Climate Variability--Winter Precipitation Anomalies

Status:

Completed

Start Date:

2005

End Date:

2007

CLIMAS Investigators:

Andrew Comrie

Collaborators:

James Tamerius

Abstract:

This research was designed to develop a better understanding of fine scale climate variability by focusing on the spatial and temporal distribution of winter precipitation anomalies within smaller sub-regions of the Southwest. Using the North American Regional Reanalysis data set, researchers analyzed differences between hypothesized controlling atmospheric variables under contrasting intra- and inter-seasonal variability for a set of key sub-regions. Researchers also identified the leading causes of the observed patterns in fine-scale precipitation anomalies.

Research Outcomes

Research outcomes include:

Interactions between synoptic and local-scale processes produce several key permutatins of locally-contrasting winter precipitation anomalies.
Many of sub-regional precipitation patterns delineated in our work are related to regional-scale precipitation patterns and their interactions with finer-scale topography and related local circulation effects.
Regional-scale precipitation patterns are closely linked to inter-annual variability of large-scale circulation (e.g. position of Pacific-high, position of Aleutian-low, activity of southern jet).
Although adjacent sub-regions in the Southwest U.S. may be highly correlated with respect to winter precipitation, correlations between sub-regions can become unstable during certain winters, when:
- Large-scale circulation regimes affect the synoptic-scale characteristics of precipitation events in a region over the course of a winter;
- The synoptics of the event favor precipitation in one sub-region over an adjacent sub-region, and precipitation relationships between the sub-regions can become skewed and result in contrasting precipitation anomalies.
- Local topographic features become partially responsible for creating finer-scale differences by amplifying and/or suppressing precipitation at distinct points under different large-scale and synoptic conditions.