Scientists in the Earth System Science Center at The University of Alabama in Huntsville will spend the next three years studying how forecast models can best use the enhanced information from the new radar system to improve storm forecasts.
Dr. Xuanli Li and Dr. John Mecikalski at UAHuntsville, and Dr. Derek Posselt at the University of Michigan, supported by a $445,000 grant from the National Science Foundation, will develop tools to help translate and input what the advanced radar units see into forecast models.
The weather service's NEXRAD Doppler radar units, which have been in service since the early 1990s, send out their radar signals in a single horizontal polarization. The advanced dual-polarimetric (dual-pol) radar being installed around the country through 2013 sends out both horizontal and vertical radar signals.
NEXRAD's single signal provides useful information about two variables, which can tell forecasters and forecast models such things as the amount of water in a cloud or storm system, and the direction in which it is moving.
By looking at the raw signal, plus differences between the vertical and horizontal radar signals, the dual-pol radar gathers information about six variables. These can provide information about the amount of water and movement of the storm, plus other factors such as the type, shape and size of water or ice particles at various places within a cloud.
"In a storm you might have clouds with many small droplets or clouds with a smaller number of large drops, but both might produce similar amounts of rain,” said Mecikalski, an associate professor of atmospheric science. "With the old NEXRAD systems those might show up with very different echoes, which would suggest different rainfall rates. With the new radar you can get more information about the type and shape of the droplets, so you can get a much improved estimate of precipitation."
The challenge, said Li, a post-doctoral research associate, is that existing forecast models don't know what to do with the extra data.
"There hasn't been much research on how to input those data into weather forecast models in real time," she said.
"We will be taking the returns from the radar and assigning those signals to variables the models can understand, such as the amount of snow per cubic meter."
"It is difficult for current forecast models to accurately predict the dynamics and physics of a storm," said Mecikalski. "We want to use data from the new radar and other instruments to help the models do a better job of describing the storm's structure and development. With the new radar's capability we will be able to get more accurate information about a storm, especially about ice particles in clouds, then use that data to make more accurate short-term forecasts."
The team will focus on convective storms, which are often difficult to forecast. They hope the dual-pol radar data will help forecast models provide several improved weather products, including more accurate detection of hail and better rainfall estimates.
UAHuntsville scientists have been working with dual-pol data for several years: The university has been operating a dual-pol radar in cooperation with a local television station for almost seven years.For additional information:
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