id summary reporter owner description type status priority milestone component version resolution keywords cc 918 VERY IMPORTANT: Updated ROMS and WRF NUOPC cap modules arango "The **ESMF** coupling was updated to enhance the **NUOPC** layer modules for **ROMS** and **WRF**. In addition, several new exchanged fields are now supported. * **WRF** now exports surface air density (**!RhoAir**), level 2 winds (**Uwind_sbl**, **Vwind_sbl**), and turbulent frictional wind magnitude (**Wstar**), so **ROMS NUOPC** ''cap'' file can compute the surface wind stress when **BULK_FLUXES** is off during coupling. In particular, we added an option to calculate the reference wind force (wind [[span(minus,style=color: red)]] current) to compute the surface wind stress into the ocean when **WIND_MINUS_CURRENT** is activated. The surface wind stress is computed as: **τ,,x,,/ρ,,w,, = ρ,,a,, C,,D,, |W,,r,,| u,,r,,** **τ,,y,,/ρ,,w,, = ρ,,a,, C,,D,, |W,,r,,| v,,r,,** Where **ρ,,w,,** is the mean seawater density, **ρ,,a,,** is the surface density of air, **τ,,x,,** and **τ,,y,,** are the wind stress components, **C,,D,,** is the transfer coefficient for momentum (drag coefficient), **u,,r,,** and **v,,r,,** are the wind components relative to the seawater (wind [[span(minus, style=color: red)]] surface ocean current), and **|W,,r,,|** is the relative wind magnitude. Here, the drag coefficient is computed as: **C,,D,, = W^*2^ / |W,,a,,|^2^** Where **W^*^** is the frictional wind magnitude from similarity theory (**WRF** variable [[span(**grid%ust**, style=color: red)]]) and **W,,a,,** is the unreferenced surface wind magnitude, **SQRT[(u,,a,,)^2^+(v,,a,,)^2^]**. The coupling is incomplete because there is no feedback on the atmosphere. **ROMS** surface currents do not modify the near-surface wind in **WRF**. We are looking for ways to do so without changing **WRF**. * **ROMS** now exports free-surface (**SSH**), barotropic momentum (**ubar**, **vbar**), surface 3D momentum (**Usur**, **Vsur**), and bathymetry (**bath**) to other coupled component. Recall that bathymetry can be time-dependent if sediment morphology is activated. * **ROMS NUOPC** module now includes a generic [[span(**ROMS_Rotate**, style=color: red)]] routine to rotate vector from computational grid to geographical **EAST** and **NORTH** directions and vice versa. * As shown in Renault'' et al.'' (2016), the feedback from surface ocean currents to the atmosphere is an eddy killing effect that stabilizes the Gulf Stream separation at Cape Hatteras in **WRF-ROMS** fully coupled applications. The result is around **0.3** N/m^2^ weaker surface wind stress in the core of the Gulf Stream Below are the results for Hurricane Irene solutions with the wind stress computed in the **WRF NUOPC** cap module (solution **A**) versus the one calculated in the **ROMS NUOPC** cap module with the **WIND_MINUS_CURRENT** option (solution **B**). The plots show the differences in the wind stress component (**B**-**A** solutions). [[Image(https://www.myroms.org/trac/roms_irene_sustr_diff.png, center, 600)]] [[Image(https://www.myroms.org/trac/roms_irene_svstr_diff.png, center, 600)]] The surface wind stress streamlines for solutions **A** and **B** are shown below, respectively: [[Image(https://www.myroms.org/trac/roms_irene_wstress.png, center, 600)]] [[Image(https://www.myroms.org/trac/roms_irene_wstress_wmc.png, center, 600)]] Notice that the difference in the maximum values is **0.28** M/m^2^ weaker in the solution with the reference wind relative to seawater (wind [[span(minus, style=color: red)]] currents). * The application IRENE input scripts were updated to compute the **WIND_MINUS_CURRENT** application. See **coupling_esmf_atm_sbl_wmc.in** input script. ---- Many thanks to John Wilkin for his help in coding and analyzing the results. ---- **References:** Edson, J.B., V. Jampana, R.A. Weller, S.P. Bigorre, A.J. Plueddemann, C.W. Farall, S.D. Miller, L. Mahrt, D. Vickers, and H. Hersbach, 2013: On the Exchange of Momentum over the Open Ocean, ''J. Phys. Oceanog.'', **43**, 1589-1610, **doi:** Renault, L., M.J. Molemaker, J. Gula, S. Masson, and J.C. McWilliams, 2016: Control and Stabilization of the Gulf Stream by Oceanic Current Interaction with the Atmosphere, ''J. Phys. Oceanog.'', **46**, 3439-3453, **doi:** 10.1175/JPO-D-16-0115.1 " upgrade closed major Release ROMS/TOMS 4.1 Nonlinear 4.0 Done