engleski

Worldwide Marine Fog Occurrence and Climatology

Herein, an analysis is presented of the world’s marine fog distribution based upon the International Comprehensive Ocean-atmosphere Data Set (ICOADS) ship observations taken during 1950–2007. Fog, shallow fog, and mist are taken from routine weather reports that are encoded in an ICOADS ship observation with the “present weather” code. Occurrence is estimated by the number of observations of a type divided by the total present weather observations in a one-degree area. The bulk of the observations are in the northern temperate and tropical oceans, with decreasing numbers south of 20 S and large data voids in the polar oceans. Marine fog is infrequent over most of the world’s oceans with the median occurrence 0.2 % while it is in isolated maxima for values larger than about 2 %. In a specific location, either fog or mist are the most frequent, followed with an order of magnitude lower occurrence by shallow fog. The two major open ocean fog maxima in the world occur on the northwestern side of northern hemisphere oceans during the summer under atmospheric subsidence over a cold polar current. The distribution of the center of the maximum and highest values are over shallow water and follow the shape of the shallow bathym- etry. For the highest occurrences, surface air is preconditioned by warming over a western boundary current followed by cooling over a negative SST gradient and stable lower atmosphere suppressing boundary layer exchange with the air above. The horizontal fog structure is set by surface ocean currents, sea surface temperature gradients and seasonal wind direction. Marine fog’s most frequent occurrence and largest areal coverage is in the NW Pacific in June–July–August, reaching its peak value of 59.8 % over the Kuril Islands on the western side of the Ohyashio current.

sea fog ; coastal fog ; climatology ; ICOADS ; ship observations ; weather report ; world fog ; climatology

nije evidentirano