The shape of the sky

There are many forms of expression in the sky, which carries the fastest light known to mankind and is the most primitive creative enlightener of mankind.

Various forms are usually expressed by weather, which refers to the specific state of the near-surface atmosphere in a short time. Weather phenomenon refers to various natural phenomena in the atmosphere, that is, the comprehensive expression of the spatial distribution of various meteorological elements in the atmosphere (such as temperature, pressure, humidity, wind, clouds, fog, rain, flash, snow, frost, thunder, hail, haze, etc.). ) in an instant. The weather process is the change process of weather phenomena with time in a certain area. All kinds of weather systems have certain time and space scales, and they are intertwined and influence each other. The combination of many weather systems constitutes a large-scale weather situation and hemispheric and even global atmospheric circulation. The weather system is always in the process of rebirth, development and extinction, and there are corresponding weather phenomena in different development stages.

wind

Wind is a natural phenomenon caused by air flow, which is caused by solar radiation heat. Sunlight shines on the earth's surface, causing the surface temperature to rise, and the surface air to expand and become lighter and lighter. After the hot air rises, the cold air with low temperature flows in horizontally, and the rising air falls down because it gradually cools and becomes heavier. Because the surface temperature is high, it will heat up the air, and this airflow will produce wind.

Scientifically speaking, wind often refers to the horizontal motion component of air, including direction and size, that is, wind direction and wind speed; But for flight, it also includes vertical motion components, so-called vertical or ascending and descending airflow. Strong winds can move objects and their directions (mass of matter). The wind is very fast.

The formation of wind is that when the gathered water vapor (cloud) forms water, its volume shrinks, and the surrounding water vapor comes to supplement it, thus forming wind. The wind on the earth is related to the water source, and the wind is produced by the expansion and contraction of water and steam. The wind blows from the ocean to the land, or the land blows to the ocean. In summer, the air and water vapor with high surface temperature expand and rise, and the air space on the ground depends on the specific gravity of air and water vapor on the sea surface, while the air with low surface temperature contracts. The air space on the sea surface should be supplemented by the air and water vapor rising from the high temperature air on the ground. In winter, when the sea surface temperature is high, the sea surface air rises, and when the ground temperature is low, the proportion of air is heavy, which supplements the sea surface space along the ground.

Due to the difference of wind speed, wind direction and humidity, many types of wind will be produced. Blast, gale, gale, gale, storm and hurricane, these common wind types, Beaufort wind force are seven, eight, nine, ten, eleven and twelve respectively.

Gust: When the air speed is high and low, the wind will be high and low, and there will be waves of feeling when blowing on people. This is a recognized gust of life. Meteorology, wind speed usually refers to the average situation within 2 minutes, with high or low wind speed, and gust usually refers to the maximum instantaneous wind speed during this period. If the weather forecast, today's wind is 4-5, and the gust is 6, which means that today's average wind is 4-5, and the maximum instantaneous wind can reach 6.

Cyclone: It is a cyclone when the air flies in the air with dust to form a vortex.

Foehn: When the air crosses the ridge, it is easy to produce warm (or hot) dry wind on the leeward slope due to the sinking of the air, which is called Foehn.

Typhoon is an atmospheric vortex that occurs in the tropical ocean, so it is also called tropical cyclone. When the maximum wind force in the vortex center reaches more than 8, it is called typhoon; The maximum wind force in the center is 6-7, which is called weak typhoon; When the maximum wind force in the center reaches 8 to 12, it is called a strong typhoon.

Tornado: A small destructive vortex of air extending from cumulonimbus clouds to the ground. What happens on land is called tornado, and what happens on the ocean is called tornado, also called waterspout. Tornado is a violent storm with strong rotating force, and the maximum wind speed can reach more than 100 meters per second.

Mountain valley wind: In mountainous areas, the wind blows upward along the slopes and valleys during the day and downward along the slopes and valleys at night. This wind, which changes direction between hills and valleys alternately day and night, is called valley wind.

Sea-land wind: In coastal areas, the wind blows from the sea to the mainland during the day and from the land to the sea at night. This kind of wind that changes direction regularly day and night is called land-sea wind.

