Role of the Polar-night Jet Oscillation on the formation of the Arctic Oscillation in the Northern Hemisphere winter

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.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.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.

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Polar stratospheric cloud observations by MIPAS on ENVISAT: detection method, validation and analysis of the northern hemisphere winter 2002/2003

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-679-2005 ◽

2005 ◽

Vol 5 (3) ◽

pp. 679-692 ◽

Cited By ~ 55

Author(s):

R. Spang ◽

J. J. Remedios ◽

L. J. Kramer ◽

L. R. Poole ◽

M. D. Fromm ◽

...

Keyword(s):

Northern Hemisphere ◽

Detection Method ◽

Michelson Interferometer ◽

The Arctic ◽

Spectral Signature ◽

Winter Period ◽

Second Phase ◽

Good Correspondence ◽

Hemisphere Winter ◽

Northern Hemisphere Winter

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT has made extensive measurements of polar stratospheric clouds (PSCs) in the northern hemisphere winter 2002/2003. A PSC detection method based on a ratio of radiances (the cloud index) has been implemented for MIPAS and is validated in this study with respect to ground-based lidar and space borne occultation measurements. A very good correspondence in PSC sighting and cloud altitude between MIPAS detections and those of other instruments is found for cloud index values of less than four. Comparisons with data from the Stratospheric Aerosol and Gas Experiment (SAGE) III are used to further show that the sensitivity of the MIPAS detection method for this threshold value of cloud index is approximately equivalent to an extinction limit of 10-3km-1 at 1022nm, a wavelength used by solar occultation experiments. The MIPAS cloud index data are subsequently used to examine, for the first time with any technique, the evolution of PSCs throughout the Arctic polar vortex up to a latitude close to 90° north on a near-daily basis. We find that the winter of 2002/2003 is characterised by three phases of very different PSC activity. First, an unusual, extremely cold phase in the first three weeks of December resulted in high PSC occurrence rates. This was followed by a second phase of only moderate PSC activity from 5-13 January, separated from the first phase by a minor warming event. Finally there was a third phase from February to the end of March where only sporadic and mostly weak PSC events took place. The composition of PSCs during the winter period has also been examined, exploiting in particular an infra-red spectral signature which is probably characteristic of NAT. The MIPAS observations show the presence of these particles on a number of occasions in December but very rarely in January. The PSC type differentiation from MIPAS indicates that future comparisons of PSC observations with microphysical and denitrification models might be revealing about aspects of solid particle existence and location.

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The role of stationary and transient planetary waves in the maintenance of stratospheric polar vortex regimes in Northern Hemisphere winter

Advances in Atmospheric Sciences ◽

10.1007/s00376-010-9163-7 ◽

2010 ◽

Vol 28 (1) ◽

pp. 187-194 ◽

Cited By ~ 2

Author(s):

Qian Li ◽

Hans-F. Graf ◽

Xuefeng Cui

Keyword(s):

Northern Hemisphere ◽

Polar Vortex ◽

Planetary Waves ◽

Stratospheric Polar Vortex ◽

Hemisphere Winter ◽

Northern Hemisphere Winter

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

Journal of Climate ◽

10.1175/jcli-d-16-0651.1 ◽

2017 ◽

Vol 30 (8) ◽

pp. 2905-2919 ◽

Cited By ~ 4

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.

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