The British Antarctic Survey operates both aircraft and ships in the Antarctic. High quality weather forecasts can have a large impact on safe operations at high southern latitudes. This paper assesses the benefits the weather forecasts have had on safety and on costs in the Antarctic during the 1995/96 season. The forecasts of cloud amount, cloud base and weather have a greater accuracy than persistence although the accuracy is lower than might be expected for an airfield in the United Kingdom. The major advantage in having good forecasts available at Rothera would seem to be an increased safety. Although cost benefits exist they are more difficult to assess.

This report is a summary of the methods and findings of a research project that evaluated the social and economic benefits of meteorological services in Australia. The meteorological services evaluated were the basic public weather services and several specialist user-pay and commercial services used by business firms in several sectors of the national economy. Overall, the results indicated that the quality of the selected services was high. In addition, the benefits of these services were extensive, resulting in high benefit-cost ratios.

A forecasting system was set up to infer the impact of mountain waves for producing mesoscale temperature anomalies in the stratosphere. It was successfully applied during a recent aircraft campaign which operated out of Rovaniemi, northern Finland, between 18 December 1996 and 15 January 1997. The forecast information led to the successful detection of mountain-induced polar stratospheric clouds on 9 January 1997. For this event mesoscale forecasts, hindcast runs including grid nesting and comparisons with lidar observations and radiosonde measurements are presented.

In order to test the current recommendation for reservoir safety that a snowmelt of 42 mm/day can be used throughout the UK, calculations of hourly snowmelt rates were made for hourly weather reporting stations in the UK. These data were analysed to give annual maximum melt totals for periods of 3, 6, 9, 12, 18, 24, 48, 72, 120 and 168 hours. Supplementary data from high altitude climate stations allowed further 24-hour melts to be calculated. The annual maxima were entered into an extreme value type one (Gumbel) analysis and estimates of the melt with return periods of 5, 20 and 50 years were made for the durations of 3, 6, etc. hours. An estimate of the return period of a 24-hour melt of 42 mm was made for the sites. These return periods were below 10 years in some high altitude Pennine and Scottish sites, but in excess of 1000 years at low altitude in England. The 24-hour melt with 5 year return period at the sites was related to altitude, northing, mean January temperature and windspeed in linear regressions which permit a calculation of snowmelt at any point in the UK.

The need for a continued reassessment of reservoir safety in relation to heavy rainfall and floods is of paramount importance. The latest advice given by the Institution of Civil Engineers states that for much of Somerset in southwest England, the Flood Studies Report underestimates the frequency of heavy rainfall and that local data should be adopted. However, this advice has not always been followed. Furthermore, the advice does not extend to other areas in southwest England. Therefore, it is essential to assess in detail the reliability of the four methods which can be used in order to estimate storm rarity at present in southwest England. These are the Bilham method, the Flood Studies Report (FSR) method, the FORGE method, and the Four Parameter Model. Both the Flood Studies Report and the FORGE method give higher values of storm rarity than either the Bilham or Four Parameter Model. The Bilham method is not sensitive to geographical variation in rainfall frequency. Comparison of all four methods with observed storm events and storm depths showed that the Four Parameter Model gave the most realistic results, followed by the Bilham method. For a given storm rarity the Four Parameter Model tends to give the highest storm depth, with the differences increasing with storm rarity. These new results suggest that in southwest England many existing dams and other drainage works have been underdesigned.

An acoustic array antenna which has a narrow main lobe and suppressed sidelobes is studied. The directivity function formed by the multiple point sources is used to estimate the aperture of an array and the spacing between the transducer elements to make a desired beam. Then the aperture tapering based on a Chebyshev distribution and the effect of an acoustic shield are evaluated to suppress the sidelobe radiation. The total performance of the phased array system has been examined by comparison with tower instruments. The field test shows that the measured beam pattern agrees with the calculated one and the sodar-derived winds have a correlation of 0.96 and a standard deviation of differences of about 0.47-0.52 m s-1 compared with in situ measurements. These statistical values are as good as or even better than those from the previous experiment.

An objective Visibility Analysis/Forecast System has been developed as part of Nimrod, the United Kingdom Meteorological Office (UKMO) very-short-range forecasting system. The analysis blends satellite imagery and surface observations with a one-hour forecast using a variational algorithm. An extrapolation forecast is produced by adding UKMO Mesoscale Model (MM) trends to the analysis values. This is merged with persistence (the analysis) and MM values, to produce the final forecast. Results from eight case studies are presented, showing the potential of the system, which demonstrates significant improvements on the MM predictions (the currently available objective forecast method).

Warning of turbulence

During test flights aboard a research aircraft over the Rocky Mountains, a lidar sensor seeking clear-air turbulence detected moderate turbulence eight to ten seconds in advance of the plane as it flew 300 miles per hour several times into disturbed air. The lidar could eventually be part of a detection and warning system used on commercial planes to prevent injuries to passengers and crews. The experiment is a collaboration among the National Aeronautics and Space Administration (NASA), National Science Foundation (NSF), and Coherent Technologies Inc. (CTI) of Lafayette, Colorado, USA.