Green Comet

Credit sleske – CC-BY-SA

Cloud of the Day – Other Phenomena Related to the Jet Stream

As promised in the original post on the jet stream, today’s post will cover related phenomena such as the polar vortex and the Southern Oscillation.

You will recall that jet streams form at the boundaries between major air masses, and at the boundary between the troposphere and the stratosphere. The Polar Jet, for instance, marks the boundary between the colder air mass to the north and the warmer one to the south. As a rule, the greater the difference in temperature of the air masses, the higher the wind speed in the jet stream. The Subtropical Jet is in addition affected by el niño and la niña. which are in turn affected by the Southern Oscillation. Whereas el niño and la niña are ocean events having to do with the warming and cooling of the surface waters of the eastern tropical Pacific Ocean, the Southern Oscillation is an equivalent atmospheric effect. When the two events synchronize they reinforce each other. During an el niño event the subtropical jet stream trends further south, and further north during la niña. When the periodic oscillations of the ocean waters and the atmosphere reinforce each other, the effect on the jet stream is greater and we experience more extreme weather modification. When they tend to cancel each other out, the weather events are less pronounced. This description is vastly simplified and once again I’m impressed by the persistence and attention to detail shown by meteorologists and other scientists.

The polar vortex has made it into the news recently as the eastern part of North America has been subjected to outflows of frigid arctic air. Strangely, people tend to blame the polar vortex, as if its existence were responsible for their frostbitten noses. The fact is, as you will see, it is the polar vortex that normally holds the cold air in, preventing their nasal misery.

Both poles have a polar vortex. They are persistent, large-scale low pressure areas generally lying poleward of sixty degrees latitude. These vortices are upper air phenomena, with their bases in the upper troposhpere and lower stratosphere, around the tropopause, where jet streams live. The strength of the vortex depends on the temperature differential between the equator and the poles. This is greater in winter, which is good for keeping that cold air in and saving our noses.

Unfortunately the vortices are more commonly ill- rather than well-defined. There is not always a strong jet stream wrapped around them. They can break up into two or more vortices, resulting in the flow of arctic air becoming disorganized, sometimes breaking out and spilling southward.

Climate change, for various reasons, is resulting in a decrease in the pressure and temperature differential between the equator and the poles, resulting in weaker vortices and less containment of arctic air. This causes the apparent paradox of localized cold snaps brought on by global warming. The atmosphere is dynamic and complex. There’s more to it than the nightly weather report.

rjb

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