How is a low pressure formed?

Answer 1

There are a couple of different ways. This can happen anywhere, not just warm areas. Check out the low in northern Canada. http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfcwbg.gif

Thermal lows--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. These happen in extremely hot regions around the world.

Lee side low--Forms when a jet stream flows perpendicular to a mountain range.

Frontal low--A trough in the jet stream has divergence downstream of it. Divergence in the upper levels pulls air upward from below to replace it. This lowers the surface pressure and can make a low. This is a cold-core low (strongest winds aloft).

Also, a jet maximum can induce a low pressure area in its left exit and right entrance quadrants.

Tropical low--latent heat released into the upper troposphere warms & expands the atmospheric column, lowering the surface pressure. This is in some ways similar to what happens in a thermal low, but not 100% same. This is a warm-core low (strongest winds at the surface).

Answer 2

A low pressure area, or a low for short, is a region where the atmospheric pressure is lowest with relation to the surrounding area. Tropical storms, extratropical cyclones, subpolar cyclones, and subarctic cyclones are called low-pressure cells in some English-speaking communities.
Lows are frequently associated with stronger winds and atmospheric lift. This lift will generally produce cloud cover, due to adiabatic cooling, once the air becomes saturated. Thus, low pressure typically brings cloudy or overcast skies, which may minimize diurnal temperature extremes in both summer and winter, due to the significant cloud cover. This is due to less incoming shortwave solar radiation and lower temperatures, since the clouds reflect sunlight. 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.
Climatologically, low pressure forms at the Intertropical convergence zone (ITCZ), as part of the Hadley cell circulation. Many of the world's rainforests are associated with these climatological low pressure systems. 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. 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 convergence lows or frontal lows.
Surface low pressure systems will tend to be smaller in area and have stronger surface winds than a given high pressure system, due to the addition of surface friction to the pressure gradient force, centrifugal force and coriolis effect that drive the circulation.

low pressure system : http://en.wikipedia.org/wiki/Image:Low_pressure_system_over_Iceland.jpg

Answer 3

If you mean weather-wise, then air at ground level comes in to replace the air that is rising due to the warming of it, thereby making ground level air pressure lower. Happens only in warm areas.

Answer 4

when the surface of earth give off its heat the air that contact with earth absorb this heat and expand. then its density decreases and go up and produce relatine vacuum and decreases pressure.

Answer 5

i have not studied about it