The blizzard that hit the U.S. state of Texas over the past week, leaving more than 4 million homes without power and more than 14.9 million people without water, has sparked global concern.

Meanwhile, water and power outages and school closures have hit many parts of Greece in southern Europe in a rare snowstorm.

Why did the blizzard strike the southern United States, known for its deserts and scorching sun, and Greece, a sunny bay?

There are, in fact, many causes of blizzards, and there are three main factors in this year's blizzard in the southern United States

Where is the cold air?

We hear a lot about cold air in Siberia, which is, in fact, not the source of the frigid air, but a source station for cold air that travels through Antarctica.

Earth receives different solar radiation at different latitudes and polar regions receive less heat, while the equator receives the most heat, which results in low temperatures on the surface of the earth, high pressure equatorial regions of the atmosphere temperature rises and the air pressure at the surface decreases, compared to the upper atmosphere in the Arctic region, the stratosphere shows low pressure, so the formation of the polar vortex is called the polar vortex.

Every winter, under normal conditions, the polar vortex in the stratosphere is surrounded by strong westerly winds, when the cold air is very cold, and China's natural climate, the temperature fluctuations are relatively small.

But under abnormal conditions, the polar vortex of the stratosphere can be disturbed, deformed or collapsed.

Who broke the cold air curse?

It is well known that the factors affecting the weather in the lower stratosphere appear atmospheric changes so that civilian aircraft can not fly, sometimes interacting with the troposphere this affects our weather.

From 2020 to the early end of 2021, changes in the stratosphere over the Arctic are typical.

The sudden increase in stratospheric temperatures is the result of lower atmospheric waves propagating into the stratosphere.

The image above shows the change in temperature in the middle of the stratosphere from about 30km to 10hPa, where we can see that the temperature in the Arctic rises rapidly in one month first year 2021 suddenly rises to only five days in the polar stratosphere.

Polar stratospheric thermal anomalies associated with weak or clockwise rotation.

Stratospheric temperatures rise from convection to explosion, it usually takes about two weeks to affect the troposphere, strong warming of the stratosphere does not occur every year, nor does it affect the weather and climate in the same region every year necessarily affect Europe and the United States.

Why did the blizzard hit Texas and Athens?

First, the cold snap pushed the Arctic vortex southward, so in the last ten days, Europe and North America have become more and more visible in the Northern Hemisphere.

Secondly, it is influenced by topographical factors; if the earth is relatively flat, the natural speed is low and consumption is low, otherwise the speed is slow and consumption is high, so the oceans and plains are less impeded by cold air.

There are many mountain ranges in the western U.S., the Middle Plains and the eastern apartments, this time, from the Middle Plains to the Rocky Mountains east of the cold air, when the cold, warm air and humidity of the Gulf of Mexico cold wave dominated the coordination of warm air and moisture, resulting in massive snowfall.

With global warming intensifying, extreme weather and extreme climate anomalies warming in February, in North America and northern China and Europe, the Yellow River and Huaihuai, and other places where the climate is very cold and could break records for future maximum temperatures, we may experience a warmer summer and more severe convection.