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WRF Development for Coupled Trop

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					WRF and Vertical Nesting: Multi-Scale
 Resolution of T-REX Measurements

     Mohamed Moustaoui, Alex Mahalov, Basil Nichols

         Program in Environmental fluid dynamics
    Department of Mechanical and Aerospace Engineering

          Department of Mathematics and Statistics

                 Arizona State University
              WRF Development for Coupled
           Tropospheric/Stratospheric Forecasting


●   For improved WRF forecasts: need for nesting, high resolution/quality input data and
    improved sub-grid scale parametrizations for shear/stratified turbulent flows near the
    tropopause and in the lower stratosphere.

●   Nesting options are implemented in WRF. However they are allowed only in the
    horizontal directions.

●   Vertical nesting and adaptive gridding are required to predict localized shear layers and
    stiff gradient of stability near the tropopause and in the lower stratosphere regions.
    Currently, vertical nesting is not implemented in WRF.

●   Resolving CAT and optical layers: issues of propagation and transmission of
    mountain/gravity waves across the tropopause and jet streams, gravity waves radiated by
    jet streams.
              WRF Development for Coupled
           Tropospheric/Stratospheric Forecasting


●   Coupling between WRF and a microscale code with adaptive vertical gridding have the capability
    to resolve these processes; in the first step, the nesting is implemented in a one-way mode.

●   WRF code run first, the output of the finest grid WRF nest are used as a coarse grid input for the
    microscale nest.

●   WRF output are interpolated in both horizontal and vertical to provide initial and boundary
    conditions for the microscale code, and finally, the fine grid microscale run is made alone.

●   Implementation with three WRF nested grids and a microscale nested grid.


●   For microscale nests, one way horizontal and vertical nesting are implemented with boundary
    conditions and initialization from 1 km WRF finest nest.
    Terrain-induced Rotor Experiment (T-REX) campaign
      of measurements, Owens Valley, CA on March-April
                  2006 at (118.8 W, 36.49 N)




Potential temperature (black), eastward wind (blue), and northward wind (red) from balloon measurments
during T-REX. The balloon was launched at (36.49 N, 118.84 W) on April 1, 2006 at 7:50 UTC.
     Terrain-induced Rotor Experiment (T-REX)
    campaign of measurements, Owens Valley, CA
                on March-April 2006

●WRF simulations conducted for the period from 03/31/2006 00 UTC to 04/2/2006
00 UTC.

WRF domains are centered over ( 36.49 N, 118.8 W).
●



●Three WRF domains (two way nesting) are used with horizontal resolutions of
15km, 3km and 1 km, and 150 vertical levels adjusted for better resolution of the
tropopause and the lower stratosphere.

●WRF simulations are initialized with ECMWF T799L91 analysis (25 km horizontal
resolution and 91 vertical levels) and GFS data.

●Innermost nesting is done using 300 X 300 grid points in the horizontal (333m grid
spacing) and 450 vertical levels up to 10 mb. One way horizontal and vertical nesting
with boundary conditions and initialization from the finest WRF nest.
Wind vector field and potential vorticity on 320 K isentrope on March 31, 2006.




  Wind vector field and wind speed on 320 K isentrope on March 31, 2006.
 GFS                                                        ECMWF

WRF simulation on April 1 at 8 UTC for the largest domain (15 km)
GFS                                                                ECNWF

      Longitude-altitude cross-section for potential temperature (contour)
      and vertical velocity (color) for the largest WRF domain
GFS                                                                 ECMWF


Longitude-altitude cross-section for potential temperature (contour) and
vertical velocity (color) for the intermediate WRF domain (3 km grid).
GFS                                                            ECMWF


