Description of the Global Scale Wave Model

Standard GSWM tidal results account for realistic tidal forcing due to ozone (absorption of solar UV radiation) and water vapor (absorption of solar IR radiation), and the effects of empirical background climatologies of zonal mean temperature, neutral density, zonal wind and ozone concentration, as well as wave dissipation.

The GSWM FORTRAN code currently runs on NCAR's Cray J90 computer. ASCII format output files containing the most recent GSWM diurnal and semidiurnal migrating tidal climatologies may be downloaded directly from this web site.

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Above 12 km the standard model run uses background winds determined from measurements made by the HRDI instrument on UARS. The data are 6-year monthly and zonally averaged values that are smoothed and interpolated. Below 12km the winds are from the semiempirical model of Groves/MSIS. The GSWM background temperature and density are taken from the MSISE90 model using a 10.7-cm solar flux value of 120 and an Ap of 4. Contour plots of the GSWM standard background zonal mean temperature and wind fields are available from this web site.

The GSWM background atmosphere may be modified to explore the sensitivity of the tidal response to variable wind and temperature conditions. Results of such numerical experiments appear in the literature but are not available from this web site (please see references).

Background ozone concentrations can also be modified for numerical experiments. The standard configuration uses 6-year monthly and zonally averaged measurements from the HALOE instrument on the UARS satellite below 50 km and UARS MLS measurements above 50km. Plots of HALOE/MLS ozone used for standard model runs are available here.

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The GSWM includes tidal forcing schemes which account for all known sources of thermal excitation, as illustrated in the figure.

In the standard model configuration only migrating sources excited by the absorption of solar radiation are specified. These include the tropospheric IR heating (blue raindrops) parameterization based on Groves (1982) which is only available for 4 months (January, April, July, October). Standard GSWM output is therefore restricted to these months which are representative of the seasons.

The standard model uses latitude and altitude-dependent ozone concentrations and the parameterization scheme of Strobel (1978) to calculate ozone (UV) forcing (red striped ellipse) in the stratosphere and lower mesosphere. The same scheme and MSISE90 molecular oxygen densities account for the absorbtion of radiation in the Schuman-Runge bands and continuum near the mesopause region (pink dotted elipse).

The current standard does not include thermospheric in-situ (EUV) forcing due to atmomic oxygen (green striped ellipse) or latent heat release due to deep convective activity (DCA pink cloud) in the troposphere. GSWM results which include latent heating effects (Forbes and Groves, 1987; Williams and Avery, 1996; Hong and Wang 1980) have appeared in the literature (please see references). Latent heating is the most significant non-migrating tidal source. Future GSWM standards will include latent heating and EUV effects.

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Latitude values range from 87 degrees (North) to -87 degrees (South), every 3 degrees, giving 59 measurements of each tide at each altitude. The values for each of the 4 fields is listed for each latitude at a given altitude, then this pattern is repeated for the next altitude. The output tables resemble a series of output 'blocks', one for each altitude.

The altitude of each block is indicated at the top of the block by the scale height index, X, and the corresponding geographic height, Z(km). Blocks are printed approximately every 4 km of altitude, beginning at 0km and continuing to 124km, making 31 blocks.

For example:

X= 7.6000 Z= 12.201
LAT= 87.0 U=.278E-02/ 8.5 V=.429E-02/ 5.3 W=.107E-04/ 14.2 T=.681E-03/ 11.1
...
LAT= 63.0 U=.189E-01/ 13.9 V=.188E-01/ 10.9 W=.111E-13/ 12.0 T=.192E-03/ 11.8
LAT= 60.0 U=.199E-01/ 14.0 V=.217E-01/ 11.0 W=.110E-12/ 12.0 T=.397E-03/ 12.0
LAT= 57.0 U=.243E-01/ 13.9 V=.247E-01/ 11.0 W=.435E-13/ 12.0 T=.165E-03/ 8.6
...
LAT=-87.0 U=.706E-02/ 6.4 V=.702E-02/ 10.4 W=.643E-05/ 6.8 T=.278E-03/ 15.7
...
X= 8.2000 Z= 16.218
LAT= 87.0 U=.188E-01/ 16.1 V=.120E-01/ 0.6 W=.140E-04/ 14.7 T=.115E-02/ 11.6
...

The format in pseudocode and FORTRAN to read each block is:

READ X,Z Read the altitude of this block
FOR LOOP 1 to 59 Read a Line for each of the Latitude values
READ(5x,f5.1,5x,e8.3,1x,f5.1,4x,e8.3,1x,f5.1,4x,e8.3,1x,f5.1, 4x,e8.3,1x,f5.1)
END FOR

The variables read in for each latitude value are: Latitude, U_amplitude, U_phase, V_amplitude, V_phase, W_amp,W_phz, and T_amp,T_phz. The units of amplitude/phase are m/s for the wind, degrees Kelvin for temperature, and phases are in local solar hours.

There are 4 lines at the top of the file which identify the run, including the month, the period, and the wave number. A positive wave number in the GSWM convention indicates a westward propagating component.

IDL Procedure

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Contour Plots of the Background Atmosphere for the Standard Model Configuration

• HALOE/MLS Ozone Background Plots(71k gif) Landscape
• Background Wind and Temperature for January and April(15k gif)
• Background Wind and Temperature for July and October(15k gif)

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