The properties of the upper air winds used by the commercial aviation community are investigated. Analysis of the spectra shows that the forecasts have errors in both power and phase. However, the constant multiplier presently applied at The Met Office to the forecast winds before they are sent to the airlines remains best for remedying the speed underestimates characteristic of the forecast winds relative to those observed. We provide evidence for the success of this multiplier including the existence of a systematic negative speed bias as a function of the forecast wind speed. A constant multiplier greater than one (presently set at 1.04) always produces reductions in the traditional speed and vector wind rms scores, as well as an aviation specific rms relative flight time error. The investigations reveal that the constant multiplier is also optimal given the verification measures used; it must therefore remain integral to the operational processing of the forecast winds before transmission to the aviation community, at least for the foreseeable future.

Cut-off lows that develop off the east coast of Australia are a major cause of elevated coastal sea levels in this region. Their duration often exceeds a day and the combination of elevated sea levels with the high rainfall that commonly accompanies these events means that coastal flooding can be a major hazard. The processes contributing to higher-than-normal sea levels are a combination of storm surge and breaking wave setup. Three events are modelled using an atmospheric model, storm surge model and wave setup model. The storm surges resulting from the depressions are found to explain between one-third and one-half of the measured sea-level residuals at the coast and are shown to develop in a regime of coast-parallel winds that produce onshore Ekman transport. The timing of the storm surges are well captured in two of the events in which the atmospheric depressions are of broad spatial scale and well simulated by the atmospheric model. However, a poor simulation by the atmospheric model of the location of the third low, which is of smaller spatial scale, results in an inaccurate timing of the onset of the surge. The wave setup model produces sea levels at the coast that are around 11% of the incident rms wave heights. The total modelled sea-level residual, obtained by adding the modelled wave setup to the storm surge, is qualitatively similar to the measured sea-level residual. However, the modelled values are higher, especially at Sydney where the tide gauge is situated in a sheltered harbour location. In such sheltered locations, it is expected that some attenuation of the wave setup would occur and suggests that sea levels on the open coast could be considerably higher during such events.

Fog is the most important physical process that reduces surface visibility, having a major negative impact on air traffic. In this study, a one-dimensional boundary layer model was developed in order to predict the occurrence and intensity of fog. The model uses a selection of parameterisations, suggested by different authors, and uses the finite element method for the vertical discretisation of the equations. The 1977 Cabauw fog event is used to validate the model and eight fog events at Lisbon Airport are simulated. The validation shows that the model is able to predict realistically the fog's onset, growth and dissipation. The fog forecasts at Lisbon Airport are, in general, quite reasonable, and a simple simulation of a fog event, where advection played a fundamental role, also gives realistic results.

The atmospheric and fuel conditions that led to the case of extreme fire behaviour registered in Puerto Madryn in north-eastern Patagonia, Argentina, on 21 January 1994 were analysed in this study. The analyses included surface and upper-air meteorological conditions, fuel composition and load, and morphometry of the burnt area. When the fire occurred the total fuel load was 16 688 ± 2 611 kg of dry matter per hectare, with fine fuel representing 66% of the total fuel load. At the time of the major fire run, the air temperature reached 32 °C and relative humidity decreased to 13%. The fuel load and its high proportion of fine fuels, the extreme temperatures, the low relative humidity, and the changes in wind directions which resulted from the conjunction of synoptic and local-scale phenomena, enhanced the development of a large convection column which favoured the interaction of surface and upper-air winds. As in similar cases reported for other ecosystems, the combination of these phenomena led to this case of extreme fire behaviour. It is intended that this analysis will contribute to the future development of fire alert systems for the region and to the worldwide knowledge of extreme fire behaviour in different scenarios.

An attempt has been made to forecast the all-India monsoon rainfall by using 30 years' pre-monsoon upper-air mean temperatures (recorded between 1959 and 1988) at stations over India. The importance of Nagpur temperatures at 850 and 700 hPa during the pre-monsoon season is discussed. Two sets of regression equations, one with April temperatures and the other with May temperatures, are fitted using the independent predictors. The equations are tested for a two-year period (1989-1990). The forecast values are found to be reasonably good.

Contributions to the notes and news section are welcome. They should be sent to: Meteorological Applications, School of Geography and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK. E-mail: J.E.Thornese@bham.ac.uk

The melting of snow as it falls through the 0 °C level is a significant meteorological process that is important for its impact as the bright band of enhanced reflectivity in radar observations. Thus, it is necessary to understand the variability of the phenomena and to determine the factors upon which it depends. This paper reports on preliminary investigations into the observations of the bright band over the UK using vertically pointing radar. These results are compared with output from a simple model of the melting of snowflakes and with other observations from Canada and the Netherlands. The vertical depth of the bright band was determined from the vertical pointing radar data for four cases of widespread frontal rainfall. An increase in the depth of the bright band was seen with increasing background reflectivities. Depths of 100-150 m at 10 dBZ increased to 200-400 m at 25 dBZ. Results from a simple model of the melting of snowflakes were compared with the vertical pointing radar observations. Similar trends were seen in the model output, but in general the model produced deeper but less intense bright bands. Notable in the model results was the lack of strong dependence of the depth on vertical air motions. Indeed, the bright band depth only increased by approximately 30 m in a downdraft of 1 m s-1. Comparisons of the bright band characteristics with other observations from elsewhere show that the bright band depth was similar to that observed by Klaasen (1988) in the Netherlands, but shallower than those observed by Fabry & Zawadski (1995) in Canada.

Contributions to the notes and news section are welcome. They should be sent to: Meteorological Applications, School of Geography and Environmental Sciences, The University of Birmingham, Birmingham B15 2TT, UK E-mail: jethornes@bham.ac.uk