Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part I: Top of Atmosphere and Surface

Abstract

This study revisits the classical problem of quantifying the radiative effects of unique cloud types in the era of spaceborne active observations. The radiative effects of nine cloud types, distinguished based on their vertical structure defined by CloudSat and CALIPSO observations, are assessed at both the top of the atmosphere and the surface. The contributions from single- and multilayered clouds are explicitly diagnosed. The global, annual mean net cloud radiative effect at the top of the atmosphere is found to be −17.1 ± 4.2 W m−2 owing to −44.2 ± 2 W m−2 of shortwave cooling and 27.1 ± 3.7 W m−2 of longwave heating. Leveraging explicit cloud base and vertical structure information, we further estimate the annual mean net cloud radiative effect at the surface to be −24.8 ± 8.7 W m−2 (−51.1 ± 7.8 W m−2 in the shortwave and 26.3 ± 3.8 W m−2 in the longwave). Multilayered clouds are found to exert the strongest influence on the top-of-atmosphere energy balance. However, a strong asymmetry in net cloud radiative cooling between the hemispheres (8.6 W m−2) is dominated by enhanced cooling from stratocumulus over the southern oceans. It is found that there is no corresponding asymmetry at the surface owing to enhanced longwave emission by southern ocean clouds in winter, which offsets a substantial fraction of their impact on solar absorption in summer. Thus the asymmetry in cloud radiative effects is entirely realized as an atmosphere heating imbalance between the hemispheres.

Toward autonomous surface-based infrared remote sensing of polar clouds: retrievals of cloud optical and microphysical properties

“…The inverse method uses radiances from 400 to 600 cm −1 (allowing thermodynamic phase determination; Rathke et al, 2002a) and from 750 to 1300 cm −1 , which is sensitive to phase, COD, and effective radius. Similar optimal nonlinear inverse methods have been used to retrieve cloud properties from AERI instruments in the Arctic (Turner, 2005;Cox et al, 2014) and from satellite instruments (Wang et al, 2016;Poulsen et al, 2012;L'Ecuyer et al, 2019). Cloud properties are retrieved from observed radiances averaged in microwindows (see Table 2).…”

Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part II: Atmospheric Heating

“…Clouds play an important role in regulating Earth's energy balance (Stephens 2005) by modulating the amount of energy reflected, emitted, and absorbed at the surface and in the atmosphere (L'Ecuyer and Stephens 2003;Stephens et al 2012a). The redistribution of energy within the atmosphere by clouds helps drive the large-scale circulation, vertical motions and the hydrological cycle (Webster and Stephens 1984;Ramanathan 1987;Chen et al 2000;Stephens and Ellis 2008;Stephens et al 2012a;Lin et al 2013;Harrop and Hartmann 2016).…”

“…The redistribution of energy within the atmosphere by clouds helps drive the large-scale circulation, vertical motions and the hydrological cycle (Webster and Stephens 1984;Ramanathan 1987;Chen et al 2000;Stephens and Ellis 2008;Stephens et al 2012a;Lin et al 2013;Harrop and Hartmann 2016). The vertical distribution of radiative heating has been shown to be the primary way that clouds impact atmospheric circulations (Hartmann and Short 1980;Randall et al 1989;McFarlane et al 2007;Fueglistaler et al 2009), the Madden-Julian oscillation (MJO), monsoons, and tropical rain belts (L'Ecuyer and Stephens 2003;Jiang et al 2015;Johansson et al 2015;Li et al 2015;Winker et al 2017). Although these studies suggest that the role of clouds in climate is significant, there are comparatively few observational constraints on how the vertical characteristics of clouds influence atmospheric heating and, in turn, affect global atmospheric energy transport.…”

FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space

“…Understanding the cloud radiative effect (CRE) of high clouds has been the subject of numerous studies in recent decades. While there is no longer evidence that the global CRE of high clouds is warming (Hartmann et al 1992;Matus and L'Ecuyer 2017;Stephens 2005), the average value of this warming and its zonal and vertical distribution remains highly uncertain (Hang et al 2019;L'Ecuyer et al 2019;Oreopoulos et al 2016).…”