Analysis of Near-Cloud Changes in Atmospheric Aerosols Using Satellite Observations and Global Model Simulations

Tamás Várnai,Alexander Marshak

doi:10.3390/rs13061151

Abstract

This paper examines cloud-related variations of atmospheric aerosols that occur in partly cloudy regions containing low-altitude clouds. The goal is to better understand aerosol behaviors and to help better represent the radiative effects of aerosols on climate. For this, the paper presents a statistical analysis of a multi-month global dataset that combines data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instruments with data from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) global reanalysis. Among other findings, the results reveal that near-cloud enhancements in lidar backscatter (closely related to aerosol optical depth) are larger (1) over land than ocean by 35%, (2) near optically thicker clouds by substantial amounts, (3) for sea salt than for other aerosol types, with the difference from dust reaching 50%. Finally, the study found that mean lidar backscatter is higher near clouds not because of large-scale variations in meteorological conditions, but because of local processes associated with individual clouds. The results help improve our understanding of aerosol-cloud-radiation interactions and our ability to represent them in climate models and other atmospheric models.

Highlights

Aerosol-cloud interactions are widely recognized to be among the largest sources of uncertainties in our estimates of human impacts on Earth’s energy budget [1]
We examine the contribution of large-scale meteorological conditions and processes to near-cloud aerosol enhancements by creating a plot similar to Figure 3a, but with one key difference: In processing each point in our dataset, we update the mean value of the appropriate distance-to-cloud bin using not the vertically integrated lidar backscatter of the point, but the MERRA-2 scattering aerosol optical depth (AOD) of the 0.5◦ X 0.625◦ latitude-longitude area that contains the point
This study sought new insights from a statistical analysis of a global dataset comprisand consider all large-scale meteorological factors and processes included in MERRA-2 ing Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite observations and MERRA-2 reanalysis

Summary

Introduction

Aerosol-cloud interactions are widely recognized to be among the largest sources of uncertainties in our estimates of human impacts on Earth’s energy budget [1]. Some studies analyzed how aerosol properties changed after clouds appeared in the area [2,3], while others examined the processes shaping aerosols in inter-cloud regions using model simulations [4,5], sometimes in combination with observations [6,7,8,9]. Several studies used satellite observations to explore the relationship between regional cloud amounts and aerosol properties [13,14,15,16]. Complimenting these investigations, several studies examined how aerosol properties change with the distance to clouds in various satellite-based, airborne, or ground-based datasets [17,18,19,20]

Methods

Results

Conclusion