#494 closed upgrade (Done)
New vertical coordinates stretching function, Vstretching = 4
Reported by: | arango | Owned by: | arango |
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Priority: | major | Milestone: | Release ROMS/TOMS 3.4 |
Component: | Nonlinear | Version: | 3.4 |
Keywords: | Cc: |
Description (last modified by )
A new vertical stretching function, Vstretching = 4, was added and it is denoted as Shchepetkin (2010). This is a major improvement to his 2005 function, Vstretching = 2. The new function, C(s), has a double stretching transformation:
C(s) = [1 - COSH(theta_s * s)] / [COSH(theta_s) - 1] with bottom refinement: C(s) = [EXP(theta_b * C(s)) - 1] / [1 - EXP(-theta_b)]
Notice that the bottom function is the second stretching of an already stretched transform. The resulting function is continuous with respect the control parameters theta_s and theta_b with a meaningful range of:
0 < theta_s <= 10.0 0 <= theta_b <= 4.0
Due to its functionality and properties Vtransform = 2 and Vstretching = 4 are now the default values for ROMS.
Notice that with Vtransform = 2 the true sigma-coordinate system is recovered as hc goes to infinity. This is useful when configuring applications with flat bathymetry and uniform level thickness. Practically, you can achieve this by setting in ocean.in:
THETA_S = 0.0d0 THETA_B = 0.0d0 TCLINE = 1.0d+17 (a large number)
Please check WikiROMS for updated documentation and plots. For example, in the coarse resolution, North Atlantic application (DAMEE_4) we get:
WARNING:
The new vertical stretching transformation Vtransform = 2 and Vstretching = 4 may have different time-step limitations due to the thickness of the discritized vertical levels. Users need to pay attention to extreme r-factor (rx1) values near the bottom
The following testcases were changed to have the default transformation Vtransform = 2 and Vstretching = 4:
OLD (1,1) NEW (2,4) theta_s theta_b Tcline theta_s theta_b Tcline --------------------------------------------------------- BASIN 3.3 0.0 1400 3.3 0.0 1400 BENCHMARK 5.0 0.4 200 0.0 0.0 400 BL_TEST 3.2 0.2 5 5.0 1.5 20 CANYON2D 1d-4 0.0 90 0.0 0.0 1d+16 DOUBLE_GYRE 1.0 1.0 50 0.0 0.0 1d+16 FLT_TEST2D 3.0 0.4 100 0.0 0.0 1d+16 FLT_TEST3D 3.0 0.4 100 0.0 0.0 1d+16 GRAV_ADJ 1d-4 0.0 50 0.0 0.0 1d+16 KELVIN 3.0 0.0 50 0.0 0.0 1d+16 LMD_TEST 1d-4 0.0 50 0.0 0.0 1d+16 RIVERPLUME1 3.0 0.4 50 3.0 0.0 30 RIVERPLUME2 3.0 0.4 50 3.0 0.0 30 SEAMOUNT 5.0 0.4 50 6.5 2.0 100 SOLITON 1d-4 0.0 50 0.0 0.0 1d+16 UPWELLING 3.0 0.0 50 3.0 0.0 25 WINDBASIN 1d-4 0.0 50 1.0 0.0 50
Many thanks to Sasha Shchepetkin for designing this nice and continuous transformation.
Change History (2)
comment:1 by , 14 years ago
Description: | modified (diff) |
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Resolution: | → Done |
Status: | new → closed |
comment:2 by , 14 years ago
Description: | modified (diff) |
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