Changes between Version 37 and Version 38 of udg/ecoms

Timestamp:

Mar 14, 2013 2:16:21 PM (9 years ago)

Author:

antonio

Comment:

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udg/ecoms

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 = Introduction and Motivation = #s.intro
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 The impact activities on seasonal timescales involved in [http://www.specs-fp7.eu SPECS] and [http://www.euporias.eu EUPORIAS] projects require the use of different data sources (mainly seasonal forecasts, reanalysis, and observations). These activities include the calibration, downscaling, and modelling of sector-specific indices in agriculture, energy, health, etc., building on meteorological information. Typically, only a reduced subset of surface variables (precipitation, temperatures, mean sea level pressure, etc.) or in a reduced number of vertical levels (circulation and termodynamic drivers at, e.g., 850, 500, 200 hPa) is required for these activities.  The ''SPECS-EUPORIAS Data Portal'' has been established by the '''Santander Meteorology Group (UC-CSIC)''' to gather the relevant information from existing datasets in order to provide a unique homogenized access to data for the SPECS and EUPORIAS partners (in particular for impact-users).
 
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 This document briefly describes the current state of the data portal, which has initially focused on data from the ''ECMWF's System4 seasonal model'', as agreed in the downscaling parallel session of the kick-off meeting.
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 = The THREDDS Data Server = #s.thredds
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 The ''SPECS-EUPORIAS Data Portal'' is based on a password-protected `THREDDS data server` providing metadata and data access to a set of georeferenced atmospheric variables using OPeNDAP and other remote data access protocols. The variables names, units and additional metadata follow the [http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html CF convention]. The variables are spatial grids based on multidimensional arrays of indexed values, following Unidata's ''_Coordinate convention''[[FootNote(http://www.unidata.ucar.edu/software/netcdf-java/reference/CoordinateAttributes.html)]][[FootNote(http://www.unidata.ucar.edu/software/netcdf-java/tutorial/GridDatatype.html)]].
 
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 Although the `TDS` provides a web interface to explore and access the datasets (shown in [#s.web.access web access section]), it is strongly recommented the use of `OPeNDAP` (a.k.a. `DODS`) client libraries to remotely access the data from scientific computing environments (`R`, `Matlab`, `Python`, etc.). For instance, the `R` function provided in this tutorial is based on the ''NetCDF Java'' OPeNDAP client[[FootNote(http://www.unidata.ucar.edu/software/netcdf-java/documentation.htm)]], using the `rJava` `R` package (a similar approach is been also made for the `Matlab` implementation). Alternatively, the most recent ''NetCDF library'' versions provide access to `OPeNDAP` datasets (this is the solution for the `Python` implementation). In the following, we show a simple example of data access using the `R` package developed as part of the data portal. In particular the ''System4'' datasets can by directly accessed using the `loadSystem4` function, allowing the retrieval of slices for a particular variable in any of the dataset dimensions (`member`/space/`runtime`/`time`). Note that a more ellaborated worked example using `R` is shown in the [#Appendix.rexample R example section].  Moreover, for a better understanding of the datasets structure, the use of the web interface for the `OPeNDAP`  service is also illustrated [#s.web.access web access section].
 
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 = Accesing the Data Portal via `R` = #s.r.access
 
 = Accesing the Data Portal via Web = #s.web.access
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 The ''SPECS-EUPORIAS Data Portal'' can be accessed through the '''Data Portal URL''' provided in the abstract. First of all, an authentication dialog will request a valid user name and password.
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 Note that the indices selected for the run coordinate correspond to the December initilizations (index positions 11, 23,...; note that indexes start in 0) and for the time coordinate correspond to January (positions, 31 to 62, in days after the run time). Note that the proper use of this service requires a full understanding of the data structure and, therefore, it is only advised for data exploration.
 
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 = Example of Data Analysis with `R` = #app1
 = References =