Study Says Moisture can Affect Upper Atmospheric Winds

BENGALURU:  Variations in atmospheric moisture can influence winds blowing in the higher reaches of the atmosphere, according to a study by Indian Institute of Science (IISc) researchers.

Winds circulating in the upper atmosphere, called Rossby waves, play a major role in the development of weather. One of the reasons why weather is predictable for five to seven days is because of regularities like waves.

Joy Monteiro, a PhD student who was part of the study led by Prof Jai Sukhatme, said, “Until recently, all the existing theories of Rossby wave dynamics assumed that the atmosphere is ‘dry’, i.e., water vapour does not play an important role in the propagation and stability of these waves. Therefore, our work tried to look at the conditions under which Rossby waves can interact with water vapour and the associated latent heat release.”

Monteiro and his professor are from the Centre for Atmospheric and Oceanic Sciences at IISc.

Rossby waves have been known to scientists since 1939 and a lot of research has gone into understanding how they affect weather. However, the influence of a common phenomenon like moisture on Rossby waves was not studied before.

The team was convinced that Rossby waves were not all that dry, and they developed equations that included the effect of moisture. “We showed that for conditions that are representative of the extra-tropical atmosphere (atmosphere outside the tropics), if there is an increase or decrease of mean water vapour in the North/South or East/West directions, they can significantly change the character of the Rossby waves and in some cases, even make them unstable,” explains Monteiro.

The study found the presence of moisture gradients from North to South slowed down Rossby waves.