National Science Foundation, Division of Ocean Sciences
Coupled Ocean-Atmosphere Feedbacks Affecting
California Coastal Climate: Current Conditions and Future Projections
Art Miller
Award: $491,193
Duration: 2020-2024
Collaborator: Hyodae Seo (WHOI)
Project Summary.
The coastal climate of California is profoundly affected by the ocean, which moderates its hot summers
and provides moisture for much-needed winter rains. While the importance and impact of the mean state
of the ocean are well appreciated, the impact of the anomalous state of the ocean on coastal climate is far
less understood. Sea surface temperature (SST) anomalies and ocean surface current anomalies, ranging
from the meso-to-frontal scales of cool coastal upwelling to the regional-to-basin scales of the marine
heat waves of the .Blobs., are inherently coupled with the atmosphere. The fundamental coupled oceanatmosphere
feedback processes that affect the climate, weather, and upwelling along the coast are the
focus of this study. In addition, we will explore how the anomalous ocean-atmosphere coupling could
affect the region.s climate under projected greenhouse-gas-forced changes in major large-scale drivers,
such as the expansion of the Hadley Cell and repositioning of the North Pacific High Pressure system,
and increases in ocean stratification. To quantify the effects of ocean-atmosphere boundary layer coupling
on California coastal regions, we will conduct a series of regional high-resolution coupled oceanatmosphere
model simulations, including full ocean-atmosphere coupling and well-resolved orography
and land-sea distribution. These will include ensembles of 10-year long runs forced by observed current
climate and projected future climate boundary conditions, as well as ensembles of runs initialized under
observed marine heat wave conditions. We will use these runs to study how the statistics of daily,
intraseasonal and interannual variability in the atmosphere and the oceanic upwelling field, are affected
by the anomalous ocean-atmosphere conditions associated with eddies, fronts, and extreme SST
anomalies, and assess how they may be altered by changes in large-scale atmospheric and oceanic drivers
associated with global warming.
Clarifying the processes that control observed and future changes in coastal climate supports the intensive
community research effort directed towards improved understanding of climate change at the regional-tolocal
scale. Our extensive physical diagnostics of model simulations and observational comparisons will
also elucidate the coupled physical processes accounting for long-term changes in coastal upwelling that
are affected by mesoscale ocean-atmosphere feedbacks and projected changes in large-scale drivers.
Determining the dynamic and thermodynamic controls of the multiple forcing drivers can also help to
improve the basic state of global coarse-resolution climate simulations, which typically suffer from strong
biases in eastern boundary upwelling systems. The results may also lead to improved short-term climate
predictions by better resolving the influence of anomalous ocean states and ocean-atmosphere interactions
in dynamical forecasting frameworks. In summary, we address a vital range of scales and processes that
are not adequately resolved by current climate datasets and global climate models in order to improve our
overall understanding of regional coastal climate variability, sensitivity, and predictability.
This research will help develop techniques for exploiting ocean-atmosphere feedbacks in improving
climate simulations, short-term climate forecasts, and projections of regional impacts of climate change.
The results may be influential in assessing how long-term changes in the coastal environment relate to
changes in rainfall, soil moisture, snowfall, SST, currents, and sea level, which can then be better
accommodated in infrastructure and economic planning for the millions of people who inhabit the coastal
regions of California.