Regional influence of decadal to multidecadal Atlantic Oscillations during the last two millennia in Morocco, inferred from two high resolution δ18O speleothem records

NASA Astrophysics Data System (ADS)

Ait Brahim, Yassine; Sifeddine, Abdelfettah; Khodri, Myriam; Bouchaou, Lhoussaine; Cruz, Francisco W.; Pérez-Zanón, Núria; Wassenburg, Jasper A.; Cheng, Hai

2017-04-01

Climate projections predict substantial increase of extreme heats and drought occurrences during the coming decades in Morocco. It is however not clear what can be attributed to natural climate variability and to anthropogenic forcing, as hydroclimate variations observed in areas such as Morocco are highly influenced by the Atlantic climate modes. Since observational data sets are too short to resolve properly natural modes of variability acting on decadal to multidecadal timescales, high resolution paleoclimate reconstructions are the only alternative to reconstruct climate variability in the remote past. Herein, we present two high resolution and well dated speleothems oxygen isotope (δ18O) records sampled from Chaara and Ifoulki caves (located in Northeastern and Southwestern Morocco respectively) to investigate hydroclimate variations during the last 2000 years. Our results are supported by a monitoring network of δ18O in precipitation from 17 stations in Morocco. The new paleoclimate records are discussed in the light of existing continental and marine paleoclimate proxies in Morocco to identify significant correlations at various lead times with the main reconstructed oceanic and atmospheric variability modes and possible climate teleconnections that have potentially influenced the climate during the last two millennia in Morocco. The results reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords. Evidence of dry conditions exist during the Medieval Climate Anomaly (MCA) period and the Climate Warm Period (CWP) and humid conditions during the Little Ice Age (LIA) period. Statistical analyses suggest that the climate of southwestern Morocco remained under the combined influence of both the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO) over the last two millennia. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably

Atlantic multi-decadal oscillation covaries with Agulhas leakage

PubMed Central

Biastoch, Arne; Durgadoo, Jonathan V.; Morrison, Adele K.; van Sebille, Erik; Weijer, Wilbert; Griffies, Stephen M.

2015-01-01

The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage', forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic. PMID:26656850

Atlantic multi-decadal oscillation covaries with Agulhas leakage

DOE PAGES

Biastoch, Arne; Durgadoo, Jonathan V.; Morrison, Adele K.; ...

2015-12-10

The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage’, forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. Lastly, this is relevant for climate in the North Atlantic.

External forcing as a metronome for Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Otterå, Odd Helge; Bentsen, Mats; Drange, Helge; Suo, Lingling

2010-10-01

Instrumental records, proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations, with potential impacts on regional climate. To understand the observed variability and to gauge any potential for climate predictions it is essential to identify the physical mechanisms that lead to this variability, and to explore the spatial and temporal characteristics of multidecadal variability modes. Here we use a coupled ocean-atmosphere general circulation model to show that the phasing of the multidecadal fluctuations in the North Atlantic during the past 600 years is, to a large degree, governed by changes in the external solar and volcanic forcings. We find that volcanoes play a particularly important part in the phasing of the multidecadal variability through their direct influence on tropical sea-surface temperatures, on the leading mode of northern-hemisphere atmosphere circulation and on the Atlantic thermohaline circulation. We suggest that the implications of our findings for decadal climate prediction are twofold: because volcanic eruptions cannot be predicted a decade in advance, longer-term climate predictability may prove challenging, whereas the systematic post-eruption changes in ocean and atmosphere may hold promise for shorter-term climate prediction.

Multidecadal Atlantic climate variability and its impact on marine pelagic communities

NASA Astrophysics Data System (ADS)

Harris, Victoria; Edwards, Martin; Olhede, Sofia C.

2014-05-01

A large scale analysis of sea surface temperature (SST) and climate variability over the North Atlantic and its interactions with plankton over the North East Atlantic was carried out to better understand what drives both temperature and species abundance. The spatio-temporal pattern of SST was found to correspond to known climate indices, namely the Atlantic Multidecadal Oscillation (AMO), the East Atlantic Pattern (EAP) and the North Atlantic Oscillation (NAO). The spatial influence of these indices is heterogeneous. Although the AMO is present across all regions, it is most strongly represented in the SST signal in the subpolar gyre region. The NAO instead is strongly weighted in the North Sea and the pattern of its influence is oscillatory in space with a wavelength of approximately 6000 km. Natural oscillations might obscure the influence of climate change effects, making it difficult to determine how much of the variation is attributable to longer term trends. In order to separate the influences of different climate signals the SST signals were decomposed in to spatial and temporal components using principal component analysis (PCA). A similar analysis is carried out on various indicator species of plankton: Calanus finmarchicus, Phytoplankton Colour Index and total copepod abundance, as well as phytoplankton and zooplankton communities. By comparing the two outputs it is apparent that the dominant driver is the recent warming trend, which has a negative influence on C. finmarchicus and total copepods, but has a positive one on phytoplankton colour. However natural oscillations also influence the abundance of plankton, in particular the AMO is a driver of diatom abundance. Fourier principal component analysis, an approach which is novel in terms of the ecological data, was used to analyse the behaviour of various communities averaged over space. The zooplankton community is found to be primarily influenced by climate warming trends. The analysis provides

Coherent Multidecadal Atmospheric and Oceanic Variability in the North Atlantic: Blocking Corresponds with Warm Subpolar Ocean

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa M.; Rhines, P. B.; Worthen, D. L.

2012-01-01

Winters with frequent atmospheric blocking, in a band of latitudes from Greenland to Western Europe, are found to persist over several decades and correspond to a warm North Atlantic Ocean. This is evident in atmospheric reanalysis data, both modern and for the full 20th century. Blocking is approximately in phase with Atlantic multidecadal ocean variability (AMV). Wintertime atmospheric blocking involves a highly distorted jetstream, isolating large regions of air from the westerly circulation. It influences the ocean through windstress-curl and associated air/sea heat flux. While blocking is a relatively high-frequency phenomenon, it is strongly modulated over decadal timescales. The blocked regime (weaker ocean gyres, weaker air-sea heat flux, paradoxically increased transport of warm subtropical waters poleward) contributes to the warm phase of AMV. Atmospheric blocking better describes the early 20thC warming and 1996-2010 warm period than does the NAO index. It has roots in the hemispheric circulation and jet stream dynamics. Subpolar Atlantic variability covaries with distant AMOC fields: both these connections may express the global influence of the subpolar North Atlantic ocean on the global climate system.

Differential response of continental stock complexes of Atlantic salmon (Salmo salar) to the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Friedland, Kevin D.; Shank, Burton V.; Todd, Christopher D.; McGinnity, Philip; Nye, Janet A.

2014-05-01

Atlantic salmon, Salmo salar, in the North Atlantic are managed as a set of population complexes distributed in North America and Europe. In recent years, these complexes have experienced reduced marine survival and many populations within the complexes are at risk, especially those at the southern ends of the species amphi-Atlantic range. Atlantic salmon is an anadromous fish dividing its life history between residence in freshwater and the marine environment. The freshwater portion of the life history includes spawning and the rearing of juveniles where in-river production has tended to be relatively stable, whereas the first year at sea, termed the post-smolt year, is characterized by more variable rates of mortality. Although their habitats are widely separated geographically along the North Atlantic seaboards, strong recruitment coherence exists between North American and European stock complexes. This recruitment coherence is correlated with ocean temperature variation associated with the Atlantic Multidecadal Oscillation (AMO). The North Atlantic Oscillation (NAO) appears to be relatively unimportant as a driver of salmon abundance. The mechanism determining the link between AMO-related thermal variation and abundance appears to differ fundamentally for the two continental stock groupings. Whereas ocean climate variability during the first springtime months of juvenile salmon migration to sea appears to be important to the survival of North American stocks, summer climate variation appears to be central to adult recruitment variation for European stocks. This contrast in seasonal effects appears to be related to the varying roles of predation pressure and size-related mortality on the continental stock complexes. The anticipated warming due to global climate change will impose thermal conditions on salmon populations outside historical context and challenge the ability of many populations to persist.

Persistent positive North Atlantic oscillation mode dominated the Medieval Climate Anomaly.

PubMed

Trouet, Valérie; Esper, Jan; Graham, Nicholas E; Baker, Andy; Scourse, James D; Frank, David C

2009-04-03

The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña-like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.

Early 20th Century Arctic Warming Intensified by Pacific and Atlantic Multidecadal Variability

NASA Astrophysics Data System (ADS)

Tokinaga, H.; Xie, S. P.; Mukougawa, H.

2017-12-01

We investigate the influence of Pacific and Atlantic multidecadal variability on the Arctic temperature, with a particular focus on the early 20th century Arctic warming. Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing than at present. We find that the concurrent phase shift of Pacific and Atlantic multidecadal variability is the major driver for the early 20th century Arctic warming. Atmospheric model simulations reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early Arctic warming is associated with the cold-to-warm phase shifts of Atlantic and Pacific multidecadal variability modes, a SST pattern reminiscent of the positive phase of the Pacific decadal and Atlantic multidecadal oscillations. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. The equatorial Pacific warming deepens the Aleutian low, advecting warm air to the North American Arctic. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, cold-to-warm phase shift of the Pacific and Atlantic multidecadal variability. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability

NASA Technical Reports Server (NTRS)

Haekkinen, Sirpa; Rhines, Peter B.; Worthlen, Denise L.

2011-01-01

Based on the 20th century atmospheric reanalysis, winters with more frequent blocking, in a band of blocked latitudes from Greenland to Western Europe, are found to persist over several decades and correspond to a warm North Atlantic Ocean, in-phase with Atlantic multi-decadal ocean variability. Atmospheric blocking over the northern North Atlantic, which involves isolation of large regions of air from the westerly circulation for 5 days or more, influences fundamentally the ocean circulation and upper ocean properties by impacting wind patterns. Winters with clusters of more frequent blocking between Greenland and western Europe correspond to a warmer, more saline subpolar ocean. The correspondence between blocked westerly winds and warm ocean holds in recent decadal episodes (especially, 1996-2010). It also describes much longer-timescale Atlantic multidecadal ocean variability (AMV), including the extreme, pre-greenhouse-gas, northern warming of the 1930s-1960s. The space-time structure of the wind forcing associated with a blocked regime leads to weaker ocean gyres and weaker heat-exchange, both of which contribute to the warm phase of AMV.

ASSOCIATIONS BETWEEN NAO VARIBILITY AND U.S. MID-ATLANTIC REGION HYDROCLIMATOLOGY

EPA Science Inventory

Variability in the climate of the US Mid-Atlantic Region is associated with larger scale variability in the El Nino-Southern Oscillation (ENSO), the Pacific North American (PNA) teleconnection pattern, and the North Atlantic Oscillation (NAO). Collectively, these three large-scal...

Evidence of multidecadal climate variability and the Atlantic Multidecadal Oscillation from a Gulf of Mexico sea-surface temperature-proxy record

USGS Publications Warehouse

Poore, R.Z.; DeLong, K.L.; Richey, J.N.; Quinn, T.M.

2009-01-01

A comparison of a Mg/Ca-based sea-surface temperature (SST)-anomaly record from the northern Gulf of Mexico, a calculated index of variability in observed North Atlantic SST known as the Atlantic Multidecadal Oscillation (AMO), and a tree-ring reconstruction of the AMO contain similar patterns of variation over the last 110 years. Thus, the multidecadal variability observed in the instrumental record is present in the tree-ring and Mg/Ca proxy data. Frequency analysis of the Gulf of Mexico SST record and the tree-ring AMO reconstruction from 1550 to 1990 found similar multidecadal-scale periodicities (???30-60 years). This multidecadal periodicity is about half the observed (60-80 years) variability identified in the AMO for the 20th century. The historical records of hurricane landfalls reveal increased landfalls in the Gulf Coast region during time intervals when the AMO index is positive (warmer SST), and decreased landfalls when the AMO index is negative (cooler SST). Thus, we conclude that alternating intervals of high and low hurricane landfall occurrences may continue on multidecadal timescales along the northern Gulf Coast. However, given the short length of the instrumental record, the actual frequency and stability of the AMO are uncertain, and additional AMO proxy records are needed to establish the character of multidecadal-scale SST variability in the North Atlantic. ?? 2009 US Government.

Speleothem records decadal to multidecadal hydroclimate variations in southwestern Morocco during the last millennium

NASA Astrophysics Data System (ADS)

Ait Brahim, Yassine; Cheng, Hai; Sifeddine, Abdelfettah; Wassenburg, Jasper A.; Cruz, Francisco W.; Khodri, Myriam; Sha, Lijuan; Pérez-Zanón, Núria; Beraaouz, El Hassane; Apaéstegui, James; Guyot, Jean-Loup; Jochum, Klaus Peter; Bouchaou, Lhoussaine

2017-10-01

This study presents the first well-dated high resolution stable isotope (δ18 O and δ13 C) and trace element (Mg and Sr) speleothem records from southwestern Morocco covering the last 1000 yrs. Our records reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords with prevailing dry conditions during the Medieval Climate Anomaly (MCA), wetter conditions during the second part of the Little Ice Age (LIA), and a trend towards dry conditions during the current warm period. These coherent regional climate signals suggest common climate controls. Statistical analyses indicate that the climate of southwestern Morocco remained under the combined influence of both the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) over the last millennium. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively.

Predictability of North Atlantic Multidecadal Climate Variability

PubMed

Griffies; Bryan

1997-01-10

Atmospheric weather systems become unpredictable beyond a few weeks, but climate variations can be predictable over much longer periods because of the coupling of the ocean and atmosphere. With the use of a global coupled ocean-atmosphere model, it is shown that the North Atlantic may have climatic predictability on the order of a decade or longer. These results suggest that variations of the dominant multidecadal sea surface temperature patterns in the North Atlantic, which have been associated with changes in climate over Eurasia, can be predicted if an adequate and sustainable system for monitoring the Atlantic Ocean exists.

European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling.

PubMed

Bastos, Ana; Janssens, Ivan A; Gouveia, Célia M; Trigo, Ricardo M; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W

2016-01-18

Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models.

Insights into Atlantic multidecadal variability using the Last Millennium Reanalysis framework

NASA Astrophysics Data System (ADS)

Singh, Hansi K. A.; Hakim, Gregory J.; Tardif, Robert; Emile-Geay, Julien; Noone, David C.

2018-02-01

The Last Millennium Reanalysis (LMR) employs a data assimilation approach to reconstruct climate fields from annually resolved proxy data over years 0-2000 CE. We use the LMR to examine Atlantic multidecadal variability (AMV) over the last 2 millennia and find several robust thermodynamic features associated with a positive Atlantic Multidecadal Oscillation (AMO) index that reveal a dynamically consistent pattern of variability: the Atlantic and most continents warm; sea ice thins over the Arctic and retreats over the Greenland, Iceland, and Norwegian seas; and equatorial precipitation shifts northward. The latter is consistent with anomalous southward energy transport mediated by the atmosphere. Net downward shortwave radiation increases at both the top of the atmosphere and the surface, indicating a decrease in planetary albedo, likely due to a decrease in low clouds. Heat is absorbed by the climate system and the oceans warm. Wavelet analysis of the AMO time series shows a reddening of the frequency spectrum on the 50- to 100-year timescale, but no evidence of a distinct multidecadal or centennial spectral peak. This latter result is insensitive to both the choice of prior model and the calibration dataset used in the data assimilation algorithm, suggesting that the lack of a distinct multidecadal spectral peak is a robust result.

The Oceanic Contribution to Atlantic Multi-Decadal Variability

NASA Astrophysics Data System (ADS)

Wills, R. C.; Armour, K.; Battisti, D. S.; Hartmann, D. L.

2017-12-01

Atlantic multi-decadal variability (AMV) is typically associated with variability in ocean heat transport (OHT) by the Atlantic Meridional Overturning Circulation (AMOC). However, recent work has cast doubt on this connection by showing that slab-ocean climate models, in which OHT cannot vary, exhibit similar variability. Here, we apply low-frequency component analysis to isolate the variability of Atlantic sea-surface temperatures (SSTs) that occurs on decadal and longer time scales. In observations and in pre-industrial control simulations of comprehensive climate models, we find that AMV is confined to the extratropics, with the strongest temperature anomalies in the North Atlantic subpolar gyre. We show that warm subpolar temperatures are associated with a strengthened AMOC, increased poleward OHT, and local heat fluxes from the ocean into the atmosphere. In contrast, the traditional index of AMV based on the basin-averaged SST anomaly shows warm temperatures preceded by heat fluxes from the atmosphere into the ocean, consistent with the atmosphere driving this variability, and shows a weak relationship with AMOC. The autocorrelation time of the basin-averaged SST index is 1 year compared to an autocorrelation time of 5 years for the variability of subpolar temperatures. This shows that multi-decadal variability of Atlantic SSTs is sustained by OHT variability associated with AMOC, while atmosphere-driven SST variability, such as exists in slab-ocean models, contributes primarily on interannual time scales.

Solar forcing synchronizes decadal North Atlantic climate variability.

PubMed

Thiéblemont, Rémi; Matthes, Katja; Omrani, Nour-Eddine; Kodera, Kunihiko; Hansen, Felicitas

2015-09-15

Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth's regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1-2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface.

Pacific and Atlantic Ocean influences on multidecadal drought frequency in the United States

USGS Publications Warehouse

McCabe, G.J.; Palecki, M.A.; Betancourt, J.L.

2004-01-01

More than half (52%) of the spatial and temporal variance in multidecadal drought frequency over the conterminous United States is attributable to the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). An additional 22% of the variance in drought frequency is related to a complex spatial pattern of positive and negative trends in drought occurrence possibly related to increasing Northern Hemisphere temperatures or some other unidirectional climate trend. Recent droughts with broad impacts over the conterminous U.S. (1996, 1999-2002) were associated with North Atlantic warming (positive AMO) and north-eastern and tropical Pacific cooling (negative PDO). Much of the long-term predictability of drought frequency may reside in the multidecadal behavior of the North Atlantic Ocean. Should the current positive AMO (warm North Atlantic) conditions persist into the upcoming decade, we suggest two possible drought scenarios that resemble the continental-scale patterns of the 1930s (positive PDO) and 1950s (negative PDO) drought.

The role of the Atlantic Water in multidecadal ocean variability in the Nordic and Barents Seas

NASA Astrophysics Data System (ADS)

Yashayaev, Igor; Seidov, Dan

2015-03-01

The focus of this work is on the temporal and spatial variability of the Atlantic Water (AW). We analyze the existing historic hydrographic data from the World Ocean Database to document the long-term variability of the AW throughflow across the Norwegian Sea to the western Barents Sea. Interannual-to-multidecadal variability of water temperature, salinity and density are analyzed along six composite sections crossing the AW flow and coastal currents at six selected locations. The stations are lined up from southwest to northeast - from the northern North Sea (69°N) throughout the Norwegian Sea to the Kola Section in the Barents Sea (33°30‧E). The changing volume and characteristics of the AW throughflow dominate the hydrographic variability on decadal and longer time scales in the studied area. We examine the role of fluctuations of the volume of inflow versus the variable local factors, such as the air-sea interaction and mixing with the fresh coastal and cold Arctic waters, in controlling the long-term regional variability. It is shown that the volume of the AW, passing through the area and affecting the position of the outer edge of the warm and saline core, correlates well with temperature and salinity averaged over the central portions of the studied sections. The coastal flow (mostly associated with the Norwegian Coastal Current flowing over the continental shelf) is largely controlled by seasonal local heat and freshwater impacts. Temperature records at all six lines show a warming trend superimposed on a series of relatively warm and cold periods, which in most cases follow, with a delay of four to five years, the periods of relatively low and high North Atlantic Oscillation (NAO), and the periods of relatively high and low Atlantic Multidecadal Oscillation (AMO), respectively. In general, there is a relatively high correlation between the year-to-year changes of the NAO and AMO indices, which is to some extent reflected in the (delayed) AW temperature

Influence of North Atlantic modes on European climate extremes

NASA Astrophysics Data System (ADS)

Proemmel, K.; Cubasch, U.

2017-12-01

It is well known that the North Atlantic strongly influences European climate. Only few studies exist that focus on its impact on climate extremes. We are interested in these extremes and the processes and mechanisms behind it. For the analysis of the North Atlantic Oscillation (NAO) we use simulations performed with the Max Planck Institute for Meteorology Earth System Model (MPI-ESM). The NAO has a strong impact especially on European winter and the changes in minimum temperature are even larger than in maximum temperature. The impact of the Atlantic Multi-decadal Variability (AMV) on climate extremes is analyzed in ECHAM6 simulations forced with AMV warm and AMV cold sea surface temperature patterns. We analyze different extreme indices and try to understand the processes.

European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

PubMed Central

Bastos, Ana; Janssens, Ivan A.; Gouveia, Célia M.; Trigo, Ricardo M.; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W.

2016-01-01

Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO–EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models. PMID:26777730

The impact of AMO and NAO in Western Iberia during the Late Holocene

NASA Astrophysics Data System (ADS)

Hernandez, A.; Leira, M.; Trigo, R.; Vázquez-Loureiro, D.; Carballeira, R.; Sáez, A.

2016-12-01

High mountain lakes in the Iberian Peninsula are particularly sensitive to the influence of North Atlantic large-scale modes of climate variability due to their geographical position and the reduced anthropic disturbances. In this context, Serra da Estrela (Portugal), the westernmost range of the Sistema Central, constitutes a physical barrier to air masses coming from the Atlantic Ocean. However, long-term climate reconstructions have not yet been conducted. We present a climate reconstruction of this region based on facies analysis, X-ray fluorescence core scanning, elemental and isotope geochemistry on bulk organic matter and a preliminary study of diatom assemblages from the sedimentary record of Lake Peixão (1677 m a.s.l.; Serra da Estrela) for the last ca. 3500 years. A multivariate statistical analysis has been performed to recognize the main environmental factors controlling the sedimentary infill. Our results reveal that two main processes explain the 70% of the total variance. Thus, changes in primary productivity, reflected in organic matter accumulation, and variations in runoff, related to external particles input, explain 53% and 17% respectively. Additionally, evidence of changes in productivity and water level regime recorded as variations in diatom assemblages correlate well with our interpretations. A comparison between the lake productivity changes and previous Atlantic Multidecadal Oscillation (AMO) reconstructions shows a good correlation, suggesting this climate mode as the main driver over lacustrine primary productivity at multi-decadal scales. In turn, changes in terrigenous inputs, linked to precipitation, seem to be more influenced by the winter North Atlantic Oscillation (NAO) variability. Hence, our results highlight that although the climate regime in this area is clearly influenced by the NAO, the AMO also plays a key role at long-term time-scales.

Influence of the Summer NAO on the Spring-NAO-Based Predictability of the East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Zheng, Fei

2017-04-01

The dominant mode of atmospheric circulation over the North Atlantic region is the North Atlantic Oscillation (NAO). The boreal spring NAO may imprint its signal on contemporaneous sea surface temperature (SST), leading to a North Atlantic SST tripolar pattern (NAST). This pattern persists into the following summer and modulates the East Asian summer monsoon (EASM). Previous studies have shown that the summer NAST is caused mainly by the preceding spring NAO, whereas the contemporaneous summer NAO plays a secondary role. The results of this study illustrate that, even if the summer NAO plays a secondary role, it may also perturb summer SST anomalies caused by the spring NAO. There are two types of perturbation caused by the summer NAO. If the spring and summer NAO patterns have the same (opposite) polarities, the summer NAST tends to be enhanced (reduced) by the summer NAO, and the correlation between the spring NAO and EASM is usually stronger (weaker). In the former (latter) case, the spring-NAO-based prediction of the EASM tends to have better (limited) skill. These results indicate that it is important to consider the evolution of the NAO when forecasting the EASM, particular when there is a clear reversal in the polarity of the NAO, because it may impair the spring-NAO-based EASM prediction.

Imprint of the Atlantic Multidecadal Oscillation on Tree-Ring Widths in Northeastern Asia since 1568

PubMed Central

Wang, Xiaochun; Brown, Peter M.; Zhang, Yanni; Song, Laiping

2011-01-01

We present a new tree-ring reconstruction of the Atlantic Multidecadal Oscillation (AMO) spanning 1568–2007 CE from northeast Asia. Comparison of the instrumental AMO index, an existing tree-ring based AMO reconstruction, and this new record show strongly similar annual to multidecadal patterns of variation over the last 440 years. Warm phases of the AMO are related to increases in growth of Scots pine trees and moisture availability in northeast China and central eastern Siberia. Multi-tape method (MTM) and cross-wavelet analyses indicate that robust multidecadal (∼64–128 years) variability is present throughout the new proxy record. Our results have important implications concerning the influence of North Atlantic sea surface temperatures on East Asian climate, and provide support for the possibility of an AMO signature on global multidecadal climate variability. PMID:21818380

Effect of Modulation of ENSO by Decadal and Multidecadal Ocean-Atmospheric Oscillations on Continental US Streamflows

NASA Astrophysics Data System (ADS)

Singh, S.; Abebe, A.; Srivastava, P.; Chaubey, I.

2017-12-01

Evaluation of the influences of individual and coupled oceanic-atmospheric oscillations on streamflow at a regional scale in the United States is the focus of this study. The main climatic oscillations considered in this study are: El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO). Unimpacted or minimally impacted by water management streamflow data from the Model Parameter Estimation Experiment (MOPEX) were used in this study. Two robust and novel non-parametric tests, namely, the rank based partial least square (PLS) and the Joint Rank Fit (JRFit) procedures were used to identify the individual and coupled effect of oscillations on streamflow across continental U.S. (CONUS), respectively. Moreover, the interactive effects of ENSO with decadal and multidecadal cycles were tested and quantified using the JRFit interaction test. The analysis of ENSO indicated higher streamflows during La Niña phase compared to the El Niño phase in Northwest, Northeast and the lower part of Ohio Valley while the opposite occurs for rest of the climatic regions in US. Two distinct climate regions (Northwest and Southeast) were identified from the PDO analysis where PDO negative phase results in increased streamflow than PDO positive phase. Consistent negative and positive correlated regions around the CONUS were identified for AMO and NAO, respectively. The interaction test of ENSO with decadal and multidecadal oscillations showed that El Niño is modulated by the negative phase of PDO and NAO, and the positive phase of AMO, respectively, in the Upper Midwest. However, La Niña is modulated by the positive phase of AMO and PDO in Ohio Valley and Northeast while in Southeast and the South it is modulated by AMO negative phase. Results of this study will assist water managers to understand the streamflow change patterns across the CONUS at decadal and multi-decadal time scales. The

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

2011-01-01

Atmospheric blocking over the northern North Atlantic involves isolation of large regions of air from the westerly circulation for 5-14 days or more. From a recent 20th century atmospheric reanalysis (1,2) winters with more frequent blocking persist over several decades and correspond to a warm North Atlantic Ocean, in-phase with Atlantic multi-decadal ocean variability (AMV). Ocean circulation is forced by wind-stress curl and related air/sea heat exchange, and we find that their space-time structure is associated with dominant blocking patterns: weaker ocean gyres and weaker heat exchange contribute to the warm phase of AMV. Increased blocking activity extending from Greenland to British Isles is evident when winter blocking days of the cold years (1900-1929) are subtracted from those of the warm years (1939-1968).

Tropical Pacific forcing on decadal-to-centennial NAO-dominated precipitation variability in northern Mediterranean over the past 6500 years

NASA Astrophysics Data System (ADS)

Hu, H. M.; Shen, C. C.; Michel, V.; Jiang, X.; Mii, H. S.; Wang, Y.; Valensi, P.

2017-12-01

We present a multi-annual-resolved absolute-dated stalagmite-inferred precipitation record, with age precision as good as ±2 years, from northern Italy, to reflect North Atlantic Oscillation (NAO) dynamics since 6.5 ka (thousand years ago, before 1950 C.E.). Our record features millennial precipitation fluctuations punctuated by several centennial-scale drought periods centered at 5.6, 6.2, 4.2, 3.0 and 2.3 ka. The phase relationship with previous NAO-sensitive records suggests a multi-millennial southward migration of the northern Westerlies and enhanced NAO variability from the middle- to late-Holocene. We also found the multi-decadal to centennial rainfall amount could dramatically vary within few decades, possibly affecting ancient Mediterranean civilizations. Concurrence between northern Mediterranean precipitation and western tropical Pacific sea surface temperature records suggests the remote forcing on this NAO-dominated rainfall. We argue that the irregular NAO change nowadays could be related to high frequency of El Niño-Southern Oscillation events and might cause an inevitable abrupt hydroclimate change and irreparable impacts on the regional human society in the near future.

The role of clouds in driving North Atlantic multi-decadal climate variability in observations and models

NASA Astrophysics Data System (ADS)

Clement, A. C.; Bellomo, K.; Murphy, L.

