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This icon generates the gridded input data and the AVAILABLE file needed to run the FLEXTRA trajectory model. The input forecast or analysis fields are automatically retrieved from ECMWF's MARS archive. The macro language equivalent is flextraconverts GRIB data into the format required by the VAPOR 3D visualisation system.

Info

From Macro/Python the icon can be called asvapor_prepare()

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About FLEXTRA input  data

FLEXTRA requires input fields on a regular latitude-longitude grid in GRIB format. The input data must contain four three-dimensional fields: the two horizontal wind components, vertical velocity and temperature. Two additional two-dimensional fields are needed as well: topography and surface pressure. The three-dimensional input data has to be available on ECMWF model (i.e. η) levels defined by a hybrid vertical coordinate system. An important restriction is that all the data fields used within a FLEXTRA run must have the same domain size, resolution, number of levels, etc.

All the required fields, with one exception, can be retrieved from ECMWF's MARS archive. The only exception is vertical velocity because FLEXTRA needs the following field for its computations:

 

Mathinline
\dot \eta \frac{\partial \eta}{\partial p}
 

Since only

 

Mathinline
\dot \eta
 

is archived in MARS the full product needs to be computed during the data preparation process (FLEXTRA Prepare does it for you).

FLEXTRA requires all the input GRIB files to be in the same folder using the following file naming convention: ENyymmddhh. In addition to the GRIBs FLEXTRA needs several parameter files as well. Most of these files are automatically generated by Metview in the background, so users do not need to create them. The only exception is the file called AVAILABLE because it can be optionally provided by the user.

 

Info
All the date parameters used for FLEXTRA Prepare has yyyymmdd format. Relative dates are allowed to use: e.g. -1 means yesterday, 0 means today etc.                   

The VAPOR Prepare Editor

VAPOR Input Mode


Tip
A tutorial about the use of the VAPOR Prepare icon can be found here. 

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3D visualisation with VAPOR
3D visualisation with VAPOR
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VAPOR

VAPOR stands for Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers. It is a software system providing an interactive 3D visualization environment that runs on most UNIX ,Windows and Mac systems equipped with modern 3D graphics cards.

The home of the software is https://www.vapor.ucar.edu.

VAPOR input files

VAPOR input data is described by .vdf  (VAPOR Data Format) files. These are XML files containing the name and dimension of all the variables and the path of the actual data files storing the data values.  VAPOR stores its data values in .vdc (VAPOR Data Collection) files. These are NetCDF files containing wavelet compressed 3D data. There is a separate file for each variable and timestep organized into a folder hierarchy.

VAPOR grids

VAPOR input data must be defined on a 3D grid,  which has to be regular horizontally (on a map projection). The vertical grid structures supported by the Metview VAPOR interface are as follows: layered and regular.  

For layered grids VAPOR expects a parameter specifying the elevation of each 3D level in the input data. This is typically the case for  pressure or model level (η levels) data with height or geopotential available (or it can be computed).

For regular grids the 3D levels are supposed to be equidistant (in the user coordinate space). This type can be used when the data is available on equidistant height levels.

The situation when pressure or model level data is present without height information is somewhat special. The grid in this case is not layered but can be regarded as regular in its own coordinate space (pressure or model levels) letting z axis simply represent pressure or model levels in the 3D scene rendered in VAPOR.

VAPOR uses a right-handed coordinate system which means that :

  • the horizontal grid has to start at the SW corner
  • the vertical coordinates have to increase along the z axis (upwards)
How does VAPOR Prepare work?

First VAPOR Prepare parses the GRIB data then generates the vdf and vdc files out of it. Internally it dumps GRIB data into a raw binary format then converts it into VAPOR format by using the raw2vdf VAPOR command line tool. VAPOR Prepare implicitly rearranges the grid to make it VAPOR compliant.

Which GRIBs are supported for the conversion?

Only GRIB fields on a regular lat-lon grid are supported at the moment. However, please note that  GRIBs can be internally interpolated to a regular lat-lon grid by using the VAPOR_AREA_SELECTION parameter. The parameters to be converted are supposed to have the same validity date and time and the same vertical levels. They also have to be valid on the same grid.


The VAPOR Prepare Editor

Vapor Input Mode

Specifies the data input Specifies the data preparation mode. The possible values are: Icon and Path. The default value is Icon.

In Forecast mode the selected steps of a given forecast can be used for data generation Icon mode a set of GRIB icons has to be specified in Vapor Input Data. If the mode is set to Period a period with a start and end date and constant time-step can be defined. In this case FLEXTRA Prepare tries to retrieve analysis fields from MARS whenever it is possible (for dates in the past) and uses forecast fields otherwise (for dates in the future).

