Coronavirus-canceled flights could affect weather forecasting at exactly the wrong time
The coronavirus pandemic may affect the accuracy of the initial weather forecast model output originating from national and global weather prediction centers because of a cutback in the number of aircraft flights that generate vital weather data, according to the European Centre for Medium-Range Weather Forecasts (ECMWF) and other experts.
The aircraft collect temperature and wind data, among other information, that help improve the initial atmospheric conditions that drive global and regional weather forecast models. This data is used routinely to improve the forecasts created by national weather prediction centers across the globe.
However, the pandemic has drastically reduced the number of such flights in Europe and increasingly in the U.S. This impact will be a reduction in global forecast performance. For regional models, the impact may be even greater.
“Regional models have the ability to resolve high-impact weather, such as thunderstorms,” said AccuWeather’s Scott Mackaro, vice president, Science, Innovation & Development. “Information about the vertical structure of the atmosphere is vital and already sparse. Aircraft measurements provide just that.
“We will likely see the biggest impacts on our ability to forecast convective weather, such as thunderstorms and other local storms, just as we are approaching severe weather season in the Northern Hemisphere,” Mackaro said.
The announcement from ECMWF notes, “At ECMWF, aircraft reports are second only to satellite data in their impact on forecasts. However, recently added satellite wind observations will help to mitigate the drop in the number of aircraft-based observations.”
The AMDAR program (Aircraft Meteorological Data Relay) uses existing aircraft onboard sensors, computers and communications systems to collect, process, format and transmit meteorological data to ground stations via satellite or radio links. The global AMDAR system, during typical air traffic, produces more than 700,000 high-quality observations a day of air temperature and wind speed and direction, together with the required positional and temporal information and with an increasing number of humidity and turbulence measurements being made.
More than 3,500 commercial aircraft provide more than 250 million observations per year in the U.S., National Weather Service (NWS) spokesperson Susan Buchanan told the Washington Post.
With less data to assist with the initial forecasts, accuracy becomes a concern.
“To run a computer model to forecast the future state of the weather you need the best current conditions possible,” said AccuWeather Founder and CEO Dr. Joel N. Myers. “If you do not have all of the observations three-dimensionally through the atmosphere, your initial state is not as accurate. So then forecast errors grow with time because it is an iterative process.”
“The latest information available from airlines suggests that European AMDAR coverage will be reduced by 65 percent or more over the coming month, which is currently expected to continue into the summer,” Steve Stringer, EUMETNET ABO Programme Manager, noted in the ECMWF release.
The numbers and geographical coverage are also expected to be reduced elsewhere over the coming weeks, according to the release.
“We are anticipating the substantial reduction in the availability of US AMDAR data to continue over the coming weeks, likely to generate some measure of impact on the output of our numerical weather prediction systems,” said Christopher Hill of the National Oceanic and Atmospheric Administration (NOAA) in the announcement.
Tests conducted by numerous national weather prediction centers for more than 25 years “have demonstrated that high-quality and high-frequency AMDAR temperature and wind observations increase the skill of forecasts at both regional and global scales and for both short- and medium-range forecasts,” an American Meteorological Society report noted. “Results show that aircraft data taken at cruise levels and during ascent and descent provide important information for improving forecasts, both in terms of long-term average performance and for individual events.”
Passenger and cargo aircraft are seen stored at Southern California Logistics Airport, Wednesday, March 25, 2020, in Victorville, Calif. As demand for air travel drops amid the coronavirus outbreak, commercial aircraft are being parked at facilities that include remote desert airports, including the Southern California Logistics Airport in Victorville about 90 miles northeast of Los Angeles. (AP Photo/Mark J. Terrill)
“In the coming days and weeks, we expect a further decrease in numbers, which will have some impact on forecast quality in the short range, particularly around the polar jet stream level (10–12 km altitude),” according to the ECMWF release. “Sensitivity studies at ECMWF have shown that removing all aircraft data degrades the short-range wind and temperature forecasts at those levels by up to 15 percent, with significant degradations at all forecast ranges up to seven days.”
Errors in short-term forecast generally increase exponentially with time, adding fuel to the concern.
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