Coupled Aerosol-Cloud Systems over Northern Vietnam during 7-SEAS/BASELInE: A Radar and Modeling Perspective

Adrian M. Loftus,Andrew M. Sayer,Si-Chee Tsay,Toshi Matsui,Philip M. Gabriel,Xuan A. Nguyen,Cuong Nguyen,Wei-Kuo Tao,Peter Pantina

doi:10.4209/aaqr.2015.11.0631

Abstract

ABSTRACTThe 2013 7-SEAS/BASELInE campaign over northern Southeast Asia (SEA) provided, for the first time ever, comprehensive ground-based W-band radar measurements of the low-level stratocumulus (Sc) systems that often exist during the spring over northern Vietnam in the presence of biomass-burning aerosols. Although spatially limited, ground-based remote sensing observations are generally free of the surface contamination and signal attenuation effects that often hinder space-borne measurements of these low-level cloud systems. Such observations permit detailed measurements of structures and lifecycles of these clouds as part of a broader effort to study potential impacts of these coupled aerosol-cloud systems on local and regional weather and air quality. Introductory analyses of the W-band radar data show these Sc systems generally follow a diurnal cycle, with peak occurrences during the nighttime and early morning hours, often accompanied by light precipitation. Preliminary results from idealized simulations of Sc development over land based on the observations reveal the familiar response of increased numbers and smaller sizes of cloud droplets, along with suppressed drizzle formation, as aerosol concentrations increase. Slight reductions in simulated W-band reflectivity values also are seen with increasing aerosol concentrations and result primarily from decreased droplet sizes. As precipitation can play a large role in removing aerosol from the atmosphere, and thereby improving air quality locally, quantifying feedbacks between aerosols and cloud systems over this region are essential, particularly given the negative impacts of biomass burning on human health in SEA. Such an endeavor should involve improved modeling capabilities along with comprehensive measurements of time-dependent aerosol and cloud profiles.

Highlights

AND MOTIVATIONAerosols are omnipresent in Earth's atmosphere and central to many environmental concerns such as air quality and climate change
The 2013 7-SEAS/BASELInE campaign over northern Southeast Asia (SEA) provided, for the first time ever, comprehensive ground-based W-band radar measurements of the low-level stratocumulus (Sc) systems that often exist during the spring over northern Vietnam in the presence of biomass-burning aerosols
As precipitation can play a large role in removing aerosol from the atmosphere, and thereby improving air quality locally, quantifying feedbacks between aerosols and cloud systems over this region are essential, given the negative impacts of biomass burning on human health in SEA

Summary

Introduction

AND MOTIVATIONAerosols are omnipresent in Earth's atmosphere and central to many environmental concerns such as air quality and climate change. The highly idealized nature (i.e., no forcing beyond the imposed supersaturation) and identical environmental conditions in these simulations help ensure that differences in cloud microphysical responses in each case are due primarily to changes in Na. As neither in-situ measurements of aerosol/CCN nor profiles of these particles are available at Yen Bai during the 2013 7-SEAS/BASELInE campaign, results from these particular simulations are not intended to draw specific conclusions regarding the effects of BB aerosols on the observed cloud system, but rather to serve as a guideline for potential impacts of aerosols on these clouds and how the impacts might be ‘observed’ from a remote sensing standpoint.

Results

Conclusion