Fog-day trends observed by the Global Surface Summary of the Day (GSSOD) dataset

Abstract:

It has long been understood that fog plays an important role in the atmospheric radiation budget, as well contributes to many transportation related fatalities and injuries around the world. This study utilizes over 8,000 Global Surface Summary of the Day (GSSOD) certified ground stations around the world to investigate the possible trends observed in fog-days over the past 44-years, as well as to examine the validity of these trends under varying observational techniques. Results show strong large-scale regional trends in the raw fog-day data, with locations such as the United States and much of Europe observing very large decreases in fog-day occurrence in the past four decades. However, when comparing fog-day counts to the simultaneous visibility, it is clear that several different fog-day data collection techniques were used throughout the time series in regions such as these. For example, many stations in the United States made data collection changes in the mid 1990’s, and again in the mid 2000’s. In order to remove the artificial trends caused by changes in the data collection techniques, a method was developed to determine which stations around the globe indeed encountered at least one false deviation to the timeseries. After applying the definition to all GSSOD stations, 1696 stations were identified as being quality long-term fog-day stations. Utilizing these stations, more robust regional trends can be identified over some specific regions. For example, Spain, Australia, and China show statistically significant decreases in fog-day occurrence. India and Japan show increases in fog day occurrence. With the ability to isolate the ground stations having the robust long-term fog record, it allows for further analysis into the driving factors of these trends such as temperature and moisture, which have shown to be changing regionally under a varying climate.