Showing papers on "Nowcasting published in 2007"

The Warning Decision Support System–Integrated Information

Abstract: The Warning Decision Support System–Integrated Information (WDSS-II) is the second generation of a system of tools for the analysis, diagnosis, and visualization of remotely sensed weather data. WDSS-II provides a number of automated algorithms that operate on data from multiple radars to provide information with a greater temporal resolution and better spatial coverage than their currently operational counterparts. The individual automated algorithms that have been developed using the WDSS-II infrastructure together yield a forecasting and analysis system providing real-time products useful in severe weather nowcasting. The purposes of the individual algorithms and their relationships to each other are described, as is the method of dissemination of the created products.

Short-Range Numerical Weather Prediction Using Time-Lagged Ensembles

Abstract: A time-lagged ensemble forecast system is developed using a set of hourly initialized Rapid Update Cycle model deterministic forecasts. Both the ensemble-mean and probabilistic forecasts from this time-lagged ensemble system present a promising improvement in the very short-range weather forecasting of 1–3 h, which may be useful for aviation weather prediction and nowcasting applications. Two approaches have been studied to combine deterministic forecasts with different initialization cycles as the ensemble members. The first method uses a set of equally weighted time-lagged forecasts and produces a forecast by taking the ensemble mean. The second method adopts a multilinear regression approach to select a set of weights for different time-lagged forecasts. It is shown that although both methods improve short-range forecasts, the unequally weighted method provides the best results for all forecast variables at all levels. The time-lagged ensembles also provide a sample of statistics, which can be...

GAS: the Geostationary Atmospheric Sounder

Abstract: This paper presents the concept and initial breadboarding results of geostationary atmospheric sounder (GAS), which is being developed by Saab Space AB and Omnisys AB, Sweden, and funded by European Space Agency (ESA). GAS utilizes interferometric synthetic aperture radiometry to obtain desired spatial (30 km) and temporal (nowcasting) resolution for measurement of atmospheric temperature and humidity profiles under all weather conditions. These parameters are decisively important to meteorological and climate models at all time scales.

Correction and downscaling of NWP wind speed forecasts

Abstract: NWP models typically parametrize the effects of unresolved orography, often through use of an effective (orographic) roughness. Whilst this parametrization realistically models the orographic drag on the synoptic-scale flow, it creates two problems for the assimilation of wind observations from high ground. First, the artificially increased surface stress causes a reduction in the predicted wind speed at the standard wind observing height of 10 m, and second, the speed-up over the unresolved summits is not modelled. A method is described for reconciling observed and modelled wind speeds. The method is based on the linear theory of neutral boundary-layer flow over hills and includes a resolution of both the problems described above. The method is applied to both the assimilation of observations and the creation of an improved 10 m wind analysis. The method has been on trial in the Met Office's nowcasting system; significant improvements are demonstrated, particularly during strong wind events. The simplified model presented here is not claimed to represent the full complexities of the boundary layer, but nevertheless produces computationally cheap, low-level wind forecasts, which are a significant improvement on the existing output from the Unified Model. © Crown Copyright 2007. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd.

Error Propagation of Radar Rainfall Nowcasting Fields through a Fully Distributed Flood Forecasting Model

Abstract: This study presents a first attempt to address the propagation of radar rainfall nowcasting errors to flood forecasts in the context of distributed hydrological simulations over a range of catchment sizes or scales. Rainfall forecasts with high spatiotemporal resolution generated from observed radar fields are used as forcing to a fully distributed hydrologic model to issue flood forecasts in a set of nested subbasins. Radar nowcasting introduces errors into the rainfall field evolution that result from spatial and temporal changes of storm features that are not captured in the forecast algorithm. The accuracy of radar rainfall and flood forecasts relative to observed radar precipitation fields and calibrated flood simulations is assessed. The study quantifies how increases in nowcasting errors with lead time result in higher flood forecast errors at the basin outlet. For small, interior basins, rainfall forecast errors can be simultaneously amplified or dampened in different flood forecast locat...

An object‐oriented technique for nowcasting heavy showers and thunderstorms

Abstract: Accurate 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 case study.

