RegCM Version 4.0 User's Guide - gforge
Contents
1. to intermediate loam to fine clay and different soil colors light to dark for the soil albedo calculations These are described in Dickinson et al 1986 In the latest release version additional modifications have been made to BATSin order to account for the subgrid variability of topography and landcover using a mosaic type approach Giorgi et al 2003a Thismodification adopts a regular fine scale surface subgrid for eachcoarse model grid cell Meteorological variables are disaggregatedfrom the coarse grid to the fine grid based on the elevationdifferences The BATS calculations are then performed separatelyfor each subgrid cell and surface fluxes are reaggregated onto thecoarse grid cell for input to the atmospheric model Thisparameterization showed a marked improvement in the representation ofthe surface hydrological cycle in mountainous regions Giorgi et al 2003a CLM optional The Community Land Model CLM Oleson et al 2008 is the land surface model developed by the National Center of Atmospheric Research NCAR as part of the Community Climate System Model CCSM described in detail in Collins et al 2006 CLM version 3 5 was coupled to RegCM for a more detailed land surface description option CLM contains five possible snow layers with an additional representation of trace snow and ten unevenly spaced soil layers with explicit solutions of temperature liquid water and ice water in each layer To account for land surfa2. 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 Soil texture type 6 6 6 6 7 8 6 3 6 6 5 12 6 6 6 6 5 6 6 0 Soil color type 5 3 4 4 4 4 4 1 3 3 2 1 5 5 5 4 3 4 4 0 Vegetation albedo for wavelengths 0 7 um 0 10 0 10 005 005 0 08 0 04 0 08 020 0 10 0 08 0 17 0 80 0 06 0 07 0 07 0 05 008 006 006 0 06 Vegetation albedo for wavelengths gt 0 7 um 0 30 0 30 023 023 0 28 020 0 30 0 40 0 30 0 28 0 34 0 60 0 18 0 20 0 20 023 0 28 0 24 0 18 0 18 Table 3 Resolution for CLM input parameters Input data Grid Spacing Lon range Lat range Glacier 0 05 x 0 05 179 975 89 975 Lake 0 05 0 05 179 975 89 975 Wetland 0 05 0 05 179 975 89 975 Land fraction 0 05 x 0 05 179 975 89 975 LAI SAI 0 5 x 0 5 179 75 89 75 PFT 0 5 x 0 5 179 75 89 75 Soil color 0 05 x 0 05 179 975 89 975 Soil texture 0 05 0 05 179 975 89 975 Max sat area 0 5 x 0 5 179 75 89 75 2 2 3 Planetary Boundary Layer Scheme The planetary boundary layer scheme developed by Holtslag et al 1990 is based on a nonlocal diffusion concept that takes into account countergradient fluxes resulting from large scale eddies in an unstable well mixed atmosphere The vertical eddy flux within the PBL is given by Fe Ke x 11 Oz where Yc is a countergradient transport term describing nonlocal transport due to dry deep convection The eddy diffusivity is given
3. distance on grid actual distance on earth and its value is usually close to one varying with latitude The projections in the model preserve the shape of small areas so that dx dy everywhere but the grid length varies across the domain to allow a representation of a spherical surface on a plane surface Map scale factors need to be accounted for in the model equations wherever horizontal gradients are used 2 Model Description 2 Dynamics The model dynamic equations and numerical discretization are described by Grell et al 1994 Horizontal Momentum Equations Opus 5 dp vu m yoo RI Op 4 98 fp v p 0 ox Op v 2 d i Lp fp u Fav 3 7 t tn nto where and v are the eastward and northward components of velocity is virtual temperature is geopotential height f is the coriolis parameter R is the gas constant for dry air m is the map scale factor for either the Polar Stereographic Lambert Conformal or Mercator map projections 6 Fg Fy represent the effects of horizontal and vertical diffusion and p p p Continuity and Sigmadot 6 Equations p dp v m P ami RV 4 The vertical integral of Equation 4 is used to compute the temporal variation of the surface
4. easier Also a new website has been developed where users can freely download the entire RegCM system as well as all of the input data necessary for a simulation The RegCM modeling system has four components Terrain ICBC RegCM and Postprocessor Terrain and ICBC are the two components of RegCM preprocessor Terrestrial variables including elevation landuse and sea surface temperature and three dimensional isobaric meteorological data are horizontally interpolated from a latitude longitude mesh to a high resolution domain on either a Rotated and Normal Mercator Lambert Conformal or Polar Stereographic projection Vertical interpolation from pressure levels to the 6 coordinate system of RegCM is also performed surfaces near the ground closely follow the terrain and the higher level surfaces tend to approximate isobaric surfaces Since the vertical and horizontal resolution and domain size can vary the modeling package programs employ parameterized dimensions requiring a variable amount of core memory and the requisite hard disk storage amount is varied accordingly 1Y 1 IY JX 1 1 J 2 1 JX Figure 2 Schematic representation showing the horizontal Arakawa B grid staggering of the dot and cross grid points 12 The RegCM Model Horizontal and Vertical Grid It is useful to first introduce the model s grid configuration The modeling system usually gets and analyzes its data on pressure surfaces but these have to be
