Document type: DU ETD
Collection: Geology Theses  
Title Synoptic Influences on Seasons of Exceptional Winter Precipitation in the Rocky Mountain Region
Author(s) Luchsinger, Deborah Anne
School/Department Department of Geography
Institution University of Denver
Degree Type Doctoral
Degree Name Ph.D.
Type of Resource text
Degree Date 1998 June
Digital Origin reformatted digital
Rights Statement All Rights Reserved
Reason for Restrictions No restrictions
Type of Restriction No restrictions
Keyword(s) Geography
Genre Dissertations, Academic
Abstract The Rocky Mountain region presents a number of problems for climatologists and meteorologists seeking to analyze weather and climate trends. The complex terrain modifies atmospheric circulation patterns and can both initiate and alter storm systems. Frequency, intensity, and duration of storm events are in tum affected by upper atmospheric circulation patterns. This research examines relations between (1) the PNA teleconnection index, (2) upper atmospheric pressure patterns, (3) storm-track preferences, and (4) frequency of cyclonic activity during seasons of exceptional winter precipitation. Map pattern analysis of standardized winter season precipitation indices calculated for each climate division inthe Rocky Mountain region yield 6 anomalous winter patterns. Composite maps of the 500-mbar surface are classified to determine modes of synoptic feature variability during the winter seasons analyzed. The significance of cyclone frequencies and the PNA index on precipitation anomaly patterns are determined through regression of the cyclone frequency and PNA indices against both divisional and regional precipitation indices. Finally, dominant storm track patterns are analyzed with respect to the anomalous precipitation patterns identified. Above-average winter precipitation patterns in the Northern region are associated with a zonal circulation regime, as indicated by a negative PNA index value and a ridge-trough-ridge configuration in the 500-mbar surface. The anomalous flow regime established by this reverse PNA synoptic pattern increases the frequency of extratropical cyclones breaching the west coast, and shifts the mean storm track such that storms enter the mountainous divisions of Idaho, western Montana, and northwestern Wyoming with little impediment. Anomalous precipitation patterns in the Southern region show no statistical significance to the frequency of cyclonic activity. Meridional circulation, as indicated by a positive PNA index value and a trough-ridge-trough synoptic pattern are strongly associated with above-average precipitation regimes in the Southern region. The increase component of anomalous flow from the subtropical Pacific Ocean and the southward displacement of the mean storm track around the Aleutian low result in an increase in winter storm system dynamics, rather than an increased frequency of storm events.
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