The Definition and Long-term Variations of Beijing Blue Days

TL;DR

This study analyzes the long-term variations of Beijing Blue days using meteorological data from 1980 to 2014, establishing standards for their definition and examining their seasonal and regional patterns.

Contribution

It introduces three standards for defining Beijing Blue days with 73.4% accuracy and investigates their long-term trends and seasonal variations across Beijing and the BTH region.

Findings

Beijing Blue days have increased significantly, especially in winter.

The growth rate of Blue days in the BTH region is 2.66 days per year.

Blue days are most frequent in January and are influenced by humidity and rainless conditions.

Abstract

The phenomenon of Beijing Blue days first occurs on June 11, 2015, and become a hot society topic in a short time. Thus, Beijing's blue day is not only what ordinary people desire but national needs. In this work, using the data of daily average meteorological observations during 1980 and 2014, we select three standards for defining Beijing blue day (BBI), which contain no rain, clear sky, and great dry visibility, and the accuracy is 73.4%.Our study finds that Beijing shares the most significant acceleration in the BTH region, with a growth rate of 2.66 d/year. The greatest seasonal average and the maximum acceleration rate appear in winter for total BBI and continuous BBI days, the least is in summer, while Beijing blue appears most frequently in January. BBI is more related to relative humidity and rainless day on an annual scale, but different in different seasons.