What are the characteristics of thunderstorms?

First, the meteorologist's thunderstorm weather forecast (in essence, the weather situation is predicted first, and the forecast judgment is made by combining the situation and the possible local impact. )

(1) Climatic Characteristics of Thunderstorms in China

Thunderstorms occur in low latitudes of China all year round. Thunderstorms in mid-latitude areas mostly appear in summer, especially in June, July and August, and generally appear in the afternoon to evening. At sea or by the sea, thunderstorms mostly occur at night. Thunderstorms are widely distributed in China, generally more in the south than in the north, more in the inland than in the coastal areas, and more in the mountainous areas than in the plains. Guangdong, Guangxi and Qinghai-Tibet Plateau are the two areas with the most thunderstorms in China. These climatic characteristics are the result of the comprehensive action of three conditions that form thunderstorms. For example, there are more thunderstorms in summer, afternoon (night at sea) and low latitudes in inland areas, mainly because water vapor and unstable stratification conditions are easy to meet in these seasons, times and regions. However, many thunderstorms in mountainous areas are related to the uplift conditions caused by topography. The Qinghai-Tibet Plateau is closely related to not only the topographic uplift conditions, but also the instability of the gas layer caused by the ground heating on the plateau and the convergence and upward movement of the system caused by the prevailing weather systems such as vortex and shear line on the plateau.

(3) Forecast of systematic thunderstorm

Thunderstorm weather is the comprehensive result of water vapor condition, unstable stratification condition and lift condition. These three conditions are gradually brewed in a certain weather situation. The weather situation that is conducive to providing these conditions is also the weather situation that is conducive to thunderstorms.

The following describes the characteristics of system thunderstorms in various situations.

1. Forecasts of frontal thunderstorms

Frontal thunderstorm is one of the main types of summer thunderstorms in China. According to the statistics of Shanghai Meteorological Observatory, from June to August, 60-70% of thunderstorms were formed on the front, while more than 80% of thunderstorms in Shijiazhuang were frontal thunderstorms.

Thunderstorms can occur on cold fronts, warm fronts and stationary fronts. Among them, cold front thunderstorms appear the most and have strong intensity. There are fewer warm front thunderstorms. Stationary front thunderstorms are often associated with shear lines. Firstly, some experience in forecasting cold front thunderstorms is introduced.

(1) The warm and humid air flow is active before the cold front (such as positive temperature change and humidification). The south wind is strong. Unstable warm air, etc. ), thunderstorms are usually formed when cold fronts cross the border.

(2) Cold front thunderstorm is closely related to the intensity, advance and retreat of Pacific high.

(3) The occurrence of cold front thunderstorm is related to the situation on the front.

(4) If there is cold advection in the upper layer and warm advection in the lower layer near the front, and the advection is strong, thunderstorms will mostly occur when the front passes.

(5) The intensity of the upper front is closely related to whether there is thunderstorm on the front and its intensity. The stronger the troposphere front, the more opportunities and intensity of thunderstorms will appear. Strong upper front usually matches upper jet. Therefore, on the front corresponding to the high-altitude jet, thunderstorms have more opportunities and greater intensity.

(6) If the axis of the wet tongue extends along the ground front after drawing the isodew point line or isohumidity line in the area where the front is located at 850 mbar. This is conducive to the occurrence of thunderstorms.

The occurrence time of cold front thunderstorm mainly depends on the moving speed of the front. Cold front thunderstorms are generally generated within 2-3 hours before and after the cold front crosses the border. When the height is forward sloping trough, the thunderstorm appears before the cold front crossing, while when the height is backward sloping trough, the thunderstorm appears after the cold front crossing. Therefore, the prediction of the occurrence time of cold front thunderstorms mainly considers the moving speed of the front and the configuration of the ground front and the upper trough. The moving speed of cold front is determined by the turning velocity, the intensity of cold high pressure behind the front, the blocking effect of warm high pressure or denatured high pressure before the front and the influence of topography.

The duration of cold front thunderstorm depends on the moving speed and intensity of cold front, the configuration of 700 MB slot line and the moving speed of slot. When the cold front moves faster or stronger, the duration of cold front thunderstorm is generally shorter; On the contrary, it is longer. In the case of backward inclined trough, when the 700 MB trough line crosses the border, the general thunderstorm has ended.

