Aviation Contributes to Better Forecasts
Piecing together weather
Aircraft weather data alphabet soup
Here are some of the acronyms for aircraft weather data systems.
ACARS: Aircraft Communication Ad-dressing and Reporting System, operated for the airlines by Aeronautical Radio Inc. (ARINC) — the communications link between pilots and their airline. Used in reference to weather data reported by U.S. carriers.
AMDAR: Aircraft Meteorological Data Relay, the generic name for automated weather reports from aircraft.
MDCRS: Meteorological Data Collection and Reporting System. This is the National Weather Service database containing ACARS data and the distribution system that feeds it to NWS computer models. The data collected by six major airlines is mostly from higher than 30,000 feet with lower altitude data from near major airports.
TAMDAR: Tropospheric Airborne Meteorological Data Reporting sensor, which collects and transmits data on humidity, pressure, temperature, winds aloft, icing, turbulence, location, time, and altitude.
If you were a pilot looking for a job back in the 1930s, you could have applied to the Weather Bureau. If you got the job, once a day you’d spiral up over the airport in an airplane carrying weather-recording instruments. If you made it to 13,500 feet, you got paid, and you earned a bonus for every 1,000 feet above that. A few U.S. Navy pilots also flew these “sounding” missions as part of their duties.
The work was dangerous, and 12 pilots died doing it in the 1930s. And, if the weather was really bad — when forecasters’ need for the data was greatest — you’d probably be grounded, because most pilots didn’t fly in what we now call instrument conditions.
In 1940 weather balloons carrying radiosondes grounded the last of the sounding airplanes. Radiosondes are packages of instruments that measure temperature, air pressure, and humidity and radio the data to forecasters. Meteorologists track the ascending balloon to get wind speeds and directions at different altitudes.
Weather balloons were the main source of upper air data until the 1990s. They are normally launched twice a day — at noon and midnight Zulu time — around the world. Only about 90 stations launch balloons in the United States. This leaves a lot of time and a lot of space between launches for the weather to do things that forecasters need to know.
Satellites and weather radar don’t supply the detailed data on wind speeds and directions and temperatures aloft that weather forecasting computer models need for really accurate forecasts. Only weather reports from aircraft can fill in the gaps. This is why the AOPA Air Safety Foundation is working with the National Weather Service (the Weather Bureau changed names in 1970) to encourage more pilots to radio in weather reports — known as pilot reports, or pireps.
To learn more about how to share information on the weather you’re experiencing during a flight, take the free SkySpotter course at the AOPA Online Safety Center.
The NWS would like to see many more pilots take the time to transmit weather information to Flight Watch on the frequency of 122.0 MHz. For forecasters, a report that the weather is beautiful — no icing, turbulence, or poor visibility — can be as important as a report of weather gone wild.
While weather data that pilots supply often includes vital information, voice reports can’t begin to provide the amount of data that computer models could use. But until the 1970s, pilot weather reports were labor intensive. Before the advent of on-board navigation computers, a pilot or navigator (airliners used to have those) would have had to use an E6B flight computer to calculate the winds. And before datalinks came along, a crew member would have keyed a microphone to read the data to someone on the ground, who would have to type it into a weather-data teletype system.
In the 1970s some airlines in various nations, including the United States, began sending automated reports for weather-forecasting computers. The number of reports zoomed in the 1990s as technology advanced.
Today, many of the jets operated by six airlines — American, Delta, FedEx, Northwest, United, and United Parcel Service — transmit wind and temperature data each 300 feet as they climb out or descend to land, and about each three minutes in cruise flight, says Kevin Johnston, chief of the NWS Aviation Services Branch. Data from the airliners allow the NWS to run a computer model called the Rapid Update Cycle hourly to produce new forecasts, including those for upper-altitude winds. “If we didn’t have the airline data, running this model each hour would be a waste of time,” Johnston says.
The resulting more accurate upper-air wind forecasts not only help pilots with flight planning, but also help to improve the accuracy of all weather forecasts, since the winds carry the heat and moisture that make the weather.
U.S. airlines supply about 35,000 weather observations each weekday (fewer on weekends). Several foreign airlines also supply data to their national weather services. The greatest amounts of such data are collected over the United States and Europe and the North America-to-Europe air routes, bringing the global total to about 130,000 daily observations.
Nations share aircraft data via the World Meteorological Organization’s Global Telecommunications System.
The September 11, 2001, terrorist attacks showed how much difference aircraft reports make, says Bill Moninger of the National Oceanic and Atmospheric Administration’s Forecasting Systems Laboratory. When airliners were grounded across the United States from September 11 until September 13, forecasts for three hours ahead became no better than those for 12 hours in the future, he says.
While the airline data is helping to improve forecasts, it’s missing two important elements: humidity readings and low-altitude information from above the vast majority of the nation’s airports, which airliners don’t use. Humidity data would help to forecast thunderstorms, icing, fog, low clouds, and other weather problems that water in the air can create for pilots. Low-altitude winds and temperatures would feed forecasting models a more complete picture of what the weather is doing now, which would help the computers to paint a more accurate picture of the future.
Aircraft need a sensor that sticks into the air to collect humidity data. (Airplanes already have outside air thermometers, whether or not they collect weather data.) Adding a humidity sensor means cutting a hole in the aircraft, which requires FAA approval and increases costs.
Commuter airline turboprops could be a good source of humidity and low-level wind and temperature data, because they use airports where jets don’t land, and they cruise at lower altitudes. With this in mind, the Georgia Tech Research Institute in Atlanta and AirDat LLC in Morrisville, North Carolina, developed the Tropospheric Airborne Meteorological Data Reporting (TAMDAR) sensor for NASA’s Aviation Safety and Security Program, which a commuter airline is now testing.
Sixty Saab 340s operated by Mesaba Airlines are flying around the Great Lakes region with TAMDAR sensors collecting and transmitting data on humidity, winds, pressure, temperature, icing, and turbulence. The Saabs’ GPS technology adds location, time, and altitude data for the Great Lakes Fleet Experiment.
NOAA’s Moninger said that after some “shakedown” problems with the data in the beginning, “it’s been getting better with every passing week.” He would like to see the experiment extended into next winter “so we can get a shot at winter with a system that’s had the bugs shaken out.”
TAMDAR data is being made available to National Weather Service offices in the region that Mesaba Airlines serves. Pilots, forecasters, and others can discuss this experiment on an online forum.
Forecasters at the National Weather Service office in Marquette, Michigan, described how TAMDAR data helped them on December 30, 2004. Freezing rain was expected to turn to ordinary rain. The big question was how long the freezing rain would last. “The frequent soundings (from airplanes with TAMDAR) showed potential for a couple of hours of freezing rain with little in the way of snow or sleet,” the forecasters wrote. “We upgraded the winter weather advisories to ice storm warnings,” which turned out to be correct: 0.25 to 0.5 inches of ice (that’s a lot of ice) was reported in the region.
Unlike the people around Marquette who were alerted to the danger of slick roads, the 1930s pilots who ventured aloft to sample the weather often flew into unpleasant surprises because forecasters didn’t have much information to work with.
Today, as forecasts improve, pilots need to worry about putting too much confidence in forecasts. While you can take off today with more confidence than the weather pilots of the 1930s had, a little 1930s caution is a good idea. The weather can still have surprises up its sleeve.