scholarly journals The Occurrence and Properties of Long-Lived Liquid-Bearing Clouds over the Greenland Ice Sheet and Their Relationship to the North Atlantic Oscillation

2018 ◽  
Vol 57 (4) ◽  
pp. 921-935 ◽  
Author(s):  
Jonathan Edwards-Opperman ◽  
Steven Cavallo ◽  
David Turner
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
The Arctic ◽  
Positive Phase ◽  
Cloud Base ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

AbstractStratiform liquid-bearing clouds (LBCs), defined herein as either pure liquid or mixed-phase clouds, have a large impact on the surface radiation budget across the Arctic. LBCs lasting at least 6 h are observed at Summit, Greenland, year-round with a maximum in occurrence during summer. Mean cloud-base height is below 1 km for 85% of LBC cases identified, 59% have mean liquid water path (LWP) values between 10 and 40 g m−2, and most produce sporadic light ice-phase precipitation. During their occurrence, the atmosphere above the ice sheet is anomalously warm and moist, with southerly winds observed over much of the ice sheet, including at Summit. LBCs that occur when the North Atlantic Oscillation (NAO) is in the negative phase correspond to strong ridging centered over the Greenland Ice Sheet (GIS), allowing for southwesterly flow over the GIS toward Summit. During the positive phase of the NAO, the occurrence of LBCs corresponds to a cyclone located off the southeastern coast of the ice sheet, which leads to easterly-to-southeasterly flow toward Summit. Furthermore, air parcels at Summit frequently originate from below the elevation of Summit, indicating that orographic lift along the ice sheet is a factor in the occurrence of LBCs at Summit. LBCs are more frequently observed during the negative NAO, and both the LWP and precipitation rate are larger in LBCs occurring during this phase. Mean LWP in LBCs occurring during the negative NAO is 15 g m−2 larger than in LBCs occurring during the positive phase.

scholarly journals Cyclones causing wind storms in the Mediterranean: characteristics, trends and links to large-scale patterns

2010 ◽  
Vol 10 (7) ◽  
pp. 1379-1391 ◽  
Author(s):  
K. M. Nissen ◽  
G. C. Leckebusch ◽  
J. G. Pinto ◽  
D. Renggli ◽  
S. Ulbrich ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Positive Phase ◽  
East Atlantic ◽  
The North ◽  
The North Atlantic ◽  
Wind Storms ◽  
The Mediterranean ◽  
Wind Events ◽  
The North Atlantic Oscillation

Abstract. A climatology of cyclones with a focus on their relation to wind storm tracks in the Mediterranean region (MR) is presented. Trends in the frequency of cyclones and wind storms, as well as variations associated with the North Atlantic Oscillation (NAO), the East Atlantic/West Russian (EAWR) and the Scandinavian variability pattern (SCAND) are discussed. The study is based on the ERA40 reanalysis dataset. Wind storm tracks are identified by tracking clusters of adjacent grid boxes characterised by extremely high local wind speeds. The wind track is assigned to a cyclone track independently identified with an objective scheme. Areas with high wind activity – quantified by extreme wind tracks – are typically located south of the Golf of Genoa, south of Cyprus, southeast of Sicily and west of the Iberian Peninsula. About 69% of the wind storms are caused by cyclones located in the Mediterranean region, while the remaining 31% can be attributed to North Atlantic or Northern European cyclones. The North Atlantic Oscillation, the East Atlantic/West Russian pattern and the Scandinavian pattern all influence the amount and spatial distribution of wind inducing cyclones and wind events in the MR. The strongest signals exist for the NAO and the EAWR pattern, which are both associated with an increase in the number of organised strong wind events in the eastern MR during their positive phase. On the other hand, the storm numbers decrease over the western MR for the positive phase of the NAO and over the central MR during the positive phase of the EAWR pattern. The positive phase of the Scandinavian pattern is associated with a decrease in the number of winter wind storms over most of the MR. A third of the trends in the number of wind storms and wind producing cyclones during the winter season of the ERA40 period may be attributed to the variability of the North Atlantic Oscillation.

The North Atlantic Oscillation and the Arctic Oscillation favour harmful algal blooms in SW Europe

Harmful Algae ◽  
2014 ◽  
Vol 39 ◽  
pp. 121-126 ◽  
Author(s):  
José C. Báez ◽  
Raimundo Real ◽  
Victoria López-Rodas ◽  
Eduardo Costas ◽  
A. Enrique Salvo ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Arctic Oscillation ◽  
The Arctic ◽  
The North ◽  
The North Atlantic ◽  
The Arctic Oscillation ◽  
The North Atlantic Oscillation

The North Atlantic Oscillation and the Greenland ice sheet in CMIP6

2020 ◽  
Author(s):  
Ruth Mottram ◽  
Susann Ascheneller ◽  
Florian Sauerland ◽  
Rasmus Anker Pedersen ◽  
Peter Thejll ◽  
...  
Keyword(s):  
North Atlantic ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atmospheric Blocking ◽  
Atlantic Region ◽  
Surface Mass ◽  
Mass Budget ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