5. interpolated to the model s vertical coordinate before input to the model The vertical coordinate is terrain following Figure 1 meaning that the lower grid levels follow the terrain while the upper surface is flatter Intermediate levels progressively flatten as the pressure decreases toward the top of the model A dimensionless o coordinate is used to define the model levels where p is the pressure p is a specified constant top pressure p is the surface pressure os p Pr 1 ps Pr It can be seen from the equation and Figure 1 that o is zero at the top and one at the surface and each model level is defined by a value of c The model vertical resolution is defined by a list of values between zero and one that do not necessarily have to be evenly spaced Commonly the resolution in the boundary layer is much finer than above and the number of levels may vary upon the user demand The horizontal grid has an Arakawa Lamb B staggering of the velocity variables with respect to the scalar variables This is shown in Figure 2 where it can be seen that the scalars T q p etc are defined at the center of the grid box while the eastward u and northward v velocity components are collocated at the corners The center points of grid squares will be referred to as cross points and the corner points are dot points Hence horizontal velocity is defined at dot points Data is input to the model the preprocessors do the necessary interpolatio
6. layer PC Personal Computer PIRCS Project to Intercompare Regional Climate Simulations PFT plant functional type PSU Pennsylvania State University PWC Physics of Weather and Climate RCM Regional Climate Model RegCM REGional Climate Model RegCMI REGional Climate Model version 1 RegCM2 REGional Climate Model version 2 RegCM2 5 REGional Climate Model version 2 5 RegCM3 REGional Climate Model version 3 RegCMA REGional Climate Model version 4 RegCNET REGional Climate Research NETwork RMIP Regional Climate Model Intercomparison Project SIMEX the Simple EXplicit moisture scheme SST sea surface temperature SUBEX the SUB grid EXplicit moisture scheme USGS United States Geological Survey JJA June July and August JJAS June July August and September JFM January February and March 24
7. pressure in the model dp u m dp v m ar a yum P After calculation of the surface pressure tendency the vertical velocity in sigma coordinates 6 is computed at each level in the model from the vertical integral of Equation 4 1 Q0p 5 p u m 27 E ra dot 6 where 0 is a dummy variable of integration and 0 0 10 Thermodynamic Equation and Equation for Omega The thermodynamic equation is Op T Qp vT m e n Qs 05 gae RT O FT 7 Cpm O Pr pas Cpm where is the specific heat for moist air at constant pressure is the diabatic heating T represents the effect of horizontal diffusion represents the effect of vertical mixing and dry convective adjustment and is dp Q p c6 8 POO 8 where op 9 d w ELT 9 The expression for Cpm 1 0 84 where cp is the specific heat at constant pressure for dry air and q is the mixing ratio of water vapor Hydrostatic Equation The hydrostatic equation is used to compute the geopotential heights from the virtual temperature 7 atal cp ae i 10 dln o p p 1 4 where T 1 0 6084 qv qc and q are the water vapor cloud water or and rain water snow mixing ratios 11 2 2 Physics 2 21 Radiation Scheme RegCMA uses the r
8. vegetation land cover 2l rs 3 Resolution for CLM input parameters rs 1 Introduction 11 History The idea that limited area models LAMs could be used for regional studies was originally proposed by Dickinson et al 1989 and Giorgi 1990 This idea was based on the concept of one way nesting in which large scale meteorological fields from General Circulation Model GCM runs provide initial and time dependent meteorological lateral boundary conditions LBCs for high resolution Regional Climate Model RCM simulations with no feedback from the RCM to the driving GCM The first generation NCAR RegCM was built upon the NCAR Pennsylvania State University PSU Mesoscale Model version 4 in the late 1980s Dickinson et al 1989 Giorgi 1989 The dynamical component of the model originated from the MMA which is a compressible finite difference model with hydrostatic balance and vertical o coordinates Later the use of a split explicit time integration scheme was added along with an algorithm for reducing horizontal diffusion in the presence of steep topographical gradients Giorgi et al 1993a b As a result the dynamical core of the RegCM is similar to that of the hydrostatic version of Mesoscale Model version 5 MM5 Grell et al 1994 For application of the MMA to climate studies a number of physics parameterizations were replaced mostly in the areas of radiative transfer and land surface physics which led to
9. vegetation land cover Parameter Land Cover Vegetation Type 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 VI Max fractional vegetation cover 0 85 0 80 080 080 080 090 0 80 000 0 60 080 0 35 0 00 0 80 0 00 0 00 0 80 080 080 080 0 80 Difference between max fractional vegetation cover and cover at 269 0 6 0 1 0 1 0 3 0 5 0 3 0 0 0 2 0 6 0 1 0 0 0 4 0 0 0 0 0 2 0 3 0 2 0 4 0 4 Roughness length m 0 08 0 05 100 1 00 080 200 0 10 0 05 0 04 0 06 0 10 001 0 03 0 0004 0 0004 0 10 0 10 080 03 0 3 Displacement height m 0 0 0 0 9 0 9 0 0 0 180 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Min stomatal resistence s m 45 60 80 80 120 60 60 200 80 45 150 200 45 200 200 80 120 100 120 120 Max Leaf Area Index 6 2 6 6 6 6 6 0 6 6 6 0 6 0 0 6 6 6 6 6 Min Leaf Area Index 0 5 0 5 5 1 1 5 0 5 0 0 5 0 5 0 5 0 0 5 0 0 5 1 3 0 5 0 5 Stem dead matter area index 0 5 4 0 2 0 2 0 2 0 2 0 2 0 0 5 0 5 2 0 2 0 2 0 2 0 2 0 2 0 2 0 2 0 2 0 2 0 2 0 Inverse square root of leaf dimension m 10 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 Light sensitivity factor m W 0 02 0 02 0 06 0 06 0 06 006 0 02 0 02 0 02 0 02 0 02 0 02 0 02 0 02 0 02 0 02 0 02 0 06 0 002 0 02 Upper soil layer depth mm 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Root zone soil layer depth mm 1000 1000 1500 1500 2000 1500 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 2000 2000 2000 Depth of total soil mm 3000 3000
