Study on long term troposphere lower stratosphere temperature (TLST) trend in tropical and subtropical northern hemisphere using ground based and COSMIC satellite data

Abstract

The troposphere, the lowest and closest layer of the atmosphere, is where all meteorological events take place. The tropospheric — lower stratospheric (TLS) temperature trend is determined using linear regression and is essential to comprehending the consequences of climate change in the future. In this article, we explored the long-term temperature variabilities and trends of TLS (1–25 km) temperature and its responses by natural drivers such as El Nino southern oscillation (ENSO), solar flux (SF), quasi-biannual oscillation (QBO), Indian ocean dipole (IOD), and aerosol indexes (AI) using monthly averaged zonal mean COSMIC satellite and ground — based Radiosonde (RS) observations for the period of 2006 – 2020 over tropical station Addis ($9^0$ N, $38.8^0$ E) and subtropical station Cairo ($30.03^0$ N, $31.23^0$ E). The tropopause is located at the tropical station Addis at 17 km with a temperature of 190–194 K, and for the subtropical station Cairo, it is located at 15 km with a temperature of 201 K, which supports the decrement of tropopause height from the tropics to the subtropics with a slight increase in temperature. The two main oscillations in the TLS region can be seen by using the wavelet analysis technique: the semiannual oscillation (SAO) and the annual oscillation (AO), with the AO being especially strong in the lower troposphere. Furthermore, Morlet wavelet analysis on cold-point tropopause temperature CPTt displays AO and cold point tropopause height CPTh reveals a QBO-like signal. The TLS region has positive peaks at heights of 7, 21, 22, 13, and 4 km for the Addis station, and at 15, 19, 25, 15, and 16 km for the Cairo station in response to natural drivers such as ENSO, SF, QBO, IOD, and aerosol. Lag analyses demonstrate a one-month delay for all natural forcings, except for oceanic indices and SSF, up to three months below the tropopause (below 15 km). There is a noticeable 3 to 4 months lag in every oscillation above the tropopause. A warming trend in the tropospheric region and a cooling trend in the UTLS regions are revealed by MLR trend analysis. In contrast to the subtropical Cairo station, which has the highest warming rate of 0.38 K/decade at 2 km and the maximum cooling rate of −0.2 K/decade at 10 km, the tropical Addis station has the highest cooling rate of −0.38 K/decade at 12 km and the highest warming rate of 0.28 K/decade at 3 km. Our trend findings are consistent with previous research.