<div><span><span>The North Atlantic Oscillation (NAO) is an important control on both northern European weather and Greenland ice sheet surface mass budget via the path of storm tracks that deliver precipitation, particularly in the winter, and by the strength and persistence of the Greenland blocking high that promotes melt in summer. Within CMIP5 models, atmospheric blocking was generally poorly represented regardless of location, we here examine an ensemble of 10 CMIP6 fully coupled earth system models (ESMs) that were available by Summer</span><span> 20</span><span>19 </span><span>in order to examine if model improvements better represent the NAO in CMIP6.</span></span></div><div><span><span>We examine </span><span> temperature over Greenland and the north Atlantic region as well as NAO position, persistence and strength in winter and summer for each model in the historical scenario. No single model performs well on all characteristics but the UKESM and EC-EARTH3 perform the best when compared to the ERA5 climate reanalysis.</span></span></div><div><span><span>We also show how the NAO is expected to change in </span><span>8 of</span><span> the</span><span>se</span><span> models under different future climate scenarios.</span><span>  </span><span>The location</span><span> </span><span>of the Icelandic low in particular migrates northwards by varying amounts, likely related to Arctic sea ice changes within the models and with a consequent impact on precipitation.</span></span></div><div><span><span>Downscaling experiments carried out using the HIRHAM5 regional climate model over the Greenland ice sheet show the importance of accurately characterising the NAO in order to correctly </span><span> </span><span>estimate both winter accumulation and summer melt and the combination that gives the ice sheet mass budget. Our study emphasises the importance of assessing a range of different climate and weather variables when selecting models to downscale for </span><span>obtaining </span><span>ice sheet mass balance. We also note that while some progress has been made in </span><span>better representing </span><span>atmospheric blocking in ESMs, largely down to higher resolution in atmospheric models, there is still a substantial improvement required before ESMs can be said to accurately characterise the climate of the North Atlantic region with consequent impacts on ice sheet surface mass budget projections.</span></span></div>

scholarly journals Influence of the North Atlantic Oscillation on air pollution transport

2012 ◽  
Vol 12 (2) ◽  
pp. 869-877 ◽  
Author(s):  
T. Christoudias ◽  
A. Pozzer ◽  
J. Lelieveld
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
North American ◽  
Trace Gases ◽  
Water Soluble ◽  
The Arctic ◽  
Pollution Transport ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. We examined the influence of the North Atlantic Oscillation (NAO) on the atmospheric dispersion of pollution by computing the emission, transport and removal of idealized insoluble gaseous and water-soluble aerosol tracers, tagged by the continent of origin. We simulated a period of 50 yr (1960–2010), using the ECHAM5/MESSy1 atmospheric chemistry (EMAC) general circulation model. The model accounts for anthropogenic, biogenic and biomass burning sources, removal of trace gases through OH oxidation, and precipitation, sedimentation and deposition of aerosols. The model is shown to reproduce the observed spatial features of the NAO, moisture transports and precipitation. During high NAO phase seasons the axis of maximum westerly North American trace gas transports extends relatively far to the north and east over Europe. The NAO phase is significantly correlated with North American insoluble gas and soluble aerosol tracer concentrations over the northwestern Atlantic Ocean and across northern Europe, and with European trace gases and aerosols over Africa and north of the Arctic circle. We find a strong anti-correlation between the phase of the NAO and European pollutant gas concentration over western and central Europe.

scholarly journals Influence of the North Atlantic Oscillation on air pollution transport

2011 ◽  
Vol 11 (9) ◽  
pp. 25967-25989
Author(s):  
T. Christoudias ◽  
A. Pozzer ◽  
J. Lelieveld
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
North American ◽  
Trace Gases ◽  
Water Soluble ◽  
The Arctic ◽  
Pollution Transport ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. We examined the influence of the North Atlantic Oscillation (NAO) on the atmospheric dispersion of pollution by computing the emission, transport and removal of insoluble gaseous and water-soluble aerosol tracers, tagged by the continent of origin. We simulated a period of 50 yr (1960–2010), using the ECHAM/MESSy atmospheric chemistry (EMAC) general circulation model. The model accounts for anthropogenic, biogenic and biomass burning sources, removal of trace gases through OH oxidation, and precipitation, sedimentation and deposition of aerosols. The model is shown to reproduce the observed spatial features of the NAO, moisture transports and precipitation. During high NAO phase seasons the axis of maximum westerly North American trace gas transports extends relatively far to the north and east over Europe. The NAO phase is significantly correlated with North American tracer concentrations over the northwestern Atlantic Ocean and across northern Europe, and with European trace gases and aerosols beyond the arctic circle. Our results indicate marked differences and partly reversed correlations for the insoluble gas and the soluble aerosol tracers. We find a strong anti-correlation over western and central Europe between European pollutant gas and aerosol concentrations and the phase of the NAO.

scholarly journals Robust winter warming over Eurasia under stratospheric sulfate geoengineering – the role of stratospheric dynamics