10. within RegCM J Geophys Res Atmospheres 105 D24 29 579 29 594 2000 Patterson J C and P F Hamblin Thermal simulation of a lake with winter ice cover Limn Oceanography 33 323 338 1988 Slingo J M A parameterization for the shortwave radiative properties of water clouds J Atmos Sci 46 1419 1427 1989 Small E E and L C Sloan Simulating the water balance of the aral sea with a coupled regional climate lake model J Geophys Res 104 6583 6602 1999 Steiner A L J S Pal S A Rauscher J L Bell N S Diffenbaugh A Boone L C Sloan and F Giorgi Land surface coupling in regional climate simulations of the West African monsoon Climate Dynamics 33 6 869 892 2009 21 Sundqvist H E Berge J E Kristjansson The effects of domain choice on summer precipitation simulation and sensitivity in a regional climate model J Climate 11 2698 2712 1989 Zeng X A prognostic scheme of sea surface skin temperature for modeling and data assimilation Geophysical Research Letters 32 114605 2005 Zeng X M Zhao and R E Dickinson Intercomparison of bulk aerodynamic algoriths for the computation of sea surface fluxes using toga coare and tao data J Climate 11 2628 2644 1998 22 BATS Biosphere Atmosphere Transfer Scheme 1 Biosphere Atmosphere Transfer Scheme version le CAM Community Atmosphere Model CAPE convective available potential energ
11. Model version 4 RegCMA is theMassachusetts Institute of Technology MIT scheme More detailed descriptions can be found in Emanuel 1991 andEmanuel and Zivkovic Rothman 1999 The scheme assumes that the mixing in clouds ishighly episodic and inhomogeneous as opposed to a continuousentraining plume and considers convective fluxes based on anidealized model of sub cloud scale updrafts and downdrafts Convection is triggered when the level of neutral buoyancy is greaterthan the cloud base level Between these two levels air is liftedand a fraction of the condensed moisture forms precipitation while theremaining fraction forms the cloud The cloud is assumed to mix withthe air from the environment according to a uniform spectrum ofmixtures that ascend or descend to their respective levels of neutralbuoyancy The mixing entrainment and detrainment rates are functionsof the vertical gradients of buoyancy in clouds The fraction of thetotal cloud base mass flux that mixes with its environment at eachlevel is proportional to the undiluted buoyancy rate of change withaltitude The cloud base upward mass flux is relaxed towards thesub cloud layer quasi equilibrium In addition to a more physical representation of convection theMIT Emanuel scheme offers several advantages compared to theother RegCM4 convection options For instance it includes aformulation of the auto conversion of cloud water into precipitationinside cumulus clouds and ice processes are accoun
12. RegCM Version 4 0 User s Guide Nellie Elguindi Xungiang Bi Filippo Giorgi Badrinath Nagarajan Jeremy Pal Fabien Solmon Sara Rauscher and Ashraf Zakey Trieste Italy June 2010 Acknowledgements This paper is dedicated to those that have contributed to the growth of RegCM system over the past 20 years the members 800 of the RegCNET and the ICTP Abstract As one of the main aims of the Abdus Salam International Centre for Theoretical Physics ICTP is to foster the growth of advanced studies and research in developing countries the main purpose of this Regional Climate Model REGional Climate Model RegCM Tutorial Class Notes is to give model users a guide to learn the whole RegCM Model System The RegCM Tutorial Class is offered as a part of extended hands on lab sessions during a series of Workshops organized by the Physics of Weather and Climate PWC group at the ICTP RegCM was originally developed at the National Center for Atmospheric Research NCAR and has been mostly applied to studies of regional climate and seasonal predictability around the world The workshop participants are welcome to use RegCM for regional climate simulation over different areas of interest The RegCM is available on the World Wide Web at https eforge escience lab org gf project regcm wiki Contents 1 Introduction 1 1 History 1 2 The RegCM Model Horizontal and Vertical Grid 1 3 Map Projections and Map Sca
13. a and Schubert closure Grell et al 1994 and 2 the Fritsch and Chappell closure Fritsch and Chappell 1980 hereafter refered to as AS74 and FC80 respectively 1 Kuo Scheme Convective activity in the Kuo scheme is initiated when the moisture convergence M in a column exceeds a given threshold and the vertical sounding is convectively unstable A fraction of the moisture convergence moistens the column and the rest is converted into rainfall PY according to the following relation pU M 1 15 B is a function of the average relative humidity RH of the sounding as follows 20 RH RH 0S5 B e 1 0 otherwise oP Note that the moisture convergence term includes only the advective tendencies for water vapor However evapotranspiration from the previous time step is indirectly included in M since it tends to moisten the lower atmosphere Hence as the evapotranspiration increases more and more of it is converted into rainfall assuming the column is unstable The latent heating resulting from condensation is distributed between the cloud top and bottom by a function that allocates the maximum heating to the upper portion of the cloud layer To eliminate numerical point storms a horizontal diffusion term and a time release constant are included so that the redistributions of moisture and the latent heat release are not performed instantaneously Giorgi and Bates 1989 Giorgi and Marinucci 1991 2 Grell Scheme The Grell scheme Gre
