At one point in the movie Jurassic Park, a mathematician dribbles water across the back of the heroine’s hand, demonstrating the chaos theory: Any little bump on her hand would cause the water to flow in a new direction. So, he explained, small things could disrupt the flow of events.
Scientists understand the truth of that moment. Events on opposite sides of the world can cause a storm anywhere in North America; no one factor shapes all weather. Today, the weatherman are looking around the world for interrelated, large-scale weather patterns called teleconnections. They understand that weather is global and are finding, for example. that a minor change of air pressure over the Arctic Ocean can signal a storm that will bury the entire East Coast in snow or bring a lush crop to the fields of Kansas.
Oceans cover 70 percent of the Earth, and only by studying them and their affect on the atmosphere will we understand the conditions shaping our weather.
Ocean Weather Basics
Teleconnection: A recurring large-scale air pressure and circulation pattern that extends over a vast geographical area. The El Nino Southern Oscillation, or ENSO, is an example of teleconnection.
Oscillation: An air pressure pattern that changes back and forth so that each phase produces a unique predictable pattern.
El Nino: The air pressure and circulation patterns that occur when the central and eastrn tropical Pacific Ocean waters are warm.
La Nina: The air pressure and circulation patterns that occur when the central and eastern tropical Pacific Ocean waters are cold.
Why E-L N-i-n-o Spells Trouble: Most people are familiar with satellite pictures of the Atlantic Ocean during hurricane season. If conditions are right, you will see a weather pattern off the coast of Africa or in the Caribbean begin to spin and grow into a depression, a tropical storm, or a hurricane. Depending on wind currents, the storm will remain at sea or aim straight at land. The direction the storm takes is determined by air pressure patterns that are shaped in part, by warm and cool patches in the ocean.
As far back as the 1400s, the Incas understood the connection between ocean temperatures and large-scale weather patterns. They knew that if the sky over the Pacific Ocean in December was so hazy that they could not see certain stars, the year would be marked by heavy rains and a poor fishing season. They probably didn’t know that the haze was caused by warm ocean water, but what they observed and predicted for centuries is the weather pattern known as El Nino. Even today, people in South America examine the horizon in an effort to predict conditions for the next year.
El Nino became famous in 1997, when the media screamed, “El Nino is coming! El Nino is coming!” They released satellite pictures of a large warm spot in the Pacific Ocean and reported that it would cause an unusually warm winter in the United States and Western Canada, floods in the southern states, landslides in California, drought and fires from Brazil to Mexico, deadly rains and mudslides in Peru, and heavy clouds of smoke to choke Indonesia–and it did!
Scientists have studied El Nino for over a century, and they have learneed how it works; Occasionally, the central tropical Pacific Ocean becomes very warm and stays warm for 12 to 18 months. The warm spot slowly floats east until it hits Peru. Then it splits with a portion flowing north and a portion flowing south.
The air above the unusually warm water heats up and takes in more moisture. As the warm air expands, it changes normal wind currents and alters weather patterns both locally and on a much larger scale. (El Nino can change weather all over the world.)
Scientists call the warm water El Nino, and they call the altered air above it and weather patterns it causes the Southern Oscillation. The entire phenomenon is called the El Nino/Southern Oscillation, or ENSO.
THE EL NINO FORECAST-El Nino brings warm winters to Canada and the Northern United States.
THE LA NINA FORECAST-La Nina brings cold winters to Canada and the Pacific Northwest.
Teleconnection patterns are constantly changing. For a number of reasons—including winds, under water volcanoes, and deep-sea-currents—the Pacific Ocean changes back and forth from the warm El Nino to the chilly La Nina. When the Pacific Ocean cools, the air above the water becomes cooler as well. The changes in ocean temperature affect the air pressure over the water, and the ridges and troughs in the atmosphere(which are caused by high and low pressure) affect the prevailing winds that, in turn, affect oyr weather.
Once scientists realized that El Ninos and La Ninas could affect global climate, they began analyzing satellite and weather buoy data from locations all over the world. They also examined old weather records for repeating patterns and discovered other teleconnections and oscillations. Here are five examples:
The Madden Julian Oscillation(MJO) is a 40-to-60-day period of alternately strong or weak trade winds that normally blow west. It is named after Roland Madden and Paul Julian, two scientists from the National Centre for Atmospheric Research who in 1971 were studying wind patterns in the tropical Pacific. For unknown reasons, these tropical winds 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. Scientists are still studying the MJO. Most agree, however, that when the MJO cycle speeds up and again warm Kelwin waves pile up in the Pacific Ocean, we have a start of an El-Nino.
The Tropical Atlantic Variability(TAV) is often called “the El-Nino of the Atlantic.” Like El-Nino, the TAV is associated with trade winds. Unlike El-Nino, which travel 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.
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 cool waters of Alaska’s Aleution 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.
As the PNA turns negative, the airflow becomes more directly west to east.
The Pacific/North American Pattern Forecast: 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 the tornadoes — and even snowstorms — along the Gulf Coast, as blasts of polar air meet warm, moist air in the South-to be continued