Annex 2
Forecast data exchange requirements for FROST-2014 project
1) Two forms of data transfer:
- Grid-point forecast (nowcast) fields for unified domains (GRIB1 or GRIB2 format);
- Forecast time series at locations associated with observation sites (XML format).
2) The finest available forecast resolution
If we have 7 km/2 km as the finest resolution for FDP/RDP ensembles and 1 km/0.25 km resolution for FDP/RDP deterministic runs (we have such proposals) it is important to retain these resolutions for the exchange purposes.
All forecasts should be interpolated to the unified common grids (see below) before their uploading. To avoid inflation of data amount due to the interpolation you can upload forecasts for the relevant subdomain of your original grid and provide us with your own interpolation program to the common grid.
3) Common grid projection – a usual geographical Lon-Lat grid. No rotation.
4) Grid domain, forecast range
The following grid domains are proposed for data exchange only. All the participants are free to run their systems for larger domains.
· Ensemble FDP
The approximate grid spacing – 7 km. This means 0.0875°/0.063° along latitude/longitude at the latitude of Sochi.
Krasnaya Poliana (43°41′0″N, 40°12′0″E) is suggested to be a reference grid point of the unified grid. As the main threat (southern cyclones) usually comes from the west the unified grid is not centred at Krasnaya Poliana - 1/3 of grid domain lies east from this reference grid point and 2/3 - west.
The recommended grid domain - 286*285 grid points(Roughly ~2000*2000 km):
- 171 steps west and 114 steps east of Krasnaya Poliana (25.2375°E-50.175°E);
- 142 steps south and 142 steps north of Krasnaya Poliana (34.737(3)°N-52.629(3)°N). Such a coverage is broad enough for synoptic interpretation (see Fig.1 below).
The recommended forecast range - 72 hr or more.
Forecast time levels for grid-point fields: 0,3,6,9,12,15…hr (every 3 hours).
Time resolution for pointwise time series at locations associated with observation sites: 1 hr.
The recommended forecast update frequency: 12 hr (2 times a day) or more frequently.
Individual ensemble members rather than products – it gives more flexibility in further processing.
· Ensemble RDP
Unified grid step – 2 km. This means 0.0250°/0. 0180° along latitude/longitude at the latitude of Sochi.
The recommended grid domain - 251*251 grid points (~500*500 km):
150 grid steps west and 100 steps east of Krasnaya Poliana (36.45°E-42.7°E);
125 grid steps south and 125 steps north of Krasnaya Poliana (41.4(3)°N-45.9(3)°N).
The recommended forecast range - 24 hr or more.
Forecast time levels for grid-point fields: 0, 1, 2, 3…24 hr (to assess model potential for nowcasting).
Time resolution for pointwise time series at observation sites: 30 min.
Forecast update: every 12 hr or more frequently.
Individual ensemble members.
· Deterministic FDP
Unified grid step – 1 km. This means 0.0125°/0.0090° along latitude/longitude at the latitude of Sochi.
The recommended domain – 301*301 grid points (roughly 300*300 km):
- 200 grid steps west and 100 steps east of Krasnaya Poliana (37.7°E-41.45°E);
- 150 grid steps south and 150 steps north of Krasnaya Poliana (42.(3)°N-45.0(3)°N).
The recommended forecast range - 24 hr.
Forecast time levels for grid-point fields: 0, 0.5, 1, 1.5, 2, 2.5, 3…24 hr (to assess model potential for nowcasting).
Time resolution for pointwise forecast time series at observation sites – 10 min.
Forecast update: every 6 hr.
· Deterministic RDP
The unified grid spacing – 250 or 500 m depending on the highest available model resolution. The exact domain is to be specified later.
The recommended forecast range - 12 hr or more.
Forecast time levels for grid-point fields: 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6…12 hr (to assess model potential for nowcasting).
The recommended time resolution for pointwise time series at locations associated with observation sites - 10 min.
The recommended update interval: every 6 hr – if there is no high-resolution data assimilation, 3 hr otherwise.
Note: Optimal choice of the set of time levels is dependent on real model resolution. For 250 m model grid spacing half an hour time resolution might not be sufficient.
· Nowcasting
The unified grid domain – as for Deterministic FDP component.
The recommended forecast range – 3-6 hr.
Nowcast temporal resolution:
for grid-point fields – 10 minutes when required, otherwise 1 hr;
for pointwise time series – 5 min when required, otherwise 1 hr. Precipitation can be provided in higher temporal resolution.
The recommended update frequency: from 10 to 60 min depending on parameter type and data availability.
Fig.2.1 Domains suggested for FROST-2014 forecast verifications: outer – for Ensemble FDP, intermediate – for Ensemble RDP, inner – for Deterministic FDP and nowcasting.
5) Parameters:
· For model ensembles and nowcasting:
sensible weather and high-impact parameters -precipitation conditions (liquid and solid precipitation rate, freezing/frozen precipitation, accumulated snow), T2m, near-surface wind speed/direction/gusts, relative humidity, dew point temperature, visibility, cloudiness and cloud base and location of the zero-degree isotherm;
Ensemble forecast fields of some other traditional synoptic variables (e.g., 500 hPa geopotential, T850) are of interest more for the purposes of synoptic interpretation rather than for forecast validation.
· For deterministic runs: as for ensembles +
- For grid fields: Temperature, relative humidity, geopotential and wind for 1000, 925, 850, 700, 500 hPa levels;
- For individual grid-points near locations of temperature/humidity and wind profilers: temperature, relative humidity, wind at original model levels + z-heights of original model levels;
- MSLP;
- …
Other forecast variables and/or levels can be collected for diagnostic purposes, interpretation and development of conceptual models of regional hydrometeorological processes. However, the potentially available observational resources for their validation are quite limited.
If meeting the listed requirements appears to be not feasible for a project participant, then relaxed requirements might be applied.