MV 4030 MODELING AND SIMULATION IN OCEAN ENVIRONMENT

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The GDEM data set is a composite gridded data set, based on all the historic data available from the Naval Oceanographic Office. Its scope is global, with 1 degree horizontal resolution and 33 fixed depths. The climateology is available monthly, seasonally, and annually. For this lab assignment you will have access to GDEM data for January and June at 19 standard depths to 1000m.

In comparison, GDEM, based on MOODS, has .5 degree horizontal resolution and is available for seasonal, semiannual, and annual intervals since 1975. SST in GDEM is available monthly. Rather than actual values of T and S, GDEM contains coefficients for equations describing the vertical distribution.

Part 1 - An extraction tool - getlev.f.

The UNIX executable to extract data from GDEM is a FORTRAN program called 'getlev.f. Fortunately, we do not have to dwell in the dark ages of punched cards and FORTRAN as the code has been precompiled for us. All we need do is link the lab directory into our working directories in the now customary manner.

bali 8% cd /data/span13/mv4030/user/username
bali 8% mkdir lev.lab
bali 8% cd lev.lab
bali 8% /data/span13/mv4030/link_lev
bali 8% ls

To warm up, we'll start with an extraction. The program is quite self-evident. Use the following example as a first take at getlev:

 
bali 8% getlev
    2 digit number for Jan/Jun       06
    4-character ID                   scs6
    most westerly lon (W lon <0)     95
    most easterly lon                125
    most southerly lat               -5
    most northerly lat               25

There are two Matlab scripts to view the GDEM data you have extracted; 'pl_lev' plots horizontal layers, 'pl_slev' plots vertical slices. Open a Matlab window in your lev.lab directory and try the following example using your extract data.

 
>> pl_lev
   4-character ID                     scs6      
   depth [0,1000]m for plot	      10
   plot title	                      T, S.China Sea depth=10m

Now try using 'pl_slev'.

 
>> pl_slev
   4-character ID                     scs6      
   x to indicate lon slice            x
      or y to indicate lat slice    
   value of lon/lat for slice         115

Note: The white hash marks in the plot represent land locations and locations where the bottom depth is less than your selected depth.

Part 2 - Comparison of GDEM Climatology and Gridded MOODs data.

Using Matlab, replot your gridded SST field for January or June in the Yellow Sea which you first created for last week's lab with 'chrtr.e'. Next, extract data for the same depth and area from the GDEM data set and plot the results as we practiced earlier in this lab.

Question #1. Looking at your two plots, what are the differences, if any, between your 1 degree resolution chrtr field and the GDEM data? Save the plots as jpg files.

Question #2. Repeat the steps for question #1 for a second depth from chrtr. Describe the changes from the first depth. Remember not to exceede the regional max depth.

Question #3. Extract GDEM data from the Gulf Stream area (280-310E, 26-46N) for January or June. Plot the surface temperature and the temperature at 200m. Select a lat/lon for vertical section plots. There's a rumor that some more interesting lat/lons are as follows:

 Jan lats: 37 39 40 41.5 N
 Jun lats: 37 38 39 40 41 N
 Jan lons: 69  65  61.5  57.5 W
 Jun lons: 53  62  64  65 W 

To complete this lab, e-mail the lab instructor at fan@nps.navy.mil with your text answers to questions #1 and #2, and include the name/path of one of your two pairs of jpg files showing the 'chrtr' and GDEM comparisons.