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This study focuses on implementing a cutting-edge parameterization for heat flux in the Regional Atmospheric Modeling System (RAMS), addressing the challenge of accurately simulating boundary layer dynamics. Through detailed experimentation and analysis, the research sheds light on the impact of this parameterization on key atmospheric processes, such as thermals and mixing. The results offer valuable insights for improving the simulation of boundary layer characteristics and CO2 concentrations. The study also outlines future research directions, including comparisons with Large-Eddy Simulation (LES) runs and observational data analysis to refine the model further.
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Implementation of a boundary layer heat flux parameterization into the Regional Atmospheric Modeling System Erica McGrath-Spangler Dept. of Atmospheric Science Colorado State University ChEAS May 14, 2007 Acknowledgements: Scott Denning, Kathy Corbin, Ian Baker
Overview • Motivation • Parameterization • Experiment Setup • Results • Conclusions • Future Work ChEAS meeting: May 14, 2007
Motivation • A 20% error in Zi produces a 20% error in CO2 tendency • Zi is very difficult to determine accurately in mesoscale models because of the coarse resolution Zi is the depth of the PBL ChEAS meeting: May 14, 2007
Large-Eddy Simulation: Morning Mixed-Layer Development White = pos buoyant Red = neg buoyant SAM model Courtesy Tak Yamaguchi ChEAS meeting: May 14, 2007
Mesoscale Models • Mesoscale models can’t resolve overshooting thermals because of grid spacing • Process is not currently parameterized in RAMS ChEAS meeting: May 14, 2007
Mixing at the top of the PBL • At the top of the boundary layer, the Richardson number is very large ( ) • Since the mixing coefficient is inversely proportional to the Richardson number, the mixing is ~ 0 within the capping inversion • Very difficult to initiate growth of the boundary layer • RAMS does not include any process to initiate mixing ChEAS meeting: May 14, 2007
Closure Assumption • Heat flux at the boundary layer top is negatively proportional to the surface heat flux • Mixes warm, dry free tropospheric air into the PBL and cool, moist boundary layer air into the capping inversion ChEAS meeting: May 14, 2007
Also mix the three wind components, TKE, and CO2 concentration • The tendencies from entrainment mixing are the quantities themselves times the mass flux divided by density and the layer thickness Units of kg m-2 s-1 ChEAS meeting: May 14, 2007
RAMS setup • RAMS version 5.04 modified to BRAMS version 2.0 • 42 vertical levels starting at 15m and vertically stretched by ~1.1 up to 6600m • Includes a shallow convection parameterization • Use Mellor and Yamada (1982) closure option for vertical diffusion • Smagorinsky (1963) used for horizontal diffusion • Coupled to SiB version 3 ChEAS meeting: May 14, 2007
Idealized simulation • Cyclic lateral boundary conditions • No weather systems can be horizontally advected into the system • Initialized horizontally homogeneously from a dry sounding • Homogeneous surface • Flat topography at sea level • Vegetation is C3 broadleaf and needleleaf trees • Loam soil type • FPAR = 0.8 • LAI = 4.0 ChEAS meeting: May 14, 2007
Conclusions • In nature, overshooting thermals warm, dry, and deepen the PBL • Mesoscale models don’t include overshooting thermals • I’ve introduced a parameterization into RAMS that accounts for this process • Hope to be able to better simulate Zi and CO2 concentrations ChEAS meeting: May 14, 2007
Future Work • Compare mesoscale simulations to an LES run of RAMS and to observations • Both with and without the parameterization included • Parameterization also affects surface temperature and dew point that are observed • Assimilate those variables in order to better determine a value for the tunable parameter ChEAS meeting: May 14, 2007
Thanks ChEAS meeting: May 14, 2007