14. adiation scheme of the NCAR CCM3 which is described in Kiehl et al 1996 Briefly the solar component which accounts for the effect of H20 CO and follows the 6 Eddington approximation of Kiehl et al 1996 It includes 18 spectral intervals from 0 2 to 5 um The cloud scattering and absorption parameterization follow that of Slingo 1989 whereby the optical properties of the cloud droplets extinction optical depth single scattering albedo and asymmetry parameter are expressed in terms of the cloud liquid water content and an effective droplet radius When cumulus clouds are formed the gridpoint fractional cloud cover is such that the total cover for the column extending from the model computed cloud base level to the cloud top level calculated assuming random overlap is a function of horizontal gridpoint spacing The thickness of the cloud layer is assumed to be equal to that of the model layer and a different cloud water content is specified for middle and low clouds 2 2 2 Land Surface Models BATS default BATS is a surface package designed to describe the role of vegetation and interactive soil moisture in modifying the surface atmosphere exchanges of momentum energy and water vapor see Dickinson et al 1993 for details The model has a vegetation layer a snow layer a surface soil layer 10 cm thick or root zone layer 1 2 m thick and a third deep soil layer 3 m thick Prognostic equations are solved for the s
15. amic algorithms 26 SH PaCpau 9 27 LH paLeu q 28 where and are mean wind components is the frictional wind velocity is the temperature scaling parameter qx is the specific humidity scaling parameter p is air density Cpa is specific heat of air and Le is the latent heat of vaporization For further details on the calculation of these parameters refer to Zeng et al 1998 2 2 7 Prognostic Sea Surface Skin Temperature Scheme RegCMA contains a option which allows for the computation of sea surface skin temperature as a prognostic variable following the scheme of Zeng 2005 This allows for a realistic representation of the diurnal sea surface skin temperature leading to improvements in the surface fluxes thus air sea interactions The scheme is based on a two layer model which includes warm layer cool skin effects as described by Fairall et al Temperatures in the two layers are calculated using a one dimensional heat transfer equation and boundary conditions determined by surface to atmosphere fluxes latent sensible and radiative and a 3 m depth sea surface temperature taken from the prescribed SSTs 2 2 8 Pressure Gradient Scheme Two options are available for calculating the pressure gradient force The normal way uses the full fields The other way is the hydrostatic deduction scheme which makes use of a perturbation temperature In this scheme extra smoothin
16. by the nonlocal formulation z2 kwz 1 12 where k is the von Karman constant is a turbulent convective velocity that depends on the friction velocity height and the Monin Obhukov length and is the PBL height The countergradient term for temperature and water vapor is given by 13 where C is a constant equal to 8 5 and is the surface temperature or water vapor flux Equation 13 is applied between the top of the PBL and the top of the surface layer which is assumed to be equal to 0 1h Outside this region and for momentum Yc is assumed to be equal to 0 For the calculation of the eddy diffusivity and countergradient terms the PBL height is diagnostically computed from Ricr u h v h 14 g 9 8 A 9s where u h v h and the wind components and the virtual potential temperature at the PBL height g is gravity Ricr is the critical bulk Richardson number and is an appropriate temperature of are near the surface Refer to Holtslag et al 1990 and Holtslag and Boville 1993 for a more detailed description 2 2 4 Convective Precipitation Schemes Convective precipitation is computed using one of three schemes 1 Modified Kuo scheme Anthes 1977 2 Grell scheme Grell 1993 and 3 MIT Emanuel scheme Emanuel 1991 Emanuel and Zivkovic Rothman 1999 15 In addition the Grell parameterization is implemented using of two closure assumptions 1 the Arakaw
17. ce complexity within a climate model grid cell CLM uses a tile or mosaic approach to capture surface heterogeneity Each CLM gridcell contains up to four different land cover types glacier wetland lake and vegetated where the vegetated fraction can be further divided into 17 different plant functional types Hydrological and energy balance equations are solved for each land cover type and aggregated back to the gridcell level A detailed discussion of CLM version 3 implemented in RegCM3 and comparative analysis of land surface parameterization options is presented in Steiner et al 2009 Since CLM was developed for the global scale 12 Table 1 Land Cover Vegetation classes l Crop mixed farming 2 Short grass 3 Evergreen needleleaf tree 4 Deciduous needleleaf tree 5 Deciduous broadleaf tree 6 Evergreen broadleaf tree 7 Tall grass 8 Desert 9 Tundra 10 Irrigated Crop 11 Semi desert 12 Ice cap glacier 13 Bog or marsh 14 Inland water 15 Ocean 16 Evergreen shrub 17 Deciduous shrub 18 Mixed Woodland 19 Forest Field mosaic 20 Water and Land mixture several input files and processes were modified to make it more appropriate for regional simulations including 1 the use of high resolution input data 2 soil moisture initialization and 3 and an improved treatment of grid cells along coastlines For the model input data CLM requires several time invariant surface input parameters soil co
18. ds a very important and far reaching element of interaction between the simulated hydrologic cycle and energy budget calculations Changes in the model physics include a large scale cloud and precipitation scheme which accounts for the subgrid scale variability of clouds Pal et al 2000 new parameterizations for ocean surface fluxes Zeng et al 1998 and a cumulus convection scheme Emanuel 1991 Emanuel and Zivkovic Rothman 1999 Also new in the model is a mosaic type parameterization of subgrid scale heterogeneity in topography and land use Giorgi et al 2003b Other improvements in RegCM3 involve the input data The USGS Global Land Cover Characterization and Global 30 Arc Second Elevation datasets are now used to create the terrain files In addition NCEP and ECMWF global reanalysis datasets are used for the intial and boundary conditions Lastly improvements in the user friendliness of the model have been made New scripts have been included which make running the programs 0 0 Nile 0 1 N N Nile 7 4 0 3 4l 5 0 4 271 55 0 5 0 6 7 R 0 7 9 0 758 10 0 84 11 0 89 12 0 93 13 0 96 16 1 00 Ps 0 0 Figure 1 Schematic representation of the vertical structure of the model This example is for 16 vertical layers Dashed lines denote half sigma levels solid lines denote full sigma levels Adapted from the PSU NCAR Mesoscale Modeling System Tutorial Class Notes and User s Guide
