A comparison of atmospheric transport and dispersion calculations over complex terrain was investigated using a mobile profiling system (MPS) versus standard meteorological balloons. Meteorological and sulfur hexafluoride (SF6) concentration data were collected and used to evaluate the performance of a transport and diffusion model coupled with a mass consistency wind field model. Meteorological data were collected throughout April 1995, and parts of August 1995. Both meteorological and concentration data were measured in December 1995. Once the models were validated, the comparison of performance with different upper-air data were accomplished. The models used included the SCIPUFF (Second-order Closure Integrated Puff) transport and diffusion model and the MINERVE mass consistency wind model. Evaluation of the models was focused primarily on their effectiveness as a short-term (one to four hours) predictive tool. These studies showed how the combination of weather and transport models could be used to help direct emergency response following a hazardous material release. The models were used in tandem to direct the deployment of mobile sensors intended to intercept and measure tracer clouds. The MINERVE model was validated for the specific terrain of interest using April 1995 data. The capability of SCIPUFF driven by realistic three-dimensional wind fields generated by MINERVE is demonstrated using data collected in December 1995.

Precipitation enhancement over a low coastal hill in winter is demonstrated for particular associations of synoptically determined onshore airflow and local geography encountered over south-eastern Newfoundland. Four such cases, involving a mixture of pre-warm-frontal precipitation types at surface temperatures just below freezing, are analysed using comparative surface gauge records from sites at the coast and hill summit and detailed volume scan data from a Doppler radar. Whilst precipitation at the hill summit and upwind coast was of similar overall duration in each case, the surface rates on the hilltop exceeded those at the coast by 1.0-4.0 mm h-1 during different stages of the events. Analysis of the Doppler reflectivity patterns reveals that intensities are especially enhanced near the windward hill crest, supporting the observed association of greatest enhancement with a strong local upslope wind component exceeding 20 m s-1. In the majority of these cases the enhancement is maintained primarily by the ‘seeder-feeder’ mechanism, which appears to be accelerated during precipitation transitions and with the surface warm front 120-150 km distant; however, a preliminary phase of enhancement due to topographically induced uplift of stable pre-frontal air is also recognised in one case.

This paper presents a prediction system for regional crop growth in Sweden, recently set up at SMHI (Swedish Meteorological and Hydrological Institute). The system includes a state-of-the-art crop growth model, WOFOST (WOrld FOod STudies) and inputs from meteorological mesoscale analysis. The simulated crops are spring barley, spring rape, oats and winter wheat, and the period of investigation is 1985-98. The simulated water-limited grain yield is used as a predictor in the yield prediction procedure. The technological time trend describing the yearly increase of the production level is accounted for as well. Yield prediction based on crop growth modelling is justified since the ability to forecast the yield is higher compared to that using the technological time trend alone. The prediction errors are of the order of 8 to 16%, with the lowest errors for winter wheat and spring barley.

Heavy rain events constitute a major operational problem in the Mediterranean area. The present work tries to contribute to a better understanding of this problem by considering the possible indirect influence of surface depressions in the triggering and location of the heavy rain. The idea is that any surface low contributes to the organisation of the low-level flow. This then affects the creation/intensification of a low-level feeding current of warm and wet air that can sustain heavy rain if there is convective instability. Two approaches have been used: (a) a numerical and synoptic approach, Part 1, and (b) a statistical approach, Part 2. In Part 1, the differences between a control run and a numerical experiment without the Iberian mountains for the 'MAP Piedmont flood event' are discussed. Among other effects, the Iberian orography seems to intensify a secondary low near Liguria as well as increase the mixing ratio convergence and the rainfall intensity near it. A few other cases of heavy rain are also briefly reviewed in order to identify the presence of a Mediterranean depression in the vicinity.

Topographic exposure is a variable which represents the degree of shelter afforded to a location. A detailed knowledge of exposure is useful for a wide variety of applications, ranging from the dynamics of drifting snow to the optimal location of wind-farms. The degree of exposure can be calculated by considering the relative heights and distances of the horizon surrounding the point of study. Numerous approaches have been developed to measure this useful variable, from the early qualitative studies of wind-shaped trees to Pyatts's quantitative TOPEX assessment. However, these studies have been superseded by the use of computers and in particular the application of digital terrain models. These provide a fast office-based solution, virtually eliminating the need for fieldwork.

During the past decade hydrologists have become increasingly aware of the problems of fluvial flood prediction during periods of intense convection, particularly in urbanised catchments whose rainfall-runoff responses tend to be rapid. Existing approaches to deterministic, short-range rainfall prediction are often deficient in their treatment of convective precipitation because they cannot resolve individual convective clouds or effectively model their evolution. In 1994 the UK Met. Office established a joint R&D programme with the Environment Agency (responsible for flood prediction in England and Wales) to explore the benefits of an Object-Oriented conceptual Model (OOM) of convection in the nowcasting of fluvial floods. This involved the development of an automated nowcasting system (GANDOLF) designed to run the OOM during episodes of air mass convection. This paper describes the structure and function of the GANDOLF system and compares the performance of the OOM with that of two other precipitation models routinely used by Thames Region of the Agency.

The introduction of a new medium-range weather forecast presented an opportunity to establish a verification procedure for monitoring the reliability and accuracy of probability of precipitation (PoP) forecasts. The need for verification is discussed and a simple verification procedure described, using reliability diagrams as a visual guide to forecaster bias, Brier Scores to give levels of accuracy and Skill Scores to demonstrate skill levels when comparing forecast methods. The application of this verification procedure in a small meteorological office, with no dedicated research facilities, is presented and discussed.

An operational procedure for alerting the public of stressful weather (exceptionally hot and cold situations) in Hong Kong has been implemented since late 1997. From a 28-year (1968-1995) climatological database, criteria based on a weather stress index (WSI) was established to define stressful weather conditions. A special bulletin is issued to the public when exceptionally high (hot, i.e. ≥ 97.5%) or low (cold, i.e. ≤ 2.5%) WSI is forecast. The bulletin provides information on current or predicted stressful weather conditions as well as statements on precautionary action to take. A study was also carried out to examine the effects of WSI on mortality rates on days with extreme WSI. Preliminary results indicate that there was a relationship between low WSI and mortality rates in winter. In summer, however, the results were not conclusive.

This paper examines the commonly used assumption that decision-makers possess accurate prior probability information about climate events that affect their well-being, and illustrates the impact of that assumption on the valuation of prediction information. A survey of large producers in the Mid-western United States is used to recover their prior beliefs about climate variables. It is found that producers systematically misrepresent the probabilities of climate events that materially affect their well-being. In particular, the most common form of the miscalibration between actual and subjective probabilities is to overstate the likelihood of adverse events and understate the likelihood of favourable events. As a result, common methods for valuing prediction information are likely to understate the true value when recipients begin with less accurate prior beliefs.

Hydrometric information is fundamental to the planning, operation and management of water resources and flood defence. The data network is greatly valued by those who use it, yet assignment of a monetary or economic value is problematic. Data managers are often frustrated by the need to continue to justify a network. The paper focuses on the uses of data within the Environment Agency of the UK, explores the difficulties in assigning a value to the data and attempts to review the value ascribed to such data by drawing on some UK and wider examples.

Comments on 'Rainfall estimates of one-day PMP for India' by P R Rakhecha and C Clark (Meteorological Applications, 1999, 6: 343-350)

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