Research / Research Highlights

Different regimes and active regions of aerosol indirect effects

Submitter

Liu, Yangang — Brookhaven National Laboratory

Area of Research

Cloud-Aerosol-Precipitation Interactions

Journal Reference

Zhao X, Y Liu, F Yu, and A Heidinger. 2018. "Using Long-Term Satellite Observations to Identify Sensitive Regimes and Active Regions of Aerosol Indirect Effects for Liquid Clouds Over Global Oceans." 123(1), 457-472.

Science

Relationships (black dots) of τ (AOT) to (a) effective radius (re ), (b) cloud optical depth (τc), (c) Cloud water path CWP, (d) Cloud Top Height CTH, (e) Cloud Top Temperature (CTT), and (f) Cloud fraction (CCF). The number of data samples (black line) is measured by the vertical coordinate on the right-hand side. The error bars indicate the one standard deviation, and the two vertical dashed lines at AOT = 0.13 and 0.30, respectively, divide the plot into three AOT regimes.

Different regimes of aerosol indirect effects and the active regions over the global ocean are studied and identified by analyzing long-term satellite measurements of aerosol and cloud properties.

Impact

The study provides additional observational evidence for existence of different aerosol-cloud interaction regimes, and identifies the primary regions where the corresponding regimes occur. The results also offer new understanding of the complex aerosol indirect effects over the global ocean, and point new directions for future research.

Summary

Long-term (1981–2011) satellite climate data records of clouds and aerosols are used to investigate the aerosol-cloud interaction of marine water cloud from a climatology perspective. Different regimes of the aerosol indirect effects (AIE) and the active regions over the global oceans are identified by analyzing the correlation features between aerosol optical depth and the key cloud variables including cloud droplet effective radius, cloud optical depth, cloud water path, cloud top height, and cloud top temperature. An aerosol optical thickness (AOT) range of 0.13 < AOT < 0.3 is identified as the sensitive regime of the conventional first AIE where effective radius is more susceptible to AOT than the other cloud variables. The first AIE that manifests as the change of long-term averaged effective radius appears only in limited oceanic regions. The signature of aerosol invigoration of water clouds as revealed by the increase of cloud fraction and cloud top height with increasing AOT at the middle/high latitudes of both hemispheres is identified for a pristine atmosphere (AOT < 0.08). Aerosol invigoration signature is also revealed by the concurrent increase of effective radius, cloud optical depth, and cloud liquid water path with increasing AOT for a polluted marine atmosphere (AOT > 0.3) in the tropical convergence zones. The regions where the second AIE is likely to manifest in the cloud fraction change are limited to several oceanic areas with high cloud fraction of the warm water clouds near the western coasts of continents. The second AIE signature as represented by the reduction of the precipitation efficiency with increasing AOT is more likely to be observed in 0.08 < AOT < 0.4. The corresponding AIE active regions, which manifested themselves as the decline of the precipitation efficiency, are mainly limited to the oceanic areas downwind of continental aerosols. The sensitive regime of the conventional AIE identified in this observational study is likely associated with the transitional regime from the aerosol-limited regime to the updraft-limited regime identified for aerosol-cloud interaction in cloud model simulations.