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Path the input data is read from a specified path on the filesystem  (yet to be implemented).

Vapor Input Data

Specifies the data preparation mode. The possible values are: Forecast and Period.

In Forecast mode the selected steps of a given forecast can be used for data generation. If the mode is set to Period a period with a start and end date and constant time-step can be defined. In this case FLEXTRA Prepare tries to retrieve analysis fields from MARS whenever it is possible (for dates in the past) and uses forecast fields otherwise (for dates in the future).

VAPOR Surface Params

input data as a set of GRIB icons. It is available when Vapor Input Mode is Icon.

Vapor 2d Params

Specifies the list of 2D parameters from the input The list of the surface parameters from the input GRIB data to be converted into VAPOR format. The parameters are identified by their short names  or parameter ids. The default value is an empty string. 

...

Vapor 3d Params

The Specifies the list of the upper level 3D parameters from the input GRIB data to be converted into VAPOR format. The parameters are identified by their short names   or parameter ids. The default value is an empty string.

...

Vapor Vertical Grid Type

The Specifies the type of the vertical grid 3D data to be used in VAPOR. The possible values are: Layered and Regular. The default value is Layered.

Vapor Elevation Param

The name of the upper level GRIB parameter interpreted as If the type is set to Layered VAPOR expects a parameter specifying the elevation of the upper levels. Available when Vapor Vertical Grid Type is Layered.

Vapor Bottom Coordinate

The name of the upper level GRIB parameter interpreted as the elevation of the upper levels. Available when Vapor Vertical Grid Type is Layered.

Vapor Top Coordinate

The name of the upper level GRIB parameter interpreted as the elevation of the upper levels. Available when Vapor Vertical Grid Type is Layered.

Vapor Area Selection

each 3D level in the input data. This parameter is then called ELEVATION in VAPOR. The Layered type is typically used when we have pressure or model level (η levels) input data with height or geopotential available.

For the Regular type the vertical grid is supposed to be equidistant (in the user coordinate space). This type can be used when we have data on equidistant height levels.

Info

The Regular type can also be used for pressure or model level data when no height information is available. In this case the 3D scene is rendered in a pressure or model level "space". Besides, because VAPOR requires vertical coordinate values increasing along the z axis the vertical coordinate values  (pressure or model level number) are multiplied by -1 for VAPOR.

Vapor Elevation Param

Specifies the short name or parameter id of of the 3D The name of the upper level GRIB parameter interpreted as the elevation of the upper 3D levels. Available when Vapor Vertical Grid Type is Layered.

Vapor Area

Specifies the area of the output grid in south/west/north/east format. The default value is  -90/-180/90/180.

Vapor Grid

Specifies the resolution of the output grid in dx/dy format, where dx is the grid increment in east-west direction, while dy is the grid increment in north-south direction (both in degrees units). The default value is: 1/1.

Vapor Refinement Level

Specifies the resolution of the output grid in dx/dy format, where dx is the grid increment in east-west direction, while dy is the grid increment in north-south direction (both in degrees units). The default value is: 1/1.

Vapor Vdf Name

Specifies the resolution of the output grid in dx/dy format, where dx is the grid increment in east-west direction, while dy is the grid increment in north-south direction (both in degrees units). The default value is: 1/1.

Vapor Output Path

Specifies the output directory (it has to be an absolute path) where the GRIB files and the AVAILABLE file will be generated. If this directory does not exist Metview will create it. The output GRIB files have the following naming convention: ENyymmddhh.

Vapor Reuse Input

If this parameter is set On FLEXTRA Prepare checks the existence of the data files to be generated and if they are already in place no new data is retrieved and processed. If it is Off all the fields are always retrieved and processed and the existing data files are overwritten. The same happens to the AVAILABLE file. The existence of a FLEXTRA input GRIB file is checked by using the file name and a set of GRIB API keys from the first message in the file. These keys are as follows: date, time, stepRange, gridType, iDirectionIncrement, jDirectionIncrement, latitudeOfFirstGridPoint, latitudeOfLastGridPoint, longitudeOfFirstGridPoint, longitudeOfLastGridPoint.

Flextra An Mars Expver

The MARS experiment identifier of the analysis fields. The default value is 1 (operational analysis). 

Flextra Date

Specifies the run date of the forecast. Available when Flextra Prepare Mode is Forecast.

Flextra Time

Specifies the run time of the forecast . Available when Flextra Prepare Mode is Forecast.

