The letter L reprents the center of a Low pressure area. L is the twelfth letter of the Latin alphabet. Its name in English is el or occasionally ell (ɛl

A large low-pressure system swirls off the southwestern coast of Iceland.

A low pressure area, or "low", is a region where the atmospheric pressure is lower in relation to the surrounding area. Tropical storms, extratropical cyclones, subpolar cyclones, and subarctic cyclones are called low-pressure cells. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of Cyclones defined as synoptic scale low

Lows are frequently associated with stronger winds and atmospheric lift. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " This lift will generally produce cloud cover through adiabatic cooling, once the air becomes saturated as it rises. Cloud cover (also known as cloudiness, cloudage or cloud amount) refers to the fraction of the Sky obscured by Clouds when observed The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere Thus, low pressure typically brings cloudy or overcast skies, which may minimize diurnal temperature extremes in both summer and winter. Overcast or overcast weather is the meteorological condition in which Clouds obscure 95% or more of the sky Diurnal temperature variation is a Meteorological term that relates to the variation in Temperature that occurs from the highs of the Day to the cool of Summer is one of the four Temperate Seasons Summer marks the warmest time of year with the longest days Winter is one of the four Seasons of Temperate zones Calculated astronomically, it begins on the Solstice and ends on the Equinox Since the clouds reflect sunlight, incoming shortwave solar radiation is less which causes lower temperatures during the day. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. Shortwave radiation (SW is a term used to describe the Radiant energy in the visible (VIS near- ultraviolet (UV and Near-infrared (NIR wavelengths Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature At night, the absorptive effect of clouds on outgoing longwave radiation, such as heat energy from the surface, allows for warmer diurnal low temperatures in all seasons. Outgoing Longwave Radiation (OLR is the energy leaving the earth as infrared radiation at low Energy. In Europe (especially in the UK), reoccurring low pressure weather systems are typically known as depressions. These tend to bring wet weather throughout the year.

Climatology

Climatologically, low pressure forms at the Intertropical convergence zone (ITCZ), as part of the Hadley cell circulation. Climatology (from Greek grc κλίμα klima, "region zone" and grc -λογία -logia) is the study of Climate, scientifically The Intertropical Convergence Zone (ITCZ, also known as the Intertropical Front, Monsoon trough, Doldrums or the Equatorial The Hadley cell is a circulation pattern that dominates the tropical atmosphere with rising motion near the equator poleward flow 10-15 kilometers above the surface descending motion Many of the world's rainforests are associated with these climatological low pressure systems. Rainforests are Forests characterized by high Rainfall with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches Frontal lows are temperate zone phenomena and develop along the polar front as a result of the interaction between cold and warm surface air masses. A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. Atmospheric circulation is the large-scale movement of air and the means (together with the smaller Ocean circulation) by which Heat is distributed on the surface For airmass in Astronomy, see Airmass. In Meteorology, an air mass is a large volume of Air that Thermal lows also form over areas such as Death Valley as the result of intense ground heating; they are much smaller in geographic extent than either convegence lows or frontal lows. Death Valley is the lowest driest and hottest Valley in the United States.

Surface low pressure systems will tend to be smaller in area and have stronger surface winds than a given high pressure system because of the addition of surface friction to the pressure gradient force, centrifugal force and coriolis effect that drive the circulation

Weather

Low pressure area is commonly associated with bad weather, while high pressure area is associated with plenty of sunlight or good weather. In physics the Coriolis effect is an apparent deflection of moving objects when they are viewed from a Rotating frame of reference. A high pressure area (also called a high or high-pressure is a region where the Atmospheric pressure is greater than surrounding areas On the land or on the sea surface, after getting heat from the sunlight, water evaporation becomes more intense, and a formation of a localized low pressure area can be expected. A rainstorm or a tropical cyclone (if on the sea) can well be formed in such conditions. Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Wind intensity can be approximately measured by the atmospheric pressure difference between two relatively nearby locations.

Thermal low

In deserts, lack of ground and plant moisture that would normally provide evaporative cooling can lead to intense, rapid solar heating of the lower layers of air. A desert is a Landscape or region that receives very little precipitation. Evaporative coolers (also called swamp, desert, or air coolers) are devices that cool air through the simple Evaporation of water The hot air is less dense than surrounding cooler air. This, combined with the rising of the hot air, results in an isolated low pressure area called a thermal low.

See also

• Cyclone
• High pressure area
• Surface weather analysis
• Weather map