Regional Climatic Model RegCM User Manual - gforge
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1. The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11 I 34151 Trieste Italy Earth System Physics Section ESP Regional Climatic Model RegCM User Manual Version 4 1 Nellie Elguindi Xunqiang Bi Filippo Giorgi Badrinath Nagarajan Jeremy Pal Fabien Solmon Sara Rauscher Ashraf Zakey and Graziano Giuliani Trieste Italy May 2011 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 Contents 1 The REGional Climate Model RegCM 2 Description be BUR de et Se at RR QI Re ie e Ro RAUS S E soda 2 2 Modelcomponehlts coe ee pd qr vene RU HR OUS TE m ae Geo em 2 3 The RegCM Model Horizontal and Vertical Grid 2 4 Map Projections and Map Scale Factors Model Physics S21 Dynamics 4 cd RI EG ESRIIBSBE Cue eee OP eR PE REB 3 1 1 Horizontal Momentum Equations 2 0 00000000 3 1 2 Continuity and Sigmadot 6 Equations 3 1 3 Thermodynamic Equation and Equation for Omega 0 3 14 Hydrostatic Equation z en ee Ste UU Ves RUSSIE eg aes 3 2 Physics parametrizationS s 2 ke a le x hh v epo x wa Ea ee a ees 32 1 Radiation Scheme soo ERU OR SLE E om Pp P S E 322 Land Surface Models csc o c2. 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 NCAR Community Climate Model version 2 CCM2 Hack et al 1993 and the mesoscale model MM5 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Climate Model CCM Community Climate Model version 3 CCM3 Kiehl et al 1996 First the CCM2 radiative transfer package has been replaced by that of the CCM3 In the package the effects of H20 O2 CO and clouds were accounted for by the model Solar radiative transfer was treated with a Eddington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 scheme retains the same structure as that of the CCM2 but it includes new features such as the effect of additional greenhouse gases NO2 CH4 CFCs at
3. 28 0 20 030 040 0 30 0 28 0 34 0 60 0 18 0 20 0 20 0 23 0 28 0 24 0 18 0 18 Table 3 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 3 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 3 10 where is a countergradient transport term describing nonlocal transport due to dry deep convection The eddy diffusivity is given by the nonlocal formulation 72 K tw 1 5 where is the von Karman constant w 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 3 11 3 12 where C is a constant equal to 8 5 and is the surface temperature or water vapor flux Equation 3 1
4. 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 Boville Local versus nonlocal boundary layer diffusion in a global climate model J Climate 6 1993 Holtslag A 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 118 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 29 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 Kueppers L et al Seasonal temperature response to land use change in the western united states Global and Planetary Change 60 2008 Laurent B B Marticorena G Bergametti J Leon and N Mahowald Modeling mineral dust emissions from the sahara desert using new surface properties and soil database Journal of Geophysical Research 113 d14218 2008 Lawrence P and T Chase Representing a new MODIS consistent land surface in the C
5. Inland water 15 Ocean 16 Evergreen shrub 17 Deciduous shrub 18 Mixed Woodland 19 Forest Field mosaic 20 Water and Land mixture 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 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 color 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 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 h
6. cooled by net longwave radiation loss and surface fluxes The bottom layer is three meters thick it is warmer by solar radiation and exchanges heat with the top layer This diurnal SST scheme appears to provide significant although not major effects on the model climatology mostly over tropical oceans for example the Indian ocean and it is now used as default in RegCM4 3 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 smoothing on the top is done in order to reduce errors related to the PGF calculation 24 3 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 2 T ke hn 3 28 where T 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 107 m
7. first introduce the model s grid configuration The modeling system usually gets and analyzes its data on pressure surfaces but these have to be interpolated to the model s vertical coordinate before input to the model The vertical coordinate is terrain following Figure 2 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 coordinate is used to define the model levels where is the pressure is a specified constant top pressure ps is the surface pressure ae p Pr 2 1 ps Pr It can be seen from the equation and Figure 2 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 12 1Y 1 IY JX 1 1 J 2 1 JX Figure 2 2 Schematic representation showing the horizontal Arakawa B grid staggering of the dot and cross grid points 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 2 where it can be seen that the scalars T q p etc are defined at the center of the grid b
