Abstract
Abstract. Over the past decade, aerosol optical depth (AOD) observations based on satellite and ground measurements have shown a significant increase over Arabia and the Arabian Sea, attributed to an intensification of regional dust activity. Recent studies have also suggested that west Asian dust forcing could induce a positive response of Indian monsoon precipitations on a weekly timescale. Using observations and a regional climate model including interactive slab-ocean and dust aerosol schemes, the present study investigates possible climatic links between the increasing June–July–August–September (JJAS) Arabian dust activity and precipitation trends over southern India during the 2000–2009 decade. Meteorological reanalysis and AOD observations suggest that the observed decadal increase of dust activity and a simultaneous intensification of summer precipitation trend over southern India are both linked to a deepening of JJAS surface pressure conditions over the Arabian Sea. In the first part of the study, we analyze the mean climate response to dust radiative forcing over the domain, discussing notably the relative role of Arabian vs. Indo-Pakistani dust regions. In the second part of the study, we show that the model skills in reproducing regional dynamical patterns and southern Indian precipitation trends are significantly improved only when an increasing dust emission trend is imposed on the basis of observations. We conclude that although interannual climate variability might primarily determine the observed regional pattern of increasing dust activity and precipitation during the 2000–2009 decade, the associated dust radiative forcing might in return induce a critical dynamical feedback contributing to enhancing regional moisture convergence and JJAS precipitations over southern India.
Highlights
Indian summer monsoon rainfall determines to a large extent food production for subcontinental India and has major socioeconomic impacts
Meteorological reanalysis and aerosol optical depth (AOD) observations suggest that the observed decadal increase of dust activity and a simultaneous intensification of summer precipitation trend over southern India are both linked to a deepening of June– July–August–September (JJAS) surface pressure conditions over the Arabian Sea
Culation and surface pressure changes when dust is present and especially when the increasing dust trend is more realistically forced. From these results we suggest that while the cyclonic changes observed between pentad in reanalyses might be primarily a feature of climate variability, the likely associated increase in JJAS west-Asian dust emissions and Arabian Sea AODs could, determine a possibly important positive feedback contributing to the intensification of easterly circulation and humidity flux convergence towards the southwestern Indian coast
Summary
Indian summer monsoon rainfall determines to a large extent food production for subcontinental India and has major socioeconomic impacts. Using global circulation model (GCM) experiments with prescribed sea surface temperature (SST), Vinoj et al (2014) attributes the cause of this correlation to the large radiative heating induced by dust radiation absorption over Arabia and the Arabian Sea resulting in an intensification of southwesterly moisture convergence towards India This mechanism involves primarily direct and semi-direct aerosol effects and is based on a fast reaction of monsoonal weather systems to dust radiative heating perturbation. Ginoux et al (2012) discuss the possible increasing contribution anthropogenic dust sources relevant to the region, and we indicate later some possible connections with the evolution of low-pressure conditions over the Arabian Sea and the Indian monsoon system In this context, the questions we wish to primarily address here are as follows: what are the main characteristic of dust radiative forcing regional climatic feedbacks, and to what extent could the recent enhancement of dust activity in the Arabian region affect the Indian monsoon dynamics and precipitations on a decadal timescale? Dust radiative and climatic impacts and the possible links between Arabian dust trend and southern India precipitation at the decadal scale are addressed in Sects. 3 and 4
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