The fog comes
on little cat feet.
It sits looking
over harbor and city
on silent haunches
and then moves on.
Crystal Cove State Park’s Mediterranean climate is characterized by moist, foggy summer mornings, with the fog burning off by midmorning to bring warm, sunny days and cool evenings.
The marine atmospheric boundary layer (MABL) is a layer or cool, moist maritime air with the thickness of a few thousand feet immediately below a temperature inversion. In the Mediterranean climate of the Los Angeles basin conditions favorable for the formation of a MABL inversion can occur during any month of the year, but are most common during the summer or “dry” season that runs from May through the middle of October. Natives of “The Southland” make reference to “May Grey” and “June Gloom” in bemoaning the frequent cool, damp, overcast days. Along the coast of California and Oregon, the MABL inversion is created when subsiding air is heated by compression associated with the North Pacific Subtropical High passes over the cold, equator-bound waters of the Pacific Current. As moist air rises from the ocean surface, it becomes trapped under dome of subsiding high pressure. If the height of the marine layer is 4000m or less, the marine air is compressed into fog. If the height is greater than 4000m, a layer of stratus clouds often forms at the top of the layer. On average the layer reaches its peak for the day at around 7:00 a.m. (local time) near the coast and around noon over interior valleys. Because of solar heating, the layer often “retreats” toward the coast during the early afternoon and is at its thinnest point during the hours prior to sundown. Although more sunlight is allowed in once this daily “retreat” begins, areas under the influence of the MABL still have a strong maritime character with lower average afternoon temperatures and higher dew points than those recorded concurrently at more elevated, continental locations only a few miles away.
The presence of a MABL inversion is also a key ingredient for the creation of stagnant air pollution (smog) in the Los Angeles basin. Smog, a noxious mixture of fog and carbon emissions cause respiratory and other health problems for Los Angeles residents and add millions or billions of dollars to health care costs.