Barometric hollow

In Meteorology, a hollow thalweg or barometric is an outgrowth of a depression. One thus indicates a zone of lower Atmospheric pressure than the surrounding areas on an isobaric chart . The hollow extends since the depression along an axis passing by its center. The isobar S encase the ones in the others and form a “V” where the pressure decrease while going towards concavity.

The barometric hollows are thus similar to a geographical valley. They can be found on the surface or altitude in the atmospheric Circulation. On the surface, one will often find a face in his axis and at the time of its passage, the observer will notice a change of Vent. The depressions of surface are formed in general in front of a hollow of altitude.

Formation

A barometric hollow is the result of the movements of the air in the atmosphere. In the areas where there is ascending movement close to the ground and diverge in altitude, one has a loss of mass. The pressure thus becomes lower at this place.

In altitude, that occurs when one with the meeting of a Masse of cold air and another heat along a thin ribbon called zone barocline. There is then the creation of a jet-stream which makes plunge the cold air towards the equator and the hot air towards the pole S, creating an undulation in the circulation which one calls a Onde of Rossby. These undulations give the hollows and peaks of altitude. In general, the advection of absolute swirl is positive between these two entities, but more close to the peak, whereas it is negative right behind a hollow.

On the surface, the movements of altitude under the positive advection of swirl are reflected by the formation of depressions and hollow. One can form barometric hollows of surface in two other ways:

orographical: created when circulation is blocked by mountains. The air is forced in altitude above the mountains and is uncoupled from circulation from surface downstream from those. The wind with the foot of the mountains is not thus any more in balance geostrophic but rather directed along the gradient of pressure (perpendicular to the isobars). The force of Coriolis then deviate it downstream from the mountains creating a loss of mass and thus a hollow.
Hollow thermics: when cold air passes above a hotter surface, the air becomes unstable and is raised in altitude. The loss mass creates a hollow or a depression.

Associated time

The barometric hollows are generally accompanied by Nuage S and of Précipitation S because one finds air in rise there as mentioned previously. One finds:

hollows or thalwegs of the average latitudes which move with the general circulation of west in east;
the hollows or thalwegs of the intertropical Zone generally moving is in west;
the equatorial waves which correspond to oscillations of the Zone of intertropical convergence;
hollows or thalwegs of the zones of trade winds which are directed perpendicular to the current;
hollows or thalweg of monsoon crossing the India of the North-West in south-east lasting the monsoon of summer;

See too

External bonds

Thalweg in the glossary of Weather France

Random links:

Barometric hollow

Formation

Associated time

See too

Related articles

External bonds