Aerosol-CO relationship and aerosol effect on ice cloud particle size:Analyses from Aura Microwave Limb Sounder and Aqua ModerateResolution Imaging Spectroradiometer observations

摘要

We examine the relation between Aqua Moderate Resolution Imaging Spectroradiometer(MODIS) aerosol optical thickness (AOT) and Aura Microwave Limb Sounder uppertropospheric (UT) carbon monoxide (CO) to address when CO can be used as a proxy foraerosols. Ice cloud effective radii (re), also from Aqua MODIS, are also analyzed toinvestigate possible aerosol effects on ice clouds. Our analysis focuses on five regions whereice clouds are collocated with high UT CO loadings: South America (SAM), southern Africa(SAF), northern Africa (NAF), South Asia (SAS), and East Asia (EAS). We find threelevels of AOT to CO sensitivity. High AOT sensitivity to CO is characterized by a rapidincrease of AOT when CO increases. SAM in August–November and SAF in June–September fall into this category. Moderate AOT sensitivity to CO is characterized bymoderate increase of AOT with CO. It includes SAF in October–May, NAF in January–March, SAS in all months, and EAS in August– September. The other months for eachregion fall into the low sensitivity category. The variations of sensitivity in different regionsand seasons result from different emission sources coupled with dynamic influence.CO can be used as an aerosol proxy for the "high" and "moderate" sensitivity cases. Duringthose times, re for polluted clouds is smaller than that for clean clouds, suggesting anindirect effect of aerosol on ice clouds. CO is not a good aerosol index in the low sensitivitycases, in which polluted clouds defined by CO loadings do not show significantdifferences from clean clouds in re.