What happens when a change in the atmosphere or ocean thousands of miles away affects your local weather? These large-scale weather patterns are called teleconnections and oscillations. From El Niño and La Niña to the Madden-Julian Oscillation, these patterns can influence temperature, precipitation, storms, and even hurricane activity far from where they begin.
Learn how teleconnections work and discover how the MJO, TAV, PNA, PDO, and NAO can affect weather across North America and beyond.
What Is a Teleconnection?
Changes in the atmosphere in one place that affect weather far away are called teleconnection patterns. A teleconnection is a recurring large-scale air pressure and circulation pattern that extends over a vast geographical area.
An example of a teleconnection is El Niño, created by El Niño–Southern Oscillation (ENSO) changes to the atmosphere and ocean.
What Is an Atmospheric Oscillation?
An oscillation is an air pressure pattern that changes back and forth so that each phase produces a unique, predictable pattern.
An example of an oscillation is the Madden-Julian Oscillation (MJO).
Major Teleconnections and Oscillations
There are several major teleconnections and oscillations that meteorologists watch when looking at large-scale weather patterns. Here’s a quick guide to what they are and where they can have the greatest influence.
| Pattern | What it is | Where it can affect weather |
|---|
| MJO | Tropical atmospheric disturbance | Pacific, U.S., hurricane activity |
|---|
| TAV | Tropical Atlantic variability | Atlantic precipitation and hurricanes |
|---|
| PNA | Pacific/North American circulation pattern | North America |
|---|
| PDO | Long-term Pacific climate pattern | Pacific and western North America |
|---|
| NAO | North Atlantic pressure pattern | Eastern U.S. and Europe |
|---|
The Madden-Julian Oscillation (MJO)
The Madden Julian Oscillation (MJO) is a 40- to 60-day period of alternately strong or weak trade winds that normally blow west, but are traveling east. For unknown reasons, tropical Pacific wind patterns sometimes weaken, and the sun-warmed pulse of ocean water that they usually cause to drift west drifts east. As this pulse of warm water, called a Kelvin wave, moves east—from the coast of Africa across the Indian and Pacific Oceans—it carries changed air patterns above it.
When the wave crashes into South America, the water stops, but the air pattern continues over land northeastward, into the Caribbean atmosphere and across the Atlantic Ocean. Before this cycle is complete, another pulse has already started in the Indian Ocean.
Tropical Atlantic Variability (TAV)
The Tropical Atlantic Variability (TAV) is often called “the El Niño of the Atlantic.” Like El Niño, the TAV is associated with trade winds. Unlike El Niño, which travels east, the TAV oscillation runs north and south. Depending on the strength of the southeast trade winds, it alternately warms the ocean water south of the equator, then north, then south again.
When the Atlantic sea-surface temperatures near the equator fluctuate, precipitation patterns change throughout the Atlantic Ocean. Like most oscillations, the TAV is affected by other global weather patterns.
When the TAV causes the water north of the equator to be unusually warm in summer, the warmed water acts as a channel for tropical storms and hurricanes striking the East Coast, especially in the Southeast. Much less is known about the effects of the TAV during winter.
Pacific/North American Pattern (PNA)
The Pacific/North American pattern (PNA) is a large teleconnection that dominates weather from Shanghai, China, to Atlanta, Georgia, every month except June and July. The air masses over the warm waters of Hawaii and in the cool waters of Alaska’s Aleutian Islands start a circulation pattern that sweeps east into North America. There the pattern interacts with a high ridge of air over the northern Rockies and a deep trough over the southern states.
When the difference in air pressure between two designated points within an atmospheric oscillation is great, conditions are described as “positive.” When the difference is low, conditions are “negative.”
As the PNA turns negative, the airflow becomes more directly west-to-east.
A positive PNA carries tropical moisture into British Columbia, and the United States ends up with cold and stormy weather in the Midwest and Southeast; cold in the East and warmth in the West; and tornadoes—and even snowstorms—along the Gulf Coast, as blasts of polar air meet warm, moist air in the South.
A negative PNA carries diminishing amounts of moisture eastward from California, resulting in cold and snowy weather in the West; rain and snow in the plains; and warm and relatively dry weather in the East.
Pacific Decadal Oscillation (PDO)
The Pacific Decadal Oscillation (PDO) is a change in ocean currents that lasts for 20 to 30 years. It affects not only water temperatures but also air currents overhead. A warm PDO means a warm central Pacific Ocean with cool water in the west, north, and south. During the cool phase, the central waters are cool and the peripheral waters are warm. During the last three decades of the 20th century, we experienced a warm phase.
A warm PDO may result in more El Niños, more precipitation, and fewer typhoons. A cool PDO results in cool air and less precipitation in the western United States.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation (NAO) affects the eastern United States. This teleconnection sits between the cool atmospheric low over Iceland and the warm high over the Azores.
In winter, a positive NAO causes Atlantic storms to veer north, and warm, wet winters to occur in the eastern United States and Europe. Northeastern Canada tends to be unusually cold. In summer, a positive NAO means fewer tropical storms and hurricanes striking the East Coast.
In winter, a negative NAO forces cold air into the eastern United States, and causes heavy rains in southern Europe. Northeastern Canada is generally warmer, and areas around the Great Lakes tend to have a cooler, wetter spring. Studies of a negative NAO in summer have proved inconclusive.
Frequently Asked Questions About Weather Teleconnections
What are examples of teleconnections?
Some well-known teleconnections and oscillations include El Niño–Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), Pacific/North American pattern (PNA), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO).
How do teleconnections affect weather?
Teleconnections can change atmospheric pressure, wind patterns, ocean temperatures, and the movement of air masses. These changes can influence weather thousands of miles away, sometimes affecting temperature, precipitation, snowfall, and storm activity.
What is the difference between a teleconnection and an oscillation?
A teleconnection describes a large-scale atmospheric pattern that connects weather in distant parts of the world. An oscillation is a pattern that shifts between different phases over time, with each phase producing different weather effects. Some oscillations, such as the MJO, can produce teleconnection effects far from their origin.
Can teleconnections help predict the weather?
Yes. Meteorologists and long-range forecasters monitor teleconnections because their different phases can provide clues about upcoming weather patterns. However, teleconnections are just one piece of the forecasting puzzle and don’t determine the weather by themselves.
Why are teleconnections important for long-range weather forecasts?
Because teleconnections operate on large geographic scales and can persist for weeks, months, or longer, they can provide useful information about potential long-range weather trends, including periods of unusual warmth, cold, precipitation, or storminess.
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