zong-liang yang guo-yue niu hua su the university of texas at austin modeling frozen soil and...

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Zong-Liang Yang Guo-Yue Niu Hua Su The University of Texas at Austin Modeling Frozen Soil and Subgrid Modeling Frozen Soil and Subgrid Snow Cover in CLM Snow Cover in CLM CCSM LWGM March 28, 2006 www.geo.utexas.edu/climate

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  • Zong-Liang YangGuo-Yue NiuHua SuThe University of Texas at AustinModeling Frozen Soil and Subgrid Snow Cover in CLM CCSM LWGMMarch 28, 2006

    www.geo.utexas.edu/climate

  • NCAR Community Land Model (CLM)a 10-layer soil sub-model a 5-layer snow sub-modela topography-based runoff schemean explicit solution of the freezing and thawing of soil watersub-grid landunits, soil columns, and plant functional types

    New developments at University of Texas at Austin

    Improved TOPMODEL (Yang and Niu, 2003; Niu and Yang, 2003; SIMTOP: Niu et al., 2005)Improved frozen soil scheme (Niu and Yang, 2006)Snow-vegetation canopy interaction (Niu and Yang, 2004)Global unconfined aquifer/groundwater component (SIMGM: Niu et al., 2006, Yang et al., 2006a)Stochastic subgrid snow cover in CLM (Yang et al., 2006b)Frozen Soil | Subgrid Snow

  • Topography-based Runoff Scheme (SIMTOP)Yang and Niu (2003), Niu and Yang (2003), Niu and Yang et al. (2005, JGR-Atmospheres)Frozen Soil | Subgrid Snow

  • Radiative Transfer within the Vegetation Canopy: Two-Stream Model Accounting for the 3-D Canopy Structure(Niu and Yang, 2004, JGR-Atmos)Frozen Soil | Subgrid Snow

  • Canopy Water and Ice BalanceFrozen Soil | Subgrid Snow(Niu and Yang, 2004, JGR-Atmos)

  • Frozen Soil Affects ClimateThermal effects: increases the inertia of the climate system by enhancing the soil heat capacity through diurnal and seasonal freezing-thawing cycles.Hydrological effects: affects snowmelt runoff and soil hydrology by reducing soil permeability. In turn, runoff from Arctic river systems affects ocean salinity and thermohaline circulation.Ecological effects: affects ecosystem diversity and productivity and carbon decomposition and release.Frozen Soil | Subgrid Snow

  • When soil water freezes, the water closest to soil particles remains in liquid form due to the absorptive and capillary forces exerted by the soil particles.

    The supercooled liquid water at subfreezing point is equivalent to a depression of the freezing-point (0C).

    However, CLM does not account for these properly.Supercooled Liquid Water Exists in Frozen SoilFrozen Soil | Subgrid Snow

  • Frozen Soil Is Permeable?Early Russian literature and recent works showed that frozen soil has very weak or no effects on runoff Russian laboratory and field experiments in 1960s and 1970s (Koren, 1980).Shanley and Chalmers (1999) in Sleepers River, USA.Lindstrom et al. (2002) in a 0.59 km2 watershed in North Sweden.Stahli et al. (2004): Dye tracer techniques revealed that water can infiltrate into deep soil through preferential pathways which are air-filled pores at the time of freezing. Frozen Soil | Subgrid Snow

  • The Frozen Soil Scheme in the NCAR CLMT > TfrzT TfrzFrozen Soil | Subgrid Snow

  • The Frozen Soil Scheme in the NCAR CLMThe freezing and thawing processes are analogous to those in snow. It has three main flaws:

    Matrix potential discontinuous at the freezing point.

    High ice fraction: the ice content is solely determined by the heat content. Thus, the ice fraction of a soil layer can reach 100% when the heat content is sufficient to freeze all the water.

