Statistical relationship among Temperature, Arctic Oscillation and Atmospheric Circulation (original) (raw)
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Journal of Geophysical Research: Atmospheres, 2015
Observational analyses using the ERA interim reanalysis and merged Hadley/OI-SST data reveal that a reduced (increased) sea-ice area in November leads to more negative (positive) phases of the AO and NAO in early and late winter, respectively. We simulate the atmospheric response to observed sea-ice anomalies using a high-top atmospheric general circulation model (AGCM for Earth Simulator, AFES version 4.1). The results from the simulation reveal that the recent Arctic sea-ice reduction results in cold winters in mid-latitude continental regions, which are linked to an anomalous circulation pattern similar to the negative phase of AO/NAO with an increased frequency of large negative AO events by a factor of over two. Associated with this negative AO/NAO phase, cold air advection from the Arctic to the mid-latitudes increases. We found that the stationary Rossby wave response to the sea-ice reduction in the Barents Sea region induces this anomalous circulation. We also found a positive feedback mechanism resulting from the anomalous meridional circulation that cools the mid-latitudes and warms the Arctic, which adds an extra heating to the Arctic air column equivalent to about 60% of the direct surface heat release from the sea-ice reduction. The results from this high-top model experiment also suggested a critical role of the stratosphere in deepening the tropospheric annular mode and modulation of the NAO in mid to late winter through stratosphere-troposphere coupling. ]. Results from numerical simulations using atmosphere-ocean coupled models suggest that Arctic sea-ice variability and the modulation of the AO/NAM are linked .
Impact of Arctic Oscillation on the East Asian climate: A review
The Arctic Oscillation (AO), which depicts a most dominant large-scale seesaw between the mid-latitudes and Arctic atmospheric mass, influences climate over Eurasia, North America, eastern Canada, North Africa, and the Middle East, especially during boreal winter. This review, with a special focus on the East Asian region, summarizes the climatic impact of AO. It begins with a description of the spatial structure of AO and the related climatic anomalies. The relationship of winter AO with the simultaneous East Asian winter climate (e.g. the East Asian winter monsoon (EAWM), cold surges/cold waves, and precipitation) and its instability are then followed. It is generally accepted that, through impacting the Siberian high, westerly wind, blocking frequency, Rossby wave activities etc., a positive phase of winter AO is associated with a weaker-than-normal EAWM, warmer conditions in East Asia, less frequency of cold surges/cold waves, increasing (decreasing) of winter precipitation in south (north) parts of East Asia; and vice versa. Notably, the pathways that the winter AO exerts impact are different. Besides, the AO-EAWM and the AO-cold surges/cold wave linkages have spatial and temporal variations. Subsequently , an overview of the inter-seasonal linkages between the East Asian summer monsoon with the preceding spring/winter AO is presented. There is a generally accepted knowledge that a positive spring AO is followed by significant positive summer precipitation anomalies in southern China and western Pacific as well as negative ones in the lower valley of Yangtze River and southern Japan. Finally, this review synthesizes the impact of win-ter/spring AO on the East Asian spring climate (e.g. dust storm, temperature, and precipitation) and discusses the potential predictive value of AO. The projection of AO and its impact on the East Asian climate in future has been barely explored. We conclude that, along with the long-term observation data, the linkage between AO and the East Asian climate on the sub-seasonal and decadal time scales, how tropical and extratropical forcing modulates the linkage and how the linkage evolves under future warming conditions should be more investigated. Notably, the change of AO during 1990–2013 winters could explain the Eurasian cooling but failed to explain the Arctic warming. In the future, the effect of Ural blocking on Arctic and Eurasian climate and their connection might be a hot topic.
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.
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.
Nonlinear impact of the Arctic Oscillation on extratropical surface air temperature
2012
1] The Arctic Oscillation (AO) is the leading climate mode of sea level pressure (SLP) anomalies during cold season in the Northern Hemisphere. To a large extent, the atmospheric climate anomalies associated with positive and negative phases of the AO are opposite to each other, indicating linear impact. However, there is also significant nonlinear relationship between the AO and other winter climate variability. We investigate nonlinear impacts of the AO on surface air temperature (SAT) using reanalysis data and a multimillennial long climate simulation. It is found that SAT response to the AO, in terms of both spatial pattern and magnitude, is almost linear when the amplitude of the AO is moderate. However, the response becomes quite nonlinear as the amplitude of the AO becomes stronger. First, the pattern shift in SAT depends on AO phase and magnitude, and second, the SAT magnitude depends on AO phase. In particular, these nonlinearities are distinct over the North America and Eurasian Continent. Based on the analyses of model output, we suggest that the nonlinear zonal advection term is one of the critical components in generating nonlinear SAT response, particularly over the North America.
