Explainer: What is the MJO?

Published: Oct. 7, 2020 at 6:08 PM EDT
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TALLAHASSEE, Fla. (WCTV) - The Pinpoint Weather Team is taking viewer requests on weather topics. A viewer asked Chief Meteorologist Mike McCall what the MJO is. It’s a bit long to explain in a standard three-minute weathercast, but it will be attempted here and now.

The MJO is an acronym for the Madden-Julian Oscillation. It’s not a new Madden game on Playstation, but an intraseasonal variability in the tropical atmosphere. In plain English, an eastward moving disturbance of clouds, winds, rainfall, and air pressure that starts in the Indian Ocean, and it returns to its starting point every 30 to 90 days. It’s almost like El Niño, except that the MJO moves from one place to another across the globe white the ocean-atmospheric interactions of El Niño and La Niña are in a same large geographic area of the equatorial Pacific.

There are two phases: A lifting and sinking phase. The lifting phase is east and west winds collide to cause rising air, which helps to create convection (thunderstorms and rain). The sinking phase is when the flow moves from above to the surface (away from the rising air) and winds flow from that to the east and west.

An illustration of the Madden-Julian Oscillation.
An illustration of the Madden-Julian Oscillation.(NOAA)

Despite it’s distance from the Big Bend and South Georgia, it can have an impact on the area’s weather.

One study found that when the MJO-associated convection was over the western and central Pacific Ocean during the cooler months (November through March), Florida’s rainfall is lower than normal.

The MJO can also impact the tropics in the Gulf of Mexico and Caribbean Sea. Another study found when the region experiences anomalous westerly winds in the lower levels of the atmosphere, it can enhance vorticity (spin). This spin is a requirement for tropical cyclone development. The authors found that tropical cyclone development is about three to four times higher than if the winds were out of the east.

This not-so-widely-known phenomena outside of the weather community can have an impact on the local weather.

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