Recents Improvements in LMZ Code

Lucio Torrisi WG2-COSMO GM, Bucharest 2006

Recents Improvements in LMZ Code

Lucio TORRISI

CNMCA – Pratica di Mare (Rome)

[email protected]


Introduction• A z-coordinate version of LM (LMZ) has been

developed at DWD using the cut cell approach (Steppeler et al., 2002: MWR).

• LMZ should provide more accurate precipitation and wind forecasts in mountainous regions than the terrain following coordinate version of LM (LMTF).

• LMZ core needs to be intensively tested and evaluated, before other development effort is done.

• A number of real forecast tests with LMZ/LMTF was performed (Steppeler and Torrisi, 2006: Adv. Num. Sem. presentation). An improvement in total precipitation forecast associated with small amount of convective precipitation was found for LMZ.


Overview• LM/LMZ configuration.

• Problem: underestimation of convection

• Problems in parallel machines

• Case study: precipitation plots for LMZ, LMTF and LMTF op.

• Summary

• Proposal for future developments



Domain size 465 x 385 (previous EuroLM domain)

Grid spacing 0.0625 (7 km)

Number of layers 35

Time step 10 sec

Forecast range 30 hrs

Initial time of model run 00 UTC

Lateral boundary conditions and initial state Op. IFS (preproc. with CNMCA-IFS2LM)

L.B.C. update frequency 3 hrs

Orography Filtered (eps = 0.1) + Extra Filtering

Prognostic precipitation Off

Turbulence parameterization Explicit Prognostic TKE (imode_turb=2)

Interval between two calls of turbulence 1 time step

Turbulence parameterization

R.damping: filter iteration number 10

R. damping: filter length 1

LM (3.20+) and LMZ (1.5+) configuration


6h Acc.Total Precipitation: LMZ Old code: spline interpolation of phys./dyn. tendencies and imode_turb=2


6h Convective Rain: LMZ Old code: spline interpolation of phys./dyn. tendencies and imode_turb=2


Underestimation of Convective Precipitation in LMZ

• Error in the trigger of convection, since dqvdt (qv advection + qv vertical turbulent flux) and qvsflx (qv surface flux) not computed– qv vertical turbulent flux for imode_turb=2 (qvtens in

turbdiff) added to dqvdt (for imode_turb=1 explicit correction not added; fixed also in LM official code)

– qv advection interpolated to physics grid (in swap_tendencies) and added to dqvdt

– qvsflx computed (in z_slow_tendencies)

• Error in the computation of physical tendencies, since radiation and convection tendencies not added to the other ones (in src_z_leapfrog).


LMZ on Parallel Machines

• Other bugs were found running LMZ on parallel machines: – boundary exchange of wind tendencies in TKE

prognostic turbulence scheme missing (only for imode_turb=2 in turbdiff)

– uncorrect final index in computation of flux limiters (in fluxlim)

– extension of subdomain size for a correct setting of horizontal boundary conditions in cut cells missing (in z_horizontal_advection)

• LMZ 1.5 upgrade to LM 3.20 (CIRA performed that one to 3.17) including also the option of the spline interpolation of phys./dyn. tendencies present in LMZ 1.4.


6h Acc.Total Precipitation: LMZSpline interpolation of physical tendencies and imode_turb=2


6h Acc.Total Precipitation: LMZLinear interpolation of phys./dyn. tendencies and imode_turb=2


6h Acc. Rain: Sp./Lin. Int. Tend. LMZ

LMZ (Lin.Int.Tend.)

Convective

Grid-scale

LMZ (Spl.Int.Tend.)


Old LMZ LMZ

6h Accumulated Rain: Old/New LMZConvective

Grid-scale


6h Acc.Total Precipitation: LMTF imode_turb=2


6h Acc.Total Precipitation: LMTF/LMZ LMTF LMZ

FC 00-06 h

FC 06-12 h


6h Acc.Total Precipitation: LMTF/LMZ

FC 12-18 h

FC 18-24 h

LMTF LMZ


6h Acc.Total Precipitation: LMTF/LMZLMTF LMZ

FC 24-30 h


6h Accumulated Rain: LMTF/LMZ

LMZLMTF

Convective

Grid-scale


6h Acc.Total Precipitation: LMTF (op.)Implicit prognostic TKE turbulence scheme (imode_turb=1) + bug correction


6h Acc. Tot. Precipit.: LMTF (op.)/LMZLMTF (op.) LMZ

FC 00-06 h

FC 06-12 h


6h Acc. Tot. Precipit.: LMTF (op.)/LMZ

FC 12-18 h

FC 18-24 h

LMTF (op.) LMZ


6h Acc. Tot. Precipit.: LMTF (op.)/LMZLMTF (op.) LMZ

FC 24-30 h


6h Accum. Rain: LMTF (op.) / LMZ

LMZ

Convective

Grid-scale

LMTF (op.)


6h Acc. Tot. Precipit.: LMTF (op.)/LMTFLMTF (op.) LMTF

FC 00-06 h

FC 06-12 h


6h Acc. Tot. Precipit.: LMTF (op.)/LMTF

FC 12-18 h

FC 18-24 h

LMTF (op.) LMTF


6h Acc. Tot. Precipit.: LMTF (op.)/LMTFLMTF (op.) LMTF

FC 24-30 h


6h Accum. Rain: LMTF (op.) / LMTFConvective

Grid-scale

LMTF (op.) LMTF


Accumul. Precipitation Comparison

Domain mean (max) 30 hr total precipitation

1.667 (177.1) 2.933 (177.5) 1.863 (110.4)

Domain mean (max) 30 hr grid-scale rain

.7413 (51.4) 1.004 (140.2) .9212 (96.5)

Domain mean (max) 30 hr convective rain

.9138 (176.9) 1.889 (110.1) .9075 (62.3)

LMZ LMTF LMTF op.


Objective verification results



~ 100 events

LMTF op. for this case study seems to be better than LMZ.LMTF produces a larger amount of precipitation than LMZand LMTF.Does the explicit TKE prognostic turbulence scheme workcorrectly?



~ 850 fc-obs


• Some bugs were fixed in LMZ code for solving the underestimation of convection precipitation and the problems with parallel machines.

• The spline interpolation of the dynamical / physical tendencies does not seem to work correctly (spots of very large precipitation). The linear one seems to give satisfying results.

• For a case study, LMZ forecasts less and slightly smoother precipitation than LMTF. The amount of accumulated total precipitation of LMTF op. (imode_turb=1) and LMZ are pretty similar. LMTF op. forecasts less convective precipitation than LMTF.

• Comparison of surface variable forecasts with observations shows that LMTF op. performs better than LMZ and LMTF.

Summary


• Wait for new LM 3.21, upgrade LMZ to this version and release new LMZ (1.6?)

• Include recent improvements in z-dynamics on the new version

• Improve computational efficiency of z-coordinate code

• Other: implicit vertical advection, use of implicit turbulence parameterization, microphysics, etc.

Proposal for Future Developments

Documents

Recents Improvements in LMZ Code