Of the full set of observations carried out at weather stations, the ‘present weather’ observation is one of the most difficult to automate. Initially, elements such as rain and fog were automated. However, during the past ten years a new group of sensors, aimed at identifying the type and intensity of precipitation, has emerged. These sensors have come to be called Present Weather Sensors (PWSs). Most of the early tests and intercomparisons have been limited to liquid precipitation. Not much attention has been given to investigating the reasons for disagreement between the primary reference, the professional meteorological observer, and the automated observations. This paper presents an analysis of an intercomparison between observer and one type of PWS (Vaisala FD12P), in conditions of both liquid and frozen precipitation. An interaction model is introduced as a new and improved tool for the quality control of PWSs.

Despite the potential importance for air pollution, the association between temperature inversions and vertical wind profiles has been paid scant attention. A preliminary statistical assessment is made, using message data from radiosonde soundings at a station in eastern England for the period 1976–1980, from the surface up to 700 mb. In spite of an expectation among many air pollution meteorologists that inversions and local wind maxima (or vertical wind shears) are ‘typically’ associated, no such typical association between inversions and significant wind levels was identified. This conclusion extended to nocturnal surface inversions and low level jets. This does not mean that there are not clear cases of association, but that either (a) the dataset does not discriminate the associations, and/or (b) the associations are not evident on a climatological, or statistical, basis.

Precipitation is one of the most variable meteorological parameters in time and space. The standard surface measurement network provides very localised information about the precipitation. The satellite and radar observations and Numerical Weather Prediction (NWP) models provide continuous information on the state of the atmosphere, but at much lower resolution.

This paper presents work undertaken in central Europe on stratiform and convective precipitation estimated from satellite microwave data. The results of analysis are prepared in the form of precipitation intensity and range maps. The data available from an Advanced Microwave Sounding Unit (AMSU) on board NOAA-15, 16 and 17 satellites enhanced the scope of the work by providing access to new meteorological precipitation-related products. These products, such as Rain Rate (RR), Scattering Index (SI), Total Precipitation Water (TPW), Precipitation Probability (PP) and Liquid Water Path (LWP), were prepared using the regression algorithms. The data from spring and summer seasons in 2001 and 2002 were used for analysis.

The temperature and precipitation thematic layers are created from the NWP model grid data. Also SYNOP (Surface Synoptic Observations) and TEMP (Sonde air temperature) data are converted into thematic coverages. Progress in GIS technology application for NOAA/AMSU microwave-derived products preparation and visualisation in the Satellite Research Department in Poland was achieved. The developed system allows the display of the rain field forecast by the NWP model Aladin and the precipitation observed with the satellite data and other ancillary information. The maps of precipitation with additional geographical data and administrative boundaries are available for weather forecasting units via the Intranet. It is also planned to make images available on the web for external customers.

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.

Unlike other currents along the subtropical west coasts of continents, the Leeuwin Current off Western Australia transports warm, fresh tropical waters poleward and is strong enough to overwhelm the upwelling tendencies of the coastal wind stress. The representation of this unusual and important current in the global eddy-permitting ¼° Parallel Ocean Climate Model (POCM) is examined, and implications for coastal fisheries and regional weather and climate discussed. Comparison of POCM fields with those from the Leeuwin Current Interdisciplinary Experiment for austral autumn and winter 1987 suggests that model Leeuwin Current is consistent with these observations in terms of its location and depth distribution, surface gradients and meridional variation in mixed layer depths but is a bit weaker, warmer and fresher. The model Leeuwin Undercurrent is similar in strength to that observed during autumn/winter 1987. Similar to satellite observations, the model Leeuwin Current displays a number of meander, eddy and offshoot features. The frequency distribution and length scales of the model features are generally consistent with estimates of these parameters derived from the satellite images. It is concluded that POCM output can be usefully applied to improve understanding of the Leeuwin Current and associated regional impacts.

