Tropical belt expansion and its impacts on climate variability in the Mediterranean from 1980 to 2022

This paper explores the long-term variability of climatic parameters over the Mediterranean region and their relationship with tropical belt expansion by investigating observational and reanalysis data from January 1980 to December 2022 through multiple approaches, including correlation, linear regression, and singular value decomposition (SVD) analysis. The lapse rate tropopause height exhibits upward trends of approximately 80.58 m per decade. Concurrently, the tropical belt shows a poleward expansion of approximately 0.14 and 0.27° per decade, estimated using the tropopause drop and tropopause gradient methods, respectively. The tropical edge latitudes (TELs) of both applied approaches show an evident seasonal variation. In addition, the two TEL definitions exhibit consistent correlation patterns with surface temperature (Ts), lower tropospheric temperature (Trp-1), upper tropospheric temperature (Trp-2), precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI). The results of the SVD analysis depict that although the leading mode explains the majority of the covariance between TELs and the examined climatic parameters, the second coupled mode shows more localized spatial structures, with TELs pronouncedly coupling with Ts and Trp-1 in the eastern Mediterranean. Furthermore, Ts and Trp-1 have significant increasing trends, which are abundant in the eastern Mediterranean. On the other hand, both precipitation and SPEI exhibit downward trends. Over the Mediterranean region, climatic parameters show an apparent spatial and temporal variation. The results confirm the linkage between climatic parameters' trends and variability with the TELs' variability patterns over the study area, especially in the eastern Mediterranean region.