Real-time simulations of weather in Iceland
(contact persons: Olafur Rögnvaldsson and Haraldur Olafsson)

The operational simulations for Iceland presented here are carried on with the the numerical Model MM5. The output is processed within the framework of IDL, using the home-made MM52IDL software. The system provides new simulations based on a new analysis/BC-run from the ECMWF system every 6 hours. The forecasts are available 7-8 hours after the analysis time. Simulations based on GFS BC-data are available about 5 hours after the analysis time. The horizontal resolution is 9 km for the 6 days forecast, and 3 km for the 36 h forecast. Vertically the model uses 40 levels.

Actual model results

The basic selection in the upper left corner of the page concerns the data basis used for MM5 initialization:

GFS: MM5 initialization by NOAA GFS data
    36 hour forecast, horizontal resolution 3 km, data presented every hour

ECMWF: MM5 initialization by ECMWF data
    168 hour forecast, horizontal resolution 9 km, data presented every 3 hours
    36 hour forecast, horizontal resolution 3 km, data presented every hour

The following information is presented (selection in the top bar):
  1) 2D fields of meteorological parameters (Yfirlitskort or Ladshlutar)
       temperature at 2 m above ground and surface pressure (Hiti)
       wind speed and winddirection at the second lowest sigma level, roughly 40 m above the ground (Vindur)
       and (in addition to both quantities above) the precipitation (Urkoma, vindur og hiti)
  2) Model soundings (Haloftaspa)
  3) Meteograms (Punktspar)

MM5 sensitivity simulations for the Hofsjokull area
(contact person: Günther Zängl)

These MM5 simulations are performed in a semi-idealized mode, combining realistic topogaphy (Iceland surrounded by water) with idealized time-dependent large-scale flow conditions. There are three interactively nested model domains (6.75 km, 2.25 km and 750 m), with the finest one covering the Hofsjökull area and the 2.25-km domain covering most of Iceland. The simulations exclude radiative processes but include parameterizations for boundary-layer and cloud processes (but the large-scale humidity is chosen to be quite low, so there are only shallow clouds due to orographic lifting). The ambient flow is time-dependent, being almost at rest initially. During the first 6 hours of the simulation, the flow is accelerated by imposing a horizontal pressure gradient at the lateral boundaries, which is in geostrophic balance (except for the boundary layer) with the wind field prescribed at the lateral boundaries. During the next 6 hours, the lateral boundary conditions are kept constant, allowing the flow in the model interior to reach a quasi-steady state via geostrophic adjustment. Between 12h and 18h, the imposed wind field is again decelerated to zero, and the simulation is then continued for 6 additional hours. The flow does not reach a quasi-steady state during this final phase because the rapid deceleration leads to substantial internal oscillations, but this shuld not affect the analysis of the preceding time period. In the present series of simulations, the maximum ambient wind speed is 15 m/s at sea level with a linear increase to 25 m/s at 250 hPa. So far, there is no directional shear, and the wind direction takes values of 180, 225, 270, 315 and 360, respectively.

MM5 Simulations

J. Reuder, H. Olafsson, S. Mayer       last modified: 13.02.2007