Rainfall Nowcasting From Multisatellite Passive-Sensor Images Using a Recurrent Neural Network

Abstract: The term now cast in hydro meteorology reflects the need for timely and accurate predictions of risky environmental situations, which are related to the development of severe meteorological events at short time scales. The objective of this paper is to apply a fully neural-network approach to the rainfall field now casting from infrared (IR) and microwave (MW) passive-sensor imagery aboard, respectively, geostationary Earth orbit (GEO) and low Earth orbit (LEO) satellites. The multisatellite space-time prediction procedure, which is named Neural Combined Algorithm for Storm Tracking (NeuCAST), consists of two consecutive steps. First, the IR radiance field measured from a geostationary satellite radiometer (e.g., Meteosat) is projected ahead in time (e.g., 30 min); second, the projected radiance field is used in estimating the rainfall field by means of an MW-IR combined rain retrieval algorithm exploiting GEO-LEO observations. The NeuCAST methodology is extensively illustrated and discussed in this paper. Its accuracy is quantified by means of quantitative error indexes, which are evaluated on selected case studies of rainfall events in Southern Europe in 2003 and 2005.

Analysis of Fog Probability from a Combination of Satellite and Ground Observation Data

Abstract: The Cloud Type product, developed by the Satellite Application Facility to support to nowcasting and very short-range forecasting (SAFNWC) of EUMETSAT and based on Meteosat-8/SEVIRI, identifies cloud categories, and especially low and very low clouds which are first estimates of areas where fog is likely to occur. This cloud type is combined with precipitation information from radar data and with hourly diagnostic analyses of 2-metre relative humidity and 10-metre wind to elaborate an hourly analysis of fog probability. This analysis provides four levels of fog probability with a 3-kilometre horizontal resolution: No risk, low-level risk, medium-level risk and high-level risk. An evaluation of such fog probability analyses versus a one-year set of French hourly SYNOP reports shows encouraging results (potential of detection = 0.73 for low and medium and high-level risks), even if false alarm ratios remain high. Most of the non-detections occur at twilight and are due to satellite non-detections. Eventually, we show case studies that clearly illustrate the high potential of the method.

Autonomous continuous atmospheric present weather, nowcasting, and forecasting system

Abstract: Apparatus and methods for passively and remotely and continuously locating, monitoring, and measuring present weather and nowcasting and forecasting weather and meteorological phenomena and parameters by utilizing observations of infrared emissions and reflections are disclosed. Based on observations of an instrument such as an infrared noncontact thermometer, the methods provide useful information on the presence of aerosol, dust, cloud, and precipitation for the purpose of determining present weather, weather tracking, weather nowcasting, and weather forecasting as well as other weather phenomena. One embodiment of this invention is an infrared sensor pointed vertically and reflected from a suitable mirror rotating about a vertical axis such that the field of view of the sensor scans azimuthally at an elevated angle above the horizon.

Wake vortex detection & monitoring by X-band Doppler radar: Paris Orly radar campaign

Abstract: In order to improve the capacity of airports to handle the expected increasing amount of traffic, the knowledge about the safety issues for wake vortexes mitigation has to be improved. Currently, safety distances are very conservative and depend only on category size of aircrafts, without taking into account local wind nowcasting. The final goal is to develop a wake vortex alert system for controllers to ensure operationally in all weather conditions adaptive appropriate not oversized separation rules. In a first step, it is necessary to perform long time data collections of wake vortex sensor signature on large European airports. For the time being, Lidar sensors has been used to collect data on wake turbulence and deliver accurate measurements, but their uses is limited to clear air conditions and are not operational in rain & fog weathers. On the other hand, radar is a good complementary sensor, which can be used for turbulence remote sensing as well. To mature this last solution, THALES did trials on Paris Orly airport in November 2006, and has proved that X-band Doppler radar was able to detect wake vortexes up to a range of 700 m. Furthermore, the Doppler resolution of around 0.2 m/s used with regularized high Doppler resolution techniques was able to characterize wake vortex speed distribution in detail. These first trials showed the usability of X-band radar as an appropriate sensor in different weather conditions like fog, rain, and dry/wet air. Long time data collection trials are planned for different airports to mature this new technology of wake vortex monitoring. The results of the trials that have been performed up to now will be presented. Moreover, the application of methods to match the recorded data with the current knowledge of the fluid mechanics will be shown. As a conclusion, X-band radar is a full-fledged alternative to a Lidar system, which is able to make a significant contribution to the improvement of airport capacity and safety. Additional radar trials should be funded, as soon 2008, by European 7th RFP and wake vortex advisory system development will be addressed by SESAR. (5 pages)

