The cause of the COVID-19 coronavirus epidemic in Wuhan.
Probably the cause of the COVID-19 coronavirus epidemic in Wuhan was a drop in air temperature in central China that occurs during a minimum of solar magnetic activity. The fall in winter temperature in Wuhan in Central China in 2020 caused an outbreak of the coronavirus epidemic, which spread all over the world by the wake of goods exported from China. The last rapid temperature drop in Wuhan occurred around 2011 during the last minimum of solar magnetic activity. We currently have a new minimum of solar activity, and there has probably been a temperature drop in central China, (usually is warm in the Wuhan) there has been a severe winter that has caused the outbreak of the epidemic of Coronavirus.
In Wall Streat Journal, I found an article explaining why harsh winters are dangerous for southern China's residents, like Wuhan without heating their homes in the winter. The harsh winter in Wuhan 2019/2020 weakened the resilience of residents and due to the cold, the COVID-19 epidemic broke out. Winter temperatures in Wuhan in January 2020 fluctuated below 10 degrees Celsius during the day and dropped below zero at night. The lack of central heating of houses at such low air temperatures caused an increase in morbidity and an outbreak of an epidemic that spread to China and the whole world. Data on air temperature in Wuhan can be found at:
https://www.accuweather.com/en/cn/wuhan/103847/january-weather/103847?year=2020
Air temperatures in Ulaanbaatar, Mongolia in January 2020 reached -30 degrees Celsius at night and -20 degrees Celsius during the day, which testifies to the cooling of the climate in January 2020 in the entire central part of the Asian continent -link:
https://www.accuweather.com/en/mn/ulan-bator/246421/january-weather/246421?year=2020
Excerpt from the Wall Street Journal article below. Link to the article:
https://www.wsj.com/articles/SB114229343067397083
China's Winter of Discontent
Mao-Era Policy Provides Heat Up North but None in South; Shivering Citizens Are Fed Up
Mr. Li isn't the only one asking. Heating systems are one of the last areas that remain under China's former centrally planned economy, with government regulators still setting the thermostat for homes, classrooms, and offices across the country. Under the policy, which dates back to Mao Zedong in the 1950s, the government provides heat in the northern half of China, and, to save money, it provides no heat in the southern half. As a result, northerners often wilt in steaming apartments, while those in southern provinces shiver through the winter.
Temperature data in Wuhan in the early 21st century and in 2011:
https://www.researchgate.net/publication/329699833_Urban_heat_island_effect_and_its_contribution_to_observed_temperature_increase_at_Wuhan_station_Central_China
T of Hong Kong flu epidemic
Jakuszowice, April 23-24, 2020, Bogdan Góralski