On the Abundance and Common Properties of Continental, Organized Shallow (Green) Clouds

Abstract

Warm convective clouds play a significant role in the earth's energy and water budgets. However, they still pose a challenge in climate research as their feedback to predicted thermodynamic changes is highly uncertain and considered critical to the overall climate system's response. The focus of this study is continental, organized shallow convective clouds that, although they are spread globally and form in a variety of environments, seem to have common properties. One of these properties seems to be their preferred formation over vegetated areas, thus referred hereafter as green Cu. In this article, we present new observations of emerging universality and explore them using a method that combines fine-and coarse-resolution remotesensing data sets. First, we use Moderate Resolution Imaging Spectroradiometer (MODIS) true-color images to visually classify cloud fields into different classes and identify green Cu fields. We show that the level and type of organization and the properties of these fields (e.g., cloud size distribution and cloud fraction) are similar throughout the world, regardless of their location. Second, we match the corresponding MODIS level-3 cloud properties to the identified cloud classes, and based on this data sets statistics, we develop a detection method for green Cu along ten years of measurements (2003-2012). We examine the geographical distribution and seasonality of this class and show that these fields are highly abundant over many continental areas and indeed mostly in the vicinity of vegetated regions.

Deciphering organization of GOES-16 green cumulus through the empirical orthogonal function (EOF) lens

“…2.2) and exhibit a regular (grid-like) pattern, which is a high level of organization. This type of organization is typical for green Cu fields (Dror et al, 2020) and was reported in several continental areas, e.g., the Amazon basin (Da Silva et al, 2011;Heiblum et al, 2014), the US Southern Great Plains (Hinkelman and Evans, 2004), and northern Germany (Müller et al, 1985). However, due to the presence of GWs, the curve of the observed NNCDF of subdomain-2 lies closer to the diagonal and leans more towards clustered organization, resulting in a larger I org comparing to that of subdomain-1 (I org = 0.44 and I org = 0.35, respectively).…”

“…Continental shallow Cu clouds, often forming during the summer season (Zhang and Klein, 2013) or dry season in the tropics, are observed in a variety of locations -low, mid, and high latitudes -and are preferably formed over forests and vegetated areas; therefore, they are referred to as "green Cu" (Dror et al, 2020). These continental clouds in general, and specifically their organization, are by far less studied than their maritime counterparts, i.e., trade Cu.…”

“…These continental clouds in general, and specifically their organization, are by far less studied than their maritime counterparts, i.e., trade Cu. The level and type of organization of continental shallow Cu were shown to often exhibit regular (grid-like) patterns and cloud streets (Nair et al, 1998;Dror et al, 2020), with the former being a special case of the latter. Complementarily, cloud streets are roll vortices that are often defined as quasi-two-dimensional organized large eddies whose wavelength is scaled by the convective boundary layer (CBL) depth with orientation along with the mean CBL wind direction (Etling and Brown, 1993).…”

“…

A subset of continental shallow convective cumulus (Cu) cloud fields has been shown to have distinct spatial properties and to form mostly over forests and vegetated areas, thus referred to as "green Cu" (Dror et al, 2020). Green Cu fields are known to form organized mesoscale patterns, yet the underlying mechanisms, as well as the time variability of these patterns, are still lacking understanding.

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Deciphering Organization of GOES–16 Green Cumulus, through the EOF Lens

“…2.2) and exhibit a regular (grid-like) pattern, which is a high level of organization. This type of organization is typical for green Cu fields (Dror et al, 2020) and was reported in several continental areas, e.g., the Amazon basin (Da Silva et al, 2011;Heiblum et al, 2014), the Southern Great Plains (Hinkelman and Evans), and Northern Germany (Müller et al, 1985). However, due to the presence of GW, the curve of the observed NNCDF of subdomain-2 lies closer to the diagonal, and leans more towards clustered organization, resulting in a larger I org comparing to that of subdomain-1 (I org = 0.43 and I org = 0.34, respectively).…”