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

Abstract

This study attempts to understand interactions between midlatitude convective systems and their environments through a heat and moisture budget analysis using the sounding data collected from the Midlatitude Continental Convective Clouds Experiment (MC3E) in central Oklahoma. Distinct large-scale structures and diabatic heating and drying profiles are presented for cases of weaker and elevated thunderstorms as well as intense squall line and supercell thunderstorm events during the campaign. The elevated cell events were nocturnal convective systems occurring in an environment having low convective available potential energy (CAPE) and a very dry boundary layer. In contrast, deeper convective events happened during the morning into early afternoon within an environment associated with large CAPE and a near-saturated boundary layer. As the systems reached maturity, the diagnosed diabatic heating in the latter deep convective cases was much stronger and of greater vertical extent than the former. Both groups showed considerable diabatic cooling in the lower troposphere, associated with the evaporation of precipitation and low-level clouds. The horizontal advection of moisture also played a dominant role in moistening the lower troposphere, particularly for the deeper convective events, wherein the near surface southeasterly flow allows persistent low-level moisture return from the Gulf of Mexico to support convection. The moisture convergence often was present before these systems develop, suggesting a strong correlation between the large-scale moisture convergence and convection. Sensitivity tests indicated that the uncertainty in the surface precipitation and the size of analysis domain mainly affected the magnitude of these analyzed fields rather than their vertical structures.

The Midlatitude Continental Convective Clouds Experiment (MC3E) sounding network: operations, processing and analysis

“…At the central ARM facility, where reliable independent measurements of PWV were available, the humidity corrections were shown to improve the agreement between the sonde and MWR PWV observations with a mean PWV difference of 0.15 mm (or 0.7 %). These corrections along with rigorous quality control of the soundings have resulted in a high-quality data set suitable for many research applications including the derivation of a model forcing data set (Xie et al, 2014). …”

“…Towards this goal, Xie et al (2014) use the constrained variational analysis approach of Zhang and Lin (1997) in order to derive the large-scale vertical velocity and advective tendencies of temperature and moisture over the MC3E domain. This technique uses a combination of sounding network observations, ARM extended facility observations, radar-derived surface precipitation and top-of-atmosphere radiative flux observations as constraints to adjust the sounding-observed atmospheric state variables in order to conserve column-integrated mass, moisture and static energy such that the resulting forcing data set is dynamically and thermodynamically consistent.…”

“…A major motivation for the sounding array is to provide large-scale forcing fields, through traditional budget analyses (e.g., Yanai et al, 1973;Johnson, 1984;Johnson and Ciesielski, 2013) and constrained variational objective analyses (Zhang and Lin, 1997;Zhang et al, 2001;Xie et al, 2010;Xie et al, 2014), that can be used for singlecolumn model (SCM) and cloud-resolving model (CRM) studies (Klein and Del Genio, 2006).…”

Comparison of Vaisala radiosondes RS41 and RS92 at the ARM Southern Great Plains site

“…The RS92 radiosonde is the current standard at all of the ARM sites and has been in use since 2005. The observations from these soundings have been used for many scientific applications, including the derivation of large-scale forcing datasets for modeling studies (e.g., Zhang and Lin, 1997;Zhang et al, 2001;Xie et al, 2010Xie et al, , 2015, constraints on cloud remote-sensing retrievals (e.g., Huang et al, 2012;Dunn et al, 2011), and quantification of atmospheric thermodynamic structure (e.g., Sawyer and Li 2013;McFarlane et al, 2013). The Vaisala RS41 (fourth generation) radiosonde was developed to replace the RS92 and was introduced in the fall of 2013 aimed at delivering improvements in measurement accuracy of profiles of atmospheric temperature, humidity, and pressure.…”

Organisation of potential vorticity on the mesoscale during deep moist convection

“…diabatic heating), and 9 denotes the three-dimensional gradient operator. Generally, deep moist convection creates a local heating anomaly with a maximum in the middle troposphere due to condensational heating (Houze, 2004;Xie et al, 2014). This diabatic heating anomaly _ h will create PV dipoles in the direction of the absolute vorticity vector f a .…”