Boundary Layer Clouds and Convection over Subtropical Oceans in our Current and in a Warmer Climate

Abstract

Purpose of ReviewWe review our understanding of mechanisms underlying the response of (sub)tropical clouds to global warming, highlight mechanisms that challenge our understanding, and discuss simulation strategies that tackle them. Recent Findings Turbulence-resolving models and emergent constraints provide probable evidence, supported by theoretical understanding, that the cooling cloud radiative effect (CRE) of low clouds weakens with warming: a positive low-cloud feedback. Nevertheless, an uncertainty in the feedback remains. Climate models may not adequately represent changing SST and circulation patterns, which determine future cloud-controlling factors and how these couple to clouds. Furthermore, we do not understand what mesoscale organization implies for the CRE, and how moisture-radiation interactions, horizontal advection, and the profile of wind regulate low cloud, in our current and in our warmer climate. Summary Clouds in nature are more complex than the idealized cloud types that have informed our understanding of the cloud feedback. Remaining major uncertainties are the coupling of clouds to large-scale circulations and to the ocean, and mesoscale aggregation of clouds.

Shallow Cumulus Cloud Feedback in Large Eddy Simulations – Bridging the Gap to Storm Resolving Models

“…Provided the identified resolution-dependence of the cloud cover feedback carries over to other model codes, then it implies that storm resolving models may exaggerate trade wind cumulus cloud feedback. It is also interesting to compare with earlier studies, where LES simulations previously have suggested trade wind cumulus feedback in the range 0.3 and 2.3 Wm −2 K −1 (Bretherton, 2015;Nuijens and Siebesma, 2019), and observational studies up until recently likewise 0.3 -1.7 Wm −2 K −1 (Klein et al, 2017). A recent observational study, however, finds a near-zero trade wind cumulus cloud feedback (Myers et al, submitted), which is in line with our results.…”

Trade-wind clouds and aerosols characterized by airborne horizontal lidar measurements during the EUREC<sup>4</sup>A field campaign

“…In contrast, lidars have the potential to detect them much better (Liou and Schotland, 1971;Spinhirne et al, 1982). Space-borne lidars associated with missions such as LITE (Lidar In-space Technology Experiment, Winker et al, 1996), GLASS (Geoscience Laser Altimeter System; Palm et al, 2005;, CALIPSO (Cloud-Aerosol LIdar with Orthogonal Polarization; Winker et al, 2003) or more recently CATS (Cloud-Aerosol Transport System, Yorks et al, 2016) have even revolutionized our knowledge of the global distribution of clouds (Berthier et al, 2008). However, cloud observations from ground-based, airborne or satellite lidar technology were made at the nadir or zenith.…”

Marine Low Clouds and their Parameterization in Climate Models

“…They showed that shallow convection becomes more vigorous and transports more water vapor from the boundary layer to a free atmosphere in a warmer climate for models in which the shallow convection scheme is active. Brient and Recent studies based on observational relationships and GCMs also tend to support decreases in low cloud cover in warmer climates and the positive low cloud feedback (e.g., Klein et al 2017, Nuijens andSiebesma 2019). It is shown that decrease in low cloud cover in warmer climates is plausible based on CMIP5 multi-model simulation data (Qu et al 2014(Qu et al , 2015 and observational relationships (e.g.…”

“…All of these processes affect the vertical profile of the cloud-topped boundary layer. Various physical processes that control MLCs and their complicated interactions are discussed in more detail in some review papers (e.g., Wood 2012, Nuijens andSiebesma 2019).…”