Abstract
Abstract. The influence of aerosols on cloud properties over North India which includes the Indo-Gangetic Plain has been investigated for the years 2000 to 2010. During the years 2004, 2009 and 2010 there has been an abrupt increase in fine mode aerosol optical depth (AOD) inducing a sharp decline in cloud effective radius (CER) in the month of January. The following monsoon during these years was a failure in the region considered for the study. In the year 2010, a highest AOD value of 0.35 was recorded in the month of January. In accordance with the aerosol indirect effect, this large increase in AOD resulted in a significant reduction in CER. The monsoon season in that year was deficient in the study region even though the rest of the country received above normal rainfall. For the years when CER diminished below 12 microns in the month of May, a delay in the advancement of monsoon towards North India is noted even after a normal or early onset in southern peninsula. Meanwhile, a rapid progression took place when it was 12 microns or above. During non-monsoon months an inverse relationship existed between cloud effective radius and liquid water path and a strong positive association occurred in the monsoon months. Present analysis suggests that the excessive aerosol loading and the associated aerosol indirect effects in the months prior to the monsoon season has an effect on the propagation and onset of the south west monsoon over the region.
Highlights
It has been well established through modelling and observational studies that the properties of clouds located in the vicinity of high aerosol concentrations are altered significantly (Ackerman et al, 2000; Penner et al, 2004; Koren et al, 2005; Rosenfeld et al, 2006)
In order to bring out the aerosol optical depth (AOD) and cloud effective radius (CER) variability precisely, the eleven year data is splitted into two panels as shown in the figure
Taking into consideration on the limitations attributed to the MODIS data sets, we summarize the results obtained from the present study as follows
Summary
It has been well established through modelling and observational studies that the properties of clouds located in the vicinity of high aerosol concentrations are altered significantly These sources inject copious amount of aerosols due to the combustion of fossil fuels such as coal, petrol and diesel (Ram and Sarin, 2010) The hygroscopic particles such as sulphates which are emitted from industries are mostly in fine mode and act as good cloud condensation nuclei (Tare et al, 2006). Using MODerate resolution Imaging Spectroradiometer (MODIS) data these studies both qualitatively and quantitatively suggest that there exists a significant positive aerosol indirect effect over IGP (Tripathi et al, 2007) and is one of the factors that modulate the Indian summer monand Legrand, 2003). Soon (Patra et al, 2005; Ravi Kiran et al, 2009; Panicker et al, 2010) It is still uncertain how much the accu- 2 Data description mulation of aerosols in the non-monsoon months affects the onset and progress of succeeding monsoon season. We recognize the errors involved in the retrieval of aerosol and cloud products from MODIS which is a limitation of this study
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