1, horizontal movement-wind

Wind always exists in a certain pressure field and flow field. The pressure field can be represented by an isobar. Influenced by the underlying surface, the isobar shapes on different isoline surfaces are different. The wind direction of the flow field is determined by the resultant force of various forces. Similarly, winds at different heights are subjected to different forces, and the relationship between wind direction and isobar is also different. The textbook talks about this problem at three levels. First, the wind direction of the upper atmosphere. The horizontal pressure gradient force is the driving force to produce the horizontal motion of the atmosphere. However, when the atmosphere began to move horizontally in the direction of horizontal pressure gradient force (perpendicular to the isobar), it was immediately subjected to geostrophic deflection force, which made the movement direction deflect (right deviation in the northern hemisphere and left deviation in the southern hemisphere). When the two forces are balanced, the wind direction is parallel to the isobar. Second, the wind direction in the atmosphere near the ground. The wind in the atmosphere near the ground is not only affected by the above two forces, but also by friction, which eventually makes the direction oblique to the isobar. Third, the actual wind direction in the sea level atmosphere, which is the real situation. It can be seen from the figure that the isobar has a closed center under the influence of the thermal difference between land and sea. Under the combined action of pressure gradient force, geostrophic deflection force and friction force, the low-pressure airflow rotates and converges counterclockwise in the northern hemisphere (clockwise in the southern hemisphere); The high-pressure airflow (anticyclone) rotates clockwise in the northern hemisphere (counterclockwise in the southern hemisphere). It should be noted that the map of "sea level isobar and wind direction" is a part of the global map. The wind direction is simplified, but it still represents the general trend of convergence and divergence.

Tropical monsoon belt

The east coast of the continent between north latitude 100 and the tropic of cancer.

The wind direction changes obviously with the seasons in a year, which is divided into two seasons: drought and rain.

With the arrival of summer monsoon (southwest wind), equatorial air mass brings a lot of rainfall, while the arrival of winter wind (northeast wind) is influenced by continental air mass, and the rainfall is obviously reduced.

Tropical seasonal rain forest belt

Subtropical region

Subtropical monsoon climate

Located on the east coast of the mainland at 300-400 degrees north latitude.

The seasonal changes of heat in summer and temperature in winter are obvious.

During the summer monsoon, tropical marine air mass brings a lot of precipitation and high temperature; Winter wind, influenced by the polar continental air mass, has reduced precipitation and low temperature.

Subtropical evergreen broad-leaved forest

temperate zone

Mid-latitude monsoon climate

Mid-latitude Central Asian continent

In the direction of Xia Feng, the winters obviously alternate, with cold and dry winters and warm and rainy summers.

During the winter monsoon, it is cold and dry under the control of the polar continental air mass; During the summer monsoon, it is warm and rainy under the control of polar or tropical ocean air masses.

Temperate deciduous broad-leaved forest belt

Temperate continental climate

Inland Asia, Europe and North America

There is little rain all year round, and it is hot in Leng Xia in winter, and the temperature changes greatly every year.

It is controlled by the polar continental air mass all year round.

Temperate grassland belt

3. Frontal cyclone

Frontal cyclone is a low-pressure system with frontal surface, which is mainly active in middle and high latitudes and more common in temperate regions, so it is also called temperate cyclone.

① Frontal cyclone structure: As can be seen from the figure, frontal cyclone is a counterclockwise vortex with the lowest central air pressure. The warm front extends forward from the center, and the cold front extends backward. There is warm air between the cold and warm fronts and cold air to the north of the cold and warm fronts. Viewed from the vertical direction, the upper layer of the cyclone is an air flow divergence area, and the lower layer of the cyclone has air flow convergence. There is an updraft in the center of the cyclone.

② Frontal cyclone weather: Frontal cyclone weather is not only determined by the structure of cyclone temperature and pressure field, but also related to air stability, water vapor conditions, upper-air circulation situation, topographic relief, cyclone development stage and other factors. Generally, cyclone is a convergent and ascending system of airflow, especially on the front, which often produces clouds, rain and even heavy rain and windy weather. The weather model of a mature frontal cyclone is that the front of the cyclone is a wide warm front cloud system and continuous precipitation weather, the back of the cyclone is a narrow cold front cloud system and precipitation weather, and the middle of the cyclone (between the two fronts) is sunny and warm weather controlled by the warm air mass.

③ Frontal cyclone teaching.

A. Students can be guided to find two cyclones and an anticyclone according to the pressure value on the map, and then analyze a cyclone and its two fronts.

B. During the analysis, according to the contour line or the counterclockwise movement of two fronts (the sign of the fronts points), it can be judged that the cyclone belongs to the northern hemisphere.

C then analyze the map of the northern hemisphere, which shows that it is northerly, with high latitude and low temperature, so the north of the two fronts is controlled by cold air masses. The lower part is south, the latitude is low, the temperature is high, and the warm air mass occupies between the two fronts.

The red front on the D map moves from the hot south to the cold north and belongs to the warm front. The blue front moves from the colder north to the hotter south and belongs to the cold front.

E. According to the rain area of the front, it can be judged that there is a wide front rain belt in front of the warm front and a narrow front rain belt behind the cold front. The space between the two fronts (from warm front to cold front) is controlled by the warm air mass, and the weather is fine.

Different positions near the cyclone have different wind directions. Because the density and sparseness of isobars at different positions are different, the wind force is also different. Two points can be marked in the picture to analyze the wind direction and wind force.