VOLUME 15 WEATHER AND FORECASTING APRIL 2000 Utilization of Automatic Weather Station Data for Forecasting High Wind Speeds at Pegasus Runway, Antarctica R. E. HOLMES AND C. R. STEARNS Space Science and Engineering Center, University of WisconsinÐMadison, Madison, Wisconsin G. A. WEIDNER AND L. M. KELLER Department of Atmospheric and Oceanic Sciences, University of WisconsinÐMadison, Madison, Wisconsin (Manuscript received 14 December 1998, in ®nal form 20 September 1999) ABSTRACT Reduced visibility due to blowing snow can severely hinder aircraft operations in the Antarctic. Wind speeds in excess of approximately 7±13 m s21 can result in blowing snow. The ability to forecast high wind speed events can improve the safety and ef®ciency of aircraft activities. The placement of automatic weather stations to the south (upstream) of the Pegasus Runway, and other air®elds near McMurdo Station, Antarctica, can provide the forecaster the information needed to make short-term (3±6 h) forecasts of high wind speeds, de®ned in this study to be greater than 15 m s21. Automatic weather station (AWS) data were investigated for the period of 1 January 1991 through 31 December 1996, and 109 events were found that had high wind speeds at the Pegasus North AWS site. Data from other selected AWS sites were examined for precursors to these high wind speed events. A temperature increase was generally observed at most sites before such an event commenced. Increases in the temperature difference between the Pegasus North AWS and the Minna Bluff AWS and increasing pressure differences between other AWS sites were also common features present before the wind speed began to increase at the Pegasus North site. Many times, changes in one or more of these parameters occurred hours before the wind began to increase at the Pegasus North site. Monitoring of these parameters can lead to an improved 3±6-h forecast of these high wind speed events at Pegasus Runway, Antarctica. 1. Introduction whiteout, the vast snow ®eld of the Ross Ice Shelf, while the wheeled aircraft can only land on runways con- The National Science Foundation's Of®ce of Polar structed on ice. The reliance on an ice runway for Programs operates the United States Antarctic Pro- wheeled aircraft increases the importance of a good gram's (USAP) year-round stations in the Antarctic at Anvers Island (Palmer Station), Ross Island (McMurdo weather forecast for these ¯ights because after passing Station), and at the South Pole (Amundsen±Scott Sta- the point of safe return, the only landing sites that can tion). While Palmer Station is generally serviced via accommodate wheeled aircraft are the two ice runways USAP research vessels from South America, McMurdo near McMurdo Station. Station is partially supplied by aircraft from Christ- Figure 1 shows the three landing sites, Williams Field church, New Zealand, and Amundsen±Scott Station is ski-way, Pegasus blue-ice runway, and the sea-ice run- supplied entirely by aircraft ¯ights from McMurdo Sta- way, in the vicinity of McMurdo Station. The sea-ice tion. Most of the personnel at McMurdo and Amund- runway is located on the annual sea ice west of the sen±Scott Stations travel by air to and from New Zea- southernmost point of Hut Point Peninsula although its land. location annually varies. The sea-ice runway is used by The aircraft used for ¯ights between Christchurch and both ski-equipped and wheeled aircraft. Its season of McMurdo Station are the ski-equipped LC-130, and the use begins in August and continues until early Decem- wheeled C-130, C-141, and C-5. In the area of McMurdo ber, when the sea ice becomes unsafe for aircraft op- Station, the ski-equipped LC-130 can land on ice, com- erations. At this time, all aircraft operations shift to pacted snow, or, in extreme circumstances such as a Williams Field and all ¯ights, whether between Mc- Murdo Station and New Zealand, Amundsen±Scott Sta- tion, or remote ®eld camps, are made exclusively by the ski-equipped LC-130. Corresponding author address: Robert Holmes, Space Science and Engineering Center, 1225 West Dayton St., Madison, WI 53706. The Pegasus blue-ice runway is used for ¯ights by E-mail: [email protected] wheeled aircraft late in the austral summer ®eld season, q 2000 American Meteorological Society 137 Unauthenticated | Downloaded 09/26/21 02:59 AM UTC 138 WEATHER AND FORECASTING VOLUME 15 TABLE 1. Locations of AWS units used in support of this study. Elevation Site Lat Long (m) Pegasus North 77.958S 166.518E 10 Minna Bluff 78.568S 166.698E 920 Elaine 83.158S 174.468E 60 Willie Field 77.858S 167.088E 40 Ferrell 78.028S 170.808E 45 Lettau 82.528S 174.438W 55 Gill 80.038S 178.638W 55 