What is the Madden Julian Oscillation (MJO)?

The Madden Julian Oscillation (MJO) is an intraseasonal fluctuation that primarily initiates over the warm waters of the Indian Ocean and western Pacific.  The MJO is comprised of regions with various atmospheric features such as deep convection and atmospheric wind anomalies that propagate eastward along the ITCZ. During a convective phase of the MJO, there is an enhanced region of tropical convection and moisture resulting in above-average rainfall. The opposite is true for a suppressed convective phase. As the MJO continues propagating eastward, the monsoon trough weakens and may shift southward. East of the MJO the easterlies are strengthened, and to the west, the easterlies are weakened. Therefore the passing of positive phase MJO can affect atmospheric wind shear, which could in turn affect tropical cyclone activity.

Phillip Klotzbach studied the relationship between the MJO and the development of tropical systems in the Atlantic Basin. In his 2010 study, Klotzbach found a direct relationship between the increase in vertical wind shear and relative humidity, and enhanced tropical cyclone activity and intensification. In the convectively enhanced phase of the MJO, upper-level easterly and low-level westerly wind anomalies act together to reduce vertical wind shear. One primary ingredient for tropical cyclone development is reduced vertical wind shear. Relative humidity throughout the atmosphere is also needed for tropical development. In Camargo’s study (2009), he found that mid-level relative humidity played the most important role, compared to low-level absolute vorticity, vertical wind shear, and potential intensity in tropical cyclogenesis by the MJO. Therefore, when an eastward moving MJO and a tropical wave meet, it is possible for the tropical wave to develop into a tropical cyclone due to the enhanced atmospheric moisture and reduced vertical wind shear created by the MJO.  If a tropical cyclone already exists, its interaction with a MJO may cause the cyclone to intensify. Kingtse C. Mo discusses an increase in tropical cyclone activity over the Atlantic Basin when the convective phase of the MJO is located the Indian Ocean rather than the Pacific Ocean.July9

 

The image above represents a forecast for Outgoing Longwave Radiation (OLR) anomalies, a key detector for active MJO regions, issued by NOAA’s Climate Prediction Center (CPC). The CPC monitors and predicts climate variability and teleconnections for government, public, and private meteorological industries. Negative OLR values indicate enhanced convection or an active MJO phase (more cloud cover indicating more convective activity). Positive OLR values represent suppressed convection (less cloud cover).

The latest forecast from the ensemble mean GFS predicts an increase in OLR, possible MJO wave, across the Indian Ocean for the next two weeks. As Kingste C. Mo found in his study, there is likely an increase in tropical activity over the Atlantic Ocean when an MJO is present over the Indian Ocean.

Although Wilkens Weather is forecasting a very low chance for tropical development in the next five days, this will be a parameter worth watching this tropical season.

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