Elevated Convection and Castellanus: Ambiguities, Significance, and Questions

Abstract

The term elevated convection is used to describe convection where the constituent air parcels originate from a layer above the planetary boundary layer. Because elevated convection can produce severe hail, damaging surface wind, and excessive rainfall in places well removed from strong surface-based instability, situations with elevated storms can be challenging for forecasters. Furthermore, determining the source of air parcels in a given convective cloud using a proximity sounding to ascertain whether the cloud is elevated or surface based would appear to be trivial. In practice, however, this is often not the case. Compounding the challenges in understanding elevated convection is that some meteorologists refer to a cloud formation known as castellanus synonymously as a form of elevated convection. Two different definitions of castellanus exist in the literature-one is morphologically based (cloud formations that develop turreted or cumuliform shapes on their upper surfaces) and the other is physically based (inferring the turrets result from the release of conditional instability). The terms elevated convection and castellanus are not synonymous, because castellanus can arise from surface-based convection and elevated convection exists that does not feature castellanus cloud formations. Therefore, the purpose of this paper is to clarify the definitions of elevated convection and castellanus, fostering a better understanding of the relevant physical processes. Specifically, the present paper advocates the physically based definition of castellanus and recommends eliminating the synonymity between the terms castellanus and elevated convection.

Interactions between cumulus convection and its environment as revealed by the MC3E sounding array

“…It is noted that the nocturnal elevated convection over the central United States has gained increased scientific attention in recent years [Horgan et al, 2007;Corfidi et al, 2008;Lee et al, 2010]. Several field campaigns have been targeted to understand what allows convection to initiate in the presence of a stable nocturnal boundary layer, such as the International H 2 O Project [Weckwerth et al, 2004] that was conducted in 2002 at SGP to improve the understanding and prediction of convective initiation.…”

The Impact of Low-Level Moisture Errors on Model Forecasts of an MCS Observed during PECAN

“…Whereas daytime convection frequently derives convective energy from the planetary boundary layer (PBL) (these types of systems are referred to as ''surface based''), nocturnal MCSs often thrive in conjunction with a statically and convectively stable PBL, and derive the majority of their energy from layers of air above the PBL (Corfidi et al 2008; these types of systems are referred to as ''elevated''). The layer(s) of air that is the primary source of air parcels that drive deep convective overturningoften defined as the layer(s) where convective available potential energy (CAPE) .…”

Empirical Examination of the Factors Regulating Thunderstorm Initiation

“…Although the conceptual definition of elevated convection as convection that does not ingest nearsurface air (Glickman 2000) is easy to grasp, practically differentiating between surface-based and elevated convection is difficult and rather uncertain (Thompson et al 2007;Corfidi et al 2008). As a result of this uncertainty, we omit the portion of the parameter space in which MUCAPE is greater than SBCAPE and both are nonzero [such as the sounding shown in Fig.…”