Comparison of MISR-MODIS aerosol optical depth over the Indo-Gangetic basin during the winter and summer seasons (2000–2005)

Aerosol Optical Depth (AOD) measurements from Aerosol Robotic NETwork (AERONET; level 2.0), Microtops -II sun-photometer and MODerate Resolution Imaging Spectroradiometer (MODIS) (Terra and Aqua; level 2, collection 5, dark target) were compared and used to characterize aerosols over Pune, India. AODs from Microtops and MODIS were compared with those measured by AERONET to evaluate the measurement quality. To the best of our knowledge, this is the first systematic comparison of MODIS aerosol products over Pune, India. The results of the analysis show that during 2008-10, 68% to 84% of the MODIS AODs fell within an expected error, as defined by the MODIS science team, and thus the retrievals from this system are validated and accepted. In addition, during pre-monsoon periods MODIS retrievals are better-matched with ground-based measurements. On the seasonal scale, MODIS retrievals corroborate well with ground-based measurements, with correlation coefficients ranging from 0.62 to 0.93. Despite an overall satellite-ground agreement, MODIS tends to under-estimate AOD during winter, and this may be due to improper assumptions of surface reflectance and the incorrect selection of aerosol types. AERONET retrieved single scattering albedo (SSA) values in winter (0.82-0.86), suggesting the dominance of absorbing aerosols, slightly increased (0.87-0.89) in pre-monsoon season, indicating more scattering type of aerosols. These values are about 8.9%-1.1% lower than those of the assumed SSA values in the MODIS algorithm.

Section: Introductionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Comparison of Aerosol Products Retrieved from AERONET, MICROTOPS and MODIS over a Tropical Urban City, Pune, India

Kumar

Gupta

et al. 2013

“…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) and composition.…”

Section: Introductionmentioning

confidence: 99%

Satellite-Based Estimates of Aerosol Washout and Recovery over India during Monsoon

Chowdhury

Dey

Ghosh

et al. 2016

Large 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 dustdominated 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 < 2 mm day -1 to > 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.

“…An intercomparison of AOD values from different satellite sensors is necessary for climatological studies, and also to improve the accuracy and the coverage achievable with a single sensor (Prasad and Singh, 2007). Xiao et al (2009) recently examined MODIS and MISR AOD retrievals for Southeast Asia from a spatial perspective and found good correlation between the retrievals from each of these sensors.…”

Section: Intercomparison Of Modis and Misr Derived Aodsmentioning

confidence: 99%

Ship-Borne Measurements of Columnar and Surface Aerosol Loading over the Bay of Bengal during W-ICARB Campaign: Role of Airmass Transport, Latitudinal and Longitudinal Gradients

Kumar

Sivakumar

Reddy

et al. 2013

The present study analyzes simultaneous and collocated measurements of spectral columnar aerosol optical depth (AOD) and the variations in total mass concentration of near surface aerosols in the marine atmosphere over the Bay of Bengal (BoB) during the winter phase of the Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) expedition of December and January 2008/2009 on board the Oceanographic Research Vessel (ORV) of Sagar Kanya. High AOD 500 values (> 0.8) are found close to coastal regions in the western and northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plain (IGP). In these regions, the Ångström exponent α 380-1020 values are also found to be high (~1.2-1.3), indicating relative abundance of accumulation-mode continental aerosols. Low AOD 500 (0.1-0.2) values are observed in central and southern BoB, far away from the mainland. The AOD 500 and total aerosol mass loading increased along with the latitude. The total mass concentration is found to vary between 15 μg/m 3 and 45 μg/m 3 , with higher loadings near the east coast and northern parts of the BoB. NCEP reanalysis of the data with winds at 925 hPa, along with airmass trajectories calculated using the HYSPLIT model, suggest transport of continental aerosols from central and northern India over the BoB at lower heights, and mineral dust aerosol transport from arid regions in the west of India at higher altitudes; while the increase in aerosol loading over eastern BoB was strongly affected by airmasses originating from Southeast Asia. The spatial correlation map between the MODIS and MISR AOD data is analyzed, revealing a strong correlation between the two datasets. The influence of wind speed and continental airmass on AOD is also examined, which provides information on the effects of the adjoining landmass on the marine aerosol field.