2013-12-01

Large scale warming and cooling periods of the North Atlantic is known as the Atlantic Multidecadal Oscillation (AMO). The pattern of warming and cooling in the North Atlantic Ocean over the 20th century that has a characteristic spatial structure with maximum warming in the mid-latitudes and subtropics. This has been most often attributed to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), which in turn affects poleward heat transport. A recent modeling study by Booth et al. (2012), however, suggested that aerosols can explain both the spatial pattern and temporal history of Atlantic SST through indirect effects of aerosols on cloud cover; although this idea is controversial (Zhang et al., 2013). We have found observational evidence that changes in cloud amount can drive SST changes on multi-decadal timescale. We hypothesize that a positive local feedback between SST and cloud radiative effect amplifies SST and gives rise to the observed pattern of SST change. During cool North Atlantic periods, a southward shift of the ITCZ strengthens the trade winds in the tropical North Atlantic and increases low-level cloud cover, which acts to amplify the SST cooling in the North Atlantic. During warm periods in the North Atlantic, the opposite response occurs. We are testing whether the amplitude of this feedback is realistically simulated in the CMIP5 models, and whether inter-model differences in the amplitude of the feedback can explain differences in model simulations of Atlantic multi-decadal variability.

The effect of the East Atlantic pattern on the precipitation δ18O-NAO relationship in Europe

NASA Astrophysics Data System (ADS)

Comas-Bru, L.; McDermott, F.; Werner, M.

2016-10-01

The North Atlantic Oscillation (NAO) is known to influence precipitation δ18O (δ18Op) through its control on air temperature and on the trajectory of the westerly winds that carry moisture onto Europe during boreal winters. Hence, paleoclimate studies seeking to reconstruct the NAO can exploit the δ18O signal that is commonly preserved in natural archives such as stalagmites, ice cores, tree rings and lake sediments. However, such reconstructions should consider the uncertainties that arise from non-stationarities in the δ18Op-NAO relationship. Here, new insights into the causes of these temporal non-stationarities are presented for the European region using both observations (GNIP database) and the output of an isotope-enabled general circulation model (ECHAM5-wiso). The results show that, although the East Atlantic (EA) pattern is generally uncorrelated to δ18Op during the instrumental period, its polarity affects the δ18Op-NAO relationship. Non-stationarities in this relationship result from spatial shifts of the δ18Op-NAO correlated areas as a consequence of different NAO/EA combinations. These shifts are consistent with those reported previously for NAO-winter climate variables and the resulting non-stationarities mean that δ18O-based NAO reconstructions could be compromised if the balance of positive and negative NAO/EA states differs substantially in a calibration period compared with the period of interest in the past. The same approach has been followed to assess the relationships between δ18Op and both winter total precipitation and winter mean surface air temperature, with similar results. Crucially, this study also identifies regions within Europe where temporal changes in the NAO, air temperature and precipitation can be more robustly reconstructed using δ18O time series from natural archives, irrespective of concomitant changes in the EA.

Cold season Africa-Asia multidecadal teleconnection pattern and its relation to the Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Sun, Cheng; Li, Jianping; Ding, Ruiqiang; Jin, Ze

2017-06-01

A prominent teleconnection pattern of multidecadal variability of cold season (November to April) upper-level atmospheric circulation over North Africa and Eurasia (NA-EA) is revealed by empirical orthogonal function analysis of the Twentieth Century Reanalysis data. This teleconnection pattern is characterized by an eastward propagating wave train with a zonal wavenumber of 5-6 between 20° and 40°N, extending from the northwest coast of Africa to East Asia, and thus is referred to as the Africa-Asia multidecadal teleconnection pattern (AAMT). One-point correlation maps show that the teleconnectivity of AAMT is strong and further demonstrate the existence of the AAMT. The AAMT shapes the spatial structure of multidecadal change in atmospheric circulation over the NA-EA region, and in particular the AAMT pattern and associated fields show similar structures to the change occurring around the early 1960s. A strong in-phase relationship is observed between the AAMT and Atlantic multidecadal variability (AMV) and this connection is mainly due to Rossby wave dynamics. Barotropic modeling results suggest that the upper-level Rossby wave source generated by the AMV can excite the AAMT wave train, and Rossby wave ray tracing analysis further highlights the role of the Asian jet stream in guiding the wave train to East Asia. The AAMT acts as an atmospheric bridge conveying the influence of AMV onto the downstream multidecadal climate variability. The AMV is closely related to the coordinated change in surface and tropospheric air temperatures over Northwest Africa, the Arabian Peninsula and Central China, which may result from the adiabatic expansion/compression of air associated with the AAMT.

Influences of North Atlantic Oscillation (NAO) on warm season temperature and crop yields in the southwestern US

NASA Astrophysics Data System (ADS)

Myoung, B.; Kim, S.; Kim, J.; Kafatos, M.

2013-12-01

Despite advancements in agricultural technology, agricultural productivity remains vulnerable to extreme meteorological conditions. This study has found significant impacts of North Atlantic Oscillation (NAO) on extreme temperatures and in turn on crop yields in the Southwestern United States (SW US) region. Analyses of multi-year data of observed temperatures and simulated maize yields reveal that NAO affects positively the daily temperature maxima and minima in the green-up periods (March-June) and that the response of maize yields to NAO varies according to the climatological mean temperatures. In warmer regions, a combination of above-normal NAO in the planting periods and below-normal NAO in the growing periods is favorable for high maize yields by reducing extremely cold days during the planting periods and extremely hot days in the later periods, respectively. In colder regions, continuously above-normal NAO conditions favor higher yields via above normal thermal conditions. Results in this study suggest that NAO predictions can benefit agricultural planning in SW US.

Impacts of the EA and SCA patterns on the 20th century NAO-winter precipitation relationship in Europe

NASA Astrophysics Data System (ADS)

Comas-Bru, Laia; McDermott, Frank

2013-04-01

Much of the 20th century multi-decadal variability in the NAO-winter precipitation relationship over the N. Atlantic / European sector can be ascribed to the combined effects of the North Atlantic Oscillation (NAO) and either the East Atlantic pattern (EA) or the Scandinavian pattern (SCA). The NAO, EA and SCA indices employed here are defined as the three leading vectors of the cross-correlation matrix calculated from monthly sea-level pressure anomalies for 138 complete winters from the 20CRv2 dataset (Compo et al., 2011). Winter precipitation data over Europe for the entire 20th century is derived from the high resolution CRU-TS3.1 climate dataset (Mitchell and Jones, 2005). Here we document for the first time, that different NAO/EA and NAO/SCA combinations systematically influence winter precipitation conditions in Europe as a consequence of NAO dipole migrations. We find that the zero-correlated line of the NAO-winter precipitation relationship migrates southwards when the EA is in the opposite phase to the NAO. This can be related to a south-westwards migration of the NAO dipole under these conditions, as shown by teleconnectivity maps. Similarly, a clockwise movement of the NAO-winter climate correlated areas occurs when the phase of the SCA is opposite to that of the NAO, reflecting a clockwise movement of the NAO dipole under these conditions. An important implication of these migrations is that they influence the spatial and temporal stationarity of climate-NAO relationships. As a result, the link between winter precipitation patterns and the NAO is not straightforward in some regions such as the southern UK, Ireland and France. For instance, much of the inter-annual variability in the N-S winter precipitation gradient in the UK, originally attributed to inter-annual and inter-decadal variability of the NAO, reflects the migration of the NAO dipole, linked to linear combinations of the NAO and the EA. Our results indicate that when the N-S winter

The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature.

PubMed

Yamamoto, Ayako; Palter, Jaime B

2016-03-15

Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air-sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline.

The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature

PubMed Central

Yamamoto, Ayako; Palter, Jaime B.

2016-01-01

Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air–sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline. PMID:26975331

Forced and Internal Multi-Decadal Variability in the North Atlantic and their Climate Impacts

NASA Astrophysics Data System (ADS)

Ting, M.

2017-12-01

Atlantic Multidecadal Variability (AMV), a basin-wide North Atlantic sea surface temperature warming or cooling pattern varying on decadal and longer time scales, is one of the most important climate variations in the Atlantic basin. The AMV has shown to be associated with significant climate impacts regionally and globally, from Atlantic hurricane activities, frequency and severity of droughts across North America, as well as rainfall anomalies across the African Sahel and northeast Brazil. Despite the important impacts of the AMV, its mechanisms are not completely understood. In particular, it is not clear how much of the historical Atlantic SST fluctuations were forced by anthropogenic sources such as greenhouse warming and aerosol cooling, versus driven internally by changes in the coupled ocean-atmosphere processes in the Atlantic. Using climate models such as the NCAR large ensemble simulations, we were able to successfully separate the forced and internally generated North Atlantic sea surface temperature anomalies through a signal-to-noise maximizing Empirical Orthogonal Function (S/N EOF) analysis method. Two forced modes were identified with one representing a hemispherical symmetric mode and one asymmetric mode. The symmetric mode largely represents the greenhouse forced component while the asymmetric mode resembles the anthropogenic aerosol forcing. When statistically removing both of the forced modes, the residual multidecadal Atlantic SST variability shows a very similar structure as the AMV in the preindustrial simulation. The distinct climate impacts of each of these modes are also identified and the implications and challenges for decadal climate prediction will be discussed.

A Tropical View of Atlantic Multidecadal SST Variability over the Last Two Millennia

NASA Astrophysics Data System (ADS)

Wurtzel, J. B.; Black, D. E.; Thunell, R.; Peterson, L. C.; Tappa, E. J.; Rahman, S.

2011-12-01

Instrumental and proxy-reconstructions show the existence of a 60-80 year periodicity in Atlantic sea surface temperature (SST), known as the Atlantic Multidecadal Oscillation (AMO). The AMO is correlated with circum-tropical Atlantic climate phenomena such as Sahel and Nordeste rainfall, as well as Atlantic hurricane patterns. Though it has been suggested that the AMO is controlled by thermohaline circulation, much debate exists as to whether the SST fluctuations are a result of anthropogenic forcing or natural climate variability. Our ability to address this issue has been limited by instrumental SST records that rarely extend back more than 50-100 years and proxy reconstructions that are largely terrestrial-based. Here we present a high-resolution marine sediment-derived reconstruction of seasonal tropical Atlantic SSTs from the Cariaco Basin spanning the past two millennia that is correlated with instrumental SSTs and the AMO for the period of overlap. The full record demonstrates that seasonality is largely controlled by variations in winter/spring SST. Wavelet analysis of the proxy data suggest that variability in the 60-80 year band evolved 250 years ago, while 40-60 year periodicities dominate earlier parts of the record. At least over the last millennia, multidecadal- and centennial- scale SST variability in the tropical Atlantic appears related to Atlantic meridional overturning circulation (AMOC) fluctuations and its associated northward heat transport that in turn may be driven by solar variability. An inverse correlation between the tropical proxy annual average SST record and Δ14C indicates that the tropics experienced positive SST anomalies during times of reduced solar activity, possibly as a result of decreased AMOC strength (Figure 1).

Atlantic multi-decadal oscillation influence on weather regimes over Europe and the Mediterranean in spring and summer

NASA Astrophysics Data System (ADS)

Zampieri, M.; Toreti, A.; Schindler, A.; Scoccimarro, E.; Gualdi, S.

2017-04-01

We analyze the influence of the Atlantic sea surface temperature multi-decadal variability on the day-by-day sequence of large-scale atmospheric circulation patterns (i.e. the ;weather regimes;) over the Euro-Atlantic region. In particular, we examine of occurrence of weather regimes from 1871 to present. This analysis is conducted by applying a clustering technique on the daily mean sea level pressure field provided by the 20th Century Reanalysis project, which was successfully applied in other studies focused on the Atlantic Multi-decadal Oscillation (AMO). In spring and summer, results show significant changes in the frequencies of certain weather regimes associated with the phase shifts of the AMO. These changes are consistent with the seasonal surface pressure, precipitation, and temperature anomalies associated with the AMO shifts in Europe.

Modulation of the Aleutian-Icelandic Low Seesaw and Its Surface Impacts by the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Li, F.; Orsolini, Y. J.

2017-12-01

Early studies suggested that the Aleutian-Icelandic low seesaw (AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation (AMO) during late winter (February-March) is explored with observational data. It is shown that, in the cold phase of the AMO (AMO|-), a clear AIS is established, while this is not the case in the warm phase of the AMO (AMO|+). The surface climate over Eurasia is significantly influenced by the AMO's modulation of the Aleutian low (AL). For example, the weak AL in AMO|- displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe, but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+. The mechanism underlying the influence of AMO|- on the AIS can be described as follows: AMO|- weakens the upward component of the Eliassen-Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro-Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific-North America-Atlantic pattern, and resulting in a significant AIS at the surface during late winter.

Modulation of the Aleutian-Icelandic low seesaw and its surface impacts by the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Li, Fei; Orsolini, Yvan J.; Wang, Huijun; Gao, Yongqi; He, Shengping

2018-01-01

Early studies suggested that the Aleutian-Icelandic low seesaw (AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation (AMO) during late winter (February-March) is explored with observational data. It is shown that, in the cold phase of the AMO (AMO|-), a clear AIS is established, while this is not the case in the warm phase of the AMO (AMO|+). The surface climate over Eurasia is significantly influenced by the AMO's modulation of the Aleutian low (AL). For example, the weak AL in AMO|- displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe, but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+. The mechanism underlying the influence of AMO|- on the AIS can be described as follows: AMO|- weakens the upward component of the Eliassen-Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro-Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific-North America-Atlantic pattern, and resulting in a significant AIS at the surface during late winter.

The influences of the AMO and NAO on an Iberian alpine lake during the Late Holocene

NASA Astrophysics Data System (ADS)

Hernández, Armand; Leira, Manel; Trigo, Ricardo; Vázquez-Loureiro, David; Carballeira, Rafael; Sáez, Alberto

2017-04-01

High mountain lakes, usually oligotrophic, in the Iberian Peninsula are particularly sensitive to the influence of North Atlantic large-scale modes of climate variability due to their geographical position and the reduced direct anthropic disturbances. In this context, Serra da Estrela (Portugal), in the westernmost of the Sistema Central Range, constitutes a physical barrier to air masses coming from the Atlantic Ocean. However, long-term climate reconstructions have not yet been conducted. We present a climate reconstruction in terms of precipitation and temperature changes of this setting based on facies analysis, X-ray fluorescence core scanning, elemental and isotope geochemistry on bulk organic matter and a preliminary study of diatom assemblages from the sedimentary record of Lake Peixão (1677 m a.s.l.; Serra da Estrela) for the last ca. 3500 years. A multivariate statistical analysis has been performed to recognize the main environmental factors controlling the lake sedimentation. Our results reveal that two main processes explain 70% of the total variance, with PC1 (accumulation of siliciclastic material vs organic matter), and PC2 (variations in lacustrine productivity, related to nutrient inputs from the catchment), explaining 53% and 17% respectively. In mountain lakes, siliciclastic and/or external organic matter accumulation tend to be governed by the snowmelt which, in turn, are frequently controlled by winter and spring temperatures. On the other hand, lake productivity, usually limited by phosphorus and nitrogen, is dependent of internal recycling and/or external inputs, mainly by catchment leaching (climatically driven by summer precipitation) and atmospheric deposition (anthropic influence). The results from Lake Peixão have been compared to other Western Iberia and Northeastern Atlantic records, as well as the Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO) indices. Thus, a tentative Late Holocene climate

The role of historical forcings in simulating the observed Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Goes, L. M.; Cane, M. A.; Bellomo, K.; Clement, A. C.

2016-12-01

The variation in basin-wide North Atlantic sea surface temperatures (SST), known as the Atlantic multidecadal oscillation (AMO), affects climate throughout the Northern Hemisphere and tropics, yet the forcing mechanisms are not fully understood. Here, we analyze the AMO in the Coupled Model Intercomparison Project phase 5 (CMIP5) Pre-industrial (PI) and Historical (HIST) simulations to determine the role of historical climate forcings in producing the observed 20th century shifts in the AMO (OBS, 1865-2005). We evaluate whether the agreement between models and observations is better with historical forcings or without forcing - i.e. due to processes internal to the climate system, such as the Atlantic Meridional Overturning Circulation (AMOC). To do this we draw 141-year samples from 38 CMIP5 PI runs and compare the correlation between the PI and HIST AMO to the observed AMO. We find that in the majority of models (24 out of 38), it is very unlikely (less than 10% chance) that the unforced simulations produce agreement with observations that are as high as the forced simulations. We also compare the amplitude of the simulated AMO and find that 87% of models produce multi-decadal variance in the AMO with historical forcings that is very likely higher than without forcing, but most models underestimate the variance of the observed AMO. This indicates that over the 20th century external rather than internal forcing was crucial in setting the pace, phase and amplitude of the AMO.

Using the Convergent Cross Mapping method to test causality between Arctic Oscillation / North Atlantic Oscillation and Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Gutowska, Dorota; Piskozub, Jacek

2017-04-01

There is a vast literature body on the climate indices and processes they represent. A large part of it deals with "teleconnections" or causal relations between them. However until recently time lagged correlations was the best tool of studying causation. However no correlation (even lagged) proves causation. We use a recently developed method of studying casual relations between short time series, Convergent Cross Mapping (CCM), to search for causation between the atmospheric (AO and NAO) and oceanic (AMO) indices. The version we have chosen (available as an R language package rEDM) allows for comparing time series with time lags. This work builds on previous one, showing with time-lagged correlations that AO/NAO precedes AMO by about 15 years and at the same time is preceded by AMO (but with an inverted sign) also by the same amount of time. This behaviour is identical to the relationship of a sine and cosine with the same period. This may suggest that the multidecadal oscillatory parts of the atmospheric and oceanic indices represent the same global-scale set of processes. In other words they may be symptoms of the same oscillation. The aim of present study is to test this hypothesis with a tool created specially for discovering causal relationships in dynamic systems.

An electrical analogy relating the Atlantic multidecadal oscillation to the Atlantic meridional overturning circulation.

PubMed

Kurtz, Bruce E

2014-01-01

The Atlantic meridional overturning circulation (AMOC) is the northward flow of surface water to subpolar latitudes where deepwater is formed, balanced by southward abyssal flow and upwelling in the vicinity of the Southern Ocean. It is generally accepted that AMOC flow oscillates with a period of 60-80 years, creating a regular variation in North Atlantic sea surface temperature known as the Atlantic multidecadal oscillation (AMO). This article attempts to answer two questions: how is the AMOC driven and why does it oscillate? Using methods commonly employed by chemical engineers for analyzing processes involving flowing liquids, apparently not previously applied to trying to understand the AMOC, an equation is developed for AMOC flow as a function of the meridional density gradient or the corresponding temperature gradient. The equation is based on the similarity between the AMOC and an industrial thermosyphon loop cooler, which circulates a heat transfer liquid without using a mechanical pump. Extending this equation with an analogy between the flow of heat and electricity explains why the AMOC flow oscillates and what determines its period. Calculated values for AMOC flow and AMO oscillation period are in good agreement with measured values.

An Electrical Analogy Relating the Atlantic Multidecadal Oscillation to the Atlantic Meridional Overturning Circulation

PubMed Central

Kurtz, Bruce E.

2014-01-01

The Atlantic meridional overturning circulation (AMOC) is the northward flow of surface water to subpolar latitudes where deepwater is formed, balanced by southward abyssal flow and upwelling in the vicinity of the Southern Ocean. It is generally accepted that AMOC flow oscillates with a period of 60–80 years, creating a regular variation in North Atlantic sea surface temperature known as the Atlantic multidecadal oscillation (AMO). This article attempts to answer two questions: how is the AMOC driven and why does it oscillate? Using methods commonly employed by chemical engineers for analyzing processes involving flowing liquids, apparently not previously applied to trying to understand the AMOC, an equation is developed for AMOC flow as a function of the meridional density gradient or the corresponding temperature gradient. The equation is based on the similarity between the AMOC and an industrial thermosyphon loop cooler, which circulates a heat transfer liquid without using a mechanical pump. Extending this equation with an analogy between the flow of heat and electricity explains why the AMOC flow oscillates and what determines its period. Calculated values for AMOC flow and AMO oscillation period are in good agreement with measured values. PMID:24940739

The Atlantic Multidecadal Oscillation without a role for ocean circulation.

PubMed

Clement, Amy; Bellomo, Katinka; Murphy, Lisa N; Cane, Mark A; Mauritsen, Thorsten; Rädel, Gaby; Stevens, Bjorn

2015-10-16

The Atlantic Multidecadal Oscillation (AMO) is a major mode of climate variability with important societal impacts. Most previous explanations identify the driver of the AMO as the ocean circulation, specifically the Atlantic Meridional Overturning Circulation (AMOC). Here we show that the main features of the observed AMO are reproduced in models where the ocean heat transport is prescribed and thus cannot be the driver. Allowing the ocean circulation to interact with the atmosphere does not significantly alter the characteristics of the AMO in the current generation of climate models. These results suggest that the AMO is the response to stochastic forcing from the mid-latitude atmospheric circulation, with thermal coupling playing a role in the tropics. In this view, the AMOC and other ocean circulation changes would be largely a response to, not a cause of, the AMO. Copyright © 2015, American Association for the Advancement of Science.

Cod Collapse and Climate in the North Atlantic

NASA Astrophysics Data System (ADS)

Oremus, K. L.; Meng, K. C.; Gaines, S.

2016-02-01

Understanding the determinants of fish population dynamics is crucial to the recovery of many fisheries. Current research emphasizes the role of environmental conditions in driving fish populations, but the magnitude of and mechanisms behind these effects on crucial populations are not well established. Despite aggressive management efforts, New England cod fisheries have been in decline for several decades and have now reached unprecedented lows. We find a strong negative relationship between the North Atlantic Oscillation (NAO) and subsequent adult cod biomass and catch. In the Gulf of Maine fishery, a 1-unit NAO increase is associated with a 13% decrease in the biomass of age-1 cod the following year, a decrease that persists as the affected cohort matures. We further detect that a 1-unit NAO increase can lower commercial catch for up to 19 subsequent years, suggesting that fishing practices may be inadvertently exacerbating NAO's direct biological effects. These results imply that 18% and 32% of the overall decline in adult biomass and catch, respectively, since 1980 can be attributed to the NAO's recent multi-decadal positive phase. The Georges Bank cod fishery displays similar patterns. Because there is a delay between an NAO event and subsequent declines in adult biomass, our finding implies that already observed NAO events can be used in stock forecasts, providing lead time for adaptive policy. More broadly, our approach can inform forecasting efforts for other fisheries strongly affected by natural and anthropogenic climatic variation.

Interactive influence of the Atlantic and Pacific climates and their contribution to the multidecadal variations of global temperature and precipitation.

NASA Astrophysics Data System (ADS)

Barcikowska, M. J.; Knutson, T. R.; Zhang, R.

2016-12-01

This study investigates mechanisms and global-scale climate impacts of multidecadal climate variability. Here we show, using observations and CSIRO-Mk3.6.0 model control run, that multidecadal variability of the Atlantic Meridional Overturning Circulation (AMOC) may have a profound impact on the thermal- and hydro-climatic changes over the Pacific region. In our model-based analysis we propose a mechanism, which comprises a coupled ocean-atmosphere teleconnection, established through the atmospheric overturning circulation cell between the tropical North Atlantic and tropical Pacific. For example, warming SSTs over the tropical North Atlantic intensify local convection and reinforce subsidence, low-level divergence in the eastern tropical Pacific. This is also accompanied with an intensification of trade winds, cooling and drying anomalies in the tropical central-east Pacific. The derived multidecadal changes, associated with the AMOC, contribute remarkably to the global temperature and precipitation variations. This highlights its potential predictive value. Shown here results suggest a possibility that: 1) recently observed slowdown in global warming may partly originate from internal variability, 2) climate system may be undergoing a transition to a cold AMO phase which could prolong the global slowdown.

Toward a Reconstruction of the Atlantic Multidecadal Oscillation Using Shell-based Records from Coastal Northern Norway

NASA Astrophysics Data System (ADS)

Mette, M.; Wanamaker, A. D.; Carroll, M.; Ambrose, W. G., Jr.; Retelle, M.

2016-02-01

North Atlantic sea surface temperatures over the past 150 years have exhibited multidecadal variability, switching between relatively warm and cool periods, described by the Atlantic Multidecadal Oscillation (AMO). The influence, persistence, and causes of the AMO, however, are debated because instrumental records of North Atlantic sea surface temperatures only capture 2 cycles of this 60 to 80 year mode. Thus far, AMO reconstructions have been largely based on terrestrial archives despite the fact that the AMO is an oceanic mode. Proxy records from the marine realm are therefore necessary to better understand the behavior of the AMO over recent centuries. We present continuous, annual shell-based records of oxygen isotopes and growth from the long-lived marine bivalve Arctica islandica from coastal northern Norway (71 °N) from 1900-2012 that strongly relate to the instrumental AMO record (r = -0.59, p < 0.01). We performed calibration/verification analysis in order to assess the potential for these records to contribute to AMO reconstructions. We also compare our record with other proxy reconstructions of AMO variability over the past century. Our results show that extending shell-based records to past centuries will provide valuable information about AMO variability.

Climate impacts of the NAO are sensitive to how the NAO is defined

NASA Astrophysics Data System (ADS)

Pokorná, Lucie; Huth, Radan

2015-02-01

We analyze the sensitivity of the effects the North Atlantic Oscillation (NAO) exerts on surface temperature and precipitation in Europe to the definition of the NAO index. Seven different NAO indices are examined: two based on station sea level pressure (SLP) data, two based on action centers, and three based on correlation/covariance structures described by principal component analysis (PCA). The analysis is based on monthly mean data; winter and summer seasons are analyzed separately. Temporal correlations between indices are weaker in summer than in winter for most pairs of indices. In particular, low correlations are found between station indices on the one hand and PCA-based indices on the other hand. The NAO effects are quantified by correlations between the indices and station data in Europe. Effects of the NAO on precipitation amount and wet day probability are very similar, while NAO effects on maximum temperature are stronger than those on minimum temperature. The sensitivity of the NAO effects on both surface temperature and precipitation to the choice of the NAO index is considerably higher in summer. Correlations differ among the NAO indices not only in their magnitude but in some regions in summer also in their sign. These effects can be explained by a northward shift of the whole NAO pattern and its action centers in summer, away from the sites on which the station indices are based, and by a decoupling of the Azores high and Icelandic low from the centers of high covariability, identified by PCA. Considerable differences in SLP anomaly patterns associated to individual NAO indices also contribute to different responses in temperature and precipitation. Finally, we formulate two recommendations to future analyses of NAO effects on surface climate: use several different NAO indices instead of a single one, and for summer do not use station indices because they do not represent the circulation variability related to the NAO.

The NAO Influence on the Early to Mid-Holocene North Atlantic Coastal Upwelling

NASA Astrophysics Data System (ADS)

Hernandez, A.; Cachão, M.; Sousa, P.; Trigo, R. M.; Freitas, M. C.

2017-12-01

Coastal upwelling regions yield some of the oceanic most productive ecosystems, being crucial for the worldwide social and economic development. Most upwelling systems, emerging cold nutrient-rich deep waters, are located in the eastern boundaries of the Atlantic and Pacific basins, and are driven by meridional wind fields parallel to the coastal shore. These winds are associated with the subsiding branch of the large-scale Anticyclonic high pressure systems that dominate the subtropical ocean basins, and therefore can be displaced or intensified within the context of past and future climate changes. However, the role of the current global warming influencing the coastal upwelling is, as yet, unclear. Therefore it is essential to derive a long-term perspective, beyond the era of instrumental measurements, to detect similar warm periods in the past that have triggered changes in the upwelling patterns. In this work, the upwelling dynamics in the Iberian North Atlantic margin during the early and mid-Holocene is reconstructed, using calcareous nannofossils from a decadally resolved estuarine sediment core located in southwestern Portugal. Results suggest that the coastal dynamics reflects changes in winds direction likely related to shifts in the NAO-like conditions. Furthermore, the reconstructed centennial-scale variations in the upwelling are synchronous with changes in solar irradiance, a major external forcing factor of the climate system that is known to exert influence in atmospheric circulation patterns. In addition, these proxy-based data interpretations are in agreement with wind field and solar irradiance simulation modelling for the mid-Holocene. Therefore, the conclusion that the solar activity via the NAO modulation controlled the North Atlantic upwelling of western Iberia during the early and mid-Holocene at decadal to centennial timescales can be derived. The financial support for attending this meeting was possible through FCT project UID/GEO/50019

On the origin of multidecadal to centennial Greenland temperature anomalies over the past 800 yr

NASA Astrophysics Data System (ADS)

Kobashi, T.; Shindell, D. T.; Kodera, K.; Box, J. E.; Nakaegawa, T.; Kawamura, K.

2013-03-01

The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies due to its association with sea level rise. However, the causes of multidecadal-to-centennial temperature changes in Greenland temperatures are not well understood, largely owing to short observational records. To examine these, we calculated the Greenland temperature anomalies (GTA[G-NH]) over the past 800 yr by subtracting the standardized northern hemispheric (NH) temperature from the standardized Greenland temperature. This decomposes the Greenland temperature variation into background climate (NH); polar amplification; and regional variability (GTA[G-NH]). The central Greenland polar amplification factor as expressed by the variance ratio Greenland/NH is 2.6 over the past 161 yr, and 3.3-4.2 over the past 800 yr. The GTA[G-NH] explains 31-35% of the variation of Greenland temperature in the multidecadal-to-centennial time scale over the past 800 yr. We found that the GTA[G-NH] has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by the North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modeling and proxy temperature records indicate that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and associated changes in northward oceanic heat transport.

