scholarly journals The Interaction of the Madden–Julian Oscillation and the Arctic Oscillation

2005 ◽  
Vol 18 (1) ◽  
pp. 143-159 ◽  
Author(s):  
Shuntai Zhou ◽  
Alvin J. Miller
Keyword(s):  
Large Scale ◽  
Arctic Oscillation ◽  
Winter Season ◽  
The Arctic ◽  
Height Anomaly ◽  
Madden Julian Oscillation ◽  
Regional Effect ◽  
The Pacific ◽  
Action Center ◽  
The Arctic Oscillation

Abstract Tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the Arctic Oscillation (AO) and the Madden–Julian oscillation (MJO). To simplify the discussion, a high (low) MJO phase is defined as strong (suppressed) convective activity over the Indian Ocean. In the Northern Hemisphere (NH) winter season, a high (low) AO phase is found more likely coupled with a high (low) MJO phase. Based on the regressed patterns and composites of various dynamical fields and quantities, possible mechanisms linking the AO and the MJO are examined. The analysis indicates that the MJO influence on extratropical circulations seems more evident than the AO influence on tropical circulations. The MJO interacts with the AO through meridional dispersion of Rossby waves in the Pacific sector. The geopotential height anomaly center over the North Pacific associated with the MJO can either reinforce or offset the AO Pacific action center. As a result, the AO pattern can be greatly affected by the MJO. When the AO and the MJO are in the same (opposite) phase, the Pacific action center becomes much stronger (weaker) than the Atlantic action center. The eddy momentum transports associated with the MJO in the Pacific sector are closely related to the retraction and extension of tropical Pacific easterlies and the subtropical Asian–Pacific jet. Because of its large scale, this regional effect is also reflected in the zonal mean state of wave transport and wave forcing on zonal wind, which in turn affects the phase of the AO.

scholarly journals Large-scale temperature and salinity changes in the upper Canadian basin of the Arctic Ocean at a time of a drastic Arctic Oscillation inversion

2012 ◽  
Vol 9 (3) ◽  
pp. 2001-2038 ◽  
Author(s):  
P. Bourgain ◽  
J. C. Gascard ◽  
J. Shi ◽  
J. Zhao
Keyword(s):  
Arctic Ocean ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Atlantic Water ◽  
The Arctic ◽  
Near Surface ◽  
Beaufort Gyre ◽  
Pacific Waters ◽  
The Pacific ◽  
Canadian Basin

Abstract. Between 2008 and 2010, the Arctic Oscillation index over Arctic regions shifted from positive values corresponding to more cyclonic conditions prevailing during IPY period (2007–2008) to extremely negative values corresponding to strong anticyclonic conditions in 2010. In this context, we investigated the recent large scale evolution of the upper Western Arctic Ocean based on temperature and salinity summertime observations collected during icebreaker campaigns and from Ice-Tethered Platforms (ITP) drifting across the region in 2008 and 2010. Particularly, we focused on (1) the freshwater content which was extensively studied during previous years, (2) the Near Surface Temperature Maximum due to incoming solar radiation and (3) the water masses advected from the Pacific and Atlantic Oceans into the deep Arctic Ocean. The observations revealed a freshwater content change in the Canadian basin during this time period. South of 80° N, the freshwater content increased, while north of 80° N, less freshening occurred in 2010 compared to 2008. This was more likely due to the strong anticyclonicity characteristic of a low AO index mode that enhanced both a wind-generated Ekman pumping in the Beaufort Gyre and a diversion of the Siberian rivers runoff toward the Eurasian basin at the same time. The Near Surface Temperature Maximum due to incoming solar radiation was almost 1 °C colder in the Southern Canada basin (south of 75° N) in 2010 compared to 2008 which contrasted with the positive trend observed during previous years. This was more likely due to higher summer sea ice concentration in 2010 compared to 2008 in that region, and surface albedo feedback reflecting more sun radiation back in space. The Pacific waters were also subjected to strong spatial and temporal variability between 2008 and 2010. In the Canada basin, both Summer and Winter Pacific waters influence increased between 75° N and 80° N. This was more likely due to a strong recirculation within the Beaufort Gyre. In contrast, south of 75° N, the PaW influence decreased indicative of the fact that they were not responsible for the freshening already mentioned, due to other sources. In addition, in the vicinity of the Chukchi Sea, both Summer and Winter Pacific waters were significantly warmer in 2010 than in 2008 as a consequence of a general warming trend of the Pacific waters entering in the deep Arctic Ocean since 2008. Finally, the warm Atlantic water remained relatively stable between 2008 and 2010 in the Canadian basin despite strong atmospheric shift, probably because of large time lag response. Atlantic water variability resulting from the presence of a warm "pulse-like" event in this region since 2005 was still noticeable even if a cooling effect was observed at a rate of 0.015 °C yr−1 between 2008 and 2010 in that region.