2. The forecast of thunderstorm in upper trough and shear line.

Upper trough and shear line are also weather systems that often cause thunderstorms. Whether the trough or shear line can cause thunderstorms depends on the air distribution before and after the trough or shear line and its cold and warm properties.

The so-called air distribution before and after the slot line is mainly manifested as the included angle of the wind direction on both sides of the slot line and the size of the wind speed. Generally speaking, the closer the wind direction intersection angle is to or less than 99 degrees, the higher the wind speed behind the trough, and the stronger the convergence and upward movement on the trough line, so the trough is beneficial to thunderstorm weather. The nature of the temperature field structure in the upper trough is also closely related to the formation of thunderstorms. Because the warm tongue and cold trough are obvious before and after the trough line, the cold and warm advection is strong, which is beneficial to the formation of thunderstorms.

The warm high-altitude trough is occupied by warm air before and after its trough line, and the vertical movement cannot develop, which is not conducive to the formation of thunderstorms. The shear line is similar to the groove line above.

3. The forecast of vortex thunderstorm

Cold vortex thunderstorms often occur in summer in Northeast China and North China, which are characterized by rapid change (from sunny to thunderstorm in a short time), long duration (usually lasting 3-6 days) and great harm (sometimes accompanied by strong wind and hail).

(1) Cold vortex thunderstorms mainly appear in the south and southeast of the cold vortex, and the most common one appears in the southeast. This is because when the cold vortex moves south, its southeast direction is close to the Pacific high. There is strong airflow convergence between the southeast of the cold vortex and the northwest of the subtropical high, and there is strong warm and humid advection in the northwest of the subtropical high, so large thunderstorms often occur in the southeast of the cold vortex. Thunderstorms can also occur in the northeast and northwest parts of the cold vortex, but the frequency is less.

(2) Cold vortex thunderstorms are generally accompanied by ground cold fronts or small transverse troughs at high altitude. Therefore, we should pay attention to the position and trend of the high-altitude transverse trough and the ground cold front. Because when the local warm ridge of the cold vortex is strong and extends to the northeast, the small transverse trough will bring cold air to the south along the north-north airflow behind the vortex, which will strengthen the convergence and upward movement of the vortex and promote the release of unstable energy. Therefore, the small transverse trough (rotating trough) at the back of the cold vortex plays an important role in the generation and persistence of cold vortex thunderstorms. When the center of the cold vortex is stable and less moving, this kind of high-altitude horizontal trough, which reflects the continuous replenishment of cold air, turns vertical again and again, resulting in the continuous emergence of cold vortex thunderstorms.

(3) When the cold vortex is stable and less moving. Due to the daily change of its stability, the gas layer will become unstable every afternoon or evening, so thunderstorms may occur.

(4) In the cold vortex control area, there is obvious warm and humid advection at 850 mbar in the lower layer, and strong thunderstorm or hail often occurs in the area with cold advection in the upper layer.

Southwest vortex often appears in southwest China. Thunderstorms often occur at the intersection of the eastward moving southwest vortex and the wet tongue in its east and southeast. In the process of southwest vortex moving eastward, cyclone waves may appear on the ground, so thunderstorms often occur in the middle and lower reaches of the Yangtze River.

4. Thunderstorm forecast in the northwest of subtropical high

In the lower troposphere, the air in the northwest of subtropical high is warm and humid, and often stores a lot of unstable energy. Thunderstorms can occur regardless of the invasion of foreign systems. When the weather system is weak and the isobar is sparse, sometimes isolated and scattered thunderstorms can be produced by the convergence of small-scale wind fields caused by topography. When the subtropical high recedes eastward obviously, it can also cause unstable energy release and cause thunderstorms. When the northwest of the subtropical high is affected by fronts, low pressure, high-altitude troughs, intersecting lines, vortices and other systems, a wide thunderstorm area will appear in the northwest of the subtropical high.

Low-level jet often appears in the northwest of subtropical high. The low-level jet stream also has great influence on convective weather such as thunderstorm and hail.

Secondly, since the appearance of meteorological satellites and weather radar, people have a deeper understanding of the internal structure, intensity and movement of thunderstorms, and the forecasting accuracy of short-term thunderstorms has been greatly improved.

Thirdly, some weather proverbs summarized by human beings for thousands of years still have certain reference value even today with the continuous progress of science and technology.

References:

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