High pressure area
A high-pressure area , also called anticyclones or high , is a large-scale air mass on the ground, which is horizontally characterized by a higher air pressure than the surrounding area . Conceptually, it is opposed to the low pressure area .
Origin and classification
In a (ground) high pressure area, air masses sink over a large area. The air is heated adiabatically so that no condensation and therefore no cloud formation can take place. Near the ground, the air flows out of the high pressure area towards the low pressure area , it diverges . There is therefore no formation of fronts in the high . As the air masses sink, an inversion forms . The clouds dissolve.
High pressure areas are divided into three categories according to the differences in their formation and frontal development:
An altitude high is a high pressure area that occurs at high altitudes and is therefore shown in altitude weather maps . It is always associated with a depth in the ground , since the vertical pressure gradient is lowered when surfaces are heated and the relative reduction in air pressure on the ground with increasing altitude is reflected in a higher pressure relative to the horizontal environment. One can, therefore, in the reverse case of a ground high (even high thermal) also derive a height low.
A cold spike occurs when, for example, air cools down over a cool land mass in winter (e.g. Central Asian high). The air then has a greater density and exerts a higher pressure on the surface. In the middle latitudes it can also arise in the form of flat wedges on the back of cyclones as an intermediate high.
There is also the so-called Azores high, which is located in the Atlantic and is associated with 1016 to 1034 hPa, the high can also provide a lot of sunshine and summer temperatures in Central Europe in summer, but this only occurs when individual high-pressure cells detach from the actual high and move to Central Europe, depending on whether the high is south or north, it may be that the "opponent" of the Azores high, the Iceland low , can then ensure changeable weather in Central Europe, i.e. the further south the Azores high, the more changeable it becomes the weather conditions and the more northerly the high, the warmer and sunnier the weather. In late autumn, however, the Azores high, despite the fact that it is north, it ensures constant fog and cold weather in the lowlands, but the higher the place, the warmer and sunnier it becomes, here one speaks also from the inversion weather situation.
A dynamic high is generated by Rossby waves ( polar front jet stream). The dynamic west wind current ( Azores high ) has a major influence on the weather in Central Europe .
Currents in the high pressure area
The wind always flows anticyclonally around a high pressure area (in the northern hemisphere this is clockwise , in the southern hemisphere it is counterclockwise). The direction of rotation is determined by the Coriolis force , which deflects a moving air mass in the northern hemisphere in the direction of movement to the right and in the southern hemisphere accordingly in the direction of movement to the left, whereby the strength of this deflection increases from the equator to the poles and depends on the wind speed ( Baric wind law ).
Naming for Europe
The names used in Germany and some neighboring countries for low and high pressure areas that influence the weather in Europe are given by the Meteorological Institute of the Free University of Berlin .
