What are high-pressure ridges and low-pressure troughs and their characteristics?

High pressure ridge: it is a ridge-like part where the isobar of horizontal pressure field protrudes to the low pressure side. A weather system with low pressure on three sides and high pressure on one side is called high pressure ridge for short, and the climate in the high pressure ridge is weak. It is often accompanied by divergent and sinking movements, and the weather is fine.

Ridge lines of high altitude pressure can be divided into three categories: ridge lines with large amplitude from north to south (sharp ridge), ridge lines with medium amplitude (middle ridge) and shallow ridge, and there are some special cases. According to the width of cloud system and the characteristics of cloud front boundary, the amplitude of ridge line and the width of ridge area can be judged.

Features:

In the ridge of high pressure, the line connecting the point with the largest anticyclone curvature on the contour line or isobar is the ridge line. When the high-pressure ridge obviously protrudes outward and is inserted between two low-pressure areas or two low-pressure grooves like a chess piece, it is also called a high-pressure wedge in the figure.

In the area controlled by the ridge of high pressure, due to the rotation of the earth, the air keeps flowing clockwise, and above it, there will be air sinking to supplement the flowing air. In the process of high-altitude air flowing to low altitude, the temperature rises gradually, and the water vapor in the air will evaporate continuously, which also makes the water vapor and dust on the ground not conducive to rising and condensation. Therefore, it is usually sunny to cloudy near the high pressure center.

The point of maximum anticyclone curvature on the isobaric (high) line of the high-pressure ridge. The connecting line of the ridge points is called the ridge line, and the airflow in the area where the ridge line is located has obvious divergent and sinking movements, and the weather is clear. Ridge points can be used as eigenvalues of system activities. For example, in China's forecasting business, the longitude value of the western ridge point of the characteristic contour line of the western Pacific subtropical high on the 500hpa or 700hpa map is often analyzed in time to judge the future change trend of the subtropical high ridge line.

Ridge lines of high altitude pressure can be divided into three categories: ridge lines with large amplitude from north to south (sharp ridge), ridge lines with medium amplitude (middle ridge) and shallow ridge, and there are some special cases. According to the width of cloud system and the characteristics of cloud front boundary, the amplitude of ridge line and the width of ridge area can be judged. Because of the different water vapor distribution on land, the cloud distribution on land and water is also different. After the position of high-pressure ridge line is determined, the wind direction at high altitude can be determined. ?

A ridge with a large north-south range winds (sharp ridge)

The cloud band associated with the sharp ridge is relatively narrow, because the distance between the trough line and the ridge line is very short, so the ascending motion zone appears in a very narrow zone. At the position of the ridge line, the sign of vertical movement suddenly changes from rising to sinking. So the ridge line is also the boundary of the cloud area.

The sharp ridge is generally located at the front edge of the cloud belt. In some cases, the ridge line is set at several longitudes before the front edge of the cloud area. On the east side of the sharp ridge, some cloudy or cloudless areas appeared. This is caused by the subsidence movement area in front of the ridge.

Medium ridge line

The cloud area related to the middle ridge line is generally wider than that in the narrow ridge line, and the front boundary of the cloud area; It doesn't end abruptly on the ridge line as it does in a sharp ridge. The position of this ridge line is roughly set at several longitudes from the front boundary to the cloud area west of the front boundary. The sign change of vertical velocity on the ridge line is not sudden, but gradual transition. Therefore, in some cases, the cloud area will extend to the front of the ridge line, and the clouds that extend beyond the ridge line are generally cirrus clouds. The position of the ridge line is probably on the front boundary of the middle cloud area, which can often be seen through cirrus clouds. If no cirrus cloud extends (advection) to the ridge line, the ridge line is located at a point behind the front boundary of the middle cloud area.

Shallow ridge

On the broad and shallow ridge, the cloud area is the widest of the three types of ridge lines. This is because the range from the gully line to the ridge line is very wide, and the range of the ascending motion zone is also very wide. The clouds at the front boundary of the cloud area gradually disappear after entering the gradually increasing subsidence movement area.