Tropical links of the Arctic Oscillation
Geophysical Research Letters, 2002
A primitive equation dry atmospheric model is used to investigate the response of the Arctic Oscillation (AO) to diabatic forcing. Integrations are made for 51 winter seasons (DJF) from 1948/49 to 1998/99. For each winter the model uses a time-averaged forcing that is calculated empirically from the NCEP/NCAR reanalyses. The ensemble mean of the simulations reproduces much of the observed AO interannual variability. Two additional sets of experiments are conducted. In one case the interannually varying forcing is prescribed only in the tropics, while in another it is prescribed only in the extratropics. These simulations indicate that a significant part of the interannual variability of the wintertime AO, as well as its trend, is linked to forcing from the tropics, and that extratropical forcing has no role to play, independent of the tropical forcing, in reconstructing the observed AO variability.
International Journal of Climatology, 2017
The increased extreme warm and decreased extreme cold temperature events across the Arctic strongly influence the natural environment as well as the societal activities. This study investigates temporal and spatial variability of wintertime extreme high and low temperature events defined by the 95 and 5% percentiles across the Arctic and subarctic regions, respectively (north of 60 ∘ N) using data from 238 stations in the Global Summary of the Day for the period 1979-2016. Empirical orthogonal function analyses indicate that the first modes (which account for 30-35% of the total variance) are out-of-phase between northern Europe, western and central Russia, and northeastern North America, and that this appears to be related to the Arctic Oscillation (AO) and the Northern Atlantic Oscillation. The second modes explain about 8% of the total variance. During the positive phase of the first and second modes the anomalous northeasterly and northerly winds decrease Arctic extreme high and increase extreme low temperature occurrences; while the anomalous southerly and southwesterly winds have the opposite effect. Symmetric and asymmetric effects of the AO index on extreme temperature events refer to the difference and sum between the composite of its positive and negative phases. The symmetric components of the spatial patterns are similar to those of the first modes. The asymmetric components occur mainly over western and central Russia for extreme high and low temperatures, respectively. In addition the impacts of six other large-scale climate modes are also explored. KEY WORDS Arctic extreme temperature events; Arctic Oscillation; Pacific North America pattern; asymmetric impact
The influence of tropical Pacific forcing on the Arctic Oscillation
Climate Dynamics, 2009
The potential role of tropical Pacific forcing in driving the seasonal variability of the Arctic Oscillation (AO) is explored using both observational data and a simple general circulation model (SGCM). A lead-lag regression technique is applied to the monthly averaged sea surface temperature (SST) and the AO index. The AO maximum is found to be related to a negative SST anomaly over the tropical Pacific three months earlier. An singular value decomposition (SVD) analysis is performed on the tropical Pacific SST and the sea level pressure (SLP) over the Northern Hemisphere. The AO-like and its associated SST appear in the second pair of SVD modes. Ensemble integrations are carried out with the SGCM to test the atmospheric response to the tropical Pacific forcing. The atmospheric response to the linear fit of the model's empirical forcing associated with the SST variability in the second SVD modes strongly projects onto the AO. Idealized thermal forcings are then designed based on the regression of the seasonally averaged tropical Pacific precipitation against the AO index. Results indicate that forcing anomalies over the western tropical Pacific are more effective in generating an AO-like response while those over the eastern tropical Pacific tend to produce a Pacific-North American (PNA)-like response. The physical mechanisms responsible for the energy transport from the tropical Pacific to the extratropical North Atlantic are investigated using wave activity flux and vorticity forcing formalisms. The energy from the western tropical Pacific forcing tends to propagate zonally to the North Atlantic because of the jet stream waveguide effect while the transport of the energy from the eastern tropical Pacific forcing mostly concentrates over the PNA area. The linearized SGCM results show that nonlinear processes are involved in the generation of the forced AO-like.