DEFINITION OF FOG

A cloud at the Earth’s surface formed by the condensation

of water vapor from the atmosphere. The fog forms

as atmospheric moisture increases and condensation occurs

on numerous nuclei, reducing visibility to less than 0.62

miles (1 km).

Fog that forms in dirty city air tends to be thicker than

fog that forms at the same atmospheric moisture count over

oceans. This is because city air has abundant nuclei that grow

more but smaller water droplets than the air over oceans,

which typically has fewer nuclei and produces fewer but larger

water droplets. Fog that forms in polluted air may be

acidic and harmful to human health, particularly if the water

droplets combine with sulfur and nitrogen oxides.

One of two main mechanisms is usually responsible for

the formation of fog. Fog may form by condensation when

the air is cooled past its saturation point (dew point), or it

may form by continuous evaporation and mixing of vapor

into the air. Radiational cooling of the air near the ground

can lower the temperature of the surface layer below the dew

point, forming radiation or ground fog. This type of fog

forms best on clear nights when a layer of moist air near the

surface is overlain by a layer of dry air, forming an atmospheric

inversion. Radiation fog forms commonly in the late

fall and winter, when nights are longest and cooling of the

surface layer lasts the longest. Low winds also help the formation

of radiation fog, as the wind promotes interaction of

the surface air with the rapidly cooling ground, promoting

faster cooling, but strong winds would mix the moist surface

layer with dry air aloft, preventing fog from forming. Since

the fog is heavy, it typically collects in valleys and low-lying

areas. During the day the fog dissipates (it does not burn off)

when the ground and low level air warms, causing the water

droplets to evaporate.

Advection fog is formed when warm moist air moves

over a cold surface, causing the air to cool below the dew

point, initiating condensation. This type of fog is common

along coastlines and is especially common in central California

in the summer. Here, warm ocean water moves over cold

upwelling ocean water near the coast, produced by westerly

winds, causing the surface air to cool below the dew point

and forming fog. Production of advection fog is enhanced by

winds that produce rolling clouds of fog moving inland during

summer months. Advection fog is also common along

headlands of other coasts where converging warm air is

cooled by the surface and forced to rise by the convergence.

Upslope fog forms as moist air flows up a mountain or

other slope, cooling below the dew point. This type of fog is

common around some mountain ranges including the Rockies

and also forms around isolated mountains such as volcanoes

where the fog may look like a small eruption in progress. A

final type of fog is known as evaporation fog, evaporationmixing

fog, or steam fog. This is produced when cold air

moves over warm water. This type of fog may commonly be

seen forming above warm lakes, rivers, and other water bodies

on cold autumn mornings. Steam fog may form over a warm

wet surface on a warm summer day, such as after a brief shower

drops water on a hot surface. The water quickly evaporates

and mixes with the air above, disappearing quickly.

See also ATMOSPHERE; CLOUDS.

Title Post:
Rating: 100% based on 99998 ratings. 99 user reviews.
Author:

Terimakasih sudah berkunjung di blog SELAPUTS, Jika ada kritik dan saran silahkan tinggalkan komentar