NAO giving me some rain
Aug. 17th, 2012 09:23 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
ljgeoffI learned a new weather term today -- Greenland High Block Effect. It's what happens when the arctic goes into a NAO, or negative arctic oscillation.
Right now, there is a high pressure system over Greenland. This has caused the jet stream that flows across the continental US to buckle and dip low over the Great Lakes, down toward the Gulf.
When this happens, the area of low has cooler than average temps, and rain. So here in Michigan, and all over the Great Lakes area (Chicago, the UP, Indianapolis, Cincinnati) we've had cooler weather and long, soaking rains.
Of course, this high over the Arctic will be the finishing blow to the arctic ice this year. Sea ice extent and thickness are already at record lows, below the historic 2007 record, and there's still four to six weeks of melt to go. We're talking a 75%-80% ice free arctic area, and maybe even extent, in September.
There is a difference between Sea Ice Extent and Sea Ice Area: (from NSIDC)
"A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.
Extent defines a region as “ice-covered” or “not ice-covered.” For each satellite data cell, the cell is said to either have ice or to have no ice, based on a threshold. The most common threshold (and the one NSIDC uses) is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is considered ice covered; less than that and it is said to be ice free"
The Arctic Ocean and its marginal seas (the Chukchi, East Siberian, Laptev, Kara, Barents, White, Greenland, and Beaufort) has an area of 5,440,000 square miles (14,090,000 square km.) The current sea ice area is around 3.11 million square kilometers. This is only about 200,000 square kilometers above the record low set in 2007. So, looking at area, the arctic ocean is currently 78% ice free.
If you look at extent, the current value is 1,970,000 square miles (5,090,000 sq km) -- which puts the current ice extent at about 64% ice free.
Right now, there is a high pressure system over Greenland. This has caused the jet stream that flows across the continental US to buckle and dip low over the Great Lakes, down toward the Gulf.
When this happens, the area of low has cooler than average temps, and rain. So here in Michigan, and all over the Great Lakes area (Chicago, the UP, Indianapolis, Cincinnati) we've had cooler weather and long, soaking rains.
Of course, this high over the Arctic will be the finishing blow to the arctic ice this year. Sea ice extent and thickness are already at record lows, below the historic 2007 record, and there's still four to six weeks of melt to go. We're talking a 75%-80% ice free arctic area, and maybe even extent, in September.
There is a difference between Sea Ice Extent and Sea Ice Area: (from NSIDC)
"A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.
Extent defines a region as “ice-covered” or “not ice-covered.” For each satellite data cell, the cell is said to either have ice or to have no ice, based on a threshold. The most common threshold (and the one NSIDC uses) is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is considered ice covered; less than that and it is said to be ice free"
The Arctic Ocean and its marginal seas (the Chukchi, East Siberian, Laptev, Kara, Barents, White, Greenland, and Beaufort) has an area of 5,440,000 square miles (14,090,000 square km.) The current sea ice area is around 3.11 million square kilometers. This is only about 200,000 square kilometers above the record low set in 2007. So, looking at area, the arctic ocean is currently 78% ice free.
If you look at extent, the current value is 1,970,000 square miles (5,090,000 sq km) -- which puts the current ice extent at about 64% ice free.
Interesting weather ahead
Date: 2012-08-18 04:15 pm (UTC)http://www.weatherbellmodels.com/weather/ecmwf/2012081700/arctic/ecm_mslp_arctic_11.png
The main discussion is about which records will fall/have fallen first. Neat, if not cheerful.