On the shallow ridge, because the sign change of vertical motion is gradual transition, the cloud can extend downstream for a considerable distance across the ridge line. Therefore, the shallow ridge is located in the cloud area west of the front boundary of the cloud area. In this vast cloud area, some anticyclone lines are sometimes seen. The position of the northern part of the ridge line is roughly the position of the ridge line determined by these ridge lines.

Ridge is Q-type blocking high pressure. There are often some small ridges in the high pressure ridge of Q-type blocking situation. These ridges generally run east-west, unlike Q-shaped high-pressure ridges. These ridges are located at the front of the cloud belt. The cloud area of this small ridge is similar to that of the pointed ridge mentioned above. A small ridge in the flat west wind. In the flat westerly airflow, some small ridges are often superimposed. The place where these ridges are located is often the place where the clouds in the cloud belt become thinner.

Low pressure trough: the long and narrow area extending from the low pressure area is called low pressure trough, or trough for short. On a plane with the same height, such as a certain area, the air pressure is lower than the adjacent three sides and higher than the other side. On the weather map, the trough of low pressure generally extends from north to south. The trough extending from south to north is called inverted trough, and the trough extending from east to west is called transverse trough. The most curved line of each isobar in the groove is called the groove line. In the middle and lower troposphere, the airflow near the trough of low pressure is in the form of convergence and rising, so it is easy to produce cyclone and other weather systems near the trough of low pressure, often accompanied by rain, snow, strong wind and cooling.

Features:

The trough of low pressure refers to the connecting line between the points with the highest cyclone curvature and the lowest pressure (or potential height) on the medium pressure (high) line. It is the area with the strongest horizontal convergence of airflow in the low pressure trough. Usually, the weather changes obviously near the trough line. For example, in the westerly belt, the southerly wind often blows in front of the trough line, and there is an upward movement. A large amount of water vapor can form clouds and precipitation. There is a northerly wind with sinking movement at the back of the trough line, and the weather is mostly cloudy and sunny. In the westerly belt, the distribution pattern and movement of various trough lines are often different. The trough lines near the meridian on the south side of the low pressure are called vertical trough lines, which often move eastward; The trough line on the west side of the low pressure is close to parallel to the weft circle, which is called transverse trough line and often moves to the southeast; The trough line extending from south to north on the north side of the low pressure or the back of the high pressure is called the inverted trough line (such as the southwest inverted trough) that slowly moves eastward or even westward. There is also a north-south easterly trough line moving from east to west in the easterly belt.

A weather system with high air pressure on three sides and low air pressure on one side is called a trough for short. The trough with low pressure is often accompanied by convergence and upward movement, which is easy to produce clouds and precipitation.

In the part of the weather map where the low pressure center extends outward, the isobar is not closed, and it is a slightly U-shaped or λ-shaped low pressure area (like a water tank with low air pressure in the middle and high air pressure on both sides).

: low pressure groove and high pressure ridge

The terms "trough of low pressure" and "ridge of high pressure" often appear in weather forecast broadcasts. They are actually cyclones and anticyclones.

In the westerlies of the northern hemisphere, the atmosphere fluctuates. The low-pressure trough is a low-pressure trough. The airflow rotates counterclockwise, and the air pressure distribution is low in the middle and high around. The air flows from the periphery to the trough, and the air in the trough converges and rises, forming rainy weather. The peak area of the wave is the ridge of high pressure, the airflow rotates clockwise, the air pressure distribution is high in the middle and low around, the air diverges outward from the center, and the downward flow prevails in the ridge, and the weather is generally sunny. A pair of ridges, one low and one high, form waves. The upper trough ridge system in the westerly belt is called westerly storm.

References:

Baidu encyclopedia-high pressure ridge

Baidu encyclopedia-low pressure tank