Experiments on COSMOsnow parameterization

J. Helmert, E. Machulskaya, B. Ritter

with support of

H. Ruppert, J. Förstner, Th. Hanisch

Background

COSMO experiments motivated from GME changes on

- snow albedo- snow cover fraction- snow albedo evolution

Aim: consistent physics in NWP models decrease of cold bias in T_2M during winter

COSMO experiments:

8050: 18.12.2010 – 02.03.2011 snow fraction8232: 18.02.2011 – 17.04.2011 snow albedo evolution8233: 18.02.2011 – 17.04.2011 snow albedo evolution + snow fraction

Csalb_snow_min = 0.400 0.500 ! snow for forest free surfaces Csalb_snow_max = 0.700 0.850 ! snow for forest free surfaces Csalb_snow_fe = 0.200 0.270 ! snow with evergreen forest Csalb_snow_fd = 0.200 0.320 ! snow with deciduous forest

Dutra et al., 2010

Snow albedo

Snow aging

)1(min,max, agesagess SS

dmm

tPS

PCTe

d

t

S

snownewage

rainsnowd

t

oldage

/20

02)1(

5.12

4

dmm

tPS

d

tS

snownewage

oldage

/5

28

Temporal evolution ofsnow albedo

Aging function S

New approach

1,

cr

snsn W

WMINf

1,

1.0

/ snsnsn

WMINf

Dutra et al., 2010

Wcr = 15mm

Hcr = 0.1m

1,

cr

snsn H

HMINf

Snow fraction

ROUTI

EXP

Snow Fraction ROUTI GME

Snow Fraction EXP GME

Snow Fraction ROUTI COSMO

Snow Fraction EXP COSMO

SYNOP VERIF EXP 8050 vs ROUTI18.12.10-30.01.11, 00 UTC

BIAS

RMSE

T2M TD2MD TMIN TMAX

PS DD FF VW

T2M TD2MD TMIN TMAX

PS DD FF VW

BIAS

T2M TD2MD TMIN TMAX

PS DD FF VW

RMSE

T2M TD2MD TMIN TMAX

PS DD FF VW

SYNOP VERIF EXP 8050 vs ROUTI31.01.11-28.02.11, 00 UTC

Snow melting 2011032112

Snow melting 2011032112

Snow melting 2011032112

Snow melting 2011032112

Snow melting 2011032112

BIAS

T2M TD2MD TMIN TMAX

PS DD FF VW

RMSE

T2M TD2MD TMIN TMAX

PS DD FF VW

SYNOP VERIF EXP 8032 vs ROUTI18.03.11-17.04.11, 00 UTC

SYNOP VERIF EXP 8033 vs ROUTI18.03.11-17.04.11, 00 UTC

BIAS

T2M TD2MD TMIN TMAX

PS DD FF VW

RMSE

T2M TD2MD TMIN TMAX

PS DD FF VW

Summary

• COSMO experiments showed the expected impact of snow parameterization changes on total albedo and T_2M • Parameterization changes are independent of used snow model (single layer, multilayer)

• Results should be used also in future COSMO with TILE

• Further routine accompanying experiments (single layer, multi layer) intended for autum 2011

• Aim: Routine change in Spring 2012

SYNOP VERIF EXP 8050 vs ROUTIRANGE 1, 12 UTC, BIAS

SYNOP VERIF EXP 8050 vs ROUTIRANGE 1, 12 UTC, RMSE

SYNOP VERIF EXP 8050 vs ROUTIRANGE 2, 12 UTC, BIAS

SYNOP VERIF EXP 8050 vs ROUTIRANGE 2, 12 UTC, RMSE