GCM studies suggest that Arctic climate change may be associated with a greater frequency of extreme weather events. In the Arctic, events of extreme temperature, heavy rain, and wind/wave events during the ice-free months are already receiving increased attention. Within our effort toward an Arctic reanalysis (discussed in a companion paper), we have been studying extreme events (e.g., extreme rain, extreme snow, and Arctic cyclones) as well as generic (or “routine”) cases during different seasons of the year.

The three-dimensional variational data assimilation (3DVAR) developed by the National Center for Atmospheric Research (NCAR) is used in this study with the Fifth Generation Penn State University (PSU)/NCAR mesoscale model (MM5). The benefit of applying MM5/3DVAR over the high latitudes and the Arctic region has been shown from our previous studies.

An extreme rain event occurred during late July 2003 in interior Alaska. In this paper, we examine this case in detail to investigate the impact of 3DVAR approach, utilized within a regional mesoscale model, on the simulation of this event.

Horizontal resolution has also been found to have significant impact on mesoscale numerical simulations and, on the basis of our work with more routine cases, 3DVAR analyses as well. This paper focuses on the application of MM5/3DVAR in simulating Arctic extreme events, and investigates the impact of horizontal resolution on both the 3DVAR analysis and the associated MM5 forecast of an extreme event. Numerical experiments have been conducted at two different spatial resolutions of 45 and 15 km for an Alaska domain. Comparison experiments are conducted using the Newtonian nudging technique available as a standard option in MM5.

Preliminary analysis indicates that spatial resolution has a substantial impact on both the MM5/3DVAR analyses and simulations. The emphasis of the conference presentation will be on the simulated airflow pattern and precipitation amounts, which are directly related to the hydrological impacts. These impacts include the potential for flooding associated with the heavy rainfall that occurred during the 2003 event.