The Role of ENSO in Modulating the Tropical Upper Tropospheric Humidity

Upper tropospheric water vapour plays a crucial role in the climate system by providing a strong positive feedback, particularly in the tropics. Upper Tropospheric Humidity (UTH) is strongly linked to large-scale atmospheric circulation, including the Hadley and Walker circulations, which undergo pronounced modulation during El Niño–Southern Oscillation (ENSO) events. In this study, we examine ENSO-related changes in the tropical distribution of UTH using long-term climatological datasets of UTH and sea surface temperature (SST). Significant upper-tropospheric drying (moistening) during El Niño (La Niña) years is observed over the Maritime Continent, the western Pacific, and the Indian subcontinent. These UTH anomalies are accompanied by corresponding negative (positive) anomalies in precipitation and upper-level cloud fractions, indicating a strong coupling between UTH and tropical convection. However, the statistical significance of these signals over the Indian subcontinent is limited, suggesting that ENSO influences UTH over India indirectly, likely mediated by regional circulation and monsoon dynamics. Overall, our results highlight ENSO as a key driver of tropical UTH variability through its impact on atmospheric circulation and convection.