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Arctic oscillation AI simulator
(@Arctic oscillation_simulator)
Hub AI
Arctic oscillation AI simulator
(@Arctic oscillation_simulator)
Arctic oscillation
The Arctic oscillation (AO) or Northern Annular Mode/Northern Hemisphere Annular Mode (NAM) is a weather phenomenon at the Arctic pole north of 55 degrees latitude. It is an important mode of climate variability for the Northern Hemisphere. The southern hemisphere analogue is called the Antarctic oscillation or Southern Annular Mode (SAM). The index varies over time with no particular periodicity, and is characterized by non-seasonal sea-level pressure anomalies of one sign in the Arctic, balanced by anomalies of opposite sign centered at about 37–45° N.
The North Atlantic oscillation (NAO) is a close relative of the Arctic oscillation. There is debate over whether one or the other is more fundamentally representative of the atmosphere's dynamics. The NAO may be identified in a more physically meaningful way, which may carry more impact on measurable effects of changes in the atmosphere.
The Arctic oscillation appears as a ringlike (or "annular") pattern of sea-level pressure anomalies centered at the poles. The presence of continents and large landmasses disrupts the ringlike structure at the Arctic pole, while anomalies surrounding the Antarctic pole are nearly circular.
The Arctic oscillation is believed by climatologists to be causally related to (and thus partially predictive of) global weather patterns. NASA climatologist James E. Hansen explained the mechanism by which the Arctic oscillation affects weather at points so[clarification needed] distant from the Arctic, as follows (note, however, that Hansen's explanation is erroneous: pressure in the Arctic is low in the positive AO phase, which configuration also enhances the jet stream):
The degree to which Arctic air penetrates into middle latitudes is related to the AO index, which is defined by surface atmospheric pressure patterns. When the AO index is positive, surface pressure is high in the polar region. This helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region. When the AO index is negative, there tends to be low pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into middle latitudes."
The Arctic oscillation index is defined using the daily or monthly 1000 hPa geopotential height anomalies from latitudes 20° N to 90° N. The anomalies are projected onto the Arctic oscillation loading pattern, which is defined as the first empirical orthogonal function (EOF) of monthly mean 1000 hPa geopotential height during the 1979-2000 period. The time series is then normalized with the monthly mean index's standard deviation.
Over most of the past century, the Arctic oscillation alternated between positive and negative phases. Data using a 60-day running mean has implied the oscillation has been trending to more of a positive phase since the 1970s,[citation needed] though it has trended to a more neutral state in the last decade. The oscillation still fluctuates stochastically between negative and positive values on daily, monthly, seasonal and annual time scales, although meteorologists have attained high levels of predictive accuracy for shorter term forecasts. The correlation between actual observations and the 7-day mean Global Forecast System ensemble AO forecasts is approximately 0.9.
This zonally symmetric seesaw between sea level pressures in polar and temperate latitudes was first identified by Edward Lorenz and named in 1998 by David W.J. Thompson and John Michael Wallace.
Arctic oscillation
The Arctic oscillation (AO) or Northern Annular Mode/Northern Hemisphere Annular Mode (NAM) is a weather phenomenon at the Arctic pole north of 55 degrees latitude. It is an important mode of climate variability for the Northern Hemisphere. The southern hemisphere analogue is called the Antarctic oscillation or Southern Annular Mode (SAM). The index varies over time with no particular periodicity, and is characterized by non-seasonal sea-level pressure anomalies of one sign in the Arctic, balanced by anomalies of opposite sign centered at about 37–45° N.
The North Atlantic oscillation (NAO) is a close relative of the Arctic oscillation. There is debate over whether one or the other is more fundamentally representative of the atmosphere's dynamics. The NAO may be identified in a more physically meaningful way, which may carry more impact on measurable effects of changes in the atmosphere.
The Arctic oscillation appears as a ringlike (or "annular") pattern of sea-level pressure anomalies centered at the poles. The presence of continents and large landmasses disrupts the ringlike structure at the Arctic pole, while anomalies surrounding the Antarctic pole are nearly circular.
The Arctic oscillation is believed by climatologists to be causally related to (and thus partially predictive of) global weather patterns. NASA climatologist James E. Hansen explained the mechanism by which the Arctic oscillation affects weather at points so[clarification needed] distant from the Arctic, as follows (note, however, that Hansen's explanation is erroneous: pressure in the Arctic is low in the positive AO phase, which configuration also enhances the jet stream):
The degree to which Arctic air penetrates into middle latitudes is related to the AO index, which is defined by surface atmospheric pressure patterns. When the AO index is positive, surface pressure is high in the polar region. This helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region. When the AO index is negative, there tends to be low pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into middle latitudes."
The Arctic oscillation index is defined using the daily or monthly 1000 hPa geopotential height anomalies from latitudes 20° N to 90° N. The anomalies are projected onto the Arctic oscillation loading pattern, which is defined as the first empirical orthogonal function (EOF) of monthly mean 1000 hPa geopotential height during the 1979-2000 period. The time series is then normalized with the monthly mean index's standard deviation.
Over most of the past century, the Arctic oscillation alternated between positive and negative phases. Data using a 60-day running mean has implied the oscillation has been trending to more of a positive phase since the 1970s,[citation needed] though it has trended to a more neutral state in the last decade. The oscillation still fluctuates stochastically between negative and positive values on daily, monthly, seasonal and annual time scales, although meteorologists have attained high levels of predictive accuracy for shorter term forecasts. The correlation between actual observations and the 7-day mean Global Forecast System ensemble AO forecasts is approximately 0.9.
This zonally symmetric seesaw between sea level pressures in polar and temperate latitudes was first identified by Edward Lorenz and named in 1998 by David W.J. Thompson and John Michael Wallace.
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