In this study of tropical storm impacts in Central America, the relationship between physical variables (available in ‘real time’) and damage is explored, and a simple tool for early approximate evaluation of the impact is developed. Land track and energy dissipation appear as the most interesting parameters that modulate the hurricane impact. Because of the difficulty of attaching a monetary estimate to the damage caused in a large number of cases (as is required in a statistical approach), an ‘Impact Index’ based on the logarithm of casualties is introduced. Thereafter, within a subset of events in which damage in monetary terms is known, a rough link between damage and the Impact Index is derived.

Shortly after a new event, as soon as land track and energy dissipation are known, either by means of an empirical equation or using a contour graph, the Impact Index may be determined. Another empirical equation allows a rough estimate of damage in monetary units, but because this estimate is based on a limited number of cases, it must be treated with caution. The methodology is tested for a small set of independent cases.

Vulnerability to tropical cyclones depends not only on natural factors but also on sociopolitical conditions. A coupled sociological and environmental approach is believed to be the best way to improve the early impact estimate methodology.

The turbulent kinetic energy (TKE) in the atmospheric surface layer (ASL) gives a measure of the intensity of turbulence that could be altered or brought about by mechanical generation, by thermal generation, through vertical transport into or away, and through dissipation. TKE is mainly responsible for the transportation of pollutants suspended in the air. In this paper, TKE evolution in the ASL is studied for Kharagpur (22.20° N, 87.18° E) during the summer monsoon by making use of data from a 30 m micrometeorological tower set up as part of the Monsoon Trough Boundary Layer Experiment (MONTBLEX). Under steady state and homogeneous conditions the various terms in the TKE equation are studied for active and non-active phases of the monsoon in 1990. Their day-to-day variations and the budgets are studied at the 8 m and 15 m levels. The study reveals strong day-to-day variation and significant vertical variations within the ASL. Despite being a tropical station, the buoyancy term is much less than the contribution by mechanical generation ostensibly due to the monsoon. There are also differences between active and non-active phases of the monsoon. Mechanical generation by wind shear has been found to be the dominating production term, while dissipation dominates the magnitude of all other terms.

In this study a non-hydrostatic version of the PSU/NCAR mesoscale model is used to simulate an active western disturbance (WD) that affected the Indian region in January 1997. The role of the planetary boundary layer (PBL) and convection parameterisation schemes in the development of the WD is investigated. Analysis and predictions for some fields, including sea level pressure, geopotential height, temperature, horizontal wind and precipitation are examined. Some statistical scores are also calculated and compared. It is found that the performance of the Hong-Pan (as implemented in the NCAR MRF model) and Betts-Miller (or Grell) schemes as PBL and convection parameterisation schemes respectively are best compared to the other schemes used in this study.

Although numerical weather prediction (NWP) models provide an objective forecast, poor representation of local topography and other features in these models, necessitates statistical interpretation (SI) of NWP products in terms of local weather. The Perfect Prognostic Method (PPM) is one of the techniques for accomplishing this. At the National Center for Medium Range Weather Forecasting, PPM models for precipitation (quantitative, probability, yes/no) and maximum/minimum temperatures are developed for monsoon season by using analyses from the European Centre for Medium-Range Weather Forecasts. The SI forecast is then obtained by using these PPM models and output from the operational NWP model at the Center. Direct model output (DMO) obtained from the NWP model and the SI forecast are verified against the actual observations. The present study shows the verification scores obtained during the 1997 monsoon season for 10 locations in India. The results show that the SI forecast has good skill and is an improvement over DMO.

There is a need to assess the areal depth of the probable maximum precipitation (PMP) over specified catchment areas for the safe construction of dam spillways. The large number of dams in India, coupled with their risk of failure, makes this need imperative both for the maximum use of water resources and for public safety. On the basis of rainfall data for the heaviest storms that occurred in different parts of India during the period 1880–1983, improved estimates of one-, two-, and three-day point PMP for India have been made. In this paper the distribution of areal PMP over specified catchment sizes is provided for the first time. The areal reduction factors (ARF) were based on envelope curves of major storms to give the ARF for areas of 10–20,000 km2. These factors were found to vary from 1.0 to 0.41, though there was no real difference between durations of rainfall. These values of ARF were then multiplied by values of one- to three-day PMP. The resulting maps allow a broad description of the spatial distribution of areal PMP and also provide a rapid and consistent estimate of the probable maximum flood (PMF) from the PMP.