8. model code towards improved flexibility portability and user friendliness The model can be interactively coupled to a 1D lake model a simplified aerosol scheme including OC BC SOA dust and sea spray and a gas phase chemistry module CBM Z Overall RegCM4 shows an improved performance in several respects compared to previous versions although further testing by the user community is needed to fully explore its sensitivities and range of applications The RegCM is available on the World Wide Web thanks to the Democritos Italy CNR group at https eforge escience lab org gf project regcm Chapter 2 Description 21 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 National Center for Atmospheric Research 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 MM4 which is a compressible finite difference model with h
9. to reduced precipitation MIT Emanuel 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 22 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 the MIT 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 accounted for by allowingt
10. 004 which we refer to as UW PBL This is a 1 5 order local down gradient diffusion parameterization in which the velocity scale is based on turbulent kinetic energy TKE The TKE is in turn calculated prognostically from the balance of buoyant production destruction shear production dissipation vertical transport and horizontal diffusion and advection The scheme also parameterizes the entrainment process and its enhancement by evaporation of cloudy air into entrained air One property of the scheme is the use of a mixing length formulation based on a 2010 paper by Grisogono ref which allows a more realistic description of sharp inversions under strongly stable conditions The UW PBL has been so far tested within the RegCM4 framework mostly in midlatitude domains such as the continental US where it considerably improved the simulation of low level stratus clouds and Europe This scheme is currently in a SVN branch of the code and will be merged into the main development trunk as soon as the accompanying paper will be published and will be available in the next model release 4 2 Tiedtke convection scheme Adrian Tompkins is developing an adaptation of the ECHAMS 4 Tiedtke 1989 cumulus convection scheme for the RegCM model The code from ECHAM has been ported into RegCM and extensive testing is planned in the second half of 2011 This option should be available for next model release 4 3 Chemistry Fabien Solmon is developing the couplin
11. 2 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 is assumed to be equal to 0 For the calculation of the eddy diffusivity and countergradient terms the PBL height is diagnostically computed from Rier u h v hy 85 3 13 where u h v h and 0 are 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 Compared to other schemes this formulation tends to produce relatively strong and often excessive turbulent vertical transfer For example after extensive testing we found excessive vertical transfer of moisture in the model resulting in low moisture amounts near the surface and excessive moisture near the PBL top Therefore in order to ameliorate this problem the countergradient term for water vapor was removed in RegCM4 Another problem of the Holtslag scheme at least in our implementation is an excessive vertical 20 transport of heat moisture and momentum in very stable conditions such as during the winter in northern hemisphere high latitude regions For example we found that in such conditions the scheme fails to simulate near surface temperature inversio
12. CM 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 coordinate system of RegCM is also performed surfaces near the ground closely follow the terrain and higher level surfaces tend to approximate isobaric surfaces Since the vertical and horizontal resolution and domain size can vary the modeling package programs employ 11 Nile ho Nil 1 gh EI C u v T q p 4 0 3 a 5 0 4 21 25 0 5 0 6 7 g 0 7 9 0 78 10 0 84 11 0 89 12 0 93 13 0 96 16 1 00 Oe og Figure 2 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 parameterized dimensions requiring a variable amount of core memory and the requisite hard disk storage amount is varied accordingly 2 3 The RegCM Model Horizontal and Vertical Grid It is useful to
13. Climate RCM Regional Climate Model RegCM REGional Climate Model RegCM1 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 ROMS Regional Oceanic Modeling System 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 32
14. ated 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 15 defined by m 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 14 Chapter 3 Model Physics 3 1 Dynamics The model dynamic equations and numerical discretization are described by Grell et al 1994 3 11 Horizontal Momentum Equations Opus ig p uu m d dy RT Op 90 m P F p o x Op v 3 dptyw m ap 20s ax fp v Fyu 3 1 apt zl 2 fp u Fyv 35 Is ap Cau OE Per SR HV oo 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 Stereogra
15. ation 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 land cover 25 Chapter 4 Future Developments We have lot of exciting plans for future model improvements some of which are in a already mature stage and under testing with some published results whereas others are done only on the paper in a whishlist for next years Nevertheless we want to share this with users to have hints and encourage contributions Some of the development results ideas are listed below in a time to market order 4 1 UFW PBL scheme One of the deficiencies identified in RegCMG has been the lack of simulation of low level stratus clouds a problem clearly tied to the excessive vertical transport in the Holtslag PBL scheme O Brien 2011 To address this problem Travis OBrien coupled to the RegCMA the general turbulence closure parameterization of Grenier and Bretherton 2001 Bretherton et al 2
