Influence of ENSO and MJO on the zonal structure of tropical tropopause inversion layer using high-resolution temperature profiles retrieved from COSMIC GPS Radio Occultation

Using COSMIC GPS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with the height resolution of about 0.1 km in the upper troposphere and lower stratosphere (UTLS). We investigated the distribution of static stability (N-2) and the zonal structure of the tropopause inversion layer (TIL) in the tropics, where a large change in the temperature gradient occurs associated with sharp variations in N-2. We show the variations in the mean N-2 profiles in coordinates relative to the cold-point tropopause (CPT). A very thin (< 1 km) layer is found with average maximum N-2 in the range of 11.0-12.0 x 10(-4) s(-2). The mean and standard deviation of TIL sharpness, defined as the difference between the maximum N-2 (maxN(2)) and minimum N-2 (minN(2)) within +/- 1 km of the CPT, is. 10.5 +/- 3.7 x 10(-4) s(-2). The maxN(2) is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions, 90-150 degrees E (Maritime Continent; MC) and 170-230 degrees E (Pacific Ocean; PO), with different land-sea distribution. Seasonal variations in TIL sharpness and thickness were related to the deep convective activity represented by low outgoing longwave radiation (OLR) during the Australian and Asian monsoons. The deviation from the mean sharpness (sharpness anomaly) was out of phase with the OLR anomaly in both the MC and PO. The correlation between the sharpness anomaly over the MC and PO and the sea surface temperature (SST) Nino 3.4 index was -0.66 and +0.88, respectively. During La Nina (SST Nino 3.4 < -0.5 K) in the MC and El Nino (SST Nino 3.4 > +0.5 K) in the PO, warmer SSTs in the MC and PO produce more active deep convection that tends to force the air upward to the tropopause layer and increase the temperature gradient there. The intraseasonal variation in sharpness anomaly during slow and fast episodes of the Madden-Julian Oscillation (MJO) demonstrates that eastward propagation of the positive sharpness anomaly is associated with organized deep convection. Deep convection during MJO will tend to decrease N-2 below CPT and increase N-2 above CPT, thus enlarging the TIL sharpness. Convective activity in the tropics is a major control on variations in tropopause sharpness at intraseasonal to interannual timescales.