[Photo by Carlye Calvin.]
While fog can occur under a variety of circumstances, the northward-surge phenomenon--especially common in the summertime--has vexed California forecasters for years. The process begins when high pressure noses eastward into Washington, Oregon, and Idaho, producing light east or southeast winds on the California coast. As they descend from the Coast Range, the breezes bring dry, sunny conditions to the shoreline while they push the marine layer (the cool, moist air that extends a few hundred meters above the Pacific) just offshore.
Forecasters can predict the large-scale pressure changes that cause the winds to blow offshore, but they cannot yet reliably tell when the marine layer might return and surge northward to bring overcast or fog. The computer models used by present-day forecasters trace the atmosphere at points separated by around 30 to 90 kilometers. That resolution is too coarse to fully outline the surges, which can be less than 100 km wide.
The surge's movement up the coast can be characterized as a Kelvin wave, a particular kind of atmospheric feature in which winds blow in the direction of movement of a pressure disturbance. Research computer models tend to handle Kelvin waves skillfully, so this bodes well for surge prediction efforts. The modelers are now using a simplified version of the coast's topography, so their next step is to add sharper resolution to incorporate the bays, inlets, and peninsulas that dot the California coast.
"This phenomenon is a tough test for a model," says Rich. "Delicate imbalances (in pressure) seem to set it off, and it's too fine-scale to show up in most models. Still, it can produce enough fog to envelop boats and airports."
A Canadian university has joined the fold as the 62nd member institution of UCAR. The application of York University was formally approved by the assembled member representatives at the 1996 UCAR members' meeting, held in October at the Mesa Lab.
York is located in North York, Ontario, just north of Toronto. Founded in 1959, it serves over 40,000 students. York offers master's- and doctoral-level programs through its departments of chemistry, earth and atmospheric science, and physics and astronomy, along with its Centre for Research in Earth and Space Science. York faculty have collaborated with each of NCAR's scientific divisions. Their specialties include remote sensing technologies, regional climate modeling, and boundary layer analysis.