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.

Over recent years most European countries have experienced destructive precipitation events, many of which have generated floods resulting in the loss of lives and economic damage. Rather surprisingly, Europe has no common database for flood events, which continue to be monitored by different national and/or local authorities, with different criteria. In the light of this situation, the main aim of the present work is to propose a classification scheme for a European-level flood database, in which severe flood episodes are related to meteorological conditions and mesoscale settings.

The meteorological systems relating to the most severe events (22 events) over a five-year period (1992-1996) were analysed using Meteosat imagery and conventional meteorological data. Most of the observed events were related to extra tropical cyclone development. The results are discussed in terms of conceptual models currently used for extra tropical cyclones: the structure and dynamics of Atlantic cyclones can very often be interpreted in terms of well- known conceptual models, while characteristics of Mediterranean systems are not fully rendered by current descriptions. Our study underpins the need to improve the knowledge of Mediterranean systems, possibly introducing new conceptual models and/or refining the current ones.

This study addresses three issues: spatial downscaling, calibration, and combination of seasonal predictions produced by different coupled ocean-atmosphere climate models. It examines the feasibility of using a Bayesian procedure for producing combined, well-calibrated downscaled seasonal rainfall forecasts for two regions in South America and river flow forecasts for the Paraná river in the south of Brazil and the Tocantins river in the north of Brazil. These forecasts are important for national electricity generation management and planning. A Bayesian procedure, referred to here as forecast assimilation, is used to combine and calibrate the rainfall predictions produced by three climate models. Forecast assimilation is able to improve the skill of 3-month lead November-December-January multi-model rainfall predictions over the two South American regions. Improvements are noted in forecast seasonal mean values and uncertainty estimates. River flow forecasts are less skilful than rainfall forecasts. This is partially because natural river flow is a derived quantity that is sensitive to hydrological as well as meteorological processes, and to human intervention in the form of reservoir management.

In Finland, winter road maintenance has been privatised, and the use of reliable predictors to measure the harshness of winter conditions has become even more important. Several indices have been developed to estimate the difficulty of winter conditions; however, many of these indices require relatively complicated input data and are in that sense vulnerable - for example, to changes in the meteorological station network. In the current study the year-to-year variation of the climatological variables describing maintenance costs were compared with the variation in costs. This made it possible to make a qualitative interpretation of the costs. This approach is ‘simple enough’ for its use to be easily accepted both by the contractors responsible for winter road maintenance and also by the administrators responsible for covering the maintenance costs.

The use of numerical weather forecast model data as a source of data for soil moisture modelling was tested. Results show that the potential evaporation calculated using the Penman-Monteith equation can be estimated accurately using data obtained from the output of a high resolution numerical atmospheric model (HIRLAM, High Resolution Limited Area Model). The mean bias error was 0.26 mm for a 36-hour sum and the root mean square error was 2.14 mm. The evaporation obtained directly from HIRLAM was systematically smaller because this direct model output represents the real evaporation rather than the potential evaporation. The precipitation forecasts were less accurate. When the accuracy of parameters required for the calculation of potential evaporation were studied for one station, no serious bias was found. When two different irrigation models (AMBAV and SWAP) were run over one summer using either measured or HIRLAM data as the input, the results given by the models were quite similar regardless of input data source. The largest differences between the model outputs were caused by the formulation of crop and soil characteristics in the irrigation models.

An attempt is made to establish a probable link between mean September upper-air temperatures at Indian stations and the ensuing winter monsoon rainfall over eight individual meteorological subdivisions of southern India where the winter monsoon accounts for a large percentage of mean annual rainfall. For this purpose, linear correlations between the winter monsoon rainfall of the subdivisions and the mean September upper-air temperatures and vertical temperature differences at the Indian stations have been evaluated using the data set for the period 1959 to 1988. The inter-correlations between the significant parameters were calculated and then tested to derive multiple linear regression equations containing the best combination of predictor variables. There is a significant positive relationship between the winter monsoon rainfall over Tamilnadu and the mean temperature difference at 500–300 hPa levels at Nagpur in September. Secondly, the winter monsoon rainfall over Coastal Andhra Pradesh is significantly negatively correlated with the mean September temperature over Visakhapatnam at 700 hPa. The most significant inverse relationship exists between the winter monsoon rainfall over Rayalaseema and the mean September temperature over Visakhapatnam at 850 hPa. By using significant parameters, algorithms have been formulated and tested for each subdivision for six succeeding years, 1989–94. These results assisted to some extent in the prediction of winter monsoon rainfall over subdivisions of South India. Finally, stationarity is tested by evaluating another set of multiple linear regression equations using the data set for the period 1965–94 and then testing the algorithms on the preceding six years.