16. ban environments Urban development not only modifies the surface albedo and alters the surface energy balance but also creates impervious surfaces with large effects on runoff and evapotranspiration These effects can be described by modifying relevant properties of the land surface types in the BATS package such as maximum vegetation cover roughness length albedo and soil characteristics For this purpose we implemented the parameters proposed in Table 1 of Kueppers et al 2008 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 surface complexity within a climate model grid cell CLM uses a tile or mosaic approach 17 Table 3 1 Land Cover Vegetation classes 1 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
17. cesses 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 At 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 RegCM4 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 ABE ae NAT 3 19 where T 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 A number of parameters present in the scheme can be used to optimize its performance and Giorgi et al 1993c discusses a wide range of sensitivity experiments We found that the parameter to which the scheme is most sensitive is by and large the fraction of precipitation evaporated in the downdraft Peff with values from 0 to 1 which essentially measures the precipitation efficiency Larger values of Peff lead
18. ch NETwork or RegCNET a widespread network of scientists coordinated by the Earth System Physics section of the Abdus Salam International Centre for Theoretical Physics Abdus Salam International Centre for Theoretical Physics ICTP being the foster the growth of advanced studies and research in developing countries one of the main aims of the ICTP The home of the model is http users ictp it RegCNET Scientists across this network currently subscribed by over 750 participants can communicate through an email list and via regular scientific workshops and they have been essential for the evaluation and sequential improvements of the model Since the release of RegCM3 described by Pal et al 2007 the model has undergone a substantial evolution both in terms of software code and physics representations and this has lead to the development of a fourth version of the model RegCM4 which was released by the ICTP in June 2010 as a prototype version RegCM4 0 and in May 2011 as a first complete version RegCM4 1 The purpose of this Manual is to provide a basic reference for RegCM4 with a description of the model with a special accent to the improvements recently introduced Compared to previous versions RegCMA includes new land surface planetary boundary layer and air sea flux schemes a mixed convection and tropical band configuration modifications to the pre existing radiative transfer and boundary layer schemes and a full upgrade of the
19. 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 soil 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 Dickinson 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 a
20. ding 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 Q p 3 14 B is a function of the average relative humidity RH of the sounding as follows B 2 0 RH RH gt 0 5 3 15 1 0 otherwise 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 Grell 1993 similar to the AS74 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 de
21. ditional flux induced by boundary layer scale variability Sensible heat SH latent heat LH and momentum t fluxes between the sea surface and lower atmosphere are calculated using the following bulk aerodynamic algorithms T paus uy 3 25 SH PaCpatlxOx 3 26 LH pyLettsqs 3 27 where uy and are mean wind components is the frictional wind velocity is the temperature scaling parameter q 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 3 2 7 Prognostic Sea Surface Skin Temperature Scheme By default in RegCM sea surface temperatures SST are prescribed every six hours from temporally interpolated weekly or monthly SST products These products which are produced from satellite retrievals and in situ measurements are representative of the mean temperature in the top few meters of the ocean However the actual SST can differ significantly from this mean temperature due to the cool skin and warm layer effects described by Fairall et al 1996 To improve the calculation of diurnal fluxes over the ocean the prognostic SST scheme described by Zeng 2005 was implemented in RegCM4 The scheme is based on a two layer one dimensional heat transfer model with the top layer representing the upper few millimeters of the ocean which is
22. e option to pursue and therefore this option was added to the model 3 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 FCS es 3 20 RA max RAmin where is the relative humidity threshold at which clouds begin to form and RH 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 Q according to the following relation P Cppt Oc FC Q FC 3 21 where 1 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 m Cacs 1070 4940 0137 3 22 where T is temperature in degrees Celsius and is the autoconversion scale factor Precipitation is assumed to fall instantaneously SUBEX also includes simple formulations for raindrop accretion and evaporation The formulatio