    Low permeability: The hydraulic conductivity and the matrix potential are a function of liquid water only. Thus, when there is no or little liquid water in the soil, the soil permeability becomes too low. Frozen Soil | Subgrid Snow

  • Introduction of supercooled liquid water by using the freezing-point depression equationMost researchersKoren et al., 1991Frozen Soil | Subgrid Snow

  • Relaxes the dependence of hydraulic properties on the soil ice contentFractional impermeable areaFrozen Soil | Subgrid Snow

  • Model Results CTRLKorenNewIce FractionInfiltrationSoil MoistureNew scheme has less ice, higher infiltration, and greater soil water Frozen Soil | Subgrid Snow

  • Soil Moisture ProfilesTotal waterLiquid waterIce FractionCTRLKorenNewNew scheme has more total soil water in the upper 0.5 m soil Frozen Soil | Subgrid Snow

  • Effects on RunoffCTRLNewThe baseline CLM produces higher peaks and lower baseflow in recession period, while the NEW scheme improves the runoff simulation Frozen Soil | Subgrid Snow

  • Effects on Runoff in Six Large RiversCLM produces higher peaks and lower baseflow in recession period, while the NEW scheme improves the runoff simulation Frozen Soil | Subgrid Snow

  • Modeled Snow Depth Earlier runoff does not result from earlier snowmeltFrozen Soil | Subgrid Snow

  • Change in Water Storage (Snow + Soil)The water storage of CLM reaches its maximum in March, while NEW in AprilFrozen Soil | Subgrid Snow

  • GRACE and CLMGRACE-derived terrestrial water storage anomalies compare well with those modeled by CLM augmented by soil freezing-thawing cycles and water table dynamics.ObAmazonFrozen Soil | Subgrid SnowYang et al., 2006, Niu and Yang, 2006, Niu et al., 2006)

  • Supercooled liquid water is improperly treated in the baseline CLM (easy to get 100% soil ice). We made the following changes:implemented the supercooled liquid water by using the freezing-point depression equation.introduced a concept of fractional unfrozen ground in CLM.relaxed the dependence of hydraulic properties on ice content.The resultant scheme produces better simulations of runoff (comparing with GRDC and ArcticNet) and soil water storage (comparing with GRACE). See Niu and Yang (2006), J. Hydromet. (in press). SummaryFrozen Soil | Subgrid Snow

  • Subgrid Snow Cover and Surface Temperature Frozen Soil | Subgrid Snow

  • Winter Warm Bias in NCAR SimulationsCCM3/CLM2 T42 - OBS CCSM3.0 T85 - OBS (Dickinson et al., 2006)(Bonan et al., 2002)Why?Excessive LW due to excessive low clouds Anomalously southerly winds Frozen Soil | Subgrid Snow

  • Snow Cover Fraction and Air TemperatureListon (2004) JCLFrozen Soil | Subgrid Snow

  • New Snow Cover Fraction SchemeThe new SCF scheme improves the simulations of snow depth in mid-latitudes in both Eurasia and North America.Eurasia (55-70N,60-90E)North America (40-65N,115-130W)Frozen Soil | Subgrid Snow

  • Representations of Snow Cover and SWENatureClimate ModelingRemote SensingA land grid has multiple PFTs plus bare ground.Energy and mass balances. For each PFT-covered area, on the ground, one mean SWE, one SCF. Canopy interception and canopy snow cover.Pixels.Integrated signals from multi-sources (e.g., snow, soil, water, vegetation), depending on many factors (e.g., view angle, aerosols, cloud cover, etc). Each pixel, MODIS provides one SCF. AMSR provides one SWE.Frozen Soil | Subgrid Snow

  • Theory of Sub-grid Snow CoverListon (2004), Representing Subgrid Snow Cover Heterogeneities in Regional and Global Models. Journal of Climate.The snow distribution during the accumulation phase can be represented using a lognormal distribution function, with the mean of snow water equivalent and the coefficient of variation as two parameters.The snow distribution during the melting phase can be analyzed by assuming a spatially homogenous melting rate applied to the snow accumulation distribution.Liston (2004) JCLFrozen Soil | Subgrid Snow

  • CV values are assigned to 9 categories. Liston (2004) JCLListon (2004) JCLThe Coefficient of Variation (CV)Frozen Soil | Subgrid Snow

  • Relationship Between Snow Cover & SWEAccumulation phase: SCF is constant =1; SWE is the cumulative value of snowfall.Melting phase: The SCF and SWE relationship can be described by equations (1) and (2), with the cumulative snowfall, snow distribution coefficient of variation (CV) and melting rate as the parameters.(1) Snow Cover Fraction(2) SWEListon (2004) JCLFrozen Soil | Subgrid Snow

  • SCF-SWE in Different MethodsListon (2004) JCLQuestions:

    Can we derive CV values from MODIS and AMSR?How is the CV method compared to traditional methods?Each curve represents a distinct SCF-SWE relationship in melting seasonFrozen Soil | Subgrid Snow

