Introducing the Lokal-Modell LMEat the German Weather Service

Jan-Peter Schulz

Deutscher Wetterdienst

COSMO General Meeting 2005

The expansion of the LM domain has been requested

by the following (internal) DWD customers:

• Aviation consulting

• Sea traffic consulting

• Particle dispersion modelling

LME: LM Europe

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

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

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

Configuration of the New Multi-Layer Soil Model

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 water2. 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.

Soil temperature without freezing/ melting

-5

-4

-3

-2

-1

0

1

2

3

4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time [h]

°C

T_SO 1

T_SO 2

T_SO 3

Soil water content without freezing/ melting

0

2

4

6

8

10

12

14

16

18

20

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time [h]

mm

W_SO 1

W_SO 2

W_SO 3

Soil temperature with freezing/ melting

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time [h]

°C

T_SO 1

T_SO 2

T_SO 3

Soil water content with freezing/ melting

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time [h]

mm

W_SO 1

W_SO 2

W_SO 3

Soil ice content with freezing/ melting

0

0,5

1

1,5

2

2,5

3

3,5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time [h[

mm

W_SO_ICE 1

W_SO_ICE 2

W_SO_ICE 3

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.

Behaviour of the SMA (07 June 2005)

2-m temperature forecast error

Moisture increment by SMA

Upper soil layers

Lower soil layers

Behaviour of the SMA (07 June 2005)

Solar net radiation at the ground Total cloud cover

Behaviour of the SMA (07 June 2005)

Solar net radiation at the ground

Moisture change (increment) during the model forecast

Upper soil layers

Lower soil layers

Experiments at DWD

Comparison of operational weather forecasts of LM and LME.

LMELM

LME GME

March 2005, 00 UTC forecasts

LME domain (land and sea)

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 outwhere evaporation over sea is reduced by adjustingone parameter in the surface layer scheme.

Kinetic Energy

Kinetic Energy

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.

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.

• Atmospheric kinetic energy is increasing during LME forecasts. This may be a hint that sub-grid scale orographic effects still need to be considered in LME (like in GME).