Here’s how the Madden Julian Oscillation could save the winter


This teleconnectivity index is very important for the overall circulation of the atmosphere.
Daniel Ingemi Daniel Ingemi 7 minutes

PUSH Madden Julian Oscillation it is a tropical interseasonal oscillation with 1-2 hemispherical waves, generally lasting 30-60 days. It is strongest in winter, especially in the Eastern Hemisphere, with maximum intensity between the central-eastern Indian Ocean and Indonesia.

This teleconnectivity index is very important for the overall circulation of the atmosphere. Typically in areas where Madden Julian Oscillation determines the increase in convective activity, intense and frequent thunderstorms develop near the equatorial or sub-equatorial zone, while simultaneously, in response to very intense convective activity, anticyclonic cells form in the upper tropical troposphere to the north and south of the region of strong convention with significant effects on the hemispheric circulation.

How does this index affect the winter season?

Most of the heavy rainfall affects the Pacific Northeast and the west coast of Canada and the United States they are associated with the movements of the “Madden-Julian Oscillation” along the western equatorial Pacific. These would be typical winter weather anomalies preceding heavy rainfall in the Pacific Northwest.

Heavy tropical rain associated with the “MJO” occurred during the 8–10 days preceding the heavy rainfall over the Northeast Pacific. they move eastward from the eastern Indian Ocean to the western tropical Pacific.

In this phase, a stream of very moist and mild air spreads from the western tropical Pacific towards the stretch of ocean near Hawaii. A strong blocking high is co-located with baric highs south of the Gulf of Alaska with a very strong “polar current” bordering its northern flank.

Madden, winter.
The “MJO” can more or less indirectly influence the weather/climate trend in the Old Continent and the Mediterranean, especially in the winter season.

Just 5 days after the arrival of heavy rainfall Heavy rains and tropical storms move eastward toward the change line and begin to weaken.

The moist, mild tropical flow reaching the Hawaiian Islands extends further northeast, supporting the weakening of a strong blocking anticyclone moving westward.

In the middle of the East Central Pacific the main branch of the “Jet Stream” splits into two, it forms a “delta” that gradually erodes the southernmost edge of the blocking high.

Major rain events on the American continent

The breaking of the blocking anticyclonic ridge will allow the flow of very moist air coming from tropical latitudes towards the Northeast Pacific off the US west coast. Warm, moist air masses collide with cooler air sliding south from Alaska, flowing along the eastern edge of a blocking high, ready to erode.

Along the confluence line, between the cold northerly currents, the subpolar extraction, descending from the Gulf of Alaska, and the much wetter and warmer currents rising directly from the tropical belt of the central Pacific, an extratropical deep pressure circulation (positive vorticity advection) develops off the west coast of North America, ready to fly towards the coast of British Columbia, Washington state, Oregon and California, intense clouds full of precipitation, over the entire American west coast.

These events are often referred to as “Pineapple Express”so called to denote the tropical origin of a stream of very moist air which moves from the central Pacific, passing through Hawaii, towards the coasts of the States of Washington, Oregon, and California, after traveling thousands of miles over the ocean, causing heavy rainfall and often flood events with floods, landslides and mudslides.

Influences of time in Europe

But “MYO” is able to influence more or less indirectly the weather/climate trend in the old continent and the Mediterranean, especially in the winter season. When the phenomenon Madden-Julian Oscillation it is located between the eastern Pacific and the sea off Central America, in the mid-latitudes of the Atlantic Ocean The development of tropospheric anticyclonic ridges is favored by the action of intense “forcing” by energetically dynamic longwave anticyclonic pulsations that rise from Central America and the western tropical Atlantic into the North Atlantic.

Madden, winter.
This index is able to influence the development of weather/climate in the Old Continent and the Mediterranean more or less indirectly, especially in winter, and also to support important circulation changes.

This creates robust blocking anticyclones that stop the moist zonal disturbed flow exiting North America, creating a more meridional type of circulation. The slow eastward migration of the “MJO” phase will cause the onset of a subtropical high pressure structure between northwestern Africa, the central western Mediterranean and western Europe.

This climate pattern is the origin of the anticyclonic fields that invade the Mediterranean in winter, while cold advection of arctic origin spreads over eastern Europe and Russia.


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