Reassessment of land–atmosphere interactions over India during summer monsoon using state-of-the-art regional climate models

Abstract

The evaluation and characteristics of land-surface processes over the Indian Summer Monsoon (ISM) region are studied using Dirmeyer's two-legged land-atmosphere coupling metrics in regional climate modelling system. Different land-atmosphere coupling metrics are used for assessing the “hot-spots” of land atmosphere feedback over the Indian subcontinent. The model simulations are performed using regional climate model (RCM)—RegCMv4.0, 4.2 and 4.4.5.10 at different horizontal resolutions. The monthly soil wetness climatology over India is calculated using European Space Agency (ESA) datasets. Maximum soil moisture(SM) is found over the western part of central India during June–September. The results from RCM simulations (RegCMv4.0, 4.2 and 4.4.5.10) indicate more soil wetness, systematically (over-predicted) over North India, Indo-Gangetic plains and central India during June, July, August and September, implying that model soil wetness is driven by precipitation minus evapotranspiration (P-E). The role of aerosols in land–atmosphere interactions along with the impact of mixed convective parameterization schemes over ocean and land on modelling SM and land–atmosphere interactions is also addressed. The spatial and temporal variation of atmospheric and terrestrial coupling indices during ISM regime concludes that May, June, July and August are the prime months of land–atmosphere interactions over central and north-west India reiterating results from previous GLACE (The Global Land–Atmosphere Coupling Experiment) studies. Model simulations also indicate that during the ISM season the terrestrial segment of land–atmosphere coupling (i.e. terrestrial coupling index of soil moisture, SM) from SM to latent heat flux varies around 35–40 W m−2, while the atmospheric segment of coupling (i.e. atmospheric coupling index of precipitation) from latent heat flux to precipitation modulates around 4–6 mm/day. Aerosols are found to influence land-atmosphere interactions over north-west India by modulating net radiation. More in-situ observations of land surface variables are required for verification of land-atmospheric interactions (along with impact of aerosols) using RCMs.