Improved nowcasting of precipitation based on convective analysis fields

Abstract: . The high-resolution analysis and nowcasting system INCA (Integrated Nowcasting through Comprehensive Analysis) developed at the Austrian national weather service provides three-dimensional fields of temperature, humidity, and wind on an hourly basis, and two-dimensional fields of precipitation rate in 15 min intervals. The system operates on a horizontal resolution of 1 km and a vertical resolution of 100–200 m. It combines surface station data, remote sensing data (radar, satellite), forecast fields of the numerical weather prediction model ALADIN, and high-resolution topographic data. An important application of the INCA system is nowcasting of convective precipitation. Based on fine-scale temperature, humidity, and wind analyses a number of convective analysis fields are routinely generated. These fields include convective boundary layer (CBL) flow convergence and specific humidity, lifted condensation level (LCL), convective available potential energy (CAPE), convective inhibition (CIN), and various convective stability indices. Based on the verification of areal precipitation nowcasts it is shown that the pure translational forecast of convective cells can be improved by using a decision algorithm which is based on a subset of the above fields, combined with satellite products.

Atmospheric Convection: Research and Operational Forecasting Aspects

Abstract: Markowski, P., An Overview of Atmospheric Convection.- Markowski, P., The Concept of Buoyancy and Its Application to Deep Moist Convection.- Markowski, P., Pressure Fluctuations Associated with Deep Moist Convection.- Markowski, P., Convective Storm Initiation and Organization.- Markowski, P., Supercell Thunderstorms.- Markowski, P., Tornadoes and Tornadogenesis.- Steinacker, R., Dynamical Aspects of Topography: the Role of Obstacles.- Steinacker, R., Thermodynamic Aspects of Topography: the Role of Elevation.- Steinacker, R., Topography: the Global Player in Meteorology.- Brooks, H., Environmental Conditions Associated with Convective Phenomena: Proximity Soundings.- Brooks, H., Development and Use of Climatologies of Convective Weather.- Brooks, H., Ingredients-Based Forecasting.- Brooks, H., Practical Aspects of Forecasting Severe Convection in the United States: Environmental Conditions and Initiation.- Brooks, H., Practical Aspects of Forecasting Severe Convection in the United States: Storm Evolution and Warning.- Giaiotti, D. B., Stel, F., General Considerations on the Operational Forecasts of Severe Convective Events: from Medium to Short Range.- Giaiotti, D. B., Stel, F., General Considerations on the Operational Forecasts of Severe Convective Events: from Short Range to Nowcasting.- Stel, F., Giaiotti, D. B., Weather Forecast Verication.

