Data Analysis using MATLAB and NCTOOLBOX

to extract and visualize the sea surface height from the WAVEWATCH III model obtained from the NOMADS data server and a downloaded GRiB2 file. % for the list of available model run dates. mydate='20160417', url=['', ... mydate,'/nww3',mydate,'_00z'], % Instantiate the data set nco=ncgeodataset(url), % Extract the longitude and latitude vectors and the surface % significant height of wind waves from NOMADS. lon=nco{'lon'}(:), lat=nco{'lat'}(:), waveheight=nco{'htsgwsfc'}(1,:,:), % The indexing into the data set is standard MATLAB array indexing. % We need to convert the data from single to double precision and remove % any singleton dimensions, as the NCTOOLBOX routines return the numbers % as they are stored in the netCDF file, in this case single precision. waveheight=double(squeeze(waveheight)), lat=double(lat), lon=double(lon), % Plot the field using M_MAP. Start with setting the map % projection using the limits of the lat/lon data itself: m_proj('miller','lat',[min(lat(:)) max(lat(:))],... 'lon',[min(lon(:)) max(lon(:))]) % Next, plot the field using the M_MAP version of pcolor. m_pcolor(lon,lat,waveheight), shading flat, % Add a coastline and axis values. m_coast('patch',[.7 .7 .7]) m_grid('box','fancy') % Add a colorbar and title. colorbar title('Example 1: WAVEWATCH III Significant Wave Height from NOMADS'), This example requires that you download a GRiB file from either our NOMADS data server or the Production FTP Server (see our for more information. For this exercise, I used the nowcast file for 20140128: multi_1.at_10m.t00z.f000.grib2 retrieved from NOMADS. This example assumes that the GRiB file is in the current working directory. Note that the file variables have different names when you access it locally instead of through the OpenDAP interface. Specifically, 'sshgsfc' becomes 'Sea_Surface_Height_Relative_to_Geoid', 'lat' is 'Latitude_of_Presure_Point_surface' and 'lon' is 'Longitude_of_Presure_Point_surface'. Once you've defined the ncgeodataset (in this case called nco), you can examine the variable names by printing out the values of nco.variables. Note that since we are working with the model's native grid (Arakawa C-Grid) the lat/lon positions for some values (ssh, temperature, mixed layer depth, others) is different from the lat/lon points for the horizontal velocity components. grib=' multi_1.at_10m.t00z.f000.grib2', nco=ncgeodataset(grib), nco.variables ans = 'Wind_direction_from_which_blowing_degree_true_surface' 'Wind_speed_surface' 'u-component_of_wind_surface' 'v-component_of_wind_surface' 'Significant_height_of_combined_wind_waves_and_swell_surface' 'Direction_of_wind_waves_degree_true_surface' 'Significant_height_of_wind_waves_surface' 'Mean_period_of_wind_waves_surface' 'Direction_of_swell_waves_degree_true_ordered_sequence_of_data' 'Significant_height_of_swell_waves_ordered_sequence_of_data' 'Mean_period_of_swell_waves_ordered_sequence_of_data' 'Primary_wave_direction_degree_true_surface' 'Primary_wave_mean_period_surface' 'lat' 'lon' 'ordered_sequence_of_data' 'time' % Extract the Significant Height of Swell Waves field. param='Significant_height_of_swell_waves_ordered_sequence_of_data', waveheight=nco{param}(1,1,:,:), lat=nco{'lat'}(:), lon=nco{'lon'}(:), % From this point on the code is identical to the previous example: waveheight=double(squeeze(waveheight)), lat=double(lat), lon=double(lon), m_proj('miller','lat',[min(lat(:)) max(lat(:))],... 'lon',[min(lon(:)) max(lon(:))]) m_pcolor(lon,lat,waveheight), shading flat, m_coast('patch',[.7 .7 .7]), m_grid('box','fancy') colorbar title('Example 2: WAVEWATCH III Significant Wave Height from GRiB'), Source.

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