23. ections depending on effective radii for the liquid and ice phase One of the problems in this formulation is that the scheme uses the cloud fractional cover to produce grid box mean cloud properties which are then treated as if the entire grid box was covered by an effectively thinner cloud layer However because of the non linear nature of radiative transfer this approach tends to produce a grayer mean grid box than if separate cloudy and clear sky fractional fluxes were calculated By taking advantage of the fact that the scheme also calculates clear sky fluxes for diagnostic purposes in iRegCM4 we modified this radiative cloud representation by first calculating the total cloud cover at a given grid point and then calculating the surface fluxes separately for the cloudy and clear sky portions of the grid box The total cloud cover at a model grid box is given by a value intermediate between that obtained using the random overlap assumption which maximizes cloud cover and that given by the largest cloud cover found in any single layer of the column overlying the grid box which implies a full overlap and it is thus is a minimum estimate of total cloud cover This modification thus accounts for the occurrence of fractional clear sky at a given grid box leading to more realistic grid box average surface radiative fluxes in fractional cloudy conditions A large scale cloud and precipitation scheme which accounts for the subgrid scale variability of cl
24. ereo mo o RR Rom 32 3 Planetary Boundary Layer Scheme eA 3 2 4 Convective Precipitation Schemes 32 5 Large Scale Precipitation Scheme 3 2 6 Ocean flux Parameterization eA 3 27 Prognostic Sea Surface Skin Temperature Scheme 3 2 8 Pressure Gradient Scheme s s s r p oen 3 2 9 Lake Mod l t zo bx RAPERE wes ee ber aid Bar Me ees 3 2 10 Aerosols and Dust Chemistry Future Developments UPW PBL scheme new RACES AURI em Wem Wee vs 4 2 Tiedtke convection scheme s s isir a p ore a ia Se ee Pe ES S RR Sees 4 3 Ba ee Me Ap ed es 4 4 Couple Sh SR UR eR Dee s 4 35 2 parallelization 2 ox Re ee ACS 5 qu E pe ENS Sd Bed A 4 6 Parallel UO uum o ae eb wel doit dae eel erue eoe 4 7 Semi Lagrangian dynamic core 2er 4 8 Non Hydrostatie Core sie m EQUES EVA SE Eee hae v 10 10 11 12 13 15 15 15 15 16 16 17 17 20 21 23 24 24 24 25 25 List of Figures 2 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 12 2 2 Schematic representat
25. eterogeneity 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 3 For a more detailed description of CLM physics parameterizations see Oleson 2004 18 61 Table 3 2 BATS 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 Max fractional vegetation cover 0 85 080 0 80 0 80 0 80 090 0 80 0 00 0 60 0 80 0 35 0 00 0 80 0 00 0 00 0 80 0 80 0 80 0 80 0 80 Difference between max fractional vegetation cover and cover at 269K 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 Roughne
26. g of RegCM model with the CBMZ chemical module with the Sillmann fast solver 4 4 Coupling We have resolved to adopt for the RegCM model a standard model coupling engine the Earth System Modeling Framework ESMF Ufuk Utku Turuncoglu is already adapting model data structures to use the ESMF framework 26 First target will be to couple the RegCM model to the Regional Oceanic Modeling System ROMS oceanic model and update the Community Land Surface Model CLM to version 4 4 5 2D parallelization This long standing limitation of the model in the parallel performances will be faced we plan to drop altogether the Serial model version does exist anymore a single core processor clean up model parallel code and perform a dynamical 2D decomposition of the model domain 4 6 Parallel O This is another limit of the current model implementation where all data need to be gathered by the master processor before being written to disk Again if running on a decent cluster all processors usually have access to disk resources and a form of parallel I O will allow a big performance boost as well as a reduction of some of the MPI communication data at the expenses of an increase of the requirements for the cluster I O channel 4 7 Semi Lagrangian dynamic core A semi Lagrangian advection scheme for the water vapor and advection tracers will allow a different timestep for the transport schemes which should result in a performance prize 4 8 No
27. gi Simulation of regional climate using a limited area model nested in a general circulation model J Climate 3 941 963 1990 Giorgi F and G 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 1991 Giorgi F L Mearns Introduction to special section Regional climate modeling revisited J Geophys Res 104 6335 6352 1999 Giorgi F G T Bates and S J Nieman The multi year surface climatology of a regional atmospheric model over the western united states J Climate 6 75 95 1993a Giorgi F 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 Giorgi E M R Marinucci G T Bates and G DeCanio Development of a second generation regional climate model regcm2 ii Convective processes and assimilation of lateral boundary conditions Mon Wea Rev 121 2814 2832 1993c Giorgi F X Bi and Y Qian Radiative forcing and regional climatic effects of anthropogenic aerosols over East Asia A regional coupled climate chemistry aeroso
