Three three-dimensional trajectory models (LAGRANTO, TRAJKS and FLEXTRA), all driven with analysis wind fields from the European Centre for Medium-Range Weather Forecasts, are intercompared. The comparison has three parts: first, a case study of strong ascent in a warm conveyor belt is performed; second, a large set of back trajectories from the tropopause region over Europe and the mid-latitude Atlantic Ocean is investigated; third, a set of low-level trajectories is compared. The intercomparison shows that all three models have been implemented correctly. The degree of model accordance depends on the interpolation methods used. Deviations between the results from a single model using different interpolation schemes are of the same magnitude as the deviations of different models. If all models use linear spatial interpolation, their respective trajectories closely agree with each other, with deviations of 2% or less for the average distance between the starting and the ending positions in the free atmosphere after 48 h. Close to the surface, where the differences in the model formulations are largest, average horizontal position deviations may be up to 10%. Compared with other sources of errors, such as inaccuracies in the wind fields or insufficient temporal and spatial resolution of the data set, these differences are much smaller. Non-linear spatial interpolation leads to stronger vertical motions than linear interpolation and, in the case study, enhanced the quality of the results.

The breakpoint format for rainfall data, by recording the rainrate and the times when the rainrate changes, consists of variable length periods during which rain of constant intensity fell. It is compact and retains a level of detail equivalent to that found in high temporal resolution data. However, breakpoint data are available only at the relatively few locations where automatic raingauges produce pluviographs. On the other hand, radar observations of rainfall provide precipitation data at a high spatial density but at poor time resolution. Advantage can be taken of this high spatial density to give more locations where breakpoints are available through interpolation between the radar images to provide precipitation data at sufficient temporal resolution for the extraction of breakpoints. The interpolation scheme, based on the PARAPLUIE method, detects the movement and evolution of precipitating echoes to provide additional interpolated radar images. Breakpoints, extracted at pixels of the images that contain raingauges, showed similar overall accumulations and characteristics when compared with those of the collocated raingauges. The similarity is particularly so for gauges within a 50 km radius of the radar where the spatial resolution of the radar and the temporal resolution of the raingauges are equivalent.

During the International Cirrus Experiment (ICE), cirrus cloud properties over the North Sea were observed from local surface-based and aircraft instruments. In order to place these measurements in the context of the general space-time evolution of the cirrus systems and smaller cloud elements, Meteosat images were used to study the evolution of the clouds along their trajectories. The trajectories were established with techniques derived from those used to compute cloud motion winds from geostationary satellite images. Thermal infrared (IR) and water vapour (WV) channel tracking was performed to take advantage of the properties of each channel: better contrast of the clouds over the surface in the IR, and better discrimination of upper layers in the WV channel. Although long tracks, up to 60 hours, could be observed, they did not correspond to the same cirrus elements, or even the same system along the track. The evolution of the brightness temperatures along the tracked elements showed periodic fluctuations. The representativeness of these fluctuations in terms of cloud life cycle is discussed, as it may be related to the quality of the tracking.

Some meteorological and geo-orographical factors related to cloud-to-ground flashes in Castilla-Leon (Spain) are studied. The relationship between flash density and the number of days with thunderstorms (thunderdays) is analysed, and a clear dependence and geographical variability is found. It is also shown that flashes have an average delay of four hours with respect to the time of the beginning of convection. The effect on flashes of dry static instability and moisture content is analysed by classifying days into four types according to the average values of the 850-700 hPa temperature difference and the 850 hPa dew-point temperature. A similar classification using the 700 hPa wind direction is used to analyse the effect of the mean-level flow on flashes. The results suggest that the daily number of flashes is mainly affected by the moisture content. Finally, a relationship between the cloud-to-ground flash density and geo-orographical factors (altitude, latitude and longitude) is deduced using multiple linear analysis.