  • DatasetsDaily SWE from AMSR Oct 2002Dec 2004Daily Snow Cover Fraction from MODIS Oct 2002Dec 2004 (MOD10C1 CMG 0.05 0.05) GLDAS 11 3-hourly, near-surface meteorological data for 20022004Frozen Soil | Subgrid Snow

  • A Flowchart for Deriving a Grid-scale SCFThree records for each sub-grid: snow cover fraction, cloud cover fraction,confidence indexFrozen Soil | Subgrid Snow

  • Upscale 0.05 snow cover data to a coarse grid (0.25, 0.5 or 1) using the upscaling algorithm described above; Average SWE to the same grid.Quality check the snow cover and SWE data for each analyzed grid and for each day to make sure there are no missing data or no cloud obscuring SCF data.Steps to Derive CVCompare MODIS SCF and AMSR SWE at the same gridEstimate snowfall at the same grid from other sourcesOptimize CV by calibrating the theory-derived SCF against the MODIS SCF through a Nonlinear-Discrete Genetic AlgorithmDesign a SCF retrieving algorithm from SWE, CV, , Dm Frozen Soil | Subgrid Snow

  • Recursive method:If snowfall at day t is zero, use Snowmelt starts from the first day when SCF is less than 1. This criteria can be relaxed to a smaller value like 0.9 because the MODIS data may underestimate SCF in forest-covered areas.to calculate Dm, then use to calculate SCFIf snowfall t at day t is larger than zero, and Dm is the cumulative melting rate at day t-1, then if t>Dm, then the cumulative snowfall as the mean of snow distribution, , would be replaced by +t-Dm, and follow the same method in (1) to calculate SCF; if tDm, then directly follow the method in (1) to calculate SCF(1)(2)This SCF retrieving algorithm is used to derive grid- or PFT-specific CV based on SCF data and SWE data with Genetic Algorithm Optimization.Retrieving SCF from SWE, CV,and DmFrozen Soil | Subgrid Snow

  • 1 1 Grid (4647N, 107108W) Grassland in Great Plains 6 January23 March, 2003Characterizing Sub-grid-scale Variability of Snow Water Equivalent Using MODIS and AMSR Satellite DatasetsIn the optimization, the relationship between snow cover fraction and SWE follows the stochastic scheme of Liston (2004).The optimized CV value is used in CLM (next slide).Frozen Soil | Subgrid Snow

  • Modeling SWE at Sleepers River, Vermont Using CLM with a Stochastic Representation of Sub-grid Snow VariabilityCV=1.38CV=0.8Blue: SimulatedRed: ObservedFrozen Soil | Subgrid Snow

  • Values of CV in CLMBarren LandVegetated LandFrozen Soil | Subgrid Snow

  • PFT Type1PFT Type2PFT Type3PFT Type4Geographic Distribution of CV in CLMFrozen Soil | Subgrid Snow

  • Monthly SWE from 2002 to 2004Frozen Soil | Subgrid Snow

  • Daily SCF for Northwest U.S. 2002-2004Frozen Soil | Subgrid Snow

  • Daily SCF for High-latitude Regions 2002-2004Frozen Soil | Subgrid Snow

  • Daily Trad for Northwest U.S. 2002-2004Frozen Soil | Subgrid Snow

  • Daily Trad for High-latitude Regions 2002-2004Frozen Soil | Subgrid Snow

  • SummaryThe high latitude wintertime warm bias in NCAR climate model simulations can be caused by an improper parameterization of snow cover fraction.

    A procedure is developed to estimate CV using MODIS and AMSR data.

    The CV method (i.e. stochastic subgrid snow cover scheme) is implemented in CLM and the results are promising.

    The density-dependent SCF scheme is sensitive to the parameters used.We will look at coupled land-atmosphere simulations using CAM3.Frozen Soil | Subgrid Snow

    Thank you for the nice introduction.

    Good morning, ladies and gentlemen. It is my honor to be invited here. It is my pleasure to talk about the relationships between the vegetation growth and precipitation in the southwestern United States and Mexico.

    A quiz here. Does anyone know which picture was taken before the monsoon? Which one was after?

    Where these pictures were taken? At about what time?

    Excellent.Thank you for the nice introduction.

    Good morning, ladies and gentlemen. It is my honor to be invited here. It is my pleasure to talk about the relationships between the vegetation growth and precipitation in the southwestern United States and Mexico.

    A quiz here. Does anyone know which picture was taken before the monsoon? Which one was after?

    Where these pictures were taken? At about what time?

    Excellent.