the new multi-layer snow model

Eidgenössisches Departement des Innern EDIBundesamt für Meteorologie und Klimatologie MeteoSchweiz

The new multi-layer snow model

Guy de Morsier1, Jean-Marie Bettems1,Ekaterina Machulskaya2

1MeteoSwiss 2DWD

COSMO General Meeting

Offenbach, 7 September 2009

2 COSMO General Meeting 2009 | COLOBOC PP Multi-layer snow model Guy de Morsier et ali

Overview

• Update of the multi-layer snow model• Available data for validations• Validation experiments• Results from the 2 layer snow model• Conclusions• Outlook


Update of the multi-layer snow model• Now in COSMO 4.7

• new fields with ke_snow levelsT_SNOW_M mean temperature of the snow layer (K)DH_SNOW_M layer thickness between interfaces (m)WL_SNOW_M liquid water content in the snow (m H2O)WT_SNOW_M total (liquid+solid) water content (m H2O)

• GRIB details checked with Uli Schättler• Start mechanisms:

• laf* files read and write all necessary variables• re-start files continue computing snow model• cold-start initialise snow variables from old 1

layer model• Additional CPU cost: less than 1% for 2 layers

• Scientific documentation available• Technical documentation:

• description of new fields• switches, namelists• tuning parameters


Available data for validation (i)

• MSG quality weighted snow mask onCOSMO-7 and COSMO-2 grid

• IMIS measurement at ca. 90 Swiss stations between 1800 and 3000mAMSL from WSL Institute for Snow and Avalanche Research, SLF http://www.slf.ch/lawineninfo/zusatzinfos/Archiv/index_EN.

• SLF snow height analysis using all IMIS/ENET & NOAA data.

• Operational snow analysis: COSMO-7, COSMO-2

• SNOWPACK finite element model of layered snow structures (including phase change, water transport and snow drifting) at7 Swiss stations.


Available data for validation (ii)

SLF analysis: original 1km resolution Re-grided with “fieldextra”:


Validation experiments

• Winter from September 2007 to May 2008

• COSMO-7 results are from the operational data assimilation including a daily merge of the snow analysis snow analysis uses surface observations and the snow

mask derived from Meteosat Second Generation SEVIRI (temporal composite)

• ReferenceTERRA stand-alone (COSMO SVAT with a single snow layer) driven by hourly atmospheric analysis including precipitation for the whole period without snow analysis

• New snow modelSame as reference but with 2 layer snow model (2LSM)


Validation experiments

Bias = 2LSM - REF [m]REF is TERRA stand-alone

without snow analysis.

Time series of domain mean [m] for 2LSM, COSMO-7 and REF

REF has less snow than COSMO-7 2LSM has more snow on the

orography

Spurious precipitation at lateral boundary (qi in IFS, lmixcld=.F.)


Percent Correct Classification (MSG) 6.6km

PCC(hits +correctneg.)

C-7


REF

MSGQualityMask

SNOWpresent


2LSM

hits=3.4% fa=2.8% cn=93.2% mis=0.6%hits=4% fa=0.0% cn=96% mis=0%

hits=3.4% fa=2.4% cn=93.6% mis=0.6%


Compare with SLF and MSG data at 6.6kmPCC (hits+cor.neg.) SLF PCC (hits+cor.neg.) REF

MSG Quality MaskSNOW analysed by SLF:

36 cases

hits=54.7% fa=41.9% cn=3.4% mis=0% hits=41.4% fa=8.8% cn=46.7% mis=3.1%

PCC (hits+cor.neg.) 2LSM

hits=41.4% fa=7.9% cn=47.1% mis=3.6%


Validation with SLF data at 6.6kmBias (COSMO-7 – SLF) [m]

Period:September 8, 2007 to May 31, 2008COSMO-7 only 35 cases.REF & 2LSM only 36 cases.

REF has too little snow 2LSM has too much snow

Bias (REF – SLF) [m]

Bias (2LSM – SLF) [m]


Results with 2 layer snow model (2LSM)Bias (2LSM – SLF) [m] ZOOM _ SNOWPACK stations

: OK Period: September 2, 2007 to May 31, 2008 : + : - EVERY day : |h|>300m

Obs!


Results with 2 layer snow model (2LSM)

OK Period: September 2, 2007 to May 31, 2008 EVERY day

Station at 2240min the Western Alps

Model at 2097m

h = -143m



Too little! Period: September 2, 2007 to May 31, 2008 EVERY day

Station at 1510mon the NorthWestern slope of theAlps

Model at1462m

h = -48m



Too little but Period: September 2, 2007 to May 31, 2008good ablation EVERY day

Station at 1650mon the NorthWestern slope of theAlps

Model at1654m

h = 4m



OK Period: September 2, 2007 to May 31, 2008 EVERY day

Station at 2230m

Next grid point South

Model at2177m

h = -53m



: OK Period: September 2, 2007 to May 31, 2008 : + : - EVERY day : |h|<300m

Obs!

Bias (2LSM – SLF) [m] ZOOM _ SNOWPACK stations



Too much Period: September 2, 2007 to May 31, 2008

Station at 2430m

In the Alps

Model at2479m

h = 49m



OK Period: September 2, 2007 to May 31, 2008

Station at 2450m

2 grid points to the East

Model at2350m

h = -100m



Obs! Period: September 2, 2007 to May 31, 2008

Station at 2195m

Within the Alps

Model at2192m

h = -3m

dubious observations!

possiblewind ablation



SNOWPACK Period: September 2, 2007 to May 31, 2008 stations!

Height difference 9m

-47m

Northslope of the Alps

2 neighbor grid points:North South

dubious observations?

or possibleaccumulation



OK but… Period: September 2, 2007 to May 31, 2008

Station at 1340m

Northslope of theAlps

Model at1331m

h = -9m

Problem when merging the analysis (red) with the new model


Conclusions• Slightly better snow/no snow with multi layer snow model

over Northern Europe• In Eastern Europe and over orography the new snow model

produces larger snow depth• The systematic underestimation of the snow height by the

original snow model is largely removed by using the2 layer snow model

• The multi layer snow model works well at different altitudesin complex topography but might overestimate the snow height in some areas

Findings: better representation of the ablation period (Spring)

with the 2 layer snow model


Outlook

Snow model:• check other snow model variables (SNOWPACK):

snow water content (liquid and total), snow temperature• look at wet and dry periods and spatial distribution of precip.• evaluate temporal evolution also outside of the Alps• re-compute winter 2007-2008 with full 3D model with

COSMO-7 and COSMO-2• in particular evaluate effect of higher resolution

Snow analysis:• Adapt to better use the good information

provided by the new snow model

the new multi-layer snow model

Documents