows the signature of the Madden-Julian oscillation (MJO) with a maximum variability over the Indian Ocean, and the signature of Kelvin wave with a maximum variability over the western to central part of the Pacific Ocean. These intraseasonal variabilities are reasonably well matched to those of outgoing long-wave radiation (OLR), although the MJO-related CPT variability has relatively larger zonal wave number than that of OLR.