365 Days of Climate Awareness 138 – Teleconnections

With the State of the Climate posts regularly pointing out the global effects of ENSO, it’s useful to take a step to the side for the moment to look at the concept and some of the mechanics involved. Long-distance effects—generally on the scale of a thousand or more kilometers (about 620 miles)--through the atmosphere are called “teleconnections”.

El Niño teleconnections throughout North America.

A teleconnection is not merely the spread of a single state or condition through the atmosphere. It is a series of effects—a cascade or dominos are good analogies—from a place of origin to a geographically remote location. To contrast some major effects of the ENSO cycle: during an El Niño episode, the warmer Pacific water leads to warmer, low-pressure air above it, and the stratospheric jet stream runs more directly west-to-east. This brings warmer weather to western Canada and the Pacific Northwest, and increased rain and storm activity across the southern United States. During a La Niña, however, the cooler ocean water leads to colder, higher-pressure air over the North Pacific, which diverts the polar jet stream there northward. That causes the jet stream farther east to be diverted to the south, bringing Arctic cold, dry air down into the United States and drier conditions to the southern part of the country.

La Niña teleconnections throughout North America.

As another example, a positive phase of the North Atlantic Oscillation (NAO), where northerly (Iceland) air pressure is low, and subtropical (Azores) air pressure is high, is correlated with high temperatures in the eastern US and northern Europe, and colder temperatures in southern Europe, the Mideast, and sometimes Russia. Meanwhile, a negative NAO (high arctic pressure, low subtropical) leads to cold weather in the southeastern US and northern Europe, and warm, wet weather in the Mideast. As with ENSO, the changes in air pressure direct the jet stream which controls weather patterns.

Generally we observe these teleconnections statistically, before we develop an analytical understanding. A further horizon in the study of climate science is the interaction between major oscillations, such as ENSO and the NAO, and their influence on each other, as well as their combined, sometimes opposed effects.

Tomorrow: 2003 state of the climate, North America and Europe.

Schematic of the North Atlantic Oscillation.

Be brave, and be well.