Cloud Patterns in the Trades Have Four Interpretable Dimensions

Abstract

Shallow cloud fields over the subtropical ocean exhibit many spatial patterns. The frequency of occurrence of these patterns can change under global warming. Hence, they may influence subtropical marine clouds’ climate feedback. While numerous metrics have been proposed to quantify cloud patterns, a systematic, widely accepted description is still missing. Therefore, this study suggests one. We compute 21 metrics for 5,000 satellite scenes of shallow clouds over the subtropical Atlantic Ocean and translate the resulting data set to its principal components (PCs). This yields a unimodal, continuous distribution without distinct classes, whose first four PCs explain 82% of all 21 metrics’ variance. The PCs correspond to four interpretable dimensions: Characteristic length, void size, directional alignment, and horizontal cloud top height variance. These dimensions span a space in which an effective pattern description can be given, which may be used to better understand the patterns’ underlying physics and feedback on climate.

Impact of a Mixed Ocean Layer and the Diurnal Cycle on Convective Aggregation

“…The possible overestimation of the degrees of freedom due to this assumption is compensated for by selecting a very high significance level to ensure statistical robustness. We note that we could have alternatively used the classical Clark‐Evans statistical test (Clark & Evans, 1954 ) directly on sub‐sampled nearest neighbor distances of the velocity field, however, we prefer the application to I org as it is a scene‐integrated quantity that has been widely applied in the field since its introduction (e.g., Bony et al., 2020 ; Brueck et al., 2020 ; Janssens et al., 2021 ; Moseley et al., 2020 ; Pscheidt et al., 2019 ).…”

Characterization and Evolution of Organized Shallow Convection in the Downstream North Atlantic Trades

“…In contrast to Denby (2020) and Janssens et al (2021) who retrieve a continuum of classes, the limitation to the few categories of Stevens et al (2020) helps to break down natures' complexity into manageable pieces, arguably the building blocks of shallow convection in the downstream trades. Understanding what factors help select these patterns may help understand factors controlling cloudiness as a whole.…”

“…During this period, observational studies such as RICO (Rauber et al, 2007) and the emergence of satellite imagery with spatial resolution on the hectometer scale began emphasizing how shallow clouds in the trades adopt different forms of organization, often in association with precipitation development and the formation of cold pools (Seifert & Heus, 2013;Seifert et al, 2015;Zuidema et al, 2012). More recently, several approaches to characterize these forms of organizations have been developed (Denby, 2020;Janssens et al, 2021;Stevens et al, 2020). Stevens et al (2020) identified that most of the largescale patterns of shallow convection can be categorized into four categories, which they called Sugar, Gravel, Flowers, and Fish. Although based solely on the subjective visual inspection of visible satellite imagery in the vicinity of the Barbados Cloud Observatory (BCO), these patterns have varied net cloud radiative effects and thus may influence Earth's climate sensitivity (Bony et al, 2020).…”

“…During this period, observational studies such as RICO (Rauber et al., 2007) and the emergence of satellite imagery with spatial resolution on the hectometer scale began emphasizing how shallow clouds in the trades adopt different forms of organization, often in association with precipitation development and the formation of cold pools (Seifert & Heus, 2013; Seifert et al., 2015; Zuidema et al., 2012). More recently, several approaches to characterize these forms of organizations have been developed (Denby, 2020; Janssens et al., 2021; Stevens et al., 2020). Stevens et al.…”

Characterization and Evolution of Organized Shallow Convection in the Trades

“…During this period, observational studies such as RICO (Rauber et al, 2007) and the emergence of satellite imagery with spatial resolution on the hectometer scale began emphasizing how shallow clouds in the trades adopt different forms of organization, often in association with precipitation development and the formation of cold pools (Seifert & Heus, 2013;Seifert et al, 2015;Zuidema et al, 2012). More recently, several approaches to characterize these forms of organizations have been developed (Denby, 2020;Janssens et al, 2021;Stevens et al, 2020). Stevens et al (2020) identified that most of the largescale patterns of shallow convection can be categorized into four categories, which they called Sugar, Gravel, Flowers, and Fish. Although based solely on the subjective visual inspection of visible satellite imagery in the vicinity of the Barbados Cloud Observatory (BCO), these patterns have varied net cloud radiative effects and thus may influence Earth's climate sensitivity (Bony et al, 2020).…”