Penetrating the Mysteries of Fog

By Tom Greco

Anyone who has spent more than a few days in the Bay Area knows that fog is an iconic feature of the region. In the late afternoon you can often see it welling up over the ocean and beginning to roll in. By the evening many areas remain blanketed by its cool embrace until the heat of the morning sun burns it away. Fog tends to follow different flow patterns in each of the unique geographies of our area but no matter where it occurs you can be sure that it carries cool air and moisture and as a result plays an integral part in the function of our ecosystems.

Morning fog in front of the Dwight Center

The redwoods of the California coast, for example, are dependent on fog for moisture during the dry summer months of our Mediterranean climate. Their foliage even shows signs of adaptation specifically to increase capture and absorption of moisture in the air. A study conducted by Emily Limm has demonstrated that redwoods often receive up to 40% of the water they require through fog. This dependence on fog means that potential changes in the fog patterns of our region may very well effect the distribution of redwoods and populations of other plant communities – and such changes could have a significant impact on agriculture and overall environmental health.

Pepperwood’s Dr. Lisa Micheli explains that “fog is the most mysterious piece of current and future climate science.” Unlike other meteorological processes, there are no physical models capable of predicting fog formation to date. So while meteorologists forecast rain based on climatic factors like temperature and relative humidity, no such equivalent has been established for fog. “Basic empirical research is needed before we can even think about formulating accurate climate models to help us understand the role of fog in the Bay Area’s ecosystems,” says Dr. Micheli.

So what is it that makes fog so mysterious? There is a complex set of drivers that shape advective fog formation including ocean upwelling, wind speed and direction, and the differential in temperature between the ocean and the land. The challenge is determining how these factors interact with each other to create the poorly understood “flow” of fog from the sea to the land that we observe on an almost daily basis.

Pepperwood is participating in a landmark fog monitoring project with Alicia Torregrosa of the U.S. Geological Survey and other researchers from the Pacific Coastal Fog Team, a multidisciplinary group of scientists including oceanographers, meteorologists and climatologists supported by the Gordon and Betty Moore Foundation’s TBC3 to Pepperwood. The goal of the project is to map historical fog frequency distributions using archival satellite images and to develop field-based monitoring protocols that will complement these remote data sources moving forward.

Fog sensor near Pepperwood's Bechtel House

To aid in the collection of data, Pepperwood steward Dave Anderson helped install a state-of-the-art fog sensor on loan from Environment Canada for the summer of 2012 to measure visibility and liquid water content of localized fog. An identical sensor was placed at the Bodega Bay Marine Laboratory managed by UC Davis. Set 50Km apart and spanning from the coast to the Mayacamas mountains of Pepperwood, data from these sensors will help scientists better understand the process of fog as it forms over the Pacific Ocean and is pulled inland by lower pressure systems to the east.  

Learn more at the Bodega Ocean Observing Node website.

Get real time data from Pepperwood’s weather station.