Glacier wind: shallow wind blowing down the mountain along the glacier during the day and night.

Monsoon: The prevailing wind direction changes regularly with the alternation of seasons. In winter, air flows from high-pressure land to low-pressure sea, which is called winter wind; In summer, the wind blows from the sea to the land, which is called summer monsoon. China is a country with remarkable monsoon, with northerly winds in winter and southerly winds in summer. This brings the monsoon climate characteristics of dry winter and wet summer to most parts of China.

Trade winds: persistent winds blowing from subtropical high to equatorial regions in the lower atmosphere. In the northern hemisphere, trade winds prevail in the northeast; In the southern hemisphere, it is in the southeast. Trade winds are characterized by a high degree of regularity, blowing in one direction with almost constant intensity all year round.

Anti-trade wind: the hot air rising from the equator flows in two layers in the upper atmosphere, which is called anti-trade wind. Because of the earth's rotation, the anti-trade winds are to the right in the northern hemisphere and to the left in the southern hemisphere. Anti-trade winds constantly bring the atmosphere to the latitude between 30 and 35, forming a state of air accumulation and forming a subtropical high pressure area. So there are more deserts in this area.

cloud

Clouds are water droplets, supercooled water droplets, ice crystals or visible polymers formed by condensation (sublimation) of water vapor in the atmosphere floating in the air. Clouds are the tangible result of the huge water cycle on the earth. The sun shines on the surface of the earth, and water evaporates to form water vapor. Once the water vapor is supersaturated, water molecules will gather around the dust (condensation nucleus) in the air, and the generated water droplets or ice crystals will scatter sunlight in all directions, thus creating the appearance of clouds. Because clouds reflect and scatter electromagnetic waves in all bands, their colors are gray, and when they are thin, they are white, but when they become too thick or dense for sunlight to pass through, they may look gray or black. Clouds can form various shapes, and they are also divided into many kinds because of their different heights and shapes in the sky.

The water on the ground absorbs heat and turns into steam, which rises to the upper layer of the steam layer in the sky. Due to the lower temperature of the upper steam layer, the steam volume decreases, the specific gravity increases and the steam decreases. Because the temperature below the steam layer is relatively high, it absorbs heat in the process of falling, rises and then falls when it is cold, so the gas molecules gradually contract and finally concentrate at the bottom of the steam layer. A low temperature zone is formed at the bottom, and water vapor is concentrated in the low temperature zone, forming a cloud.

Generally speaking, there are three main kinds of clouds: large cumulus, large stratus and fibrous cirrus.

The scientific classification of clouds was first put forward by the French naturalist Jean-Baptist Lamarck in 180 1 year. 1929, according to the classification made by British scientist luke howard in 1803, the international meteorological organization divided clouds into ten major cloud genera according to their shapes, components and formation reasons. These ten cloud genera can be divided into three cloud systems according to the height of cloud bottom: high cloud system, middle cloud system and low cloud system. Another classification method is to separate cumulonimbus clouds from low cloud systems, which is called direct expansion cloud systems. The cloud base height used here is only applicable to mid-latitude areas. (Except Britain and the United States, countries such as the World Gas Organization generally adopt the international system of units).

thunder

Thunder is the sound that clouds make when they discharge. Thunder and lightning are two completely different natural phenomena, one is sound, the other is hearing; One refers to the image, that is, to look. Most of the time at the same time.

English thunder; ; Thunder is an atmospheric detection phenomenon accompanied by lightning. Due to lightning discharge, the air in the lightning channel instantly produces high temperature and high pressure, and its rapid expansion causes agitation waves, which propagate around the channel. This high-pressure agitation wave decays rapidly in a short distance and degenerates into powerful audible waves and infrasound waves. Generally, it can be divided into three types: thunderbolt, muffled thunderbolt and thunderbolt (long-lasting deep voice). Generally speaking, the propagation distance of lightning does not exceed 25 kilometers, and the farthest distance can reach the sea 100 kilometers. The peak frequency of thunder sound intensity spectrum is 4- 125 Hz, some of which are infrasound and some are audible waves.

