The cold is due to the descent of mesospheric air in the circulation at left centred over Russia and spiralling in to the surface in the proximity of Lake Baikal. The diagram below shows the circulation of the air and its temperature at 10hPa or 30 km in elevation. Reputedly China is experiencing its coldest winter for thirty years. The winds streaming out of the Arctic are warm by comparison with the air near Lake Baikal and the interior of Iceland. The great bulk of the northern landmasses are experiencing sub zero temperatures. The middle stratosphere at 30 hPa has been off the scale cold since the end of November as the Arctic began to experience Polar night.
The diagram above serves as a reference frame.
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