Numerical Data from Atmosphere-Ocean-Ice forecast system for the Gulf of St. Lawrence - GRIB2 Format

Brief description of the system

The Atmosphere-Ocean-Ice forecast system for the Gulf of St. Lawrence is a circulation model to better understand Canadian inland seas. This system includes two main parts:

  1. An oceanic pseudo-analysis cycle (Smith et al., 2012) including a superimposed sea ice analysis based on direct insertion of Radarsat analysis
  2. A coupled forecast cycle.

Note that the coupled forecast cycle is a 48 hour simulation based on 00 UTC data where both of its models (GEM-LAM and OCEAN-ICE) run at the same time. It provides 00-48 hour weather, sea ice and ocean forecasts.

Technical Native Grid Specifications (Computational Domain)

The atmospheric component is a limited area configuration (GEM-LAM) of the Regional Deterministic Prediction System ( RDPS) centered over the Gulf of St. Lawrence (GSL). This grid has 935x824 points in the horizontal with a spacing of 10 km (0.09 degrees) on a rectangular latitude-longitude projection. The required lateral boundary conditions for this model configuration are taken at every hour from the 00 UTC operational RDPS forecasts at the same resolution (0.09 degrees).

For the oceanic component, the system uses the Ocean-Ice model (GSL) which includes a 3D oceanic circulation model taking into account the tides and freshwater inflows of river boundaries. This Ocean-Ice model computational domain consists of a 150x236 grid in the horizontal direction and extends from the Cabot Strait and Belle Isle Strait to Quebec City and to the head of the Saguenay Fjord near Tadoussac. A one-dimensional hydrological model is used from Montreal to Quebec to absorb tides at Quebec. The horizontal resolution is 5 km on a rotated-Mercator projection. The ocean is layered in the vertical with a uniform resolution of 5 m down to 300 m depth and 10 m further below. The surface and bottom layers are adjusted to the water level and local depth respectively. The boundary conditions for river runoffs, temperature and salinity are taken from climatological data and tides are implicitly calculated (Saucier et al. (2003)).

Technical lat-lon Grid Specifications used for GRIB2 product



10 km resolution grid



Table lists the values of various parameters of latitude-longtitude grid

Parameter Value
ni 500
nj 325
resolution 0.02 x 0.03°
Coordinate of first grid point 45° 30' N 71° W

GRIB data specifications

The fields in the GRIB2 data set for the two components of the system are made available on a latitude-longitude grid of 500x325 (with 0.02x0.03 degrees of resolution). The list of fields made available in GRIB2 format are:

Variable
Description
System Component
UU
Zonal component of wind at diagnostic (surface) level [m/s]
Atmospheric
VV
Meridional component of wind at diagnostic (surface) level [m/s] Atmospheric
TEMP
Sea surface temperature (between 0 and 5m)  [Kelvin]
Oceanic
GL Ice fraction
Oceanic
GE Ice thickness (averaged over model grid cell) [m] Oceanic 
SEVI Ice severity index [%] Oceanic
UICE Zonal component of Ice speed vector (m/s) Oceanic
VICE Meridional component of Ice speed vector (m/s) Oceanic
UWAT Zonal component of the surface ocean current (m/s) Oceanic
UWAT Meridional component of the surface ocean current (m/s) Oceanic
ISTX Zonal component of the vertically integrated ice internal pressure (or stress) (N/m ou Pa x m) Oceanic
ISTY Meridional component of the vertically integrated ice internal pressure (or stress) (N/m ou Pa x m). Oceanic

Download

The data is available using the HTTP protocol and resides in a directory that is plainly accessible to a web browser. Visiting that directory with an interactive browser will yield a raw listing of links, each link being a downloadable GRIB2 file. In practice, we recommend writing your own script to automate the downloading of the desired data (using wget or equivalent). If you are unsure of how to proceed, you might like to take a look at our brief wget usage guide. The data can be accessed at the following URLs:

where
  • HH: model run start, in UTC [00]
  • hhh: forecast hour [001,002,003,...,048]

File nomenclature

  • File name for the atmospheric data: CMC_coupled-rdps-stlawrence-atmosphere_latlon0.02x0.03_AAAAMMJJHH_P0hh.grib2
  • File name for the oceanic data: CMC_coupled-rdps-stlawrence-ocean_latlon0.02x0.03_AAAAMMJJHH_P0hh.grib2
where:
  • CMC: constant string indicating that the data is from the Canadian Meteorological Centre.
  • coupled-rdps-stlawrence-ocean: constant string indicating that the data is from the Atmospherre-Ocean-Ice forecast system for the Gulf of St. Lawrence.
  • latlon0.02x0.03: constant string indicating that the projection used is latitude-longitude grid of 500x325 (with 0.02x0.03 degrees of resolution).
  • YYYYMMDD : Year (YYYY), month (MM) and day (DD) of the beginning of the forecast.
  • HH: UTC run time [00].
  • Phhh : "P" is a constant character. "hhh" is the forecast hour [001,002,003,...,048].
  • grib2 : constant string indicating the GRIB2 format is used.
Example of file name:
  • Atmospheric data: CMC_coupled-rdps-stlawrence-atmosphere_latlon0.02x0.03_2012091800_P048.grib2
  • Oceanic data: CMC_coupled-rdps-stlawrence-ocean_latlon0.02x0.03_2012091800_P048.grib2

These files originate from the Canadian Meteorological Center (CMC) and contain the data of the Atmospherre-Ocean-Ice forecast system for the Gulf of ST-Lawrence using a latitude-longitude grid of 500x325 (with 0.02x0.03 degrees of resolution). The forecast has been produced on September 13th 2012 at 00Z (2012091800) and contains the 48 hour forecast (P048) in GRIB2 format (.grib2).

Levels

These variables are only available for the surface level.

Data in GRIB2 format

References