28. he 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 The MIT scheme is the most complex of the three and also includes a number of parameters that can be used to optimize the model performance in different climate regimes Differently from the Grell scheme however test experiments did not identify a single parameter to which the model is most sensitive A major augmentation in RegCM4 compared to previous versions of the model is the capability of running different convection schemes over land and ocean a configuration which we refer to as mixed convection Extensive test experiments showed that different schemes have different performance over different regions and in particular over land vs ocean areas For example the MIT scheme tends to produce excessive precipitation over land areas especially through the occurrence of very intense individual precipitation events In other words once the scheme is activated it becomes difficult to decelerate Conversely we found that the Grell scheme tends to produce excessively weak precipitation over tropical oceans These preliminary tests suggested that a mixed convection approach by which for example the MIT scheme is used over oceans and the Grell scheme over land might be the most suitabl
29. ion showing the horizontal Arakawa B grid staggering of the dot and cross prd points dnm pone LUE St Sapa le ge pe TR EAM el Es 13 List of Tables 3 1 Land Cover Vegetation classes 3 2 BATS vegetation land cover 3 3 Resolution for CLM input parameters Chapter 1 The RegCM The RegCM is a regional climate model developed throughout the years with a wide base of model users It has evolved from the first version developed in the late eighties RegCM1 Dickinson et al 1989 Giorgi 1990 to later versions in the early nineties RegCM2 Giorgi et al 1993b Giorgi et al 1993c late nineties RegCM2 5 Giorgi and Mearns 1999 and 2000s RegCM3 Pal et al 2000 The RegCM has been the first limited area model developed for long term regional climate simulation it has participated to numerous regional model intercomparison projects and it has been applied by a large community for a wide range of regional climate studies from process studies to paleo climate and future climate projections Giorgi and Mearns 1999 Giorgi et al 2006 The RegCM system is a community model and in particular it is designed for use by a varied community composed by scientists in industrialized countries as well as developing nations Pal et al 2007 As such it is designed to be a public open source user friendly and portable code that can be applied to any region of the World It is supported through the Regional Climate resear
30. l climate models pp 52 72 American Geophysical Union 1984 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 Atmospheric Research 1993 Emanuel K A 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 1996 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 28 Gior
31. ls model study J Geophys Res 107 2002 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 Giorgi F J S Pal X Bi L Sloan N Elguindi and Solmon Introduction to the tac special issue The regcnet network Theoretical and Applied Climatology 86 1 4 2006 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 Grenier H and C S Bretherton A moist pbl parameterization for large scale models and its application to subtropical cloud topped marine boundary layers Monthly Weather Review 129 357 377 2001 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
32. mospheric aerosols and cloud ice Scattering and absorption of 10 solar radiation by aerosols are also included based on the aerosol optical properties Absorption Coefficient and Single Scattering Albedo A simplified explicit moisture scheme Hsie et al 1984 is included where only a prognostic equation for cloud water is used 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 Prognosed cloud water variable is directly used in the cloud radiation calculations and not diagnosed in terms of the local relative humidity adding a very important and far reaching element of interaction between the simulated hydrologic cycle and energy budget calculations The solar spectrum optical properties are based on the cloud liquid water path which is in turn based on the cloud liquid water amount prognostically calculated by the model cloud fractional cover which is calculated diagnostically as a function of relative humidity and effective cloud droplet radius which is parameterized as a function of temperature and land sea mask for liquid water and as a function of height for ice phase In addition the scheme diagnostically calculates a fraction of cloud ice as a function of temperature In the infrared spectrum the cloud emissivity is calculated as a function of cloud liquid ice water path and cloud infrared absorption cross s
33. n Hydrostatic core We want to implement the non hydrostatic core to allow physical downscaling of large scale model simulation under the 20 kilometers limit of the hydrostatic model 27 Bibliography Alfaro S C and L Gomes Modeling mineral aerosol production by wind erosion Emission intensities and aerosol size distributions in source areas Journal of Geophysical Research 106 416 2001 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 Bretherton C S J McCaa and H Grenier A new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i Description and Id results Monthly Weather Review 132 864 882 2004 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 R E Climate Processes and Climate Sensitivity chap Modeling evapotranspiration processes for three dimensional globa
