Variability of Marine Fog Along the California Coast

Visibility in coastal regions has a significant impact on government, commercial, and private sector activities. The primary phenomenon significantly affecting visibility along the western United States coastal regions is fog. Fog is a natural hazard to boating, commercial shipping, and other waterway activities.The West Coast of the United States has been identified as one of the major fog producing regions of the world. Present accuracy in predicting marine coastal fog and low stratus clouds is limited. Although most weather forecasting has improved with recent advances in atmospheric circulation models and satellite observations, there is relatively little operational guidance for the prediction of marine and coastal fog.Currently the forecasting of visibility relies mainly on the availability of local observations and experience with local weather tendencies. National Weather Service and other forecasters typically focus on selected local conditions which usually presage fog formation and if a sufficient number are present, they will forecast possible fog for the region. However, this level of information and experience is not available in all coastal areas. Results in this study suggest that attention to the large-scale circulation in addition to local conditions may lead to increased skill and accuracy in extended range forecasts.The large-scale structure and interannual variability of fog have not been well described because data has been unavailable and a large volume of data is required. In the present analysis, several years of observations from a set of coastal weather stations and a set of comprehensive marine weather reports (primarily ships) is used to examine large-scale processes and local conditions which affect fog formation. A discussion of fog observation criteria is given. In addition, evidence is provided by a collection of observations of hours of fog-horn operations at several coastal sites over 15 years, starting in 1950.The relationship between local and large-scale conditions, and fog and stratus formation may yield improved predictability of fog. This study indicates that large-scale conditions, especially regional-hemispheric circulation, are a vital component of both high and low fog occurrences; moreover, atmospheric circulation in the Eastern North Pacific Ocean and on the West Coast may contribute to improved forecasts for the development and persistence of fog

Learning Analytics and Measurement in Behavioral Sciences (LAMBS)

LAMBS Lab at University of Notre Dam

Spatial and Temporal Patterns of Cloud Cover and Fog Inundation in Coastal California: Ecological Implications

Abstract: The presence of low-lying stratocumulus clouds and fog has been known to modify biophysical and ecological properties in coastal California where forests are frequently shaded by low-lying clouds or immersed in fog during otherwise warm and dry summer months. Summer fog and stratus can ameliorate summer drought stress and enhance soil water budgets and often have different spatial and temporal patterns. Here, this study uses remote sensing datasets to characterize the spatial and temporal patterns of cloud cover over California’s northern Channel Islands. The authors found marine stratus to be persistent from May to September across the years 2001–12. Stratus clouds were both most frequent and had the greatest spatial extent in July. Clouds typically formed in the evening and dissipated by the following early afternoon. This study presents a novel method to downscale satellite imagery using atmospheric observations and discriminate patterns of fog from those of stratus and help explain patterns of fog deposition previously studied on the islands. The outcomes of this study contribute significantly to the ability to quantify the occurrence of coastal fog at biologically meaningful spatial and temporal scales that can improve the understanding of cloud–ecosystem interactions, species distributions, and coastal ecohydrology

Significance of summer fog and overcast for drought stress and ecological functioning of coastal California endemic plant species

Fog drip is a crucial water source for plants in many ecosystems, including a number of global biodiversity hotspots. In California, dozens of rare, drought-sensitive plant species are endemic to coastal areas where the dominant summer moisture source is fog. Low clouds that provide water to these semi-arid ecosystems through fog drip can also sharply reduce evaporative water losses by providing shade. We quantified the relative hydrological importance of cloud shading vs. fog drip. We then examined how both factors influence the range dynamics of an apparently fog-dependent plant species spanning a small-scale cloud gradient. The study area is on Santa Cruz Island off the coast of southern California. It is near the southern range limit of bishop pine (Pinus muricata D. Don), a tree endemic to the coasts of California and Baja, Mexico. We measured climate across a pine stand along a 7 km, coastal-inland elevation transect. Short-term (1-5 years) monitoring and remote sensing data revealed strong climatic gradients driven primarily by cloud cover. Long-term (102 years) effects of these gradients were estimated using a water balance model. We found that shade from persistent low clouds near the coast reduced annual drought stress by 22-40% compared with clearer conditions further inland. Fog drip at higher elevations provided sufficient extra water to reduce annual drought stress by 20-36%. Sites located at both high elevation and nearer the coast were subject to both effects. Together, these effects reduced average annual drought stress by 56% and dramatically reduced the frequency of severe drought over the last century. At lower elevation (without appreciable fog drip) and also near the inland edge of the stand (with less cloud shading) severe droughts episodically kill most pine recruits, thereby limiting the local range of this species. Persistent cloud shading can influence hydrology as much as fog drip in cloud-affected ecosystems. Understanding the patterns of both cloud shading and fog drip and their respective impacts on ecosystem water budgets is necessary to fully understand past species range shifts and to anticipate future climate change-induced range shifts in fog-dependent ecosystems