Coupling of atmospheric and ocean/sea ice models over Arctic continental shelf areas. University of Bergen, Bergen, Norway

Transcription

1 Coupling of atmospheric and ocean/sea ice models over Arctic continental shelf areas Alastair D. Jenkins 1, W. Paul Budgell 2,1, Chris Moore 3, and Anne D. Sandvik 1 1 Bjerknes Centre for Climate Research & Geophysical Institute, University of Bergen, Bergen, Norway 2 Institute of Marine Research, Bergen, Norway 3 University of Washington/JISAO/NOAA-PMEL, Seattle, Washington, U.S.A. Alastair.Jenkins@gfi.uib.no jenkins

2 Introduction Brine rejection during ice formation over polar continental shelf areas is thought to make a substantial contribution to the generation of oceanic deep water, with significant consequences for the interior ocean circulation, and for the global climate on decadal to millenial timescales.

3 A substantial proportion of the ice-formation and brine-rejection process is associated with the formation of coastal polynyas during periods with offshore winds. S and T 10m above bottom September- October 2000 August 2001 (From I. Fer et al. JGR 109(C1), C01005 (2004))

4 Storfjord outflow plume path after Killworth (2001): Descent rate: 1/400. Green path: derived over smoothed bathymetry. Red path: derived over raw bathymetry: better fit to observations! Blue dots: Stations where the core of the plume was observed during Lance, July 01. (See I. Fer et al. JGR 109(C1), C01005 (2004))

5 Computed airflow over Svalbard, using MM5 model (Anne D. Sandvik)

6 Models In order to quantify the air-sea exchange processes involved, we are running ROMS with a dynamic-thermodynamic sea ice component, with input from the MM5 mesoscale atmospheric model, for Storfjorden (Svalbard).

7 Coupling Since there are great differences in the surface boundary conditions between ice-covered and open water areas, which will cause substantial changes in the atmospheric boundary layer, we are in addition implementing two-way coupling of ROMS+ice with the WRF mesoscale atmospheric model. Size of grid: 1 n. mile (2 km) grid, grid boxes. Fixed parameters: Terrain elevation, sea ice, Sea surface temperature, Substrate temperature, Snow cover, Latitude, Longitude, Map scale factor, Coriolis parameter, Land-use category

8 Exchanged variables chosen from: U 10, V 10, Surface sensible and latent heat flux, Surface downward shortwave and longwave radiation, 2 m temperature, 2 m water vapour mixing ratio, surface albedo, Ground and sea-ice temperature, sea-ice fraction, Frictional velocity, roughness length, Monin-Obukhov length, snow height, snow cover, rainfall (convective and non-convective), Surface net radiation, water-equivalent snow depth.

9 Coupling method proposed Initially, we proposed to use the OASIS model coupler: Developed under Program for Integrated Earth System Modelling (PRISM) Version 3 available from CERFACS, Toulouse OASIS3 synchronizes the exchanges of coupling fields between the models being coupled, and performs 2D interpolations and transformations between the source and target model. Modularity and flexibility have been particularly emphasized in the OASIS3 design. But the ROMS code would have to be modified to run under OASIS

10 Coupling method used The WRF I/O API MCT Coupling Implementation. An implementation of the WRF I/O Application Programming Interface using the Argonne Model Coupling Toolkit (MCT) and the Message Passing Environment Utilities (MPEU) libraries. ROMS 2.1 and the WRF atmospheric model now contain code implementing this coupling software (written by Dan Schaffer (NOAA) and Chris Moore). Versions used in the BCCR implementation: WRF version 1.3, with coupling code made available to us by Dan Schaffer ROMS 2.1 beta with ice code by Paul Budgell (ROMS2.1beta+ice), plus the ROMS 2.1 (ROMS2.1final) coupling code

11 Grid remapping Mapping of grids WRF from/to ROMS, using SCRIP software package Written by Philip W. Jones of Los Alamos National Laboratory Conservative remapping using Stokes theorem (integrating around boundaries of grid intersection polygons) Simpler algorithm than finding areas of intersection polygons Converges more rapidly than Monte-Carlo area determination

12 Test run ROMS and WRF compile successfully on the IBM Regatta at Bergen (Para//ab). Two unix (AIX) processes, one for the WRF part and one for the ROMS part of the model). Compiled with debugging enabled. Grids: Rectangular WRF 40 80, 100 km, ROMS 41 41, 6 km WRF ideal case, baroclinic wave. ROMS driven with a percentage of wind speed.

13 Test case, WRF 40 80, 100 km grid, ROMS 41 41, 6 km grid WRF pressure WRF U ROMS u P (pascals) U_1 (m s{-1}) u-momentum component (meter second-1) south_north south_north eta_u west_east gbsaj Sat Sep 2 21:18: west_east_stag gbsaj Sat Sep 2 21:16: xi_u ROMS/TOMS Wind-Driven Upwelling/Downwelling over a Periodic Channel Range of u-momentum component: to meter second-1 Range of xi_u: 0 to 42 Range of eta_u: 0 to 43 Current time: 360 Current s_rho: 14 Frame 361 in File ocean_his.nc gbsaj Sat Sep 2 21:36: Range of P: to pascals Range of west_east: 0 to 39 Range of south_north: 0 to 79 Current Time: 0 Current bottom_top: 0 Frame 1 in File wrfrst_d01_ Range of U_1: to m s{-1} Range of west_east_stag: 0 to 40 Range of south_north: 0 to 79 Current Time: 0 Current bottom_top: 0 Frame 1 in File wrfrst_d01_000720

14 Status (two-way coupling) grid now set up, compiled coupled WRF/ROMS system with debugging enabled. WRF and ROMS initial and boundary data set up (Feb. 2000).

15 WRF height ROMS T (top) ROMS T (bottom) HGT (m) potential temperature (Celsius) potential temperature (Celsius) gbsaj Sat Sep 2 18:49: south_north eta_rho xi_rho gbsaj Sat Sep 2 22:08: eta_rho xi_rho gbsaj Sat Sep 2 22:09: west_east Range of HGT: 0 to m Range of west_east: 0 to 180 Range of south_north: 0 to 260 Current Time: 0 Frame 1 in File wrfinput_d01 From LA04 avg file Range of potential temperature: to Celsius Range of xi_rho: 0 to 181 Range of eta_rho: 0 to 261 Current time: 0 Current s_rho: 31 Frame 1 in File STFJ2_init_ nc From LA04 avg file Range of potential temperature: to Celsius Range of xi_rho: 0 to 181 Range of eta_rho: 0 to 261 Current time: 0 Current s_rho: 0 Frame 1 in File STFJ2_init_ nc

16 MPI data communication was successful for simple test case, and starts up OK for grid. Debugger (IBM xldb), with 2 windows, one for each process. Debugging continues...