On the Origin of Multidecadal to Centennial Greenland Temperature Anomalies Over the Past 800 yr

NASA Technical Reports Server (NTRS)

Kobashi, T.; Shindell, D. T.; Kodera, K.; Box, J. E.; Nakaegawa, T.; Kawamura, K.

2013-01-01

The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies due to its association with sea level rise. However, the causes of multidecadal-to-centennial temperature changes in Greenland temperatures are not well understood, largely owing to short observational records. To examine these, we calculated the Greenland temperature anomalies (GTA[G-NH]) over the past 800 yr by subtracting the standardized northern hemispheric (NH) temperature from the standardized Greenland temperature. This decomposes the Greenland temperature variation into background climate (NH); polar amplification; and regional variability (GTA[G-NH]). The central Greenland polar amplification factor as expressed by the variance ratio Greenland/NH is 2.6 over the past 161 yr, and 3.3-4.2 over the past 800 yr. The GTA[G-NH] explains 31-35%of the variation of Greenland temperature in the multidecadal-to-centennial time scale over the past 800 yr. We found that the GTA[G-NH] has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by the North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modeling and proxy temperature records indicate that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and associated changes in northward oceanic heat transport.

The role of historical forcings in simulating the observed Atlantic multidecadal oscillation

NASA Astrophysics Data System (ADS)

Murphy, Lisa N.; Bellomo, Katinka; Cane, Mark; Clement, Amy

2017-03-01

We analyze the Atlantic multidecadal oscillation (AMO) in the preindustrial (PI) and historical (HIST) simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to assess the drivers of the observed AMO from 1865 to 2005. We draw 141 year samples from the 41 CMIP5 model's PI runs and compare the correlation and variance between the observed AMO and the simulated PI and HIST AMO. The correlation coefficients in 38 forced (HIST) models are above the 90% confidence level and explain up to 56% of the observed variance. The probability that any of the unforced (PI) models do as well is less than 3% in 31 models. Multidecadal variability is larger in 39 CMIP5 HIST simulations and in all HIST members of the Community Earth System Model Large Ensemble than their corresponding PI. We conclude that there is an essential role for external forcing in driving the observed AMO.

An out of phase coupling between the atmosphere and the ocean over the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Ribera, Pedro; Ordoñez, Paulina; Gallego, David; Peña-Ortiz, Cristina

2017-04-01

An oscillation band, with a period ranging between 40 and 60 years, has been identified as the most intense signal over the North Atlantic Ocean using several oceanic and atmospheric reanalyses between 1856 and the present. This signal represents the Atlantic Multidecadal Oscillation, an oscillation between warmer and colder than normal conditions in SST. Simultaneously, those changes in SST are accompanied by changes in atmospheric conditions represented by surface pressure, temperature and circulation. In fact, the evolution of the surface pressure pattern along this oscillation shows a North Atlantic Oscillation-like pattern, suggesting the existence of an out of phase coupling between atmospheric and oceanic conditions. Further analysis shows that the evolution of the oceanic SST distribution modifies atmospheric baroclinic conditions in the mid to high latitudes of the North Atlantic and leads the atmospheric variability by 6-7 years. If AMO represents the oceanic conditons and NAO represents the atmospheric variability then it could be said that AMO of one sign leads NAO of the opposite sign with a lag of 6-7 years. On the other hand, the evolution of atmospheric conditions, represented by pressure distribution patterns, favors atmospheric circulation anomalies and induces a heat advection which tends to change the sign of the existing SST distribution and oceanic conditions with a lag of 16-17 years. In this case, NAO of one sign leads AMO of the same sign with a lag of 16-17 years.

The Atlantic Multidecadal Variability in surface and deep ocean temperature and salinity fields from unperturbed climate simulations

NASA Astrophysics Data System (ADS)

Zanchettin, D.; Jungclaus, J. H.

2013-12-01

Large multidecadal fluctuations in basin-average sea-surface temperature (SST) are a known feature of observed, reconstructed and simulated variability in the North Atlantic Ocean. This phenomenon is often referred to as Multidecadal Atlantic Variability or AMV. Historical AMV fluctuations are associated with analog basin-scale changes in sea-surface salinity, so that warming corresponds to salinification and cooling to freshening [Polyakov et al., 2005]. The surface imprint of the AMV further corresponds to same-sign fluctuations in the shallow ocean and with opposite-sign fluctuations in the deep ocean for both temperature and salinity [Polyakov et al., 2005]. This out-of-phase behavior reflects the thermohaline overturning circulation shaping North Atlantic's low-frequency variability. Several processes contribute to the AMV, involving both ocean-atmosphere coupled processes and deep ocean circulation [e.g., Grossmann and Klotzbach, 2009]. In particular, recirculation in the North Atlantic subpolar gyre region of salinity anomalies from Arctic freshwater export may trigger multidecadal variability in the Atlantic meridional overturning circulation, and therefore may be part of the AMV [Jungclaus et al., 2005; Dima and Lohmann, 2007]. With this contribution, we aim to improve the physical interpretation of the AMV by investigating spatial and temporal patterns of temperature and salinity fields in the shallow and deep ocean. We focus on two unperturbed millennial-scale simulations performed with the Max Planck Institute Earth system model in its paleo (MPI-ESM-P) and low-resolution (MPI-ESM-LR) configurations, which provide reference control climates for assessments of pre-industrial and historical climate simulations. The two model configurations only differ for the presence, in MPI-ESM-LR, of an active module for dynamical vegetation. We use spatial-average indices and empirical orthogonal functions/principal components to track the horizontal and vertical

Atlantic Multidecadal Oscillation footprint on global high cloud cover

NASA Astrophysics Data System (ADS)

Vaideanu, Petru; Dima, Mihai; Voiculescu, Mirela

2017-12-01

Due to the complexity of the physical processes responsible for cloud formation and to the relatively short satellite database of continuous data records, cloud behavior in a warming climate remains uncertain. Identifying physical links between climate modes and clouds would contribute not only to a better understanding of the physical processes governing their formation and dynamics, but also to an improved representation of the clouds in climate models. Here, we identify the global footprint of the Atlantic Multidecadal Oscillation (AMO) on high cloud cover, with focus on the tropical and North Atlantic, tropical Pacific and on the circum-Antarctic sector. In the tropical band, the sea surface temperature (SST) and high cloud cover (HCC) anomalies are positively correlated, indicating a dominant role played by convection in mediating the influence of the AMO-related SST anomalies on the HCC field. The negative SST-HCC correlation observed in North Atlantic could be explained by the reduced meridional temperature gradient induced by the AMO positive phase, which would be reflected in less storms and negative HCC anomalies. A similar negative SST-HCC correlation is observed around Antarctica. The corresponding negative correlation around Antarctica could be generated dynamically, as a response to the intensified upward motion in the Ferrel cell. Despite the inherent imperfection of the observed and reanalysis data sets, the AMO footprint on HCC is found to be robust to the choice of dataset, statistical method, and specific time period considered.

Positive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation

DOE PAGES

Yuan, Tianle; Oreopoulos, Lazaros; Zelinka, Mark; ...

2016-02-04

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropicalmore » trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.« less

Positive Low Cloud and Dust Feedbacks Amplify Tropical North Atlantic Multidecadal Variability

NASA Technical Reports Server (NTRS)

Yuan, Tianle; Oraiopoulos, Lazaros; Zelinka, Mark; Yu, Hongbin; Norris, Joel R.; Chin, Mian; Platnick, Steven; Meyer, Kerry

2016-01-01

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

Changes in the relationship NAO-Northern hemisphere temperature due to solar activity

NASA Astrophysics Data System (ADS)

Gimeno, Luis; de la Torre, Laura; Nieto, Raquel; García, Ricardo; Hernández, Emiliano; Ribera, Pedro

2003-01-01

The influence of the North Atlantic Oscillation (NAO) on wintertime Northern Hemisphere Temperature (NHT) is investigated. The results suggest that this relationship has different sign according to the phase of the solar cycle. For solar maximum phases NAO and NHT are positively correlated - a result assumed up to the moment - but for solar minimum phases correlations are not significant or even negative. This result is in agreement with the different extension of the NAO for solar cycle phases [Kodera, Geophys. Res. Lett. 29 (2002) 14557-14560] - almost hemispheric for maximum phases and confined to the eastern Atlantic for minimum phases.

Statistical Aspects of Tropical Cyclone Activity in the North Atlantic Basin, 1945-2010

NASA Technical Reports Server (NTRS)

Wilson, Robert M.

2012-01-01

Examined are statistical aspects of the 715 tropical cyclones that formed in the North Atlantic basin during the interval 1945-2010. These 715 tropical cyclones include 306 storms that attained only tropical storm strength, 409 hurricanes, 179 major or intense hurricanes, and 108 storms that struck the US coastline as hurricanes. Comparisons made using 10-year moving average (10-yma) values between tropical cyclone parametric values and surface air and ENSO-related parametric values indicate strong correlations to exist, in particular, against the Armagh Observatory (Northern Ireland) surface air temperature, the Atlantic Multi-decadal Oscillation (AMO) index, the Atlantic Meridional Mode (AMM) index, and the North Atlantic Oscillation (NAO) index, in addition to the Oceanic Ni o index (ONI) and Quasi-Biennial Oscillation (QBO) indices. Also examined are the decadal variations of the tropical cyclone parametric values and a look ahead towards the 2012 hurricane season and beyond.

Multidecadal Increase in North Atlantic Coccolithophores and Potential Role of Increasing CO2

NASA Astrophysics Data System (ADS)

Rivero-Calle, S.; Gnanadesikan, A.; del Castillo, C. E.; Balch, W. M.; Guikema, S.

2016-02-01

As anthropogenic CO2 emissions acidify the oceans, calcifiers are expected to be negatively impacted. Using data from the Continuous Plankton Recorder, we show that coccolithophore occurrence in the North Atlantic has increased from 2 to over 20% from 1965 through 2010. We used Random Forest models to examine more than 20 possible environmental drivers of this change. CO2 and the Atlantic Multidecadal Oscillation were the best predictors. Since coccolithophore photosynthesis is strongly carbon-limited, we hypothesize that higher CO2 levels might be encouraging growth. A compilation of 41 independent laboratory studies supports our hypothesis. Our study shows a long-term basin-scale increase in coccolithophores and suggests that increasing pCO2 and temperature accelerated the growth rate of a key phytoplankton group for carbon cycling.

A robust empirical seasonal prediction of winter NAO and surface climate.

PubMed

Wang, L; Ting, M; Kushner, P J

2017-03-21

A key determinant of winter weather and climate in Europe and North America is the North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability in the Atlantic domain. Skilful seasonal forecasting of the surface climate in both Europe and North America is reflected largely in how accurately models can predict the NAO. Most dynamical models, however, have limited skill in seasonal forecasts of the winter NAO. A new empirical model is proposed for the seasonal forecast of the winter NAO that exhibits higher skill than current dynamical models. The empirical model provides robust and skilful prediction of the December-January-February (DJF) mean NAO index using a multiple linear regression (MLR) technique with autumn conditions of sea-ice concentration, stratospheric circulation, and sea-surface temperature. The predictability is, for the most part, derived from the relatively long persistence of sea ice in the autumn. The lower stratospheric circulation and sea-surface temperature appear to play more indirect roles through a series of feedbacks among systems driving NAO evolution. This MLR model also provides skilful seasonal outlooks of winter surface temperature and precipitation over many regions of Eurasia and eastern North America.

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.

PubMed

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-02-25

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO.

Evolution of multidecadal variability in the West African monsoon during the last deglaciation

NASA Astrophysics Data System (ADS)

Shanahan, T. M.; McKay, N.

2017-12-01

The West African monsoon system is strongly linked to changes in Atlantic variability on multidecadal to millennial timescales. Understanding the nature of these linkages thus provides important insights into the susceptibility of West African precipitation to past and future changes in Atlantic circulation. Here, we use an annually-resolved record of lamination thickness variations from Lake Bosumtwi, Ghana to generate an unprecedented record of changes in the West African monsoon spanning the last deglaciation ( 12.8-24 ka BP) and the latest Holocene (0-2.6 ka BP). Millennial-scale variability in varve thickness is consistent with published data from hydrogen isotopes in leaf waxes, showing a dramatic and sustained shift to drier conditions during HS1, a rapid recovery at the onset of the Bølling-Allerød and a gradual shift towards drier conditions following the end of the African Humid Period. The varve thickness record also indicates the presence of significant multidecadal ( 40- 80 years) West African monsoon variability throughout much of the record, disappearing only during the later portion of HS1 ( 14.8-16 ka BP). Previous studies have linked multidecadal variability in the West African monsoon to the Atlantic Multidecadal Oscillation (AMO), a low frequency mode of North Atlantic sea surface temperature variability that is hypothesized to be controlled by changes in North Atlantic heat transport via the Atlantic Meridional Overturning Circulation (AMOC). Our reconstruction indicates that this mode of multidecadal variability was active not only throughout the late Holocene but during the Last Glacial Maximum and much of the deglaciation, including the first half of HS1. The later result is unexpected in that it suggests that the AMO remained active even as the Atlantic overturning circulation collapsed and the African monsoon weakened during the initial phase of HS1. The decoupling of multidecadal and millennial scale variability suggests either a

Atlantic and Pacific Influences on Mesoamerican Climate Over the Past Millennium (Invited)

NASA Astrophysics Data System (ADS)

Stahle, D. W.; Burnette, D. J.; Villanueva, J.; Cleaveland, M. K.

2010-12-01

Montezuma baldcypress (Taxodium mucronatum) trees in Queretaro have been used to develop the first exactly dated millennium-long tree-ring chronology in central Mexico. The chronology is sensitive to both precipitation and temperature, and has been used to reconstruct the Palmer Drought Severity Index (PDSI) for June from AD 771-2008 for a large sector of Mesoamerica (most of central and southern Mexico). Fourier-transform spectral analyses of the 1,238-year long reconstruction indicate strong concentrations of variance at frequencies associated with the El Nino/Southern Oscillation (ENSO; representing over 14% of the total reconstructed variance between periods of 4.5 and 5.5 years), and at multi-decadal frequencies potentially associated with the Atlantic Multidecadal Oscillation (AMO; representing over 10% of the total variance between periods of 50 and 75 years). Weaker but statistically significant concentrations of variance are also detected with the Multi-Taper Method of spectral analysis at subdecadal timescales potentially linked with the North Atlantic Oscillation (NAO; 7.5 years) and at timescales possibly associated with the Pacific Decadal Oscillation (~33 years). The reconstruction is significantly correlated with sea surface temperatures (SST) in the ENSO cold tongue region from 1871-2008 (during the boreal cool season, DJFM), and this SST correlation strengthens in the 20th Century (1931-2008). Summer drought tends to develop over central Mexico during El Nino events, and the record warm events observed in 1983 and 1998 were associated with the two most extremely dry June PDSI conditions in the past 1,238 years (reconstructed ranks 1 and 2 for 1983 and 1998, respectively). The reconstruction is also significantly correlated with SSTs over the tropical North Atlantic, and is coherent with long instrument-based indices of the NAO at periods near 7.5 years, but only during the 20th century. The June PDSI reconstruction is coherent (P<0.05) with a 600

The variability of the North Atlantic Oscillation throughout the Holocene

NASA Astrophysics Data System (ADS)

Wassenburg, Jasper; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Wei, Wei; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev; Sabaoui, Abdellah; Lohmann, Gerrit; Andreae, Meinrat; Immenhauser, Adrian

2013-04-01

-of-the-art earth system model COSMOS for the Early and Mid Holocene (Wei and Lohmann, 2012) indicate that this change in the NAO teleconnection is related to large-scale circulation changes due to the ice sheet configuration and deglaciation. References: Fohlmeister, J., Schroder-Ritzrau, A., Scholz, D., Riechelmann, D.F.C., Mudelsee, M., Wackerbarth, A., Gerdes, A., Riechelmann, S., Immenhauser, A., Richter, D.K., Mangini, A., 2012. Bunker Cave stalagmites: an archive for central European Holocene climate variability. Climate of the Past 8, 1751-1764. Olsen, J., Anderson, J.N., Knudsen, M.F., 2012. Variability of the North Atlantic Oscillation over the past 5,200 years. Nature Geoscience DOI:10.1038/NGEO1589, Trouet, V., Esper, J., Graham, N.E., Baker, A., Scourse, J.D., Frank, D.C., 2009. Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly. Science 324, 78-80. Wei, W., Lohmann, G., 2012. Simulated Atlantic Multidecadal Oscillation during the Holocene. Journal of Climate 6989-7002.

Multidecadal increase in North Atlantic coccolithophores and the potential role of rising CO₂.

PubMed

Rivero-Calle, Sara; Gnanadesikan, Anand; Del Castillo, Carlos E; Balch, William M; Guikema, Seth D

2015-12-18

As anthropogenic carbon dioxide (CO2) emissions acidify the oceans, calcifiers generally are expected to be negatively affected. However, using data from the Continuous Plankton Recorder, we show that coccolithophore occurrence in the North Atlantic increased from ~2 to more than 20% from 1965 through 2010. We used random forest models to examine more than 20 possible environmental drivers of this change, finding that CO2 and the Atlantic Multidecadal Oscillation were the best predictors, leading us to hypothesize that higher CO2 levels might be encouraging growth. A compilation of 41 independent laboratory studies supports our hypothesis. Our study shows a long-term basin-scale increase in coccolithophores and suggests that increasing CO2 and temperature have accelerated the growth of a phytoplankton group that is important for carbon cycling. Copyright © 2015, American Association for the Advancement of Science.

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age

PubMed Central

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Multidecadal increase in North Atlantic coccolithophores and the potential role of rising CO2

NASA Astrophysics Data System (ADS)

Rivero-Calle, Sara; Gnanadesikan, Anand; Del Castillo, Carlos E.; Balch, William M.; Guikema, Seth D.

2015-12-01

As anthropogenic carbon dioxide (CO2) emissions acidify the oceans, calcifiers generally are expected to be negatively affected. However, using data from the Continuous Plankton Recorder, we show that coccolithophore occurrence in the North Atlantic increased from ~2 to more than 20% from 1965 through 2010. We used random forest models to examine more than 20 possible environmental drivers of this change, finding that CO2 and the Atlantic Multidecadal Oscillation were the best predictors, leading us to hypothesize that higher CO2 levels might be encouraging growth. A compilation of 41 independent laboratory studies supports our hypothesis. Our study shows a long-term basin-scale increase in coccolithophores and suggests that increasing CO2 and temperature have accelerated the growth of a phytoplankton group that is important for carbon cycling.

Influence of prolonged Anomalies in North Atlantic Sea Surface Temperature on Winter Windstorms

NASA Astrophysics Data System (ADS)

Höschel, Ines; Schuster, Mareike; Grieger, Jens; Ulbrich, Uwe

2016-04-01

The focus of this presentation is on decadal scale variations in the frequency and in the intensity of mid-latitude winter windstorms. Projections for the end of the next century are often beyond the time horizon of business, thus there is an increasing interest on decadal prediction, especially for infrastructural planning and in the insurance industry. One source of decadal predictability is the Atlantic multidecadal variability (AMV), a change in the sea surface temperature of the North Atlantic, strongly linked to the meridional overturning circulation. Correlation patterns between annual AMV-indices and annual mean of geopotential height at 500 hPa in reanalysis data show an anti-correlation in the North Atlantic. That is, during AMV warm phases the North Atlantic Oscillation (NAO) is more negative. Consequently, AMV should influence the characteristics of winter windstorms at multi-year scales. For the presented investigations a 10-member ensemble of 38-year-long idealized simulations with the atmosphere model ECHAM6 with lower boundary conditions, representing warm and cool phases of the AMV, is used. In the idealized simulations, the anti-correlation between AMV and NAO is well represented. For the identification of winter windstorms an objective wind tracking algorithm based on the exceedance of the local 98th percentile of 10m wind speed is applied. Storms under AMV-warm and AMV-cool conditions will be compared in terms of storm track density and probability distribution of storm characteristics.

Urban NO 2 and NO pollution in relation to the North Atlantic Oscillation NAO

NASA Astrophysics Data System (ADS)

Grundström, M.; Linderholm, H. W.; Klingberg, J.; Pleijel, H.

2011-02-01

The North Atlantic Oscillation (NAO), a measure of the strength of the zonal wind across the North Atlantic Ocean, strongly influences weather conditions in NW Europe, e.g. temperature, precipitation and wind, especially during winter. It was hypothesised that elevated concentrations of nitrogen oxides in Gothenburg would be enhanced during negative NAO index (NAOI) conditions, representing more anticyclonic weather situations and thus leading to limited air mixing in the urban atmosphere, than situations with NAOI > 0. Hourly wintertime (December-February) concentrations (1997-2006) of NO 2, NO, air pressure, temperature and wind direction from an urban rooftop (30 m above street level) in the centre of the City of Gothenburg were analysed in relation to NAOI. Air pressure, the average concentration of nitrogen oxides (NO x = NO 2 + NO), as well as the fraction of hourly NO 2 and NO concentrations exceeding 90 μg m -3 and the fraction of daily NO concentrations exceeding 60 μg m -3, were significantly and negatively related to NAOI. Air temperature was positively correlated with NAOI. Southerly and westerly winds were more common in months with positive NAOI, while easterly and northerly winds were overrepresented in months with negative NAOI. High pollution concentrations dominantly occurred in situations with northerly and easterly wind directions. High NO 2 and NO concentrations were associated with negative NAOI, especially in the morning when the traffic rush coincided with restricted air mixing. Over the ten-year period there were trends for more negative NAOI and increased time fractions with hourly NO 2 concentrations exceeding 90 μg m -3. The conclusion of this study is that a climate shift towards higher or lower NAOI has the potential to significantly influence urban air pollution in North-West Europe, and thus the possibility to reach air quality standards, even if emissions remain constant.

Interannual Modulation of Subtropical Atlantic Boreal Summer Dust Variability by ENSO

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeFlorio, Mike; Goodwin, Ian D.; Cayan, Dan

2016-01-01

Dust variability in the climate system has been studied for several decades, yet there remains an incomplete understanding of the dynamical mechanisms controlling interannual and decadal variations in dust transport. The sparseness of multi-year observational datasets has limited our understanding of the relationship between climate variations and atmospheric dust. We use available observations and a century-length fully coupled Community Earth System Model (CESM) simulation to show that the El Niño- Southern Oscillation (ENSO) exerts a control on North African dust transport during boreal summer. In CESM, this relationship is stronger over the dusty tropical North Atlantic than near Barbados, onemore » of the few sites having a multi-decadal observed record. During strong La Niña summers in CESM, a statistically significant increase in lower tropospheric easterly wind is associated with an increase in North African dust transport over the Atlantic. Barbados dust and Pacific SST variability are only weakly correlated in both observations and CESM, suggesting that other processes are controlling the crossbasin variability of dust. We also use our CESM simulation to show that the relationship between downstream North African dust transport and ENSO fluctuates on multidecadal timescales and may be modulated by the North Atlantic Oscillation (NAO). Our findings indicate that existing observations of dust over the tropical North Atlantic are not extensive enough to completely describe the variability of dust and dust transport, and demonstrate the importance of global models to supplement and interpret observational records.« less

The near-term prediction of drought and flooding conditions in the northeastern United States based on extreme phases of AMO and NAO

NASA Astrophysics Data System (ADS)

Berton, Rouzbeh; Driscoll, Charles T.; Adamowski, Jan F.

2017-10-01

A series of hydroclimatic teleconnection patterns were identified between variations in either Atlantic or Pacific oceanic indices with precipitation and discharge anomalies in the northeastern United States. We hypothesized that temporal annual or seasonal changes in discharge could be explained by variations in extreme phases of the Atlantic Multi-decadal Oscillation (AMO index, SST: Sea Surface Temperature anomalies) and the North Atlantic Oscillation (NAO index, SLP: Sea-Level Pressure anomalies) up to three seasons in advance. The Merrimack River watershed, the fourth largest basin in New England, with a drainage area of 13,000 km2, is a compelling study site because it not only provides an opportunity to investigate the teleconnection between hydrologic variables and large-scale climate circulation patterns, but also how those patterns may become obscured by anthropogenic disturbances such as river regulation or urban development. We considered precipitation and discharge data of 21 gauging stations within the Merrimack River watershed, including the Hubbard Brook Experimental Forest (HBEF), NH, with a median record length of 55 years beginning as early as 1904. The discharge anomalies were statistically significant (p-value ≤ 0.2) between extreme positive and negative phases of AMO (1857-2011) and NAO (1900-2011) and revealed the potential teleconnectivity of climate circulation patterns with discharge. Annual and seasonal correlations of discharge were examined with the extreme phases of AMO and NAO at zero-, one-, or two- year/season lags (total of 30 scenarios). When AMO was greater than 0.2, the strongest correlations of AMO and NAO with discharge were observed at headwater catchments. This correlation weakened downstream towards larger regulated and/or developed sub-basins. We introduced a simple approach for near-term prediction of drought and flooding events. An exponential decay function was regressed through the historic occurrence of the relative

The influences of the AMO and NAO on the sedimentary infill in an Azores Archipelago lake since ca. 1350 CE

NASA Astrophysics Data System (ADS)

Hernández, Armand; Sáez, Alberto; Bao, Roberto; Raposeiro, Pedro M.; Trigo, Ricardo M.; Doolittle, Sara; Masqué, Pere; Rull, Valentí; Gonçalves, Vítor; Vázquez-Loureiro, David; Rubio-Inglés, María J.; Sánchez-López, Guiomar; Giralt, Santiago

2017-07-01

The location of the Azores Archipelago in the North Atlantic makes this group of islands an excellent setting to study the long-term behavior of large oceanic and atmospheric climate dynamic patterns, such as the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). Here, we present the impacts of these patterns on Lake Empadadas (Azores Archipelago) from the Medieval Climate Anomaly (MCA) - Little Ice Age (LIA) transition to the present based on sedimentological, geochemical and biological characterizations of the sedimentary record. Multivariate analyses of a number of proxies including X-ray fluorescence (XRF), X-ray diffraction (XRD), total organic and inorganic carbon (TOC and TIC) and diatom life forms abundance reveal that the sedimentary infill evolution has been controlled by (i) fluctuations in the lake level and (ii) variations in organic matter accumulation. Both processes are governed by climate variability and modulated by anthropogenic activities associated with changes on the lake catchment. Changes in these two sedimentary processes have been used to infer five stages: (i) the MCA-LIA transition (ca. 1350-1450 CE) was characterized by a predominantly positive AMO phase, which led to intermediate lake levels and high organic matter concentration; (ii) the first half of the LIA (ca. 1450-1600 CE) was characterized by predominant lowstand conditions and intermediate organic matter deposition mainly related to negative AMO phases; (iii) the second half of the LIA (ca. 1600-1850 CE) was characterized by negative AMO and NAO phases, implying intermediate lake levels and high organic matter deposition; (iv) the Industrial era (ca. 1850-1980 CE) was characterized by the lowest lake level and organic matter accumulation associated with negative AMO phases; and (v) the period spanning between 1980 CE and the present reveals the highest lake levels and low organic matter deposition, being associated with very positive AMO

Changes in the relationship NAO-Northern Hemisphere Temperature due to solar activity

NASA Astrophysics Data System (ADS)

de La Torre, L.; Gimeno, L.; Añel, J. A.; Nieto, R.; Tesouro, M.; Ribera, P.; García, R.; Hernández, E.

2003-04-01

The influence of the North Atlantic Oscillation (NAO) on wintertime Northern Hemisphere Temperature (NHT) is investigated. To check the hypothesis that the solar cycle is modulating this relationship, the sample was divided into two groups, one included the years corresponding to the three consecutive lowest values of sunspots number for every 11-years cycle (43 years) and the other the ones corresponding to the three consecutive highest numbers (39 years) for every 11-years cycle. If the data of each year were independent, the correlation coefficients between NAO index and NHT for 43 (39) years would be 0.30 (0.32) at 95% confidence level. Correlation index corresponding to the solar minimum phases was -0.17 and to the solar maximum phases was 0.35. The second result is statistically significant and indicates that there are periods when a positive phase of the NAO is related to positive anomalies of NHT- result that supports our current idea of the influence of the NAO on temperature- but there are other periods when NAO and NHT are not correlated. So, results suggest that this relationship has different sign according to the phase of the solar cycle. For solar maximum phases NAO and NHT are positively correlated -result assumed up to the moment- but for solar minimum phases correlations are not significant or even negative. This result is in agreement with the different extension of the NAO for solar cycle phases [1] - almost hemispheric for maximum phases and confined to the eastern Atlantic for minimum phases-.

Changes in Greenland's peripheral glaciers linked to the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Bjørk, A. A.; Aagaard, S.; Lütt, A.; Khan, S. A.; Box, J. E.; Kjeldsen, K. K.; Larsen, N. K.; Korsgaard, N. J.; Cappelen, J.; Colgan, W. T.; Machguth, H.; Andresen, C. S.; Peings, Y.; Kjær, K. H.

