摘要:

AbstractMesoscale vortices originating as tropopause folds can lead to cyclogenesis, cloud formation and/or convective overturning. The presence of such mesoscale vortices can often be inferred from the nature and behaviour of dry zones in Meteosat water vapour imagery. Diagnostics from an operational limited‐area forecast model are presented for one such dry zone, which appeared to rotate in the water vapour imagery. Model and imagery show that a vortex‐induced combination of potential instability and ascent led to the development of a small band of cloud and thundery r

ISSN:1350-4827    

DOI:10.1002/met.5060030101

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractSimultaneous rainfall analyses using Special Sensor Microwave/Imager (SSM/I) passive microwave measurements and thermal infrared measurements from Meteosat are presented for two storms over northern Italy that caused damaging floods. Upwelling brightness temperatures over precipitating clouds in the mm‐cm spectrum are directly associated with precipitation microphysics throughout the cloud column down into the rain layer. In contrast, brightness temperatures in the thermal infrared window, which arise from emission near cloud top, are not directly responsive to precipitation processes. However, because of the diffraction‐limited nature of passive microwave detectors, microwave radiometer ground footprints are considerably larger than those characteristic of infrared sensors, even those flown at geosynchronous altitude. Furthermore, passive microwave radiometers are flown on low‐earth orbiters, which produce less than ideal sampling rates, whereas optical‐infrared radiometers flown on geosynchronous orbiters produce high frequency sampling concomitant with precipitation time scales. In this study, we investigate how these two types of measuring systems could be used in a complementary fashion to improve rainfall estimation. A physically based microwave algorithm is used to estimate rainfall with SSM/I measurements, whereas a two‐threshold statistical technique is used for corresponding estimates from Meteosat. Results suggest that an infrared‐based analysis of rainfall derived from half‐hourly geosynchronous images can be improved with a calibration‐transfer approach using a microwave algorithm sensitive to vertical

ISSN:1350-4827    

DOI:10.1002/met.5060030102

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAerological data from the European area and Czech ground data were used to derive predictor vectors that would be efficient for making categorical forecasts of convective events over the Czech Republic. A series of simulated forecasts were performed with sets of predictor vectors. The Critical Success Index (CSI) was chosen to be the measure of the forecast accuracy. The convective precipitation and thunderstorms that occurred during the periods,andUTC were forecast with the use of the data from 0000 UTC. Likewise, the data from 1200 UTC were used to predict event occurrences during periods,andUTC. The resultant maximum CSI values corresponding to the different predictands are discussed, and their dependence on the event frequency is described. The Heidke Score and the Equitable Score determined for the predictor vectors with maximum CSI are indicated. The diagnostic predictor vectors can be viewed as the representation of the prognostic information under the Perfect Prog assumption.

ISSN:1350-4827    

DOI:10.1002/met.5060030103

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAccurate forecasting of heavy showers and thunderstorms with associated hazards is vitally important for many business sectors and national utilities. In the UK a fully automated procedure is being developed in the Met. Office for the National Rivers Authority. The GANDOLF (Generating Advanced Nowcasts for Deployment in Operational Land surface Flood forecasting) system seeks to provide warnings of heavy rain and forecast accumulations in sensitive river catchments to flood hydrologists. GANDOLF will automatically choose the most appropriate nowcasting technique depending upon synoptic conditions. In a convective situation an important method available to GANDOLF is an object‐oriented nowcasting procedure. Multi‐beam, high resolution radar data and Meteosat IR satellite data are used to analyse convective cells in all stages of growth; subsequent movement and development up to 3 hours ahead is then predicted using a conceptual life‐cycle model combined with mesoscale NWP data. This paper describes the object‐oriented technique and demonstrates its usefulness in a severe convective situation with a cas

