GOES-derived fog and low cloud indices for coastal north and central California ecological analyses

Fog and low cloud cover (FLCC) strongly influences the water, energy, and nutrient flux of
coastal ecosystems. Easy-to-use FLCC data are needed to quantify the impacts of FLCC on ecosystem
dynamics especially during hot and dry Mediterranean climate summers. Monthly, annual, and decadal FLCC
digital maps (indices) were derived for June–September 1999–2009 for coastal California, latitude 34.50°N
(south of Monterey Bay) to latitude 41.95°N (north of Crescent City) from 26,000 hourly night and day
Geostationary Operational Environmental Satellite (GOES) images. Monthly average FLCC ranges from <2 to
18 hours per day (h/d). Average FLCC over the ocean increases from north (9 h/d) to south (14 h/d), whereas
on land, FLCC is highest where land juts into the prevailing NW winds and is lowest in the lee of major capes.
FLCC advects farthest inland through low-lying NW ocean-facing valleys. At night, average total hours of
FLCC are higher more frequently on land than over the ocean. The interannual FLCC coefficient of variation
shows long-term geographic stability that is strongly associated with landform position. FLCC hours per day
mapped contours, derived from decadal average FLCC, delineate the commonly used term “fog belt” into
FLCC zones with increased locational precision. FLCC indices are available for download from the California
Landscape Conservation Cooperative Climate Commons website (http://climate.calcommons.org/datasets/summertime-fog).

FLCC indices can improve analyses of biogeographic and bioclimatic species distribution
models; understanding meteorological mechanisms driving FLCC patterns; solar energy feasibility studies;
investigations of ecohydrology, evapotranspiration, and agricultural irrigation demand; and viticulture
ripening models.