From ancient times to the present, weather observation has played a very important guiding role in people's production and life. In ancient times, people speculated about weather changes by watching celestial phenomena and watching clouds. However, such observations from the ground and by eye do not provide accurate weather and forecast information.
In modern times, meteorologists can use weather satellites to monitor the weather from top to bottom and get more information. Today we will take this opportunity to talk about how weather satellites monitor the weather, and what other interesting weather pictures we can see on satellite cloud images.
How do weather satellites monitor the weather?
Unlike ground-based observations, meteorological satellites can make large-scale observations of the Earth's atmosphere (or surface targets) in space about 800 kilometers to 36,000 kilometers above the ground. This large-scale observation is not limited to horizontal observation, but also can make vertical detection of the atmosphere and obtain three-dimensional weather system characteristics.
In addition to the large observation range, meteorological satellites also have the advantage of real-time monitoring of the weather over the ocean. Due to the scarcity of meteorological stations on the ocean and the shortage of data, it is difficult to find and track the development and movement of the ocean surface weather system with conventional meteorological data, and meteorological satellites can directly monitor weather conditions such as low pressure and typhoons on the tropical ocean from high altitude, which is a very important marine weather system monitoring tool.
Continental satellite cloud image recorded by the meteorological satellite Fengyun 4A. Photo courtesy of Jiang Jianying
With the help of meteorological satellites, meteorologists can obtain a large number of meteorological satellite cloud images and their derivatives, and obtain weather conditions through analysis. In general, the satellite cloud images we see in weather forecasts are mostly in the visible light band, in addition to the infrared band and water vapor channels. A cloud map only remotely senses a certain attribute of the cloud and the earth's atmosphere, which is one-sided, and the comprehensive use of a variety of cloud maps and products can better help meteorologists analyze weather conditions and help improve the accuracy of weather forecasting.
In recent times, you may often see meteorological satellite images of typhoons.
Satellite image of Typhoon Du Suri of this year's No. 5 typhoon taken by Fengyun-4B.
But in addition to "typhoons", we can also see many familiar scenes through satellite cloud images, such as "subtropical high", "cold front" and "warm front" meteorological phenomena in middle school geography textbooks. Next, let's ask Fengyun Satellite to review these middle school geography knowledge for us.
The true appearance of weather phenomena
1
Subtropical high pressure
A " subtropical high " is a large mass of warm air that is often present but relatively stable in the tropics and subtropics. The state of the subtropical high in the western Pacific region has a great impact on the continental weather, such as the regional high temperature in summer in some years, which is inseparable from the abnormal west-northerly position, abnormal intensity, stability and little movement of the subtropical high position.
Photo courtesy of Jiang Jianying
As can be seen from the above figure, under the control of the sub-height, most of the areas from the east of the southwest region of the mainland to the middle and lower reaches of the Yangtze River and the sea area are cloudless, because the sub-height control area is prevalent in the downdraft, which is not conducive to the formation of cloud system. On the northern side of the sub-high north, the eastern part of the northwest region and the northern part of China are covered by a cloudy system. This is because the water vapor conditions and power conditions on the west and north sides of the sub-high are good, and rainfall is prone to occur.
2
Cold front vs. warm front
The interface or transition zone of two air masses with different physical properties such as temperature and humidity is called "front". The line where the front meets the ground is called a front, also referred to as a front. The length of the front can generally be hundreds to thousands of kilometers, and the vertical direction can be extended for more than ten kilometers. If the cold air mass plays a leading role during the movement of the front, and the push front moves towards the side of the heating mass, it is called a cold front. When cold fronts pass through, they cause weather phenomena such as increased winds, increased air pressure and falling temperatures. Conversely, if the heating mass pushes the cold air mass forward, it is a warm front.
Cold air moves southward to affect the continent's cold front that is thousands of kilometers long
If the forces of the cold and warm masses are equal, it is called a quasi-stationary front.
Quasi-stationary fronts in the southwest. Photo courtesy of Jiang Jianying
3
typhoon
A typhoon is a powerful and deep tropical weather system that occurs on the surface of a tropical or subtropical ocean with a warm heart. Its central air pressure is very low, the lower layer has a significant convergence of air flow towards the center, and the top air flow mainly radiates outward. The structure of the typhoon is divided into the typhoon eye area, the cloud wall area, and the spiral rain belt area from the center to the outside. Typhoons are always accompanied by violent storms, most of which bring severe damage to the affected areas.
