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GrADS: A Handy Tool for Data Access, Analysis, and Visualization

GrADS: A Handy Tool for Data Access, Analysis, and Visualization. Jennifer M. Adams and Brian Doty IGES/COLA. What is GrADS?. GrADS is an interactive tool that integrates data access, analysis, and visualization … it handles gridded and station data

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GrADS: A Handy Tool for Data Access, Analysis, and Visualization

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  1. GrADS:A Handy Tool forData Access, Analysis, and Visualization Jennifer M. Adams and Brian DotyIGES/COLA

  2. What is GrADS? GrADS is an interactive tool that integrates data access, analysis, and visualization … it handles gridded and station data … it has a programmable interface for scripting … it runs on Unix, MS Windows, and Apple Mac … it has a busy users forum with 1800+ subscribers … it has been under active development since 1989 … and it is open source software under GPL

  3. What Types of Data Can GrADS Read? GrADS handles the following data formats: Flat Binary NetCDF GRIB (versions 1 and 2) HDF (versions 4 and 5) BUFR (for station data)

  4. Data Formats and Metadata Data are arrays of numbers Metadata provides information about the data so we know what the numbers mean Some data formats are self-describing: data and metadata are contained in the same file Accurate metadata is absolutely essential

  5. Metadata and GrADS Metadata is communicated to GrADS with a separate Data Descriptor File (a.k.a. Control File) Gives the user more flexibility and control Aggregates numerous data files into a single data set Supplements or overrides the metadata in the data file Descriptor file may not be necessary if the metadata in data file is good enough

  6. GrADS Gridded Data Model Internal grid structure supports 5 dimensions:X ~ Longitude Y ~ Latitude Z ~ Level T ~ Time E ~ Ensemble T and E axes must be linear X, Y, and Z axes may be non-linear Grid coordinate values must be 1-dimensional

  7. GrADS Station Data Model Used for in situ observational data Individual reports may be located anywhere in space and time Required metadata for each report: Station Identifier (8-character string) Longitude Latitude Level (for level-dependent variables) Time Linear time axis is used to organize reports

  8. Visualization in GrADS Display options include:Contour (lines or shaded) Grid fill (colors or numbers) Bar graph (with error bars) Scatter plot Winds: Vectors, Barbs, or Streamlines Output options include:Images Vector Graphics (e.g. Postscript) ASCII Binary or NetCDF file GIS-Compatible Formats

  9. Data Analysis in GrADS GrADS expressions are formulas that contain:Operands (variables, functions, or constants)Operators (add, subtract, multiply, divide)Parentheses (to control the order of operation) Expression handling is recursive, so an expression may be embedded within another. Some examples: temp*9/5+32 aave((temp*9/5+32),global) hgt(lev=500)-hgt(lev=1000) ave(uwnd,lon=0,lon=360) sum(precip,t+0,t+24)

  10. GOES VIS Image with Radar, 500mb Heights, and SLP 18z 4 June 2009

  11. QuikSCAT Winds (HDF), Surface Obs (BUFR), and ETA Model SLP (GRIB) Another Example of GrADS Graphics Output 00z 6 Dec 2003

  12. Analysis of Surface METAR Observations with Radar 18z 29 May 2009

  13. GrADS Output in Google Earth

  14. Palmer Drought Severity IndexJuly 2009

  15. Ensemble Forecast Time Series(Longitude, Latitude, and Level are fixed) Forecast Time --->

  16. Ensemble Forecast Grid(Longitude, Latitude, and Level are fixed) Ensemble Member Forecast Time --->

  17. Ten Ensemble Forecasts(Longitude, Latitude, and Level are fixed) Ensemble Member Forecast Time --->

  18. Ensemble Forecast Time Series(Longitude, Latitude, and Level are fixed) Forecast Time --->

  19. Ensemble Mean,Ensemble Min/Max,+/- StdDev of Ensemble Mean Forecast Time --->

  20. What is OPeNDAP? OPeNDAP (formerly known as DODS) is an Open-source Project for a Network Data Access Protocol OPeNDAP servers make local data files accessible from remote locations OPeNDAP clients (such as GrADS) can access remote data files Open a data set with http://server/filenameinstead of /disk/filename