scholarly journals Influence of the Arctic Oscillation on the vertical distribution of clouds as observed by the A-Train constellation of satellites

2012 ◽  
Vol 12 (21) ◽  
pp. 10535-10544 ◽  
Author(s):  
A. Devasthale ◽  
M. Tjernström ◽  
M. Caian ◽  
M. A. Thomas ◽  
B. H. Kahn ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Dominant Mode ◽  
The Arctic ◽  
Dipole Structure ◽  
The Arctic Oscillation

Abstract. The main purpose of this study is to investigate the influence of the Arctic Oscillation (AO), the dominant mode of natural variability over the northerly high latitudes, on the spatial (horizontal and vertical) distribution of clouds in the Arctic. To that end, we use a suite of sensors onboard NASA's A-Train satellites that provide accurate observations of the distribution of clouds along with information on atmospheric thermodynamics. Data from three independent sensors are used (AQUA-AIRS, CALIOP-CALIPSO and CPR-CloudSat) covering two time periods (winter half years, November through March, of 2002–2011 and 2006–2011, respectively) along with data from the ERA-Interim reanalysis. We show that the zonal vertical distribution of cloud fraction anomalies averaged over 67–82° N to a first approximation follows a dipole structure (referred to as "Greenland cloud dipole anomaly", GCDA), such that during the positive phase of the AO, positive and negative cloud anomalies are observed eastwards and westward of Greenland respectively, while the opposite is true for the negative phase of AO. By investigating the concurrent meteorological conditions (temperature, humidity and winds), we show that differences in the meridional energy and moisture transport during the positive and negative phases of the AO and the associated thermodynamics are responsible for the conditions that are conducive for the formation of this dipole structure. All three satellite sensors broadly observe this large-scale GCDA despite differences in their sensitivities, spatio-temporal and vertical resolutions, and the available lengths of data records, indicating the robustness of the results. The present study also provides a compelling case to carry out process-based evaluation of global and regional climate models.

scholarly journals Large-scale temperature and salinity changes in the upper Canadian Basin of the Arctic Ocean at a time of a drastic Arctic Oscillation inversion

Ocean Science ◽  
2013 ◽  
Vol 9 (2) ◽  
pp. 447-460 ◽  
Author(s):  
P. Bourgain ◽  
J. C. Gascard ◽  
J. Shi ◽  
J. Zhao
Keyword(s):  
Solar Radiation ◽  
Arctic Ocean ◽  
Large Scale ◽  
Arctic Oscillation ◽  
The Arctic ◽  
Near Surface ◽  
Beaufort Gyre ◽  
The Pacific ◽  
The Arctic Ocean ◽  
Canadian Basin

Abstract. Between 2008 and 2010, the Arctic Oscillation index over Arctic regions shifted from positive values corresponding to more cyclonic conditions prevailing during the 4th International Polar Year (IPY) period (2007–2008) to extremely negative values corresponding to strong anticyclonic conditions in 2010. In this context, we investigated the recent large-scale evolution of the upper western Arctic Ocean, based on temperature and salinity summertime observations collected during icebreaker campaigns and from ice-tethered profilers (ITPs) drifting across the region in 2008 and 2010. Particularly, we focused on (1) the freshwater content which was extensively studied during previous years, (2) the near-surface temperature maximum due to incoming solar radiation, and (3) the water masses advected from the Pacific Ocean into the Arctic Ocean. The observations revealed a freshwater content change in the Canadian Basin during this time period. South of 80° N, the freshwater content increased, while north of 80° N, less freshening occurred in 2010 compared to 2008. This was more likely due to the strong anticyclonicity characteristic of a low AO index mode that enhanced both a wind-generated Ekman pumping in the Beaufort Gyre and a possible diversion of the Siberian River runoff toward the Eurasian Basin at the same time. The near-surface temperature maximum due to incoming solar radiation was almost 1 °C colder in the southern Canada Basin (south of 75° N) in 2010 compared to 2008, which contrasted with the positive trend observed during previous years. This was more likely due to higher summer sea ice concentration in 2010 compared to 2008 in that region, and surface albedo feedback reflecting more sun radiation back in space. The Pacific water (PaW) was also subjected to strong spatial and temporal variability between 2008 and 2010. In the Canada Basin, both summer and winter PaW signatures were stronger between 75° N and 80° N. This was more likely due to a strong recirculation within the Beaufort Gyre. In contrast, south of 75° N, the cooling and warming of the summer and winter PaW, respectively, suggest that either the PaW was less present in 2010 than in 2008 in this region, and/or the PaW was older in 2010 than in 2008. In addition, in the vicinity of the Chukchi Sea, both summer and winter PaW were significantly warmer in 2010 than in 2008, as a consequence of a general warming trend of the PaW entering in the deep Arctic Ocean as of 2008.

