WRF Post Processing Software

The most important variable to be deduced form the WRF output data files is wind speed with respect to location and time. Other important data include pressure, temperature, precipitation etc. WRF ARW files are mostly in the netCDF format where the data is stored in the form of arrays.There are a number of visualization tools available to display WRF-ARW products including NCL, GRADS, IDV, Plot_WRF etc.

4.5.1 Plot_WRF

Plot_WRF is a program developed by Dr. Peter Rye, DER, Perth, Western Australia in 2012. This program is capable of plotting data from both WRF input and output files. It has numerous options and can plot any variables likely to be needed from produced by the WRF. It is capable of interpolating the output variables from WRF at any desirable height and location. It also has the capability of reading multiple WRF output files at one time and products can be adjusted either to local time or UTC. It can cross compare measurements and modelled values with appropriate availability of the necessary databases. Its graphical output includes GIF files (which can be displayed on screen), plots within a separate X-window (using the Cairo graphics library) and, Windows Metafiles that can be read directly by Microsoft Office or OpenOffice software.

The program was compatible with the WRF 3.4.1 version and has been used extensively in this research to obtain wind speed and direction time series plots. But with the introduction of WRF 3.6.1, the current version of Plot_WRF is now incompatible. The developer is no longer providing software support. Alternative code had to be developed in NCL to compare wind speed output from WRF.

4.5.2 NCAR Command Language (NCL)

The NCAR Command Language (NCL) is a programming language designed specifically for the analysis and visualization of data. NCL can be run in interactive mode or in batch mode as an interpreter of complete scripts. NCL has robust file input and output. It can read in netCDF, HDF4, HDF4-EOS, GRIB, binary and ASCII data.

The graphics are world-class and highly customizable. The power and utility of the language are evident in three areas:

• File input and output • Data processing • Graphical display.

NCL can readily read and process WRF ARW netCDF files. In July 2007, the WRF- NCL processing scripts have been incorporated into the NCL Libraries, thus only the NCL Libraries are now needed.

This language has been utilized to develop two indigenous codes, one of which is used for interpreting wind speed and direction time series output from WRF. The other code can retrieve radial wind speeds from CDL and can compare them with the WRF output spatially at any desired location and at any instant of time.

4.5.3 Grid Analysis and Display System (GRADS)

The Grid Analysis and Display System (GRADS) is an interactive desktop tool to display earth science data and is freely available on the internet. It has two data models for handling gridded and station data and supports many data file formats, including binary, GRIB (version 1 and 2), NetCDF, HDF (version 4 and 5), and BUFR.

GRADS uses a 5-Dimensional data environment: the four conventional dimensions (longitude, latitude, vertical level, and time) plus an optional 5th dimension for grids that are generally implemented but designed to be used for ensembles. Data sets are placed within the 5-D space by use of a data descriptor file. GRADS handles grids that are regular, non-linearly spaced, gaussian, or of variable resolution. Data from different data sets may be graphically overlaid, with correct spatial and time registration. Operations are executed interactively by entering FORTRAN-like expressions at the command line. A rich set of built-in functions are provided, but users may also add their own functions as external routines written in any programming language. It can run in interactive or batch mode and can be used to produce scatter plots, time series and other plots.

In the current research the use of GRADS was particularly useful in acquiring the time series output from the NCEP data and comparing it with the WRF output.

4.5.4 Integrated Data Viewer (IDV)

The Integrated Data Viewer (IDV) from Unidata is a JavaTM-based software framework for analysing and visualizing geoscience data.The IDV is developed at the Unidata Program Center (UPC), part of the University Corporation for Atmospheric Research, Boulder, Colorado, which is funded by the National Science Foundation. It brings together the ability to display and work with satellite imagery, gridded, surface observations, balloon soundings, etc., all within a unified interface. It also provides 3-D views of the earth system and allows users to interactively slice, dice, and probe the data, creating cross-sections, profiles, animations and value read-outs of multi-dimensional data sets.

Initially IDV was utilized in this study. The problem with using IDV is that it cannot retrieve the vertical coordinate correctly. The GUI requires the user to enter probe height interactively even using 10 m wind speed variable which already has vertical height specified. It also rounds off the latitude and longitude to one decimal place and hence it is not possible to obtain precise location of mast and compare that to WRF output. It is unable to handle large amount of data and therefore is not able to manipulate 3D wind vectors over a large period of time. Therefore, Plot_WRF and NCL were used for more precision.

4.6 Summary

This chapter provides a comprehensive review of the WRF software, its flexibility and how it has been implemented for this study. This chapter explains the architecture of the WRF software and its two main components i.e. WPS and WRF ARW. The chapter first explains the structure of these two packages and how they are integrated and their usage for running the simulations. It also explains the physical and parametrization models used in the software. An introduction to sensitivity testing has been discussed and it has been shown how an optimal configuration may be achieved for the Lake Turkana site in East Africa using WSDSA. It explains why a certain set of physical

and parametrization schemes, grid configurations, as well as the influence of different initialization fields and terrain complexity were utilized for this research. It also explains the criteria for model validation between masts and WRF output. The results of this sensitivity analysis along with the detail of model validation are presented in the next chapter.