Implementing a new suite of remapping functions within

NCL

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Mohammad AboualiSIPARCS Intern at CISL/NCAR, 2011Computational Science Ph.D. Studentat Joint Program between SDSU & CGU

Mentor:David BrownCISL/VETS/NCAR

Co-Mentors:Mary Haley

(CISL/VETS/NCAR)Dennis Shea

(NESL/CGD/NCAR)

Numerical Modeling of The Environment

Understanding the Environment

• Measurements

• Satellite based measurements

• Numerical models

Ship Tracks Satellite Tracks

“The purpose of computingis insight, not numbers”.(Richard Hamming)

• Once the environment is described by numbers andequations, further mathematical operations can help usto understand our environment and predict how it may(re)act.

Model Performance

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Selecting a coordinate system (grid) is one of the most important steps while developing a numerical model (Griffies et al., 2000).

Different parameters affect the performance of a numerical model.

Different models use different grids with different types and resolutions.

Take your pick

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• Grid Types:– Structured:

• Rectangular

• Rectilinear

• Curvilinear…

– Hybrids:• Cube-Sphere

• Blocks

• Adaptive…

– Unstructured:• Triangular

• Quadrilateral

• Hexagonal...

Therefore, there existsmore than one best gridever.

Each model claims to bethe best model ever,

Sample Structured Grids

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gridgen.c

http://code.google.com/p/gridgen-c/

Variational Method:Abouali

Sample Structured Grid

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Tripolar Grid, using SCRIP2KML (NCL):

Sample Unstructured Grid

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MPAS Grid, Using Unstruct2KML (NCL)

Comparison and Interaction

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• To compare the results of different models anddata sets quantitatively, the data must be in thesame grid.

• Some models rely on the output of one or moremodels for their input, such as Surface EnergyBalance System (SEBS) (Su, 2002).

An Easy procedure tointerpolate data from one gridto another is needed.

Interpolation as a Transform Operator

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• Interpolation can be considered to be a transformoperator, matrix A.

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Source Grid

Destination Grid

A

Datadestination grid = A ∗Datasource grid

•The interpolation schemedefines the entries of A.

•The majority of interpolationschemes only examine how thenodes in the destination andsource grids are located relativeto each other.

As long as the source anddestination grids are notchanged, matrix A remainsthe same.

A: InterpolationWeights

• Is a suite of functions and command lineoperators that facilitate the remappingcapabilities within the NCAR Command Language(NCL)

• Uses a software package from the Earth SystemModeling Framework (ESMF) to generateinterpolation weights, matrix A

• Available interpolation methods are:– Bilinear

– Conservative

– Patch

NCL Remapping Tools

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www.ncl.ucar.edu

www.earthsystemmodeling.org

Remapping Procedure

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Converting to SCRIP or ESMF

Generating interpolation weights

Applying the interpolation weights and remapping

Step

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Step

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Step

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Converting to SCRIP or ESMF

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• Several functions and procedures have been developed tofacilitate this step:– SCRIP Convention Files:

• GenBox_with_LLURCorner

• GenBox_with_Center_Dim

• Rectilinear2SCRIP

• Curvilinear2SCRIP

• Auto2SCRIP

– ESMF Convention Files:• Unstructured2ESMF

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Sample interface:function Auto2SCRIP (

sourceFileName [1] : string,varName [1] : string,SCRIPFileName [1] : string,fileTitle [1] : string,options [1] : logical

)return_val [1] : integer

CRCM GRID

• Calls “ESMF_RegridWeightGen” applicationwithin NCL

• ESMF must be compiled with NetCDF and LAPACK.

• If ESMF is compiled for multiprocessors, this stepwould be in parallel (requires mpirun).

