Abstract
ABSTRACTLarge aerosol optical depth (AOD) observed over the Indian subcontinent during the monsoon season in the satellite data challenges the common notion of aerosol washout by monsoon rain. Here, we examined recovery of aerosol field after washout by monsoon rain over various rainfall homogeneous zones of India in view of the duration of rainfall, recovery time and source strength. Mean (± 1 standard deviation) seasonal aerosol optical depth, AOD is highest over the central northeast 1 (0.74 ± 0.22) followed by central northeast 2 (0.60 ± 0.11), northwest (0.61 ± 0.15), west-central (0.54 ± 0.13), northeast (0.29 ± 0.08), peninsular India (0.39 ± 0.07) and hilly region (0.33 ± 0.08) in the monsoon season. Post-washout aerosol recovery in India is not a linear function to the recovery period relative to the two successive satellite overpasses. Fastest recovery is observed in the central northeast region dominated by anthropogenic emission. In general, washout is more for 9-hour spell than 3-hour spell, but not spatially uniform over the various rainfall homogeneous zones. In central northeast region it is observed that updraft plays an important role in post precipitation aerosol build up whereas in dust-dominated northwest India, monsoon rainfall (whenever occurs) suppresses dust emission because of the increased soil moisture and therefore inhibits the recovery. The number of grids where washout outweighs recovery during the monsoon season for a 3-hour rainfall increases by 5.6% with an increase in rain rate from 4 mm day–1, while the corresponding increase for a 9-hour rainfall event is 2.8%. AOD reduces in ‘cloudy-sky’ condition relative to ‘clear-sky’ condition because aerosols are scavenged by cloud drops as the clouds grow vertically during the monsoon. Quantitatively, AOD decreases by 16% per 100 hPa increase in cloud base height.
Highlights
Mean (± 1 standard deviation) seasonal aerosol optical depth, AOD is highest over the central northeast 1 (0.74 ± 0.22) followed by central northeast 2 (0.60 ± 0.11), northwest (0.61 ± 0.15), west-central (0.54 ± 0.13), northeast (0.29 ± 0.08), peninsular India (0.39 ± 0.07) and hilly region (0.33 ± 0.08) in the monsoon season
Precipitation Window and Recovery Time In the analysis, if a 3-hour precipitation window is considered from 6 UTC to 9 UTC the condition that it has not rained during any other time period is taken into account
Results are presented for three time windows (Table 1) for precipitation duration of 3 hour, 6 hour and 9 hour
Summary
The Indian subcontinent has been recognized as a major aerosol hot spot (Ramanathan et al, 2001; Kaufman et al, 2002; Lau et al, 2008), where the aerosol characteristics show large spatio-temporal variations (e.g., Prasad and Singh, 2007; Dey and Di Girolamo, 2010; Ramachandran et al, 2012).The aerosol loading continues to increase over the recent years (Dey and Di Girolamo, 2011; Kaskaoutis et al, 2011; Krishna Moorthy et al, 2013) as opposed to a decreasing global trend (Mishchenko et al, 2007).There is a growing evidence of the potential impacts of aerosols on monsoon circulation through dynamic and microphysical connections (Ramanathan et al, 2005; Gautam et al, 2009; Bollasina et al, 2011; Ganguly et al, 2012; Das et al, 2014) that strongly depends on the aerosol load (typically represented in terms of aerosol optical depth, AOD) andIndia is the high AOD during the monsoon season as observed by satellites (e.g., Ramachandran and Cherian, 2008; Dey and Di Girolamo, 2010) and ground-based measurements (e.g., Singh et al, 2004; Dey and Tripathi, 2008; Lodhi et al, 2013). We examined recovery of aerosol field after washout by monsoon rain over various rainfall homogeneous zones of India in view of the duration of rainfall, recovery time and source strength.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
