Essays: Atmospheric Rivers

Saturday, June 28, 2014

Atmospheric Rivers

Like an atmospheric river, jet streams are narrow, fast-flowing currents that bend and meander due to the forces of nature.

Jet streams flow at an altitude of 5 to 9 miles above the surface of the Earth. Air currents are created by temperature gradients.

Six jet streams flow west-to-east around the Earth:

2 polar jet streams flow near the Arctic and Antarctic circle;
2 subtropical jet streams flow halfway between the poles and the Equator; and
2 jet streams flow on either side of the equator.

The polar jet stream in the Northern Hemisphere is created by the cold, dense air masses descending from the Arctic and deflecting warm air masses ascending from the tropics. The currents typically flow at speeds greater than 100 miles per hour (160 km/h).

Jet stream troughs and ridges over North America (NASA)

Jet streams are driven by atmospheric heating (solar radiation) and by the planet's rotation on its axis. The steeper the temperature gradient, the straighter and faster the air current. On the contrary, the gentler the temperature gradient, the slower the air current and the more prone the jet stream path is to undulations. The wavy undulations of the polar jet stream propagate across the mid-latitudes. Large, pronounced meanders of the jet stream path are called Rossby Waves.