An empirical formulation of An empirical formulation of soil ice fraction based on in soil ice fraction based on in

situ observationssitu observations

Mark Decker, Xubin ZengMark Decker, Xubin Zeng

Department of Atmospheric Sciences, Department of Atmospheric Sciences, the University of Arizonathe University of Arizona

CCSM Land/BGC, March 28, 2006, Boulder

(GRL 33, L05402, doi:10.1029/2005GL024914, 2006)

OutlineOutline

IntroductionIntroduction– Purpose, Motivation, Fundamentals, General Purpose, Motivation, Fundamentals, General

Model DescriptionModel Description

Dataset OverviewDataset OverviewMethodologyMethodology– Calculation of ice fractionCalculation of ice fraction

Parameterization ComparisonParameterization Comparison– ECMWF, NCEP Noah, ProposedECMWF, NCEP Noah, Proposed

Offline Simulation ResultsOffline Simulation Results

PurposePurpose

In situ soil water and temperature In situ soil water and temperature observationsobservations

Derive a relation between soil ice and Derive a relation between soil ice and temperature for use in climate and temperature for use in climate and weather predictionweather prediction

Compare new and current Compare new and current parameterizationsparameterizations

Test the sensitivity of CLMTest the sensitivity of CLM

MotivationMotivation

Why be concerned with frozen soil water?Why be concerned with frozen soil water?

– Water ice transition alters various time scalesWater ice transition alters various time scalesDiurnalDiurnal

– Latent Heat releaseLatent Heat release

SeasonalSeasonal– Infiltration of Spring RunoffInfiltration of Spring Runoff

FundamentalsFundamentals

Soil water doesn’t freeze at 0Soil water doesn’t freeze at 0oo Celsius? Celsius?– Dissolved saltsDissolved salts– Capillary forcesCapillary forces– Forces between minerals and soil waterForces between minerals and soil water– Heterogeneous CompositionHeterogeneous Composition

DatasetsDatasets

Various sourcesVarious sources– CEOP CAMPCEOP CAMP– GEWEX GAMEGEWEX GAME– National Snow Ice Data CenterNational Snow Ice Data Center

Data from various climate regimesData from various climate regimes

DatasetsDatasets

SiteSite LonLon LatLat Depths (cm)Depths (cm) DatesDates

AK ShrubAK Shrub 64.9 N64.9 N 164.7 W164.7 W 16,2616,26 9/2000-9/20019/2000-9/2001

AK WoodlandAK Woodland 64.9 N64.9 N 163.7 W163.7 W 16,4316,43 9/2000-9/20019/2000-9/2001

AK ForestAK Forest 64.9 N64.9 N 163.7 W163.7 W 15,3115,31 9/2000-9/20019/2000-9/2001

AK TundraAK Tundra 70.4 N70.4 N 148.5 W148.5 W 2323 9/1999-8/20019/1999-8/2001

Mongolia GrassMongolia Grass 46 N46 N 107 E107 E 1515 10/2002-10/200310/2002-10/2003

Siberia TundraSiberia Tundra 71.6 N71.6 N 128.9 E128.9 E 1010 10/2000-10/200110/2000-10/2001

ObservationsObservations

MethodologyMethodology

Assume total soil moisture constantAssume total soil moisture constant– ii = = tt – – ll

DefineDefine

– t

iif

lit

ss the Saturated Volumetric Moisture the Saturated Volumetric Moisture

– 10 km soil composition data10 km soil composition data– CLM formulationCLM formulation

Observed fObserved fii

Current FormulationsCurrent FormulationsECMWFECMWF

]}4

)2(sin[1{

2

frzcapi

TT

0i T > Tfrz + 1

Tfrz - 3 < T < Tfrz +1

capi

capi

T < Tfrz - 3

cap = 0.323 m3/m3

Current FormulationsCurrent Formulations

016.273

)()1( 2

T

Tc

L

g b

s

itik

s

•Noah

•If divergent ck=0 then solved explicitly

•CLM3

0i

ti

T < Tfrz

T >Tfrz

T < Tfrz

Modeled fModeled fii vs. Observations vs. Observations

SiteSite tt//ss obsobs ECMWFECMWF NoahNoah

AK Shrub 16 AK Shrub 16 cmcm 0.9660.966 0.7620.762 0.7080.708 0.8210.821

AK Shrub 26 AK Shrub 26 cmcm 0.8220.822 0.8680.868 0.8320.832 0.8010.801

AK Wood 16 AK Wood 16 cmcm 0.8820.882 1.0001.000 0.7760.776 0.8100.810

AK Wood 43 AK Wood 43 cmcm 0.9020.902 0.9120.912 0.7570.757 0.8130.813

AK Forest 15 AK Forest 15 cmcm 0.9440.944 0.8380.838 0.7760.776 0.8180.818

AK Forest 31 AK Forest 31 cmcm 0.9020.902 0.7950.795 0.7570.757 0.8130.813

AK Tundra AK Tundra 19991999 0.9550.955 0.7520.752 0.7170.717 0.8200.820

AK Tundra AK Tundra 20002000 0.9640.964 0.7430.743 0.7100.710 0.8210.821

AK Tundra AK Tundra 20012001 0.9720.972 0.7950.795 0.7040.704 0.8220.822

Mongolia Mongolia GrassGrass 0.2440.244 0.1500.150 1.0001.000 0.5270.527

Proposed FormulationProposed Formulation

)1exp(

)}()(exp{1

s

t

frzs

t

t

iTT

• Derived to capture observed trends

•rapid increase of i/t to a value greater than 0.8 as T drops below Tfrz when t/s is greater than 0.8

