What does the Earth look like from space? These images are guaranteed to be something you've never seen before!

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 on weather changes by observing celestial phenomena and the movement of clouds. However, this kind of observation from the ground and relying on visual observation cannot obtain accurate weather and forecast information.

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In modern times, meteorologists can use meteorological satellites to monitor the weather from top to bottom and obtain more information. Today, let's take this opportunity to talk about how meteorological satellites monitor the weather and what other interesting meteorological images we can see on satellite cloud images.

How do meteorological satellites monitor the weather?

Unlike ground-based observations, meteorological satellites can conduct large-scale observations of the Earth's atmosphere (or surface objects) in space at a distance of about 800 km to 36,000 km from the ground. This large-scale observation is not limited to horizontal observations, but can also detect the atmosphere vertically and obtain three-dimensional weather system characteristics.

In addition to a large observation range, another benefit of meteorological satellites is that they can monitor the weather over the ocean in real time. Due to the scarcity of meteorological stations on the ocean and the lack of data, it is difficult to detect and track the occurrence, development and movement of ocean weather systems using conventional meteorological data. Meteorological satellites can directly monitor low pressure and typhoons on tropical oceans from high altitudes, making them a very important tool for monitoring ocean weather systems .

Satellite cloud images of my country recorded by the Fengyun-4A meteorological satellite. Photo courtesy: Jiang Jianying

With the help of meteorological satellites, meteorologists can obtain a large number of meteorological satellite cloud images and their derivative products, and obtain weather conditions through analysis. Generally speaking, the satellite cloud images we see in weather forecasts are mostly in the visible light band, in addition to infrared bands and water vapor channels . A cloud image only remotely senses a certain attribute of clouds and the earth's atmosphere, which is one-sided. The comprehensive use of multiple cloud images and products can better help meteorologists analyze weather conditions and help improve the accuracy of weather forecasts.

In recent times, you may often see meteorological satellite cloud images of typhoons.

Satellite cloud image of this year's fifth typhoon Dusurui taken by Fengyun-4B.

But in addition to "typhoons", we can also see many familiar scenes through satellite cloud images, such as "subtropical high pressure", "cold front" and "warm front" meteorological phenomena in middle school geography textbooks. Next, let us ask Fengyun satellites to review these middle school geography knowledge for us.

1. The true appearance of weather phenomena

1 Subtropical High

"Subtropical high pressure" is a large warm air mass that is often present but relatively stable in tropical and subtropical regions. The state of subtropical high pressure in the western Pacific has a great impact on my country's weather. For example, the regional high temperatures in summer in some years are closely related to the abnormal westward and northward position of subtropical high pressure, abnormally strong intensity, and stability and little movement.

Photo courtesy: Jiang Jianying

As can be seen from the above figure, under the control of the subtropical high, the eastern part of Southwest my country to the middle and lower reaches of the Yangtze River and the sea are mostly cloudless. This is because the subtropical high control area is dominated by sinking airflow, which is not conducive to the formation of clouds. The eastern part of Northwest China and North China to the north of the subtropical high are covered by clouds. This is because the water vapor and dynamic conditions to the west and north of the subtropical high are better, and it is easy to have rainy weather.

2 Cold fronts and warm fronts

The interface or transition zone between two air masses with different physical properties such as temperature and humidity is called a "front". The intersection of the front and the ground is called the front line, also referred to as the front. The length of a front can generally range from hundreds to thousands of kilometers, and can extend more than ten kilometers in the vertical direction. If the cold air mass plays a leading role in the movement of the front, pushing the front to the side of the warm air mass, it is called a cold front. When a cold front passes through, it will cause weather phenomena such as increased wind speed, increased air pressure and dropped temperature. On the contrary, if the warm air mass pushes the cold air mass forward, it is a warm front.

The cold air moved southward in large numbers, affecting my country's cold front that was several thousand kilometers long.

If the cold and warm air masses are of equal strength, it is called a quasi-stationary front .

Quasi-stationary front in the southwest. Photo courtesy: Jiang Jianying

3 Typhoon

A typhoon is a strong cyclonic vortex with a warm core structure that occurs on tropical or subtropical oceans. It is a powerful and deep tropical weather system. Its central air pressure is very low, and there is a significant convergence of airflows toward the center in the lower layers, while the top airflows mainly diverge outwards. The structure of a typhoon can be divided into: typhoon eye area, cloud wall area, and spiral rain belt area from the center outward. Typhoons are always accompanied by strong winds and heavy rains, and most of them bring serious disasters to the affected areas.

