New Mobile Atmospheric River Observations Deployed on the Washington Coast


October 27, 2009


The Mobile Atmospheric River Monitoring System (MARMS) close to completion in Erie, CO (Photo credit: Barb DeLuisi)

Installation at the Westport, WA field site in October (Photo credit: Clark King, NOAA)

The NOAA Earth System Research Laboratory (ESRL) is deploying a newly developed Mobile Atmospheric River Monitoring System (MARMS) to Westport, Washington, roughly 250 km upwind of the Cascade foothills, in a data poor area. MARMS, a form of an "Atmospheric River Observatory" (ARO) will monitor the wind speed, direction, snow level and water vapor content in real-time above the Earth's surface to help researchers better understand Atmospheric Rivers (AR); the phenomenon that fuels potentially dangerous winter storms on the West Coast of the U.S. Data from MARMS will begin flowing to researchers and others, such as the Seattle Weather Forecast Office starting November 1, 2009, via the Internet. This deployment is an extension of NOAA's Hydrometeorology Testbed (HMT) program and ESRL's weather and climate/water cycle research already being performed in California. The Westport deployment is a first step in assessing the role of ARs in flooding in the Pacific Northwest, and the potential of new observing capabilities. Another component that will support this effort is ESRL's Reforecast Model. This model is a compilation of historical observations and their corresponding 2-day forecasts, which are rerun using today's current forecasting model (i.e., reforecasts). The reforecasts represent an additional tool for anticipating heavy precipitation and is being evaluated in the context of the AR phenomenon.

Atmospheric Rivers are the regions of ocean storms where high winds and water vapor are concentrated. These factors combine to produce heavy rainfall upon landfall, especially over mountainous terrain. Most flooding events in the several watersheds studied thus far on the West Coast in winter are associated with the landfall of AR conditions. ARs are visible in satellite images over the oceans, but their impact over land is not captured well by NOAA's current operational observing system. Each AR monitoring station includes a Doppler wind profiler for measuring wind profiles and snow level, and a Global Positioning System receiver for measuring the column-integrated water vapor concentration. The Water Vapor Flux Tool uses these measurements to calculate the horizontal transport or flux of water vapor and correlates this to rainfall in the mountains.

From four years of winter storm observations along the coast of central California, NOAA has developed scientifically based AR thresholds for water vapor content and upslope wind speed, which identify an AR event. Deployment of MARMS in Westport will allow researchers to evaluate whether these thresholds can be applied to the Washington coast. Real-time data and tools from MARMS can be used to evaluate model forecasts as storms strike the coast. Together with the Reforecast Model, these tools will give researchers and forecasters more insight into winter storms and associated heavy precipitation.


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