A Review of Cold Air Pool Events in the Intermountain West using Radiosondes and the North American Mesoscale Model (NAM)
Abstract
Cold air pools (CAPs) are a topographically confined stagnant layer of air that is colder than the air above, preventing the air mass and air pollution from rising. Mountainous valleys in the Western U.S. experience CAPs frequently during winter months, which are induced by large-scale subsidence, surface radiative cooling, stagnant winds and cold front passages. With the inability of air to rise, pollutants accumulate within the valley impacting human health (e.g. increase in emergency department visits during CAPs). Thus, it is important to understand and accurately quantify CAP characteristics, including the vertical boundary layer structure, stability strength and duration.
The goal of this research is to determine the variability in the existing criteria methods for classifying CAP events and to present a revised method of CAP classification. There are multiple methods for quantifying CAP events, including a valley heat deficit (VHD) threshold and a criterion based on 10-meter wind speed and temperature lapse rate. Radiosondes provide a vertical profile of the atmosphere and can be used to calculate the atmospheric stability. However, many regions of the U.S. do not have balloon soundings. In these regions, gridded three-dimensional meteorology data from NAM can provide vertical boundary layer structures of CAPs. We will present results using NAM products (12-km horizontal resolution and 40 vertical levels), to evaluate its ability to quantify CAP strength compared to radiosonde data. Additionally, radiosondes at several locations are released more than 100-meters above the valley, which leads to an incorrect representation of atmospheric stability. We will present a new method to append valley station meteorological data to radiosonde data to provide a complete profile of the valley basin. Using this method, more representative VHD values, temperature lapse rates and 10-meter wind speeds are obtained to classify CAP events. For example, in Reno, the mean VHD for 2002-2018 winter months increased from 1.1 MJ m-2 to 2.0 MJ m-2 after appending valley station data to radiosonde data. This work will explore new methods for classifying CAP events for valleys across the Western U.S., which will aid epidemiologists, meteorologists, geographers, etc. in determining risks and impacts associated with CAP events.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A51O2861C
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3329 Mesoscale meteorology;
- ATMOSPHERIC PROCESSES;
- 3354 Precipitation;
- ATMOSPHERIC PROCESSES;
- 3390 Wildland fire model;
- ATMOSPHERIC PROCESSES