2018-01-01

Glaciers and ice caps peripheral to the main Greenland Ice Sheet contribute markedly to sea-level rise1-3. Their changes and variability, however, have been difficult to quantify on multi-decadal timescales due to an absence of long-term data4. Here, using historical aerial surveys, expedition photographs, spy satellite imagery and new remote-sensing products, we map glacier length fluctuations of approximately 350 peripheral glaciers and ice caps in East and West Greenland since 1890. Peripheral glaciers are found to have recently undergone a widespread and significant retreat at rates of 12.2 m per year and 16.6 m per year in East and West Greenland, respectively; these changes are exceeded in severity only by the early twentieth century post-Little-Ice-Age retreat. Regional changes in ice volume, as reflected by glacier length, are further shown to be related to changes in precipitation associated with the North Atlantic Oscillation (NAO), with a distinct east-west asymmetry; positive phases of the NAO increase accumulation, and thereby glacier growth, in the eastern periphery, whereas opposite effects are observed in the western periphery. Thus, with projected trends towards positive NAO in the future5,6, eastern peripheral glaciers may remain relatively stable, while western peripheral glaciers will continue to diminish.

Length of the solar cycle influence on the relationship NAO-Northern Hemisphere Temperature

NASA Astrophysics Data System (ADS)

de La Torre, L.; Gimeno, L.; Tesouro, M.; Añel, J. A.; Nieto, R.; Ribera, P.; García, R.; Hernández, E.

2003-04-01

The influence of the length of the solar cycle on the relationship North Atlantic Oscillation (NAO)-Northern Hemisphere Temperature (NHT) is investigated. The results suggest that this relationship is different according to the length of the solar cycle. When the sunspot cycle is 10 or 11 years long, wintertime NAO and NHT are positively correlated, being the signal more intense during 11 years period, but when the sunspot cycle is longer (12 years) correlations between wintertime NAO and NHT are not significant. In fact there are significant negative correlations between wintertime NAO and spring NHT, with predictive potential.

The Role of the North Atlantic Oscillation (NAO) on Recent Greenland Surface Mass Loss and Mass Partitioning

NASA Astrophysics Data System (ADS)

Tedesco, M.; Alexander, P.; Porter, D. F.; Fettweis, X.; Luthcke, S. B.; Mote, T. L.; Rennermalm, A.; Hanna, E.

2017-12-01

Despite recent changes in Greenland surface mass losses and atmospheric circulation over the Arctic, little attention has been given to the potential role of large-scale atmospheric processes on the spatial and temporal variability of mass loss and partitioning of the GrIS mass loss. Using a combination of satellite gravimetry measurements, outputs of the MAR regional climate model and reanalysis data, we show that changes in atmospheric patterns since 2013 over the North Atlantic region of the Arctic (NAA) modulate total mass loss trends over Greenland together with the spatial and temporal distribution of mass loss partitioning. For example, during the 2002 - 2012 period, melting persistently increased, especially along the west coast, as a consequence of increased insulation and negative NAO conditions characterizing that period. Starting in 2013, runoff along the west coast decreased while snowfall increased substantially, when NAO turned to a more neutral/positive state. Modeled surface mass balance terms since 1950 indicate that part of the GRACE-period, specifically the period between 2002 and 2012, was exceptional in terms of snowfall over the east and northeast regions. During that period snowfall trend decreased to almost 0 Gt/yr from a long-term increasing trend, which presumed again in 2013. To identify the potential impact of atmospheric patterns on mass balance and its partitioning, we studied the spatial and temporal correlations between NAO and snowfall/runoff. Our results indicate that the correlation between summer snowfall and NAO is not stable during the 1950 - 2015 period. We further looked at changes in patterns of circulation using self organizing maps (SOMs) to identify the atmospheric patterns characterizing snowfall during different periods. We discuss potential implications for past changes and future GCM and RCM simulations.

Norwegian fjord sediments reveal NAO related winter temperature and precipitation changes of the past 2800 years

NASA Astrophysics Data System (ADS)

Faust, Johan; Fabian, Karl; Giraudeau, Jacques; Knies, Jochen

2016-04-01

The North Atlantic Oscillation (NAO) is the leading mode of atmospheric circulation variability in the North Atlantic region. Associated shifts of storm tracks, precipitation and temperature patterns affect energy supply and demand, fisheries and agricultural, as well as marine and terrestrial ecological dynamics. Long-term NAO reconstructions are crucial to better understand NAO variability in its response to climate forcing factors, and assess predictability and possible shifts associated with ongoing climate change. Fjord deposits have a great potential for providing high-resolution sedimentary records that reflect local terrestrial and marine processes and, therefore, offer unique opportunities for the investigation of sedimentological and geochemical climatically induced processes. A recent study of instrumental time series revealed NAO as main factor for a strong relation between winter temperature, precipitation and river discharge in central Norway over the past 50 years. Here we use the gained knowledge to establish the first high resolution NAO proxy record from marine sediments. By comparing geochemical measurements from a short sediment core with instrumental data we show that marine primary productivity proxies are sensitive to NAO changes. Conditioned on a stationary relation between our climate proxy and the NAO we establish the first high resolution NAO proxy record (NAO-TFJ) from marine sediments covering the past 2,800 years. The NAO-TFJ shows distinct co-variability with climate changes over Greenland, solar activity and Northern Hemisphere glacier dynamics as well as climatically associated paleo-demographic trends.

Dependence of winter precipitation over Portugal on NAO and baroclinic wave activity

NASA Astrophysics Data System (ADS)

Ulbrich, U.; Christoph, M.; Pinto, J. G.; Corte-Real, J.

1999-03-01

The relationship between winter (DJF) rainfall over Portugal and the variable large scale circulation is addressed. It is shown that the poles of the sea level pressure (SLP) field variability associated with rainfall variability are shifted about 15° northward with respect to those used in standard definitions of the North Atlantic Oscillation (NAO). It is suggested that the influence of NAO on rainfall dominantly arises from the associated advection of humidity from the Atlantic Ocean. Rainfall is also related to different aspects of baroclinic wave activity, the variability of the latter quantity in turn being largely dependent on the NAO.A negative NAO index (leading to increased westerly surface geostrophic winds into Portugal) is associated with an increased number of deep (ps<980 hPa) surface lows over the central North Atlantic and of intermediate (980NAO is the mid-tropospheric storm track (defined by the 500 hPa bandpass-filtered geopotential height variance). A possible local influence of the storm track due to vertical motions ahead of the upper air troughs cannot be unambiguously separated from the effect of advection. A separate influence of local surface cyclones over the Iberian peninsula which may, for instance, arise from the large scale ascent of air, is revealed by the statistics: for a given advection, rainfall amounts for months with local cyclone cores over the considered region tend to exceed those without.

The role of Atlantic overturning circulation in the recent decline of Atlantic major hurricane frequency.

PubMed

Yan, Xiaoqin; Zhang, Rong; Knutson, Thomas R

2017-11-22

Observed Atlantic major hurricane frequency has exhibited pronounced multidecadal variability since the 1940s. However, the cause of this variability is debated. Using observations and a coupled earth system model (GFDL-ESM2G), here we show that the decline of the Atlantic major hurricane frequency during 2005-2015 is associated with a weakening of the Atlantic Meridional Overturning Circulation (AMOC) inferred from ocean observations. Directly observed North Atlantic sulfate aerosol optical depth has not increased (but shows a modest decline) over this period, suggesting the decline of the Atlantic major hurricane frequency during 2005-2015 is not likely due to recent changes in anthropogenic sulfate aerosols. Instead, we find coherent multidecadal variations involving the inferred AMOC and Atlantic major hurricane frequency, along with indices of Atlantic Multidecadal Variability and inverted vertical wind shear. Our results provide evidence for an important role of the AMOC in the recent decline of Atlantic major hurricane frequency.

Empirical seasonal forecasts of the NAO

NASA Astrophysics Data System (ADS)

Sanchezgomez, E.; Ortizbevia, M.

2003-04-01

We present here seasonal forecasts of the North Atlantic Oscillation (NAO) issued from ocean predictors with an empirical procedure. The Singular Values Decomposition (SVD) of the cross-correlation matrix between predictor and predictand fields at the lag used for the forecast lead is at the core of the empirical model. The main predictor field are sea surface temperature anomalies, although sea ice cover anomalies are also used. Forecasts are issued in probabilistic form. The model is an improvement over a previous version (1), where Sea Level Pressure Anomalies were first forecast, and the NAO Index built from this forecast field. Both correlation skill between forecast and observed field, and number of forecasts that hit the correct NAO sign, are used to assess the forecast performance , usually above those values found in the case of forecasts issued assuming persistence. For certain seasons and/or leads, values of the skill are above the .7 usefulness treshold. References (1) SanchezGomez, E. and Ortiz Bevia M., 2002, Estimacion de la evolucion pluviometrica de la Espana Seca atendiendo a diversos pronosticos empiricos de la NAO, in 'El Agua y el Clima', Publicaciones de la AEC, Serie A, N 3, pp 63-73, Palma de Mallorca, Spain

Warmer, deeper, and greener mixed layers in the North Atlantic subpolar gyre over the last 50 years.

PubMed

Martinez, Elodie; Raitsos, Dionysios E; Antoine, David

2016-02-01

Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom-up processes, the top-down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi-decadal Oscillation (AMO). While previous studies have hypothesized that climate-driven warming would facilitate seasonal stratification of surface waters and long-term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom-up (NAO control) and top-down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales. © 2015 John Wiley & Sons Ltd.

North Atlantic climate variability: The role of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Hurrell, James W.; Deser, Clara

2009-08-01

Marine ecosystems are undergoing rapid change at local and global scales. To understand these changes, including the relative roles of natural variability and anthropogenic effects, and to predict the future state of marine ecosystems requires quantitative understanding of the physics, biogeochemistry and ecology of oceanic systems at mechanistic levels. Central to this understanding is the role played by dominant patterns or "modes" of atmospheric and oceanic variability, which orchestrate coherent variations in climate over large regions with profound impacts on ecosystems. We review the spatial structure of extratropical climate variability over the Northern Hemisphere and, specifically, focus on modes of climate variability over the extratropical North Atlantic. A leading pattern of weather and climate variability over the Northern Hemisphere is the North Atlantic Oscillation (NAO). The NAO refers to a redistribution of atmospheric mass between the Arctic and the subtropical Atlantic, and swings from one phase to another producing large changes in surface air temperature, winds, storminess and precipitation over the Atlantic as well as the adjacent continents. The NAO also affects the ocean through changes in heat content, gyre circulations, mixed layer depth, salinity, high latitude deep water formation and sea ice cover. Thus, indices of the NAO have become widely used to document and understand how this mode of variability alters the structure and functioning of marine ecosystems. There is no unique way, however, to define the NAO. Several approaches are discussed including both linear (e.g., principal component analysis) and nonlinear (e.g., cluster analysis) techniques. The former, which have been most widely used, assume preferred atmospheric circulation states come in pairs, in which anomalies of opposite polarity have the same spatial structure. In contrast, nonlinear techniques search for recurrent patterns of a specific amplitude and sign. They reveal

North Atlantic climate variability: The role of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Hurrell, James W.; Deser, Clara

2010-02-01

Marine ecosystems are undergoing rapid change at local and global scales. To understand these changes, including the relative roles of natural variability and anthropogenic effects, and to predict the future state of marine ecosystems requires quantitative understanding of the physics, biogeochemistry and ecology of oceanic systems at mechanistic levels. Central to this understanding is the role played by dominant patterns or "modes" of atmospheric and oceanic variability, which orchestrate coherent variations in climate over large regions with profound impacts on ecosystems. We review the spatial structure of extratropical climate variability over the Northern Hemisphere and, specifically, focus on modes of climate variability over the extratropical North Atlantic. A leading pattern of weather and climate variability over the Northern Hemisphere is the North Atlantic Oscillation (NAO). The NAO refers to a redistribution of atmospheric mass between the Arctic and the subtropical Atlantic, and swings from one phase to another producing large changes in surface air temperature, winds, storminess and precipitation over the Atlantic as well as the adjacent continents. The NAO also affects the ocean through changes in heat content, gyre circulations, mixed layer depth, salinity, high latitude deep water formation and sea ice cover. Thus, indices of the NAO have become widely used to document and understand how this mode of variability alters the structure and functioning of marine ecosystems. There is no unique way, however, to define the NAO. Several approaches are discussed including both linear (e.g., principal component analysis) and nonlinear (e.g., cluster analysis) techniques. The former, which have been most widely used, assume preferred atmospheric circulation states come in pairs, in which anomalies of opposite polarity have the same spatial structure. In contrast, nonlinear techniques search for recurrent patterns of a specific amplitude and sign. They reveal

Decadal-timescale changes of the Atlantic overturning circulation and climate in a coupled climate model with a hybrid-coordinate ocean component

NASA Astrophysics Data System (ADS)

Persechino, A.; Marsh, R.; Sinha, B.; Megann, A. P.; Blaker, A. T.; New, A. L.

2012-08-01

A wide range of statistical tools is used to investigate the decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) and associated key variables in a climate model (CHIME, Coupled Hadley-Isopycnic Model Experiment), which features a novel ocean component. CHIME is as similar as possible to the 3rd Hadley Centre Coupled Model (HadCM3) with the important exception that its ocean component is based on a hybrid vertical coordinate. Power spectral analysis reveals enhanced AMOC variability for periods in the range 15-30 years. Strong AMOC conditions are associated with: (1) a Sea Surface Temperature (SST) anomaly pattern reminiscent of the Atlantic Multi-decadal Oscillation (AMO) response, but associated with variations in a northern tropical-subtropical gradient; (2) a Surface Air Temperature anomaly pattern closely linked to SST; (3) a positive North Atlantic Oscillation (NAO)-like pattern; (4) a northward shift of the Intertropical Convergence Zone. The primary mode of AMOC variability is associated with decadal changes in the Labrador Sea and the Greenland Iceland Norwegian (GIN) Seas, in both cases linked to the tropical activity about 15 years earlier. These decadal changes are controlled by the low-frequency NAO that may be associated with a rapid atmospheric teleconnection from the tropics to the extratropics. Poleward advection of salinity anomalies in the mixed layer also leads to AMOC changes that are linked to processes in the Labrador Sea. A secondary mode of AMOC variability is associated with interannual changes in the Labrador and GIN Seas, through the impact of the NAO on local surface density.

Serial clustering of extratropical cyclones and relationship with NAO and jet intensity based on the IMILAST cyclone database

NASA Astrophysics Data System (ADS)

Ulbrich, Sven; Pinto, Joaquim G.; Economou, Theodoros; Stephenson, David B.; Karremann, Melanie K.; Shaffrey, Len C.

2017-04-01

Cyclone families are a frequent synoptic weather feature in the Euro-Atlantic area, particularly during wintertime. Given appropriate large-scale conditions, such series (clusters) of storms may cause large socio-economic impacts and cumulative losses. Recent studies analyzing reanalysis data using single cyclone tracking methods have shown that serial clustering of cyclones occurs on both flanks and downstream regions of the North Atlantic storm track. Based on winter (DJF) cyclone counts from the IMILAST cyclone database, we explore the representation of serial clustering in the ERA-Interim period and its relationship with the NAO-phase and jet intensity. With this aim, clustering is estimated by the dispersion of winter (DJF) cyclone passages for each grid point over the Euro-Atlantic area. Results indicate that clustering over the Eastern North Atlantic and Western Europe can be identified for all methods, although the exact location and the dispersion magnitude may vary. The relationship between clustering and (i) the NAO-phase and (ii) jet intensity over the North Atlantic is statistically evaluated. Results show that the NAO-index and the jet intensity show a strong contribution to clustering, even though some spread is found between methods. We conclude that the general features of clustering of extratropical cyclones over the North Atlantic and Western Europe are robust to the choice of tracking method. The same is true for the influence of the NAO and jet intensity on cyclone dispersion.

The lagged connection of the positive NAO with the MJO phase 3 in a simplified atmospheric model

NASA Astrophysics Data System (ADS)

Shao, Xiaolu; Song, Jie; Li, Shuanglin

2018-03-01

Based on a simplified nonlinear model and reanalysis data, the lagged connection of the North Atlantic Oscillation (NAO) with the Madden-Julian Oscillation (MJO) in boreal winters is investigated. The positive NAO is observed to occur more frequently about 8-20 days after the onset of the MJO phase 3. A series of heating forcing experiments and initial-value experiments are conducted by utilizing the Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model. The extratropical responses to the tropical heating associated with the MJO phase 3 are characterized by a wave train over the Pacific-North American region with an anticyclone anomaly over the northeastern Pacific and then followed by a positive-NAO-like pattern over the North Atlantic sector. These circulation anomalies generally match the observed lagged-connection well. At the earlier stage, the Rossby wave train excited by the MJO convection propagates into the North Atlantic, leading to a planetary wave anomaly with a low-over-high dipole prior to the positive NAO. At the later stage, the anomalous synoptic eddy vorticity forcing (EVF) streamfunction tendency has a negative-over-positive dipole, which plays a key role in the development of the positive NAO. Further analysis of the initial-value experiments indicates that, for the subsequent formation of the positive NAO, the anomalous circulation over the Indian Ocean aroused by the MJO phase 3 is more crucial than that over the northeastern Pacific.

Climate variability and marine ecosystem impacts: a North Atlantic perspective

NASA Astrophysics Data System (ADS)

Parsons, L. S.; Lear, W. H.

In recent decades it has been recognized that in the North Atlantic climatic variability has been largely driven by atmospheric forcing related to the North Atlantic Oscillation (NAO). The NAO index began a pronounced decline around 1950 to a low in the 1960s. From 1970 onward the NAO index increased to its most extreme and persistent positive phase during the late 1980s and early 1990s. Changes in the pattern of the NAO have differential impacts on the opposite sides of the North Atlantic and differential impacts in the north and south. The changes in climate resulting from changes in the NAO appear to have had substantial impacts on marine ecosystems, in particular, on fish productivity, with the effects varying from region to region. An examination of several species and stocks, e.g. gadoids, herring and plankton in the Northeast Atlantic and cod and shellfish in the Northwest Atlantic, indicates that there is a link between long-term trends in the NAO and the productivity of various components of the marine ecosystem. While broad trends are evident, the mechanisms are poorly understood. Further research is needed to improve our understanding of how this climate variability affects the productivity of various components of the North Atlantic marine ecosystem.

Norwegian fjord sediments reveal NAO related winter temperature and precipitation changes of the past 2800 years

NASA Astrophysics Data System (ADS)

Faust, Johan C.; Fabian, Karl; Milzer, Gesa; Giraudeau, Jacques; Knies, Jochen

2016-02-01

The North Atlantic Oscillation (NAO) is the leading mode of atmospheric circulation variability in the North Atlantic region. Associated shifts of storm tracks, precipitation and temperature patterns affect energy supply and demand, fisheries and agricultural, as well as marine and terrestrial ecological dynamics. Long-term NAO records are crucial to better understand its response to climate forcing factors, and assess predictability and shifts associated with ongoing climate change. A recent study of instrumental time series revealed NAO as main factor for a strong relation between winter temperature, precipitation and river discharge in central Norway over the past 50 years. Here we compare geochemical measurements with instrumental data and show that primary productivity recorded in central Norwegian fjord sediments is sensitive to NAO variability. This observation is used to calibrate paleoproductivity changes to a 500-year reconstruction of winter NAO (Luterbacher et al., 2001). Conditioned on a stationary relation between our climate proxy and the NAO we establish a first high resolution NAO proxy record (NAOTFJ) from marine sediments covering the past 2800 years. The NAOTFJ shows distinct co-variability with climate changes over Greenland, solar activity and Northern Hemisphere glacier dynamics as well as climatically associated paleo-demographic trends. The here presented climate record shows that fjord sediments provide crucial information for an improved understanding of the linkages between atmospheric circulation, solar and oceanic forcing factors.

Decadal changes in North Atlantic atmospheric circulation patterns recorded by sand spits since 1800 CE

NASA Astrophysics Data System (ADS)

Poirier, Clément; Tessier, Bernadette; Chaumillon, Éric; Bertin, Xavier; Fruergaard, Mikkel; Mouazé, Dominique; Noël, Suzanne; Weill, Pierre; Wöppelmann, Guy

2017-03-01

Present-day coastal barriers represent around 15% of the world's oceanic shorelines, and play an important role as early warning indicators of environmental change. Among them, wave-dominated barriers are dynamic landforms that tend to migrate landward in response to storms and sea-level change. High rates of sediment supply can locally offset the global retrogradation trend, providing valuable records of past environmental change occurring on transgressive coasts. However, geochronological control limits the temporal resolution of such records to millennial or centennial timescales, and the decadal or even faster response of wave-built barriers to historical climate changes is therefore poorly understood. In this study, we show that shoreline dynamics of sand spits reconstructed from old cartographic documents has been synchronous on both margins of the North Atlantic Ocean since about 1800 CE. Spit growth accelerated drastically during three periods lasting about 15 years, characterised by positive North Atlantic Oscillation (NAO) and negative East Atlantic-West Russia (EA-WR) atmospheric circulation patterns. These changes are in phase with periods of increased volcanic activity. We use a high-resolution wave hindcast (1948-2014 CE) in a reference area to confirm the association between NAO and EA-WR as a proxy for offshore and nearshore wave height and for associated longshore sediment transport (LST) involved in spit growth. A 24-month lagged correlation between sediment transport and volcanic aerosol optical thickness (concentration of ashes in the atmosphere) is observed, suggesting that spit shoreline dynamics at the decadal timescale is partially forced by external climate drivers via cascading effects on atmospheric circulation patterns and wave climate. Our results imply that NAO variability alone is not sufficient to understand the evolution of wave-built coastal environments. The associated sediment record can be used to reconstruct multi-decadal

Evidence of the Atlantic Multidecadal Oscillation driving multi-decadal variability of summertime surface air quality in the eastern United States: Implications for air quality management in the coming decades

NASA Astrophysics Data System (ADS)

Shen, L.; Mickley, L. J.

2016-12-01

Atlantic sea surface temperatures have a significant influence on the summertime meteorology and air quality in the eastern United States. In this study, we investigate the effect of the Atlantic Multidecadal Oscillation (AMO) on two key air pollutants, surface ozone and PM2.5, over the eastern United States. The shift of AMO from cold to warm phase increases surface air temperatures by 0.5 K across the East and reduces precipitation, resulting in a warmer and drier summer. By applying observed, present-day relationships between these pollutants and meteorological variables to a variety of observations and historical reanalysis datasets, we calculate the impacts of AMO on U.S. air quality. Our study reveals a multidecadal variability in mean summertime (JJA) maximum daily 8-hour (MDA8) ozone and surface PM2.5 concentrations in the eastern United States. In one-half cycle ( 30 years) of the AMO from negative to positive phase with constant anthropogenic emissions, JJA MDA8 ozone concentrations increase by 1-3 ppbv in the Northeast and 2-5 ppbv in the Great Plains; JJA PM2.5 concentrations increase by 0.8-1.2 μg m-3 in the Northeast and Southeast. The resulting impact on mortality rates is 4000 excess deaths per half cycle of AMO. We suggest that a complete picture of air quality management in coming decades requires consideration of the AMO influence.

On the persistence and coherence of subpolar sea surface temperature and salinity anomalies associated with the Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Zhang, Rong

2017-08-01

This study identifies key features associated with the Atlantic multidecadal variability (AMV) in both observations and a fully coupled climate model, e.g., decadal persistence of monthly mean subpolar North Atlantic (NA) sea surface temperature (SST) and salinity (SSS) anomalies, and high coherence at low frequency among subpolar NA SST/SSS, upper ocean heat/salt content, and the Atlantic Meridional Overturning Circulation (AMOC) fingerprint. These key AMV features, which can be used to distinguish the AMV mechanism, cannot be explained by the slab ocean model results or the red noise process but are consistent with the ocean dynamics mechanism. This study also shows that at low frequency, the correlation and regression between net surface heat flux and SST anomalies are key indicators of the relative roles of oceanic versus atmospheric forcing in SST anomalies. The oceanic forcing plays a dominant role in the subpolar NA SST anomalies associated with the AMV.

North Atlantic sub-decadal variability in climate models

NASA Astrophysics Data System (ADS)

Reintges, Annika; Martin, Thomas; Latif, Mojib; Park, Wonsun

2017-04-01

The North Atlantic Oscillation (NAO) is the dominant variability mode for the winter climate of the North Atlantic sector. During a positive (negative) NAO phase, the sea level pressure (SLP) difference between the subtropical Azores high and the subpolar Icelandic low is anomalously strong (weak). This affects, for example, temperature, precipitation, wind, and surface heat flux over the North Atlantic, and over large parts of Europe. In observations we find enhanced sub-decadal variability of the NAO index that goes along with a dipolar sea surface temperature (SST) pattern. The corresponding SLP and SST patterns are reproduced in a control experiment of the Kiel Climate Model (KCM). Large-scale air-sea interaction is suggested to be essential for the North Atlantic sub-decadal variability in the KCM. The Atlantic Meridional Overturning Circulation (AMOC) plays a key role, setting the timescale of the variability by providing a delayed negative feedback to the NAO. The interplay of the NAO and the AMOC on the sub-decadal timescale is further investigated in the CMIP5 model ensemble. For example, the average CMIP5 model AMOC pattern associated with sub-decadal variability is characterized by a deep-reaching dipolar structure, similar to the KCM's sub-decadal AMOC variability pattern. The results suggest that dynamical air-sea interactions are crucial to generate enhanced sub-decadal variability in the North Atlantic climate.

Atlantic Multidecadal Oscillation Modulates the Impacts of Arctic Sea Ice Decline

NASA Astrophysics Data System (ADS)

Li, Fei; Orsolini, Yvan J.; Wang, Huijun; Gao, Yongqi; He, Shengping

2018-03-01

The Arctic sea ice cover has been rapidly declining in the last two decades, concurrent with a shift in the Atlantic Multidecadal Oscillation (AMO) to its warm phase around 1996/1997. Here we use both observations and model simulations to investigate the modulation of the atmospheric impacts of the decreased sea ice cover in the Atlantic sector of the Arctic (AASIC) by the AMO. We find that the AASIC loss during a cold AMO phase induces increased Ural blocking activity, a southeastward-extended snowpack, and a cold continent anomaly over Eurasia in December through northerly cold air advection and moisture transport from the Arctic. The increased Ural blocking activity and more extended Eurasian snowpack strengthen the upward propagation of planetary waves over the Siberian-Pacific sector in the lower stratosphere and hence lead to a weakened stratospheric polar vortex and a negative Arctic Oscillation (AO) phase at the surface in February. However, corresponding to the AASIC loss during a warm AMO phase, one finds more widespread warming over the Arctic and a reduced snowpack over Northern Eurasia in December. The stratosphere-troposphere coupling is suppressed in early winter and no negative AO anomaly is found in February. We suggest that the cold AMO phase is important to regulate the atmospheric response to AASIC decline, and our study provides insight to the ongoing debate on the connection between the Arctic sea ice and the AO.

Impact of ENSO longitudinal position on teleconnections to the NAO

NASA Astrophysics Data System (ADS)

Zhang, Wenjun; Wang, Ziqi; Stuecker, Malte F.; Turner, Andrew G.; Jin, Fei-Fei; Geng, Xin

2018-02-01

While significant improvements have been made in understanding how the El Niño-Southern Oscillation (ENSO) impacts both North American and Asian climate, its relationship with the North Atlantic Oscillation (NAO) remains less clear. Observations indicate that ENSO exhibits a highly complex relationship with the NAO-associated atmospheric circulation. One critical contribution to this ambiguous ENSO/NAO relationship originates from ENSO's diversity in its spatial structure. In general, both eastern (EP) and central Pacific (CP) El Niño events tend to be accompanied by a negative NAO-like atmospheric response. However, for two different types of La Niña the NAO response is almost opposite. Thus, the NAO responses for the CP ENSO are mostly linear, while nonlinear NAO responses dominate for the EP ENSO. These contrasting extra-tropical atmospheric responses are mainly attributed to nonlinear air-sea interactions in the tropical eastern Pacific. The local atmospheric response to the CP ENSO sea surface temperature (SST) anomalies is highly linear since the air-sea action center is located within the Pacific warm pool, characterized by relatively high climatological SSTs. In contrast, the EP ENSO SST anomalies are located in an area of relatively low climatological SSTs in the eastern equatorial Pacific. Here only sufficiently high positive SST anomalies during EP El Niño events are able to overcome the SST threshold for deep convection, while hardly any anomalous convection is associated with EP La Niña SSTs that are below this threshold. This ENSO/NAO relationship has important implications for NAO seasonal prediction and places a higher requirement on models in reproducing the full diversity of ENSO.

Multi-decadal storminess fluctuations of Black Sea due to North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Kuznetsov, Sergey; Saprykina, Yana; Grigorieva, Victoria; Aydoǧan, Berna; Aydoǧan, Burak

2017-04-01

Storminess variability is of key importance for many marine applications, naval and coastal engineering. Studying the evolution of this phenomenon along with large scale atmospheric patterns and being able to predict them is crucial for in the context of rising sea level due to climate change what make the low-lying coasts in the Black Sea to become increasingly vulnerable to marine hazards. The aim of this work is to clarify the trends, statistics and reasons of variations of storminess in dependence of such climatic characteristic as NAO (North Atlantic Oscillation Index). The analysis of Black Sea storminess activity was performed on the base of visual wave observations (Voluntary Observing Ship or VOS) for the period 1970-2011. Annual means and maximum heights of wind-driven seas and swell waves averaging over whole Black Sea area were investigated separately. The both wind-driven seas and swell demonstrate the decreasing in heights about 10% the same as their periods for the chosen time frame. Parametric spectral analysis was performed. The periods of wave height fluctuations for wind-driven seas and swell were shown to coincide with each other and with periods of low frequency fluctuation of NOA: 14 and 4 year respectively. Correlation coefficients of wave height and NOA were 0.3 for swell and 0.4 for wind-driven sea. Nonlinear regularities of NAO fluctuations were investigated using wavelet and spavlet (spectra of modules of wavelet coefficients) analyses. Their influence on variability of storminess in Black Sea is discussed. The reported study was funded by RFBR (project No. 16-55-76002 ERA_a) and by TUBITAK (project No. 116M061) in frame of BS STEMA project.

Statistical Aspects of North Atlantic Basin Tropical Cyclones During the Weather Satellite Era, 1960-2013. Part 2

NASA Technical Reports Server (NTRS)

Wilson, Robert M.

2014-01-01

This Technical Publication (TP) is part 2 of a two-part study of the North Atlantic basin tropical cyclones that occurred during the weather satellite era, 1960-2013. In particular, this TP examines the inferred statistical relationships between 25 tropical cyclone parameters and 9 specific climate-related factors, including the (1) Oceanic Niño Index (ONI), (2) Southern Oscillation Index (SOI), (3) Atlantic Multidecadal Oscillation (AMO) index, (4) Quasi-Biennial Oscillation (QBO) index, (5) North Atlantic Oscillation (NAO) index of the Climate Prediction Center (CPC), (6) NAO index of the Climate Research Unit (CRU), (7) Armagh surface air temperature (ASAT), (8) Global Land-Ocean Temperature Index (GLOTI), and (9) Mauna Loa carbon dioxide (CO2) (MLCO2) index. Part 1 of this two-part study examined the statistical aspects of the 25 tropical cyclone parameters (e.g., frequencies, peak wind speed (PWS), accumulated cyclone energy (ACE), etc.) and provided the results of statistical testing (i.e., runs-testing, the t-statistic for independent samples, and Poisson distributions). Also, the study gave predictions for the frequencies of the number of tropical cyclones (NTC), number of hurricanes (NH), number of major hurricanes (NMH), and number of United States land-falling hurricanes (NUSLFH) expected for the 2014 season, based on the statistics of the overall interval 1960-2013, the subinterval 1995-2013, and whether the year 2014 would be either an El Niño year (ENY) or a non-El Niño year (NENY).

Influence of the North Atlantic Oscillation on European tropospheric composition: an observational and modelling study

NASA Astrophysics Data System (ADS)

Pope, R.; Chipperfield, M.

2017-12-01

The North Atlantic Oscillation (NAO) has a strong influence on winter-time North Atlantic and European circulation patterns. Under the positive phase of the NAO (NAO+), intensification of the climatological Icelandic low and Azores high pressure systems results in strong westerly flow across the Atlantic into Europe. Under the NAO negative phase (NAO-), there is a weakening of this meridional pressure gradient resulting in a southerly shift in the westerlies flow towards the sub-tropical Atlantic. Therefore, NAO+ and NAO- introduce unstable stormy and drier stable conditions into Europe, respectively. Under NAO+ conditions, the strong westerlies tend to enhance transport of European pollution (e.g. nitrogen oxides) away from anthropogenic source regions. While during NAO-, the more stable conditions lead to a build up of pollutants. However, secondary pollutants (i.e. tropospheric ozone) show the opposite signal where NAO+, while transporting primary pollutants away, introduces Atlantic ozone enriched air into Europe. Here ozone can form downwind of pollution from continental North America and be transported into Europe via the westerly flow. Under NAO-, this westerly ozone transport is reduced yielding lower European ozone concentrations also depleted further by ozone loss through the reaction with NOx, which has accumulated over the continent. Peroxyacetyl nitrate (PAN), observed in the upper troposphere - lower stratosphere (UTLS) by satellite, peaks over Iceland/Southern Greenland in NAO-, between 200-100 hPa, consistent with trapping by an anticyclone at this altitude. During NAO+, PAN is enhanced over the sub-tropical Atlantic and Arctic. Model simulations show that enhanced PAN over Iceland/Southern Greenland in NAO- is associated with vertical transport from the troposphere into the UTLS, while peak Arctic PAN in NAO+ is its accumulation given the strong northerly meridional transport in the UTLS. UTLS ozone spatial anomalies, relative to the winter

Linking North Atlantic Teleconnections to Latitudinal Variability of Wave Climate Along the North American Atlantic Coast

NASA Astrophysics Data System (ADS)

Provancha, C.; Adams, P. N.; Hegermiller, C.; Storlazzi, C. D.

2015-12-01

Shoreline change via coastal erosion and accretion is largely influenced by variations in ocean wave climate. Identifying the sources of these variations is challenging because the timing of wave energy delivery varies over multiple timescales within ocean basins. We present the results of an investigation of USACE Wave Information Studies hindcast hourly wave heights, periods, and directions along the North American Atlantic coast from 1980-2012, designed to explore links between wave climate and teleconnection patterns. Trends in median and extreme significant wave heights (SWHs) demonstrate that mean monthly SWHs increased from 1 to 5 cm/yr along the roughly 3000 km reach of study area, with changes in hurricane season waves appearing to be most influential in producing the overall trends. Distributions of SWHs categorized by North Atlantic Oscillation (NAO) phase, show that positive-period NAO SWHs are greater than negative-period NAO SWHs along the entire eastern seaboard (25°N to 45°N). The most prominent wave direction off Cape Cod, MA during positive-period NAO is approximately 105°, as compared to approximately 75° during negative-period NAO. Prominent wave directions between Cape Canaveral, FL, and Savannah, GA exhibit a similar shift but during opposite phases of the NAO. The results of this analysis suggest that the atmosphere-ocean interactions associated with contrasting NAO phases can significantly change the wave climate observed offshore along the North American Atlantic coast, altering alongshore wave energy fluxes and sediment transport patterns along the coast.

A multiproxy reconstruction of NAO evolution in the Azores archipelago since 1350 AD

NASA Astrophysics Data System (ADS)

Hernández, Armand; Doolittle, Sara; Bao, Roberto; Trigo, Ricardo M.; Rubio-Inglés, Maria J.; Sánchez-López, Guiomar; Vázquez-Loureiro, David; Gonçalves, Vitor; Raposeiro, Pedro M.; Marques, Helena S.; Sáez, Alberto; Giralt, Santiago

2014-05-01

The North Atlantic Oscillation (NAO) is the main atmospheric circulation pattern affecting climate variability in the Northern Hemisphere, having a major impact on both marine and terrestrial ecosystems. Instrumental records of the NAO are relatively short, and therefore paleoenvironmental multiproxy approaches become fundamental to better understand its behaviour for longer scale periods. The NAO is often defined as a large-scale meridional oscillation dipole of air pressure between the Azores High and the Iceland Low. Some of the NAO definitions include the use of sea level pressure from Ponta Delgada station in Azores, and thus any NAO reconstruction would gain in robustness if it includes paleoenvironmental information from this archipelago located at the southern end of the meridional dipole that characterizes the NAO pattern. However, to the best of our knowledge, very few historical and long-term reconstructions have been conducted in the Azores Islands. We present a ca. 600-year-long multiproxy reconstruction of the NAO evolution based on facies analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF) core scanning, elemental and isotope geochemistry on bulk organic matter and the preliminary study of diatom and chironomid content from the sedimentary record of Lake Empadadas (37° 49' N - 25° 44' W, Azores Archipelago, Portugal). The precipitation regime in Azores Archipelago (i.e. intra and inter-annual variability) is clearly influenced by the NAO index, thus periods with dominant positive NAO index values (NAO+) are usually characterized by low winter precipitation in the Azores. Conversely, negative NAO phases (NAO-) induce high winter precipitation in the archipelago. These patterns suggest that past (winter) precipitation changes on the Azores may be partially used as a proxy for NAO changes, and thus a proxy for more large-scale changes in the North Atlantic region. According to this multiproxy characterization of the Lake Empadadas sediments

Beyond the NAO: Dynamics and Precipitation Implications of the Azores High Since AD 800

NASA Astrophysics Data System (ADS)

Thatcher, D.; Wanamaker, A. D.; Denniston, R. F.; Asmerom, Y.; Ummenhofer, C.; Polyak, V. J.; Haws, J.; Gillikin, D. P.

2016-12-01

Atmospheric circulation in the North Atlantic region during the last millennium, particularly the state of the North Atlantic Oscillation (NAO), a system closely tied to regional precipitation dynamics, remains the subject of considerable debate in both proxy- and model-based studies. It has been suggested that the winter NAO was in a persistently positive state during the Medieval Climate Anomaly (MCA; AD 850-1250), resulting in increased precipitation across much of northern Europe and decreased rainfall across Iberia. However, besides changes in atmospheric circulation and precipitation dynamics that could be associated with an altered mean state of the NAO, relatively little attention has been given to atmospheric dynamics, namely the intensity and location, of the subtropical high system (Azores High, the southern node of the NAO) in driving hydroclimate in Iberia. Presented here is a continuous, precisely dated, and sub-decadally-resolved stalagmite isotopic and elemental time series from Buraca Gloriosa (BG) cave, western Portugal, situated within the center of the Azores High at the southern node of the NAO, which preserves evidence of regional hydroclimate from approximately AD 800 to the present. Stalagmite oxygen and carbon isotopic values and magnesium/calcium ratios primarily reflect effective moisture and reveal generally dry conditions during the MCA with a rapid shift to wetter conditions during the Little Ice Age (LIA; AD 1250-1850) at this location. Our proxy data reveal that substantial short-term hydroclimate variability characterized the last 1200 years. They support the hypothesis that while an intensified, semi-persistent subtropical high (and likely positive NAO state) characterized much of the MCA, the NAO remained variable over this time period. Climate model results also suggest that the Azores High pressure system both migrated southward and weakened from the MCA into the LIA.

Links between North Atlantic atmospheric blocking and recent trends in European winter precipitation

NASA Astrophysics Data System (ADS)

Ummenhofer, Caroline; Seo, Hyodae; Kwon, Young-Oh; Joyce, Terrence

2015-04-01

European precipitation has sustained robust trends during wintertime (January - March) over recent decades. Central, western, and northern Europe have become wetter by an average 0.1-0.3% per annum for the period 1901-2010, while southern Europe, including the Iberian Peninsula, much of Italy and the Balkan States, has sustained drying of -0.2% per annum or more over the same period. The overall pattern is consistent across different observational precipitation products, while the magnitude of the precipitation trends varies amongst data sets. Using cluster analysis, which identifies recurrent states (or regimes) of European winter precipitation by grouping them according to an objective similarity criterion, changes in the frequency of dominant winter precipitation patterns over the past century are evaluated. Considerable multi-decadal variability exists in the frequency of dominant winter precipitation patterns: more recent decades are characterised by significantly fewer winters with anomalous wet conditions over southern, western, and central Europe. In contrast, winters with dry conditions in western and southern Europe, but above-average rainfall in western Scandinavia and the northern British Isles, have been more common recently. We evaluate the associated multi-decadal large-scale circulation changes across the broader extratropical North Atlantic region, which accompany the observed wintertime precipitation variability using the 20th Century reanalysis product. Some influence of the North Atlantic Oscillation (NAO) is apparent in modulating the frequency of dominant precipitation patterns. However, recent trends in the characteristics of atmospheric blocking across the North Atlantic sector indicate a change in the dominant blocking centres (near Greenland, the British Isles, and west of the Iberian Peninsula). Associated changes in sea level pressure, storm track position and strength, and oceanic heat fluxes across the North Atlantic region are also

A new record of Atlantic sea surface salinity from 1896-2013 reveals the signatures of climate variability and long-term trends

NASA Astrophysics Data System (ADS)

Friedman, A. R.; Reverdin, G. P.; Khodri, M.; Gastineau, G.

2017-12-01

In the North Atlantic, sea surface salinity is both an indicator of the hydrological cycle and an active component of the ocean circulation. As an indirect "ocean rain gauge", surface salinity reflects the net surface fluxes of evaporation - precipitation + runoff, along with advection and vertical mixing. Subpolar surface salinity also may influence the strength of deep convection and the Atlantic Meridional Overturning Circulation (AMOC). However, continuous surface salinity time series beginning before the 1950s are rare, limiting our ability to resolve modes of variability and long-term trends. Here, we present a new gridded surface salinity record in the Atlantic from 1896-2013, compiled from a variety of historical sources. The compilation covers most of the Atlantic from 20°S-70°N, at 100-1000 km length scale and interannual temporal resolution, allowing us to resolve major modes of variability and linkages with large-scale Atlantic climate variations. We find that the low-latitude (tropical and subtropical) Atlantic and the subpolar Atlantic surface salinity are negatively correlated, with subpolar anomalies leading low-latitude anomalies by about a decade. Subpolar surface salinity varies in phase with the Atlantic Multidecadal Oscillation (AMO), whereas low-latitude surface salinity lags the AMO and varies in phase with the low-frequency North Atlantic Oscillation (NAO). Additionally, northern tropical surface salinity is anticorrelated with the AMO and with Sahel rainfall, suggesting that it reflects the latitude of the Intertropical Convergence Zone. The 1896-2013 long-term trend features an amplification of the mean Atlantic surface salinity gradient pattern, with freshening in the subpolar Atlantic and salinification in the tropical and subtropical Atlantic. We find that regressing out the AMO and the low-frequency NAO has little effect on the long-term residual trend. The spatial trend structure is consistent with the "rich-get-richer" hydrological

Winter Eurasian cooling linked with the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Luo, Dehai; Chen, Yanan; Dai, Aiguo; Mu, Mu; Zhang, Renhe; Ian, Simmonds

2017-12-01

In this paper, we analyze observational and reanalysis data to demonstrate that the Atlantic Multidecadal Oscillation (AMO) significantly modulates winter Eurasian surface air temperature through its impact on the shape, frequency and persistence of Ural blocking (UB) events that last for 10-20 d. This impact results from changes in mid-high latitude westerly winds over Eurasia associated with the warming in the Barents-Kara Seas (BKS) through the AMO-driven high sea surface temperature and sea-ice decline and resultant weakening in meridional temperature gradients. The BKS warming has a strongest positive correlation with the AMO at a time lag of about 14 years. During the recent positive AMO phase, more persistent northwest-southeast (NW-SE) oriented UB events are favored by weakened westerly winds in Eurasian mid-high latitudes. Through cold atmospheric advection and radiative cooling, such UB events produce a strong, persistent and widespread cooling over Eurasia and enhance BKS warming during 1999-2015. However, the positive AMO phase cannot directly produce the Eurasian cooling if the UB is absent. Thus, we conclude that the recent AMO phase change is a major cause of the recent winter cooling over Eurasia through its impact on BKS temperature and sea ice, which in turn affect the meridional temperature gradient, the westerly winds and the UB events.

Cod Collapse and the Climate in the North Atlantic

NASA Astrophysics Data System (ADS)

Meng, K. C.; Oremus, K. L.; Gaines, S.

2014-12-01

Effective fisheries management requires forecasting population changes. We find a negative relationship between the North Atlantic Oscillation (NAO) index and subsequently surveyed biomass and catch of Atlantic cod, Gadus morhua, off the New England coast. A 1-unit NAO increase is associated with a 17% decrease in surveyed biomass of age-1 cod the following year. This relationship persists as the cod mature, such that observed NAO can be used to forecast future adult biomass. We also document that an NAO event lowers catch for up to 15 years afterward. In contrast to forecasts by existing stock assessment models, our NAO-driven statistical model successfully hindcasts the recent collapse of New England cod fisheries following strong NAO events in 2007 and 2008 (see figure). This finding can serve as a template for forecasting other fisheries affected by climatic conditions.

Wavelet-based time series bootstrap model for multidecadal streamflow simulation using climate indicators

NASA Astrophysics Data System (ADS)

Erkyihun, Solomon Tassew; Rajagopalan, Balaji; Zagona, Edith; Lall, Upmanu; Nowak, Kenneth

2016-05-01

A model to generate stochastic streamflow projections conditioned on quasi-oscillatory climate indices such as Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO) is presented. Recognizing that each climate index has underlying band-limited components that contribute most of the energy of the signals, we first pursue a wavelet decomposition of the signals to identify and reconstruct these features from annually resolved historical data and proxy based paleoreconstructions of each climate index covering the period from 1650 to 2012. A K-Nearest Neighbor block bootstrap approach is then developed to simulate the total signal of each of these climate index series while preserving its time-frequency structure and marginal distributions. Finally, given the simulated climate signal time series, a K-Nearest Neighbor bootstrap is used to simulate annual streamflow series conditional on the joint state space defined by the simulated climate index for each year. We demonstrate this method by applying it to simulation of streamflow at Lees Ferry gauge on the Colorado River using indices of two large scale climate forcings: Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO), which are known to modulate the Colorado River Basin (CRB) hydrology at multidecadal time scales. Skill in stochastic simulation of multidecadal projections of flow using this approach is demonstrated.

Multidecadal climate variability of global lands and oceans

USGS Publications Warehouse

McCabe, G.J.; Palecki, M.A.

2006-01-01

Principal components analysis (PCA) and singular value decomposition (SVD) are used to identify the primary modes of decadal and multidecadal variability in annual global Palmer Drought Severity Index (PDSI) values and sea-surface temperature (SSTs). The PDSI and SST data for 1925-2003 were detrended and smoothed (with a 10-year moving average) to isolate the decadal and multidecadal variability. The first two principal components (PCs) of the PDSI PCA explained almost 38% of the decadal and multidecadal variance in the detrended and smoothed global annual PDSI data. The first two PCs of detrended and smoothed global annual SSTs explained nearly 56% of the decadal variability in global SSTs. The PDSI PCs and the SST PCs are directly correlated in a pairwise fashion. The first PDSI and SST PCs reflect variability of the detrended and smoothed annual Pacific Decadal Oscillation (PDO), as well as detrended and smoothed annual Indian Ocean SSTs. The second set of PCs is strongly associated with the Atlantic Multidecadal Oscillation (AMO). The SVD analysis of the cross-covariance of the PDSI and SST data confirmed the close link between the PDSI and SST modes of decadal and multidecadal variation and provided a verification of the PCA results. These findings indicate that the major modes of multidecadal variations in SSTs and land-surface climate conditions are highly interrelated through a small number of spatially complex but slowly varying teleconnections. Therefore, these relations may be adaptable to providing improved baseline conditions for seasonal climate forecasting. Published in 2006 by John Wiley & Sons, Ltd.

Associations of multi-decadal sea-surface temperature variability with US drought

USGS Publications Warehouse

McCabe, G.J.; Betancourt, J.L.; Gray, S.T.; Palecki, M.A.; Hidalgo, H.G.

2008-01-01

Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th century, but during the 19th century the tropical Pacific is a more consistent indicator of D2 M drought. The interaction between El Nin??o-Southern Oscillation (ENSO) and the AMO explain a large part of the D2M drought variability in the conterminous US. More modeling studies are needed to reveal possible mechanisms linking low-frequency ENSO variability and the AMO with drought in the conterminous US. ?? 2007 Elsevier Ltd and INQUA.

Variability of the Tropical Ocean Surface Temperatures at Decadal-Multidecadal Timescales. Part I: The Atlantic Ocean.

NASA Astrophysics Data System (ADS)

Mehta, Vikram M.

1998-09-01

Gridded time series from the Global Ocean Surface Temperature Atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical Atlantic sea surface temperature (SST) variations at decadal timescales, and to develop physical interpretations of statistical patterns of decadal SST variations. Each time series was 110 yr (1882-1991) long. The tropical Atlantic SST variations were compared with decadal variations in a 74-yr-long (1912-85) north Nordeste Brazil rainfall time series and a 106-yr-long (1886-1991) tropical Atlantic cyclone activity index time series. The tropical Atlantic SST variations were also compared with decadal variations in the extratropical Atlantic SST.Multiyear to multidecadal variations in the cross-equatorial dipole pattern identified as a dominant empirical pattern of the tropical Atlantic SST variations in earlier and present studies are shown to be variations in the approximately north-south gradient of SST anomalies. It is also shown that there was no dynamical-thermodynamical, dipole mode of SST variations during the analysis period. There was a distinct decadal timescale (12-13 yr) of SST variations in the tropical South Atlantic, whereas no distinct decadal timescale was found in the tropical North Atlantic SST variations. Approximately 80% of the coherent decadal variance in the cross-equatorial SST gradient was `explained' by coherent decadal oscillations in the tropical South Atlantic SSTs. There were three, possibly physical, modes of decadal variations in the tropical Atlantic SSTs during the analysis period. In the more energetic mode of the North Atlantic decadal SST variations, anomalies traveled into the tropical North Atlantic from the extratropical North Atlantic along the eastern boundary of the basin. The anomalies strengthened and resided in the tropical North Atlantic for several years, then frequently traveled northward into the mid-high-latitude North Atlantic along

Mechanisms and Early Detections of Multidecadal Oxygen Changes in the Interior Subpolar North Atlantic

NASA Astrophysics Data System (ADS)

Tjiputra, J. F.; Goris, N.; Lauvset, S. K.; Heinze, C.; Olsen, A.; Schwinger, J.; Steinfeldt, R.

2018-05-01

The oxygen response in the subpolar North Atlantic (SPNA) to future climate change is poorly understood. We investigate the multidecadal variability in interior oxygen and its association with the subpolar gyre index (a gyre strength proxy) for models and data. During positive phases, persistent strong Labrador Sea (LS) lateral and vertical mixing entrains oxygen-rich water into the interior southern SPNA and vice versa during negative phases. This is indicated by the observed anomalously fresh, cold, and low apparent oxygen utilization, resembling LS water mass during positive phases. We use this relationship to benchmark Earth system models. Under a high CO2 future, the best performing models project a steady decline in SPNA oxygen, driven partly by lower solubility and increases in apparent oxygen utilization. The deoxygenation depends on the sensitivity of the LS mixing to warming. The time of emergence of interior oxygen is projected to be decades earlier than that of temperature and salinity.

Multi-decadal Variability of the Wind Power Output

NASA Astrophysics Data System (ADS)

Kirchner Bossi, Nicolas; García-Herrera, Ricardo; Prieto, Luis; Trigo, Ricardo M.

2014-05-01

The knowledge of the long-term wind power variability is essential to provide a realistic outlook on the power output during the lifetime of a planned wind power project. In this work, the Power Output (Po) of a market wind turbine is simulated with a daily resolution for the period 1871-2009 at two different locations in Spain, one at the Central Iberian Plateau and another at the Gibraltar Strait Area. This is attained through a statistical downscaling of the daily wind conditions. It implements a Greedy Algorithm as classificator of a geostrophic-based wind predictor, which is derived by considering the SLP daily field from the 56 ensemble members of the longest homogeneous reanalysis available (20CR, 1871-2009). For calibration and validation purposes we use 10 years of wind observations (the predictand) at both sites. As a result, a series of 139 annual wind speed Probability Density Functions (PDF) are obtained, with a good performance in terms of wind speed uncertainty reduction (average daily wind speed MAE=1.48 m/s). The obtained centennial series allow to investigate the multi-decadal variability of wind power from different points of view. Significant periodicities around the 25-yr frequency band, as well as long-term linear trends are detected at both locations. In addition, a negative correlation is found between annual Po at both locations, evidencing the differences in the dynamical mechanisms ruling them (and possible complementary behavior). Furthermore, the impact that the three leading large-scale circulation patterns over Iberia (NAO, EA and SCAND) exert over wind power output is evaluated. Results show distinct (and non-stationary) couplings to these forcings depending on the geographical position and season or month. Moreover, significant non-stationary correlations are observed with the slow varying Atlantic Multidecadal Oscillation (AMO) index for both case studies. Finally, an empirical relationship is explored between the annual Po and the

The North Atlantic Oscillation and the ITCZ in a climate simulation

NASA Astrophysics Data System (ADS)

Cavalcanti, I. F. A.; Souza, P.

2009-04-01

The North Atlantic Oscillation (NAO) and the Atlantic Intertropical Convergence Zone (ITCZ) features are analyzed in a climate simulation with the CPTEC/COLA AGCM. The CPTEC/COLA AGCM reproduces the ITCZ seasonal north-south displacement as well as the seasonal east-west intensity, but the model overestimates the convection. The two phases of NAO are well simulated in the four seasons and also the largest intensity in DJF. The main mode of atmospheric variability considering the North and South Atlantic region, which displays a shifting of the NAO centers and a center of action over South Atlantic to the south of Africa is also reproduced. This mode, in DJF, is associated with the north-south ITCZ displacement in April, in the observed data. The displacement of the NAO centers southwestward allows the increase of pressure over the tropical North Atlantic Ocean and the increase of trade winds and displacement of the confluence and convergence zone southwards. The opposite occurs when the centers are displaced northeastward. The model Atlantic ITCZ position in April is associated with the anomalous (observed) Atlantic SST and the southward displacement of the confluence zone, but the simulated atmospheric features in DJF does not display the main mode of variability, as in the observations. This occurs due to the lack of interaction between the atmosphere and ocean in the atmospheric model. While in the observations the physical mechanism that links the NAO centers of action to the ITCZ position is the ocean-atmosphere interaction, from DJF to April, the atmospheric model responds to the prescribed SST at the same month, in April.

On the spectral characteristics of the Atlantic multidecadal variability in an ensemble of multi-century simulations

NASA Astrophysics Data System (ADS)

Mavilia, Irene; Bellucci, Alessio; J. Athanasiadis, Panos; Gualdi, Silvio; Msadek, Rym; Ruprich-Robert, Yohan

2018-01-01

The Atlantic multidecadal variability (AMV) is a coherent pattern of variability of the North Atlantic sea surface temperature field affecting several components of the climate system in the Atlantic region and the surrounding areas. The relatively short observational record severely limits our understanding of the physical mechanisms leading to the AMV. The present study shows that the spatial and temporal characteristics of the AMV, as assessed from the historical records, should also be considered as highly uncertain. Using 11 multi-century preindustrial climate simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) database, we show that the AMV characteristics are not constant along the simulation when assessed from different 200-year-long periods to match the observed period length. An objective method is proposed to test whether the variations of the AMV characteristics are consistent with stochastic internal variability. For 7 out of the 11 models analysed, the results indicate a non-stationary behaviour for the AMV time series. However, the possibility that the non-stationarity arises from sampling errors can be excluded with high confidence only for one of the 7 models. Therefore, longer time series are needed to robustly assess the AMV characteristics. In addition to any changes imposed to the AMV by external forcings, the detected dependence on the time interval identified in most models suggests that the character of the observed AMV may undergo significant changes in the future.

Suborbital Holocene Climate Variability over Continental Western Eurasia Coupled with Poleward Heat Transport to the Northeastern Atlantic Ocean

NASA Astrophysics Data System (ADS)

Baker, J. L.; Lachniet, M. S.; Asmerom, Y.; Polyak, V. J.

2016-12-01

The centennial-scale coupling between the Holocene paleoclimate of Eurasia and ocean-atmosphere dynamics in the North Atlantic sector remains weakly understood, due to a paucity of high-resolution data from the continental interior. To investigate these links, we detrended a composite record of stalagmite δ18O from Kinderlinskaya Cave (southern Urals Mountains), which exhibits long-term warming from 11.7 ka to present. The chronologies of two stalagmites were constrained by 29 U-Th dates obtained through MC-ICP-MS analysis. Stable-isotope analysis at 0.5-mm resolution along the growth axes resulted in an average sampling frequency of 12.5 years. Stalagmite δ18O reflects multidecadal changes in the δ18O of winter half-year precipitation, which is highly sensitive to AO/NAO-like shifts in the strength and position of mid-latitude westerlies. Spectral density and wavelet analysis of the detrended record revealed significant periodicities near 2.4 ka, 1.4 ka, and 1.0 ka, which are common in northern hemispheric paleoclimate records and possibly related to solar and oceanic forcing during the Holocene. Coherent hemispheric coupling of continental and oceanic paleoclimate at suborbital timescales is demonstrated by comparison of our record with reconstructions of sea-surface temperature (SST) and meridional flow strength in the North Atlantic sector. Specifically, SST at cores MD-23258 and LO09-14 in the Barents Sea and Reykjanes Ridge, respectively, exhibit opposite phasing during the Holocene, due to alternating strength between the eastern and western branches of the North Atlantic Current, a major component of AMOC. Estimating the SST gradient between these sites as a proxy for poleward heat transport to the northeastern Atlantic Ocean, we find a strong covariance with detrended stalagmite δ18O. This relationship suggests that persistent strengthening (weakening) of wintertime westerlies, analogous to positive (negative) phases of the AO/NAO, was forced by

Trends in characteristics of daily rainfall in Northern Iberia: Is the NAO signal behind the observed variability?

