Rossby Waves

Space Studies describe Rossby waves as “slowmoving waves in the ocean or atmosphere, driven from west to east by the force of Earth spinning.” These are naturally occurring phenomena first recognized in 1939 by Swedish American meteorologist Carl-Gustav Rossby. These waves, which are found in both the atmosphere and the oceans, are important mechanisms for the redistribution of energy around the globe.

Atmospheric and Oceanic Waves This phenomenon was first identified as atmospheric oscillations that occurred in the mid-latitudes in the Northern and Southern Hemispheres. In Europe and North America, people typically experience a Rossby wave as a large cold front plunging southward.

The jet stream, guised as a tongue of cold air, dips southward as a large tropical air mass moves northward. The interaction between these air masses, affected by the Coriolis affect that intensifies at lower latitudes, generates changing weather on a day-to-day and week-to-week basis. During televised weather reports, North American Rossby waves appear as large-scale oscillations of clouds moving from west to east across a continent.

Scientists later identified a similar phenomenon at work in the water of all ocean basins. Researchers discovered that oceanic Rossby waves represent a mechanism by which the ocean responds to significant atmospheric “forcing” or windrelated disruption. Rossby waves disperse the atmospheric energy across ocean basins and can be measured through satellite imagery. Because of the impact of the Earth’s axial rotation and the Coriolis effect, the oceanic Rossby waves tend to spiral away from the equator in both the Northern and Southern Hemispheres.

Scientists are increasingly interested in Rossby waves because of the possible connection between these atmospheric and oceanic waves and global warming. An understanding of atmospheric Rossby waves enabled researchers to effectively study long term temperature fluctuations and provide concrete evidence that global warming was occurring. Rossby waves can affect entire ocean basins.

They also tend to move from the eastern part of the Pacific and Atlantic oceans toward the west on either side of the equator. A complementary Kelvin wave moves in the opposite direction from west to east along the equator. The multiple axes along which the ocean moves has the ability to disrupt oceanic circulation. Researchers propose that global warming will generate stronger weather events with greater frequency. Because oceanic Rossby waves transmit atmospheric disruptions, the theory is that as storms occur more frequently, the wavelength and frequency of Rossby waves will also change—with a potentially disruptive impact on ocean currents such as the Gulf Stream.

A disrupted Gulf Stream could cause cooling at higher latitudes in the North Atlantic. Researchers also see a connection between changes in Rossby waves and the intensity of El Niño and La Niña ocean surface water temperature fluctuations in the Pacific Ocean. Also known as the El Niño-Southern Oscillation (ENSO), sea surface temperature increases during El Niño events, and decreases in La Niña events can alter or intensify the monsoonal rainfall and hurricane patterns in North and South America. The challenge for climatologists and oceanographers is to understand how disrupted Rossby waves are a cause and consequence of global warming.

The broader point is that global climate change is a complex process that involves the interplay between large scale atmospheric and oceanic processes operating at multiple scales.