Advanced four-dimensional air traffic management tools necessitate very accurate prediction of wind and temperature in the very short term. A method based on optimal interpolation of observational data was developed and tested within the framework of Eurocontrol's PHARE programme and the 4MIDaBLE programme under the auspices of the European Commission. It takes advantage of the growing density of automated aircraft reports to update background forecasts and produce nowcasts valid twenty minutes to a couple of hours ahead with an improved accuracy. The emergence of surveillance techniques such as the Automatic Dependent Surveillance based on the use of aircraft-to-aircraft and aircraft-to-ground data links and the Aeronautical Telecommunications Network is generating much interest in nowcasting techniques because they may facilitate the acquisition of observational data on selected areas with a given observation density. The basis of the nowcasting method is presented along with different evaluations, one of which lasted several months, using routine aircraft data over France. The evaluation shows that operational forecasts can be improved by taking into account the latest aircraft observations, but it is necessary to select aircraft data to obtain a positive response.

This study examines the influence of urban and meteorological factors on the surface air temperature field of the medium-sized city of Szeged, Hungary, using mobile and stationary measurements under different weather conditions between March and August 1999. This city, with a population of about 160 000, is situated on a low, flat flood plain. Efforts have been concentrated on investigating the maximum development of the urban heat island (UHI). Tasks include the determination of the spatial distribution of seasonal mean maximum UHI intensity and modelling of existing conditions in the period being studied. Multiple correlation and regression analyses are used to examine the effects of urban parameters (land-use characteristics and distance from the city centre determined in a grid network) and of meteorological parameters (wind speed, temperature) on thermal conditions in the study area. The results indicate isotherms increasing in regular concentric shapes from the suburbs towards the inner urban areas where the mean maximum UHI intensity reaches more than 3 °C in the studied periods. A strong relationship exists between urban thermal excess and distance, as well as built-up ratio. In contrast, meteorological conditions do not have any significant effect on the UHI intensity at the time of its maximum development.

A recent requirement charged to the Aviation Weather Center (AWC) is to produce significant weather charts for aviation users with, among other forecast products, forecast locations of significant fronts. To increase forecaster productivity, the AWC decided to evaluate the possibility that fronts should be first drawn objectively. Hewson (1998) describes the basic technique which uses a variation on the Renard & Clarke (1965) frontal locator function to find the fronts. The AWC had to overcome many problems in implementing Hewson's techniques. This paper illuminates the problems and describes the AWC solutions. As a result of the AWC's success, objective frontal analyses and forecasts are now a reality, and the productivity of forecasters increased.

A mesoscale diagnostic wind model, based on mass conservation, is utilised to develop a wind climatology for the southern Appennines in Italy, with the aim of identifying areas suitable for wind energy production plants. The model includes the kinematic effects of the high ground, anabatic and katabatic flows along mountain slopes as well as blocking effects. The climatological analysis carried out appears quite effective in selecting favourable areas where a more detailed investigation based on boundary layer models and observational field studies may lead to the final specification of locations suitable for mountain wind farms.

An approach to evaluating probability forecasts for dichotomous events, based on their economic value over all possible cost/loss ratio decision problems, is proposed. The resulting Value Score (VS) curve shows non-dimensionalised relative economic value as a function of the cost/loss ratios for different decision-makers, over their full meaningful range. The VS curve is similar in terms of computational mechanics and graphical display to the Relative Operating Characteristic (ROC) curve, but the ROC curve is shown to be insensitive to either conditional or unconditional biases and thus to reflect potential rather than actual skill. The possibility of collapsing the VS curve into a single scalar score is addressed, and it is shown that the results can depend very strongly on the assumed distribution of cost/loss ratios in the community of forecast users.

The feasibility of using the proposed relationship between model-generated upper-tropospheric potential vorticity (PV) fields and Meteosat water vapour images in forecast initialisation has been investigated by a number of case studies involving model forecasts of North Atlantic cyclones. The objective of each case study was to reduce the errors in the forecast track and depth of a cyclone by re-initialising the forecast via upper-level PV adjustment and PV inversion. The methodology has employed the PV-water vapour relationship to detect mismatches between PV fields and water vapour images, and has attempted to correct these mismatches by manual adjustment of the PV fields. These PV adjustments have been converted to wind and temperature increments by means of PV inversion and used to initialise the model fields in a way that preserves dynamical balance. Five case studies with small initialisation errors were carried out. The results of the case studies show some partial positive impacts on forecasts of cyclonic development, but overall the results do not demonstrate that the use of the PV-water vapour relation for forecast initialisation is a practical proposition for operational use.

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.

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