UCLA Regional Earth System Modeling for VOCALS For the past two years, we’ve been developing regional earth system modeling capabilities at UCLA. To date, these have been mostly applied to the Southern California region; However, the model is set up to deal with the science questions critical to VOCALS because of the broad similarities between Southern California and the Peru-Chile region.

Similarities between SoCal and VOCALS region include…  thermally and topographically driven atmospheric flows clearly linked to critical and poorly simulated features of oceanic circulation, including upwelling.  mesoscale SST organization arising from eddying oceanic flows, with likely couplings to mesoscale wind and stratus organization.  poorly understood constraints on the overall heat budget. These arise from difficulties in simulating stratus and oceanic heat fluxes associated with mesoscale eddies.  biogenic and anthropogenic aerosol sources and transport, with likely effects on stratus optical properties and amount.

WRF/ROMS coupling We’ve developed a regional coupled ocean-atmosphere model, and applied it to the Southern California region. WRF resolution is 6km, and ROMS resolution is 2km. This resolution is chosen to study and improve mesoscale coupling and organization of atmospheric and oceanic flows. The models exchange heat and momentum every 12 hours, roughly the evolution time scale of mesoscale oceanic flows. ROMS lateral boundary conditions are supplied by SODA, while WRF’s come from the eta model reanalysis.

snapshot of SST as simulated by the WRF/ROMS coupled model during a March 2002 upwelling event.

WRF/SSiB coupling In collaboration with Yongkang Xue, we have coupled WRF to a land surface model, SSiB (Simplified Simple Biosphere Model). The coupling interface is complete. Testing is currently underway with two WRF PBL schemes to maximize realism of land surface--PBL interactions. This component is critical to simulation of thermally-driven diurnal winds in the Andes, and associated effects on coastal oceanic solutions.

Main mode of simulated diurnal flow in Southern California in MM5 Main mode of simulated diurnal flow in Southern California in MM5. The daytime phasing is shown. These flows arise from the thermal contrast between land and ocean and mountain slopes and the adjacent atmosphere, and typically twice as large as the mean. In a region of more intense topography such as the Andes, the diurnal mode is likely more important. Clearly the thermal properties of the land surface are critical to simulating these flows. (Hughes et al, 2007)

Stratus parameterization We implemented the UW stratus parameterization in MM5, WRF’s predecessor. In short, this scheme accounts for the fact that the PBL/stratus top may not coincide with the model’s vertical discretization. This parameterization was shown to improve status simulation in larger-scale simulations (McCaa and Bretherton 2004), and we found roughly 50% improvement in overall stratus amount in the Southern California Bight with this scheme, when comparing with GOES satellite data. We aim to implement this in WRF.

Cloud/aerosol issues We are developing links to groups with expertise in cloud/aerosol issues. Liou/Gu (UCLA) have developed radiative transfer algorithms for the direct effect of 18 species of aerosols. They’ve already decided to develop parameterizations for the indirect effect of these aerosols (i.e. the effect on cloud optical properties), and implement these in WRF.