NASA Astrophysics Data System (ADS)

Saez de Cámara, E.; Gangoiti, G.; Alonso, L.; Iza, J.

2012-04-01

A trend analysis of intensity and frequency of daily precipitation over Northern Iberia (NIB), with a primary focus on extreme events, is presented. It is based on 14 NOAA-NCDC daily records covering the last 35 years (1973-2007) plus two centenarian databases sited in eastern NIB: San Sebastián (1929-2007) (daily resolution) and Bilbao (1857-2007) (monthly resolution). It is the first time that this interfacial region between the Atlantic and the Mediterranean has been studied with such a density of monitoring stations. Spatial and temporal characteristics and changes in rainfall's distribution have been analyzed using the suite of indices developed and recommended by the Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI). They include annual and seasonal accumulated precipitation, number of dry and rainy days, and mean precipitation per rainy day, among others. The observed trends have been tested for statistical significance using the Mann-Kendall's non-parametric test. Additionally, links between the North Atlantic Oscillation (NAO) and the precipitation in the aforementioned region have been explored. The analysis shows a significant tendency towards less intensive rainy days for the whole region together with a decreasing trend in the number of wet days for the Central NIB. The consequence is a decline of total rainfall, statistically significant in Central and Eastern NIB. The evolution to drier conditions may be seen in both annual and seasonal indices. Conversely, strong regional differences have been found in the response to the NAO signal: whereas the rainfall decrease in the Western NIB might be associated to the dominance of a positive mode of the NAO during the last decades, the lack of correlation between the NAO signal and the observed precipitation in the stations with significant decreases rises an important argument against a direct association. Using the global gridded 6-hourly NCEP-DOE Reanalysis 2 data (1979-2010) we

A 3000-year annual-resolution record of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Kelly, B. F.; Mariethoz, G.; Hellstrom, J.; Baker, A.

2013-12-01

The North Atlantic Oscillation provides an index of North Atlantic climate variability. The 947-yr long annual resolution record of the North Atlantic Oscillation (NAO) of Trouet et al. (2009, Science, 324, 78-81), the NAO Morocco-Scotland index, combined tree ring and stalagmite data, the latter a single stalagmite growth rate archive from NW Scotland. Trouet et al (2009) noted the unusual persistence of the positive phase of the NAO during the Medieval Climate Anomaly (MCA; 1050-1400AD). In order to better assess the uniqueness of the persistently positive NAO in the MCA, we extend the speleothem portion of the proxy NAO record with a composite of five stalagmites from the same cave system. We present the first-ever composite speleothem growth rate record. Using a combination of lamina counting, U-Th dating, and correlation between growth rate series, we build a continuous, annual-resolution, annually laminated, stalagmite growth rates series for the last 3000 years. We use geostatistical and stochastic approaches appropriate to stalagmite growth rate time series to characterise uncertainty in the stalagmite series and to screen them for periods of relative climate sensitivity vs. periods where there is hydrologically introduced, non-climatic variability. We produce the longest annual-resolution annual lamina record of the NAO for the last 3000 years. The screened stalagmite series is compared to instrumental and proxy records of the NAO. Spectral and wavelet analysis demonstrates that the series contains significant decadal to centennial scale periodicity throughout the record. We demonstrate that the persistently positive NAO during the MCA (1080-1460 CE) is remarkable within the last 3000 years. Two other phases of persistent, positive NAO, occur at 290-550 CE and 660-530 BCE, in agreement with the lower resolution, 5,200-yr Greenland lake sediment NAO proxy (Olsen et al, 2012, Nature Geoscience, 5, 808-812).

Atmospheric Circulation and West Greenland Precipitation

NASA Astrophysics Data System (ADS)

Auger, J.; Birkel, S. D.; Maasch, K. A.; Schuenemann, K. C.; Mayewski, P. A.; Osterberg, E. C.; Hawley, R. L.; Marshall, H. P.

2016-12-01

The surface mass balance of the Greenland Ice Sheet has declined substantially in recent decades across West Greenland with important implications for global sea level and freshwater resources. Here, we investigate changes in heat and moisture delivery to West Greenland through changes in atmospheric circulation in order to gain insight into possible future climate. Particular focus is placed on the role of known climate variability, including the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO), in influencing the intensity, frequency, and track of cyclones across the North Atlantic. This study utilizes multiple daily climate reanalysis models (CFSR, ERA-Interim, JRA-55) in addition to observational data. Preliminary results indicate a primary influence from the NAO, with a secondary influence from the low frequency oscillation connected to the AMO. Work is ongoing, and a complete synthesis will be presented at the fall meeting.

Multidecadal accumulation of anthropogenic and remineralized dissolved inorganic carbon along the Extended Ellett Line in the northeast Atlantic Ocean

NASA Astrophysics Data System (ADS)

Humphreys, Matthew P.; Griffiths, Alex M.; Achterberg, Eric P.; Holliday, N. Penny; Rérolle, Victoire M. C.; Menzel Barraqueta, Jan-Lukas; Couldrey, Matthew P.; Oliver, Kevin I. C.; Hartman, Susan E.; Esposito, Mario; Boyce, Adrian J.

2016-02-01

Marine carbonate chemistry measurements have been carried out annually since 2009 during UK research cruises along the Extended Ellett Line (EEL), a hydrographic transect in the northeast Atlantic Ocean. The EEL intersects several water masses that are key to the global thermohaline circulation, and therefore the cruises sample a region in which it is critical to monitor secular physical and biogeochemical changes. We have combined results from these EEL cruises with existing quality-controlled observational data syntheses to produce a hydrographic time series for the EEL from 1981 to 2013. This reveals multidecadal increases in dissolved inorganic carbon (DIC) throughout the water column, with a near-surface maximum rate of 1.80 ± 0.45 µmol kg-1 yr-1. Anthropogenic CO2 accumulation was assessed, using simultaneous changes in apparent oxygen utilization (AOU) and total alkalinity (TA) as proxies for the biogeochemical processes that influence DIC. The stable carbon isotope composition of DIC (δ13CDIC) was also determined and used as an independent test of our method. We calculated a volume-integrated anthropogenic CO2 accumulation rate of 2.8 ± 0.4 mg C m-3 yr-1 along the EEL, which is about double the global mean. The anthropogenic CO2 component accounts for only 31 ± 6% of the total DIC increase. The remainder is derived from increased organic matter remineralization, which we attribute to the lateral redistribution of water masses that accompanies subpolar gyre contraction. Output from a general circulation ecosystem model demonstrates that spatiotemporal heterogeneity in the observations has not significantly biased our multidecadal rate of change calculations and indicates that the EEL observations have been tracking distal changes in the surrounding North Atlantic and Nordic Seas.

East Atlantic (EA) and North Atlantic Oscillation (NAO) interplay over the Iberian Peninsula for the last two millennia

NASA Astrophysics Data System (ADS)

Hernandez, A.; Sánchez-López, G.; Pla-Rabes, S.; Trigo, R.; Toro, M.; Granados, I.; Sáez, A.; Masque, P.; Pueyo, J. J.; Rubio-Inglés, M. J.; Giralt, S.

2016-12-01

The multi-proxy approach from sediments of an Iberian alpine lake allowed us to establish the climatic conditions in the Iberian Central Range (ICR) over the last two millennia. The comparison with other Iberian reconstructions permitted to identify possible forcing climate mechanisms. Climatic conditions would be transmitted to the sediments via the frequency of intense run-off events, derived from rain-on-snow events, and the lake productivity, ruled by ice-cover duration. The early Roman Period (RP; 200 BC - 350 AD) in the ICR was characterized by oscillations of intense run-off events, as a consequence of an alternation between cold and warm periods. From the second half of the RP to the onset of the Early Middle Ages (EMA; 350 - 500 AD) an increase in the intense run-off events suggests warm conditions, although a noticeable decrease during the rest of the EMA (500 - 900 AD) evidences a shift to very cold temperatures in this region. In terms of humidity, both RP and EMA climatic periods displayed a transition from a dry to a wet scenario that led to a decrease in lake productivity. These climatic conditions have been registered by other reconstructions in the Iberian Peninsula (IP), and a North-South humidity gradient could be envisaged, although spatial climatic discrepancies were significant. Precipitation and temperature in the IP present a more homogeneous spatial pattern when the NAO and EA modes have the same sign than when they have the opposite sign. Hence, a predominance of periods with NAO - EA in opposite phases could explain the climatic spatial heterogeneity in the IP during these two periods. The Medieval Climate Anomaly (MCA; 900 - 1300 AD) in the ICR was characterized by warm and dry conditions represented by an increase in exceptional run-off episodes and lake productivity whereas the Little Ice Age (LIA; 1300 - 1850 AD) showed the opposite scenario. Similar climatic conditions were registered in all the IP, reflecting a spatial climatic

Three centuries of winter temperature change on the southeastern Tibetan Plateau and its relationship with the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Shi, Shiyuan; Li, Jinbao; Shi, Jiangfeng; Zhao, Yesi; Huang, Gang

2017-08-01

Long-term, high-resolution proxy records containing cold season temperature signals are scarce on the southeastern Tibetan Plateau (TP), limiting our understanding of regional climate and the potential driving forces. In this study, we present a nearly three centuries long reconstruction of winter (December-February) mean temperature for the central Hengduan Mountains, southeastern TP. The reconstruction is derived from a composite tree-ring width chronology of Pinus yunnanensis Franch from two high elevation sites (>3000 m above sea level). Our reconstruction passes all standard calibration-verification schemes and explains nearly 73 % of the variance of the original instrumental data. However, we were constrained to calibrate our full period (1718-2013) reconstruction of December-February mean temperature on the calibration period from 1959 to 1992 only, due to a decrease in temperature sensitivity of tree-ring index exhibited after 1992. Spatial correlation analysis shows that our reconstruction represents large-scale temperature variations in southwest China and the eastern TP. Our reconstructed December-February mean temperature shows a close association with the Atlantic Multidecadal Oscillation (AMO) over the past three centuries, with warm (cold) periods coinciding with the positive (negative) phases of the AMO. This persistent relationship suggests that the AMO may have been a key driver of multidecadal winter temperature variations on the southeastern TP.

On the origin of multi-decadal to centennial Greenland temperature anomalies over the past 800 yr

NASA Astrophysics Data System (ADS)

Kobashi, T.; Shindell, D. T.; Kodera, K.; Box, J. E.; Nakaegawa, T.; Kawamura, K.

2012-11-01

The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies associated with accelerating sea level rise. However, the causes of multi-decadal-to-centennial temperature changes in Greenland are not well understood, largely owing to short observational records. To examine the causes of the Greenland temperature variability, we calculated the Greenland temperature anomalies (GTA(G-NH)) over the past 800 yr by subtracting the standardised NH temperature from the standardised Greenland temperature. It decomposes the Greenland temperature variation into background climate (NH); Polar amplification; and Regional variability (GTA(G-NH)). The Central Greenland polar amplification factor as expressed by the variance ratio = Greenland/NH is 2.6 over the past 161 yr, and 3.3-4.2 over the past 800 yr. The GTA explains 31-35% of the variation of Greenland temperature in the multi-decadal-to-centennial time scale over the past 800 yr. Another orthogonal component of the Greenland and NH temperatures, GTP(G+NH) (Greenland temperature plus = standardized Greenland temperature + standardized NH temperature) exhibited the multi-decadal variations that were likely induced by large volcanic eruptions, increasing greenhouse gasses, and internal variation of climate. We found that the GTA(G-NH) has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modelling indicates that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and to associated changes in northward oceanic heat transport.

Volcanic forcing of the North Atlantic Oscillation over the last 2,000 years

NASA Astrophysics Data System (ADS)

Breitenbach, Sebastian F. M.; Ridley, Harriet E.; Lechleitner, Franziska A.; Asmerom, Yemane; Rehfeld, Kira; Prufer, Keith M.; Kennett, Douglas J.; Aquino, Valorie V.; Polyak, Victor; Goswami, Bedartha; Marwan, Norbert; Haug, Gerald H.; Baldini, James U. L.

2015-04-01

The North Atlantic Oscillation (NAO) is a principal mode of atmospheric circulation in the North Atlantic realm (Hurrell et al. 2003) and influences rainfall distribution over Europe, North Africa and North America. Although observational data inform us on multi-annual variability of the NAO, long and detailed paleoclimate datasets are required to understand the mechanisms and full range of its variability and the spatial extent of its influence. Chronologies of available proxy-based NAO reconstructions are often interdependent and cover only the last ~1,100 years, while longer records are characterized by low sampling resolution and chronological constraints. This complicates the reconstruction of regional responses to NAO changes. We present data from a 2,000 year long sub-annual carbon isotope record from speleothem YOK-I from Yok Balum Cave, Belize, Central America. YOK-I has been extensively dated using U-series (Kennett et al. 2012). Monitoring shows that stalagmite δ13C in Yok Balum cave is governed by infiltration changes associated with tropical wet season rainfall. Higher (lower) δ13C values reflect drier (wetter) conditions related to Intertropical Convergence Zone position and trade winds intensity. Comparison with NAO reconstructions (Proctor et al. 2000, Trouet et al. 2009, Wassenburg et al. 2013) reveals that YOK-I δ13C sensitively records NAO-related rainfall dynamics over Belize. The Median Absolute Deviation (MAD) of δ13C extends NAO reconstructions to the last 2,000 years and indicates that high latitude volcanic aerosols force negative NAO phases. We infer that volcanic aerosols modify inter-hemispheric temperature contrasts at multi-annual scale, resulting in meridional relocation of the ITCZ and the Bermuda-Azores High, altering NAO and tropical rainfall patterns. Decade-long dry periods in the 11th and the late 18th century relate to major high northern latitude eruptions and exemplify the climatic response to volcanic forcing by

The Energy Cascade Associated with the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Castanheira, J. M.; Marques, C. A. F.

2017-12-01

The North Atlantic Oscillation or Arctic Oscillation (NAO/AO), in a more hemispheric expression, is the dominant mode of variability of the extratropical atmospheric circulation. In the literature which analyses the association of low frequency variability of the NAO/AO with other climate variables, it is very common to find the idea of circulation and climate impacts of the NAO/AO. It is usually suggested that the NAO influences the position of North Atlantic storm tracks and the related transport of heat and moisture. However, in spite of the long time since the NAO variability mode was uncovered (Walker and Bliss, 1932), its underlying dynamical mechanisms are not well understood yet. In fact, it is not yet consensual that the NAO influences the position of the storm tracks, being possible that the relationship is in the opposite way with the storm track activity influencing de NAO. In this communication we will present an analysis of anomalies of the energy cascade associated with the NAO. A detailed version of the Lorenz energy cycle, which decomposes the energy flows into baroclinic and barotropic terms and into zonal mean and eddy components, was applied to the 6-hourly ERA-I reanalysis for the period of 1979 to 2016. The obtained results show that the positive NAO phase is preceded by an significant increase of synoptic baroclinic eddy activity. The eddy available potential energy is converted into kinetic energy and transferred to barotropic synoptic eddies. Then, the kinetic energy is transferred upscale into the barotropic planetary waves, which reproduce the NAO pattern. Therefore, we conclude that the synoptic baroclinic eddy activity forces the NAO variability. No clear signal was found for a modulating role of the NAO in the baroclinic eddy activity.

North Atlantic Oscillation modulates total ozone winter trends

NASA Astrophysics Data System (ADS)

Appenzeller, Christof; Weiss, Andrea K.; Staehelin, Johannes

2000-04-01

The North Atlantic Oscillation (NAO) is modulating the Earth's ozone shield such that the calculated anthropogenic total ozone decrease is enhanced over Europe whereas over the North Atlantic region it is reduced (for the last 30 years). Including the NAO in a statistical model suggests a more uniform chemical winter trend compared to the strong longitudinal variation reported earlier. At Arosa (Switzerland) the trend is reduced to -2.4% per decade compared to -3.2% and at Reykjavik (Iceland) it is enhanced to -3.8% compared to 0%. The revised trend is slightly below the predictions by 2D chemical models. Decadal ozone variability is linked to variations in the dynamical structure of the atmosphere, as reflected in the tropopause pressure. The latter varies in concert with the NAO index with a distinct geographical pattern.

The Influence of the North Atlantic Oscillation on Tropospheric Distributions of Ozone and Carbon Monoxide.

NASA Astrophysics Data System (ADS)

Knowland, K. E.; Doherty, R. M.; Hodges, K.

2015-12-01

The influence of the North Atlantic Oscillation (NAO) on the tropospheric distributions of ozone (O3) and carbon monoxide (CO) has been quantified. The Monitoring Atmospheric Composition and Climate (MACC) Reanalysis, a combined meteorology and composition dataset for the period 2003-2012 (Innes et al., 2013), is used to investigate the composition of the troposphere and lower stratosphere in relation to the location of the storm track as well as other meteorological parameters over the North Atlantic associated with the different NAO phases. Cyclone tracks in the MACC Reanalysis compare well to the cyclone tracks in the widely-used ERA-Interim Reanalysis for the same 10-year period (cyclone tracking performed using the tracking algorithm of Hodges (1995, 1999)), as both are based on the European Centre for Medium-Range Weather Forecasts' (ECMWF) Integrated Forecast System (IFS). A seasonal analysis is performed whereby the MACC reanalysis meteorological fields, O3 and CO mixing ratios are weighted by the monthly NAO index values. The location of the main storm track, which tilts towards high latitudes (toward the Arctic) during positive NAO phases to a more zonal location in the mid-latitudes (toward Europe) during negative NAO phases, impacts the location of both horizontal and vertical transport across the North Atlantic and into the Arctic. During positive NAO seasons, the persistence of cyclones over the North Atlantic coupled with a stronger Azores High promotes strong horizontal transport across the North Atlantic throughout the troposphere. In all seasons, significantly more intense cyclones occur at higher latitudes (north of ~50°C) during the positive phase of the NAO and in the southern mid-latitudes during the negative NAO phase. This impacts the location of stratospheric intrusions within the descending dry airstream behind the associated cold front of the extratropical cyclone and the venting of low-level pollution up into the free troposphere within

Lagged correlations between the NAO and the 11-year solar cycle: forced response or internal variability?

NASA Astrophysics Data System (ADS)

Oehrlein, J.; Chiodo, G.; Polvani, L. M.; Smith, A. K.

2017-12-01

Recently, the North Atlantic Oscillation has been suggested to respond to the 11-year solar cycle with a lag of a few years. The solar/NAO relationship provides a potential pathway for solar activity to modulate surface climate. However, a short observational record paired with the strong internal variability of the NAO raises questions about the robustness of the claimed solar/NAO relationship. For the first time, we investigate the robustness of the solar/NAO signal in four different reanalysis data sets and long integrations from an ocean-coupled chemistry-climate model forced with the 11-year solar cycle. The signal appears to be robust in the different reanalysis datasets. We also show, for the first time, that many features of the observed signal, such as amplitude, spatial pattern, and lag of 2/3 years, can be accurately reproduced in our model simulations. However, in both the reanalysis and model simulations, we find that this signal is non-stationary. A lagged NAO/solar signal can also be reproduced in two sets of model integrations without the 11-year solar cycle. This suggests that the correlation found in observational data could be the result of internal decadal variability in the NAO and not a response to the solar cycle. This has wide implications towards the interpretation of solar signals in observational data.

Reconstructing the history of the Atlantic Multidecadal Oscillation using high-resolution Mg/Ca paleothermometry from a Cariaco Basin core

NASA Astrophysics Data System (ADS)

Wurtzel, J. B.; Black, D. E.; Rahman, S.; Thunell, R.; Peterson, L. C.; Tappa, E.

2010-12-01

Instrumental and proxy-reconstructions show the existence of an approximately 70-year periodicity in Atlantic sea surface temperature (SST), known as the Atlantic Multidecadal Oscillation (AMO). The AMO is correlated with circum-tropical Atlantic climate phenomena such as Sahel and Nordeste rainfall, and Atlantic hurricane patterns. Though it has been suggested that the AMO is controlled by thermohaline circulation, much debate exists as to whether the SST fluctuations are a result of anthropogenic forcing or a natural climate mode, or even if the AMO is a true oscillation at all. Our ability to address this issue has been limited by instrumental SST records that rarely extend back more than 50-100 years and proxy reconstructions that are mostly terrestrial-based. Additionally, the modern instrumental variability likely contains an anthropogenic component that is not easily distinguished from the natural background of the system. From a marine sediment core taken in the Cariaco Basin, we have developed a high-resolution SST reconstruction for the past ca. 1500 years using Mg/Ca paleothermometry on seasonally-representative foraminifera, with the most recent data calibrated to the instrumental record. Previous studies have shown Cariaco Basin Mg/Ca-SSTs to be well-correlated to the Caribbean Sea and much of the western tropical Atlantic, which allows us to create a record that can be used to determine pre-anthropogenic rates and ranges of SST variability and observe how they change over time. Averaging the seasonal temperatures derived from the two foraminiferal species over the instrumental period yields a strong correlation to the AMO index from A. D. 1880 through 1970 (r = 0.44, p<0.0001). Wavelet analysis of the proxy average annual SST data indicates that modern AMO variability is not a consistent feature through time, and may be a function of warm-period climate.

Re-emerging ocean temperature anomalies in late-2010 associated with a repeat negative NAO

NASA Astrophysics Data System (ADS)

Taws, Sarah L.; Marsh, Robert; Wells, Neil C.; Hirschi, Joël

2011-10-01

Northern Europe was influenced by consecutive episodes of extreme winter weather at the start and end of the 2010 calendar year. A tripole pattern in North Atlantic sea surface temperature anomalies (SSTAs), associated with an exceptionally negative phase of the North Atlantic Oscillation (NAO), characterized both winter periods. This pattern was largely absent at the surface during the 2010 summer season; however equivalent sub-surface temperature anomalies were preserved within the seasonal thermocline throughout the year. Here, we present evidence for the re-emergence of late-winter 2009/10 SSTAs during the following early winter season of 2010/11. The observed re-emergence contributes toward the winter-to-winter persistence of the anomalous tripole pattern. Considering the active influence of the oceans upon leading modes of atmospheric circulation over seasonal timescales, associated with the memory of large-scale sea surface temperature anomaly patterns, the re-emergence of remnant temperature anomalies may have also contributed toward the persistence of a negative winter NAO, and the recurrence of extreme wintry conditions over the initial 2010/11 winter season.

Large-scale Controls on Atlantic Tropical Cyclone Activity on Seasonal Time Scales

PubMed Central

Lim, Young-Kwon; Schubert, Siegfried D.; Reale, Oreste; Molod, Andrea M.; Suarez, Max J.; Auer, Benjamin M.

2018-01-01

Interannual variations in seasonal tropical cyclone (TC) activity (e.g., genesis frequency and location, track pattern, and landfall) over the Atlantic are explored by employing observationally-constrained simulations with the NASA Goddard Earth Observing System version (GEOS-5) atmospheric general circulation model. The climate modes investigated are El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Atlantic Meridional Mode (AMM). The results show that the NAO and AMM can strongly modify and even oppose the well-known ENSO impacts, like in 2005, when a strong positive AMM (associated with warm SSTs and a negative SLP anomaly over the western tropical Atlantic), led to a very active TC season with enhanced TC genesis over the Caribbean Sea and a number of landfalls over North America, under a neutral ENSO condition. On the other end, the weak TC activity during 2013 (characterized by weak negative Niño index) appears caused by a NAO-induced positive SLP anomaly with enhanced vertical wind shear over the tropical North Atlantic. During 2010, the combined impact of the three modes produced positive SST anomalies across the entire low- latitudinal Atlantic and a weaker subtropical high, leading to more early recurvers and thus fewer landfalls despite enhanced TC genesis. The study provides evidence that TC number and track are very sensitive to the relative phases and intensities of these three modes, and not just to ENSO alone. Examination of seasonal predictability reveals that predictive skill of the three modes is limited over tropics to sub-tropics, with the AMM having the highest predictability over the North Atlantic, followed by ENSO and NAO. PMID:29928071

Large-Scale Controls on Atlantic Tropical Cyclone Activity on Seasonal Time Scales

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon; Schubert, Siegfried D.; Reale, Oreste; Molod, Andrea M.; Suarez, Max J.; Auer, Benjamin M.

2016-01-01

Interannual variations in seasonal tropical cyclone (TC) activity (e.g., genesis frequency and location, track pattern, and landfall) over the Atlantic are explored by employing observationally-constrained simulations with the NASA Goddard Earth Observing System version (GEOS-5) atmospheric general circulation model. The climate modes investigated are El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Atlantic Meridional Mode (AMM). The results show that the NAO and AMM can strongly modify and even oppose the well- known ENSO impacts, like in 2005, when a strong positive AMM (associated with warm SSTs and a negative SLP anomaly over the western tropical Atlantic), led to a very active TC season with enhanced TC genesis over the Caribbean Sea and a number of landfalls over North America, under a neutral ENSO condition. On the other end, the weak TC activity during 2013 (characterized by weak negative Nio index) appears caused by a NAO-induced positive SLP anomaly with enhanced vertical wind shear over the tropical North Atlantic. During 2010, the combined impact of the three modes produced positive SST anomalies across the entire low-latitudinal Atlantic and a weaker subtropical high, leading to more early recurvers and thus fewer landfalls despite enhanced TC genesis. The study provides evidence that TC number and track are very sensitive to the relative phases and intensities of these three modes, and not just to ENSO alone. Examination of seasonal predictability reveals that predictive skill of the three modes is limited over tropics to sub-tropics, with the AMM having the highest predictability over the North Atlantic, followed by ENSO and NAO.

North Atlantic sea-level variability during the last millennium

NASA Astrophysics Data System (ADS)

Gehrels, Roland; Long, Antony; Saher, Margot; Barlow, Natasha; Blaauw, Maarten; Haigh, Ivan; Woodworth, Philip

2014-05-01

Climate modelling studies have demonstrated that spatial and temporal sea-level variability observed in North Atlantic tide-gauge records is controlled by a complex array of processes, including ice-ocean mass exchange, freshwater forcing, steric changes, changes in wind fields, and variations in the speed of the Gulf Stream. Longer records of sea-level change, also covering the pre-industrial period, are important as a 'natural' and long-term baseline against which to test model performance and to place recent and future sea-level changes and ice-sheet change into a long-term context. Such records can only be reliably and continuously reconstructed from proxy methods. Salt marshes are capable of recording decimetre-scale sea-level variations with high precision and accuracy. In this paper we present four new high-resolution proxy records of (sub-) decadal sea-level variability reconstructed from salt-marsh sediments in Iceland, Nova Scotia, Maine and Connecticut that span the past 400 to 900 years. Our records, based on more than 100 new radiocarbon analyses, Pb-210 and Cs-137 measurements as well as other biological and geochemical age markers, together with hundreds of new microfossil observations from contemporary and fossil salt marshes, capture not only the rapid 20th century sea-level rise, but also small-scale (decimetre, multi-decadal) sea-level fluctuations during preceding centuries. We show that in Iceland three periods of rapid sea-level rise are synchronous with the three largest positive shifts of the reconstructed North Atlantic Oscillation (NAO) index. Along the North American east coast we compare our data with salt-marsh records from New Jersey, North Carolina and Florida and observe a trend of increased pre-industrial sea-level variability from south to north (Florida to Nova Scotia). Mass changes and freshwater forcing cannot explain this pattern. Based on comparisons with instrumental sea-level data and modelling studies we hypothesise that

Evidence of long-term NAO influence on East-Central Europe winter precipitation from a guano-derived δ15N record.

PubMed

Cleary, Daniel M; Wynn, Jonathan G; Ionita, Monica; Forray, Ferenc L; Onac, Bogdan P

2017-10-26

Currently there is a scarcity of paleo-records related to the North Atlantic Oscillation (NAO), particularly in East-Central Europe (ECE). Here we report δ 15 N analysis of guano from a cave in NW Romania with the intent of reconstructing past variation in ECE hydroclimate and examine NAO impacts on winter precipitation. We argue that the δ 15 N values of guano indicate that the nitrogen cycle is hydrologically controlled and the δ 15 N values likely reflect winter precipitation related to nitrogen mineralization prior to the growing season. Drier conditions indicated by δ 15 N values at AD 1848-1852 and AD 1880-1930 correspond to the positive phase of the NAO. The increased frequency of negative phases of the NAO between AD 1940-1975 is contemporaneous with higher δ 15 N values (wetter conditions). A 4‰ decrease in δ 15 N values at the end of the 1970's corresponds to a strong reduction in precipitation associated with a shift from negative to positive phase of the NAO. Using the relationship between NAO index and δ 15 N values in guano for the instrumental period, we reconstructed NAO-like phases back to AD 1650. Our results advocate that δ 15 N values of guano offer a proxy of the NAO conditions in the more distant past, helping assess its predictability.

Precipitation, temperature, and teleconnection signals across the combined North American, Monsoon Asia, and Old World Drought Atlases

NASA Astrophysics Data System (ADS)

Smerdon, J. E.; Baek, S. H.; Coats, S.; Williams, P.; Cook, B.; Cook, E. R.; Seager, R.

