Influence of continental advection on aerosol characteristics over Bay of Bengal (BoB) in winter: results from W-ICARB cruise experiment

Abstract

Abstract. The transport of aerosols and pollutants from continental India to the adjoining oceanic areas is a major topic of concern and several experimental campaigns have been conducted over the region focusing on aerosol characteristics and their climate implications. The present study analyzes the spectral aerosol optical depth (AOD) variations over Bay of Bengal (BoB) during Winter-Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) from 27 December 2008 to 30 January 2009 and investigates the influence of the adjoining landmass to the marine aerosol field. High AOD 500 values (>0.7) occurred over northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plains (IGP); low AOD 500 (0.1-0.2) was observed in central and southern BoB, far away from the mainland. The Angstrom exponent "α" was observed to be high (>1.2) near coastal waters, indicating relative abundance of accumulation-mode continental aerosols. On the other hand, over southern BoB its values dropped below ∼0.7. National Center for Environmental Prediction (NCEP) reanalysis data on winds at 850 and 700 hPa, along with airmass trajectories calculated using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, suggested transport of continental aerosols from central and northern India over the BoB. On the other hand, when the ship was crossing the eastern BoB, the aerosol loading was strongly affected by air-masses originating from Southeast Asia, causing an increase in AOD and α. Biomass-burning episodes over the region played an important role in the observed aerosol properties. Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD 550 and cruise measured AOD 550 showed good agreement (R 2 = 0.86 and 0.77, Correspondence to: S. K. Kharol (shaileshan2000@yahoo.co.in) respectively) over BoB, exhibiting similar AOD and α spatiotemporal variation.

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

“…When the ship is crossing very near to coastal regions at higher latitudes (> 14°N), α 380-1020 values observed to be high (1.4) represents the abundance of fine particles which are mainly from anthropogenic sources that are transported from central Indian peninsula and IGP. The similar spatial features for AOD 500 and α 380-1020 are reported by several authors over the BoB for the W-ICARB cruise campaign (Moorthy et al, 2010;Kaskaoutis et al, 2011;Kharol et al, 2011;Kumar et al, 2011;Sinha et al, 2011a). In Fig.…”

“…While the ship was surveying in the southern BoB region, the weather was disturbed with moderate to heavy rain. Recently, similar synoptic wind pattern prevailed at 850 and 700 mb was reported by Kharol et al (2011) over the entire BoB during the campaign period. It may be noted that these figures provide only the synoptic conditions that prevailed during the campaign period.…”

“…After adopting the criteria applied in Kaskaoutis et al (2011) to avoid the cloud contamination in the Sun photometric measurements recorded in the morning hours of 2 January, only few data points were left that are not used in the present study are considered as high turbid. Kharol et al (2011) reported the presence of intense hazy aerosol layer over Indo-Gangetic Plain (IGP) and Bangladesh which is clearly shown by Terra/Aqua MODIS true color images on 7 January 2009 traps the aerosols and pollutants near the ground, indicating a strong continental outflow towards the marine environment, results in dramatic increase in aerosol loading and limitation of visibility. The large amount of water-soluble aerosols over IGP provides the necessary condensation nuclei for the formation of fog near the ground, especially when the RH is high (Badarinath et al, 2007a;Das et al, 2008).…”

“…Even the lidar systems on board satellites such as CALIPSO detected the presence of thick aerosol layer, extending from surface up to ~3 km altitude covering IGP and northwestern part of BoB (for more details see Fig. 7 of Kharol et al (2011)). These elevated aerosol layers observed in variable intensity between 0.5 and 2.0 km over the whole BoB contribute to the vertical heterogeneity in aerosol load and characteristics over the region (Sinha et al, 2011a).…”

Multi-year investigations of aerosols from an island station, Port Blair, in the Bay of Bengal: climatology and source impacts

“…Consequently, the spatial variation gets coupled with the temporal variations. The inferences drawn from those papers Kumar et al, 2010;Kaskaoutis et al, 2011;Kharol et al, 2011;Srinivas et al, 2011;Babu et al, 2012), though suggestive and valuable in themselves, suffer from the above limitation. In the present study, we examine 7-year of continuous data (constrained by the weather conditions) from a fixed location, and as such offer insights into the climatological features of aerosols which are useful inputs to regional aerosol models.…”