  Longitude-altitude cross-section for potential temperature (contour)
  and vertical velocity (color) for the finest WRF domain (1 km grid).
GFS                                                      ECMWF
  Longitude-altitude cross-section for potential temperature (contour)
  and spanwise vorticity (color) for the finest WRF domain (1 km grid).
Upper: longitude-altitude cross-section of Richardson number.
Lower: longitude-altitude cross-section of the shear field for the
finest WRF domain (1 km grid) with FNL/NCEP initialization.
Upper: longitude-altitude cross-section of Richardson number. Lower: longitude-
altitude cross-section of the shear field for the finest WRF domain (1 km grid)
with ECMWF T799L91 initialization. Patches of low Richardson number
indicate location of mixed layers.
    Along the balloon trajectory                              At (36.84N, 118.18W)
Potential temperature (black), eastward wind (blue), and northward wind (red) along the the balloon
trajectory; from WRF simulations initialized with ECMWF T799L91 (solid), and GFS (dashed). The
balloon was launched at (36.49 N, 118.84 W) on April 1, 2006 at 7:50 UTC.
Eastward and northward wind profiles from balloon measurments during T-REX
(black), from WRF with ECMWF (blue), and with GFS (red) initializations . The
balloon was launched at (36.49 N, 118.84 W) on April 1, 2006 at 7:50 UTC.
               WRF Development for Coupled
            Tropospheric/Stratospheric Forecasting

●   The boundary conditions are implemented in the same way as in WRF code: relaxation or
    nudging zone with prescribed width surrounding the microscale domain are specified
    both in the horizontal and the vertical. The microscale fields are gradually relaxed
    towards those of WRF finest nest as the boundary is approached.

●   The boundary conditions data are interpolated in time since smaller time steps are
    needed, and the microscale nest is allowed to start at times that are different than the
    starting time of WRF .

●   The reference state is constructed by averaging in the horizontal the finest WRF nest
    fields over the microscale domain. This results in small perturbations and reduces the
    numerical errors.
                     Numerical scheme
Temporal Discretization (Skamarock and Klemp, 1992,
Wicker and Skamarock, 2002)
    The model uses a time-split integration scheme:
    • Low-frequency modes that are meteorologically significant are integrated
      using a third-order Runge-Kutta time integration scheme.
    • High-frequency acoustic modes are integrated implicitly in the vertical over
      smaller time steps to maintain stability.
Spatial Discretization
    • The model uses a C grid staggering: Normal velocity are staggered one-half
       grid length from the thermodynamic variables.
    • Advection of vector and scalar fields is in the form of flux divergence,
      and is performed using the third order Runge-Kutta time-integration scheme.
      the advection uses a fifth and third order accurate spatial discretization.
Lateral and Upper Boundary Conditions
    • Both upper and lateral boundary conditions are nudged within relaxation zones
      to the finest WRF nest fields including the vertical velocity.
Zero gradient lateral condition for W                        W relaxed to the finest WRF

     Longitude-altitude cross-section for potential temperature (contour) and vertical
     velocity (color) for the innermost domain (333m grid, 450 vertical levels).
   No relaxation in the vertical                   Vertical relaxation to the finest WRF nest

Longitude-altitude cross-section for potential temperature (contour) and vertical velocity
(color) for the innermost domain (333m grid).
     No relaxation                                  Vertical relaxation to the initial profiles


Longitude-altitude cross-section for potential temperature (contour) and vertical velocity
(color).
Topography for the microscale nest domain (04) (333m grid, 450
levels) and wind vector field at 12 km altitude. The black curve
shows the trajectory of balloon launched at (36.49 N, 118.84 W)
on April 1, 2006 at 7:50 UTC
Longitude (118.56 W, 117.42 W)-altitude cross-section at latitude 36.82 N for potential temperature (contour) and vertical
velocity (color) for the innermost microscale domain (333m grid); 300 grid points in horizontal directions, 450 vertical
levels.. Both upper and lateral boundary conditions are relaxed to the finest WRF nest. The time is 8:00 UTC, April 1, 2006.
Upper: longitude(118.56W, 117.42W)-altitude cross-section at latitude 36.82N for Richardson number. Lower:
cross-section for the shear field for the innermost microscale domain (333m grid); 300 grid points in horizontal
directions, 450 vertical levels. The time is 8:00 UTC, April 1, 2006.
Eastward and northward wind profiles from balloon measurments during T-REX
(black), from the finest WRF (red), and from the innermost miscroscale nest (blue).
The balloon was launched at (36.49 N, 118.84 W) on April 1, 2006 at 7:50 UTC.

				
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posted:3/14/2010
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