19. egrees Celsius and Cacs is the autoconversion scale factor Precipitation is assumed to fall instantaneously SUBEX also includes simple formulations for raindrop accretion and evaporation The formulation for the accretion of cloud droplets by falling rain droplets is based on the work of Beheng 1994 and is as follows P acc CaccQPsum 24 where Pacc is the amount of accreted cloud water is the accretion rate coefficient and is the accumulated precipitation from above falling through the cloud 17 Precipitation evaporation is based on the work of Sundqvist et al 1989 and is as follows Povap Cevap 1 RH P P sum 25 where Pevap is the amount of evaporated precipitation and Cevap is the rate coefficient For a more detailed description of SUBEX and a list of the parameter values refer to Pal et al 2000 2 2 6 Ocean flux Parameterization 1 BATS BATS uses standard Monin Obukhov similarity relations to compute the fluxes with no special treatment of convective and very stable conditions In addition the roughness length is set to a constant i e it is not a function of wind and stability 2 Zeng The Zeng scheme describes all stability conditions and includes a gustiness velocity to account for the additional flux induced by boundary layer scale variability Sensible heat SH latent heat LH and momentum fluxes between the sea surface and lower atmosphere are calculated using the following bulk aerodyn
20. environment as fast as non convective processes destabilize it as follows ABE ABE HW _ NAM oC where ABE is the buoyant energy available for convection ABE is the amount of buoyant energy available for convection in addition to the buoyant energy generated by some of the non convective processes during the time interval Ar and NA is the rate of change of ABE per unit mp The difference ABE ABE can be thought of as the rate of destabilization over time ABE is computed from the current fields plus the future tendencies resulting from the advection of heat and moisture and the dry adiabatic adjustment In the latest RegCMA version by default we use a stability based closure assumption the FC80 type closure assumption that is commonly implemented in GCMs and RCMs In this closure it is assumed that convection removes the ABE over a given time scale as follows 19 20 mb 16 where is the ABE removal time scale The fundamental difference between the two assumptions is that the AS74 closure assumption relates the convective fluxes and rainfall to the tendencies in the state of the atmosphere while the FC80 closure assumption relates the convective fluxes to the degree of instability in the atmosphere Both schemes achieve a statistical equilibrium between convection and the large scale processes 3 MIT Emanuel scheme The newest cumulus convection option to the REGional Climate
21. g on the top is done in order to reduce errors related to the PGF calculation 2 2 9 Lake Model The lake model developed by Hostetler et al 1993 can be interactively coupled to the atmospheric model In the lake model fluxes of heat moisture and momentum are calculated based on meteorological inputs and the lake surface temperature and albedo Heat is transferred vertically between lake model layers by eddy and convective mixing Ice and snow may cover part or all of the lake surface In the lake model the prognostic equation for temperature is oT ac 2 where is the temperature of the lake layer and ke and km are the eddy and molecular diffusivities respectively The parameterization of Henderson Sellers 1986 is used to calculate ke and km is set to a constant value of 39 x 1077 m s except under ice and at the deepest points in the lake 29 18 Sensible and latent heat fluxes from the lake are calculated using the BATS parameterizations Dickinson et al 1993 The bulk aerodynamic formulations for latent heat flux F and sensible heat flux F are as follows F paCpYVa 45 z qa 30 PaCpCpVa Ts Ta 31 where the subscripts s and a refer to surface and air respectively pa is the density of air V is the wind speed 4 is specific humidity and T is temperature The momentum drag coefficient Cp depends on roughness length and the surface bulk Richardson number Under ice free cond
22. itions the lake surface albedo is calculated as a function of solar zenith angle Henderson Sellers 1986 Longwave radiation emitted from the lake is calculated according to the Stefan Boltzmann law The lake model uses the partial ice cover scheme of Patterson and Hamblin 1988 to represent the different heat and moisture exchanges between open water and ice surfaces and the atmosphere and to calculate the surface energy of lake ice and overlying snow For further details refer to Hostetler et al 1993 and Small and Sloan 1999 2 2 10 Aerosols and Dust Chemistry Model The representation of dust emission processes is a key element in a dust model and depends on the wind conditions the soil characteristics and the particle size Following Marticorena and Bergametti 1995 and Alfaro and Gomes 2001 here the dust emission calculation is based on parameterizations of soil aggregate saltation and sandblasting processes The main steps in this calculation are The specification of soil aggregate size distribution for each model grid cell the calculation of a threshold friction velocity leading to erosion and saltation processes the calculation of the horizontal saltating soil aggregate mass flux and finally the calculation of the vertical transportable dust particle mass flux generated by the saltating aggregates In relation to the BATS interface these parameterizations become effective in the model for cells dominated by desert and semi desert