ATC-Wake: Integrated Wake Vortex Safety and Capacity System

Abstract: With the steady increase in air traffic, civil aviation authorities are under continuous pressure to increase aircraft handling capacity. One potential approach is to reduce the separation distance between aircraft at takeoff and landing witliout compromising safety. ATC-Wake aims to develop and build an integrated system for ATC (Air Traffic Control) that would allow variable aircraft separation distances, as opposed to the fixed distances presently applied at airports. The ATC-Wake project has developed and built an integrated ATC Wake Vortex Safety and Capacity platform. A variety of subsystems is integrated and used within a test bed role: - To evaluate the interoperability of ATC-Wake with existing ATC systems currently used at various European airports; - To assess the safety and capacity improvements that can be obtained by local installation of the ATC-Wake system at various European airports; - To evaluate operational usability and acceptability of the ATC-Wake system; The ATC-Wake system is used in the planning phase where weather and wake vortex forecast information are used together with aircraft separation rules to establish the arrival and/or departure sequence. For approaches, the aim is to manage separation distances down to 2.5 nautical miles, in favorable weather conditions, for all aircraft types regardless of size. For departures, the aim is to reduce the time separation between departing aircraft to 90 seconds (in favorable wind conditions). Weather nowcasting and wake vortex prediction and detection information is used in the tactical phase to monitor and control safe separation. Wind forecast data is used to determine time frames suitable for reduced separation. Criteria on crosswind and associated safe separation minima are derived from safety assessment results obtained with the NLR WAke Vortex Induced Risk assessment (WAVIR) methodology. As main conclusion the ATC-Wake technical and operational feasibility analyses and the safety and capacity studies have built sufficient confidence in the operational concept and system design for the application of reduced separations to represent a sound evolution from existing ATC procedures and working practices, to deliver significant benefits for runway throughput and average delay per flight without major rework to the current ATC systems,while maintaining safety. The next step will be to complete the validation through production of a Safety Case, Human Factors Case, Business Case, and a Technology Case towards installation of the ATC-Wake at one or more European airports. The best would be to continue with airport shadow mode field trials, i.e., with direct involvement of airports and air traffic control centers.

A new module for the tracking of radar-derived precipitation with model-derived winds

Abstract: . A new approach for the nowcasting of precipitation has been developed at the German Weather Service combining extrapolation techniques and Numerical Weather Prediction (NWP) for a lead time range of several hours. Radar-derived precipitation fields serve as input data for a tracking algorithm using model-derived wind data. The composite precipitation field is derived from the precipitation scans which are performed every five minutes at the 16 German radar stations. The data are corrected from clutter and shading effects. The tracking of this radar-derived precipitation field is performed using the temporally and spatially resolved horizontal wind fields at different pressure levels provided by the Local Model Europe (LME). The optimal wind field is derived from minimization of the least-squares difference between a linear combination of model wind data from different pressure levels and the linear displacement vectors calculated via pattern recognition from previous radar measurements. An area-preserving displacement of the precipitation fields is realized by eliminating the wind field divergence and by omitting the dynamical evolution of the precipitation fields. Advection is performed using the fourth-order Bott scheme. Forecasted data comprise precipitation rates for every five minutes lead time as well as hourly sums of precipitation. The verification of a case study's results against radar precipitation measurements lead to a mean Equitable Threat Score (ETS) of 70%, 46%, and 38% for the first, second, and third forecast hour, respectively.

Statistic characteristics and weather significance of infrared TBB during May-August in Beijing and its vicinity

Abstract: In order to meet the demand of nowcasting convective storms in Beijing, the climatological characteristics of convective storms in Beijing and its vicinity were analyzed based on the infrared (IR) temperature of black body (TBB) data during May–August of 1997–2004. The climatological probabilities, the diurnal cycle and the spatial distribution of convective storms are given respectively in this paper. The results show that the climatological characteristics of convective storms denoted by TBB⩽−52°C are consistent with those statistic studies based on the surface and lightning observations. Furthermore, the climatological characteristics of May and June are very different from those of July and August, showing that there are two types of convective storms in this region. One occurs in the transient polar air mass on the midlatitude continent during the late spring and early summer. This type of convection arises with thunder, strong wind gust and hail over the mountainous area in the northern part of this region from afternoon to nightfall, the other occurs with heavy rainfall in the warm and moist air mass over the North China Plain and vicinity of Bohai Sea. This study also shows that the long-term data of IR TBB observed by geostationary satellite can complement the temporal and spatial limitation of the weather radar and surface observations.

Lightning Initiation and Intensity Nowcasting based on Isothermal Radar Reflectivity—A Conceptual Model

Abstract: Intense convective activity associated with summer monsoon, monsoon troughs and tropical cyclones poses a major weather threat in the warm seasons of Hong Kong. Very often, such intense convective activity will also trigger other types of hazardous weathers. As shown in Table I, lightning strikes, heavy rainstorms, damaging downbursts/squalls, hails, waterspouts and even tornadoes are not uncommon in Hong Kong. In terms of occurrence frequencies as shown in Table I, thunderstorm lightning is actually the most frequent type of weather hazard in Hong Kong. At the Hong Kong Observatory (HKO), a second generation nowcasting system is currently under development to track and nowcast such severe weather phenomena. For more details on SWIRLS (Short-range Warning of Intense Rainstorms in Localized Systems ), readers are referred to Li and Lai 2004.

