Coastal Fog along the NE United States and E Canada Based on 58 years of Ship Observations

An analysis is presented of the marine fog distribution based upon the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) ship observations taken during 1950–2007. Fog occurrence is reported in routine weather reports that are encoded in an ICOADS ship observation. Fog and its intensity in this work is based on man-made visibility observations. Fog occurrence is estimated using hourly observations of the number of fog events divided by the total present weather observations (e.g., 24 hrs) in a one-degree area centered on latitude and longitude grid point intersections. The mean fog occurrence for the summer (June-July-August) of 1950-2007 was computed for each grid area over the entire world. Results suggested that fog occurs with high frequency over the NW Atlantic shallow water areas during the summer. The maximum fog occurrence is found over the Grand Banks with water depth less than 200 m. Another similar fog frequency but smaller area occurs off Nova Scotia (NS). The south and south westerly winds bringing in moist and warm air from warm areas of Atlantic Ocean over the cold Labrador currents and colder ocean waters off the NS and NFL of Canada are main reasons fog high fog occurrence. The strongest SST gradient is also found within 200 km of the continental shelf edge. In this work, fog occurrence over the world oceans and specifically NW of Atlantic Ocean off the Canadian continental shelf are presented and challenges of fog occurrence calculation are summarized.