34. n for the accretion of cloud droplets by falling rain droplets is based on the work of Beheng 1994 and is as follows P acc CaccOPsum 3 23 23 where Pycc is the amount of accreted cloud water Cace is the accretion rate coefficient and P is the accumulated precipitation from above falling through the cloud Precipitation evaporation is based on the work of Sundqvist et al 1989 and is as follows Povap Cevap 1 RH PP sum 3 24 where Peyap 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 Traditionally REGional Climate Model version 3 RegCM3 has shown a tendency to produce excessive precipitation especially at high resolutions and optimizations of the in cloud liquid water threshold for the activation of the autoconversion term Qcth and the rate of sub cloud evaporation Cevap parameters have proven effective in ameliorating this problem greater values of Oth and Cevap lead to decreased precipitation amounts 3 2 6 Ocean flux Parameterization 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 The Zeng scheme describes all stability conditions and includes a gustiness velocity to account for the ad
35. ns This in turn leads to large warm winter biases even 10 degrees over regions such as Northern Siberia and Northern Canada As an ad hoc fix to address this problem in RegCM4 we implemented the following modification to the scheme e We first define very stable conditions within the Holtslag parameterization as conditions in which the ratio of the height from the surface over the Monin Obhukov length is lower than 0 1 e When such conditions are found we set to 0 the eddy diffusivity and counter gradient terms for all variables Preliminary tests showed that this modification reduces the warm bias in high latitude winter conditions and allows the model to better capture surface inversions These modifications have thus been incorporated as default in the RegCM4 code 3 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 In addition the Grell parameterization is implemented using one of two closure assumptions 1 the Arakawa 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 soun
36. ommunity Land Model CLM3 0 J Geophys Res 112 g01023 2007 Brien T e a A new turbulence parameterization in regcm allows long term mesoscale simulation of marine stratocumuls Climate Dynamics 2011 Oleson K 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 within RegCM J Geophys Res Atmospheres 105 D24 29 579 29 594 2000 Pal J S Giorgi X Bi et al The ICTP RegCM3 and RegCNET Regional climate modeling for the developing world Bull Amer Meteor Soc 88 1395 1409 2007 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 gcm 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 Solmon M Mallet Elguindi Giorgi A Zakey and A Konare Dust aerosol impact on regional preci
37. on 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 ESMF Earth System Modeling Framework 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 LAMs 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 3l MERCURE Modelling European Regional Climate Understanding and Reducing Errors NNRP NCEP NCAR Reanalysis Product 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 layer PC Personal Computer PIRCS Project to Intercompare Regional Climate Simulations PFT plant functional type PSU Pennsylvania State University PWC Physics of Weather and
38. ouds Pal et al 2000 parameterizations for ocean surface fluxes Zeng et al 1998 and multiple cumulus convection scheme Anthes 1977 Grell 1993 Emanuel 1991 Emanuel and Zivkovic Rothman 1999 are the same as in RegCM3 but a new mixed scheme Grell Emanuel is introduced it allows the user to select one of the two schemes in function of the ocean land mask The other main development compared to RegCM3 concerns the aerosol radiative transfer calculations In RegCM3 the aerosol radiative forcing was based on three dimensional fields produced by the aerosol model and included only scattering and absorption in the shortwave spectrum see Giorgi et al 2002 In RegCM4 we added the contribution of the infrared spectrum following Solmon et al 2008 This is especially important for relatively large dust and sea salt particles and it is calculated by introducing an aerosol infrared emissivity calculated as a function of aerosol path and absorption cross section estimated from aerosol size distribution and long wave refractive indices Long wave diffusion which could be relevant for larger dust particles is not treated as part of this scheme The mosaic type parameterization of subgrid scale heterogeneity in topography and land use Giorgi et al 2003b allows finer surface resolution in the Biosphere Atmosphere Transfer Scheme version le BATS le 2 2 Model components The RegCM modeling system has four components Terrain ICBC Reg
39. ox 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 interpolation to assure consistency with the grid All 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 2 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 o 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 2 4 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 13 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 and v components need to be rot