In this study, profiles of temperature and humidity (<250 cm above the road and 5 m into the surroundings) have been used to examine the development of temperature differences in the air layer close to the road. Temperature, humidity and wind profiles were measured, together with net radiation and observations of road surface state, at a test site at Road 45, Surte, Sweden. Measured temperature differences were compared with present weather, preceding weather, surface status, wind direction and other parameters thought to be important for the development of temperature differences. The results showed that large temperature differences (1-3 °C between 250 cm and 10 cm above the road) occurred when there was a high risk of slipperiness caused by hoarfrost, snow or ice on the road. The temperature differences between different levels were associated with the exchange of humidity and temperature between the air layer and the road surface. The 10 cm level reflected the surface processes well. Higher levels were influenced by the surroundings because of turbulence and advection. This study emphasises the need for measurements to be taken at a height and place that reflects the processes at the road surface.

Following upon previous efforts to associate standard measures of forecast skill to relative economic value, the connection is established between the Clayton skill score and the range of users who realise positive value from the forecasts. It is also shown that, whereas the maximum relative value that can be obtained from a set of forecasts is based on the probabilities conditioned on the observations, the range of users for whom the forecasts provide positive relative value is based on the probabilities conditioned on the forecasts.

A straightforward model for the spatial calculation of the time of fog clearance is presented which is based on thermodynamic equations, spatial data sets such as NOAA-AVHRR satellite data, Digital Elevation Model, and horizontal and vertical meteorological observations. The model has been tested on two days with extended fog layers within the study area. The local validation of the model reveals an accuracy in fog clearance of 4 minutes by comparing the model result with meteorological observations. A spatial validation by means of a reference NOAA overpass indicates an under-estimation of the fog-covered area by the model of 2.9% at the time of the reference image. Five minutes before reference time, the spatial correspondence of the modelled and the reference fog coverage increases to 98.9%. The temporal deviation of uncoinciding pixels between reference and modelled fog image at reference time is less than ±30 minutes in 68% of the total number of fog-covered pixels and therefore matches the accuracy of local tephigram methods. However, for individual pixels a time error of up to ±60 minutes occurs for the time of fog clearance. Time errors are probably mainly due to an inaccurate estimation of fog thickness.

Springtime meteorological and satellite data from 1971 to 2000 have been used to assess surface desertification and grassland deterioration to obtain a better understanding of the synoptic characteristics of dust storms observed in Inner Mongolia, the relationship between dust storms and their impact on the Beijing-Tianjin Region, and the effect of climatic change on the surface environment of dust storm source areas in Inner Mongolia. Based on the statistics and the analysis of weather charts during each dust storm event, details and characteristics of sand and dust source regions, such as cold air paths, areas of strong winds and typical synoptic types were obtained. Temperature was found to be the most significant indicator of climate change in the dust storm source regions, having increased by 1.01 °C in the Alxa source region and by 0.96 °C in Hunshdak over the past three decades. Other factors include lack of precipitation, higher evaporation, lower relative humidity, soil desertification and decrease of grasslands in the source regions. As a consequence, nearly two-thirds of the very strong dust storm events observed in Inner Mongolia (characterised by horizontal visibility below 1000 m and wind speeds of 12 m s−1 or over) led to suspended dust or dust storms in the downwind area, the Beijing-Tianjin Region. This study also analyses the upper air and surface weather charts of 58 very strong dust storm events and established the direction of three cold air paths: northwesterly, westerly and northerly. The northwesterly cold air path is seen as the major one, responsible for 58.6% of the dust storm episodes. In addition, the observed areas where strong winds occur lie mostly across the central-west and central regions of Inner Mongolia. Finally, the synoptic situations associated with dust storm events can be classified into three types: trough, northwesterly current and Mongolian vortex. The predominant synoptic system is the trough, responsible for 63.8% of the 58 events analysed in this study.

The aim is to evaluate the use of infrared satellite precipitation estimates for nowcasting purposes in the context of a real-time flood-warning scheme. A radar-based calibration technique is described which is applied to the Negri–Adler–Wetzel scheme. This procedure employs radar data over a defined calibration area to estimate, for each satellite image, actual rain-rates to be used in the Negri–Adler–Wetzel scheme. Calibrated satellite estimates obtained from this procedure can be used to diagnose areas of precipitation beyond radar range, thus allowing an extension of precipitation nowcasting lead time. Calibrated estimates are compared with radar rainfall measurements and results are discussed for various sizes of integration area. Calibration reduces consistently both bias and variance of the error of the original Negri–Adler–Wetzel estimates, even for integration areas as small as 2000 km2. This indicates the capabilities of the new technique for nowcasting purposes over medium-sized river basins.

Different options for funding the provision of meteorological services and for charging for the information provided are described and evaluated. The basic infrastructure and general forecasts and warnings have public good properties of non rival consumption and high costs of exclusion. For these, direct government funding and free provision to all are favoured. Value added meteorological services for use by small groups of specialised users have mixed good properties, and in some cases private good properties. In this case, setting fees at marginal incremental costs for value added services is favoured for reasons of efficiency and practicality. The other options considered include government funding with zero price, and loading user fees for a contribution to funding the public good supply costs.

