Space weather affects aviation too

 - March 26, 2008, 11:05 AM

While the term space weather may at first invoke visions of Capt. Kirk and his starship Enterprise encountering ion storms, it is in reality something which affects radio communications, satellite transmissions and signals intelligence. And because HF radio is particularly susceptible, it often forces airlines and any other aircraft operating on polar routes to switch to different tracks, and sometimes make unscheduled fuel stops.

At a recent half-day conference on “Space Weather and Aircraft Communications” at the Air Transport Association (ATA) in Washington, Joe Kunches, chief of space weather operations at the National Oceanic and Atmospheric Administration (NOAA) Space Environment Center (SEC) in Boulder, Colo., explained that space weather refers to changes in the space environment near Earth.

Through its Space Weather Now Web site, the SEC maintains real-time reporting on geomagnetic storms, solar radiation storms and radio blackouts. The SEC has developed numbered scales to inform the general public of the current and future space weather conditions and their possible effects on people and systems.

All three can affect HF radio propagation. Depending on severity, geomagnetic storms can knock out HF in many areas for one or two days, satellite navigation may be degraded for days and low-frequency radio can be out for hours. It can also affect power systems and spacecraft operations.

Solar radiation storms can cause high radiation exposure to passengers and crew in jets at high latitudes, with dosages equal to approximately 100 chest X-rays possible.
Extreme radio blackout can cause complete HF radio blackout on the entire sunlit side of Earth lasting for a numbers of hours, resulting in no HF radio contact with mariners and en route aviators in this sector. Low-frequency navigation signals used by maritime and general aviation systems (loran-C) experience outages on the sunlit side of Earth for many hours, causing loss in positioning. Further, there can be increased satellite navigation errors in positioning for several hours on the sunlit side of Earth, which may spread into the night side.

Jeff Zimmerman, a forecast techniques meteorologist with Northwest Airlines, said that the recent session in Washington had been planned for November, but the events of September 11 caused it to be delayed. He said airlines are using polar routes “a lot less” than before the attacks.

The sun goes through cycles of high and low activity that repeat about every 11 years, and 2001 was considered the peak of the current cycle. Although the next solar maximum won’t occur for about another 11 years, Zimmerman reminded the group that “it is still an issue for us.”

NOAA, through its SEC, and the Air Force jointly operate the Space Weather Operations (SWO) branch. It is the national and world warning center for disturbances that can affect people and equipment working in space, and provides forecasts and warnings of solar and geomagnetic activity to users in government, industry and the private sector.

According to NOAA, the SWO continuously monitors, analyzes and forecasts the environment between the sun and Earth. The SEC receives solar and geophysical data in real time from a large number of ground-based observatories and satellite sensors around the world. SWO forecasters use these data to predict solar and geomagnetic activity and issue worldwide alerts of extreme events.

Three U.S. airlines are using the four polar routes because they reduce flying time by up to two hours, which in turn provides for increases in payload and/or reserve fuel capability, said Gene Cameron, manager of international dispatch and flight operations for United Airlines.

As longer-legged airliners become available, they will open the possibility of new services to Asia.

But airlines must be aware of solar activity, and they cannot plan a polar operation if a level-4 solar radiation storm (classified as “severe” on a five-tier scale) is active or expected. A storm of that level elevates radiation exposure to passengers and crew at high latitudes; further, there is blackout of HF radio communications through the polar regions and for several days there is an increased likelihood of navigation errors.

Cameron said that a level-3 solar storm (strong) will allow polar operations at Flight Level 280 or 310. Passengers and crew may receive low-level radiation exposure there (approximately equal to one X-ray). HF radio is degraded through the polar regions and navigation position errors are likely.

Jay Bjornstad, international chief dispatcher for Northwest Airlines, said that flight planning for a Detroit-Beijing trip that departs at 2030Z begins at 1200Z and is complete by 1700Z. Available routes are either polar or Russian Far East routes, but the use of polar routes requires “considerable coordination” with Russian and Chinese ATC authorities.

Dispatchers must plan to avoid turbulence/hazardous weather, provide the best fuel burn/shortest en route time, keep the fuel above the freeze point and comply with ATC rules and Notams, all the while ensuring continuous communications with ATC and dispatch.

Bjornstad said that space weather Web sites are checked, and if problems are detected before departure, the Russian Far East Route is selected. If a problem occurs before reaching the polar area, the flight is rerouted, which likely results in an unplanned fuel stop that adds hours to the trip. If the problem occurs after the aircraft has entered the area, the flight continues.

Arinc, which provides HF messaging from ground stations, said that increased solar activity causes its operators communications problems. Since there is a language difficulty inherent in international communications, any noise or signal degradation exacerbates the problem.