2020 ◽  
Author(s):  
Antara Banerjee ◽  
Amy H. Butler ◽  
Lorenzo M. Polvani ◽  
Alan Robock ◽  
Isla R. Simpson ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Volcanic Eruptions ◽  
Forced Response ◽  
Positive Phase ◽  
Dynamical Response ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. It has been suggested that increased stratospheric sulfate aerosol loadings following large, low latitude volcanic eruptions can lead to wintertime warming over Eurasia through dynamical stratosphere-troposphere coupling. We here investigate the proposed connection in the context of hypothetical future stratospheric sulfate geoengineering in the Geoengineering Large Ensemble simulations. In those geoengineering simulations, we find that stratospheric circulation anomalies that resemble the positive phase of the Northern Annular Mode in winter is a distinguishing climate response which is absent when increasing greenhouse gases alone are prescribed. This stratospheric dynamical response projects onto the positive phase of the North Atlantic Oscillation, leading to associated side-effects of this climate intervention strategy, such as continental Eurasian warming and precipitation changes. Seasonality is a key signature of the dynamically-driven surface response. We find an opposite response of the North Atlantic Oscillation in summer, when no dynamical role of the stratosphere is expected. The robustness of the wintertime forced response stands in contrast to previously proposed volcanic responses.

scholarly journals Intercontinental transport of tropospheric ozone: a study of its seasonal variability across the North Atlantic utilizing tropospheric ozone residuals and its relationship to the North Atlantic Oscillation

2003 ◽  
Vol 3 (6) ◽  
pp. 2053-2066 ◽  
Author(s):  
J. K. Creilson ◽  
J. Fishman ◽  
A. E. Wozniak
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Tropospheric Ozone ◽  
Total Ozone ◽  
Western Europe ◽  
Positive Phase ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Impact

Abstract. Using the empirically-corrected tropospheric ozone residual (TOR) technique, which utilizes coincident observations of total ozone from the Total Ozone Mapping Spectrometer (TOMS) and stratospheric ozone profiles from the Solar Backscattered Ultraviolet (SBUV) instruments, the seasonal and regional distribution of tropospheric ozone across the North Atlantic from 1979-2000 is examined. Its relationship to the North Atlantic Oscillation (NAO) is also analyzed as a possible transport mechanism across the North Atlantic. Monthly climatologies of tropospheric ozone for five different regions across the North Atlantic exhibit strong seasonality. The correlation between these monthly climatologies of the TOR and ozonesonde profiles at nearby sites in both eastern North America and western Europe are highly significant (R values of +0.98 and +0.96 respectively) and help to validate the use of satellite retrievals of tropospheric ozone. Distinct springtime interannual variability over North Atlantic Region 5 (eastern North Atlantic-western Europe) is particularly evident and exhibits similar variability to the positive phase of the NAO (R=+0.61, r=<0.01). Positive phases of the NAO are indicative of a stronger Bermuda-Azores high and a stronger Icelandic low and thus faster more zonal flow across the North Atlantic from west to east. This flow regime appears to be causing the transport of tropospheric ozone across the North Atlantic and onto Europe. The consequence of such transport is the impact on a downwind region's ability to meet their ozone attainment goals. This link between the positive phase of the NAO and increased tropospheric ozone over Region 5 could be an important tool for prediction of such pollution outbreaks.

scholarly journals The North Atlantic Oscillation controls air pollution transport to the Arctic

2003 ◽  
Vol 3 (5) ◽  
pp. 1769-1778 ◽  
Author(s):  
S. Eckhardt ◽  
A. Stohl ◽  
S. Beirle ◽  
N. Spichtinger ◽  
P. James ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Model Simulation ◽  
The Arctic ◽  
Pollution Transport ◽  
Pollution Levels ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Strong Control

Abstract. This paper studies the interannual variability of pollution pathways from northern hemisphere (NH) continents into the Arctic. Using a 15-year model simulation of the dispersion of passive tracers representative of anthropogenic emissions from NH continents, we show that the North Atlantic Oscillation (NAO) exerts a strong control on the pollution transport into the Arctic, particularly in winter and spring. For tracer lifetimes of 5 (30) days, surface concentrations in the Arctic winter are enhanced by about 70% (30%) during high phases of the NAO (in the following referred to as NAO+) compared to its low phases (NAO-). This is mainly due to great differences in the pathways of European pollution during NAO+ and NAO- phases, respectively, but reinforced by North American pollution, which is also enhanced in the Arctic during NAO+ phases. In contrast, Asian pollution in the Arctic does not significantly depend on the NAO phase. The model results are confirmed using remotely-sensed NO2 vertical atmospheric columns obtained from seven years of satellite measurements, which show enhanced northward NO2 transport and reduced NO2 outflow into the North Atlantic from Central Europe during NAO+ phases. Surface measurements of carbon monoxide (CO) and black carbon at high-latitude stations further corroborate the overall picture of enhanced Arctic pollution levels during NAO+ phases

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