Nanjing experienced an unseasonable 25 degrees or so on Saturday. Yesterday, the temperature was half that. The overnight shift can be much more dramatic too; it’s been known for the temperature to go up or down as much as 20 degrees. Begging the question why?
It boils down to large temperature fluctuations related to cold-air activity and solar radiation.
And our particular location on the world’s surface. Last month, The Paper reported on the issue, speaking with Wang Ji, Director of the Beijing Climate Centre.
“China is located between the largest continent in the world, Eurasia; and the largest ocean in the world, the Pacific. The huge differences in thermal properties between land and sea make for the region being the most monsoon-like climatic area in the world”, said Wang.
And when it comes down to our locale in particular, on the one hand, Nanjing is far enough away from the coast not to benefit from the sea’s natural warming and cooling effects. On the other, we remain sufficiently close that the big ol’ Pacific Ocean still exerts an enormous influence over our weather.
As to why the temperature fluctuations are concentrated around this time of year, that’s down to the passing of the autumnal equinox and climate change.
Every year, solar radiation received at higher latitudes decreases significantly as the end of October comes. The air cools and sinks, forming a large-scale mass of cold air. As the specific heat capacity for land is limited and the temperature drops extremely rapidly, cold air will gather at high latitudes in Siberia and Mongolia.
Then it comes our way.
As for climate change, with artic sea ice largely melted, the temperature difference between cold air in the polar region and warm air in the tropics has decreased. This has led to a weakening of the impact of polar eddies on the global climate. At the same time, under the influence of the atmospheric circulation system, cold air in the polar vortex will move south more easily and frequently.
While temperature fluctuations experienced by southern parts of China are generally not as fast and intense as those in the north in the past, this year’s situation is indeed somewhat special.
