Near-Real-Time Modelling of the Indian Ocean Wind-Driven Circulation

Mark E. Luther, Zaihua Ji, and Haihua Liu

University of South Florida Department of Marine Science

This directory contains a "quick-look" hindcast of the Indian Ocean wind-driven circulation from a numerical ocean model being run at USF using near-real-time observed winds. The model products are produced under support from the Office of Naval Research and the National Science Foundation Chemical Oceanography Program. The model is that described in Jensen (1991) as modified by Jorge Capella to include a finer spatial resolution, an improved bathymetry, and an extended domain. The present version of the model has 4 layers, with the horizontal pressure gradient assumed to vanish in the lowest layer (the reduced gravity approximation). The mean layer depths are: layer 1: 0 - 200 m; layer 2: 200 - 450 m; layer 3: 450 - 850 m. The model domain covers the Indian Ocean basin from 30 degrees S to 26 degrees N and from 35 degrees E to 120 degrees E at a resolution of 1/12 degree in latitude and longitude. A 20-year integration, driven by climatological monthly mean winds from the FSU analysis, has been used to "spin-up" the model. Using the end of this 20-year integration as an initial condition, the model was run using the FSU monthly mean real-time winds for the period January 1977 through December 1991. This integration has been updated through the 16th of the most recently ended month using the FSU "quick-look" winds to provide a near-real- time estimate of conditions in the Indian Ocean. Model output and images are available via anonymous ftp to kelvin.marine.usf.edu.

The wind stress fields used to drive the ocean model are compiled by David Legler and Jim O'Brien at Florida State University. Monthly mean wind fields are derived from all volunteer observing fleet ship reports that are received during each month via the GTS. The fields consist of monthly mean pseudostress (vector wind times wind speed) components objectively analyzed on a 1 degree by 1 degree grid using the method of Legler et al. (1988). About 6 months after the end of the year, all the monthly mean fields are re- analyzed using additional data that is received in "delayed-mode" to produce a research-grade product. These data now cover the period from January 1977 through the end of the most recent month and are available on the Internet via anonymous ftp to coaps.fsu.edu (128.186.28.11).

DISCLAIMER: The Indian Ocean model is a research product. No warranty is made, express or implied, regarding the accuracy or validity of the model results, or regarding the suitability of the model output for any particular application.

For further information on the ocean model and wind analysis, see the reference list at the end of this file.

The ftp directory contains both graphics from the model and compressed model output for the 16th of each month since January 1992. Output for the last month is usually available by the 5th working day of the present month. Contact Mark Luther (luther@marine.usf.edu; 813-893-9528) for model output from 1977 through 1992 in digital or video format or for additional information.

There are five subdirectories under ~ftp/pub/ndnocn:

dat -- Compressed data files.

arab.gif -- GIF image files for the Arabian Basin.

full.gif -- GIF image files for the entire model basin.

ncar -- NCAR Graphics Computer Graphics Metafiles (cgm files).

movies -- FSU animation (gasp) files for SGI workstations

Files in each directory are named as follows:

mmyy_n.ext

where

mm = month

yy = year

n = layer number

ext = dat, gif, cgm, or mv depending on file type.

For example; '0192_1.dat' is a file containing the data for layer one on Jan. 16, 1992.

1. Directory dat:

This directory contains the compressed model output. To uncompress a *.Z file; use the UNIX command:

uncompress filename.Z

Data in each file can be read by a FORTRAN program using the following format:

      parameter	(jmax=266,kmax=167)
      dimension	U(jmax,kmax),V(jmax,kmax),H(jmax,kmax)

c
      read(infile,10) ryear,rmon,rday,((H(j,k),j=1,jmax),k=1,kmax)

      read(infile,20) ((U(j,k),j=1,jmax),k=1,kmax),

     *		      ((V(j,k),j=1,jmax),k=1,kmax)

c
   10 format(10F8.3)

   20 format(10F8.5)

The model output variables are depth of the layer interface H (ie. the depth of the interface between layer n and layer n+1), the zonal component of the velocity U, and the meridional component of the velocity V. The velocity components have been averaged onto the H grid points and represent a vertically averaged velocity within the layer. Only every second model grid point in longitude and latitude are archived. Grid point (1,1) of each field is located at longitude 31.0 degrees E, latitude 29 degrees 20 minutes S (29.33333 S). The spacing between grid points is 1/3 degree in each direction. Special values in the H field of H=9999 indicate grid points over land. U and V = 0 at land points.

2. Directories arab.gif and full.gif

Files in these directories are interlaced GIF images of the model output for each layer with 34 unique colors. They can be viewed on an X11 workstation by issuing the command:

xloadimage filename

or by using other image tools that can display GIF images. Also you may convert these images to another format so that they can be displayed on your machine using the imconv utility, which is available via anonymous ftp from the San Diego Supercomputer Center (Contact SDSC consultants, (619)534-5100, consult@y1.sdsc.edu).

3. Directory ncar

CGMs (Computer Graphics Metafiles) in this directory are created by the NCAR Graphics Package. They can be viewed via NCAR's translators 'ictrans', 'ctrans', 'ftrans' and so on. (For more details of the translators, please refer to the NCAR Graphics Package.)

For example; to display a CGM on a workstation:

ictrans filename

ictrans> p

To plot a CGM on a PostScript printer:

ctran -d ps.mono filename | lpr

To plot a CGM on a HP LaserJet printer:

ftrans -d hplj300p filename | lpr

4. Directory movies

This directory contains graphical animations (movies) produced for the Silicon Graphics IRIS workstation using the FSU Graphical Animation Software Package (gasp). You must have gasp installed on your IRIS to display the animations. gasp is available via anonymous ftp to masig.fsu.edu (128.186.28.11). Contact Alan Davis (904-644-3798, davis@masig.fsu.edu) for more information on gasp. The movie files must be uncompressed and then displayed with the lookat command. The images in arab.gif are still frames from these movies.

References:

Jensen, T., 1991: Modelling the seasonal undercurrents in the Somali Current system, J. Geophys. Res., 96, 22,151-22,168.

Legler, D. M., I. M. Navon, and J. J. O'Brien, 1988: Objective Analysis of pseudostress over the Indian Ocean using a direct-minimization approach, Mon. Wea. Rev., 117, 709- 720.

Luther, M. E., and J. J. O'Brien, 1985. A model of the seasonal circulation in the Arabian Sea forced by observed winds. Prog. Oceanogr., 14, 353-385.

Luther, M. E., and J. J. O'Brien, 1989. Modelling the variability in the Somali Current, Mesoscale/Synoptic Coherent Structures in Geophysical Turbulence, J.C.J. Nihoul and B. M. Jamart, eds., pp. 373-386.

Luther, M. E., J. J. O'Brien and A. H. Meng, 1985. Morphology of the Somali Current System during the southwest monsoon. In: J. C. J. Nihoul (Editor), Coupled Ocean- Atmosphere Models, Elsevier, Amsterdam, pp. 405-437.

Luther, M. E., J. J. O'Brien, and W. L. Prell, 1990: Variability in upwelling fields in the northwestern Indian Ocean over the past 18,000 years; 1, Model experiments, Paleoceanogr., 5, 433-445.

Potemra, J. T., M. E. Luther, and J. J. O'Brien, 1991: The seasonal circulation of the upper ocean in the Bay of Bengal, J. Geophys. Res., 96, 12 667-12 684.

Simmons, R. C., M. E. Luther, J. J. O'Brien and D. M. Legler, 1988: Verification of a numerical model of the Arabian Sea. J. Geophys. Res. - Oceans, 93, 15 437-15 455.

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