The Simulation of the Southern Great Plains Nocturnal Boundary Layer and the Low-Level Jet with a High-Resolution Mesoscale Atmospheric Model

Abstract

field project over the Atmospheric Radiation Measurement?Cloud and Radiation Test Bed (ARM?CART) site during a period of several nights in September 2007 was conducted to explore the evolution of the low-level jet (LLJ). Data were collected from in situ (a multilevel tower) and remote (sodar) sensors, and the observed LLJ activity during the project was found to agree well with data from earlier studies regarding jet speed, height, and direction. To study nocturnal boundary layer (NBL) behavior, the Regional Atmospheric Modeling System was used to simulate the ARM?CART NBL field experiment and was validated against the data collected from the site. This model was run at high resolution for calculating the interactions among the various motions within the boundary layer and their influence on the surface. The model faithfully simulated the formation and dissolution of the low-level nocturnal jet during a synoptic situation in which low pressure with warm southerly advection replaced high pressure. An additional simulation at 32.5-m resolution was performed for the most stable 5.5-h period, using a turbulence scheme adjusted to allow for greater resolved turbulent kinetic energy, and the model reproduced the turbulence statistics as determined by a power spectrum. The benefit of the high-resolution simulation is evident in the much more realistically resolved model turbulent kinetic energy and the fluxes of momentum, heat, and water vapor.