For 500 km2 the areal PMP varies from 40 to 120 cm for one-day duration; from 70 to 200 cm for two-day duration; and from 75 to 270 cm for three-day duration. The pattern of PMP is consistent with the geography and available moisture.

A recursive statistical method is given to post-process the 2-metre temperature ECMWF General Circulation Model by using the SAR network of surface stations in Sardinia. The method calculates daily maximum and minimum temperature forecasts up to 5 days ahead for 55 stations. Forecasts over one year for 55 ground stations have been analysed. A comparison with Direct Model Output (DMO) and persistence is then made, giving special attention to the winter season and to freezing conditions. The error analysis shows a BIAS very close to zero (between 0°C and 0.5°C) on all the stations and a marked reduction of mean absolute error compared to the DMO forecast. The error reduction is more marked in the case of freezing conditions than with the DMO forecast. Such situations are difficult to forecast and the very high BIAS of DMO has not been eliminated completely. The advantages of the procedure are: (a) there is no need to store large numbers of measurements and large amounts of model forecast data; (b) the estimated correction is easily adapted to new meteorological conditions; (c) the procedure is transparent to the updating of the model; and (d) the procedure is very easy to implement operationally.

This paper is concerned with meteorological processes that may have an influence on the occurrence of episodes of high pollution involving chimney plumes. It reviews meteorological mechanisms that could lead to or maintain high concentrations at distances beyond the range normally considered in dispersion models (distances greater than 30 km). Fundamental parameters of the atmospheric boundary layer are shown to largely determine short-range and long-range dispersion, but their values are usually not well known in specific cases. A simple estimate is provided of the magnitude of the maximum hourly average concentrations during a long-range fumigation episode from a tall stack.

This paper reports on work that demonstrates that weather radar can yield remarkably accurate rainfall measurements in Scotland. Analysis of data during 1999 and 2000 shows Nimrod radar data to have no consistent error bias and a 24% mean error in storm rainfall totals. For rivers such as the Ruchill Water in the Perthshire Highlands this highlights the fact that the observations and quality control corrections utilised by the Met Office Nimrod system may offer particular benefits in certain flood warning applications. Assessment of wind data indicates that smaller errors occur in Nimrod radar observations during lower wind speeds (less than 15 knots) and with an easterly airflow. However, errors may also be attributed to occasions when the Numerical Weather Prediction model fails to represent the wind conditions correctly at ground level.

Insured weather losses in the US reached record highs in the early 1990s, leading to major concerns in the insurance industry about the causes, including the possibility of climate change due to global warming. Several studies addressing the interpretation of the record high losses used historical insurance data sets, those for crop-hail losses and others based on the catastrophic events to the property insurance industry, both covering the 1949–1995 period. The past loss values were adjusted by insurance experts for shifting coverage, inflation, and evolving construction practices. The resulting adjusted values of crop loss and costly catastrophes to property both showed similar distributions for 1949–1995, with losses being high in the 1950s and again in the early 1990s. This distribution was found to have a weak relationship with extra-tropical cyclone activity in the US, but most of the recent increase in weather losses to insured property was found to be related to shifting societal factors that have put ever more property at risk in storm-prone areas, including coastal areas and large metropolitan areas. The low property and crop storm losses of the 1966–1985 period had created an incorrect perception of the weather risk in the insurance industry, which did not understand nor appreciate the existence of the decadal-scale fluctuations that exist in climate conditions.

When computers became available in the 1950s meteorologists were among the first to display a keen interest in their use. They also placed the highest demands on their capacity. The earliest NWP initiatives came both from the universities and from the meteorological institutes, especially when the development of computers allowed operational runs.

