Simulations of Large Temperature Fluctuations on the Lee Side of a Mountain due to Interactions between an Orographic Wake and a Cold Air Pool
Abstract
Large-eddy simulations are performed with the Weather Research and Forecasting (WRF) model to aid the understanding of temperature fluctuations observed on the lee slope of Utah's Granite Peak during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) project. The observed temperature fluctuations are characterized by a drop in near-surface temperature of several Kelvin followed by partial recovery of temperature within about a half hour. These fluctuations can occur several times in a given night and are accompanied by bursts of turbulent kinetic energy in the otherwise calm nocturnal boundary layer. Dynamical explanations of these large temperature fluctuations focus on the role of upstream blocking in the formation of vertical axis eddies in the orographic wake (Jeglum et al., J. Appl. Meteor. Climatol., submitted). In addition to the orographic wake, a cold air pool must be present for the vertical axis eddies to effect large temperature fluctuations that are distinguishable from other sources of temperature variation. The ability of the model to reproduce this cold air pool is sensitive to the initial state of the soil moisture field and the parameterization of the soil thermal conductivity. Additionally, the model is sensitive to choice in turbulence closure and numerical configurations including resolution, domain size, and the steepness of model topography. With an appropriate setup, the WRF model results show good qualitative agreement with the MATERHORN observation data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A21I..06A
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSESDE: 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 3379 Turbulence;
- ATMOSPHERIC PROCESSESDE: 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES