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[en] What will be the climate in 2050? From specialists, 2050 is the date of the first signs of the climatic change consequences. In France the daily life will not be very modified, but some activities which depend on the hydrology, will have to adapt. The vegetation modifications, will be little in some areas. Elsewhere, they would be radical: no more arctic ice field in summer, some island flooded by the sea. The authors show also the human activities which will be favored by the climatic change. (A.L.B.)
[en] The objective of this study is to quantitatively evaluate the type and amount of cloudiness most present during the winter months (December - February). The principal finding is that the occurrence of clouds over the Gulf Stream Locale during the winter months is dependent on atmospheric processes and their likely interaction with the Gulf Stream. A cloud climatology consisting of seven winters indicates that clouds occur approximately 70% of the time. However, during periods of cold air outbreaks (CAO), cloudiness occurs much less frequently. From the limited number of analyzed CAO events, VAS observations indicate that the Gulf Stream Locale plays an important role in the formation and maintenance of clouds, particularly shallow, opaque clouds downwind of the Gulf Stream Locale. Future work will focus on isolating other atmospheric processes and their relationship to cloud production over the Gulf Stream Locale. In addition, diurnal effects of cloud distribution and the land, air-sea interaction process will be investigated and reported on in the future
[en] We analyze the time dependency of decadal hindcast skill in the North Atlantic subpolar gyre within the time period 1961–2013. We compare anomaly correlation coefficients and temporal interquartile ranges of total upper ocean heat content and sea surface temperature for three differently initialized sets of hindcast simulations with the global coupled model MPI-ESM. All initializations use weakly coupled assimilation with the same full value nudging in the atmospheric component and different assimilation techniques for oceanic temperature and salinity: (1) ensemble Kalman filter assimilating EN4 observations and HadISST data, (2) nudging of anomalies to ORAS4 reanalysis, (3) nudging of full values to ORAS4 reanalysis. We find that hindcast skill depends strongly on the evaluation time period, with higher hindcast skill during strong multiyear trends, especially during the warming in the 1990s and lower hindcast skill in the absence of such trends. Differences between the prediction systems are more pronounced when investigating any 20-year subperiod within the entire hindcast period. In the ensemble Kalman filter initialized hindcasts, we find significant correlation skill for up to 5–8 lead years, albeit along with an overestimation of the temporal interquartile range. In the hindcasts initialized by anomaly nudging, significant correlation skill for lead years greater than two is only found in the 1980s and 1990s. In the hindcasts initialized by full value nudging, correlation skill is consistently lower than in the hindcasts initialized by anomaly nudging in the first lead years with re-emerging skill thereafter. The Atlantic meridional overturning circulation reacts on the density changes introduced by oceanic nudging, this limits the predictability in the subpolar gyre in the first lead years. Overall, we find that a model-consistent assimilation technique can improve hindcast skill. Further, the evaluation of 20 year subperiods within the full hindcast period provides essential insights to judge the success of both the assimilation and the subsequent hindcast quality.
[en] Based on the principal findings from an extensive study of the Arctic, the subject of an international symposium held in Reykjavik, Iceland, in November of 2004, the Arctic Region is heating up twice as fast as the average for the rest of the world. If warming continues at this pace, or even faster, the most significant effects of future climate changes will occur in the polar regions, and the greatest threat seems to be the collapse of the Gulf Stream
[it]Il riscaldamento che si sta verificando nella regione artica potrebbe comportare il collasso della corrente del Golfo e l'avvio di un'era di glaciazione. Uno scenario possibile se nei prossimi decenni si continuera a bruciare combustibili ed emettere gas serra
Purpose of ReviewThis paper reviews recent progress in the understanding and prediction of pacific decadal variability (PDV). The PDV is now recognized to consist of multiple ocean-atmosphere modes and to be caused by multiple processes. At the leading order, PDV can be viewed as the reddening process of stochastic atmospheric variability on the extratropical ocean. However, PDV is also strongly tied to teleconnection dynamics interacting with the tropics, primarily the interactions between meridional modes in the extra-tropics and ENSO, and between the ENSO teleconnections and the dominant modes of atmospheric variability in the mid-latitude.
Recent FindingsExtratropical oceanic Rossby waves are found to be crucial for determining the decadal time scales of the PDV and provide potentially an important source of predictability of PDV. Preliminary experiments with GCMs and empirical linear inverse models have shown some skill for the prediction of PDV in ocean surface temperatures. While the climate predictions in the first few years depend significantly on the oceanic initial condition, predictions of near decadal time scales are contributed mostly by the global warming trend. In addition, recent studies explored the role of ocean subsurface dynamics for multi-decadal predictability in the Pacific and suggest that subsurface dynamics may lead to important sources of decadal predictability in regional upwelling systems, namely the eastern boundary and polar gyre. Overall, the predictability of PDV and the related surface and subsurface signals remain to be much studied.
SummaryRecent studies also start to explore the relation between PDV and global warming. It has been suggested that PDV can slow down or accelerate the global warming trend significantly. The influence of the anthropogenic climate change on PDV, however, has remained unclear.
