A Study of the Role of Daytime Land–Atmosphere Interactions on Nocturnal Convective Activity in the Southern Great Plains during CLASIC

Abstract

This study examines whether and how land-atmosphere interactions can have an impact on nocturnal convection over the southern Great Plains (SGP) through numerical simulations of an intense nocturnal mesoscale convective system (MCS) on 19-20 June 2007 with the Weather Research and Forecasting (WRF) Model. High-resolution nested simulations were conducted using realistic and idealized land surfaces and two planetary boundary layer (PBL) parameterizations (PBLp): Yonsei University (YSU) and Mellor-Yamada-Janji c (MYJ). Differences in timing and amount of MCS precipitation among observations and model results were examined in the light of daytime land-atmosphere interactions, nocturnal prestorm environment, and cold pool strength. At the meso-g scale, land cover and soil type have as much of an effect on the simulated prestorm environment as the choice of PBLp: MYJ simulations exhibit strong sensitivity to changes in the land surface in contrast to negligible impact in the case of YSU. At the end of the afternoon, as the boundary layer collapses, a more homogeneous and deeper PBL (and stronger low-level shear) is evident for YSU as compared to MYJ when initial conditions and land surface properties are the same. At the meso-b scale, propagation speed is faster and organization (bow echo morphology) and cold pool strength are enhanced when nocturnal PBL heights are higher, and there is stronger low-level shear in the prestorm environment independent of the boundary layer parameterization for different land surface conditions. A comparison of one-and two-way nested MYJ results demonstrates how daytime land-atmosphere interactions modify the prestorm environment remotely through advection of low-level thermodynamic features. This remote feedback strongly impacts the MCS development phase as well as its spatial organization and propagation velocity and, consequently, nocturnal rainfall. These results indicate that synoptic-and meso-a-scale dynamics can play an important role in determining the spatial and temporal scales over which precipitation feedbacks of land-atmosphere interactions emerge regionally. Finally, this study demonstrates the high degree of uncertainty in defining the spatial and temporal scales of land-atmosphere interactions where and when organized convection is dominant.

Impact of Amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the tropical Andes

“…This deviates from prior research on soil moisture-precipitation feedbacks and LULC change, where changes in latent heat energy lead to changes in sensible heat and outgoing long-wave radiation that result in substantial variations in the thermodynamic structure of the lower atmosphere (e.g. Schär et al, 1999;Koster et al, 2004;Dirmeyer et al, 2012;Erlingis and Barros, 2014; among many others). For nearly the same amounts of energy, but in different form, a much deeper layer can be potentially convective (Figure 17).…”

Landform controls on low level moisture convergence and the diurnal cycle of warm season orographic rainfall in the Southern Appalachians

“…Based on previous work (e.g. Erlingis and Barros, 2014), the MYJ, a local PBL (Planetary Boundary Layer) parameterization was selected with the objective of better capturing the spatial heterogeneity of low level structure associated with topography and land cover. Other studies have found that the MYJ produces a colder (more stable), moister PBL than other schemes (Sun and Barros, 2013;Hu et al, 2010), that local closure schemes such as the MYJ tend to reproduce stable atmospheric conditions better than non-local while the opposite is true for unstable conditions (Shin and Hong, 2011), and that the MYJ performed the best of five PBL schemes in reproducing deep convective cores over India (Madala et al, 2014).…”

Observational Study of the Thermodynamics and Morphological Characteristics of a Midlatitude Continental Cold Pool Event

“…Over the past decades, several numerical studies aimed to understand the characteristics and governing mechanisms associated with cold pools (e.g., von Kármán 1940;Benjamin 1968). The importance of representing convective cold pools has also been recognized by developers of multiscale modeling frameworks (e.g., Randall et al 2003;Pritchard et al 2011), as well as by the growing community of users of convection-permitting models (e.g., Erlingis and Barros 2014;Snively and Gallus 2014). Numerous studies showed that latent cooling by particles melting, sublimating, or evaporating is likely to strengthen the downdrafts, and thus affects the convective cool outflow near the surface (e.g., McCumber et al 1991;van den Heever and Cotton 2004).…”