The MJO can be defined as an eastward moving 'pulse' of clouds, rainfall, winds and pressure near the equator that typically recurs every 30 to 60 days. It’s a traversing phenomenon and is most prominent over the Indian and Pacific Oceans.
How does MJO affect Indian Monsoon?
The Indian Ocean Dipole (IOD), El Nino and MJO are all oceanic and atmospheric phenomena, which affect weather on a large scale. IOD only pertains to the Indian Ocean, but the other two affect weather on a global scale, up to the mid-latitudes.
IOD and El Nino remains over their respective positions, while MJO is a traversing phenomenon. The journey of MJO goes through eight phases. When it is over the Indian Ocean during the Monsoon season, it brings good rainfall over the Indian subcontinent. On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, MJO brings bad news for the Indian Monsoon.
Basically, it is linked with enhanced and suppressed rainfall activity in the tropics and is very important for the Indian monsoonal rainfall. It has also been established that if the periodicity of MJO is nearly 30 days then it brings good rainfall during the Monsoon season. If it is above 40 days then MJO doesn't give good showers and could even lead to a dry Monsoon. Shorter the cycle of MJO, better the Indian Monsoon. Simply because, it then visits the Indian Ocean more often during the four month-long period.
Presence of MJO over the Pacific Ocean along with an El Nino is detrimental for Monsoon rains.
What is the history of MJO?
In the year 1971, Roland Madden and Paul Julian were analyzing zonal wind data in the lower troposphere, over the Canton Island. They found a low frequency 40-50 day oscillation in the central equatorial Pacific. Further in 1972, they noticed oscillations of the similar type over a large area in the equatorial belt in the zonal wind and surface pressure. They also noticed that these oscillations have maximum amplitude (power) at the equator. Latter, these oscillations were named as Madden-Julian oscillations (MJO).
After that, many researchers worked in this direction and found that MJO is responsible for both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Ocean. Further, researchers found that periodicity of MJO is not limited to 40-50 days; it varies between approximately 30-60 days. Because of this pattern, the Madden–Julian oscillation is also known as the 30-60 day oscillations or intraseasonal oscillations.
Image credit- National Geographic