Météo-France is preparing the implementation of a revised graphical summary of the synoptic situation. This graphical product has been developed since 1993 as, as far as possible, an extension of the existing framework published by WMO. Graphics remain the best way to convey rapidly a lot of information. However, the existing graphical language for meteorology has seldom changed over the years, while our dynamical understanding has improved. Its current use is in fact poorer than the one allowed by the WMO reference definition. In an attempt to overcome these drawbacks, a richer graphical language is proposed. Its goal is to show and, often, to explain areas of synoptic weather activity in the initial spirit of the Norwegian method, since it has been so successful in shaping modern operational meteorology. However, it takes into account the present understanding of cyclogenesis and large-scale dynamics: the actual and potential baroclinic interactions replace the polar front concept. Dynamical meteorology also provides rather precise guidance for structuring and preparing the summary. The proposed code is described and explained. Examples are shown, with most cases taken from the recent FASTEX (Fronts and Atlantic Storm-Track Experiment) project.

Radar rainfall nowcasting at short lead times has important hydrometeorological applications in the fields of weather prediction and flood forecasting. The predictability of rainfall events can vary significantly with scale as smaller storm features are less predictable than the storm envelope motion. As a result, various techniques have been developed for filtering a radar image and deriving short-term forecasts from the more predictable, larger storm scales. In this study, the effects of image filtering on radar nowcasting performance using the Storm Tracker Nowcasting Model (STNM) are evaluated. Radar rainfall nowcasts are evaluated for three storms exhibiting varying degrees of organisation over the Arkansas-Red River basin. In each case, it is found that the nowcast skill decreases with the forecast lead time, increases with the verification area used around a forecast location, and decreases with higher rainfall thresholds. Furthermore, it is demonstrated that a set of properly tuned filtering nowcasts are superior to simple ‘persistence’ and slightly better than ‘uniform advection’. At the scale of a large hydrologic basin (∼ 6000 km2), filter-based nowcasting is shown to capture the temporal variation in rainfall amount and its spatial distribution based on a set of catchment-based metrics. Finally, a method for relating changes in nowcasting skill to errors associated with storm dynamics not captured by image filtering techniques is evaluated.

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.

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.

The Otaki Precipitation Estimation by Radar (OPERA) programme was designed to investigate the processes that lead to enhancement of rainfall over the Tararua ranges of New Zealand. These ranges rise to 1500 m above the coastal plain and enhancement of rainfall by windflow over these hills leads to annual hill-top rainfall of over four times that upwind. The OPERA experimental campaigns aimed to characterise the enhancement processes by analysing data collected from a transect of high-resolution rain gauges and a locally deployed, high-resolution radar, supported by scanning radar and satellite observations. Measurements made during these experiments showed that orographic enhancement led to hill-top accumulations often twice that upwind, and up to as much as a factor of seven in one case. The data suggest that the most frequent occurring enhancement mechanism was triggered convection. This mechanism leads to an increase in rainfall over the hills of around a factor of two, primarily through an increase inthe duration of rain. Seeder/feeder-type enhancement occurs less frequently but leads to larger enhancements.

In this study 320 people in Hong Kong were interviewed to assess their understanding and perception of severe weather warnings. The majority of the respondents (72%) received warnings from mass media. Although 99.4% of the interviewees claimed they knew all the warning signals, results indicate that most of them have only a basic understanding of what they mean. The study revealed that the warnings often lack other important information, such as the time of issue, validity period and precautions to be taken. Only 31% of the respondents stated they would take precautions at the issue of warnings, although people aged over 60 tended to be well prepared for the onset of severe weather. Public education is necessary to promote people's understanding of the warnings and awareness of the risks of severe weather.

A mesoscale numerical weather prediction model and its associated diagnostics are evaluated to gauge their ability to forecast convection and the convective environment for ten case-study days. The diagnostic indices and parameters evaluated are those used to assess atmospheric instability, mesoscale forcing, inhibition and low-level moisture supply. In addition, bulk Richardson number and helicity diagnostics are examined for convection organisation. Convection over mountainous regions is not considered. The case-study days are grouped according to their synoptic type in order to evaluate the usefulness of the forecast diagnostics. In the evaluation it is found that by combining the CAPE (convective available potential energy) and low-level relative humidity diagnostics one can delineate quite large areas where convective triggering is possible and outside which convection will not develop. Organisation of the mesoscale convective systems is also considered. It is found that forecast strong low-level shears tend to be well correlated with observed linear convective systems. A set of stability indices are evaluated quantitatively and qualitatively by comparing the forecast stability indices with observations at a sounding location. CAPE and a simple index based on a moist temperature difference between two layers (Adedokun2) are identified as the most useful forecast stability indices for all of the cases.

The Internet is increasingly used as a means for exchanging large amounts of spatial data. Professional data centres have found secure ways to share their data resources with peers and third-party users, either as a free service or as a commercial activity. Ranging from a simple download of tables to online queries of distributed SQL databases, the role of the Internet is undeniable. It is obvious that extended security measurements are needed in order to share data over the Internet, such as a DMZ or ‘demilitarized zone’ and firewalls. Increasingly, dedicated server-side applications contribute to a straightforward data retrieval procedure.