Generating Interpolation Weights

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NCL interface:function esmf_remap_weights (

sourceGrid [1] : string,destinationGrid [1] : string,weightFile [1] : string,options [1] : logical

)return_val [1] : integer

Options:•OverWrite•ForceOverWrite•method•pole•bothRegional•srcGridRegional

•dstGridRegional•isBothESMF•isSrcESMF•isDstESMF•showCMD

NOTE: All the interpolation weights aregenerated using ESMF software package;SCRIP weight generator is not used.

Remapping

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• Using “sparse matrix multiplier” of NCL to applypreviously generated interpolation weights toperform the actual remapping/regridding

NCL remapping interface:function esmf_remap (

sourceData : numeric,weightFile [1] : string,Err [1] : integer

)return_val : numeric

Sample Code: Step 1

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load "$ESMFRegridToolsPATH/ESMFRegridingTools.ncl"begin

sourceFile=”iceh.0070-01.nc"SCRIPFileName=“TGrid.nc”VarName="sst"fileTitle="A curvilinear Tripolar grid."Opt=True

Err=Auto2SCRIP(sourceFile,VarName, \SCRIPFileName,fileTitle,Opt)

if (Err.ne.0) thenprint("Not Successful!")exit

end ifend

Loading the Library

Initializing

Converting

Checking for Error

Sample Code: Step 2

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load "$ESMFRegridToolsPATH/ESMFRegridingTools.ncl"begin

srcGrid="HRM3_SCRIP.nc"dstGrid="CRCM_SCRIP.nc"weightFile="HRM3_2_CRCM.nc"

Opt=TrueOpt@method="conserve”

Err=esmf_remap_weights(srcGrid,dstGrid, \weightFile,Opt)

if (Err.ne.0) thenprint("Not successful!")exit

end ifEnd

Loading the Library

Initializing

Checking for Error

Setting Options

Generating Weights

Sample Code: Step 3

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load "$ESMFRegridToolsPATH/ESMFRegridingTools.ncl"begin

WFile=”WRF_2_Rect.nc"

fid=addfile("../data/WRF.grb","r")GH=todouble( fid->HGT_GDS5_ISBL_10 )

Err=0;dstGH=esmf_remap(GH(1,:,:),WFile,Err)

if (Err.ne.0) thenprint("Not Successful!")exit

end if end

Loading the Library

Initializing

Loading Source Data

Interpolating

Checking for Error

Sample Interpolation Results

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• Temperature – HRM3 to CRCM

Sample Interpolation Results

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• Surface Pressure - MPAS to 15arcmin World

Sample Interpolation Results

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• Surface Pressure - MPAS to 15arcmin World

Sample Interpolation Results

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• Surface Pressure - MPAS to Tripolar

Sample Interpolation Results

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• Geopotential Height – WRF to Rectilinear

Purple Color shows the coverage of the rectilinear grid.

Sample Interpolation Results

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• Sea Surface Temperature – Tripolar to MPAS

Sample Interpolation Results

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• SWE – EASE to NH

Sample Interpolation Results

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• SLP – CCSM4 to EASE

Command-Line Tools

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• Some of the functions are also accessible fromthe command-line (Terminal).

• These commands can be used to convert grids toeither SCRIP or ESMF convention files.

• Once ESMF is compiled, the user gets acommand-line operator that generates weights.

• The user can apply the remapping weights withinthe command-line or a bash script on one ormultiple data files.

Want to Learn More?

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• If you are interested in learninghow to use the package, pleaserefer to the NCL Remapping ToolsUser Guide.

• Only a subset of functions werediscussed in this presentation.

• The command line tools alongwith some extra useful functionsare described in the manual.

• 21+ Examples

• 5+ Comprehensive Examples

Thanks for the Support

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• David Brown, Dennis Shea, Mary Haley

• NCAR and CISL personnel for assisting inevery step to make this internship happen

• Particular thanks to Kristin and Jennifer

• Dr. Robert Oehmke from NOAA for hiscollaboration and help on ESMF

• Christopher Kruse for the nice discussionsduring this internship

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