Topographic Influence on SNAO-Driven Summer Precipitation Variability in the Central-Eastern Himalayas

Significant progress has been made in understanding the relationship between Tibetan Plateau (TP) summer precipitation and the summer North Atlantic Oscillation (SNAO). However, the role of topography on this relationship remains unclear. The central-eastern Himalayas (CEH), a key high-altitude barrier on the southern edge of the TP, experiences concentrated summer rainfall and is a crucial water source. Analysis of long-term observations and reanalysis data revealed that the SNAO-driven positive summer precipitation in the CEH was influenced more by topographic mechanical forcing than by the impacts of atmospheric circulation. Topography forces horizontal winds to generate a strong climb flow component, driving changes in the precipitation distribution. Experiments removing topographic features show that the original positive precipitation distribution shifts into a dipole-like pattern, dominated by negative distribution, which are directly governed by atmospheric circulation. Thus, accurate predictions of future summer precipitation in the CEH should consider both dynamic topographic and atmospheric processes.