Photo courtesy of Jiang Jianying
4
Roller clouds
Roller clouds are horizontal tube-shaped clouds. When stable air is disturbed, a wave cloud is created, causing the air to move along the disturbance. This disturbance usually comes from the collision of dry cold air with relatively stable warm and moist air in a moving cold front. If a stable layer of moist air flows upwards, a cloud forms at the top; When flowing downward, the clouds evaporate. The alternating absence and presence of clouds is the main cause of the wave effect.
Looking at the scroll clouds on a satellite cloud image, like ripples in a pond, is very special. Photo courtesy of Jiang Jianying
If you stand on the ground and look at the roller cloud, it will look like this.
Image source: NASA
If you look at it from an airplane, it will be the following scene.
View the roller cloud from an airplane. Image credit: Wikimedia
5
Dust
The geostationary meteorological satellite Fengyun-4A can obtain monitoring images every five minutes, which can realize real-time monitoring of dust storms. The following shows the strongest sandstorm process in the past 10 years on March 15, 2021, as can be seen from the animation, the system that affects the sand and dust weather process is a frontal cyclone cloud system, and sandstorms have appeared in central and western Inner Mongolia, Gansu, Ningxia, northern Shaanxi, northern Shanxi, most of Hebei, Beijing, Tianjin and other places on the south side of the ground cold front (yellowish area in the figure).
Photo courtesy of Jiang Jianying
6
snow cover
Because snow has a high reflectivity in the visible light band, it is similar to that of clouds, while the reflectivity of the ground surface is lower. There is a big difference between the reflectivity of snow and clouds and the reflectivity of the earth's surface. And because clouds are moving and snow cover is fixed, snow and clouds can be distinguished from the animation of visible cloud maps.
Photo courtesy of Jiang Jianying
7
Squall line
The squall line is a thunderstorm group arranged in a line (band) shape, which is characterized by a small range and a short life history. Its width ranges from hundreds of meters to several kilometers, the widest to tens of kilometers, the length is generally from tens of kilometers to hundreds of kilometers, and the maintenance time is from a few hours to more than ten hours. When the squall line crosses, the wind direction changes abruptly, the air pressure rises, the temperature drops sharply, and at the same time, the wind and hail are mixed. Therefore, when the squall line occurs, it is usually accompanied by thunderstorms, strong winds, hail and other processes, which are highly destructive and often cause serious disasters.
The thunderstorm, gales and hailstorms that occurred on the afternoon of July 1, 2021 were affected by the squall line system. Photo courtesy of Jiang Jianying
8
Northeast Cold Vortex
The Northeast Cold Cyclone is a deep cold cyclone weather system that produces near the Northeast. Due to the unstable state of upper cold and warm down, the air in the cold vortex often produces unstable weather such as (thunder) showers, thunderstorms, strong winds or hail; Sometimes, a strong developing cold vortex can also cause a wide range of heavy rainfall.
Photo courtesy of Jiang Jianying
Because the cold vortex rotates counterclockwise around the center, it is affected by the cloud system around the cold vortex, resulting in a certain place under the influence of the cold vortex that is sunny for a while and cloudy for a while.
9
fog
Fog is a weather phenomenon composed of tiny water droplets or ice crystals suspended in the air near the ground, and is the product of condensation (or condensation) of water vapor in the air near the ground. The fog has a noticeable diurnal variation. The temperature is relatively high during the day, and more water vapor can be accommodated in the air.
Photo courtesy of Jiang Jianying
But at night, the temperature drops, the ability of the air to hold water vapor decreases, and some of the water vapor becomes fog. Fog is most likely to occur from midnight to early morning and dissipates quickly after sunrise as the temperature rises. The dissipation of fog in Hebei, Henan, Shanxi and Shaanxi can be clearly seen in the animation.
Use of meteorological satellites for disaster monitoring
In addition to weather, Fengyun satellite can also carry out ecological environment monitoring, agricultural remote sensing monitoring and meteorological disasters for effective monitoring. For example, the figure below is the use of Fengyun No. 3D star to monitor forest and grassland fires in Inner Mongolia Autonomous Region. Since there is generally smoke when there is a fire point, in the figure below we can clearly see the direction of smoke drifting, which can be used to monitor the fire or find the fire source in time.
Photo courtesy of Jiang Jianying
At present, Fengyun meteorological satellite has been included in the global operational application meteorological satellite sequence by the World Meteorological Organization, as an important member of the global integrated observation system, the duty satellite of the International Charter for Space and Major Disasters, its open and shared data policy has widely benefited users around the world, playing an important role in international meteorological disaster prevention and mitigation and serving the construction of the "Belt and Road", and has become a shining business card of China's diplomatic deployment.
Source: Popular Science China