23. land cover 19 References Climate Processes and Climate Sensitivity chap Modeling evapotranspiration processes for three dimensional global climate models pp 52 72 American Geophysical Union 1984 Anthes R A A cumulus parameterization scheme utilizing a one dimensional cloud model Mon Wea Rev 105 270 286 1977 Beheng D A parameterization of warm cloud microphysical conversion processes Atmos Res 33 193 206 1994 Briegleb B P Delta eddington approximation for solar radiation in the ncar community climate model J Geophys Res 97 7603 7612 1992 Collins W D et al The Community Climate System Model version 3 CCSM3 Journal of Climate 19 2122 2143 2006 Deardoff J W Efficient prediction of ground surface temperature and moisture with inclusion of a layer of vegetation J Geophys Res 63 1889 1903 1978 Dickinson P J Kennedy A Henderson Sellers and M Wilson Biosphere atmosphere transfer scheme bats for the ncar community climate model Tech Rep NCARE TN 275 STR National Center for Atmospheric Research 1986 Dickinson R E R M Errico F Giorgi and G T Bates A regional climate model for the western United States Climatic Change 15 383 422 1989 Dickinson R E A Henderson Sellers and P J Kennedy Biosphere atmosphere transfer scheme bats version le as coupled to the ncar community climate model Tech rep National Center for At
24. le Factors 2 Model Description 2 1 Dynamics xu mU noB ROVER E pace E 2 2 PhysIeS coe ead eo as oe we oe Pe Ie e e e 2 1 Scheme uersus xU b bow RUE RU e eg oe RI AD AU ae REO 252 27 SbandSurface Models Re eR Dex RU oe eee Aus 2 2 3 Planetary Boundary 2 24 Convective Precipitation Schemes 2 2 5 Large Scale Precipitation Scheme 2 2 6 Ocean flux Parameterization 2 2 7 Prognostic Sea Surface Skin Temperature Scheme 2 2 8 Pressure Gradient Scheme 2 3 so ls go IE E p ERE 22 9 Lake Model ae dese Udo be Oe ee p TORRE osos ue ied 2 2 10 Aerosols and Dust Chemistry Model List of Figures 1 Schematic representation of the vertical structure of the model This example is for 16 vertical layers Dashed lines denote half sigma levels solid lines denote full sigma levels Adapted from the PSU NCAR Mesoscale Modeling System Tutorial Class Notes and User s Guide 2 Schematic representation showing the horizontal Arakawa B grid staggering of the dot and cross 020m EGO xke PERCHE OUR Eus Quis cau ow eede YP Ra Less ds List of Tables 1 Land Cover Vegetation classes 2 BATS
25. ll 1993 similar to the 574 parameterization considers clouds as two steady state circulations an updraft and a downdraft No direct mixing occurs between the cloudy air and the environmental air except at the top and bottom of the circulations The mass flux is constant with height and no entrainment or detrainment occurs along the cloud edges The originating levels of the updraft and downdraft are given by the levels of maximum and minimum moist static energy respectively The Grell scheme is activated when a lifted parcel attains moist convection Condensation in the updraft is calculated by lifting a saturated parcel The downdraft mass flux mo depends on the updraft mass flux mj according to the following relation mo Bh s 17 h where J is the normalized updraft condensation Jy is the normalized downdraft evaporation and is the fraction of updraft condensation that re evaporates in the downdraft B depends on the wind shear and typically varies between 0 3 and 0 5 Rainfall is given by PU 1 p 18 Heating and moistening in the Grell scheme are determined both by the mass fluxes and the detrainment at the cloud top and bottom In addition the cooling effect of moist downdrafts is included Due to the simplistic nature of the Grell scheme several closure assumptions can be adopted RegCM4 s earlier version directly implements the quasi equilibrium assumption of AS74 It assumes that convective clouds stabilize the
26. lle Local versus nonlocal boundary layer diffusion in a global climate model J Climate 6 1993 Holtslag A M E I F de Bruijn and H L Pan A high resolution air mass transformation model for short range weather forecasting Mon Wea Rev 116 1561 1575 1990 Hostetler S W G T Bates and F Giorgi Interactive nesting of a lake thermal model within a regional climate model for climate change studies Geophysical Research 98 5045 5057 1993 Hsie E Y R A Anthes and D Keyser Numerical simulation of frontogenisis in a moist atmosphere J Atmos Sci 41 2581 2594 1984 Kiehl J T J J Hack G B Bonan B A Boville B P Breigleb D Williamson and P Rasch Description of the ncar community climate model ccm3 Tech Rep NCAR TN 420 STR National Center for Atmospheric Research 1996 Lawrence P and T Chase Representing a new MODIS consistent land surface in the Community Land Model CLM3 0 J Geophys Res 112 g01023 2007 Oleson e a Technical description of the Community Land Model CLM Tech Rep Technical Note NCAR TN 461 STR NCAR 2004 Oleson K W et al Improvements to the Community Land Model and their impact on the hydrological cycle Journal of Geophysical Research Biogeosciences 113 G1 2008 Pal J S E E Small and E A B Eltahir Simulation of regional scale water and energy budgets Representation of subgrid cloud and precipitation processes
27. lor soil texture percent cover of each land surface type leaf and stem area indices maximum saturation fraction and land fraction Lawrence and Chase 2007 Table 3 shows the resolution for each input parameter used at the regional scale in RegCM CLM compared to resolutions typically used for global simulations The resolution of surface input parameters was increased for several parameters to capture surface heterogeneity when interpolating to the regional climate grid Similar to Lawrence and Chase 2007 the number of soil colors was extended from 8 to 20 classes to resolve regional variations The second modification was to update the soil moisture initialization based on a climatological soil moisture average Giorgi and Bates 1989 over the use of constant soil moisture content throughout the grid generally used for global CLM By using a climatological average for soil moisture model spin up time is reduced with regards to deeper soil layers The third modification to the CLM is the inclusion of a mosaic approach for gridcells that contain both land and ocean surface types With this approach a weighted average of necessary surface variables was calculated for land ocean gridcells using the land fraction input dataset This method provides a better representation of coastlines using the high resolution land fraction data described in Table 3 For a more detailed description of CLM physics parameterizations see Oleson 2004 13 Table 2 BATS
