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. Using COSMIC GPS Radio Occultation (RO) observations fromJanuary 2007 to December 2016, we retrieved temperature profiles with theheight resolution of about 0.1 km in the upper troposphere and lowerstratosphere (UTLS). We investigated the distribution of static stability( N2 ) and the zonal structure of the tropopause inversion layer (TIL) inthe tropics, where a large change in the temperature gradient occurs associatedwith sharp variations in N2 . We show the variations in the mean N2 profiles in coordinates relative to the cold-point tropopause (CPT). A verythin (  km) layer is found with average maximum N2 in therange of 11.0– 12.0 × 10 - 4  s −2 . The mean and standarddeviation of TIL sharpness, defined as the difference between the maximum N2 ( max⁡N2 ) and minimum N2 ( min⁡N2 )within ±1  km of the CPT, is ( 10.5 ± 3.7 ) × 10 - 4  s −2 . The max⁡N2 is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions,90–150 ∘  E (Maritime Continent; MC) and 170–230 ∘  E(Pacific Ocean; PO), with different land–sea distribution. Seasonalvariations in TIL sharpness and thickness were related to the deep convectiveactivity represented by low outgoing longwave radiation (OLR) during theAustralian and Asian monsoons. The deviation from the mean sharpness(sharpness anomaly) was out of phase with the OLR anomaly in both the MC andPO. The correlation between the sharpness anomaly over the MC and PO and the seasurface 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 andEl Nino (SST Nino 3.4 > + 0.5  K) in the PO, warmer SSTs in the MCand PO produce more active deep convection that tends to force the air upwardto the tropopause layer and increase the temperature gradient there. Theintraseasonal variation in sharpness anomaly during slow and fast episodesof the Madden–Julian Oscillation (MJO) demonstrates that eastwardpropagation of the positive sharpness anomaly is associated with organized deepconvection. Deep convection during MJO will tend to decrease N2 belowCPT and increase N2 above CPT, thus enlarging the TIL sharpness. Convectiveactivity in the tropics is a major control on variations in tropopausesharpness at intraseasonal to interannual timescales.

atmospheric chemistry and physics

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