j. helmert, g. zängl, m. raschendorfer, d. mironov, h. frank, b. ritter

J. Helmert, G. Zängl, M. Raschendorfer, D. Mironov, H. Frank, B. Ritter

Enhancement of the single layer snow model in TERRA: Global

numerical experiments

Outline

Computing the snow density

Snow depth, snow heat conductivity

Scalar roughness length over snow

Global numerical experiments

Single layer snow model

sT

snowT

sTsh

1soT

snowf )1( snowf

radQ

SWEs ,

Snow depth, heat conductivity, snow density:

ft

SWEh

nw

s

s)(

sn

sfsnn

sns PSWE

PTSWEt

)()( ,1

sfs P,,

nns SWE,

88.1

22.2

w

ns

s

Routine

Snow density: Experiment

fs

sns

n

ns

n

fs

sns

n

wfns

PSWESWE

PSWEhh

,1

1

,

)(

fs

sns

ns

nns PSWE

PSWE

,

1

fsfs hP ,,,

ns

nns hSWE ,,

Case study: Snow storm „Daisy“January 2010

Pictures from Tagesschau.de

PEPS 2010010812

Experiment: Daisy 2010010800 96h GME

Experiment: Daisy 2010010800 96h GME

Experiment: Daisy 2010010800 96h GME

Fresh snow

Snow depth

Snow density

ROUTI - EXP

ROUTI - EXP

The main camp for the SHEBA project was based around the CCG Ice Breaker DeGroseilliers

Baltimore site with ridge in background.

Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment

http://www.esrl.noaa.gov/psd/psd3/arctic/sheba/

http://www.crrel.usace.army.mil/sid/SeaIceDynamics/SHEBA.htm

Scalar roughness length over snow

Scalar roughness length over snow

Experiment: additional variable for z0t: gz0s:

Minimum: zT= 1.E-4 m

Andreas et al., 2004 Ice station Weddel

GME Exp

Tzszst

szs

zfzfz

gzSWESWE

SWEf

0,00,0

0min0,

)1(

Example:

SWE=40mm, SWEmin=10mmbeta_s=0.408s^2/mz0=10cm

f_s=0.09z0t=9.1cm

Scalar roughness length over snow: SURFEX

Experiment 7667

Computing the adapted snow density with implications for snow depth, snow heat conductivity

Scalar roughness length over snow

Winter 2009/2010; first month: December 2009

Verification T850 BIAS

Verification G500 ANOC

Verification

Europe

East Sibiria

North America

EXP 7667 SNOW 02.12.2009-31.12.2009 00 UTC i192f

Global Verification

SK: -0.57SK: 2.37 SK: -0.39

SK: -4.21 SK: -1.88 SK: -0.27

SK: 1.32 SK: 0.22 SK: 0.69

T_2M TDD_2M P_SURF

North-West SibiriaSK: -4.03

SK: 0.45 SK: -3.82

South-West SibiriaSK: -4.74

SK: -0.14 SK: -2.74

Routine snow density formulation leads to underestimation of snow depth, overestimation of snow heat conductivity

Revised formulation could alleviate to a certain degree this problem

Introduction of scalar roughness length over snow accounts for decrease in roughness length with increasing grid point snow amount

Verification of EXP7667 for December 2009 shows positive impact of model changes for regions with warm 2m-temperature bias

Conclusions