Marine layer
Encyclopedia
A marine layer is an air mass which develops over the surface of a large body of water such as the ocean or large lake in the presence of a temperature inversion. The inversion itself is usually initiated by the cooling effect of the water on the surface layer of an otherwise warm air mass. As it cools, the surface air becomes denser than the warmer air above it, and thus becomes trapped below it. The layer may thicken through turbulence generated within the developing marine layer itself. It may also thicken if the warmer air above it is lifted by an approaching area of low pressure. The layer will also gradually increase its humidity by evaporation of the ocean or lake surface, as well as by the effect of cooling itself. Fog
will form within a marine layer where the humidity is high enough and cooling sufficient to produce condensation. Stratus
and stratocumulus will also form at the top of a marine layer in the presence of the same conditions there.
In the case of coastal California
, the offshore marine layer is typically propelled inland by a pressure gradient which develops as a result of intense heating inland, blanketing coastal communities in cooler air which, if saturated, also contains fog. The fog lingers until the heat of the sun becomes strong enough to evaporate it, often lasting into the afternoon during the "May gray" or "June gloom
" period. An approaching frontal system or trough can also drive the marine layer onshore. With Southern California
's high concentration of military bases, a marine layer propelled inland can be colloquially described as "the marines coming inland".
A marine layer will disperse and break up in the presence of instability such as may be caused by the passage of frontal system or trough, or any upper air turbulence which reaches the surface. A marine layer can also be driven away by sufficiently strong winds.
It is not unusual to hear media weather reporters discuss the marine layer as synonymous with the fog or stratus it may contain, but this is erroneous. In fact, a marine layer can exist with virtually no cloudiness of any kind, although it usually does contain some. The marine layer is a medium within which clouds may form under the right conditions, not the layers of clouds themselves.
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
will form within a marine layer where the humidity is high enough and cooling sufficient to produce condensation. Stratus
Stratus cloud
A stratus cloud is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide . More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color...
and stratocumulus will also form at the top of a marine layer in the presence of the same conditions there.
In the case of coastal California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, the offshore marine layer is typically propelled inland by a pressure gradient which develops as a result of intense heating inland, blanketing coastal communities in cooler air which, if saturated, also contains fog. The fog lingers until the heat of the sun becomes strong enough to evaporate it, often lasting into the afternoon during the "May gray" or "June gloom
June Gloom
June Gloom is a southern California term for a weather pattern that results in cloudy, overcast skies with cool temperatures during the late spring and early summer. June Gloom in southern California is caused by the marine layer effect common to the West Coast, and is enhanced by the Catalina eddy...
" period. An approaching frontal system or trough can also drive the marine layer onshore. With Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
's high concentration of military bases, a marine layer propelled inland can be colloquially described as "the marines coming inland".
A marine layer will disperse and break up in the presence of instability such as may be caused by the passage of frontal system or trough, or any upper air turbulence which reaches the surface. A marine layer can also be driven away by sufficiently strong winds.
It is not unusual to hear media weather reporters discuss the marine layer as synonymous with the fog or stratus it may contain, but this is erroneous. In fact, a marine layer can exist with virtually no cloudiness of any kind, although it usually does contain some. The marine layer is a medium within which clouds may form under the right conditions, not the layers of clouds themselves.
See also
- InversionInversion (meteorology)In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...
- June GloomJune GloomJune Gloom is a southern California term for a weather pattern that results in cloudy, overcast skies with cool temperatures during the late spring and early summer. June Gloom in southern California is caused by the marine layer effect common to the West Coast, and is enhanced by the Catalina eddy...
- Santa Ana fog
- MarineMarine (ocean)Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
- Catalina eddyCatalina eddyThe "Catalina eddy," also called the "coastal eddy," is a localized weather phenomenon that occurs in the so-called "Bight of California", the mostly convex portion of the Southern California coast running from Point Conception to San Diego...