Is there a difference between the front and the front?
The front is a narrow transition zone where cold and warm air masses meet.
(A) the concept of front
The front is formed by the contact of two air masses with different properties, and its horizontal range is equivalent to the horizontal scale of air masses, ranging from several hundred kilometers to several Qian Qian meters. The horizontal width is generally tens of kilometers near the ground, narrow only a few kilometers, wide only a few hundred kilometers, and can be widened to 200-400 kilometers or even wider at high altitude.
Frontal zone refers to the narrow transition zone between cold and warm air masses;
Because the width of the front area is very narrow compared with the width of the air mass, the front area is often regarded as a geometric surface, which is called the front.
The intersection of the front and the ground is called the front.
Front and front are collectively referred to as front.
(B) the characteristics of the front
1, frontal slope
The degree of frontal slope is called frontal slope.
The formation and maintenance of front slope is the result of the joint action of earth deflection force and pressure gradient force. As shown in the figure
The horizontal pressure gradient force (G) generated between two air masses forces the interface between them to be horizontal.
When the geostrophic force and the pressure gradient force are balanced, the airflow makes geostrophic motion parallel to the front, and then the interface between the cold and warm air masses does not transition to the horizontal direction, showing an inclined state.
2. Temperature field
On the weather map, the temperature field in the front area shows that the isotherms are very dense and almost parallel to the front. Because the front is inclined in space, the location of isothermal dense area on each isobaric surface shifts to the cold area side with the increase of height.
Near the front area, because the lower part of the front is a cold air mass and the upper part is a warm air mass, the temperature rises with the height when passing through the front area from bottom to top, which is called front inversion.
3. Air pressure field
There are cold and warm air masses with different densities on both sides of the front, so the pressure tendency on both sides of the front is discontinuous. When the isobar crosses the front, a corner is generated, the tip of the corner points to the high-pressure side, and the front falls into the low-pressure groove.
4. Wind field
Because the ground front is in a trough of low pressure, according to the gradient wind principle, there should be cyclone shear in the wind field near the front. As shown in the figure, when the cold front is northeast-southwest, the front is mostly southwest wind, and the back is mostly northwest wind, showing wind cyclone shear.
(3) Front type and weather
1. Types of fronts
According to the moving direction and structure of cold and warm air masses on both sides of the front, the front is generally divided into four types: cold front, warm front, quasi-static front and blocking front.
A cold front is a front that a cold air mass pushes the front surface to move to one side of a warm air mass. Due to different moving speeds, cold fronts can be divided into (slow) cold fronts and (fast) cold fronts.
The warm front is the front that the warm air mass pushes the front surface to move to the side of the cold air mass.
Quasi-static front refers to the front where the cold air mass and the warm air mass are equal in strength, or sometimes the cold air mass is dominant, sometimes the warm air mass is dominant, and the front rarely moves or swings back and forth.
Blocking front is the front formed when the cold front catches up with the warm front. The warm air between the two fronts is lifted off the ground and trapped at high altitude, and the cold air mass behind the cold front contacts with the cold air mass in front of the warm front.
2. Positive weather
(1) Warm Front Weather
As shown in the figure, the slope of the warm front is relatively small, and the warm air mass slowly slides upward along the front in the process of pushing the cold air mass. When it rises to the condensation height, a broad and systematic layered cloud system is generated on the front. Typical cloud sequences are Cirrus (Ci), cirrostratus (Cs), Stratosphere (As) and nimbostratus (Ns). Warm front precipitation mainly occurs in the middle of nimbostratus, mostly continuous precipitation.
There are few obvious warm fronts in China, and most of them are accompanied by cyclones. In spring and autumn, it generally appears in the Jianghuai Basin and Northeast China, and it mostly appears in the Yellow River Basin in summer.
(2) Cold front weather
Cold front can be divided into two types according to the moving speed, one is cold front and the other is cold front.
The first type of cold front (slow moving cold front) moves slowly, with a small front slope (about1100), and its weather pattern is shown in the figure. Layered cloud system similar to warm front is produced, but the distribution order of cloud system is opposite to warm front, and cloud system and rain area are mainly located behind ground front. Because the front slope is greater than the warm front, the cloud area and rain area are narrower than the warm front, and the precipitation is more stable.
The second kind of cold front (fast cold front) moves fast and has a large slope (1/40— 1/80), and its weather pattern is shown in the figure. The cold air mass behind the cold front is powerful and moving fast, which violently impacts the warm air, making the warm air rise rapidly, forming a narrow range of cumulus clouds arranged along the front, resulting in convective precipitation weather. In summer, the air is heated unevenly and has strong convection. When the cold front moves, there are often strong winds, dark clouds, heavy rains and lightning, and the meteorological elements change dramatically. However, this kind of weather lasted for a short time. After reaching the front line, the temperature dropped sharply and the weather suddenly became sunny.
(3) Quasi-static frontal weather
Similar to the warm front weather, the cloud area and precipitation area are wider than the warm front, and the precipitation intensity is relatively small, but it lasts for a long time, which may cause cloudy weather with rain in Mao Mao for several days.
(4) Blocking front weather
The occlusion front is formed by merging two moving front edges. So its weather still retains the weather characteristics of the original two fronts.
(4) frontogenesis and frontogenesis
1, horizontal airflow convergence and divergence
In the process of convergence, the airflow can make the cold and warm air masses close, and the horizontal temperature gradient increases, which is beneficial to frontogenesis. On the contrary, the divergence of horizontal airflow makes the cold and warm air mass far away, and the horizontal temperature gradient decreases, which is beneficial to the elimination of front.
2. Vertical movement of air
The vertical movement near the front is that warm air rises and cold air sinks. Without condensation, it is generally not conducive to frontogenesis but beneficial to frontogenesis.
3. Air heat exchange
If the cold and warm air mass stays on the cold and warm underlying surface, the front will be strengthened.
The air masses on both sides of the front move to the underlying surface with similar properties, which is beneficial to the elimination of the front.
Most of China is in temperate zone, with frequent cold and warm air mass activities and obvious frontogenesis. According to statistics, there are mainly two frontogenesis areas:
One is in the northeast and Inner Mongolia, corresponding to the northern branch area.
The other is in the south of the Yangtze River, corresponding to the southern branch front area. The release of latent heat of condensation in South China is relatively large, which plays an important role in frontogenesis.
I think you should understand after reading this.