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EXTRACTION OF INFORMATION FROM DOPPLER WINDS

Workpackage number :

2

 

Start date or starting event:

+0

 

Partner code: Person-months

P1: 6

P2: 0

P3: 14

P4: 10

P5:0

P6: 28

 

P7: 0

P8: 0

P9: 0

     

Objectives

While reflectivity data are regularly used in operational forecasting procedure much efforts should be devoted to improve the use of Doppler data. This WP seeks to increase the exploitation of these informations following two complementary strategies. On one hand Doppler data will be processed in order to be use in NWP models (i.e. define a super observation product), on the other extraction of information from Doppler data (VAD or multiple Doppler wind retrieving) will improve the understanding of weather phenomena and will give a detailed wind field to be compared with NWP models output and Meso-scale analysis.

Identify the limitations for improving clear air retrievals of wind and boundary layer processes at the operational weather radar frequencies used in Europe.

 

Methodology/work description

Super observation Product. Partner 4 - Due to the irregular geometric characteristics of polar radar data, and the necessity of managing data from several radars in a network, the original polar volumes must be merged to form so-called super observations . These are homogenised 3-D volumes containing variables suitable for assimilation into numerical modelling systems. This work deals with defining such super observations and generating data sets of them from an international network of Doppler radars in the Baltic Sea's catchment area. Special attention will be taken to retain the characteristics and information content of the original polar data while rendering a quality-controlled product with general geometric characteristics, which can be included in data assimilation systems.

Partner 6 - Doppler radars provide information on radial winds. Hence a combination of two Doppler radars provides the possibility of deriving two components of the wind field, except along the line joining the two radars. In practice, the possibility is limited by the topography of the region, and by the distance apart of the radars. The first stage will be to examine the terrain height of the region to establish the areas amenable to dual-Doppler analysis, given the two radars operated by Partner 1, and other radars available in the area from a multi-agencies network. This study will also reveal whether any volumes are being scanned by three different radars, and so are amenable to a triple Doppler analysis. Consultation will be had with partner 1 to try to synchronise scan cycles for their radars which mean that the volumes of interest are scanned as closely in time as is possible.

It is possible, using VAD methods, to obtain information on the horizontal wind field from a single Doppler radar. However, the VAD method assumes that the wind field across the radar is uniform. Without that assumption it is still possible to obtain limited information on the wind field. Specific cases will be investigated to determine how this can be applied in the framework of operational radar.

Dual-Doppler analysis of wind fields is fairly standard in an experimental framework, where radars are being operated with the specific objective of obtaining such analysis. During a previous EU funded project two or three events were successfully analysed. The objective here is to renew and extend the analysis to the partner 1 radars. It is anticipated that the NCAR software CEDRIC will be obtained and adapted for this purpose.

Dual-Doppler analyses can provide information on the third component of the wind, the vertical motion, by means of the continuity equation. However, if it proves possible to obtain simultaneous Doppler data from three different radars, then it may be possible to obtain all three components without this assumption. At the very least it should prove possible to obtain dual-Doppler wind fields over a much greater spatial extent. This may enable a study to be made within the project of the development and life cycle of convective storms in the Po Valley, depending on suitable storms passing through the region when all the radars are operational.

Partner 3 - A particularly important issue in European use of weather radar for NWP assimilation is to develop the use of clear air radar echoes for obtaining wind profiles and boundary layer characteristics. This might be through the use of pre-processing techniques such as VAD or VVP, or through the direct assimilation of measured quantities. A knowledge of scattering properties employed in conjunction with modified signal handling may serve to improve the frequency and accuracy with which information can be retrieved. This will serve to better define the interface between on-site processing and data processing done as part of the assimilation process. In addition, an assessment will be made of the seasonal and other factors which affect the frequency and accuracy of retrievals.

 

WorkPackage Deliverables :

  1. Super-observation dataset; Delivery date: 12.
  2. Maps of the partner 1 region detailing those areas accessible to dual-Doppler analyses, and any accessible to three Doppler radars. Delivery date: 12.
  3. Multiple Doppler dataset. Delivery date: 18.
  4. Analysis of Multiple Doppler wind field. Delivery date: 24.
  5. Extraction of clear-air wind. Delivery date: 24.

 

Contribution to Project Milestones:

M1

M2 Definition of the data sets, implementation of algorithms, commencement of data set generation. Data quality assessment. Definition of multiple Doppler possibility.

M3 Report on improvement of single Doppler wind field retrieval when assumption of uniform wind field over the radar fails.

M4 Report containing 2-dimensional Doppler wind field retrievals for a number of events. Improved techniques for clear air retrievals of wind and boundary layer information

M5 Report containing conclusions of the triple-Doppler study and comparison with dual-Doppler retrievals

M6

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