This dissertation investigates the complicated troposphere-lower stratosphere (TLS) region, with an emphasis on trace gas transport across the tropical tropopause and how it a ects climate and weather systems. There is a paucity of extensive research on the spatial and temporal variations of TLS temperature over tropical Ethiopia and subtropical Egypt using numerous data sources, despite earlier research on natural inuences. This study analyzes long-term trends in TLS temperature from 2006 to 2020 by utilizing both ground-based and COSMIC satellite data, focusing on TLS variability and its inuencing drivers through wavelet analysis and multivariate linear regression methods. It also examines Kelvin wave patterns observed from 2019 to 2020 using Radiosonde and AIRS satellite datasets, along with the exchange of trace gases ozone and water vapor in the UTLS region. Our study demonstrates that the tropopause height decreases from the tropics to the subtropics with a slight increase in temperature. The tropical station Addis is located at 17 km and has a temperature of 190-194 K, while the subtropical Cairo is located at 15 km and has a temperature of 201 K. Morlet wavelet analysis applied to cold point tropopause temperature (CPTt) exhibits AO and cold point tropopause height (CPTh) exposes QBO-like signal patterns. An investigation of the response to natural drivers such as ENSO, SF, QBO, IOD, and aerosols on temperature variability reveals positive peaks at various altitudes. Lag analysis indicates delays in natural forcing e ects, revealing a warming trend in the tropospheric region and a cooling trend in the upper troposphere lower stratosphere (UTLS) region identi ed through multiple linear regression trend analysis. 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, 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. Further studies explore the activity of waves (KW), focusing on their distinctive features such as periodicity and wavelengths in tropical and subtropical regions. This analysis uses longitude-time and altitude-time data sourced from RS and AIRS satellite observations, covering the period from March 2019 to February 2020 in the TLS region. In Addis Ababa, KW periodicity ranges from 9.2 to 14.5 days with vertical wavelengths of 3.8 to 12.5 km, while in Cairo, it ranges from 6.4 to 13.3 days with vertical wavelengths of 6 to 11.2 km. KW shows downward propagation, especially summer, with maximum amplitudes of 8 K in Ethiopia and 4 K in Egypt. This suggests that the KW exponentially decreases as it moves from the tropics to the subtropics. The study nds strong correlations between tropopause height and KW is 0.86 and gravity waves with tropopause height is 0.48. High KW activity is linked to low Outgoing Longwave Radiation (OLR) values, indicating signi cant convective activity during summer KW events. Our study further focuses on the roles of trace gases such as water vapor and ozone in the upper troposphere and lower stratosphere (UTLS), as well as their impact on climate change. Ozone distribution remains stable in the UTLS, except during spring in Ethiopia and autumn in Egypt. The transport of ozone and water vapor across the tropopause is controlled by the cold-point tropopause height (CPTh) and temperature (CPTt), respectively. In Egypt, the annual mean ozone volume mixing ratio (OVMR) ranges from 6 to 9 ppmv, while in Ethiopia, it ranges from 6 to 10 ppmv. Water vapor mixing ratio (WVMR) peaks at 600-400 ppmv in Ethiopia and 200-100 ppmv in Egypt. Egypt has a higher ozone mass ux (5 kg/s) compared to Ethiopia (3.4 kg/s), while Ethiopia has a higher water vapor mass ux (68 kg/s) compared to Egypt (30 kg/s). The study also identi es semi-annual oscillation (SAO) in WVMR and annual oscillation (AO) in OVMR in Ethiopia, and triannual oscillation (TAO) in WVMR and AO in OMR in Egypt.