Pacific Turbulence

last updated 6 January 1998

On 28 December 1997, United Airlines Flight 826 experience severe turbulence on a routine flight from Japan to Hawaii, killing one person and injuring more than one hundred.

On 30 December, the National Transportation Safety Board (NTSB) issued a press release describing the incident.

The episode was reported as occuring at 1410 UTC (which is 1:10 am local time in mid-ocean) at 32.5N 159.0E, and 31,000 feet altitude (9.5 km).

GMS weather satellite observations

Images from the Japanese Geosynchronous Meteorological Satellite (GMS) at the reported location of the turbulence show the ragged southern end of a storm front popping with individual convective towers.

However, none of the GMS images show anything extraordinary for the storm.

GMS 11-micron animation

The GMS-5 11 micron cloudtop temperatures are around 240 K, which is probably below flight altitude. The cloudtops appear strongly sheared by upper level winds from the northwest.

GMS 6.7-micron animation

The corresponding 6.7 micron images, which reveal the moisture swirls in the middle troposphere, show fast-changing dry slots (folding and mixing) around the west and southern sides of the front. Before the plane arrives, there are deep dry slots, which disappear by the time of the incident.

The University of Wisconsin has posted a nice wind analyis of this case.

Background Information

The UA flight 826 was in the vicinity of a mid-ocean winter storm of substantial but not extraordinay intensity. This sort of storm forms routinely as the winter upper air jet stream off the Tibetean plateau crosses the warm Kiroshio current and spins up a trough. Clear-air turbulence is common in the vicinity of an upper-level jet stream, as the fast-moving air roils the environment.

Thanks to Jim Dodge NASA/HQ and Torben Nielsen Un-Hawaii, Goddard Space Flight Center is the prime server for real time GMS data in the USA:
http://rsd.gsfc.nasa.gov/goesg/earth/Weather/GMS-5/

We put together video loops from the GMS hourly IR data for 28 December using Hasler's Image Spreadsheet, and mailed a copy of the video tape to the NTSB:

   Greg Salottolo
   NTSB, AS-30
   490 L'Enfont Plaza, SW
   Washington, DC 20594-2000
   202-314-6338

The flight recorder shows a drop of only a 100 feet, but g-forces ranging from +1.8 (almost double gravity) to -0.8 ("gravity" upward) within 7 seconds.

Jim Weinman of NASA-GSFC is looking into getting other satellite data. With luck, there could have been a TRMM overpass.

Dennis.F.Chesters@nasa.gov
GOES Project Scientist