scholarly journals Reconsideration of the True versus Apparent Arctic Oscillation

2008 ◽  
Vol 21 (10) ◽  
pp. 2047-2062 ◽  
Author(s):  
Hisanori Itoh
Keyword(s):  
Spatial Correlation ◽  
Arctic Oscillation ◽  
Physical Reality ◽  
The Arctic ◽  
Sea Level Pressure ◽  
The North ◽  
The Pacific ◽  
The Arctic Oscillation ◽  
The North Atlantic Oscillation ◽  
Almost All

Abstract The physical reality of the Arctic Oscillation (AO; or northern annular mode) is considered. The data used are mainly the monthly mean sea level pressure (SLP). A schematic figure is first presented to illustrate the relationship between the North Atlantic Oscillation (NAO)–Pacific–North American Oscillation (PNA) system and the AO–negative correlation mode between the Atlantic and the Pacific (AO–NCM) system. Although the NAO–PNA (apparent AO–NCM) and true AO–NCM systems give rise to the same EOFs, the probability density functions for the time coefficients of the two leading modes are different. Therefore, the discrimination of the two systems is possible. Several pieces of evidence indicate that, in the real world, the NAO–PNA and the AO–NCM are located on almost the same plane in phase space. This means that the NAO–PNA and AO–NCM systems have the same variations on the plane in common, implying that when the NAO–PNA system is real, the AO–NCM is unlikely to be real. Simple independent component analysis is carried out to distinguish between the true and apparent AO–NCM systems, indicating that the NAO and PNA are independent oscillations, that is, true ones. The analysis is extended to the winter mean SLP field, for which the EOF shows the NAO–PNA but not the AO–NCM. This may be due to the fact that the winter mean NAO and PNA patterns have little spatial correlation. Calculations using randomly selected samples also indicate that when the NAO and PNA patterns have little spatial correlation, the AO never appears as EOF1. All the preceding results show that almost all characteristics of the AO–NCM can be explained from those of the NAO–PNA. Hence it is concluded that the AO, which is extracted by EOF analysis from the temporarily independent but spatially overlapping variations of the NAO and PNA, is almost apparent.

The Impact of the Stratospheric Polar Vortex Shift on the Arctic Oscillation

2021 ◽  
Vol 34 (10) ◽  
pp. 4129-4143
Author(s):  
Yongjia Lu ◽  
Wenshou Tian ◽  
Jiankai Zhang ◽  
Jinlong Huang ◽  
Ruhua Zhang ◽  
...  
Keyword(s):  
Arctic Oscillation ◽  
Polar Vortex ◽  
The Arctic ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Eurasian Continent ◽  
Time Period ◽  
Action Center ◽  
The Arctic Oscillation ◽  
The Impact

AbstractUsing the ERA-Interim reanalysis dataset for the time period 1979–2016, we analyzed the influence of the stratospheric polar vortex shift on the Arctic Oscillation (AO) in winter (December–March). The results show that a shift in the stratospheric polar vortex toward the Eurasian continent is favorable for the occurrence of the negative phase of the AO. The duration of the AO events accompanied by the stratospheric polar vortex shift toward the Eurasian continent (AO-shift events) is longer than that of the remaining negative AO events (AO-noshift events), and the intensity of AO-shift events is greater than that of AO-noshift events from day 4 to day 15 of the life cycle of the events. The enhancement in the AO intensity during AO-shift events is likely due to downward extension of the stratospheric northern annular mode (NAM) signals and more poleward-propagating planetary waves in the troposphere and lower stratosphere and their convergence in the mid-high latitudes. Furthermore, the polar vortex shift can lead to changes in the intensity of the three action centers in the AO spatial pattern at 500 hPa. In general, during AO-shift events, the three action centers are stronger than those during AO-noshift events. There is an overall westward shift of the Arctic action center during AO-shift events, which may be closely related to the changes of Greenland blocking frequency.

scholarly journals Influence of the Madden–Julian Oscillation on the Arctic Oscillation Prediction in S2S Operational Models

2021 ◽  
Vol 9 ◽  
Author(s):  
Yang Zhou ◽  
Yang Wang
Keyword(s):  
Arctic Oscillation ◽  
Time Lag ◽  
Prediction Skill ◽  
The Arctic ◽  
Negative Phase ◽  
Initial Time ◽  
Madden Julian Oscillation ◽  
Global Circulation Models ◽  
The Arctic Oscillation ◽  
The Relationship

