The North Atlantic Oscillation ranks among the dominant planetary scale phenomena that exert a strong climatological grip over most of the northern hemisphere (NH). Its main action centers form an approximate north-south atmospheric pressure dipole over the north Atlantic Ocean and act as a meteorological pinball machine; depending on their relative strength the prevailing westerly winds over the NH mid-latitudes are either weakened and deflected towards northern latitudes or strengthened and carry on undisturbed towards Europe and the Mediterranean. Model simulations, satellite and ground observations reveal that the NAO phase strongly regulates wintertime storm tracks hence precipitation, sea and air temperatures at various heights all the way from the U.S. east coast, the northern Atlantic ocean, Greenland and Europe. Since the late 1980‘s the NAO has been extensively studied and under no circumstances did it escape from the “global warming†context. A number of studies have shown that a possible link between the NAO, atmospheric greenhouse gases and the tropospheric warming of the NH may exist.
The North Atlantic Oscillation ranks among the dominant planetary scale phenomena that exert a strong climatological grip over most of the northern hemisphere (NH). Its main action centers form an approximate north-south atmospheric pressure dipole over the north Atlantic Ocean and act as a meteorological pinball machine; depending on their relative strength the prevailing westerly winds over the NH mid-latitudes are either weakened and deflected towards northern latitudes or strengthened and carry on undisturbed towards Europe and the Mediterranean.
!ADVERTISEMENT!Model simulations, satellite and ground observations reveal that the NAO phase strongly regulates wintertime storm tracks hence precipitation, sea and air temperatures at various heights all the way from the U.S. east coast, the northern Atlantic ocean, Greenland and Europe. Since the late 1980‘s the NAO has been extensively studied and under no circumstances did it escape from the global warming context. A number of studies have shown that a possible link between the NAO, atmospheric greenhouse gases and the tropospheric warming of the NH may exist.
NAO’s characterization of strength is expressed via an indexed value. For example, the NAO negative phase refers to the indexed values below zero and vice versa. There are several methods to calculate the aforementioned indexes and admittedly each one has its own prons and cons. Some methods can track the NAO’s evolution back to 1800’s, based on single point ground observations. Other methods comprise of more complex mathematical implementations and combine more spatially expanded observations but have a time constrain.
Based on a widely adopted method, the National Oceanographic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) evaluates the monthly NAO variability. The following observations are made from the NOAA-CPC NAO index covering a period between 1950-present and can be freely accessed at http://www.cpc.noaa.gov/products/precip/CWlink/pna/norm.nao.monthly.b5001.current.ascii.table.
For the full story please go to: http://web.me.com/evdoxiachronis/NAO/
