Effects of Land-Surface Heterogeneity on Sea-Breeze Convection

More than two billion people worldwide live within 100km of the coast. For these populations, and particularly those in the tropics and subtropics, sea-breeze driven convection is a critical component of the weather and climate system. These storms bring necessary rainfall, but can also produce hazards to life and property such as flooding, lightning, and strong winds. These storms, which are often short-lived, remain difficult to forecast, with operational models often failing to capture their timing, location, and intensity. The role of the sea-breeze in triggering coastal convection has long been recognized, but the effects of heterogeneous land surfaces in modifying this convection has received less attention. Land surface heterogeneity impacts local heat fluxes, albedo, and winds, all of which affect the initiation and behavior of convective storms. This study focuses on the effects of heterogeneous land surface characteristics on the strength of the sea breeze and subsequent convection.
This study uses the Regional Atmospheric Modeling System (RAMS), a compressible non-hydrostatic cloud-resolving model, to simulate an idealized subtropical summer sea-breeze event over flat topography. These simulations are initialized with soundings taken on 21 June 2022 during the Experiment of Sea-breeze Convection, Aerosols, Precipitation, and Environment (ESCAPE) field campaign in the Houston area. The 400km by 200km model domain consists of a 250km by 200km land area north of a 150km by 200km uniform ocean, with a straight coastline in the east-west direction. The land portion of the domain is divided into two equal-width stripes which are uniform in the north-south direction. This division of land surface ensures that, if circulations develop on the edges of each land surface type due to horizontal temperature and/or moisture gradients, these circulations will be perpendicular to the sea breeze front.
In order to investigate the impacts of heterogeneous land surfaces, and accompanying secondary circulations, on deep convection, the land surface type assigned to each stripe is varied. In the control simulation, both land sections are assigned as uniform pasture, while experimental setups include: 1) coniferous forest adjacent to pasture, 2) coniferous forest adjacent to urban, 3) pasture adjacent to urban, 4) uniform urban, and 5) uniform coniferous forest. Preliminary results indicate that, relative to a uniform land surface, adjacent stripes of different land surface type lead to changes in storm timing and location, and enhance domain-wide precipitation. This presentation will describe the impacts of these land surface changes on the strength and timing of the sea breeze, boundary-layer circulations, low-level temperature and humidity profiles, and the subsequent effects on the development of deep convection.