The temperature in Shanghai is the highest since 1873. What is the abnormal temperature this year?

In fact, if we carefully observe the national or global meteorological records, we will find that there are so-called "anomalies" every year.

It can only be said that the frequency of record-breaking extreme events has become higher, so we can often see news reports that a certain meteorological element somewhere has broken records.

Macroscopically, it is actually an inevitable result. Because the trend of global warming is obvious to all. The impact of global warming is actually a positive feedback process. Simply put, the global average temperature rises-sea ice melts more; Evaporation increased; There is more water vapor in the atmosphere-it feels more sultry, the precipitation is abnormal-and the temperature is further abnormal.

Specifically, China's summer climate (precipitation, temperature) is closely related to the northwest Pacific subtropical high (referred to as the western Pacific subtropical high).

The western Pacific subtropical high will move in the north-south direction in spring, summer, autumn and winter (mainly in summer), from the beginning to the south. Every time you jump north (or withdraw south), it will bring the movement of rain belt and the corresponding weather changes.

In this regard, the stable existence of the western Pacific subtropical high dominates the sunny weather. When the western Pacific subtropical high is stable in one place for a long time, the area is controlled by sunny weather for a long time. In this case, if it is in winter and spring, everyone is probably very happy. Unfortunately, it appears in summer. In summer, subtropical high stays for a long time, which is prone to high temperature anomalies, and sunny days last too long, which may even lead to drought.

Back to Shanghai, this year. As can be seen from the weather situation map of these days, Line 588 (synonymous with subtropical high) has been stable in place, leading the weather changes there. In the middle and high latitudes, the circulation is stable, the ridge line moves less, the cold and warm air converges less, and the rain is less.

So why does the subtropical high exist stably? Generally speaking, either the circulation situation is stable or there is a systematic confrontation with it (such as the South Asian High).

In addition, the impact of human activities on weather and climate can not be ignored. Human activities largely determine the content of aerosols in the atmosphere, and aerosols have a sunshade effect. Simply put, when the aerosol content in the atmosphere increases, solar radiation will be reflected back, resulting in a decrease in solar radiation reaching the ground and a lower temperature.

In the past two years, due to the epidemic situation, aerosols and greenhouse gases caused by human activities have decreased at the same time, so it also has some impact on the weather and climate.

Generally speaking, the outbreak of an extreme high temperature event depends not only on a single factor, but also on a complex atmospheric process, so the detailed process is still very complicated.