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.

Internal variability of the Arctic Oscillation and its projections

2020 ◽  
Author(s):  
Annalisa Cherchi ◽  
Paolo Oliveri ◽  
Aarnout van Delden
Keyword(s):  
Northern Hemisphere ◽  
Arctic Oscillation ◽  
Internal Variability ◽  
The Arctic ◽  
Positive Phase ◽  
Cmip5 Models ◽  
Modes Of Variability ◽  
The Future ◽  
The Arctic Oscillation

<p>The Arctic Oscillation (AO) is one of the main modes of variability of the Northern Hemisphere winter, also referred as Northern Annular Mode (NAM). The positive phase of the AO is characterized by warming/cooling over Northern Eurasia and the United States and cooling over Canada, especially over eastern Canada. Its positive phase is also characterized by very dry conditions over the Mediterranean and wet conditions over Northern Europe. A positive trend of the AO is observed for the period 1951-2011 and it is captured in CMIP5 models only when GHG-only forcing are included. In CMIP5 models the change expected is mostly mitigated by the effects of the aerosols. When considering AR5 scenarios, the AO is projected to become more positive in the future, though with a large spread among the models.</p><p>Overall the spread in the representation of the AO variability and trend is large also in experiments with present-day conditions, likely associated with the large internal variability. Unique tools to identify and measure the role of the internal variability in the model representation of the large-scale modes of variability are large ensembles where multiple members are built with different initial conditions.</p><p>Here we use the NCAR Community Model Large Ensemble (CESM-LE) composing the historical period (1920-2005) to the future (2006-2100) in a RCP8.5 scenario to measure the role of the internal variability in shaping AO variability and changes. Potential predictability of the AO index is quantified in the historical and future periods, evidencing how the members spread remain large without specific trends in these characteristics. Preliminary results indicate that the internal variability has large influence on the AO changes and related implications for the Northern Hemisphere climate.</p>

scholarly journals Influence of the Arctic Oscillation on the Vertical Distribution of Wintertime Ozone in the Stratosphere and Upper Troposphere over the Northern Hemisphere

2017 ◽  
Vol 30 (8) ◽  
pp. 2905-2919 ◽  
Author(s):  
Jiankai Zhang ◽  
Fei Xie ◽  
Wenshou Tian ◽  
Yuanyuan Han ◽  
Kequan Zhang ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Northern Hemisphere ◽  
Arctic Oscillation ◽  
Stratospheric Ozone ◽  
The Arctic ◽  
Upper Troposphere ◽  
Eddy Transport ◽  
The Arctic Oscillation ◽  
The Vertical Distribution ◽  
Middle Stratosphere

The influence of the Arctic Oscillation (AO) on the vertical distribution of stratospheric ozone in the Northern Hemisphere in winter is analyzed using observations and an offline chemical transport model. Positive ozone anomalies are found at low latitudes (0°–30°N) and there are three negative anomaly centers in the northern mid- and high latitudes during positive AO phases. The negative anomalies are located in the Arctic middle stratosphere (~30 hPa; 70°–90°N), Arctic upper troposphere–lower stratosphere (UTLS; 150–300 hPa, 70°–90°N), and midlatitude UTLS (70–300 hPa, 30°–60°N). Further analysis shows that anomalous dynamical transport related to AO variability primarily controls these ozone changes. During positive AO events, positive ozone anomalies between 0° and 30°N at 50–150 hPa are related to the weakened meridional transport of the Brewer–Dobson circulation (BDC) and enhanced eddy transport. The negative ozone anomalies in the Arctic middle stratosphere are also caused by the weakened BDC, while the negative ozone anomalies in the Arctic UTLS are caused by the increased tropopause height, weakened BDC vertical transport, weaker exchange between the midlatitudes and the Arctic, and enhanced ozone depletion via heterogeneous chemistry. The negative ozone anomalies in the midlatitude UTLS are mainly due to enhanced eddy transport from the midlatitudes to the latitudes equatorward of 30°N, while the transport of ozone-poor air from the Arctic to the midlatitudes makes a minor contribution. Interpreting AO-related variability of stratospheric ozone, especially in the UTLS, would be helpful for the prediction of tropospheric ozone variability caused by the AO.

