The Relationship of Transient Upper-Level Troughs to Variability of the North American Monsoon System

Relationships between transient upper-tropospheric troughs and warm season convective activity over the southwest United States and northern Mexico are explored. Analysis of geopotential height and vorticity fields from the North American Regional Reanalysis and cloud-to-ground lightning data indica...

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Bibliographic Details
Published in:Journal of climate 2009-08, Vol.22 (15), p.4213-4227
Main Authors: Bieda, Stephen W., Castro, Christopher L., Mullen, Steven L., Comrie, Andrew C., Pytlak, Erik
Format: Article
Language:English
Subjects:
Atmospheric circulation
Climate models
Climatic zones
Convection
Datasets
Earth, ocean, space
El Nino
Exact sciences and technology
External geophysics
La Nina
Lightning
Marine
Meteorology
Monsoons
Precipitation
Rainy seasons
Sea surface temperature
Summer
Tropical regions
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Summary:Relationships between transient upper-tropospheric troughs and warm season convective activity over the southwest United States and northern Mexico are explored. Analysis of geopotential height and vorticity fields from the North American Regional Reanalysis and cloud-to-ground lightning data indicates that the passage of mobile inverted troughs (IVs) significantly enhances convection when it coincides with the peak diurnal cycle (1800–0900 UTC) over the North American monsoon (NAM) region. The preferred tracks of IVs during early summer are related to the dominant modes of Pacific sea surface temperature (SST) variability. When La Niña–like (El Niño–like) conditions prevail in the tropical Pacific and the eastern North Pacific has a horseshoe-shaped negative (positive) SST anomaly, IVs preferentially track farther north (south) and are slightly (typically one IV) more (less) numerous. These results point to the important role that synoptic-scale disturbances play in modulating the diurnal cycle of precipitation over the NAM region and the significant impact that the statistically supported low-frequency Pacific SST anomalies exert on the occurrence and track of these synoptic transients.
ISSN:0894-8755
1520-0442
DOI:10.1175/2009JCLI2487.1