28. mospheric Research 1993 Emanuel A scheme for representing cumulus convection in large scale models J Atmos Sci 48 21 2313 2335 1991 Emanuel K A and M Zivkovic Rothman Development and evaluation of a convection scheme for use in climate models J Atmos Sci 56 1766 1782 1999 Fairall C E Bradley J Godfrey G Wick J Edson and G Young Cool skin and warm layer effects on sea surface temperature Journal of Geophysical Research 101 1295 1308 Fritsch J M and C F Chappell Numerical prediction of convectively driven mesoscale pressure systems part i Convective parameterization J Atmos Sci 37 1722 1733 1980 Giorgi F Two dimensional simulations of possible mesoscale effects of nuclear war fires J Geophys Res 94 1127 1144 1989 Giorgi E Simulation of regional climate using a limited area model nested in a general circulation model J Climate 3 941 963 1990 Giorgi and T Bates The climatological skill of a regional model over complex terrain Mon Wea Rev 117 2325 2347 1989 Giorgi F and M R Marinucci Validation of a regional atmospheric model over europe Sensitivity of wintertime and summertime simulations to selected physics parameterizations and lower boundary conditions Quart J Roy Meteor Soc 117 1171 1206 199 Giorgi F G T Bates and S J Nieman The multi year surface climatology of a regional atmospheric model over
29. n to assure consistency with the grid the above variables are defined in the middle of each model vertical layer referred to as half levels and represented by the dashed lines in Figure 1 Vertical velocity is carried at the full levels solid lines In defining the sigma levels it is the full levels that are listed including levels at 0 and 1 The number of model layers is therefore always one less than the number of full sigma levels The finite differencing in the model is of course crucially dependent upon the grid staggering wherever gradients or averaging are represented terms in the equation 1 3 Map Projections and Map Scale Factors The modeling system has a choice of four map projections Lambert Conformal is suitable for mid latitudes Polar Stereographic for high latitudes Normal Mercator for low latitudes and Rotated Mercator for extra choice The x and y directions in the model do not correspond to west east and north south except for the Normal Mercator projection and therefore the observed wind generally has to be rotated to the model grid and the model u and v components need to be rotated before comparison with observations These transformations are accounted for in the model pre processors that provide data on the model grid Please note that model output of u and v components raw or postprocessed should be rotated to a lat lon grid before comparing to observations The map scale factor m is defined by m
30. oil layer temperatures using a generalization of the force restore method of Deardoff 1978 The temperature of the canopy and canopy foilage is calculated diagnostically via an energy balance formulation including sensible radiative and latent heat fluxes The soil hydrology calculations include predictive equations for the water content of the soil layers These equations account for precipitation snowmelt canopy foiliage drip evapotranspiration surface runoff infiltration below the root zone and diffusive exchange of water between soil layers The soil water movement formulation is obtained from a fit to results from a high resolution soil model Dic 1984 and the surface runoff rates are expressed as functions of the precipitation rates and the degree of soil water saturation Snow depth is prognostically calculated from snowfall snowmelt and sublimation Precipitation is assumed to fall in the form of snow if the temperature of the lowest model level is below 271 K Sensible heat water vapor and momentum fluxes at the surface are calculated using a standard surface drag coefficient formulation based on surface layer similarity theory The drag coefficient depends on the surface roughness length and on the atmospheric stability in the surface layer The surface evapotranspiration rates depend on the availability of soil water Biosphere Atmosphere Transfer Scheme BATS has 20 vegetation types Table 2 soil textures ranging from coarse sand
31. ted for by allowingthe auto conversion threshold water content to be temperaturedependent Additionally the precipitation is added to a single hydrostatic unsaturated downdraft that transports heat and water Lastly the MIT Emanuel scheme considers the transport of passive tracers 2 2 5 Large Scale Precipitation Scheme Subgrid Explicit Moisture Scheme SUBEX is used to handle nonconvective clouds and precipitation resolved by the model This is one of the new components of the model SUBEX accounts for the subgrid variability in clouds by linking the average grid cell relative humidity to the cloud fraction and cloud water following the work of Sundqvist et al 1989 The fraction of the grid cell covered by clouds FC is determined by RH RA nin s RAmin en where RH is the relative humidity threshold at which clouds begin to form and is the relative humidity where FC reaches unity FC is assumed to be zero when RH is less than RHmin and unity when RH is greater than RA max Precipitation P forms when the cloud water content exceeds the autoconversion threshold according to the following relation P Cop Qc FC Q FC 22 where 1 Cppr can be considered the characteristic time for which cloud droplets are converted to raindrops The threshold is obtained by scaling the median cloud liquid water content equation according to the following Co 22 Good Ver UL 23 where T is temperature in d
