Numerical study of the role of land-air-sea interactions for the northeasterly monsoon circulations over Indian Ocean during INDOEX

Abstract

One of the principal objectives of the Indian Ocean Experiment (INDOEX) was to study the aerosol transport from the Indian subcontinent to the pristine oceanic environment. The underlying hypothesis for INDOEX is that, during the northeasterly monsoon, the intruding aerosols and other anthropogenic pollutants can entrain into the Inter Tropical Convergence Zone (ITCZ) and the Equatorial Indian Ocean and finally into the clouds. The altered clouds influence the radiative transfer processes at the regional and possibly global scale. The driving mechanism for the regional transport was the boundary layer circulation. In this study, it was hypothesized that the circulation pattern, which affects the regional transport, was strongly influenced by the land-air-sea interactions. To test this, a zonally symmetric version of a primitive equation numerical weather prediction model, called the Advanced Regional Prediction System (ARPS), was used. A number of numerical experiments were performed for a 2-D domain ranging from 14°N to 16°S centered over 76°E. In the experiments, the influence of land-sea interaction (differential heating), topography (Western Ghats), and the thermal gradients (SST and land surface temperature) on the coastal circulations over Equatorial Indian Ocean were studied. Results indicated a strong land-air-sea interaction and feedback teleconnection between the local and large scale features. Interestingly, the model generated land influence to the order of 1000 km offshore in the simulation domain, consistent with different observations. Results suggest that the oceanic environment in the northeast monsoon over Arabian Sea and the Indian Ocean can display significant diurnal variability and heterogeneity due to topography and surface temperature gradients, and that the local features have interactive feedback on the large scale circulations and transport.