ISSN:1350-4827    

DOI:10.1002/met.5060030104

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper investigates the impact of sampling errors on the estimation of the parameters of the relation Z = aRbused in the measurement of rainfall (R) from radar reflectivity (Z). Simulation results show that, at levels of sampling errors likely to be observed in real data sets, of the order 100 gauge and radar observation pairs are required to estimate a with an accuracy better than 15% and b better than 10%. Errors in radar rainfall estimates for rain rates less than 15 mm h−1are insensitive to the Z‐R parameters. High‐resolution measurements from a vertically pointing radar (300 to 400 m above ground level, 1‐minute averages) are compared with raingauge measurements taken at the radar site during a period of widespread rainfall. The radar provided surprisingly poor estimates of rain rates, with mean standard errors of 80% for rain rates less than 2 mm h−1. The auto‐correlations of the residuals in the radar estimates were found to be very low after only 2 minutes, leading to the conclusion that radar estimates of rainfall intensities should be made at a high space/time resolution and then averaged so as to reduce measurement errors arising from sampli

ISSN:1350-4827    

DOI:10.1002/met.5060030105

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAn attempt is made to identify and investigate the structure, behaviour and synoptic characteristics of cyclogenesis over the Aegean Sea. A simple, realistic and easily used methodology of identification, in an analytical form, was established. This combines two types of criteria: synoptic and dynamic/thermodynamic. Six synoptic categories that could favour cyclogenesis over the Aegean Sea are distinguished according to the synoptic criteria. Grid‐point values of geopotential height and temperature are used to calculate the dynamic/thermodynamic criteria, which are used to identify potential cases of cyclogenesis with respect to the thermodynamic prerequisites and the time continuance. It is demonstrated that cyclogenesis over the Aegean Sea is not as rare as was believed. The majority of cases result from the prevalence of a south‐westerly flow, a long‐wave trough and a closed system over the Aegean Sea. The cyclogenesis appears to occur primarily in the cold period of the year, mainly from October to May, and to have a small intensity and lif

ISSN:1350-4827    

DOI:10.1002/met.5060030106

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAt a time when the commercialisation of weather forecasting is proceeding at an alarming rate around the world, it is essential to review the quality and accuracy of weather forecasts to ensure that current standards are at least maintained. The privatisation of meteorological services in some countries (e.g. New Zealand) and the vigorous commercialisation of established Met. Offices such as in the United Kingdom, France and Sweden suggests that customer satisfaction, increased income and reduced expenditure will dominate the weather forecasting scene over the next decade. It is important that the quality of weather forecasts is closely monitored before and after commercialisation to ensure that the accuracy of weather forecasts continues to improve and that public weather forecasting does not suffer. The improved technologies for data collection such as weather satellites, weather radar, wind profilers, road weather information systems, sferics, etc. should make it easier to assess forecast accuracy ‐ but with the exception of road weather forecasts there is little sign that the new technology has been used for this purpose. The current accuracy of a sample of weather forecasts in the UK is discussed and a framework for publishing future weather forecast verification statistics is presente

ISSN:1350-4827    

DOI:10.1002/met.5060030107

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractUltraviolet (UV) radiation from the sun affects the biosphere and chemical processes of atmospheric trace gases. The amount of atmospheric ozone as well as the amount of clouds and atmospheric aerosols determine the UV radiation reaching the earth's surface at a definite place and time. Using numerically forecast meteorological parameters such as temperature and relative vorticity at different pressure levels, a short‐term forecast of atmospheric ozone was calculated. This ozone value and the numerically forecast cloud cover were fed into a UV forecasting model to determine a short‐term forecast of biologically effective UV radiation. UV radiation forecasts were calculated for three stations in the northern, central and southern part of Germany. Comparisons between ozone forecasts and ground‐based as well as satellite‐based ozone measurements for the summer months of 1994 showed the uncertainty of ozone forecasts to be within ±3% and ±6%. Values of the modelled biologically effective UV radiation were compared with measured UV radiation data taken with UV filter instruments and with a spectro‐radidmeter at Potsdam in the period September 1993 to September 1994. It turned out that for a cloud cover of less than 4/8 to 5/8, the model calculations overestimated the measured irradiation by about 10 to 15%. The main reason for the discrepancy between model calculations and measurements may be the cloud parameterization in the model. Also, the method of estimating the aerosol load as well as uncertainties in the measured UV radiation may have contributed to the

ISSN:1350-4827    

DOI:10.1002/met.5060030108

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

ISSN:1350-4827    

DOI:10.1002/met.5060030109

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY

ISSN:1350-4827    

DOI:10.1002/met.5060030110

出版商:John Wiley&Sons, Ltd    

年代:1996

数据来源: WILEY