Surface Turbulent Fluxes during Persistent Cold-Air Pool Events in the Salt Lake Valley, Utah. Part I: Observations

Abstract

The land surface is coupled to the atmospheric boundary layer through surface turbulent fluxes. Persistent cold-air pools (PCAPs) form in topographic depressions where cold, dense air fills the valley basin and in the presence of air pollution is accompanied by poor air quality. For the first time, the surface turbulence dataset from seven monitors during the Persistent Cold-Air Pool Study conducted in Salt Lake Valley, Utah (December 2010–February 2011), are analyzed. We found that the surface sensible (H) and latent (LE) heat fluxes were lower during strong PCAP events compared with non-PCAPs. The higher ratio of heat flux to net radiation (H/Rn and LE/Rn) for strong PCAPs compared with weak PCAPs is suspected to be related to the presence of boundary layer clouds, which could enhance the turbulent mixing through cloud top–down mixing. The daily average ground heat flux (G) was a similar order of magnitude to H and LE during wintertime. The highest surface turbulent fluxes and energy balance closure occurred in the stability range of −0.05 < ξ ≤ −0.02, or under slightly unstable conditions, near the neutral stability range. The median surface exchange coefficient (Ch), a crucial parameter to determine surface turbulent fluxes in land surface models, was slightly higher at the bare land site (BL) than the short vegetation sites (PH and CR) in wintertime, suggesting the importance of dynamic land-use information in numerical models.

Surface temperature inversion characteristics in dissimilar valleys, Yukon Canada

“…For the study period (August 2017 -August 2021), the Pearson correlation (PC) was calculated between each transect and the statistical significance of each correlation (including ECT and TST). The evolution of persistent cold pooling and subsequent SBI events has been studied extensively (Wolyn and McKee 1989;Zhong et al 2001;Zangl 2003;Yu et al 2017;McCaffrey et al 2019;Sun and Holmes 2019). For example, persistent cold-air pools and subsequent SBIs develop through cold-air drainage and (or) synoptic conditions that lead to warm air advection aloft or subsidence of air aloft producing a warmer air cap above the cold air layer near the surface (Lareau et al 2013).…”

Polos fríos en el Calar de Hernán Pelea y Cabrilla (Jaén, España), factores sinópticos y de microescala

“…Crosman & Horel (2017) determinan que el modelo WRF LES de 250 m fue capaz de simular la evolución y erosión turbulenta de la piscina fría, al igual que el WRF ARW, que fue capaz de simular un evento de PCAP en el valle del río Arve (Alpes franceses) (Arduini et al, 2020). La mejora en la predicción de las CAP abre una línea de investigación en la meteorología operativa (Sun et al, 2020).…”

Evaluation of a cloudy cold-air pool in the Columbia River Basin in different versions of the HRRR model

“…In the presence of clouds, the diurnal temperature cycle near the surface is weakened due to reduced shortwave downward radiation flux during daytime and reduced longwave net radiation flux during nighttime (e.g. Sun and Holmes, 2019). Too few simulated nocturnal low-level clouds can lead to large cold biases in the simulated near-surface temperature during nights when low-level clouds are observed as they reduce longwave outgoing radiation flux (e.g.…”