Lightning is a kind of discharge phenomenon. Due to different charging properties, a strong electric field is formed between different parts of thunderstorm clouds or between clouds and the ground. Because the lightning passage is narrow and the current passes too much, the air column in the lightning passage burns white and glows, and the surrounding air suddenly expands due to heat, and the cloud drops suddenly vaporize and expand due to high heat, thus making a huge sound-thunder. The speed of thunder is not the speed of ordinary sound in air, but in the form of shock wave, which is much faster than that of ordinary sound. Lightning generated in and between clouds is high-altitude lightning; The lightning generated in cloud lightning is "floor lightning".

rain

After the water on the earth is irradiated by sunlight, it becomes steam and is evaporated into the air. Water vapor condenses into small water droplets when it meets cold air at high altitude. These water droplets are very small, with a diameter of only 0.000 1 ~ 0.0002 mm, and the largest is only 0.002 mm. They are small and light, and are held up in the air by the updraft in the air. It is these small water droplets that gather in the air to form clouds. These small water droplets will become raindrops and fall to the ground, and the volume will increase by about 1 10,000 times.

There are two main ways to rain in the sky:

One is the increase of condensation and sublimation.

The second is to rely on the collision and increase of cloud droplets.

In the initial stage of raindrop formation, cloud droplets mainly condense and condense themselves by constantly absorbing water vapor around the cloud. If the water vapor in the cloud can be continuously supplied and replenished, so that the surface of cloud droplets is often in a state of supersaturation, then this condensation process will continue, making cloud droplets grow and become raindrops. However, sometimes the water vapor content in the cloud is limited, and in the same cloud, the water vapor is often in short supply, so it is impossible to make every cloud droplet grow into a larger raindrop, and some smaller cloud droplets have to be merged into a larger cloud droplet.

If there are water droplets and ice crystals in the cloud, the process of condensation and sublimation will be greatly accelerated. When the cloud drops increase to a certain extent, due to the increasing volume and weight of large cloud drops, they can not only catch up with the slower small cloud drops, but also "swallow" more small cloud drops, making themselves stronger. When the big cloud drops get bigger and bigger until the air can no longer hold them, they fall straight from the clouds to the ground and become our common rain.

Besides acid rain and colorful rain, there are many interesting rains, such as frog rain, iron rain, golden rain and even modesty. Are all masterpieces of tornadoes.

aurora

Aurora Borealis (aurora borealis) appears over the high magnetic latitudes of the earth, which is a colorful luminous phenomenon. Aurora is produced by the high-energy charged particle flow (solar wind) from the earth's magnetosphere or the sun exciting (or ionizing) molecules or atoms in the upper atmosphere. Aurora often appears in the sky near the earth's magnetic pole in latitude, generally in the form of strips, arcs, curtains and radiations, and these shapes are sometimes stable and sometimes constantly changing. Aurora has three conditions: atmosphere, magnetic field and high-energy charged particles. These three are indispensable. Aurora not only appears on the earth, but also on other planets with magnetic fields in the solar system.

According to the study of the distribution of aurora, the shape of aurora is not a circle with the geomagnetic pole as the center, but an ellipse. The spectral range of aurora is about 3 100 ~ 6700 angstroms, and the most important spectral line is the oxygen atom green line of 5577 angstroms, which is called the aurora green line. The height of the lower boundary of the aurora is less than 100 km from the ground, and the height of the maximum luminous place is about 1 10 km from the ground. The normal maximum boundary is about 300 kilometers from the ground, and in extreme cases it can reach more than 1000 kilometers.

Aurora generally only appears in the high latitudes of the north and south poles, but the solar storm on August 1 day in 2065438 just happened to erupt against the earth. The solar wind carrying a large number of charged particles accurately "hits" the earth and interacts with the earth's magnetic field to produce a "magnetic storm", which makes Michigan, Denmark, Britain and other low-latitude areas in the United States see the beautiful northern lights landscape. Experts said that this solar storm did not destroy global satellites and telecommunications systems as predicted in advance, but brought a magnificent "fireworks show" to the earth.