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CR 06:227-235 (1996)  -  DOI:

An air mass-based approach to regional GCM validation

Schwartz MD

Current Global Climate Models (GCMs) lack the resolution and physics to provide detailed assessments of changes on the regional scale, where many important societal impacts occur. Model improvement efforts can be facilitated by a systematic characterization of regional control-run (1 x CO2) values. Synoptic-scale analyses offer appropriate methods for this task, such as air mass analysis. Comparison of air mass types derived from a GCM control run and observed data provides an assessment of GCM circulation, near-surface temperature, and moisture patterns. In this study, 10 simulated years of control-run data from the GENESIS Version 1.02 GCM are evaluated in light of 1961-1990 observed data from the North Central United States (NCUS). The GCM simulation fares much better in recreating a proper mix of synoptic patterns in seasons where 1 air mass type is not overwhelmingly dominant. That is, the prominence of Continental air in winter, and Tropical air in summer are overemphasized, while spring and autumn seasonal distributions are more accurate. The circulation patterns associated with each air mass category are simulated rather well in most cases by the GCM. Air mass temperatures and dew points, however, are not well represented in the non-winter seasons. Cold air masses tend to be too warm, and warm air masses too cold in spring and autumn. In summer, all air masses are too warm. While the seasonal GCM performance in the NCUS is promising, these results suggest that there may be substantial differences between the GENESIS GCM Version 1.02 control run and observed climate data at the daily time scale.

Air mass · Global Climate Model · Regional validation

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