[en] Of the five primary CART sites, the Gulf Stream locale, a western boundary current location, uniquely experiences positive sensible and latent heat fluxes that span wide ranges and are likely the largest on earth. Scientific issues relating to this area are grouped under two objectives: (1) Relate observed instantaneous radiative properties of the atmosphere to the then-present atmospheric temperature and composition and surface radiative properties, both as a function of position, and develop parameterizations for these relationships. (2) Develop parameterizations to describe atmospheric composition and surface properties governing atmospheric radiation in terms of relevant prognostic variables, with the objective of incorporating these parameterizations into general circulation and related models
[en] The seasonal timing or onset date of the stratospheric final warming (SFWOD) events has a considerable interannual variability. This paper reports a statistically significant relationship between the North Pacific Gyre Oscillation (NPGO) and SFWOD in the Northern Hemisphere in two sub-periods (1951–1978 and 1979–2015). Specifically, in the first (second) sub-period, the NPGO is negatively (positively) linked with SFWOD. Composite analyses associated with anomalous NPGO years are conducted to diagnose the dynamic processes of the NPGO–SFWOD link. During 1951–1978, positive NPGO years tend to strengthen the Pacific–North America (PNA) pattern in the mid-troposphere in boreal winter. The strengthened PNA pattern in February leads to strong planetary wave activity in the extratropical stratosphere from late February to March and causes the early onset of SFW in early April. By contrast, a strengthened Western Pacific pattern from January to early February in negative NPGO years causes a burst of planetary waves in both the troposphere and extratropical stratosphere from late January to mid-February and results in more winter stratospheric sudden warming events, which, in turn, leads to a dormant spring and a late onset of SFW in late April. During 1979–2015, positive (negative) NPGO years strongly strengthen (weaken) the mid-tropospheric Aleutian low and the Western Pacific pattern from January to mid-March, leading to increased (decreased) planetary wavenumber-1 activity in the stratosphere from mid- to late winter and thus more (less) winter stratospheric sudden warming events and late (early) onsets of SFW in early May (mid-April).
[en] Our decadal climate prediction system, which is based on the Max-Planck-Institute Earth System Model, is initialized from a coupled assimilation run that utilizes nudging to selected state parameters from reanalyses. We apply full-field nudging in the atmosphere and either full-field or anomaly nudging in the ocean. Full fields from two different ocean reanalyses are considered. This comparison of initialization strategies focuses on the North Atlantic Subpolar Gyre (SPG) region, where the transition from anomaly to full-field nudging reveals large differences in prediction skill for sea surface temperature and ocean heat content (OHC). We show that nudging of temperature and salinity in the ocean modifies OHC and also induces changes in mass and heat transports associated with the ocean flow. In the SPG region, the assimilated OHC signal resembles well OHC from observations, regardless of using full fields or anomalies. The resulting ocean transport, on the other hand, reveals considerable differences between full-field and anomaly nudging. In all assimilation runs, ocean heat transport together with net heat exchange at the surface does not correspond to OHC tendencies, the SPG heat budget is not closed. Discrepancies in the budget in the cases of full-field nudging exceed those in the case of anomaly nudging by a factor of 2–3. The nudging-induced changes in ocean transport continue to be present in the free running hindcasts for up to 5 years, a clear expression of memory in our coupled system. In hindcast mode, on annual to inter-annual scales, ocean heat transport is the dominant driver of SPG OHC. Thus, we ascribe a significant reduction in OHC prediction skill when using full-field instead of anomaly initialization to an initialization shock resulting from the poor initialization of the ocean flow.
[en] Full text: Open ocean fisheries depend on vast and diverse assemblages of pelagic crustaceans, molluscs, squid,and mid water fish (known as micronekton). These assemblages form complex, size-structured food web interactions that dictate the availability and flow of energy throughout the ecosystem. As ecosystems vary from one another in terms of community structure and biodiversity, the flow of energy through a food web also changes, creating quantifiable metrics that can describe the ocean habitats. The East Australian Current (EAC) produces two types of ocean habitats in the form of gyres, or eddies. Cyclonic eddies have a strong upwelling current which promotes higher productivity and creates a more favourable habitat for micronekton than the surrounding waters. Anticyclonic eddies are characterised by a downwelling force and therefore tend to have lower production. We sampled four ocean eddies off the coast of eastern Australia from the Research Vessel Investigator in September 2017. Fish, zooplankton and other micronekton were sampled from the top 100 m of the eddies using trawl and plankton nets. The catch was sorted into size classes and broad morphological groups representing all tropic levels from producers to predators. 256 samples, consisting of individuals from each size class and group, were selected for stable isotope analysis to model food chain length and trophic interactions in these size-structured eddy habitats.The stable carbon (δ13C) and nitrogen (δ15N) isotopes identified relationships between body size and trophic level of species. Predator-Prey mass ratio (PPMR), Food Chain Length (FCL) and energy transfer efficiency varied within each of the eddies, with more productive habitats within the cyclonic eddies showing a much larger PPMR and shorter FCL compared to anticyclonic eddies. The application of stable isotopes to quantify food web metrics is beneficial for the estimation of fish populations throughout the food web by identifying the extent of productivity within ocean habitats. Traditional methods of managing fisheries are often based on the population and growth of individual target species, but by understanding the flow of energy through the whole habitat we can interpret satellite-derived data and more effectively and manage Australia's $3.1 billion fisheries from a perspective that considers the ecosystem as a whole. (author)