Using radar data quality in computing composites and nowcasting products

Abstract: Although data quality has been a recognized problem since the early days of radar, utilizing numerical quality information in actual processing has been rare until the recent years. In Europe, extensive common efforts in describing, assessing and applying radar data quality have been carried out in COST-717 (Michelson et al., 2005) and EUMETNET/OPERA projects (Divjak et al., 1999; Holleman et al., 2006). Likewise in the United States, the state-ofart seems to be towards incorporating quality information in national radar composites (mosaics) (Langston et al., 2007). In this paper, we continue the discussion on radar data quality information, focusing on data quality in terms of both accuracy (in measurement units) and reliability (in a probabilistic framework). We have already showed how radar data quality can be applied in data visualization, client-specific basic products and radar image composites (Peura et al., 2006). In this study, we review these techniques and focus on using radar data quality also in computing nowcasting products. Originally, end users of weather radars had much of the responsibility in understanding, recognizing and correcting data quality problems such as those originating from bad calibration, Earth curvature and nonmeteorological targets. Many of these problems still remain, but nevertheless automated quality control is widely used at least in detecting evident or likely errors and then marking (flagging) and/or deleting them. There is also automated corrections that change measured values (dBZ, wind) continuously. Examples of these are corrections based on vertical profiles of reflectivity (VPR) and radar-gauge corrections. Increased computational power has enabled developing and computing various quality descriptors and indices. In fact, it is slowly starting to be a problem to properly manage and exploit miscellaneous quality information. It is evident that just like bin-resolution radar data undergoes various transformations and interpolations in product generation, quality information should be treated similarly as well, in parallel. Practically, this means combining quality descriptors some kind of quality algebra. Of course, within a closed system, one is free to design and use whatsoever combination rules – summing,

Status of nowcasting thunderstorm initiation: where do we go from here?

Abstract: Arguably, the greatest challenge in providing accurate spatial and temporal nowcasts of thunderstorms is in forecasting storm initiation. Operational 10 cm wavelength radars can be used to analyze, monitor and track existing thunderstorms (>35 dBZ) but is of limited use in monitoring the rapid growth of nascent(>10 dBZ) and non-precipitating cumulus clouds (< 10 dBZ) beyond ~50 km in range. Other data sources must be used to capture when and where new storms will form. Satellite (Roberts and Rutledge, 2003) and surface station data, numerical model output, radar-detected surface convergence boundaries, stability profiles, terrain, storm climatology (Wilson et al. 2007) and forecaster input are all ingredients that are currently being factored into the production of 0-2 hr storm initiation nowcasts (Saxen et al, 2006). In this paper, we evaluate the current state-ofthe-art in producing storm initiation nowcasts using statistical results from two demonstrations of the NCAR thunderstorm nowcasting (Auto-nowcaster) system conducted during the summer of 2006. However, standard methodologies computing PODs, FARs, and CSIs over very large domains fail to illustrate the true skill of most nowcasting systems because initiation nowcasts represent a significantly smaller fraction of events when compared to the large number of storm extrapolation nowcasts that typically dominate the statistics. Thus, two new approaches are presented here for computing statistical performance of storm initiation nowcasts that serve to highlight the value of forecaster input and improved accuracy in storm initiation nowcasts. Following these results, we explore if further improvements in accuracy can be achieved. 2. AUTO-NOWCASTER DEMONSTRATIONS

Spatio-temporal rainfall estimation and nowcasting for flash flood forecasting.