32. the first generation RegCM Dickinson et al 1989 Giorgi 1990 The first generation RegCM included the Biosphere Atmosphere Transfer Scheme BATS Dickinson et al 1986 for surface process representation the radiative transfer scheme of the Community Climate Model version 1 CCM1 a medium resolution local planetary boundary layer scheme the Kuo type cumulus convection scheme of Anthes 1977 and the explicit moisture scheme of Hsie et al 1984 A first major upgrade of the model physics and numerical schemes was documented by Giorgi et al 1993a b and resulted in a second generation RegCM hereafter referred to as REGional Climate Model version 2 RegCM2 The physics of RegCM2 was based on that of the NCAR Community Climate Model version 2 CCM2 Hack et al 1993 and the mesoscale model 5 Grell et al 1994 In particular the CCM2 radiative transfer package Briegleb 1992 was used for radiation calculations the non local boundary layer scheme of Holtslag et al 1990 replaced the older local scheme the mass flux cumulus cloud scheme of Grell 1993 was added as an option and the latest version of BATSIE Dickinson et al 1993 was included in the model In the last few years some new physics schemes have become available for use in the RegCM mostly based on physics schemes of the latest version of the Community Climate Model CCM Community Climate Model version 3 CCM3 Kiehl et al 1996 First the CCM2 radiati
33. the western united states J Climate 6 75 95 1993a Giorgi E M R Marinucci and G T Bates Development of a second generation regional climate model regcm2 i Boundary layer and radiative transfer processes Mon Wea Rev 121 2794 2813 1993b 20 Giorgi F X Q Bi and Y Qian Indirect vs direct effects of anthropogenic sulfate on the climate of east asia as simulated with a regional coupled climate chemistry aerosol model Climatic Change 58 345 376 2003a Giorgi F R Francisco and J S Pal Effects of a subgrid scale topography and land use scheme on the simulation of surface climate and hydrology part 1 Effects of temperature and water vapor disaggregation Journal of Hydrometeorology 4 317 333 2003b Grell G Prognostic evaluation of assumptions used by cumulus parameterizations Mon Wea Rev 121 764 787 1993 Grell G A J Dudhia and D R Stauffer Description of the fifth generation Penn State NCAR Mesoscale Model MMS Tech Rep TN 398 STR NCAR Boulder Colorado pp 121 1994 Hack J J B A Boville B P Briegleb J T Kiehl P J Rasch and D L Williamson Description of the ncar community climate model ccm2 Tech Rep NCAR TN 382 STR National Center for Atmospheric Research 1993 Henderson Sellers B Calculating the surface energy balance for lake and reservoir modeling A review Rev Geophys 24 3 625 649 1986 Holtslag A A M and B A Bovi
34. ve transfer package has been replaced by that of the CCM3 In the package the effects of H20 O2 CO and clouds were accounted for by the model Solar radiative transfer was treated with a 6 Eddington approach and cloud radiation depended on three cloud parameters the cloud fractional cover the cloud liquid water content and the cloud effective droplet radius The CCM3 scheme retains the same structure as that of the CCM2 but it includes new features such as the effect of additional greenhouse gases CH4 CFCs atmospheric aerosols and cloud ice The other primary changes are in the areas of cloud and precipitation processes The original explicit moisture scheme of Hsie et al 1984 has been substituted with a simplified version because the original scheme was computationally too expensive to be run in climate mode In the simplified scheme only a prognostic equation for cloud water is included which accounts for cloud water formation advection and mixing by turbulence re evaporation in sub saturated conditions and conversion into rain via a bulk autoconversion term The main novelty of this scheme does not reside of course in the simplistic microphysics but in the fact that the prognosed cloud water variable is directly used in the cloud radiation calculations In the previous versions of the model cloud water variables for radiation calculations were diagnosed in terms of the local relative humidity This new feature ad
35. y CCM Community Climate Model CCMI Community Climate Model version 1 CCM2 Community Climate Model version 2 CCM3 Community Climate Model version 3 CLM0 Common Land Model version 0 CLM2 Community Land Model version 2 CLM3 Community Land Model version 3 CMAP CPC Merged Analysis of Precipitation CRU Climate Research Unit CPC Climate Prediction Center ECMWF European Centre for Medium Range Weather Forecasts ERA40 ECMWF 40 year Reanalysis ESP Earth Systems Physics FAO Food and Agriculture Organization of the United Nations fvGCM NASA Data Assimilation Office atmospheric finite volume general circulation model GLCC Global Land Cover Characterization GCM General Circulation Model HadAM3H Hadley Centre Atmospheric Model version 3H ICTP Abdus Salam International Centre for Theoretical Physics IPCC Intergovernmental Panel on Climate Change IBIS Integrated Blosphere Simulator LAI leaf area index LAMSs limited area models LBCs lateral boundary conditions MC2 Mesoscale Compressible Community model MIT Massachusetts Institute of Technology MMA Mesoscale Model version 4 MMS Mesoscale Model version 5 MERCURE Modelling European Regional Climate Understanding and Reducing Errors NNRP NCEP NCAR Reanalysis Product 23 NNRP1 NCEP NCAR Reanalysis Product version 1 NNRP2 NCEP NCAR Reanalysis Product version 2 NCAR National Center for Atmospheric Research NCEP National Centers for Environmental Prediction PBL planetary boundary
Download Pdf Manuals
Related Search