Oscillation nord-atlantique

L’oscillation nord-atlantique (ONA, plus connue sous le sigle anglais NAO) désigne un phénomène touchant le système climatique du nord de l'océan Atlantique. L'ONA décrit les variations du régime océan-atmosphère sur la région et se mesure généralement comme la différence de pression atmosphérique entre l'anticyclone des Açores et la dépression d'Islande. Elle est notamment corrélée à l’oscillation arctique. L’ONA a été découverte durant les par Sir Gilbert Walker, qui avait découvert précédemment l’oscillation australe dans l'océan Pacifique et à laquelle est relié le phénomène El Niño. Comme l’oscillation australe, l'ONA est un facteur climatique déterminant à l'échelle régionale car elle est reliée à la position et la trajectoire des perturbations météorologiques qui touchent l'Europe de l'Ouest ainsi qu'aux températures océaniques du bassin de l'Atlantique nord. Description La circulation atmosphérique au-dessus de l'Atlantique nord montre une alternance rapide de

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Greenland precipitation trends in a long-term instrumental climate context (1890-2012): evaluation of coastal and ice core records

Konrad Steffen

Here, we present an analysis of monthly, seasonal, and annual long-term precipitation time-series compiled from coastal meteorological stations in Greenland and Greenland Ice Sheet (GrIS) ice cores (including three new ice core records from ACT11D, Tunu2013, and Summit2010). The dataset covers the period from 1890 to 2012, a period of climate warming. For approximately the first decade of the new millennium (2001-2012) minimum and maximum mean annual precipitation conditions are found in Northeast Greenland (Tunu2013 c. 120mm water equivalent (w.e.) year(-1)) and South Greenland (Ikerasassuaq: c. 2300mm w.e. year(-1)), respectively. The coastal meteorological stations showed on average increasing trends for 1890-2012 (3.5mm w.e. year(-2)) and 1961-2012 (1.3mm w.e. year(-2)). Years with high coastal annual precipitation also had a: (1) significant high number of precipitation days (r(2) = 0.59); and (2) high precipitation intensity measured as 24-h precipitation (r(2) = 0.54). For the GrIS the precipitation estimated from ice cores increased on average by 0.1mm w.e. year(-2) (1890-2000), showing an antiphase variability in precipitation trends between the GrIS and the coastal regions. Around 1960 a major shift occurred in the precipitation pattern towards wetter precipitation conditions for coastal Greenland, while drier conditions became more prevalent on the GrIS. Differences in precipitation trends indicate a heterogeneous spatial distribution of precipitation in Greenland. An Empirical Orthogonal Function analysis reveals a spatiotemporal cycle of precipitation that is linked instantaneously to the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation and with an approximate to 6 years lag time response to the Greenland Blocking Index.

Wiley-Blackwell2015

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Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012

Konrad Steffen

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a heat dome' over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in south, west and north-west Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994-2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2 degrees C at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future average' summers projected this century.

Wiley-Blackwell2014

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Export of Pollution from Europe: Seasonal and Interannual Variation

Isabelle Bey

Pollution can undergo long-range transport and impact the tropospheric chemistry thousands of kilometers downwind from the source region. Recently, there is interest in the intercontinental transport (ICT) of pollution between the main industrial regions of the extratropics of the Northern Hemisphere, especially the contribution of foreign pollution to regional episodes of high ozone. We present the results of a modelling investigation of the seasonal and interannual variations in the ICT of pollution from Europe from 1988 to 1997 using the GEOS-CHEM 3-d model of transport and chemistry. The model simulates tropospheric ozone-nitrogen oxides-hydrocarbon chemistry including the radiative and heterogeneous chemical effects of sulfate, sea salt, black carbon, organic carbon, and dust aerosols. It captures interannual variations in transport as it is driven by assimilated meteorological data. We identify the important dynamical transport mechanisms and their seasonal and interannual variations. We consider a number of phenomena which impact the ICT of pollution from Europe: i. the impact of the North Atlantic Oscillation (NAO); ii. the important trends in fossil fuel combustion caused by regulation of emissions in Western Europe and the economic contraction of Eastern Europe; and iii. the interannual variability of boreal forest fires.

2003

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Océan Atlantique

L'océan Atlantique est l'un des cinq grands océans de la Terre. L'Atlantique fait partie de l'océan Mondial et comporte deux océans : l'Atlantique Nord et l'Atlantique Sud. Sa superficie de en fait

Gulf Stream

Le Gulf Stream (hydronyme anglais qui signifie littéralement en français : « Courant du Golfe » en référence au golfe du Mexique) est un courant océanique chaud de surface prenant sa source entre la

Cyclone tropical

Un cyclone tropical est un type de cyclone (dépression) qui prend forme dans les océans de la zone intertropicale à partir d'une perturbation atmosphérique qui s'organise en dépression tropicale pu

ENV-410: Science of climate change

The course equips students with a comprehensive scientific understanding of climate change covering a wide range of topics from physical principles, historical climate change, greenhouse gas emissions, the IPCC assessment to future scenarios and climate action.