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Equatorial climate
Equatorial climate
A hot climate, with rain in every month, and with two periods of maximum rain just after the time when the overhead Sun crosses the equator. Temperatures vary by less than 5°C throughout the year. (For features of equatorial climates see: Doldrums; Equatorial low; and Supercells.)
Equatorial low
A zone of low pressure air that encircles the Earth in the tropics, and whose position is influenced by the overhead Sun.
Equinox
The two times of the year when the midday Sun is overhead at the equator, and the length of day and night are the same everywhere in the world. This happens in March and September.
Evaporation
The loss of water from the surface due to the drying effect of the air.
Evapotranspiration
The loss of water from plants, bodies of water and ground surfaces due to the twin processes of evaporation (on water and ground) and transpiration (on plants). It is a more accurate description of the amount of water lost from forests and fields than evaporation.
Eye
The central, calm region of a tropical cyclone. The eye may be just 2 to 3km across, compared with the diameter of the storm, which may be over 500km. There is no cloud over the eye, while all around the cyclone contains raging winds and torrential rain.
Eye wall
The towering clouds that make the edge of the eye in a tropical cyclone.
F
Fill, filling
When a cyclone is weakening and air pressure is rising, weather forecasters say that the depression is filling.
Foehn
A dry, warm wind that blows down the leeward side of mountains. It is caused as winds flow across mountains, warming as they descend. The name foehn is given to the warm winds that blow
over the European Alps, where the ferocious winds create a roaring sound. The chinook is the name for a similar wind that blows down the eastern slopes of the North American Rocky Mountains.
Freezing point
The temperature at which water turns to ice. It is usually 0°C.
Freezing rain
When rain falls onto frozen surfaces, it often freezes, creating sheets of ice. This often happens in winter in mid-latitudes when a depression blows over an area that has been below freezing for many days.
Friagem
A cold, antarctic wind that blows across southerly regions of South America in the lee of the Andes. It moves with the trailing edge of a passing depression (similar to a North American norther or an Australian buster).
Front
Used in meteorology to describe the boundary between two types of air in the atmosphere. Fronts are nearly always marked by a broad
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Fog
Cloud that forms at ground level. Cold sea or land conditions make the air cool, and some of the moisture in it condenses into tiny water droplets (see: Condensation). The more water droplets that form, the thicker the fog. The thinnest form
of fog is called mist. (See also: Advection fog and Radiation fog.)
 Fog – Fog is the result of a combination of low temperatures and moist air. Valley bottoms are places where cold air builds up during the night, while moisture from a warm river may feed extra vapour into the air. As a result, fogs form first and last longest over rivers.