Decadal climatology of the spatial and vertical distributions of tropospheric aerosol over the Arabian Sea based on satellite observations

Abstract

The climatology of aerosol optical properties is retrieved and analysed for the period from June 2006 to November 2017 over the Arabian Sea from the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua satellite. Strong seasonality and latitudinal gradients in the columnar aerosol optical depth, dust aerosol optical depth (DOD) over the Arabian Sea are observed. Most of the aerosols over the North Arabian Sea (NAS) and the Central Arabian Sea are confined to the surface (i.e., 0–3 km). However, the seasonal mean high extinction coefficient is found during summer over the Arabian Sea. The high vertical extent of aerosols (with higher extinction coefficient) at altitudes >4 km emphasizes the continental aerosol effluence from the southwestern peninsular Indian subcontinent during winter, spring and autumn seasons. The contribution of dust extinction coefficient to the total columnar DOD has been observed to be high over NAS (>35%) at 0–1 km altitude bin during all the seasons and it is lowest (<15%) at the altitude range of 5–6 km. Dust fraction (DF) shows a clear latitudinal variation with a peak over NAS and diminishes towards SAS. The highest DF is observed over NAS during spring (82%) even though the dust extinction coefficient attained maximum during summer (0.81 ± 0.07 km−1). This is due to the strong westerly winds over NAS from the coast of Oman during spring. A positive difference between DF derived from MODIS and CALIPSO is noticed, and it might be due to the limitation of MODIS in discriminating the aerosol and the cloud from its passive sensor reliable than an active sensor like lidar in CALIPSO. The outcomes of the present study will serve as a reliable source for future studies of dust‐regional scale climate interactions over the Arabian Sea.

On the net primary productivity over the Arabian Sea due to the reduction in mineral dust deposition

“…The satellite-based approach is subjected to uncertainties based on sensor type, viewing locations, instrument calibration errors, poor data accuracy, uncertainties in retrieval algorithms, and much more. In satellite-based quantification, active sources are more advantageous than any other passive instruments that cannot capture information like vertical profiles of aerosols and discrimination of aerosols and clouds 23 .…”

“…There is an enormous contribution of dust from Central Asia, followed by the southern Arabian Peninsula, Central Africa, East Africa, and West Africa to the north Indian Ocean 21 . As the southwest monsoon associated with the low-level Findlater jet is a conduit for natural aerosols (e.g., dust and sea salt) influencing monsoon precipitation on short timescales 6 , several studies have focused on the qualitative analysis of dust 22 , 23 and its impact on the radiation budget 9 and monsoon system over India 7 . However, quantitative analysis of dust aerosols over the AS is very limited except for a few studies reporting some episodic events 24 , 25 and several others focussing on the anthropogenic impact of aerosols over the AS 26 , 27 .…”

The Impact of Lockdown on eBC Mass Concentration over a Semi-arid Region in Southern India: Ground Observation and Model Simulations

“…GOCART treats the sources, sinks, and chemistry of 15 externally mixed aerosol mass mixing ratio tracers: dust (five noninteracting size bins), sea salt (five noninteracting size bins), hydrophobic and hydrophilic black and organic carbon (eBC and OC, respectively; four tracers), and sulfate (SO4 2-) . Both dust and sea salt have wind speeddependent emissions (Tandule et al, 2020). Primary sulfate and carbonaceous aerosol species are emitted principally from fossil fuel combustion, biomass burning, and biofuel consumption, with additional biogenic sources of organic carbon.…”