Collaborative Research: VOCALS--Climate Simulation and Operational Forecasting Using a Regional Earth System Modeling Framework

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study - VAMOS is the Variability of the American Monsoon System project) region within the Southeast Pacific is a globally important regional coupled climate regime involving equatorward winds, orographic channeling, arid land margins, upwelling currents, oceanic biogeochemical cycling, marine stratus clouds, and aerosols. A principal motivation for the VOCALS project is that global model errors in this region degrade the quality of their simulations throughout the tropical Pacific, with substantial impacts on the modeled and predicted global climate. It is difficult or impossible to address these errors directly in global models with currently available computational resources, because the mechanisms that determine the mean state and variability have much finer spatial scales than global models can resolve. Moreover, these mechanisms do not lend themselves to unique and physically constrained treatments. A further complication is that the mechanisms involve interactions among all major components of the Earth system, including physical processes in the atmosphere, ocean, and land surface, as well as natural and anthropogenic influences on marine and atmospheric chemistry. Simulating these interlocking processes requires high resolution (several kilometers) with coupled atmosphere, ocean, and land components in both physical and chemical submodels. In this project a regional Earth-system modeling framework will be developed, with an atmospheric model coupled to a land surface model and an oceanic model. The atmospheric model includes chemical transport and process models, while the regional oceanic model contains full biogeochemistry. This framework will be used to explicate the climate dynamics of the VOCALS region and to leverage VOCAL REx (Regional Experiment) measurements through careful experimental design and model-validation and data-interpretation studies. First, meteorological and aerosol forecasts will be provided for VOCALS REx during the campaign. After VOCALS REx, a retrospective simulation of the VOCAL REx period will be carried out using the full Earth-system model. The simulation's high resolution is intended to increase the interpretability of measurements by placing them in geographical and climate-variability context and to enhance the usefulness of measurements for model validation and evaluation. A simulation of the VOCALS region covering the past 60 years will place the VOCALS-REx observations and simulations in the context of climate variability. Finally, the VOCALS region will be downscaled from an NCAR CCSM (National Center for Atmospheric Research Community Climate System Model) global solution, placing the realism gained through careful development and VOCALS-REx-based validation of the regional model in the context of the errors in a major global climate model. All these simulations will be performed on the same model grid to allow for systematic comparison of model solutions with observations and with each other. The simulations will provide opportunities for analyses of interlocking physical and chemical processes that determine the climate of the VOCALS region. These include studies of the geographical distribution of natural and anthropogenic aerosols; the impact of these aerosols on cloud properties and the effects of clouds on aerosol scavenging; the intricate and highly-structured couplings in the physical system determining key climate variables such as stratus amount and upwelling; and the oceanographic processes controlling air-sea fluxes of DMS (dimethyl sulfide). Broader impacts of this project are in its contributions to building human infrastructure for science research. Through interactions with colleagues in Peru and Chile, the investigators will foster international scientific collaboration, and they will train graduate students and postdoctoral fellows. The project will leave a legacy of modeling infrastructure, as the first time a holistic regional Earth-systems approach has been applied so systematically to any region. The modeling framework to be developed can serve as a prototype for Earth-system modeling in the service of climate prediction and climate applications. Finally, the PIs propose to capitalize on the unique measurements to be taken during the VOCALS-REx field campaign to understand the interlocking physical and chemical dynamics of the VOCALS region and to diagnose the causes of large, persistent errors in global models errors, potentially paving the way for improvements in climate predictions.