Introducing the Lokal-Modell LME at the German Weather Service

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Introducing the Lokal-Modell LMEat the German
Weather Service

• Jan-Peter Schulz
• Deutscher Wetterdienst
• 27th EWGLAM and 12th SRNWP Meeting 2005

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The expansion of the LM domain has been requested
by the following (internal) DWD customers
LME LM Europe

• Aviation consulting
• Sea traffic consulting
• Particle dispersion modelling

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Modifications from LM to LME

• Number of grid points per layer enhanced from
  325 x 325 to 665 x 657, mesh size unchanged at
  7 km x 7 km

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LME LM Europe

• Model Configuration
• Grid spacing 0.0625 ( 7 km)
• 665 x 657 grid points per layer
• 40 vertical layers
• Timestep 40 sec
• Daily runs at 00, 12, 18 UTC, 78h
• Boundary Conditions
• Interpolated GME forecasts with
• ds 40 km and 40 layers (hourly)
• Hydrostatic pressure at lateral
• boundaries
• Data Assimilation
• Nudging analysis scheme
• Variational soil moisture analysis
• SST analysis at 00 UTC
• Snow depth analysis every 6 hrs

Model Domain of LME
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Modifications from LM to LME

• Number of grid points per layer enhanced from
  325 x 325 to 665 x 657, mesh size unchanged at
  7 km x 7 km
• Number of layers increased from 35 to 40.
  Lowest model layer now 10 m above ground (before
  34 m)
• Coordinate system rotated differently. LME grid
  points do not exactly match with LM grid points
  (important for post processing).
• Forecast period enhanced from 48h to 78h
• New multi-layer soil model with solution of heat
  conduction equation, inclusion of the effects
  of freezing/melting of soil water and improved
  snow model
• Planned operational introduction 28 September
  2005

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Configuration of the New Multi-Layer Soil Model
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Multi-Layer Soil Model
In order to demonstrate the capabilities of the
new multi-layer soil model the following
forecasts were carried out 24 November 2004, 00
UTC 24h. 1. Without freezing/melting of soil
water 2. With freezing/melting of soil water The
grid point Essen (Germany) is considered. Shown
are the soil temperature T_SO, the soil water
content W_SO and the soil ice content W_SO_ICE.
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Variational Soil Moisture Analysis (SMA)
The SMA is active in LME since 3 May 2005, 00
UTC. Before switching on the SMA in LME the
verification results for 2-m temperature were of
lower quality for LME than for LM. Meanwhile,
the verification results for LME improved
continuously, as expected, and have reached the
level of the LM results.
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Behaviour of the SMA (07 June 2005)
Moisture increment by SMA Upper soil
layers Lower soil layers
2-m temperature forecast error
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Behaviour of the SMA (07 June 2005)
Solar net radiation at the ground
Total cloud cover
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Behaviour of the SMA (07 June 2005)
Moisture change (increment) during the model
forecast Upper soil layers Lower soil layers
Solar net radiation at the ground
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Soil moisture
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Experiments at DWD
Comparison of operational weather forecasts of LM
and LME.
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LME
LM
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LME
GME
March 2005, 00 UTC forecasts LME domain (land and
sea)
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Verification results
There is positive trend in the simulated
precipitation amount during the forecasts of LME
which is not present in LM or the global model
GME. Furthermore, when comparing LME and GME it
turns out that evaporation over sea is
considerably higher in LME. Therefore, an LME
experiment has been carried out where evaporation
over sea is reduced by adjusting one parameter in
the surface layer scheme.
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Conclusions

• LM and LME give generally very similar forecasts
  on the LM domain.
• But in some cases the LME solution deviates from
  the LM solution and the weather given by the
  driving model. LME is more able to develop its
  own weather regime in the interior of the model
  domain.
• Objective verification shows some advantages for
  LME gusts, but some disadvantages for mean sea
  level pressure and 2-m temperature. The latter
  can be explained by the fact that the SMA was not
  active in LME in this period.

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Conclusions

• There is a positive trend in the simulated
  precipitation amount during the forecasts of LME.
• This trend can be substantially reduced by
  reducing evaporation over sea. By this,
  atmospheric water vapour content is decreased
  which leads to less intense cyclogenesis. This
  improves the negative bias in surface pressure.