Abstract: Flood s cannot be prevented , but their devastating effects can be minimized if advance warning of the eve nt is available. The South African Disaster Management Act (Act 57 of 2002) advocates a paradigm shift fro m the current "bucket and blanket brigade" response-b ased mind set to one where disaster prevention or mitigation are the preferred options. It is in the co ntext of mitigating the effects of fl oods that the development and impl ementation of a reli able flood forecasting sys tem has major significance. In the case of flash floods, a few hours lead time can afford disaster man agers the opportunity to take steps which may significantly reduce loss of life and damage to property. The engineering cha llenges in deve loping and imp lementing such a sys tem are numerous. In this thesis, the design and implement at ion of a flash flood forecasting sys tem in South Afri ca is cr itically exa mined. The technical aspects relating to spatio-temporal rainfall es timation and nowcasting are a key area in which new co ntributions are made. In particular, field and optical flow advec tion algorithms are adapted and refined to help pred ict future paths of storms; fast and pragmatic algorithms for co mbining rain gauge and remote sensing (rada r and satellite) es timates are re fi ned and validated; a two-dimensional adaptation of Empirical Mode Decomposit ion is devised to extrac t the temporally persistent struc ture embedded in rainfall fi elds. A second area of significant contribution relates to real-time forecast updates, made in response to the most recent observed information. A number of techniques embedded in the rich Kalm an and adaptive filtering literature are adopted for this purpose. The work captures the curre nt "s tate of play" in the South African context and hopes to provide a blueprint for future development of an essential tool for disaster management. There are a number of natural spin-offs fro m this work for related field s in water resources man agement.

An algorithm on convective weather potential in the early rainy season over the Pearl River Delta in China

Abstract: This paper describes the procedure and methodology to formulate the convective weather potential (CWP) algorithm. The data used in the development of the algorithm are the radar echoes at 0.5° elevation from Guangzhou Doppler Radar Station, surface observations from automatic weather stations (AWS) and outputs of numeric weather prediction (NWP) models. The procedure to develop the CWP algorithm consists of two steps: (1) identification of thunderstorm cells in accordance with specified statistical criteria; and (2) development of the algorithm based on multiple linear regression. The thunderstorm cells were automatically identified by radar echoes with intensity greater than or equal to 50 dB(Z) and of an area over 64 square kilometers. These cells are generally related to severe convective weather occurrences such as thunderstorm wind gusts, hail and tornados. In the development of the CWP algorithm, both echo-and environment-based predictors are used. The predictand is the probability of a thunderstorm cell to generate severe convective weather events. The predictor-predictand relationship is established through a stepwise multiple linear regression approach. Verification with an independent dataset shows that the CWP algorithm is skillful in detecting thunderstorm-related severe convective weather occurrences in the Pearl River Delta (PRD) region of South China. An example of a nowcasting case for a thunderstorm process is illustrated.

Climatic Background of Warm-Season Convective Weather in North China Based on the NCEP Analysis

Abstract: Due to the demand of nowcasting of convective weather in North China(including Beijing,Tianjin,and Hebei Province),the authors use the averaged fields of NCEP 1°× 1° final analyses during May to August of 2000-2005 to analyze the climatic background of convective weather in warm season in north China.The averaged fields include mean circulation of the lower and upper troposphere,mean humidity,temperature,pseudo-equivalent potential temperature,convective available potential energy(CAPE),convective inhibition(CIN),and so on.The results show that the climatic background in May and June is different to that in July and August.In May and June,cold air mass from north is more active,and North China is mainly influenced by disturbances of westerly wind systems in mid-latitudes,in contrast,in July and August this area is influenced by both disturbances of westerly wind systems in mid-latitudes and disturbances in lower latitudes.There are more hailstorms and thunderstorms in May and June,but more heavy rains in July and August.The mean daily variation of relative humidity of lower troposphere reveals that there is one dry line(dew point front)in the afternoon to the east of Beijing,and the averaged streamlines of 850 hPa indicate that there exists a large-scale convergence line in boundary layer at the north of Beijing.The above results provide nowcasting of convective weather in north China with a climatic background.

Research of radar mosaic software system based on CINRAD

Abstract: China is constructing the CINRAD(China new generation Doppler weather radar) network.The three dimensional radar mosaic data is very important for detecting and monitoring the severe weather,improving the nowcasting accuracy and enhancing the radar data application.This paper developed the three dimensional radar data mosaic software system based on the CINRAD network,introduced software's architecture and its implementation.