Atmospheric & Oceanic Processes Lecture 4: The changing Arctic

Here, the 2015 maximum is compared to the 1979-2014 average maximum shown in yellow. A distance indicator shows the difference between the two in the Sea of Okhotsk north of Japan.

2012

Arctic Ice Melt Since 1979, the size of the summer polar ice cap has shrunk more than 20% Average temperatures in the Arctic region are rising twice as fast as they are elsewhere in the world. Arctic ice is getting thinner, melting and rupturing. For example, the largest single block of ice in the Arctic, the Ward Hunt Ice Shelf, had been around for 3,000 years before it started cracking in 2000. Within two years it had split all the way through and is now breaking into pieces. The polar ice cap as a whole is shrinking. Images from NASA satellites (above picture) show that the area of permanent ice cover is contracting at a rate of 9 percent each decade. If this trend continues, summers in the Arctic could become ice-free by the end of the century. Arctic icemelt http://www.nrdc.org/globalwarming/qthinice.asp

Sea ice reformed or refroze later than average throughout most of the Arctic, especially in the Kara and Barents seas where the freeze-up happened about two months later than average. Ice was also late to form in the Beaufort, Chukchi, East Siberian, and Laptev seas, between ten and forty days later than average. In contrast, the timing of freeze-up over the central Arctic Ocean near the pole was near average, as was also the case in Baffin Bay and parts of Hudson Bay. When freeze-up happens late, the ice has less time to thicken before the melt season starts, leading to a thinner ice cover that is more prone to melting out in summer READ more

Ice becomes weaker, and can be broken more easily GREENHOUSE GAS THICK ICE (10m) THINNER ICE (5m) ICE ICE Melt& Broken Leads expose seawater Absorb more heat Ice becomes weaker, and can be broken more easily More melting ICE ICE ICE

In this schematic drawing of North Atlantic and Arctic Ocean circulation, red arrows represent relatively warm water from lower latitudes entering the Arctic, while blue arrows show the export of colder water from the Arctic. Shaded white shows the average area covered by sea ice.

The Arctic Oscillation (AO) is a large scale mode of climate variability, also referred to as the Northern Hemisphere annular mode. The AO is a climate pattern characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. When the AO is in its positive phase, a ring of strong winds circulating around the North Pole acts to confine colder air across polar regions. This belt of winds becomes weaker and more distorted in the negative phase of the AO, which allows an easier southward penetration of colder, arctic airmasses and increased storminess into the mid-latitudes.

Possible consequences of Arctic ice melt What atmospheric chain reactions occur when warming causes the Arctic ice to melt? Why has the tropospheric pressure increased, so that the cyclonic polar wind weakened? What happens to the Jet Stream when the Arctic warms? Why as the jet stream slows, the amplitude of its meander can become larger?

Homework #4 Arctic ice melt and consequences to weather: Read & write summary: http://shoni2.princeton.edu/ftp/lyo/journals/GreeneMonger-ArcticWildCardInWeather-JO2012.pdf Related "easy" reading: http://shoni2.princeton.edu/ftp/lyo/journals/Jones-ArcticIceLossWeatherFeatureReport-NClimC2012.pdf