Coastal ridging is an important component of the weather of south-eastern Australia during the summer. The mesoscale aspects of such an event are often not well forecast, and this can have serious implications for aviation, shipping, air quality and bushfire control. A previous study by Speer & Leslie (1997) identified three types of coastal ridging according to the associated synoptic conditions. In this study, a coastal ridging event, which appears to have aspects of all three types, is examined with the aid of mesoscale manual analyses, surface and radiosonde data and simulations with a mesoscale numerical model (Colorado State University Regional Atmospheric Modeling System).

It is found that the model is able to capture the salient features of the event but, on the east coast, tends to produce a weaker event than that observed. The model ridging also tends to lag the observed feature on the east coast by a few hours. It is suggested that these model deficiencies may relate to deficiencies in the lower atmosphere air mass characteristics, which, in turn, may relate to the surface parameterisations in the model.

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.

Satellite images occasionally show the existence of mesocyclones (MCs) close to the eastern coast of Greenland, especially in the region of Angmagssalik/Tasiilaq. The forcing mechanisms of such MCs are investigated by means of numerical simulations with a three-dimensional mesoscale model. The special characteristics of the East Greenland topography are shown to be a key factor for the development of the MCs. The channeling of the flow in large valleys along the East Greenland coast leads to a convergence, implying a vertical stretching of the flow through the valleys and the generation of cyclonic vorticity. This convergence can be strong during intense katabatic storms, so-called Piteraqs, which are a much-feared phenomenon in that area of Greenland. During these situations the synoptic environment enforces the katabatic flow. The results of the simulations suggest a close relationship between the occurrence of Piteraqs and the generation of mesoscale vortices close to the East Greenland coast. An improved understanding of these processes will help forecasters to advise aircraft and ship operations near the coast of East Greenland.

This paper deals with the utility of Monin-Obukhov similarity theory for wind speed simulation in stable conditions over flat terrain in northern Croatia. Wind speed profiles observed through a 150-m deep layer are compared with those obtained from two simple wind speed models. For this purpose, the similarity functions for two stable classes based on Monin-Obukhov theory are locally determined. They are tested in wind speed simulations using a model based on the Monin-Obukhov theory (MO) and a model which combines the surface-layer model of Monin-Obukhov theory and the Ekman-Taylor type model (MOE). Under less stable conditions the combined model (MOE) produces better skill, whereas the model based on the Monin-Obukhov theory (MO) performed better under more stable conditions.

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.

A one-dimensional Kalman filter is proposed for the correction of maximum and minimum near surface (2 m) temperature forecasts obtained by a Numerical Weather Prediction model. In our study we used only one parameter (observed temperature), employing in this way scalar system and observation equations, and a limited time interval (7 days). As a result, our algorithm can be easily run on any PC with only minor technical support. The corresponding results are rather impressive, since the systematic error of our time series almost disappears, and they show the merit of post-processing even when only a simple method is applied.

In-situ methods for measuring upper tropospheric humidity are important for two reasons: (i) they can be used as accurate spot measurements with which to calibrate more extensive data from satellites and other sensors; (ii) they can provide high accuracy measurements from aircraft or balloon with which individual processes of transport, phase change or chemistry can be studied.

In either case the accuracy of the in-situ measurement is of paramount importance. This study compares the performance and accuracy of a resonance fluorescence type of sensor (the Fluorescence Water Vapour Sensor) with a standard frost-point hygrometer.

An intercomparison of these two hygrometers has confirmed a long-standing difference between these two types of sensors (the FWVS overestimates the water vapour volume mixing ratio by 10–20%, depending on pressure). Testing the FWVS experimentally in the laboratory, along with a modelling study of the sensor has revealed that a significant source of error is due to contamination of the FWVS source emission, and the subsequent underestimation of the oxygen absorption cross-section.

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.

Historical climate conditions were examined to determine whether climate information could improve decisions concerning the seasonal maintenance and operations of regional outdoor swimming pools in heavily urbanised northeastern Illinois. Key weather-sensitive issues defined for pool companies concern time periods for maintenance (including pool painting), weather limits to pools being open, and hot days which extend hours of pool operation. The specific conditions included the frequency of spring and fall painting periods (defined as dry conditions for two or more days with Tmax ≥18 °C (65 °F) and Tmin ≥ 4 °C (40 °F)); summer inclement weather days (days with precipitation ≥ 2.54 mm (0.10 inch) with not more than 2 consecutive hours of dry conditions during open swimming hours and/or Tmax ≤ 21 °C (70 °F)); and hot days (Tmax ≥ 32 °C (90 °F)) were examined.

Climatic records for the region going back 42 years revealed that there were nearly twice as many fall painting periods as those in the spring, indicating that greater emphasis should be placed on pool painting after the swimming season. The average number of inclement weather days was more than twice the number the company budgeted for at the beginning of each swimming season. Plans to extend swimming hours on hot days involves a risky decision since the number of hot days varies dramatically from year-to-year in the Chicago region. Studies showed that winter negative sea-surface temperature anomalies in the central Pacific were related to an above average number of spring painting periods. Also, a higher number of hot summer days occur following El Niño-classified winters. Results reveal that decision-makers in the swimming pool management industry can improve several management decisions by including climate information.