40. phic Lambert Conformal or Mercator map projections 6 and Fy and Fy represent the effects of horizontal and vertical diffusion and p p pr 3 1 2 Continuity and Sigmadot Equations bE s 5c 89 The vertical integral of Equation 3 3 is used to compute the temporal variation of the surface pressure in the model dp u m dp v m W Lom y do 34 After calculation of the surface pressure tendency the vertical velocity in sigma coordinates is computed at each level in the model from the vertical integral of Equation 3 3 15 1 9 fdp u m dp v m oh E s 3x 3 5 where is a dummy variable of integration and o 0 0 3 1 3 Thermodynamic Equation and Equation for Omega The thermodynamic equation is p vT op T6 p o ep CRUE IM OREM OR ot ox RT pa past Cpm FyT FyT 3 6 where Cpm is the specific heat for moist air at constant pressure is the diabatic heating represents the effect of horizontal diffusion represents the effect of vertical mixing and dry convective adjustment and is dp 7 0 6 di 3 7 where a m 3x v 3 8 The expression for Cpm Cp 1 0 8q where is the specific heat at constant pressure for dry air and q is the mixing ratio of
41. pitation over western africa mechanisms and sensitivity to absorption properties Geophysical Research Letters 35 124705 2008 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 Sundqvist H E Berge and 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 Tiedtke M A comprehensive mass flux scheme for cumulus parameterization on large scale models Mon Wea Rev 117 1779 1800 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 30 BATS Biosphere Atmosphere Transfer Scheme 1 Biosphere Atmosphere Transfer Scheme version le CAM Community Atmosphere Model CAPE convective available potential energy CCM Community Climate Model CCMI Community Climate Model version 1 CCM2 Community Climate Model version 2 CCM3 Community Climate Model version 3 CLM Community Land Surface Model CLM0 Common Land Model version 0 CLM2 Community Land Model versi
42. s except under ice and at the deepest points in the lake 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 paCpVa ds qa 3 29 Fs PaCpCpVa Ts Ta 3 30 where the subscripts s and a refer to surface and air respectively pa is the density of air V4 is the wind speed Cp q 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 conditions 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 3 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 Laurent et al 2008 and Alfaro and Gomes 2001 here the dust emission calcul
43. ss length m 0 08 0 05 1 00 1 00 0 80 2 00 010 005 0 04 0 06 010 0 01 0 03 0 0004 0 0004 0 10 0 10 0 80 0 3 0 3 Displacement height m 0 0 0 0 9 0 9 0 0 0 18 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 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 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 1 2 10 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 Light sensitivity factor m W7 0 02 0 02 0 06 0 06 0 06 0 06 0 02 0 02 002 0 02 0 02 0 02 0 02 0 02 0 02 0 00 0 02 0 06 0 02 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 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 lt 0 7 um 0 10 010 0 05 0 05 0 08 0 04 0 08 020 0 10 0 08 0 17 0 80 0 06 0 07 0 07 0 05 0 08 0 06 0 06 0 06 Vegetation albedo for wavelengths gt 0 7 um 0 30 030 023 0 23 0
44. t 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 3 2 soil textures ranging from coarse sand 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 This parameterization showed a marked improvement in the representation ofthe surface hydrological cycle in mountainous regions Giorgi et al 2003a As a first augmentation in REGional Climate Model version 4 RegCM4 two new land use types were added to BATS to represent urban and sub ur
45. trainment 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 21 A 3 16 h where 7 is the normalized updraft condensation Jy is the normalized downdraft evaporation and p is the fraction of updraft condensation that re evaporates in the downdraft depends on the wind shear and typically varies between 0 3 and 0 5 Rainfall is given by PU nmp 1 p 3 17 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 environment as fast as non convective processes destabilize it as follows ABE ABE mp NAN 3 18 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 pro
46. water vapor 3 1 4 Hydrostatic Equation The hydrostatic equation is used to compute the geopotential heights from the virtual temperature T 3 9 din o p p oe 1 RT sia 1 9 where T 1 0 6084 qv qc qr are the water vapor cloud water and rain water or snow mixing ratios 16 3 2 Physics parametrizations 3 21 Radiation Scheme RegCM4 uses the radiation scheme of the NCAR CCM3 which is described in Kiehl et al 1996 Briefly the solar component which accounts for the effect of H20 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 3 2 2 Land Surface Models BATS
47. ydrostatic 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 the RegCMA is thus a hydrostatic compressible sigma p vertical coordinate model run on an Arakawa B grid in which wind and thermodynamical variables are horizontally staggered using a time splitting explicit integration scheme in which the two fastest gravity modes are first separated from the model solution and then integrated with smaller time steps 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 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
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