Will La Nina Bring "the coldest winter in 60 years" to Shenzhen?
30 Oct 2020
According to the forecast of the National Climate Center, Shenzhen will be affected by La Nina this fall, and a weak to moderate La Niña event is expected in this winter.
▲Distribution map of global sea surface temperature anomalies on October 24, 2020
La Niña's influence
Generally speaking, in most winters when La Niña events occur, the meridian of the atmospheric circulation in the middle and high latitudes of Europe and Asia may increase, and the cold air activities affecting the country are more frequent than usual. For southern China, in the winter of years where La Niña events occur, there is a greater probability that the temperature will be lower than normal, and the precipitation will be less than normal.
In the winter of 2007-2008, affected by the La Niña event, cold air moved south frequently, and the average temperature in Shenzhen was 15.5°C. From January 24-February 13, 2008, there was a low temperature and rainy weather, and the lowest temperature was below 10 ℃ for 21 consecutive days. It was the longest duration and the lowest average temperature on record. In southern parts of the country, there was rare heavy snow, blizzards, and freezing rain events. Many railways and roads had been interrupted, and airports closed.
▲The continuous cold and rainy days at the beginning of 2008 caused the stranded train station passengers
La Nina Incident
La Nina refers to the cold water phenomenon in which the sea surface temperature in the equatorial central and eastern Pacific is abnormally cold in a wide range, and the intensity and duration reach certain conditions. When the temperature of this sea area is 0.5 ℃ lower than in normal years, it enters a La Niña state. When lasting more than 6 months, it forms a La Niña event.
▲ Schematic diagram of La Nina phenomenon sea temperature
It's important to note that ——
The impact of each La Niña event is actually different. Not every La Niña year has a low winter average temperature in Shenzhen. The factors affecting Shenzhen’s winter climate are more complex. Factors such as melting of Arctic sea ice and changes in snow cover in Europe and Asia will affect the variability of the East Asian winter monsoon circulation, which in turn affects Shenzhen’s winter climate anomalies.
La Niña's impact on the weather in Shenzhen
From the meteorological data of the five La Niña events that occurred since 2000, in the winter of La Niña (December-February of the following year), the temperature in Shenzhen was 0.3°C lower than the same period of normal years, and the number of cold days (the daily minimum temperature) ≤10℃) 21 days on average, 3 days longer than the climate value. In terms of rainfall, La Niña's winter rainfall in Shenzhen was 9% less than normal. The average number of dry days (minimum daily relative humidity ≤50%) is 44 days, which is 6 days more than usual.
Generally speaking, in the years when the La Niña phenomenon appeared, Shenzhen's winter temperature was slightly lower, rainfall was less, and the weather was dry.
The relationship between La Nina and a Shenzhen Cold Winter
There is a high probability of a cold winter in Shenzhen in a La Nina year.
Since 2000, the period of La Niña incidents have been October 2000-February 2001, August 2007-May 2008, June 2010-May 2011, August 2011-March 2012, From October 2017 to March 2018, the winter of 2000/2001 was a weak and warm winter, the winter of 2007/2008, 2010/2011, and 2011/2012 were cold, and the winter of 2017/2018 was a normal year. In the year where the La Niña event occurred, the probability of a cold winter in Shenzhen in winter was 60%, but there were also warm winters and normal years in the La Niña year.
There are also cold winters in non-La Niña years.
Such as the winter of 2012/2013 and 2015/2016. On January 22-24, 2016, Shenzhen recorded a rare cold wave weather process. Ice grains were recorded for the first time since meteorological records, and "freezing" occurred in Wutong Mountain and other mountainous areas. Affected by this, the lowest temperature was 10 ℃ or below for 6 consecutive days from January 22-27. Affected by the high-altitude trough and strong warm and humid air currents, the city experienced a rare continuous rainstorm precipitation process on January 28-29, 2016.
▲The "snowman" made from ice particles and the "freezing" phenomenon in Wutong Mountain (picture from the Internet)
Will 2020 be a cold winter?
Shenzhen is expected to be slightly colder and dry in the autumn and winter. The coldest and less rainy period may occur in mid-January. In early February, there may be cold weather lasting for about a week. The lowest temperature in the city can reach 5-8℃. The possibility of continuous low-temperature rain, snow and freezing weather in 2008 and extreme cold wave and heavy rain in 2016 is unlikely. Many articles are circulating only stating that Shenzhen will experience the coldest winter in 60 years. Although it may not be a bad idea to get your winter clothes ready, before seeing the actual meteorological data, it's just too early to tell.
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