Response of the Summer and Autumn Circulation to the Wintertime Arctic Oscillation (original) (raw)
Related papers
On the temporal character and regionality of the Arctic Oscillation
Geophysical Research Letters, 2001
Decadal differences between the 1990s and 1980s in winter (JFM) sea-level pressure and 300 mb zonal winds have an Arctic-centered character with nearly equal contributions from the Atlantic and Pacific sectors. In contrast, the differences between positive and negative Arctic Oscillation (AO) composites defined from monthly values of Principal Components from the same period have similar magnitudes in the Pacific and Arctic, but have an additional large North Atlantic Oscillation (NAO) signature in the Atlantic sector. Thus Arctic changes on decadal scales are more symmetric with the pole than suggested by the standard AO index definition. Change point analysis of the AO shows that a shift in value near 1989 is an alternate hypothesis to a linear trend. Analysis of zonal and meridional winds by longitudinal sectors shows the importance of the standing wave pattern in interpreting the AO, which supplements the view of the AO as a simple zonal-average (annular) mode.
Linking Arctic sea‐ice and atmospheric circulation anomalies on interannual and decadal timescales
Atmosphere-ocean, 1997
The relationship between Arctic sea‐ice concentration anomalies, particularly those associated with the “Great Salinity Anomaly” of 1968–1982, and atmospheric circulation anomalies north of 45°N is investigated. Empirical orthogonal function (EOF) analyses are performed on winter Arctic ice concentration from 1954 to 1990, sea level pressure and 500‐hPa heights from 1947 to 1994, and 850‐hPa temperatures from 1963 to 1994. Variability on both interannual and decadal timescales is apparent in the time series of the leading winter EOFs of all variables. The first EOF of winter sea‐ice concentration was found to characterize the patterns of ice variability associated with the Great Salinity Anomaly in the northern North Atlantic from 1968–82. Spatial maps of temporal correlation coefficients between the time series of the first EOF of winter sea‐ice concentration and the winter atmospheric anomaly fields are calculated at lags of 0 and ±7 year. Maximum correlations were found to exist when the time‐series of this ice EOF 1 leads the atmospheric anomaly fields by one year. A particularly interesting result is the connection between the presence of ice anomalies in the Greenland and Barents Seas and subsequent pressure anomalies of the same sign over the Irminger Basin and the Canadian Arctic. The main emphasis of the paper is to identify connections between Arctic sea‐ice and atmospheric circulation anomalies at interannual time‐scales.Cette étude vise à déterminer s'il existe une relation entre les anomalies de la concentration de glace marine arctique, en particulier celles reliées à la grande anomalie de salinité de la période 1968–1982, et les anomalies de la circulation au nord de 45°N. Des analyses en terme de Fonctions Empiriques Orthogonales (FEO) sont effectuées sur la concentration hivernale de glace arctique entre 1954 et 1990, la pression au niveau de la mer et les hauteurs géopotentielles au niveau 500 hPa de 1947 à 1994, et les températures au niveau 850 hPa de 1963 à 1994. D'une année à l'autre et à l'échelle décennale, la variabilité est apparente dans la série chronologique de la principale analyse FEO hivernale de toutes les variables. La première analyse FEO de la concentration hivernale de glace marine représente les caractéristiques de la variabilité de la glace, associées à la grande anomalie de salinité dans le nord de l'Atlantique Nord entre 1968 et 1982. Des cartes de coefficient de corrélations temporelles, entre la série chronologique de la première analyse FEO de la concentration hivernale de glace marine et les champs des anomalies atmosphériques hivernales, sont établies en déphasage de 0 et ± 1 année. Des corrélations maximales sont observées lorsque la série chronologique de cette analyse FEO 1 de glace mène les champs des anomalies atmosphériques par une année. Un résultat particulièrement intéressant est la relation entre les anomalies de glace dans les mers du Groenland et de Barents, et les anomalies subséquentes de pression du même signe sur le bassin Irminger et l'Arctique canadien. Cet article met l'accent sur l'identification des relations, d'une année à l'autre, entre la glace marine arctique et les anomalies de la circulation atmosphérique.
