Upscale Growth of Oceanic MCSs

1. Why study Oceanic Mesoscale Convective Systems (MCSs)?

MCSs produce large changes in the atmosphere due to latent heat release and evaporative cooling (Johnson and Young 1983; Houze 1989; Liu et al. 2015), absorption and emittance of radiation (Fu et al. 1995), and the redistribution of momentum (Sanders and Emanuel 1977; LeMone 1983; Tung and Yanai 2002) and moisture (Johnson and Young 1983; Kuo and Anthes 1984). The effects of MCSs are often more significant and/or different to those for individual deep convective clouds or low-level stratiform clouds, as a result of their widespread areas of upper-level stratiform cloud (Houze and Hobbs 1982). As such MCSs can have a significant and distinct influence on weather and climate. For example, latent heating produced in MCSs is a first order control on much of tropical weather and climate (Gill 1980; Mapes 2000; Schumacher et al. 2004; Raymond et al. 2015) as well as influencing mid-latitude (Raymond and Jiang 1990) and polar weather (Shapiro et al. 1987). Similar such examples can be found for moisture (Taylor et al. 2011), momentum (Wolf and Johnson 1995), and radiative changes (Hartmann et al. 2001; Randall et al. 1989). Thus the misrepresentation of MCSs in numerical models can have significant impacts on weather and climate forecasts (Hartmann et al 1984; Zhang et al. 2003; Lillo et al. 2017).

In addition to the effects of oceanic MCSs on the atmosphere, they can have direct effects on human activities and economies. Air turbulence associated with deep convection (Lane and Sharman 2006; Lane et al. 2012) can lead to disruption, damage, injuries, and even fatalities for air traffic (Golding 2000; Kaplan et al. 2005; Sharman et al. 2006; Meneguz et al. 2016). Such issues are also apparent for sea travel (Sanders 1972). Further, these issues can have significant economic repercussions (Cruz and Krausmann 2013).


2. Controls on Land-based MCSs

Before we focus on oceanic MCSs, it is important to focus on their counterparts over land in order to contextualize our understanding. The causes of upscale growth of convection over land are well studied, especially over North America. Specific controls include wind shear (), the thermodynamic profile including convective available potential energy (CAPE) and convective inhibition (CIN) (), availability of moisture (), and synoptic-scale ascent ().


3. The Upscale Growth of Oceanic Deep Convective Clouds to MCSs

In contrast to those systems over land, there are various reasons that make the processes leading to upscale growth of oceanic MCSs more difficult to characterize.

The first is simply a lack of observations. Relative to say the tropical or sub-tropical Pacific or Atlantic there are numerous regular surface and upper-air observations over continents such as North America where MCSs form and grow up-scale in abundance. Further, there have also been numerous focused field programs to examine such processes across the US and other countries relative to those over ocean. Some recent primarily land-based campaigns focusing on MCSs include PECAN in the US (Geerts et al. 2015), CACTI (Varble et al. 2018) and RELAMPAGO in Argentina, and AMMA in North Africa (Redelsperger et al. 2006). Meanwhile, there are relatively few with focused observations of MCSs over the oceans (CPEX)

cold pools over the ocean

Holloway and Neelin (2009) --- column water vapor is strongly correlated with deep convective cloud growth. Mid-tropospheric water vapor limits entrainment of dry air into deep convective plumes.

Entrainment hypothesis is supported by Tompkins and Semie (2017)


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