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Two Projects Extend HMT Findings on Atmospheric Rivers

July 15, 2010

Composite satellite image of total integrated water vapor from the Defense Meteorological Satellite Program's Special Sensor Microwave Imager for 16 February 2004. Warmer colors indicate enhanced water vapor content in the atmosphere. Atmospheric rivers are the narrow corridors of water vapor emanating mostly from the band of enhanced water vapor in the tropics. The white symbols show the locations of the two Global Positioning System (GPS) receiver networks, with meteorological sensors to allow for integrated water vapor measurements, being installed or upgraded as part of the projects described in the text.
(Click image to enlarge)

Two projects led by the Earth System Research Laboratory (ESRL), the National Weather Service (NWS), and the California Department of Water Resources (CA-DWR) will help detect and monitor flood producing atmospheric rivers (ARs), narrow regions of enhanced water vapor transport in landfalling, midlatitude storms. First, CA-DWR is sponsoring a Hydrometeorolgy Testbed (HMT) legacy project that includes upgrading 32 existing Global Positioning System (GPS) receivers in California with meteorological data packages that will allow the receivers to measure integrated water vapor, a key ingredient of ARs and the fuel for generating precipitation. The existing GPS receivers are part of the Plate Boundary Observatory operated by the National Science Foundation to precisely monitor the position of the Earth's crust.

The second project is sponsored by NOAA's Coastal Storms Program (CSP) and will fund the NWS Pacific Region to deploy GPS receivers at nine key locations across the Pacific Basin, several of which will be within the breeding grounds of ARs. Data from these sensors and improved modeling through data assimilation will likely promote advanced detection of developing oceanic storms and signs of their rapid development or weakening. The data from all of the GPS sites in California and across the Pacific will be made available to the public on the NOAA GPS Meteorology Program web page and to NWS operations through the Meteorological Assimilation Data Ingest System (MADIS).

In a maritime environment, a deep corridor of concentrated water vapor transport is often found in landfalling storms. These corridors are referred to as ARs because they tend to be quite narrow relative to their length scale and because they are responsible for almost all of the poleward water vapor transport. Consequently, ARs play a crucial role in the global water cycle and represent a key phenomenon linking weather and climate, yet until now, water vapor and its transport in ARs have not been adequately monitored in space and time by other observations.

Floods cause more damage nationwide than any other type of natural disaster. NOAA's HMT-West has provided an opportunity for NWS hydrologists and meteorologists in California, Oregon and Washington to work closely with NOAA researchers to develop and evaluate new methods of monitoring and predicting ARs and their resulting impacts, including extreme precipitation that leads to floods. This work is important given the general expectation from climate models that extreme precipitation events will increase in a changing climate. To help guide climate model diagnostics, ongoing research in ESRL is focusing on explaining the origins of some of the strongest ARs, which can connect to the tropics, and is exploring the role of the Sierra Nevada's in modifying landfalling ARs. The GPS projects described here represent a major step forward in regional climate-related research and monitoring associated with the water cycle.

Contact: Allen White