The connections between the Madden–Julian Oscillation (MJO) and the Arctic Oscillation (AO) are examined in both observations and model forecasts. In the observations, the time-lag composites are carried out for AO indices and anomalies of 1,000-hPa geopotential height after an active or inactive initial MJO. The results show that when the AO is in its positive (negative) phase at the initial time, the AO activity is generally enhanced (weakened) after an active MJO. Reforecast data of the 11 operational global circulation models from the Sub-seasonal to Seasonal (S2S) Prediction Project are further used to examine the relationship between MJO activity and AO prediction. When the AO is in its positive phase on the initial day of the S2S prediction, an initial active MJO can generally improve the AO prediction skill in most of the models. This is consistent with results found in the observations that a leading MJO can enhance the AO activity. However, when the AO is in its negative phase, the relationship between the MJO and AO prediction is not consistent among the 11 models. Only a few S2S models provide results that agree with the observations. Furthermore, the S2S prediction skill of the AO is examined in different MJO phases. There is a significantly positive relationship between the MJO-related AO activity and the AO prediction skill. When the AO activity is strong (weak) in an MJO phase, including the inactive MJO, the models tend to have a high (low) AO prediction skill. For example, no matter what phase the initial AO is in, the AO prediction skill is generally high in MJO phase 7, in which the AO activity is generally strong. Thus, the MJO is an important predictability source for the AO forecast in the S2S models.

scholarly journals The Climatology and Characteristics of Rossby Wave Packets Using a Feature-Based Tracking Technique

2014 ◽  
Vol 142 (10) ◽  
pp. 3528-3548 ◽  
Author(s):  
Matthew B. Souders ◽  
Brian A. Colle ◽  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Wave Packets ◽  
The Arctic ◽  
Average Intensity ◽  
Feature Based ◽  
The Arctic Oscillation

Abstract This paper describes an objective, track-based climatology of Rossby wave packets (RWPs). NCEP–NCAR reanalysis wind and geopotential height data at 300 hPa every 6 h were spectrally filtered using a Hilbert transform technique under the assumption that RWPs propagate along a waveguide defined by the 14-day running average of the 300-hPa wind. Track data and feature-based descriptive statistics, including area, average intensity, intensity volume (intensity multiplied by area), intensity-weighted centroid position, and velocity, were gathered to describe the interannual, annual, seasonal, and regime-based climatology of RWPs. RWPs have a more pronounced seasonal cycle in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). RWPs are nearly nonexistent in the summer months (June–August; JJA) in the NH, while there is nearly continuous RWP activity downstream of South Africa during austral summer (December–February; DJF). Interannual variability in RWP frequency and intensity in the Northern Hemisphere is found to be strongly connected with the large-scale flow regimes such as El Niño–Southern Oscillation and the Arctic Oscillation. Enhanced RWP activity is also found to coherently propagate from the Pacific into the Atlantic on average when the Arctic Oscillation switches from a positive to a negative phase. No significant long-term (~30 yr) trend in RWP frequency, activity, or amplitude is found.

scholarly journals Influence of the Arctic Oscillation on the vertical distribution of clouds as observed by the A-Train constellation of satellites

2012 ◽  
Vol 12 (4) ◽  
pp. 10305-10329 ◽  
Author(s):  
A. Devasthale ◽  
M. Tjernström ◽  
M. Caian ◽  
M. A. Thomas ◽  
B. H. Kahn ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Dominant Mode ◽  
The Arctic ◽  
Dipole Structure ◽  
The Arctic Oscillation

Abstract. The main purpose of this study is to investigate the influence of the Arctic Oscillation (AO), the dominant mode of natural variability over the northerly high latitudes, on the spatial (horizontal and vertical) distribution of clouds in the Arctic. To that end, we use a suite of sensors onboard NASA's A-Train satellites that provide accurate observations of the distribution of clouds along with information on atmospheric thermodynamics. Data from three independent sensors are used (AIRS-AQUA, CALIOP-CALIPSO and CPR-CloudSAT) covering two time periods (winter half years of 2002–2011 and 2006–2011, respectively) along with data from the ERA-Interim reanalysis. We show that the zonal vertical distribution of cloud fraction anomalies averaged over 67° N–82°; N to a first approximation follows a dipole structure (referred to as "Greenland cloud dipole anomaly", GCDA), such that during the positive phase of the AO, positive and negative cloud anomalies are observed eastwards and westward of Greenland, respectively, while the opposite is true for the negative phase of AO. By investigating the concurrent meteorological conditions (temperature, humidity and winds), we show that differences in the meridional energy and moisture transport during the positive and negative phases of the AO and the associated thermodynamics are responsible for the conditions that are conducive for the formation of this dipole structure. All three satellite sensors broadly observe this large-scale GCDA despite differences in their sensitivities, spatio-temporal and vertical resolutions, and the available lengths of data records, indicating the robustness of the results. The present study also provides a compelling case to carry out process-based evaluation of global and regional climate models.

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