Flextra Steps

Specifies the forecast steps in hours. Here a list of values is given. Available when Flextra Prepare Mode is Forecast.

Flextra Period Start Date

Specifies the start date of the period. Available when Flextra Prepare Mode is Period.

Flextra Period Start Time

Specifies the start time of the period. Available when Flextra Prepare Mode is Period.

Flextra Period End Date

Specifies the end date of the period. Available when Flextra Prepare Mode is Period.

Flextra Period End Time

Specifies the end time of the period. Available when Flextra Prepare Mode is Period.

Flextra Period Step

Specifies the time step of the period in hours. The allowed values are as follows: 3 or 6. Available when Flextra Prepare Mode is Period.

This parameter has to be either the height or the geopotential (z) of the levels. If geopotential is specified it is converted into metres by Metview for Vapor. The default value is z.

Info
titleDerive elevation for model levels

Please note that neither the height nor the geopotential of model levels are archived in MARS. It means that for model level data either of these fields has to be computed for Layered mode. These computations can be done with VAPOR Prepare by simply specifying z for Vapor Elevation Param. The computations can only be carried out if the input data contains temperature (t) and specific humidity (q) on model levels and geopotential (z) and logarithm of surface pressure (lnsp) on the bottommost model level.

Vapor Bottom Coordinate

The bottom elevation level. Available when Vapor Vertical Grid Type is Layered. The default value is 0.

Vapor Top Coordinate

The top elevation level. Available when Vapor Vertical Grid Type is Layered. The default value is 16000.

Vapor Area Selection

Specifies the area selection mode. The possible values are: Native and Interpolate. The default value is Native.

If it is set to Native the whole area of the input data is converted into VAPOR format. While if it is set to Interpolate the input data is interpolated to a specific (lat-lon) grid and area.

Vapor

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Area

Specifies the area of the output grid in south/west/north/east format. The default value is  -90/-180/90/180.

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Available when Vapor Area Selection is Interpolate.

Vapor Grid

Specifies the resolution of the output grid in dx/dy format, where dx is the grid increment in east-west direction, while dy is the grid increment in north-south direction (both in degrees units). The default value is: 1/1. Available when Vapor Area Selection is Interpolate.

Flextra Top Level

Only data on and below this model level will be used to generate the FLEXTRA input fields. This level can be specified either as a model level or as a pressure value. In the latter case FLEXTRA Prepare will use the data retrieved for the first date to determine the topmost model level. The default value of this parameter is 1, which mens that all the model levels will be used if Flextra Top Level Units is set to Model Levels.

Flextra Top Level Units

Specifies the units of the value of Flextra Top Level. The allowed values are Model Levels or hPa. The default value is Model Levels. 

Flextra Reuse Input

If this parameter is set On FLEXTRA Prepare checks the existence of the data files to be generated and if they are already in place no new data is retrieved and processed. If it is Off all the fields are always retrieved and processed and the existing data files are overwritten. The same happens to the AVAILABLE file. The existence of a FLEXTRA input GRIB file is checked by using the file name and a set of GRIB API keys from the first message in the file. These keys are as follows: date, time, stepRange, gridType, iDirectionIncrement, jDirectionIncrement, latitudeOfFirstGridPoint, latitudeOfLastGridPoint, longitudeOfFirstGridPoint, longitudeOfLastGridPoint.

Vapor Step Number

Specifies the number of steps from the input dataset that will be converted into the VAPOR format. The default value is -1 meaning that all the available steps will be converted.  

Vapor Refinement Level

This option specifies the number of refinement levels in a VAPOR data approximation hierarchy where the resolution of each successive level is a factor of two finer along each dimension. If level is 0 no hierarchy will be created (all data will be stored at their native resolution). If level is 1 a single approximation will be created, thus the hierarchy will have two levels: the first approximation (indexed as 0 in VAPOR) and the native grid resolution (indexed as 1 in VAPOR). And so on.

The default value is: 2.

Vapor Vdf Name

Specifies the name of the resulting VDF file (the .vdf suffix is automatically appended to the filename). The default value is an empty string.

Vapor

...

Output Path

Specifies the output directory (it has to be an absolute can be a relative path) where the GRIB files and the AVAILABLE file VDF file and VDC directory hierarchy will be generated. If this directory does not exist Metview will create it. The output GRIB files have the following naming convention: ENyymmddhh.

Vapor Bottom Coordinate

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default value is /tmp.

Warning
VAPOR data files can be huge (gigabytes) so the output path to store the results of the GRIB to VAPOR conversion should always be carefully selected.