DOING AWAY WITH FOG

THE AIR WEATHER SERVICE (AWS) OF THE U.S. AIR FORCE HAS BEEN EXPERIMENTING WITH VARIOUS MEANS OF FOG DISPERSAL AT AIRPORTS. OF THE THREE TYPES OF FOG-ICE, SUPERCOOLED, AND WARM---THE AWS HAS DIRECTED MOST OF ITS ATTENTION TO THE SECOND, WHICH IS COMPOSED OF LIQUID WATER DROPLETS AT TEMPERATURES BELOW FREEZING. THIS KIND OF FOG ACCOUNTS FOR LESS THAN 5% OF ALL OCCURRENCES BUT SIGNIFICANTLY INTERFRERES WITH MILITARY OPERATIONS IN EUROPE, ALASKA, AND THE NORTHWESTERN UNITED STATES DURING THE WINTER. THE THEORETICAL TECHNIQUE FOR DISPERSING SUPERCOOLED FOG HAS BEEN KNOWN SINCE THE 1940'S, BUT THE WORK OF TRANSLATING THEORY INTO PRACTICE WAS NOT UNDERTAKEN UNTIL 1967. AWS HAS DEVELOPED ROUTINE SUPPORT TECHNIQUES USING BOTH AIRBORNE AND GROUNDBASED SEEDING SYSTEMS THAT ARE DESCRIBED IN THE ARTICLE. ENGINEERING WORK IS BEING COMPLETED TO IMPROVE THE GROUND SYSTEM. WHEN COMPLETED, PROPANE DISPENSER ARRAYS WILL BE INSTALLED AT ALL AIR FORCE BASES REQUIRING SUPERCOOLED FOG DISPERSAL SUPPORT. WARM FOG IS MORE DIFFICULT TO DISSIPATE THAN SUPERCOOLED FOG, BUT TWO APPROACHES HAVE SHOWN PROMISE. THE FIRST IS TO EMPLOY A HYGROSCOPIC SEEDING AGENT WHICH WILL CAUSE THE WATER IN THE FOG TO EVAPORATE AND RECONDENSE ON THE SEEDING AGENT. THIS INCREASES THE MEAN SIZE OF THE DROPS AND EVENTUALLY CAUSES PRECIPITATION, WHICH RESULTS IN IMPROVED VISIBILITY. THE SECOND METHOD EVAPORATES THE FOG DROPLETS BY ADDING EITHER HEAT OR DRY AIR. DURING TESTS IN 1968 IT WAS DEMONSTRATED THAT A HELICOPTER HOVERING ABOVE THE TOP OF A FOG BANK COULD FORCE ENOUGH DRY AIR INTO IT TO CREATE CLEARINGS LARGE ENOUGH FOR VTOL LANDINGS. THIS METHOD IS NOT EFFECTIVE WHEN THE FOG IS MORE THAN 300 FEET THICK. THE HYGROSCOPIC METHOD IS NOT YET OPERATIONAL, AND A SERIES OF TESTS IN 1971 WAS DISCOURAGING.

• Authors:
  • Lease, J C
  • Zeigler, G S
• Publication Date: 1972-7

Media Info

• Features: Figures; Photos; Tables;
• Pagination: p. 258-61
• Serial:
  • Military Engineer
  • Volume: 64
  • Issue Number: 420
  • Publisher: Society of Military Engineers

Subject/Index Terms

• TRT Terms: Fog dispersal
• Subject Areas: Highways; Safety and Human Factors;

Filing Info

• Accession Number: 00221819
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 31 1972 12:00AM