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

Abstract

Abstract. Using COSMIC GPS Radio Occultation (RO) observations from\nJanuary 2007 to December 2016, we retrieved temperature profiles with the\nheight resolution of about 0.1\u2009km in the upper troposphere and lower\nstratosphere (UTLS). We investigated the distribution of static stability\n( N2 ) and the zonal structure of the tropopause inversion layer (TIL) in\nthe tropics, where a large change in the temperature gradient occurs associated\nwith sharp variations in N2 . We show the variations in the mean N2 \nprofiles in coordinates relative to the cold-point tropopause (CPT). A very\nthin ( \u2009km) layer is found with average maximum N2 in the\nrange of 11.0– 12.0 × 10 - 4 \u2009s −2 . The mean and standard\ndeviation of TIL sharpness, defined as the difference between the maximum\n N2 ( max\u2061N2 ) and minimum N2 ( min\u2061N2 )\nwithin ±1 \u2009km of the CPT, is ( 10.5 ± 3.7 ) × 10 - 4 \u2009s −2 . The max\u2061N2 is typically located within 0.5\u2009km above CPT. We focused on the variation in TIL sharpness in two longitude regions,\n90–150 ∘ \u2009E (Maritime Continent; MC) and 170–230 ∘ \u2009E\n(Pacific Ocean; PO), with different land–sea distribution. Seasonal\nvariations in TIL sharpness and thickness were related to the deep convective\nactivity represented by low outgoing longwave radiation (OLR) during the\nAustralian and Asian monsoons. The deviation from the mean sharpness\n(sharpness anomaly) was out of phase with the OLR anomaly in both the MC and\nPO. The correlation between the sharpness anomaly over the MC and PO and the sea\nsurface temperature (SST) Nino\xa03.4 index was −0.66 and +0.88 ,\nrespectively. During La Nina (SST Nino\xa03.4 - 0.5 \u2009K) in the MC and\nEl Nino (SST Nino\xa03.4 > + 0.5 \u2009K) in the PO, warmer SSTs in the MC\nand PO produce more active deep convection that tends to force the air upward\nto the tropopause layer and increase the temperature gradient there. The\nintraseasonal variation in sharpness anomaly during slow and fast episodes\nof the Madden–Julian Oscillation (MJO) demonstrates that eastward\npropagation of the positive sharpness anomaly is associated with organized deep\nconvection. Deep convection during MJO will tend to decrease N2 below\nCPT and increase N2 above CPT, thus enlarging the TIL sharpness. Convective\nactivity in the tropics is a major control on variations in tropopause\nsharpness at intraseasonal to interannual timescales.