Photo courtesy: Jiang Jianying

4 Roller Cloud

Roll clouds are horizontal, tube-shaped clouds. Wave clouds are created when stable air is disturbed, causing the air to move along the disturbance. This disturbance usually comes from the collision of cold, dry air with relatively stable warm, moist air in a moving cold front. If the stable layer of moist air flows upward, clouds form at the top; if it flows downward, the clouds evaporate. The alternating absence and presence of clouds is the main reason for the wave effect.

Roll clouds look like ripples in a pond when viewed from satellite images. They are very special. Photo courtesy: Jiang Jianying

If you were standing on the ground and looking at a roller cloud, it would look something like this.

Image credit: NASA

If you were to watch it from an airplane, it would look like this.

Roll clouds viewed from an airplane. Image source: Wikimedia

5. Dust

The geostationary meteorological satellite Fengyun-4A can obtain monitoring images every five minutes, which can realize real-time monitoring of sandstorms. The following is the strongest sandstorm process in the past 10 years that occurred on March 15, 2021. It can be seen from the animation that the system affecting this sandstorm weather process is a frontal cyclone cloud system. Sandstorms occurred 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 (the yellowish area in the picture).

Photo courtesy: Jiang Jianying

6 Snow

Since the reflectivity of snow in the visible light band is high, similar to that of clouds, while the reflectivity of the ground surface is low, there is a big difference between the reflectivity of snow and clouds and the reflectivity of the ground surface. And since clouds are moving and snow is fixed, it is possible to distinguish snow from clouds in the animation of the visible light cloud map .

Photo courtesy: Jiang Jianying

7 Squall Line

A squall line is a group of thunderstorms arranged in a line (belt) shape, which is characterized by a small range and a short life span. Its width ranges from a few hundred meters to a few thousand meters, with a maximum width of tens of kilometers, and its length generally ranges from tens of kilometers to a few hundred kilometers, and its duration ranges from a few hours to more than ten hours. When a squall line passes through, the wind direction changes suddenly, the air pressure rises, and the temperature drops sharply. At the same time, there are strong winds, rain and hail. Therefore, when a 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, gale and hail weather that occurred on the afternoon of July 1, 2021 were affected by the squall line system. Photo courtesy: Jiang Jianying

8 Northeast Cold Vortex

The Northeast Cold Vortex is a deep cold cyclonic weather system generated near the Northeast region. The air in the cold vortex is in an unstable state of being cold on top and warm on the bottom, which often produces unstable weather such as (thunder) showers, thunderstorms, gale or hail; sometimes, a strongly developed cold vortex can also cause heavy rain weather over a large area.

Photo courtesy: Jiang Jianying

As the cold vortex rotates counterclockwise around the center, it is affected by the clouds around the cold vortex, causing the weather in a certain place to be sunny and cloudy at the same time .

9. Fog

Fog is a weather phenomenon composed of tiny water droplets or ice crystals suspended in the air near the ground. It is the product of condensation (or sublimation) of water vapor in the air near the ground. Fog has obvious daily changes. The temperature is relatively high during the day, and the air can accommodate more water vapor.

Photo courtesy: Jiang Jianying

However, at night, the temperature drops, and the air's ability to hold water vapor decreases, so some of the water vapor turns into fog. Fog is most likely to appear between midnight and early morning, and will quickly dissipate after sunrise as the temperature rises. The animation clearly shows the dissipation of fog in Hebei, Henan, Shanxi, and Shaanxi.

2. Using meteorological satellites for disaster monitoring

In addition to weather monitoring, Fengyun satellites can also conduct effective monitoring of ecological environment monitoring, agricultural remote sensing monitoring, and meteorological disasters . For example, the following picture shows the monitoring of forest and grassland fire points in Inner Mongolia Autonomous Region using Fengyun-3D satellite. Since there is usually smoke when a fire point appears, we can clearly see the direction of the smoke in the picture below, which can be used to monitor the fire situation or find the fire source in time.

Photo courtesy: Jiang Jianying

At present, Fengyun meteorological satellites have been included in the global operational application meteorological satellite sequence by the World Meteorological Organization. As an important member of the Global Integrated Observing System and a duty satellite of the International Charter on Space and Major Disasters, their open and shared data policy has benefited users around the world. It plays an important role in international meteorological disaster prevention and mitigation and in serving the construction of the "Belt and Road Initiative", and has become a shining business card of China's diplomatic deployment.

Planning and production

Author: Jiang Jianying, Chief of the National Satellite Meteorological Center

Review | Ai Wanxiu, Chief Expert Researcher, Climate Service Office, National Climate Center

Planning丨Cui Yinghao

Editor: Cui Yinghao