  21. Internet • Client (User’s Program) • Local or Remote Data Analysis • Visualization • Web-Based Interface OPeNDAP Server-Client Interaction Data • Server • Handles Metadata Requests • Returns Data Subsets • Evaluates Analysis Expressions Observational data Model-based analyses and forecasts AnalysisResult Cache

  22. What is the GrADS Data Server? The GrADS Data Server (GDS) is a type of OPeNDAP server … it can serve any GrADS-readable data set … it translates all data formats into NetCDF … it offers subsetting and server-side analysis … it has a user-friendly browser interface … and it is running operationally at NCEP, NCDC, NASA, and many other locations

  23. Why is Server-Side Analysis Important? Reading data over the internet is slower than reading data from a local file Some analysis tasks need a lot of dataCompute the monthly mean annual cycle from a 100-year climate model run Analysis expressions are evaluated at the server, where the data reside on disk Only the analysis result is delivered to the client Server-side analysis saves a lot of time when: (size of result) << (size of data operated on)

  24. THORPEX Interactive Grand Global Ensemble TIGGE is an international collaboration between operational centers and universities for the development of ensemble prediction Ten participating centers provide their ensemble forecasts in near real time:BoM (Australia) CMA (China) CMC (Canada) CPTEC (Brazil) ECMWF (Europe) JMA (Japan) KMA (Korea) MeteoFrance (France) NCEP (USA) UKMO (England) TIGGE data portals are at ECMWF, NCAR, and CMA

  25. TIGGE Data Behind GDS at NCAR • Data neatly handled by GrADS • Boost to usage of TIGGE data • Forecasts organized by date and by provider • Time series of initialization analyses • Server-side analysis capability • 48-hour data embargo • Only a 3-week window of data is online • Int’l agreement requires password protection

  26. TIGGE Multi-Member Multi-Model Ensemble500mb Geopotential Height valid August 30, 2008 7-day Lead 5-day Lead 3-day Lead 1-day Lead

  27. Washington Post Weather Page

  28. Extreme Makeover: Weather Graphics Edition

  29. Step 1: Get the Daily Normals and Extremes Check the web site of the local Weather Service Forecast Office for local climate data:http://www.weather.gov/climate/local_data.php?wfo=lwx Grab ASCII files, which will require some manual editing:DY NMX NMN NPCP NS RMX /YEAR LOMX/YEAR RMN /YEAR HIMN/YEAR MXPCP YEAR MXSN YEAR 01 43 29 0.10 0.1 69 /2005 17 /1918 -14*/1881 51 /1876 1.52 2003 4.5 1899 02 43 28 0.10 0.2 71 /1876 15 /1918 -1 /1899 52 /1876 1.44 1979 4.5 1925 03 43 28 0.10 0.2 68 /2004+ 10 /1879 -3 /1877 52 /2000 1.87 1914 2.4 1988 04 43 28 0.10 0.2 73 /1997 16 /1879 -3 /1877 60*/1950 2.28 1886 2.1 1980 05 43 28 0.10 0.2 71 /1997 18 /1896 -3 /1877 56 /1950 1.44 1949 4.8 1980 Convert ASCII to GrADS station data format (txt2stn.c)

  30. Daily Normal and Extreme Temperatures Observed at Reagan National Airport

  31. Step 2: Get Forecast Data for Next 10 Days Browse through available TIGGE forecasts and select which initial date and model to use: http://vetscomm.ucar.edu:9090/dods/tigge/ Run the GrADS script: ga-> get_fcst yyyymmddhh model The script creates a local data set (binary data and a descriptor file) containing daily min and max 2-meter temperatures for the first 10 days of the given forecast http://vetscomm.ucar.edu:9090/dods/tigge get_fcst

  32. Step 3: Get Observed Data for Past 10 Days Recent hourly observations (past 15 days) are here:http://monsoondata.org:9090/dods/stn/metar/past360 Run the GrADS script (note date format is different): ga-> get_past ddMONyyyy The script creates a local data set (binary data and a descriptor file) containing daily min and max surface temperatures observed over the past 10 days http://monsoondata.org:9090/dods/stn/metar/past360 get_past

  33. Combine Climate, Forecast, and Observed Data in a New and Improved Graphic

  34. Some URLs to Remember http://iges.org/gradsGrADS Home Page http://iges.org/jma/AMS2010This Presentation (plus all scripts and programs) http://vetscomm.ucar.edu:9090TIGGE GDS Jennifer Miletta Adamsjma@iges.org

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