Cold pool dissipation

Abstract

The mechanisms by which sensible heat fluxes (SHFs) alter cold pool characteristics and dissipation rates are investigated in this study using idealized two-dimensional numerical simulations and an environment representative of daytime, dry, continental conditions. Simulations are performed with no SHFs, SHFs calculated using a bulk formula, and constant SHFs for model resolutions with horizontal (vertical) grid spacings ranging from 50 m (25 m) to 400 m (200 m). In the highest resolution simulations, turbulent entrainment of environmental air into the cold pool is an important mechanism for dissipation in the absence of SHFs. Including SHFs enhances cold pool dissipation rates, but the processes responsible for the enhanced dissipation differ depending on the SHF formulation. The bulk SHFs increase the near-surface cold pool temperatures, but their effects on the overall cold pool characteristics are small, while the constant SHFs influence the near-surface environmental stability and the turbulent entrainment rates into the cold pool. The changes to the entrainment rates are found to be the most significant of the SHF effects on cold pool dissipation. SHFs may also influence the timing of cold pool-induced convective initiation by altering the environmental stability and the cold pool intensity. As the model resolution is coarsened, cold pool dissipation is found to be less sensitive to SHFs. Furthermore, the coarser resolution simulations not only poorly but sometimes wrongly represent the SHF impacts on the cold pools. Recommendations are made regarding simulating the interaction of cold pools with convection and the land surface in cloud-resolving models.Idealized modeling simulations have been instrumental in advancing our understanding of varying aspects of cold pool, or density current, characteristics. These modeling studies have examined the turbulent and dynamic characteristics of density currents and the impact of the environment, such as the background stability and shear, on the cold pool dynamics [e.g., Droegemeier and Wilhelmson, 1987, hereafter DW87;Xu, 1992; Liu and Moncrieff, 2000, hereafter LM00; Seigel and van den Heever, 2012, hereafter SvdH12; Bryan and Rotunno, 2014; Rooney, 2015]. Other studies have examined the role of microphysical processes and GRANT AND VAN DEN HEEVER COLD POOL DISSIPATION 1138

Circling in on Convective Organization

“…Describing extremes may be accomplished by our model, by coupling precipitation intensity and gust front speed, thereby relaxing the assumption of constant speed c 0 . Further, due to the effect of surface heat fluxes and energy conservation, the speed of spreading should decrease with radius (Grant & van den Heever, 2016, 2018Gentine et al, 2016;Romps & Jeevanjee, 2016). Here, h denotes the effective CP height, and g is the gravitational acceleration.…”

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

“…5. Domain size is 64 km by 64 km, with the model output saved every 30 min over 2.5 days of the thermodynamics to the cold pool dynamics as well as conceivably interaction with surface fluxes (Ross et al 2004;Gentine et al 2016;Grant and van den Heever 2016). Future challenges also remain on the modeling front.…”

“…Work has been done to determine the entrainment in gravity currents (see e.g., Hacker et al 1996;Hallworth et al 1996;Fragoso et al 2013), but mostly in idealized scenarios, which raises questions on the applicability of these results to real-world cold pools. To address this question using numerical models is a challenging task as the simulations required for this purpose would have to be conducted in a large enough domain, and, at the same time, with a spatial grid spacing capable of properly representing turbulent mixing at the gust front (see Grant and van den Heever (2016) for such an attempt). Such efforts will also improve parameterizations of the boundary layer turbulent transports towards representing clear-air entrainment and up/downdrafts correctly (see also Tompkins and Semie 2017).…”

“…Measurements either came from one point, e.g., a ship (Addis et al 1984;Young et al 1995;Saxen and Rutledge 1998) or from aircraft (e.g., Zipser 1977;Kingsmill and Houze 1999), convoluting space and time. Modeling capabilities are improving also, either in their spatial grid spacing (Romps and Jeevanjee 2016;Grant and van den Heever 2016) or domain size Hohenegger 2014, 2016), and at times both (Seifert and Heus 2013;Vogel et al 2016). The recent years have also seen advances in the formulation of cold pool parameterizations (e.g., Qian et al 1998;Rozbicki et al 1999;Rio et al 2009Rio et al , 2013Hohenegger and Bretherton 2011;Del Genio et al 2015;Pantillon et al 2015) and their coupling with convective schemes.…”

Cold Pool‐Land Surface Interactions in a Dry Continental Environment

“…Cold pools behave like density currents (Benjamin, ; Charba, ). They can initiate new convection through lifting at their leading edge and by colliding with other cold pools (Purdom, ; Rotunno et al, ), interact with boundary layer features (Achtemeier, ; Grant & van den Heever, , hereafter GvdH16), and influence convective organization (Gentine et al, ; Khairoutdinov & Randall, ).…”