文章基本信息

标题：Cold Pool Responses to Changes in Soil Moisture
本地全文：下载
作者：Aryeh J. Drager ; Leah D. Grant ; Susan C. van den Heever 等
期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2020
卷号：12
期号：8
页码：1-22
DOI：10.1029/2019MS001922
出版社：John Wiley & Sons, Ltd.
摘要：This study examines the role of soil moisture in modulating convective cold pool properties in an idealized modeling framework that uses a cloud‐resolving model coupled to an interactive land surface model. Five high‐resolution simulations of tropical continental convection are conducted in which the initial soil moisture is varied. The hundreds of cold pools forming within each simulation are identified and composited across space and time using an objective cold pool identification algorithm. Several important findings emerge from this analysis. Lower soil moisture results in greater daytime heating of the surface, which produces a deeper, drier subcloud layer. As a result, latent cooling through the evaporation of precipitation is enhanced, and cold pools are stronger and deeper. Increased propagation speed, combined with wider rain shafts, results in wider cold pools. Finally, the rings of enhanced water vapor that surround each cold pool when soil is wet disappear when the soil moisture is reduced, due to the suppression of surface latent heat fluxes. Instead, short‐lived “puddles” of enhanced water vapor permeate the cold pools. The results are nonlinear in that the properties of the cold pools in the two driest‐soil simulations depart substantially from the cold pool properties in the three simulations initialized with wetter soil. The dividing line between the resulting wet‐soil and dry‐soil regimes is the permanent wilting point. Below the permanent wilting point, transpiration is subdued due to a sharp increase in water stress. These results emphasize the role of land surface‐boundary layer‐cloud interactions in modulating cold pool properties. Plain Language Abstract When rain falls from storm clouds, some of the rain evaporates. In order to evaporate, the rain absorbs energy from the air around it, cooling the surrounding air. As the air cools, it becomes denser and accelerates toward the ground, forming a region of wind that blows downward (a “downdraft”). Then, upon reaching the surface, this cool, dense air collects and spreads out to form a cold pool. Cold pools are important because, as the cold pool spreads out, it pushes the environmental air in its path out of the way, forcing it upward. When this surrounding air is pushed upward, it can create a new storm cloud. In this study, we use computer model simulations to examine the effects of changing the wetness of the soil (the “soil moisture”) on the cold pools. We first identify and track the cold pools forming in each simulation, and we then measure their sizes and strengths. The results indicate that the simulations with the driest soil have the largest and strongest (coldest and densest) cold pools. Previous cold pool modeling studies have documented “rings” of very humid air that surround cold pools forming over an ocean surface. We find that these rings occur in the three simulations with the highest soil moisture but not in the two driest‐soil simulations. Instead, the cold pools in the two driest‐soil simulations have “puddles” of humid air in their interiors and low humidity at their peripheries. Many previous modeling studies examining cold pools over land have not included any sort of land surface in their simulations. That is, there are no plants or soil layers, and the ground does not interact, that is, exchange moisture and heat, with the air above. Our results indicate that these sorts of interactions can make a substantial difference in cold pool properties, and we therefore recommend that simulations take these factors into account when simulating and forecasting storm clouds.
关键词：cold pools;soil moisture;convection;density currents