Arctic oscillation and Arctic sea-ice oscillation
Geophysical Research Letters, 2000
The variability of the sea-ice cover in the Arctic and subpolar regions associated with the Arctic Oscillation (AO) was investigated using historical data from 1901 to 1997. Unrotating principal component analyses (or empirical orthogonal functions, EOFs) were applied to demeaned, normalized sea-level pressure (SLP), surface air temperature (SAT), and sea-ice area (SIA) for the periods 1901-97 and 1953-97. The leading SLP EOF mode is the AO. The leading SIA EOF mode is named the Arctic Sea-Ice Oscillation (ASIO), which accounts for 41% of the total variance for the period of 1901-1995. This dominant ASIO is AO-related; its spatial and temporal patterns are consistent with the leading modes of SLP and SAT, and with the total arctic sea-ice anomalies. The second SIA mode is North Atlantic Oscillation (NAO)-related because sea-ice anomalies in the Labrador Sea region and the Greenland Sea region are out of phase. During the last three decades, the arctic sea ice has significantly decreased, which may be the decreasing phase of long term variations.
The Arctic oscillation signature in the wintertime geopotential height and temperature fields
Geophysical Research Letters, 1998
The leading empirical orthogonal function of the wintertime sea-level pressure field is more strongly coupled to surface air temperature fluctuations over the Eurasian continent than the North Atlantic Oscillation (NAO). It resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance. Coupled to strong fluctuations at the 50-hPa level on the intraseasonal, interannual, and interdecadal time scales, this "Arctic Oscillation" (AO)can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft. It is proposed that the zonally asymmetric surface air temperature and mid-tropospheric circulation anomalies observed in association with the AO may be secondary baroclinic features induced by the land-sea contrasts. The same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature, sea-level pressure, and 50-hPa height over the past 30 years: parts of Eurasia have warmed by as much as several K, sea-level pressure over parts of the Arctic has fallen by 4 hPa, and the core of the lower stratospheric polar vortex has cooled by several K. These trends can be interpreted as the development of a systematic bias in one of the atmosphere's dominant, naturally occurring modes of variability.
Arctic sea-ice oscillation: regional and seasonal perspectives
Annals of Glaciology, 2001
Variability of the sea-ice cover (extent) in the Northern Hemisphere (Arctic and subpolar regions) associated with the Arctic Oscillation (AO) is investigated using historical data from 1901 to 1997. A principal-component analysis (empirical orthogonal functions (EOFs)) was applied to sea-ice area (SIA) anomalies for the period 1953−95. The leading EOF mode for the SI A anomaly shows an in-phase fluctuation in response to the AO and is called the Arctic sea-ice oscillation (ASIO). Arctic sea ice experiences seasonal variations that differ in timing and magnitude. Four types of seasonal variation are identified in the Arctic sea ice, and are superimposed on long-term interannual to decadal variability. Consistent with the total Arctic SIA anomaly eight regional SIA anomalies have shown significant in-phase decrease (downward trend) since 1970, possibly part of a very long-term (century) cycle. Thus, it is recommended that SIA anomalies in the sensitive seasons be used to better captu...
Geophysical Research Letters, 2005
1] The interannual variability of winter surface air temperature (SAT) in the Northern Hemisphere (NH) associated with the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) is studied. The AO and the NAO show different impacts on winter NH SAT variations. The AO affects the SAT over the Euro-Asian and African continents, whereas the NAO is more regional with the major effect on the SAT in the western North Africa. This discrepancy can be reflected in other atmospheric variables such as sea level pressure and geopotential height fields as well. The analyses in this paper also suggest that the AOrelated signal can penetrate deeply into the stratosphere while the NAO one is largely a tropospheric phenomenon.