Linda 78.508S 168.358E 50 Schwerdtfeger 79.948S 169.838E 60 Marilyn 79.988S 165.038E 75 AWS site than that at Ferrell AWS site. The wind di- rection associated with the maximum monthly wind speed at Pegasus was from the direction of Minna Bluff, which lies 55 km to the south of the Pegasus AWS site. Data for 1989 for Ferrell and Pegasus AWS sites are given by Stearns and Weidner (1990). Plans were made to install AWS units at the north and south ends of the Pegasus Runway, on top of Minna Bluff, at Williams Field, and on the Ross Ice Shelf east of Minna Bluff based on the information initially pro- vided by the Pegasus AWS unit. The purpose of the AWS site on top of Minna Bluff, at an elevation of 920 m, was to detect the strong winds ¯owing over Minna Bluff and continuing toward the Pegasus Runway. The AWS site east of Minna Bluff (Linda AWS site) was installed to investigate the air¯ow near the east end of Minna Bluff. The AWS units on each end of the Pegasus Runway were installed to observe any differences in the FIG. 1. Location map of the Pegasus runway site (adapted from wind speed, wind direction, atmospheric pressure, and Blaisdell et al. 1995). air temperature along the runway. The AWS unit on the west end of the Williams Field ski-way was installed to provide a nearby AWS test site and to obtain meteo- approximately late January into March. During most of rological data for the entire year. Previously, meteoro- the austral summer, the runway is covered with snow logical data were collected only when Williams Field to maintain the integrity of the ice surface, and then the was in operation. snow is removed prior to the commencement of air op- The Pegasus North AWS site was installed in January erations. The use of the Pegasus runway also allows the 1990 at the north end of the now established Pegasus ski-equipped LC-130 to operate on wheels and not on runway. The AWS sites at Minna Bluff, Linda, and Peg- skis, which allows for as much as a 50% increase in asus South were established in January 1991. The Peg- the payload. asus South AWS unit also measures a vertical temper- The ®rst automatic weather station (AWS) unit near ature pro®le in the ice. Stearns and Weidner (1991, all three runway facilities was installed near the wrecked 1992) reported that while the wind directions at both aircraft named Pegasus in January 1989. It provided the Pegasus North and South AWS sites were most com- atmospheric pressure, air temperature, and wind speed monly from the east-northeast, winds with speeds great- and direction data until the unit was removed in No- er than 8 m s21 had a strong tendency to blow from the vember 1989. The data record over this time period south. showed that the Pegasus AWS site monthly mean air Several AWS units have also been deployed near Mc- temperature was approximately 18C warmer than the Murdo and to the south (upstream) of the Ross Island monthly mean temperature at Ferrell AWS site, ap- area to aid in operational forecasting. Fleming (1983) proximately 88 km to the east and at approximately the utilized data from many of these units to forecast fog same latitude (Table 1). The monthly average wind at the Williams Field runway. He found that during the speed was 1±2 m s21 less at Pegasus AWS site than that period from 1 November 1982 to 13 January 1983 there at Ferrell AWS site, but the maximum monthly wind was a strong correlation between a wind from the south- speed had a tendency to be 8±10 m s21 greater at Pegasus east quadrant (908±1708) at Ferrell AWS site and dense Unauthenticated | Downloaded 09/26/21 02:59 AM UTC APRIL 2000 HOLMES ET AL. 139 The data for this study were obtained from the AWS sites, whose geographic location and elevation are found in Table 1; Fig. 4 shows the locations for these AWS sites. Data from 1991 through 1996 were chosen for this study. Unfortunately, not all of the units were op- erating at all times. Missing data can be the result of any number of events that occur while the AWS unit is unattended. 3. Statement of the problem Because of its remote location, air travel in the Ant- arctic can be dangerous. A downed aircraft could lead to loss of life not only from the crash itself, but from exposure or because of the lack of nearby medical fa- cilities. Therefore, safety is a high priority for those involved in air transportation. FIG. 2. Layout of the AWS unit used in the Antarctic. The installed Most of the personnel working for USAP are trans- AWS unit has a 3-m tower with a horizontal boom supporting the antenna, aerovane, air temperature thermometer, upper themopile, and ported to the continent by air, using one of three runway the relative humidity sensor.