Versions Compared

Old Version 3

changes.mady.by.user Bob Owens

Saved on

compared with

New Version 4

changes.mady.by.user Bob Owens

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

  • the atmosphere affects the ocean through its wind, heat and net exchange of moisture by precipitation and/or evaporation
  • the ocean affects the atmosphere through its sea-surface temperature, ocean surface current and ice concentration.

The HRES* and HRES and ENS use the atmosphere-wave-ocean coupling framework from the start of the forecast.  This is because it is important to capture two-way feedback between the atmosphere and the sea-surface temperatures, sea-ice extent and ocean waves (e.g. a slow-moving tropical cyclone can cool the sea surface).  

...

These data are assimilated by NEMOVAR.

 

...

Handling of Sea Ice

Throughout the forecast period the changing extent of sea-ice and the variation of the ice shelf with time have important effects upon the energy and moisture balance at the atmosphere/surface boundary. The Louvain-la-Neuve Sea Ice Model (LIM2) is a prognostic sea-ice model that deals with the dynamic and thermodynamic evolution of the sea surface so that sea-ice cover evolves dynamically.  It is incorporated into the dynamic ocean model.  The  The ice extent will change through the forecast period in response to sea temperatures and air temperatures, ocean currents and wind.

Sea-surface temperature (SST) and ice concentration

Sea-surface temperature are initialised using analyses received daily from the Met Office (OSTIA, 5 km resolution). Additionally NEMO, and the LIM2 subprogram within it, forecast changes in the sea-surface temperature (SST) and sea ice evolution.  Output from these programs are used interactively by all IFS atmospheric models.  HRES and ENS use the same initial ice extent.

Note: ECMWF uses LIM2 which is an earlier version of the Louvain-la-Neuve sea ice model currently available (Version 3.6)    

The impacts of differently-evolving SST and ice cover distributions should be considered when comparing different forecasts, even when they are from the same data time.


Image Added

Fig2.1.11: Sequence of sea-ice and sea-surface temperatures from the ENS CTRL run data time 00UTC 27 April 2017.  T+0hr (00UTC 27 April 17), T+120hr (00UTC 02 May 17),  T+240hr (00UTC 07 May 17), and  T+360hr (00UTC 12 May 17).  On such plots the climatological average sea ice cover is shown in pink (contour and stippling, for >50%), just discernible in the northern Gulf of Bothnia and in the White Sea.   Dark purple areas (SST between 0C and -2C) are prone to ice formation if not already in existence.   Areas of sea ice are shown as turquoise. 

Note: 

  • Movement of ice (turquoise) in the northern Gulf of Bothnia  due to the winds.
  • Steady rise of sea-surface temperatures in the Black Sea, and especially in the shallow waters of both the Sea of Azov and the northern Caspian Sea.  In the White Sea (east of Finland, top of plot) sea ice cover is less than the climatological average for this time of year.  Using these plots, the user can assess where sea ice cover is above/below average.

Three-Dimensional Data Assimilation  - NEMOVAR

...