VietNamNet Bridge – La Nina cooling pattern has been cited as the main reason behind the unusual climate in many places in the world, including the north of Vietnam which is facing a very cold winter.

Dao Thi Thuy, Head of the Climate Forecasting Division under the Institute of Meteorology and Hydrology, in the interview given to VnExpress, explained why it is unusually cold in the north.

What are the causes of the current unusual coldness?

In 2010, we saw the unusual El Nino and La Nina, which are the names of the global coupled ocean-atmosphere phenomena. El Nino occurred at the beginning of the year, while La Nina appeared at the end of the year. The manifestations of the La Nina have become clearer, which brought unusually cold temperatures.

ENSO (El-Nino Southern Oscillation) is a periodic climate pattern that occurs across the tropical Pacific Ocean. It is characterized by variations in the temperature of the surface of the tropical eastern Pacific Ocean - warming or cooling known as El Niño and La Niña respectively.

La Nina cools the temperature in the east and the central region of the Pacific Ocean. Vietnam, though situated in the northwest of the Pacific Ocean, can still be influenced by La Nina. This cold spell can be explained as the impact of La Nina on Vietnam’s climate. La Nina comes in mid winter – December, January and February, forcing the temperature down.

Besides, Vietnam’s climate is characterized by high humidity. In dry climates, the felt air temperature is not as cold as in Vietnam. This also means that, in Vietnam, it snows when the temperature goes to minus three degrees Celsius, while in other countries, it will only snow when the temperature drops to minus four or five. That explains why for example in European countries, the cold is not as chilling as in Vietnam.

Leading world scientists believe that 2011 will witnesses abnormal coldness, not only in Vietnam, but all over the world.

As far as I know, in previous years, El Nino and La Nina also occurred, but we did not experience such severe coldness like we do now. Why?

You are right. In previous years, El Nino and La Nina succeeded each other, and the interval between the two phenomena was long. Meanwhile, in 2010, both the phenomena occurred in the same year.

In general, in the periods of El Nino and La Nina, when one of the two phenomena finishes, there is an “intermediate” year (the year with normal climate). Every period lasts 2-7 years. For example, after El Nino occurred in 2007, it was very cold the following winter due to the La Nina

We think that El Nino means “hot”, while La Nina means “cold”. Is that right?

It is right only for Vietnam, where El Nino brings hot weather, while La Nina brings cold weather. However, this does not always apply to other countries, because they impact different regions differently.

How long will La Nina affect Vietnam’s climate?

The period of coldest weather will fall in January 2011. Scientists have forecast that La Nina will last until the end of the spring. If La Nina begins late, the summer will be relatively cool. I can say for sure that it will not be hot on Tet days, though it may be warmer than now. Especially, spring rain may occur, thus making people feel cold.

No one can say for sure if the 2011 winter is the coldest in the history. The lowest temperature in Vietnam were in 1974, reaching minus six degree Celsius.

Source: VnExpress