Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

Abstract

Abstract. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust-ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day −1 (∼ 10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan Plateau. This study demonstrates a thermodynamic mechanism that links remote desert dust emissions in the Middle East to ISM circulation and precipitation variability on subseasonal timescales, which may have implications for ISM rainfall forecasts.

Emission, transport, and radiative effects of mineral dust from the Taklimakan and Gobi deserts: comparison of measurements and model results

“…The SW forcing induced by dust at the TOA over East Asia was generally negative, with greatest values of −6 to −8 and −2 to −4 W m −2 over the GD and TD, respectively. Compared with the dust aerosols over the Sahara Desert, East Asian dust has a complex refractive index with a small imaginary part, and the back scattering of East Asian dust particles is relatively strong, which led to the high negative values of SW radiation forcing at the TOA (Wang et al, 2004;Jin et al, 2015). The magnitude of the direct radiative forcing at the TOA was dominated by the SW radiative forcing because the LW radiative forcing induced by dust was much smaller (0-1 W m −2 ).…”

“…The region of significant LW radiative forcing occurred mainly over the TD and GD, whereas the higher SW radiative forcing almost covered all of northern China. As a result, the dust caused a strong cooling effect at the surface by weakening the incoming radiation through absorption and scattering by the dust particles (Kumar et al, 2014;Jin et al, 2015). The maximum net radiative forcing at the surface reached −14 W m −2 over the GD and −9.2 W m −2 along the dust transport pathway from northern China to Japan and the Korean Peninsula, which is similar to the conclusions of Zhang et al (2009).…”

“…Airborne dust over the TD may play an important role in the global radiative energy budget (Huang et al, , 2015. Special efforts have been dedicated to understanding the spatial and temporal features of the TD dust (Liu et al, 2016), including emission Zhao et al, 2003Zhao et al, , 2006aShao et al, 2011;Chen et al, 2013Chen et al, , 2014aXiong et al, 2013), long-range transport (Uno et al, 2001;Han et al, 2005Han et al, , 2006Han et al, , 2008Zhao et al, 2006bZhao et al, , 2007Huang et al, 2007), radiative forcing (Takamura et al,2004(Takamura et al, , 2005Su et al, 2008;Huang et al, 2009;Ye et al, 2012), and its climatic effects (Huang et al, 2006a(Huang et al, , b, 2007 over the TD.…”

The relationship between anthropogenic dust and population over global semi-arid regions

“…Guan et al (2015a) found that the enhanced warming in drylands was a result of radiativeforced temperature, which has a close relationship with aerosol column burden. The aerosol in drylands has an obvious warming effect (Huang et al, 2006aChen et al, 2010;Ye et al, 2012;Jin et al, 2015), and the aerosol has a wide distribution and tends to have a relatively large optical depth (H. Bi et al, 2011;Liu et al, 2011;, leading to a significant radiative effect in the drylands. According to the results of Tegen and Fung (1995), the existing atmospheric dust load is hard to explain by natural sources alone.…”

Development of an improved aerosol product over the Indian subcontinent: Blending model, satellite, and ground‐based estimates

“…In addition, we illustrated the AOD and rainfall relationship in the form of a spatial correlation (Figure ), as shown by Jin et al . [] in Figure b. We have shown the spatial correlation between AOD and the area‐averaged rainfall (rectangular box as shown in Figure a) for Lags of 0, 5, 10, and 15 days.…”