Summer minimum Arctic sea ice extent and the associated summer atmospheric circulation
Geophysical Research Letters, 2007
1] Interrelationships between year-to-year variations in September Arctic sea ice extent and summer sea level pressure and surface air temperature at high northern latitudes are examined making use of microwave satellite imagery and atmospheric data for the period 1979 -2006. Linear trends and year-to-year variability about the linear trend lines are considered separately: the latter gives a clearer indication of the physical linkages between fields. Years with low September sea ice extent tend to be characterized by anticyclonic circulation anomalies over the Arctic, with easterly wind anomalies over the marginal seas where the year-to-year variability of sea ice concentration is largest. It is hypothesized that the summer circulation anomalies cause sea ice extent principally by way of the Ekman drift in the marginal seas. The associated surface air temperature anomalies also tend to be largest over the marginal seas, with positive anomalies over the regions of reduced sea ice. Citation: Ogi, M., and J. M. Wallace , Summer minimum Arctic sea ice extent and the associated summer atmospheric circulation, Geophys. Res. Lett., 34, L12705,
Summers with low Arctic sea ice linked to persistence of spring atmospheric circulation patterns
Climate Dynamics
The declining trend of Arctic September sea ice constitutes a significant change in the Arctic climate system. Large yearto-year variations are superimposed on this sea-ice trend, with the largest variability observed in the eastern Arctic Ocean. Knowledge of the processes important for this variability may lead to an improved understanding of seasonal and long-term changes. Previous studies suggest that transport of heat and moisture into the Arctic during spring enhances downward surface longwave radiation, thereby controlling the annual melt onset, setting the stage for the September ice minimum. In agreement with these studies, we find that years with a low September sea-ice concentration (SIC) are characterized by more persistent periods in spring with enhanced energy flux to the surface in forms of net longwave radiation plus turbulent fluxes, compared to years with a high SIC. Two main atmospheric circulation patterns related to these episodes are identified: one resembles the so-called Arctic dipole anomaly that promotes transport of heat and moisture from the North Pacific, whereas the other is characterized by negative geopotential height anomalies over the Arctic, favoring cyclonic flow from Siberia and the Kara Sea into the eastern Arctic Ocean. However, differences between years with low and high September SIC appear not to be due to different spring circulation patterns; instead it is the persistence and intensity of processes associated with these patterns that distinguish the two groups of anomalous years: Years with low September SIC feature episodes that are consistently stronger and more persistent than years with high SIC.
Monthly Weather Review, 2013
December 2010 was unusual both in the strength of the negative North Atlantic Oscillation (NAO) intense atmospheric blocking and the associated record-breaking low temperatures over much of northern Europe. The negative North Atlantic Oscillation for November-January was predicted in October by 8 out of 11 World Meteorological Organization Global Producing Centres (WMO GPCs) of long-range forecasts. This paper examines whether the unusual strength of the NAO and temperature anomaly signals in early winter 2010 are attributable to slowly varying boundary conditions [El Niño-Southern Oscillation state, North Atlantic sea surface temperature (SST) tripole, Arctic sea ice extent, autumn Eurasian snow cover], and whether these were modeled in the Met Office Global Seasonal Forecasting System version 4 (GloSea4). Results from the real-time forecasts showed that a very robust signal was evident in both the surface pressure fields and temperature fields by the beginning of November. The historical reforecast set (hindcasts), used to calibrate and bias correct the real-time forecast, showed that the seasonal forecast model reproduces at least some of the observed physical mechanisms that drive the NAO. A series of ensembles of atmosphere-only experiments was constructed, using forecast SSTs and ice concentrations from November 2010. Each potential mechanism in turn was systematically isolated and removed, leading to the conclusion that the main mechanism responsible for the successful forecast of December 2010 was anomalous ocean heat content and associated SST anomalies in the North Atlantic. FIG. 1. December surface pressure and temperature anomalies. Observed (a) pressure anomalies (HadSLP2r) and (b) temperature anomalies (HadCRUT3). The region outlined in (b) corresponds to northern Europe as referred to in the text. Contour intervals for HadSLP2r are 2 hPa, with a maximum positive anomaly south of Greenland of 18 hPa and a minimum negative anomaly west of Gibraltar of 212 hPa. Forecast anomalies for forecasts initialized on (for the details of the lagged ensemble approach. Blank regions in (b) are due to missing data: HadCRUT3 does not interpolate. Observed anomalies are relative to the period 1981-2010. Forecast anomalies are relative to the operational hindcast periods used [1989-2002 prior to the operational upgrade in (c)