During November and December 1998, ten cyclonic disturbances over the North Atlantic and Mediterranean area were studied. Features in potential vorticity (PV) fields were tracked in the analyses and short-range forecasts of the Spanish version of the HIRLAM model (HIRLAM-INM) and the ECMWF model. They were superimposed on the corresponding Meteosat water vapour (WV) images with the aim of ascertaining the qualitative relationship between Meteosat WV imagery and PV fields that might be used to assess NWP model behaviour. Two cases predicted incorrectly by HIRLAM-INM were studied in detail: a rapidly deepening depression over the Atlantic (26–27 November 1998) and a cut-off low process over the western Mediterranean (3–4 December 1998). For evaluating HIRLAM-INM model behaviour, absolute vorticity at 2 PVU surface, positive PV anomalies at 500 hPa as well as pseudo WV images were compared with Meteosat WV pictures. Being synthetic products of the numerical model, the pseudo WV images were used to indicate the strength of the relationship between the Meteosat WV imagery and the PV fields, and to indicate whether any mismatches correspond to real NWP model errors. It is demonstrated that the HIRLAM-INM phase error at 3–4 December 1998 was clearly seen in the comparison between Meteosat and pseudo WV images.

The amount of solar radiation absorbed, reflected or transmitted by vegetation depends on the radiation distribution and the canopy properties. This study of the optical properties of an oak forest under foliated and non-foliated conditions is attempted in order to better understand radiation use and exchange. Canopy absorptivity, reflectivity and transmittivity to global solar and photosynthetically active radiation (S and PAR, respectively) are considered. To estimate the forest optical properties, radiation measurements above and below the canopy were taken in the middle of a 0.97 km2 natural, slightly sloped, 50-year-old, oak forest in the Northern Peloponese, Greece.

It was found that the greatest part of the incident S is absorbed by the foliated or non-foliated canopy. In the first case, absorptivity is close to 0.7, with reflectivity and transmittivity sharing the remaining portion. Before leaf appearance, although reflectivity may be only a little lower, transmittivity is considerably higher, allowing more than 40% of the incoming radiation to reach the ground. PAR is absorbed to an even higher degree by the green elements of the canopy, allowing only a 5% radiation loss, via transmission, since canopy reflectivity is practically zero. The ground contribution to the canopy short-wave radiation balance is small during the dense foliation period, but it becomes considerable during the leafless period. Especially when considering the balance in the PAR region, the ground has no effect.

To provide ice warnings for road maintenance, a forecasting model has been developed that computes the state of the road several hours in advance. The model, which is called HS4Cast, runs autonomously and does not need human input. The current version of the forecast model features a fuzzy logic engine that determines the best forecast by evaluating certain patterns in the measured parameters. Using this forecast engine, predictions up to 24 hours in advance are possible with reasonable accuracy. If available, additional forecasts from a weather centre may be imported into the model so that the effects of precipitation are taken into account, this further reduces forecast errors. Statistics summarising the model's performance are presented using data from several measurement sites along an Austrian motorway, where HS4Cast has been in use since about 1990.

Emerging developments in geographic information systems and distributed computing offer a roadmap towards an unprecedented spatial data infrastructure in the climate sciences. Key to this are the standards developments for digital geographic information being led by the International Organisation for Standardisation (ISO) technical committee on geographic information/geomatics (TC211) and the Open Geospatial Consortium (OGC). These, coupled with the evolution of standardised web services for applications on the internet by the World Wide Web Consortium (W3C), mean that opportunities for both new applications and increased interoperability exist. These are exemplified by the ability to construct ISO-compliant data models that expose legacy data sources through OGC web services. This paper concentrates on the applicability of these standards to climate data by introducing some examples and outlining the challenges ahead. An abstract data model is developed, based on ISO standards, and applied to a range of climate data–both observational and modelled. An OGC Web Map Server interface is constructed for numerical weather prediction (NWP) data stored in legacy data files. A W3C web service for remotely accessing gridded climate data is illustrated. Challenges identified include the following: first, both the ISO and OGC specifications require extensions to support climate data. Secondly, OGC services need to fully comply with W3C web services, and support complex access control. Finally, to achieve real interoperability, broadly accepted community-based semantic data models are required across the range of climate data types. These challenges are being actively pursued, and broad data interoperability for the climate sciences appears within reach.

The Meteorological Office of the United Kingdom (UKMO) began its operational NWP in November 1965. This marked the start of very successful activity that would gradually bring it to the forefront of NWP development, where it stands today.