IMPROVE: Improvement of Microphysical Parameterization through Observational Verification Experiment

Summary

The goals of the offshore field project IMPROVE-1 (Improvement of Microphysical PaRameterization through Observational Verification Experiment-1) was to isolate the errors in the microphysical scheme by obtaining simultaneous ground-based radar, ground-released rawinsondes, and airborne microphysical measurements of precipitation within those portions of cyclones in which moisture and vertical air velocity should be accurately modeled by the MM5 mesoscale model. Past research in the Pacific Northwest carried out in the CYCLES project, and experience gained from analyzing daily runs of the MM5 model, indicated that portions of cyclones that were suitable in this respect included:

• widespread, continuous precipitation ahead of a warm front;
• mesoscale rainbands ahead of a warm front;
• wide cold-frontal rainbands that develop 10-100 km behind a surface cold front; and
• mesoscale rainbands associated with a cold front aloft in occluded frontal systems. Advanced data assimilation techniques will be used to force the MM5 model to accurately model the moisture and vertical air velocity fields in this situation.

Since the goal of the frontal study was to isolate frontal dynamics as the precipitation generating mechanism, a region was sought that had a uniform lower boundary in terms of topography, roughness, moisture availability, and surface temperature; was sufficiently far (a Rossby radius) from significant topography; and experiences a high frequency of wintertime frontal precipitation events.

The time of year (4 January -- 14 February 2001) and location, satisfying these requirements, was the northeastern Pacific Ocean off the Washington Coast (see map) in winter.  This area exhibits a relatively uniform sea-surface temperature distribution (compared to storm tracks in the western parts of the Atlantic and Pacific Oceans), and it experiences a high frequency of cyclonic storms and frontal passages from November through February. The advantage of focusing on this particular section of coast is that there is a large gap in the Coastal Mountains. Thus, most of the region within the study area exceeds a Rossby radius from the Olympic and Coastal Mountains.

The University of Washington (UW) Department of Atmospheric Sciences in Seattle was the Forecasting and Operations Control Center (FOCC) for IMPROVE-1. Between Intensive Observing Periods (IOPs), the NCAR S-Pol radar on the Washington Coast was used for surveillance of incoming storms, and this radar imagery was available to forecasters at the FOCC. When forecasts indicated that a frontal system was approaching within ~200 km of the Washington Coast, 3-hourly launches of rawinsondes were commenced at Quillayute, Westport, and Salem stations.