High vs. low latitude influence on seasonal stratospheric pathways in the atmospheric model ICON

2021 ◽  
Author(s):  
Raphael Köhler ◽  
Dörthe Handorf ◽  
Ralf Jaiser ◽  
Klaus Dethloff
Keyword(s):  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Atmospheric Model ◽  
The Arctic ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
Enso Events ◽  
Hemisphere Winter

<p>Stratospheric pathways play an important role in connecting distant anomaly patterns to each other on seasonal timescales. As long-lived stratospheric extreme events can influence the large-scale tropospheric circulation on timescales of multiple weeks, stratospheric pathways have been identified as one of the main potential sources for subseasonal to seasonal predictability in mid-latitudes. These pathways have been shown to connect Arctic anomalies to lower latitudes and vice versa. However, there is an ongoing discussion on how strong these stratospheric pathways are and how they exactly work.</p><p> </p><p>In this context, we investigate two strongly discussed stratospheric pathways by analysing a suite of seasonal experiments with the atmospheric model ICON: On the one hand, the effect of El Niño-Southern Oscillation (ENSO) on the stratospheric polar vortex, and thus the circulation in mid and high latitudes in winter. And on the other hand, the effect of a rapidly changing Arctic on lower latitudes via the stratosphere. The former effect is simulated realistically by ICON, and the results from the ensemble simulations suggest that ENSO has an effect on the large-scale Northern Hemisphere winter circulation. The ICON experiments and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. Unlike the effect of ENSO, ICON simulations and the reanalysis do not agree on the stratospheric pathway for Arctic-midlatitude linkages. Whereas the reanalysis exhibits a weakening of the stratospheric vortex in midwinter and a connected tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, this is not the case in the ICON simulations. Implications and potential reasons for this discrepancy are further analysed and discussed in this work.  </p>

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 Non-Stationary Effects of the Arctic Oscillation and El Niño–Southern Oscillation on January Temperatures in Korea

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 538
Author(s):  
Jae-Seung Yoon ◽  
Il-Ung Chung ◽  
Ho-Jeong Shin ◽  
Kunmnyeong Jang ◽  
Maeng-Ki Kim ◽  
...  
Keyword(s):  
El Niño ◽  
Arctic Oscillation ◽  
El Nino ◽  
Southern Oscillation ◽  
The Arctic ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Winter Temperatures ◽  
Temperature And Pressure ◽  
The Arctic Oscillation

In recent decades, extremely cold winters have occurred repeatedly throughout the Northern Hemisphere, including the Korean Peninsula (hereafter, Korea). Typically, cold winter temperatures in Korea can be linked to the strengthening of the Siberian High (SH). Although previous studies have investigated the typical relationship between the SH and winter temperatures in Korea, this study uniquely focused on a change in the relationship, which reflects the influence of the Arctic Oscillation (AO) and El Niño–Southern Oscillation (ENSO). A significant change in the 15-year moving correlation between the SH and the surface air temperature average in Korea (K-tas) was observed in January. The correlation changed from −0.80 during 1971–1990 to −0.16 during 1991–2010. The mean sea-level pressure pattern regressed with the temperature, and a singular value decomposition analysis that incorporated the temperature and pressure supports that the negative high correlation during 1971–1990 was largely affected by AO. This connection with AO is substantiated by empirical orthogonal function (EOF) analysis with an upper-level geopotential height at 300 hPa. In the second mode of the EOF, the temperature and pressure patterns were primarily affected by ENSO during 1991–2010. Consequently, the interdecadal change in correlation between K-tas and the SH in January can be attributed to the dominant effect of AO from 1971–1990 and of ENSO from 1991–2010. Our results suggest that the relative importance of these factors in terms of the January climate in Korea has changed on a multidecadal scale.

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