• i/t increases more slowly as T decreases for small t/s

• Partially based on Noah formulation

• and are adjustable parameters

•Chosen as 2 and 4 respectively

ComparisonComparison Noah b = 4.5

Noah b = 5.5

Noah b = 4.5 ck=0

Noah b = 5.5 ck=0

ECMWF

Proposed

Observations vs ProposedObservations vs Proposed

Sensitivity of CLMSensitivity of CLM

Offline NCEP Reanalysis ForcingOffline NCEP Reanalysis Forcing

T-42 ResolutionT-42 Resolution

20 Year run cycling 199820 Year run cycling 1998

Model Defined Initial ConditionModel Defined Initial Condition

Only Soil Ice Calculation Was AlteredOnly Soil Ice Calculation Was Altered

Results ECMWF-ControlResults ECMWF-ControlSensible Heat Flux

Latent Heat Flux

Ground Temperature

Results Noah-ControlResults Noah-ControlSensible Heat Flux

Latent Heat Flux

Ground Temperature

Results Proposed-ControlResults Proposed-ControlSensible Heat Flux

Latent Heat Flux

Ground Temperature

Results ProposedResults Proposed

Fi Proposed

Fi Difference

Proposed-Control

Summary of ResultsSummary of Results

All Three:All Three:– Showed a reduction in ground temperatureShowed a reduction in ground temperature– Drying of the soil columnDrying of the soil column– Reduction in sensible heat fluxReduction in sensible heat flux– Increase in ground heat flux to balance the change in Increase in ground heat flux to balance the change in

sensiblesensible– Reduction in latent heat fluxReduction in latent heat flux

The proposed formulation had a larger The proposed formulation had a larger magnitude and extent of all these changesmagnitude and extent of all these changes

SummarySummary

In situ data used toIn situ data used to– Calculate ratio of volumetric ice content to Calculate ratio of volumetric ice content to

total moisture content versus temperaturetotal moisture content versus temperature– Evaluate current model formulationsEvaluate current model formulations– Derive a new empirical formulationDerive a new empirical formulation

Sensitivity of CLM testedSensitivity of CLM tested– Reduction in ground temperatureReduction in ground temperature– Lowering of ice fractionLowering of ice fraction

Derivation of a New Maximum Snow Derivation of a New Maximum Snow Albedo Dataset Using MODIS DataAlbedo Dataset Using MODIS Data

M.Barlage, X.Zeng, H.Wei, K.Mitchell; GRL 2005M.Barlage, X.Zeng, H.Wei, K.Mitchell; GRL 2005

MotivationMotivationMaximum snow albedo is used as an end Maximum snow albedo is used as an end member of the interpolation from snow- to member of the interpolation from snow- to non-snow covered gridsnon-snow covered gridsCurrent dataset is based on 1-year of Current dataset is based on 1-year of DMSP observations from 1979DMSP observations from 1979Current resolution of 1°Current resolution of 1°Create new dataset using 4+ years of Create new dataset using 4+ years of MODIS data with much higher resolutionMODIS data with much higher resolution

Raw MODIS Albedo DataRaw MODIS Albedo Data•Tucson: little variation; no snow

•Minnesota: cropland; obvious annual cycle

•Canada: annual snow cycle; little summer variation

•Moscow: some cloud complications

How can you be sure it’s snow?How can you be sure it’s snow?

NDSINDSI: Exploiting the differences in spectral : Exploiting the differences in spectral signature between visible and NIR albedo.signature between visible and NIR albedo.

)64.1(6)55.0(4

)64.1(6)55.0(4

NDSI

NDSI and NDVI NDSI and NDVI

Final 0.05° Maximum Snow AlbedoFinal 0.05° Maximum Snow Albedo

Comparison with RKComparison with RK0.05deg MODIS RK Figure 5

High-resolution ImprovementsHigh-resolution Improvements

Application of MODIS Maximum Snow Albedo to WRF-NMM/NOAHApplication of MODIS Maximum Snow Albedo to WRF-NMM/NOAH

• WRF-NMM Model: 10min(0.144°) input dataset converted from 0.05° by simple average; model run at 12km; initialized with Eta output;

• Winter simulation: 24hr simulation beginning 12Z 31 Jan 2006

Comparison of MODIS Maximum Snow Albedo with CCSMComparison of MODIS Maximum Snow Albedo with CCSM

• Structure of CCSM maximum albedo is similar to MODIS maximum snow albedo

• Albedo of boreal regions is high compared to MODIS

• Albedo of high latitude open shrub/tundra is low compared to MODIS