2017-12-01

The tree-ring-based North American Drought Atlas (NADA), Monsoon Asia Drought Atlas (MADA), and Old World Drought Atlas (OWDA) collectively yield a near-hemispheric gridded reconstruction of hydroclimate variability over the last millennium. To test the robustness of the large-scale representation of hydroclimate variability across the drought atlases, the joint expression of seasonal climate variability and teleconnections in the NADA, MADA, and OWDA are compared against two global, observation-based PDSI products. Predominantly positive (negative) correlations are determined between seasonal precipitation (surface air temperature) and collocated tree-ring-based PDSI, with average Pearson's correlation coefficients increasing in magnitude from boreal winter to summer. For precipitation, these correlations tend to be stronger in the boreal winter and summer when calculated for the observed PDSI record, while remaining similar for temperature. Notwithstanding these differences, the drought atlases robustly express teleconnection patterns associated with the El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). These expressions exist in the drought atlas estimates of boreal summer PDSI despite the fact that these modes of climate variability are dominant in boreal winter, with the exception of the Atlantic Multidecadal Oscillation. ENSO and NAO teleconnection patterns in the drought atlases are particularly consistent with their well-known dominant expressions in boreal winter and over the OWDA domain, respectively. Collectively, our findings confirm that the joint Northern Hemisphere drought atlases robustly reflect large-scale patterns of hydroclimate variability on seasonal to multidecadal timescales over the 20th century and are likely to provide similarly robust estimates of hydroclimate variability prior to the existence of widespread instrumental data.

Interdecadal modulation of the Atlantic Multi-decadal Oscillation (AMO) on southwest China's temperature over the past 250 years

NASA Astrophysics Data System (ADS)

Fang, Keyan; Guo, Zhengtang; Chen, Deliang; Wang, Lei; Dong, Zhipeng; Zhou, Feifei; Zhao, Yan; Li, Jinbao; Li, Yingjun; Cao, Xinguang

2018-05-01

The temperature gradient between southwestern China and Indian Ocean is one key driver of the Indian Summer Monsoon, suggesting the necessity to understand temperature variability in southwestern China. Contrary to the general warming experienced in most of China, a few regions in southwestern China have undergone a cooling trend since the 1950s. To place this cooling trend in a historical context, this study develops an Abies fabri tree-ring width chronology in the Sichuan Basin, the most populated region in southwest China. The chronology spans from 1590 to 2012, with its reliable portion from 1758 to 2012, by far the longest in the Sichuan Basin. To better extract regional climate signals encoded in tree rings with strong local disturbances, we incorporate climate signals of nearby tree-ring chronologies to generate a large-scale tree-ring chronology (LSC). The LSC shows higher correlations with temperature near the sampling site on Mount Emei and sea surface temperatures of the northern Atlantic Ocean than chronologies developed using traditional methods. The highest correlations between the LSC and temperature are found from current February to July in the Sichuan Basin for the period 1901-1950 (r = 0.70), with a sharp decrease afterwards. Interdecadal variations of the LSC match well with Atlantic Multi-decadal Oscillation reconstructions, except for the late nineteenth century and after 1980s. This study provides evidence that southwest China is a transitional region both affected by the interdecadal temperature variations of the northern Atlantic and Asian areas, although their influences weakened in recent possible due to enhanced human activities.

AO/NAO Response to Climate Change. 2; Relative Importance of Low- and High-Latitude Temperature Changes

NASA Technical Reports Server (NTRS)

Rind, D.; Perlwitz, J.; Lonergan, P.; Lerner, J.

2005-01-01

Using a variety of GCM experiments with various versions of the GISS model, we investigate how different aspects of tropospheric climate changes affect the extratropical Arctic Oscillation (AO)/North Atlantic Oscillation (NAO) circulation indices. The results show that low altitude changes in the extratropical latitudinal temperature gradient can have a strong impact on eddy forcing of the extratropical zonal wind, in the sense that when this latitudinal temperature gradient increases, it helps force a more negative AO/NAO phase. In addition, local conditions at high latitudes can stabilize/destabilize the atmosphere, inducing negative/positive phase changes. To the extent that there is not a large temperature change in the tropical upper troposphere (either through reduced tropical sensitivity at the surface, or limited transport of this change to high levels), the changes in the low level temperature gradient can provide the dominate influence on the extratropical circulation, so that planetary wave meridional refraction and eddy angular momentum transport changes become uncorrelated with potential vorticity transports. In particular, the climate change that produces the most positive NAO phase change would have substantial warming in the tropical upper troposphere over the Pacific Ocean, with high latitude warming in the North Atlantic. An increase in positive phase of these circulation indices is still more likely than not, but it will depend on the degree of tropical and high latitude temperature response and the transport of low level warming into the upper troposphere. These are aspects that currently differ among the models used for predicting the effects of global warning, contributing to the lack of consensus of future changes in the AO/NAO.

An Anatomy of the 1960s Atlantic Cooling.

NASA Astrophysics Data System (ADS)

Hodson, Dan; Robson, Jon; Sutton, Rowan

2014-05-01

North Atlantic Sea Surface Temperatures (SSTs) exhibited pronounced multidecadal variability during the 20th Century. In particular, the North Atlantic SSTs exhibited a rapid warming between 1920 and 1940 followed by a rapid cooling between 1960 and 1980. SSTs outside the North Atlantic display a much smaller level of decadal variability over the 20th Century. This pattern of North Atlantic warming and cooling has been linked to subsequent changes in rainfall over the Sahel and Nordeste Brazil, Summertime North American Climate and Atlantic Hurricane Genesis. Several hypotheses for the rapid 1960s Atlantic cooling have been proposed, including a reduction in northward ocean heat transport due to a reduced Atlantic Meridional Overturning Circulation (AMOC) and the significant rise in anthropogenic sulphur dioxide emissions during the latter half of the 20th century. Here we examine the observed 1960s Atlantic cooling in more detail. We describe the evolution of the rapid cooling by constructing a detailed multivariate anatomy of the cooling period in order to illuminate the possible explanations and mechanisms involved. We show that the observed 1960s cooling began around 1964-68 in the Greenland-Iceland-Norway (GIN) seas, later spreading to the Atlantic Sub Polar Gyre and much of the subtropical Atlantic. This initial cooling of the Sub Polar Gyre is associated with a marked reduction in salinity (the Great Salinity Anomaly). The cooling peaked between 1972-76, extending into the Tropical North Atlantic. This period also saw the development of a significant Winter North-South Dipole Mean Sea Level Pressure dipole pattern reminiscent of a positive NAO (High over the Azores, Low over Iceland). The cooling then retreated back to higher latitudes during 1976:80. Our analysis demonstrates that the cooling of the North Atlantic during the 1960s cannot be understood as a simple thermodynamic response to aerosol induced reductions in shortwave radiation. Dynamical changes

The subpolar North Atlantic - Response to North Atlantic oscillation like forcing and Influence on the Atlantic meridional overturning circulation

NASA Astrophysics Data System (ADS)

Lohmann, Katja; Drange, Helge; Jungclaus, Johann

2010-05-01

The extent and strength of the North Atlantic subpolar gyre (SPG) changed rapidly in the mid-1990s, going from large and strong in 1995 to substantially weakened in the following years. The abrupt change in the intensity of the SPG is commonly linked to the reversal of the North Atlantic Oscillation (NAO) index, changing from strong positive to negative values, in the winter 1995/96. In this study we investigate the impact of the initial SPG state on its subsequent behavior by means of an ocean general circulation model driven by NCEP-NCAR reanalysis fields. Our sensitivity integrations suggest that the weakening of the SPG cannot be explained by the change in the atmospheric forcing alone. Rather, for the time period around 1995, the SPG was about to weaken, irrespective of the actual atmospheric forcing, due to the ocean state governed by the persistently strong positive NAO during the preceding seven years (1989 to 1995). Our analysis indicates that it was this preconditioning of the ocean, in combination with the sudden drop in the NAO in 1995/96, that lead to the strong and rapid weakening of the SPG in the second half of the 1990s. In the second part, the sensitivity of the low-frequency variability of the Atlantic meridional overturning circulation to changes in the subpolar North Atlantic is investigated using a 2000 year long control integration as well as sensitivity experiments with the MPI-M Earth System Model. Two 1000 year long sensitivity experiments will be performed, in which the low-frequency variability in the overflow transports from the Nordic Seas and in the subpolar deep water formation rates is suppressed respectively. This is achieved by nudging temperature and salinity in the GIN Sea or in the subpolar North Atlantic (up to about 1500m depth) towards a monthly climatology obtained from the last 1000 years of the control integration.

Strain identification and quorum sensing inhibition characterization of marine-derived Rhizobium sp. NAO1

NASA Astrophysics Data System (ADS)

Chang, Hong; Zhou, Jin; Zhu, Xiaoshan; Yu, Shenchen; Chen, Lu; Jin, Hui; Cai, Zhonghua

2017-03-01

A novel strategy for combating pathogens is through the ongoing development and use of anti-quorum sensing (QS) treatments such as therapeutic bacteria or their anti-QS substances. Relatively little is known about the bacteria that inhabit the open ocean and of their potential anti-pathogenic attributes; thus, in an initiative to identify these types of therapeutic bacteria, planktonic microbes from the North Atlantic Ocean were collected, isolated, cultured and screened for anti-QS activity. Screening analysis identified one such strain, Rhizobium sp. NAO1. Extracts of Rhizobium sp. NAO1 were identified via ultra-performance liquid chromatography (UPLC) analysis. They were shown to contain N-acyl homoserine lactone (AHL)-based QS analogues (in particular, the N-butyryl homoserine lactone (C4-AHL) analogue) and could disrupt biofilm formation by Pseudomonas aeruginosa PAO1. QS inhibition was confirmed using confocal scanning laser microscopy and growth curves, and it was shown to occur in a dose-dependent manner without affecting bacterial growth. Secondary metabolites of Rhizobium sp. NAO1 inhibited PAO1 pathogenicity by downregulating AHL-mediated virulence factors such as elastase activity and siderophore production. Furthermore, as a result of biofilm structure damage, the secondary metabolite products of Rhizobium sp. NAO1 significantly increased the sensitivity of PAO1 to aminoglycoside antibiotics. Our results demonstrated that Rhizobium sp. strain NAO1 has the ability to disrupt P. aeruginosa PAO1 biofilm architecture, in addition to attenuating P. aeruginosa PAO1 virulence factor production and pathogenicity. Therefore, the newly identified ocean-derived Rhizobium sp. NAO1 has the potential to serve as a QS inhibitor and may be a new microbial resource for drug development.

Understanding the NAO from Iberian and UK paleoclimate records. The NAOSIPUK project

NASA Astrophysics Data System (ADS)

Garcia-Alix, Antonio; Toney, Jaime L.; Jiménez-Moreno, Gonzalo; Slaymark, Charlotte; José Ramos-Román, Maria; Camuera, Jon; Jiménez-Espejo, Francisco J.; Anderson, R. Scott

2017-04-01

The main goal of the NAOSIPUK project was to understand the North Atlantic Oscillation (NAO) during the Holocene, because the NAO is one major climate mode influencing climate patterns across Europe, and therefore, economy and society (Hurrell, 1995). We analysed several sedimentary records in two regions with opposing NAO responses. Our sedimentary surface survey from numerous lakes and bogs, led to further investigation of four records in the southern Iberian Peninsula and three in the central/northern UK. Past environments of the different sites were analysed using pollen and charcoal analysis, organic and inorganic geochemistry analyses, and sedimentary and geophysical surveys were performed. This work compares general environmental trends in both regions as deduced from the organic matter from bulk sediment to get an idea of the organic matter source, as well as specific organic compounds extracted from the sediment, such as leaf waxes (n-alkanes), algae-related compounds (diols and alkenones), and bacteria-related compounds (hopanes), to specify the sources of the organic matter, environmental temperature ranges, as well as hydrological changes. Our preliminary results show that the palaeoenvironmental indices developed from n-alkanes agree with the variations deduced from the carbon and nitrogen atomic ratios, as well as the carbon isotopic composition from bulk sediments in southern Iberia records. Interestingly, these indices show that some locations display opposite trends from one another, and are used to distinguish regional versus local effects of climate change, human impacts, and aeolian dust inputs. During the late Holocene solar forcing and NAO fluctuations are the main drivers of the environmental evolution in most of the Iberian and UK sites. However, we do detect the influence of the NAO in the temperatures oscillations of the studied sites in southern Iberia. This influence is much more important in the north/central UK sites. The regional

High-Performance Na-O2 Batteries Enabled by Oriented NaO2 Nanowires as Discharge Products.

PubMed

Khajehbashi, S Mohammad B; Xu, Lin; Zhang, Guobin; Tan, Shuangshuang; Zhao, Yan; Wang, Lai-Sen; Li, Jiantao; Luo, Wen; Peng, Dong-Liang; Mai, Liqiang

2018-06-13

Na-O 2 batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO 2 nanowires inside Na-O 2 batteries that significantly boosts the performance of Na-O 2 batteries. For this purpose, a high-spin Co 3 O 4 electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO 2 nanowires are 10-20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na-O 2 batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g -1 , an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na-O 2 batteries but also opens up the opportunity to explore growing nanowires in novel conditions.

Observed linkages between the northern annular mode/North Atlantic Oscillation, cloud incidence, and cloud radiative forcing

NASA Astrophysics Data System (ADS)

Li, Ying; Thompson, David W. J.; Huang, Yi; Zhang, Minghong

2014-03-01

The signature of the northern annular mode/North Atlantic Oscillation (NAM/NAO) in the vertical and horizontal distribution of tropospheric cloudiness is investigated in CloudSat and CALIPSO data from June 2006 to April 2011. During the Northern Hemisphere winter, the positive polarity of the NAM/NAO is marked by increases in zonally averaged cloud incidence north of ~60°N, decreases between ~25 and 50°N, and increases in the subtropics. The tripolar-like anomalies in cloud incidence associated with the NAM/NAO are largest over the North Atlantic Ocean basin/Middle East and are physically consistent with the NAM/NAO-related anomalies in vertical motion. Importantly, the NAM/NAO-related anomalies in tropospheric cloud incidence lead to significant top of atmosphere cloud radiative forcing anomalies that are comparable in amplitude to those associated with the NAM/NAO-related temperature anomalies. The results provide observational evidence that the most prominent pattern of Northern Hemisphere climate variability is significantly linked to variations in cloud radiative forcing. Implications for two-way feedback between extratropical dynamics and cloud radiative forcing are discussed.

Role of the North Atlantic Ocean in Low Frequency Climate Variability

NASA Astrophysics Data System (ADS)

Danabasoglu, G.; Yeager, S. G.; Kim, W. M.; Castruccio, F. S.

2017-12-01

The Atlantic Ocean is a unique basin with its extensive, North - South overturning circulation, referred to as the Atlantic meridional overturning circulation (AMOC). AMOC is thought to represent the dynamical memory of the climate system, playing an important role in decadal and longer time scale climate variability as well as prediction of the earth's future climate on these time scales via its large heat and salt transports. This oceanic memory is communicated to the atmosphere primarily through the influence of persistent sea surface temperature (SST) variations. Indeed, many modeling studies suggest that ocean circulation, i.e., AMOC, is largely responsible for the creation of coherent SST variability in the North Atlantic, referred to as Atlantic Multidecadal Variability (AMV). AMV has been linked to many (multi)decadal climate variations in, e.g., Sahel and Brazilian rainfall, Atlantic hurricane activity, and Arctic sea-ice extent. In the absence of long, continuous observations, much of the evidence for the ocean's role in (multi)decadal variability comes from model simulations. Although models tend to agree on the role of the North Atlantic Oscillation in creating the density anomalies that proceed the changes in ocean circulation, model fidelity in representing variability characteristics, mechanisms, and air-sea interactions remains a serious concern. In particular, there is increasing evidence that models significantly underestimate low frequency variability in the North Atlantic compared to available observations. Such model deficiencies can amplify the relative influence of external or stochastic atmospheric forcing in generating (multi)decadal variability, i.e., AMV, at the expense of ocean dynamics. Here, a succinct overview of the current understanding of the (North) Atlantic Ocean's role on the regional and global climate, including some outstanding questions, will be presented. In addition, a few examples of the climate impacts of the AMV via

Intraseasonal interaction between the Madden-Julian Oscillation and the North Atlantic Oscillation.

PubMed

Cassou, Christophe

2008-09-25

Bridging the traditional gap between the spatio-temporal scales of weather and climate is a significant challenge facing the atmospheric community. In particular, progress in both medium-range and seasonal-to-interannual climate prediction relies on our understanding of recurrent weather patterns and the identification of specific causes responsible for their favoured occurrence, persistence or transition. Within this framework, I here present evidence that the main climate intra-seasonal oscillation in the tropics-the Madden-Julian Oscillation (MJO)-controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic-European region in winter. North Atlantic Oscillation (NAO) regimes are the most affected, allowing for medium-range predictability of their phase far exceeding the limit of around one week that is usually quoted. The tropical-extratropical lagged relationship is asymmetrical. Positive NAO events mostly respond to a mid-latitude low-frequency wave train initiated by the MJO in the western-central tropical Pacific and propagating eastwards. Precursors for negative NAO events are found in the eastern tropical Pacific-western Atlantic, leading to changes along the North Atlantic storm track. Wave-breaking diagnostics tend to support the MJO preconditioning and the role of transient eddies in setting the phase of the NAO. I present a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of the NAO regimes when they occur. Forecasts are successful in approximately 70 per cent of the cases based on the knowledge of the previous approximately 12-day MJO phase used as a predictor. This promising skill could be of importance considering the tight link between weather regimes and both mean conditions and the chances of extreme events occurring over Europe. These findings are useful for further stressing the need to better simulate and forecast the tropical

North Atlantic Oscillation influence on the stramflows of the Iberian Rivers

NASA Astrophysics Data System (ADS)

Lorenzo-Lacruz, J.; González-Hidalgo, J. C.; Vicente-Serrano, S. M.; López-Moreno, J. I.

2010-09-01

"NORTH ATLANTIC OSCILLATION INFLUENCE ON THE STREAMFLOWS OF THE IBERIAN RIVERS" LORENZO-LACRUZ, J. ¹, GONZÁLEZ-HIDALGO, J.C.², VICENTE-SERRANO, S.M. ¹, LÓPEZ-MORENO, J.I.¹ ¹Instituto Pirenaico de Ecología, CSIC (Spanish Research Council), Campus de Aula Dei, P.O. Box 202, Zaragoza 50080, Spain ²Departamento de Geografía, Universidad de Zaragoza, Zaragoza, Spain. We analyzed the North Atlantic Oscillation (NAO) influence on the monthly river discharges of Iberian rivers from 1945 to 2005. The study covers most of the Iberian river basins, using 187 monthly discharge series. The aim of this study is to determine the role of the variability of the NAO on the Iberian river discharges. Using the winter NAO we calculated correlations with the monthly river discharge series. We identified the positive and negative phases of the winter NAO for the period 1945-2006, and related to river discharge anomalies. Significant differences in river discharge were found between the positive and negative NAO phases with negative anomalies (dry conditions) during positive NAO periods, and positive anomalies (wet conditions) during negative NAO periods The results show a consistent and strong control of the river discharges by the winter NAO, but some spatial differences are shown, as three different domains were defined: a region under the direct influence of the NAO (central and western part of the Iberian Peninsula), a transition zone (Ebro Valley) and region free from that influence (Eastern part of the Iberian Peninsula). The spatial differences are also identified in the annual pattern of discharge anomalies. The basin characteristics, the location of the gauging stations and the human management are the possible drivers of these differences.

The Low-Frequency Variability of the Tropical Atlantic Ocean

NASA Technical Reports Server (NTRS)

Haekkinen, Sirpa; Mo, Kingtse C.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Upper ocean temperature variability in the tropical Atlantic is examined from the Comprehensive Ocean Atmosphere Data Set (COADS) as well as from an ocean model simulation forced by COADS anomalies appended to a monthly climatology. Our findings are as follows: Only the sea surface temperatures (SST) in the northern tropics are driven by heat fluxes, while the southern tropical variability arises from wind driven ocean circulation changes. The subsurface temperatures in the northern and southern tropics are found to have a strong linkage to buoyancy forcing changes in the northern North Atlantic. Evidence for Kelvin-like boundary wave propagation from the high latitudes is presented from the model simulation. This extratropical influence is associated with wintertime North Atlantic Oscillation (NAO) forcing and manifests itself in the northern and southern tropical temperature anomalies of the same sign at depth of 100-200 meters as result of a Rossby wave propagation away from the eastern boundary in the wake of the boundary wave passage. The most apparent association of the southern tropical sea surface temperature anomalies (STA) arises with the anomalous cross-equatorial winds which can be related to both NAO and the remote influence from the Pacific equatorial region. These teleconnections are seasonal so that the NAO impact on the tropical SST is the largest it mid-winter but in spring and early summer the Pacific remote influence competes with NAO. However, NAO appears to have a more substantial role than the Pacific influence at low frequencies during the last 50 years. The dynamic origin of STA is indirectly confirmed from the SST-heat flux relationship using ocean model experiments which remove either anomalous wind stress forcing or atmospheric forcing anomalies contributing to heat exchange.

600 yr High-Resolution Climate Reconstruction of the Atlantic Multidecadal Oscillation deduced from a Puerto Rican Speleothem

NASA Astrophysics Data System (ADS)

Vieten, Rolf; Winter, Amos; Scholz, Denis; Black, David; Spoetl, Christoph; Winterhalder, Sophie; Koltai, Gabriella; Schroeder-Ritzrau, Andrea; Terzer, Stefan; Zanchettin, Davide; Mangini, Augusto

2016-04-01

A multi-proxy speleothem study tracks the regional hydrological variability in Puerto Rico and highlights its close relation to the Atlantic Multidecadal Oscillation (AMO) describing low-frequency sea-surface temperature (SST) variability in the North Atlantic ocean. Our proxy record extends instrumental observations 600 years into the past, and reveals the range of natural hydrologic variability for the region. A detailed interpretation and understanding of the speleothem climate record is achieved by the combination of multi-proxy measurements, thin section petrography, XRD analysis and cave monitoring results. The speleothem was collected in Cueva Larga, a one mile-long cave system that has been monitored since 2012. MC-ICPMS 230Th/U-dating reveals that the speleothem grew constantly over the last 600 years. Trace element ratios (Sr/Ca and Mg/Ca) as well as stable isotope ratios (δ18O and δ13C) elucidate significant changes in atmospheric precipitation at the site. Monthly cave monitoring results demonstrate that the epikarst system responds to multi-annual changes in seepage water recharge. The drip water isotope and trace element composition lack short term or seasonal variability. This hydrological system creates favorable conditions to deduce decadal climate variability from Cueva Larga's climate record. The speleothem time series mimics the most recent AMO reconstruction over the last 200 years (Svendsen et al., 2014) with a time lag of 10-20 years. The lag seems to results from slow atmospheric signal transmission through the epikarst but the effect of dating uncertainties cannot be ruled out. Warm SSTs in the North Atlantic are related to drier conditions in Puerto Rico. During times of decreased rainfall a relative increase in prior calcite precipitation seems to be the main process causing increased Mg/Ca trace element ratios. High trace element ratios correlate to higher δ13C values. The increase in both proxies indicates a shift towards time

The combined influence of Pacific decadal oscillation and Atlantic multidecadal oscillation on central Mexico since the early 1600s

NASA Astrophysics Data System (ADS)

Park, Jungjae; Byrne, Roger; Böhnel, Harald

2017-04-01

Periodic droughts have been one of the most serious environmental issues in central Mexico since the earliest times. The impacts of future droughts are likely to become even more severe as the current global warming trend increases potential evaporation and moisture deficits. A full understanding of the mechanism underlying climate variability is imperative to narrow the uncertainty about future droughts and predict water availability. The climatic complexity generated by the combined influence of both Atlantic and Pacific forcings, however, causes considerable difficulty in interpreting central Mexican climate records. Also, the lack of high-resolution information regarding the climate in the recent past makes it difficult to clearly understand current drought mechanisms. Our new high-resolution δ18 O record from Hoya Rincon de Parangueo in central Mexico provides useful information on climate variations since the early 1600s. According to our results, the central Mexican climate has been predominantly controlled by the combined influence of the 20-year Pacific Decadal Oscillation (PDO) and the 70-year Atlantic Multidecadal Oscillation (AMO). However, the AMO probably lost much of its influence in central Mexico in the early 20th century and the PDO has mostly driven climate change since. Marked dryness was mostly associated with co-occurrence of highly positive PDO and negative AMO between ∼1600 and 1900.

Variability modes of precipitation along a Central Mediterranean area and their relations with ENSO, NAO, and other climatic patterns

NASA Astrophysics Data System (ADS)

Kalimeris, Anastasios; Ranieri, Ezio; Founda, Dimitra; Norrant, Caroline

2017-12-01

This study analyses a century-long set of precipitation time series in the Central Mediterranean (encompassing the Greek Ionian and the Italian Puglia regions) and investigates the statistically significant modes of the interannual precipitation variability using efficient methods of spectral decomposition. The statistical relations and the possible physical couplings between the detected modes and the global or hemispheric patterns of climatic variability (the El Niño Southern Oscillation or ENSO, the North Atlantic Oscillation or NAO, the East Atlantic or EA, the Scandinavian or SCAND, and others) were examined in the time-frequency domain and low-order synchronization events were sought. Significant modes of precipitation variability were detected in the Taranto Gulf and the southern part of the Greek Ionian region at the sub-decadal scales (mostly driven by the SCAND pattern) and particularly at the decadal and quasi-decadal scales, where strong relations found with the ENSO activity (under complex implications of EA and NAO) prior to the 1930s or after the early-1970s. The precipitation variations in the Adriatic stations of Puglia are dominated by significant bi-decadal modes which found to be coherent with the ENSO activity and also weakly related with the Atlantic Ocean sea surface temperature intrinsic variability. Additionally, important discontinuities characterize the evolution of precipitation in certain stations of the Taranto Gulf and the Greek Ionian region during the early-1960s and particularly during the early-1970s, followed by significant reductions in the mean annual precipitation. These discontinuities seem to be associated with regional effects of NAO and SCAND, probably combined with the impact of the 1970s climatic shift in the Pacific and the ENSO variability.

Role of the Atlantic Multidecadal Variability on extreme climate conditions over North America

NASA Astrophysics Data System (ADS)

Ruprich-Robert, Yohan; Delworth, Thomas; Msadek, Rym; Castruccio, Frederic; Yeager, Stephen; Danabasoglu, Gokhan

2017-04-01

The Atlantic Multidecadal Variability (AMV) is associated with marked modulations of climate anomalies observed over many areas of the globe like droughts, decline in sea ice or changes in the atmospheric circulation. However, the shortness of the historical observations compared to the AMV period ( 60-80yr) makes it difficult to show that the AMV is a direct driver of these variations. To isolate the AMV climate response, we use a suite of global coupled models from GFDL and NCAR, in which the North Atlantic sea surface temperatures are restored to the observed AMV pattern, while the other ocean basins are left fully coupled. In order to explore and robustly isolate the AMV impacts on extreme events, we use large ensemble simulations (between 30 and 100 members depending on the model) that are integrated for 10 years. We investigate the importance of model resolution by analyzing GFDL models that vary in their atmospheric resolution and we assess the robustness of the results by comparing them to similar experiments performed with the NCAR coupled model. Further, we investigate the influence of model surface temperature biases on the simulated AMV teleconnections using a flux-adjusted experiment based on a model configuration that corrects for momentum, enthalpy and freshwater fluxes. We focus in this presentation on the impact of the AMV on the occurrence of the North American heat waves. We find that the AMV modulates by about 30% the occurrence of heat waves over North Mexico and the South-West of USA, with more heat waves during a warm phase of the AMV. The main reason for such an increase is that, during a warm AMV phase, the anomalously warm sea surface temperature leads to an increase of the atmospheric convection over the tropical Atlantic, as well as to a an anomalous downward motion over North America. This atmospheric response to AMV inhibits the precipitation over there and drives a deficit of soil moisture. In the summer, the latent heat of

AO/NAO Response to Climate Change. 1; Respective Influences of Stratospheric and Tropospheric Climate Changes

NASA Technical Reports Server (NTRS)

Rind, D.; Perlwitz, J.; Lonergan, P.

2005-01-01

We utilize the GISS Global Climate Middle Atmosphere Model and 8 different climate change experiments, many of them focused on stratospheric climate forcings, to assess the relative influence of tropospheric and stratospheric climate change on the extratropical circulation indices (Arctic Oscillation, AO; North Atlantic Oscillation, NAO). The experiments are run in two different ways: with variable sea surface temperatures (SSTs) to allow for a full tropospheric climate response, and with specified SSTs to minimize the tropospheric change. The results show that tropospheric warming (cooling) experiments and stratospheric cooling (warming) experiments produce more positive (negative) AO/NAO indices. For the typical magnitudes of tropospheric and stratospheric climate changes, the tropospheric response dominates; results are strongest when the tropospheric and stratospheric influences are producing similar phase changes. Both regions produce their effect primarily by altering wave propagation and angular momentum transports, but planetary wave energy changes accompanying tropospheric climate change are also important. Stratospheric forcing has a larger impact on the NAO than on the AO, and the angular momentum transport changes associated with it peak in the upper troposphere, affecting all wavenumbers. Tropospheric climate changes influence both the A0 and NAO with effects that extend throughout the troposphere. For both forcings there is often vertical consistency in the sign of the momentum transport changes, obscuring the difference between direct and indirect mechanisms for influencing the surface circulation.

Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay

USGS Publications Warehouse

Cronin, T. M.; Dwyer, G.S.; Kamiya, T.; Schwede, S.; Willard, D.A.

2003-01-01

We present paleoclimate evidence for rapid (< 100 years) shifts of ~2-4oC in Chesapeake Bay (CB) temperature ~2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (~1400-1900 AD) and the Medieval Warm Period (~800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between ~450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average ~70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450-1000 AD, by 2-3oC, suggesting anomalous recent behavior of the climate system.

Reconstructing Late Holocene North Atlantic atmospheric circulation changes using functional paleoclimate networks

NASA Astrophysics Data System (ADS)

Franke, Jasper G.; Werner, Johannes P.; Donner, Reik V.

2017-11-01

Obtaining reliable reconstructions of long-term atmospheric circulation changes in the North Atlantic region presents a persistent challenge to contemporary paleoclimate research, which has been addressed by a multitude of recent studies. In order to contribute a novel methodological aspect to this active field, we apply here evolving functional network analysis, a recently developed tool for studying temporal changes of the spatial co-variability structure of the Earth's climate system, to a set of Late Holocene paleoclimate proxy records covering the last two millennia. The emerging patterns obtained by our analysis are related to long-term changes in the dominant mode of atmospheric circulation in the region, the North Atlantic Oscillation (NAO). By comparing the time-dependent inter-regional linkage structures of the obtained functional paleoclimate network representations to a recent multi-centennial NAO reconstruction, we identify co-variability between southern Greenland, Svalbard, and Fennoscandia as being indicative of a positive NAO phase, while connections from Greenland and Fennoscandia to central Europe are more pronounced during negative NAO phases. By drawing upon this correspondence, we use some key parameters of the evolving network structure to obtain a qualitative reconstruction of the NAO long-term variability over the entire Common Era (last 2000 years) using a linear regression model trained upon the existing shorter reconstruction.

On the Stability of NaO2 in Na-O2 Batteries.

PubMed

Liu, Chenjuan; Carboni, Marco; Brant, William R; Pan, Ruijun; Hedman, Jonas; Zhu, Jiefang; Gustafsson, Torbjörn; Younesi, Reza

2018-04-25

Na-O 2 batteries are regarded as promising candidates for energy storage. They have higher energy efficiency, rate capability, and chemical reversibility than Li-O 2 batteries; in addition, sodium is cheaper and more abundant compared to lithium. However, inconsistent observations and instability of discharge products have inhibited the understanding of the working mechanism of this technology. In this work, we have investigated a number of factors that influence the stability of the discharge products. By means of in operando powder X-ray diffraction study, the influence of oxygen, sodium anode, salt, solvent, and carbon cathode were investigated. The Na metal anode and an ether-based solvent are the main factors that lead to the instability and decomposition of NaO 2 in the cell environment. This fundamental insight brings new information on the working mechanism of Na-O 2 batteries.

Pacific and Atlantic influences on Mesoamerican climate over the past millennium

NASA Astrophysics Data System (ADS)

Stahle, D. W.; Burnette, D. J.; Diaz, J. Villanueva; Heim, R. R.; Fye, F. K.; Paredes, J. Cerano; Soto, R. Acuna; Cleaveland, M. K.

2012-09-01

A new tree-ring reconstruction of the Palmer Drought Severity Index (PDSI) for Mesoamerica from AD 771 to 2008 identifies megadroughts more severe and sustained than any witnessed during the twentieth century. Correlation analyses indicate strong forcing of instrumental and reconstructed June PDSI over Mesoamerica from the El Niño/Southern Oscillation (ENSO). Spectral analyses of the 1,238-year reconstruction indicate significant concentrations of variance at ENSO, sub-decadal, bi-decadal, and multidecadal timescales. Instrumental and model-based analyses indicate that the Atlantic Multidecadal Oscillation is important to warm season climate variability over Mexico. Ocean-atmospheric variability in the Atlantic is not strongly correlated with the June PDSI reconstruction during the instrumental era, but may be responsible for the strong multidecadal variance detected in the reconstruction episodically over the past millennium. June drought indices in Mesoamerica are negatively correlated with gridded June PDSI over the United States from 1950 to 2005, based on both instrumental and reconstructed data. Interannual variability in this latitudinal moisture gradient is due in part to ENSO forcing, where warm events favor wet June PDSI conditions over the southern US and northern Mexico, but dryness over central and southern Mexico (Mesoamerica). Strong anti-phasing between multidecadal regimes of tree-ring reconstructed June PDSI over Mesoamerica and reconstructed summer (JJA) PDSI over the Southwest has also been detected episodically over the past millennium, including the 1950-1960s when La Niña and warm Atlantic SSTs prevailed, and the 1980-1990s when El Niño and cold Atlantic SSTs prevailed. Several Mesoamerican megadroughts are reconstructed when wetness prevailed over the Southwest, including the early tenth century Terminal Classic Drought, implicating El Niño and Atlantic SSTs in this intense and widespread drought that may have contributed to social

The influence of sea surface temperature anomalies on low-frequency variability of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Manganello, Julia V.

2008-05-01

The influence of sea surface temperature anomalies (SSTA) on multi-year persistence of the North Atlantic Oscillation (NAO) during the second half of the twentieth century is investigated using the Center for Ocean-Land-Atmosphere Studies (COLA) Atmospheric GCM (AGCM) with an emphasis on isolating the geographic location of the SSTA that produce this influence. The present study focuses on calculating the atmospheric response to the SSTA averaged over 1988 1995 (1961 1968) corresponding to the observed period of strong persistence of the positive (negative) phase of the decadal NAO. The model response to the global 1988 1995 average SSTA shows a statistically significant large-scale pattern characteristic of the positive phase of the NAO. Forcing with the global 1961 1968 average SSTA generates a NAO of the opposite polarity compared to observations. However, all large-scale features both in the model and observations during this period are weaker in magnitude and less significant compared to 1988 1995. Additional idealized experiments show that over the northern center of the NAO the non-linear component of the forced response appears to be quite important and acts to enhance the positive NAO signal. On the other hand, over the southern center where the model response is the strongest, it is also essentially linear. The 1988 1995 average SSTA restricted to the western tropical Pacific region produce a positive NAO remarkably similar in structure but stronger in magnitude than the model response to the global and tropical Indo-Pacific 1988 1995 forcing. A 200-hPa geopotential height response in these experiments shows a positive anomaly over the southern center of the NAO embedded in the Rossby wave trains propagating from the western tropical Pacific. Indian Ocean SSTA lead to much weaker positive NAO primarily through the effect on its northern center. SST forcing confined to the North Atlantic north of equator does not produce a response statistically different

Is there a connection between Earth's core and climate at multidecadal time scales?

NASA Astrophysics Data System (ADS)

Lambert, Sébastien; Marcus, Steven; de Viron, Olivier

2017-04-01

The length-of-day (LOD) undergoes multidecadal variations of several milliseconds (ms) attributed to changes in the fluid outer core angular momentum. These variations resemble a quasi-periodic oscillation of duration 60 to 70 years, although the periodicity (and its accurate length) are disputable because of the relatively short observational time span and the lower quality of the observations before the 20th century. Interestingly, similar variations show up in various measured or reconstructed climate indices including the sea surface (SST) and surface air (SAT) temperatures. It has been shown in several studies that LOD variations lead SST and SAT variations by a few years. No clear scenarios have been raised so far to explain the link between external, astronomical forcing (e.g., Solar wind), Earth's rotation (core-driven torsional) oscillations, and Earth's surface processes (climate variations) at these time scales. Accumulating evidence, however, suggests the centrifugal tides generated by multidecadal LOD variations as a 'valve' to control the transfer of thermal energy from the lithosphere to the surface via geothermal fluxes. This hypothesis is supported by recent studies reporting significant correlations between tidal and rotational excitation and seafloor and surface volcanism. In this study, we extend recent works from us and other independent authors by re-assessing the correlations between multidecadal LOD, climate indices, Solar and magnetic activities, as well as gridded data including SST, SAT, and cloud cover. We pay a special attention to the time lags: when a significant correlation is found, the value of the lag may help to discriminate between various possible scenarios. We locate some `hot spots', particularly in the Atlantic ocean and along the trajectory of the upper branch of the Atlantic meridional overturning circulation (AMOC), where the 70-yr oscillation is strongly marked. In addition, we discuss the possibility for centrifugal

The Caspian Sea Catchment influenced by Atlantic Teleconnections in CESM1.2.2 and Observations

NASA Astrophysics Data System (ADS)

Nandini, S. D.; Prange, M.; Schulz, M.

2017-12-01

The Caspian Sea (CS) is the world's largest inland sea and located within a closed (endorheic) drainage basin [ 37°-47N, 47°-54°E]. It has undergone dynamic variations (>3 m) during the past century with huge impacts on the economy, ecosystem and livelihood of coastal people. The origin of these variations as well as future changes are disputable. Here, we examine the impact of the major seasonal North Atlantic teleconnection patterns, the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA) on Caspian hydroclimate variability from 1850-2100 CE. Five Numerical experiments at different atmospheric grid resolutions (2° and 1°) and atmospheric model versions (CAM4 and CAM5) are carried out with the coupled Community Earth System Model (CESM1.2.2). Results reveal the 1° CESM1.2.2 CAM5 captures DJF NAO (46.5%) and EA (13.4%), agreeing well with observational data (1850-2000). The DJF NAO has a strong influence on the DJF temperature, rainfall and evaporation minus precipitation (E-P) over the Caspian sub-basins (Volga, Ural, Terek and Kura). Furthermore, 1° model climate projections (2020-2100 CE) are performed with different Representative Concentration Pathways (RCP4.5 and RCP8.5) to examine likely changes in the NAO and EA and their influence on the Caspian catchment. The NAO under the RCP4.5 and RCP8.5 scenarios remains the leading mode with the highest variance and influences E-P with increased precipitation over the Volga basin and increased evaporation over the Caspian Sea. The above canceling effects act on the hydroclimate variability in the Caspian sub-basins. Moreover, it is indicated that no substantial change is predicted in the CSL by the year 2100. Keywords: North Atlantic Oscillation (NAO), CESM1.2.2 resolutions, Evaporation minus Precipitation (E-P), RCP4.5, RCP8.5

Evidence for the role of the Atlantic multidecadal oscillation and the ocean heat uptake in hiatus prediction

NASA Astrophysics Data System (ADS)

Pasini, Antonello; Triacca, Umberto; Attanasio, Alessandro

2017-08-01

The recent hiatus in global temperature at the surface has been analysed by several studies, mainly using global climate models. The common accepted picture is that since the late 1990s, the increase in anthropogenic radiative forcings has been counterbalanced by other factors, e.g., a decrease in natural forcings, augmented ocean heat storage and negative phases of ocean-atmosphere-coupled oscillation patterns. Here, simple vector autoregressive models are used for forecasting the temperature hiatus in the period 2001-2014. This gives new insight into the problem of understanding the ocean contribution (in terms of heat uptake and atmosphere-ocean-coupled oscillations) to the appearance of this recent hiatus. In particular, considering data about the ocean heat content until a depth of 700 m and the Atlantic multidecadal oscillation is necessary for correctly forecasting the hiatus, so catching both trend and interannual variability. Our models also show that the ocean heat uptake is substantially driven by the natural component of the total radiative forcing at a decadal time scale, confining the importance of the anthropogenic influences to a longer range warming of the ocean.

Impacts of radiation management techniques on the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Adakudlu, Muralidhar; Helge Otterå, Odd; Tjiputra, Jerry; Muri, Helene; Grini, Alf; Schulz, Michael

2017-04-01

The effectiveness of various climate engineering techniques in limiting the global warming signal to reasonable levels has been the topic of state-of-the-art research on climate change. Using an Earth system model, we show that these techniques have the potential to bring down the high CO2 concentration climate in RCP8.5 to a moderate climate similar to RCP4.5 in terms of global temperature. Nevertheless, their influence on the regional aspects of atmospheric circulation is not clear. The regional circulation patterns in the atmosphere are largely characterized by the natural variability modes, such as the North Atlantic Oscillation (NAO). In this study, we assess the impacts of three radiation managment techniques, namely, Stratospheric Aerosol Injection (SAI), Marine Sky Brightening (MSB) and Cirrus Cloud Thinning (CCT), on the structure and features of the NAO. The results indicate an east-northeastward shift as well as intensification of the NAO spatial pattern in the global warming scenarios of RCP4.5 and RCP8.5, with the signal being most intense in the latter. The climate engineering forcings when applied to the RCP8.5 case tend to reduce the strength of the NAO with little impact on its position. The CCT case appears to have the maximum effect on the NAO signal. The patterns of cloud radiative forcing, expressed as the difference between net radiative forcing at TOA under average conditions and clear sky conditions, reveal a northeastward shift of the radiative heating in the north Atlantic region. This implies a possible link between the changes in the NAO signal and the cloud radiative forcing.

THE RESPONSE OF MARINE ECOSYSTEMS TO CLIMATE VARIABILITY ASSOCIATED WITH THE NORTH ATLANTIC OSCILLATION

EPA Science Inventory

A strong association is documented between variability of the North Atlantic Oscillation (NAO) and changes in various trophic levels of the marine ecosystems of the North Atlantic. Examples are presented for phytoplankton, zooplankton, benthos, fish, marine diseases, whales and s...

The changing relationship between the December North Atlantic Oscillation and the following February East Asian trough before and after the late 1980s

NASA Astrophysics Data System (ADS)

Feng, Guolin; Zou, Meng; Qiao, Shaobo; Zhi, Rong; Gong, Zhiqiang

2018-03-01

This study investigates the changing relationship between the December North Atlantic Oscillation (NAO) and the following February East Asian trough (EAT) throughout the past 60 years. We found that the relationship between the December NAO and the following February EAT is significantly enhanced after the late 1980s compared with the period before the late 1980s. The changing relationship mainly results from the enhanced relationship between the December NAO and the following February North Atlantic mid-latitudes' sea surface temperature (SST) anomalies (NAMA) during the same period. During the period after the late 1980s, the persistent positive (negative) NAO pattern from December to the following January contributes to a positive (negative) NAMA, which reaches its maximum magnitude in the following February and excites an anomalous wave train along the North Atlantic and northern Eurasia, and significantly impacts the EAT. During the period before the late 1980s, the positive (negative) NAO pattern during December cannot persist into the following January, and the related positive (negative) NAMA is insignificant during the following February, causing the response of the simultaneous EAT to be insignificant as well. Moreover, there exists a significant impact of the December NAO on the December-January NAMA after the late 1980s, while the December-January NAMA is relatively less affected by the December NAO before the late 1980s. As a result, the simultaneous response of the atmospheric circulation anomalies to the December-January NAMA are evident before the late 1980s, and the positive (negative) NAMA can excite an anomalous wave train along the North Atlantic and northern Eurasia and significantly deepen (shallow) the downstream EAT. By contrast, after involving a feature of atmosphere forcing of SST, the simultaneous feedback of the December-January NAMA on EAT is significantly decreased after the 1980s.

Projection of North Atlantic Oscillation and its effect on tracer transport

NASA Astrophysics Data System (ADS)

Bacer, Sara; Christoudias, Theodoros; Pozzer, Andrea

2016-12-01

The North Atlantic Oscillation (NAO) plays an important role in the climate variability of the Northern Hemisphere, with significant consequences on long-range pollutant transport. We investigate the evolution of pollutant transport in the 21st century influenced by the NAO under a global climate change scenario. We use a free-running simulation performed by the ECHAM/MESSy Atmospheric Chemistry (EMAC) model coupled with the ocean general circulation model MPIOM, covering the period from 1950 until 2100. Similarly to other works, the model shows a future northeastward shift of the NAO centres of action and a weak positive trend of the NAO index (over 150 years). Moreover, we find that NAO trends (computed over periods shorter than 30 years) will continue to oscillate between positive and negative values in the future. To investigate the NAO effects on transport we consider carbon monoxide tracers with exponential decay and constant interannual emissions. We find that at the end of the century, the south-western Mediterranean and northern Africa will, during positive NAO phases, see higher pollutant concentrations with respect to the past, while a wider part of northern Europe will, during positive NAO phases, see lower pollutant concentrations. Such results are confirmed by the changes observed in the future for tracer concentration and vertically integrated tracer transport, differentiating the cases of "high NAO" and "low NAO" events.

Post-1980 shifts in the sensitivity of boreal tree growth to North Atlantic Ocean dynamics and seasonal climate. Tree growth responses to North Atlantic Ocean dynamics

NASA Astrophysics Data System (ADS)

Ols, Clémentine; Trouet, Valerie; Girardin, Martin P.; Hofgaard, Annika; Bergeron, Yves; Drobyshev, Igor

2018-06-01

The mid-20th century changes in North Atlantic Ocean dynamics, e.g. slow-down of the Atlantic meridional overturning thermohaline circulation (AMOC), have been considered as early signs of tipping points in the Earth climate system. We hypothesized that these changes have significantly altered boreal forest growth dynamics in northeastern North America (NA) and northern Europe (NE), two areas geographically adjacent to the North Atlantic Ocean. To test our hypothesis, we investigated tree growth responses to seasonal large-scale oceanic and atmospheric indices (the AMOC, North Atlantic Oscillation (NAO), and Arctic Oscillation (AO)) and climate (temperature and precipitation) from 1950 onwards, both at the regional and local levels. We developed a network of 6876 black spruce (NA) and 14437 Norway spruce (NE) tree-ring width series, extracted from forest inventory databases. Analyses revealed post-1980 shifts from insignificant to significant tree growth responses to summer oceanic and atmospheric dynamics both in NA (negative responses to NAO and AO indices) and NE (positive response to NAO and AMOC indices). The strength and sign of these responses varied, however, through space with stronger responses in western and central boreal Quebec and in central and northern boreal Sweden, and across scales with stronger responses at the regional level than at the local level. Emerging post-1980 associations with North Atlantic Ocean dynamics synchronized with stronger tree growth responses to local seasonal climate, particularly to winter temperatures. Our results suggest that ongoing and future anomalies in oceanic and atmospheric dynamics may impact forest growth and carbon sequestration to a greater extent than previously thought. Cross-scale differences in responses to North Atlantic Ocean dynamics highlight complex interplays in the effects of local climate and ocean-atmosphere dynamics on tree growth processes and advocate for the use of different spatial scales in

Biological and climate controls on North Atlantic marine carbon dynamics over the last millennium: Insights from an absolutely-dated shell based record from the North Icelandic Shelf

NASA Astrophysics Data System (ADS)

Hall, I. R.; Reynolds, D.; Scourse, J. D.; Richardson, C.; Wanamaker, A. D.; Butler, P. G.

2017-12-01

Given the rapid increase in atmospheric carbon dioxide concentrations (pCO2) over the industrial era there is a pressing need to construct longterm records of natural carbon cycling prior to this perturbation and to develop a more robust understanding of the role the oceans play in the sequestration of atmospheric carbon. Here we reconstruct the historical biological and climatic controls on the carbon isotopic (δ13C-shell) composition of the North Icelandic shelf waters over the last millennium derived from the shells of the long-lived marine bivalve mollusc Arctica islandica. Variability in the annually resolved δ13C-shell record is dominated by multi-decadal variability with a negative trend (-0.003±0.002‰yr-1) over the industrial era (1800-2000). This trend is consistent with the marine Suess effect brought about by the sequestration of isotopically light carbon (δ13C of CO2) derived from the burning of fossil fuels. Comparison of the δ13C-shell record with contemporary proxy archives, over the last millennium, and instrumental data over the 20th century, suggests that primary productivity and climate conditions over the sub-polar North Atlantic region played a vital role in driving inter-annual to multi-decadal scale variability in the δ13C-shell record. Our results highlight that relative shifts in the proportion of sub-polar mode waters and Arctic intermediate waters entrained onto the North Icelandic shelf, coupled with atmospheric circulation patterns associated with the winter North Atlantic Oscillation (wNAO), are the likely physical mechanisms that drive natural variations in seawater δ13C variability on the North Icelandic shelf.

The North Atlantic Oscillation system and plant phenology

NASA Astrophysics Data System (ADS)

Hubálek, Zdenek

2016-05-01

The onset of flowering in 78 wild and domesticated terrestrial plant species recorded in South Moravia (Czech Republic) from 1965 to 2014 was correlated with the North Atlantic Oscillation (NAO) index of the preceding winter. Flowering occurred significantly earlier following positive winter NAO phases (causing spring to be warmer than normal in Central Europe) in nearly all early-flowering (March, April) species; high Pearson correlation values were recorded in, e.g., goat willow, spring snowflake, golden bell, cornelian cherry, sweet violet, cherry plum, grape hyacinth, apricot, blackthorn, common dandelion, cherry, southern magnolia, common apple, cuckoo flower, European bird cherry, and cherry laurel. In contrast, the timing of later-flowering plant species (May to July) did not correlate significantly with the winter NAO index. It was found that local temperature is obviously a proximate factor of plant phenology, while the winter NAO is the ultimate factor, affecting temperature and other meteorological phenomena in Central Europe during spring season.

Inter-Relationship Between Subtropical Pacific Sea Surface Temperature, Arctic Sea Ice Concentration, and the North Atlantic Oscillation in Recent Summers and Winters

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon; Cullather, Richard I.; Nowicki, Sophie M.; Kim, Kyu-Myong

2017-01-01

The inter-relationship between subtropical western-central Pacific sea surface temperatures (STWCPSST), sea ice concentration in the Beaufort Sea (SICBS), and the North Atlantic Oscillation (NAO) are investigated for the last 37 summers and winters (1980-2016). Lag-correlation of the STWCPSST×(-1) in spring with the NAO phase and SICBS in summer increases over the last two decades, reaching r = 0.4-0.5 with significance at 5 percent, while winter has strong correlations in approximately 1985-2005. Observational analysis and the atmospheric general circulation model experiments both suggest that STWCPSST warming acts to increase the Arctic geopotential height and temperature in the following season. This atmospheric response extends to Greenland, providing favorable conditions for developing the negative phase of the NAO. SIC and surface albedo tend to decrease over the Beaufort Sea in summer, linked to the positive surface net shortwave flux. Energy balance considering radiative and turbulent fluxes reveal that available energy that can heat surface is larger over the Arctic and Greenland and smaller over the south of Greenland, in response to the STWCPSST warming in spring. XXXX Arctic & Atlantic: Positive upper-level height/T anomaly over the Arctic and Greenland, and a negative anomaly over the central-eastern Atlantic, resembling the (-) phase of the NAO. Pacific: The negative height/T anomaly over the mid-latitudes, along with the positive anomaly over the STWCP, where 1degC warming above climatology is prescribed. Discussion: It is likely that the Arctic gets warm and the NAO is in the negative phase in response to the STWCP warming. But, there are other factors (e.g., internal variability) that contribute to determination of the NAO phase: not always the negative phase of the NAO in the event of STWCP warming (e.g.: recent winters and near neutral NAO in 2017 summer).

600 yr High-Resolution Climate Reconstruction of the Atlantic Multidecadal Variability deduced from a Puerto Rican Speleothem

NASA Astrophysics Data System (ADS)

Winter, A.; Vieten, R.

2015-12-01

A multi-proxy speleothem study tracks the regional hydrological variability in Puerto Rico and highlights its close relation to the Atlantic Multidecadal Oscillation. Our proxy record extends instrumental observations 600 years into the past, and reveals the range of natural hydrologic variability for the region. A detailed interpretation and understanding of the speleothem climate record is achieved by the combination of multi-proxy measurements, thin section petrography, XRD analysis and cave monitoring results. The speleothem was collected in Cueva Larga, a one mile-long cave system that has been monitored since 2012. MC-ICPMS 230Th/U-dating reveals that the speleothem grew constantly over the last 600 years. Trace element ratios (Sr/Ca and Mg/Ca) as well as stable isotope ratios (δ18O and δ13C) elucidate significant changes in atmospheric precipitation at the site. Monthly cave monitoring results demonstrate that the epikarst system responds to multi-annual changes in seepage water recharge. The drip water isotope and trace element composition lack short term or seasonal variability. This hydrological system creates favorable conditions to deduce decadal climate variability from Cueva Larga's climate record. The speleothem time series mimics the most-recently published AMO reconstruction over the last 200 years with a time lag of 10-20 years. The time lag seems to results from slow atmospheric signal transmission through the epikarst but the effect of dating uncertainties cannot be ruled out. Warm SSTs in the North Atlantic are related to drier conditions in Puerto Rico. During times of decreased rainfall a relative increase in prior calcite precipitation seems to be the main process causing increased Mg/Ca trace element ratios. High trace element ratios correlate to higher δ13C values. The increase in both proxies indicates a shift towards time periods of decreased rainfall. Over the past 600 years there are two intervals of increased Mg/Ca and δ13C values

Hydro-climate variability and teleconnection patterns during the last millennium in NW Africa, inferred from speleothem records

NASA Astrophysics Data System (ADS)

Ait Brahim, Y.; Cheng, H.; Sifeddine, A.; Wassenburg, J. A.; Khodri, M.; Cruz, F. W., Sr.

2017-12-01

In this study, we present new paleoclimate records from two well dated Moroccan speleothems. Our stalagmites were sampled from Ifoulki cave in the Western High Atlas Mountains in SW Morocco and Chaara cave in the Eastern Middle Atlas Mountains in NE Morocco. The new paleo-records cover the last 1000 years with a high resolution and reveal substantial swings of dry and humid periods with decadal to multidecadal frequencies. The Medieval Climate Anomaly (MCA) is characterized by generally dry conditions, while wetter conditions are recorded during the Little Ice Age (LIA) and a trend towards dry conditions during the 20th century. These observations are consistent with regional climate signals, providing new insights on common climate controls and teleconnection patterns in NW Africa. We emphasize that the hydro-climate conditions in Morocco remained under the influence of the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). At longer timescales, we hypothesize that the generally warmer MCA and colder LIA influenced the regional climate in NW Africa through interactions with local mechanisms, such as the Sahara Low, which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively.

A multi-decadal study of Polar and Atlantic Water changes on the North Iceland shelf during the last Millennium

NASA Astrophysics Data System (ADS)

Perner, Kerstin; Moros, Matthias; Simon, Margit; Berben, Sarah; Griem, Lisa; Dokken, Trond; Wacker, Lukas; Jansen, Eystein

2017-04-01

The region offshore North Iceland is known to be sensitive to broad scale climatic and oceanographic changes in the North Atlantic Ocean. Changes in surface and subsurface water conditions link to the varying influence of Polar-sourced East Icelandic Current (EIC) and Atlantic-sourced North Irminger Icelandic Current (NIIC). Cold/fresh Polar waters from the East Greenland Current feed the surface flowing EIC, while warm/saline Subpolar Mode Waters (SPMW) from the Irminger Current (IC) feed the subsurface flowing NIIC. Here, we present a new and well-dated multi-proxy record that allows high-resolution reconstruction of surface and subsurface water mass changes on the western North Iceland shelf. An age-depth model for the last Millennium has been developed based on the combined information from radionuclide measurements (137Cs, 210Pb) dating, 25 AMS 14C radiocarbon dates, and identified Tephra horizons. Our dating results provide further support to previous assumptions that North of Iceland a conventional reservoir age correction application of 400 years (ΔR=0) is inadequate (e.g., Eikíksson et al., 2000; Wanamaker Jr. et al., 2012). The combined evidence from radionuclide dating and the identified Tephra horizons point to a ΔR of c. 360 years during the last Millennium. Our benthic and planktic foraminiferal assemblage and stable oxygen isotope (18O) record of Neogloboquadrina pachyderma s. (NPS) resolve the last Millennium at a centennial to multi-decadal resolution. Comparison of abundance changes of the Atlantic Water related species Cassidulina neoteretis and NPS, as well as the 18O record agree well with the instrumental data time series from the monitoring station Hunafloi nearby. This provides further support that our data is representative of relative temperature and salinity changes in surface and subsurface waters. Hence, this new record allows a more detailed investigation on the timing of Polar (EIC) and Atlantic (NIIC, IC) Water contribution

The dominant role of Arctic surface buoyancy fluxes for AMOC slow-down on multi-decadal timescales

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Sevellec, F.

2016-12-01

One of the most dramatic consequences of the ongoing climate change is the reduction in the Arctic sea ice cover observed over the past few decades. This sea ice loss increases net heat flux into the ocean and at the same time exposes the ocean to additional freshwater flux from the atmosphere. These two effects imply positive anomalies in surface buoyancy fluxes over the Arctic ocean. In this study we estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to global changes in surface buoyancy forcing, especially in the context of changes in the Arctic. We find that, whereas on decadal timescale the subpolar region (especially east and south of Greenland) is the primarily driver of AMOC weakening due to positive buoyancy fluxes, on multidecadal timescales (longer than 20 years) it is the Arctic region that largely controls the AMOC slow-down. On timescales close to one century surface buoyancy fluxes over the Arctic ocean are nearly twice as effective for weakening the AMOC than those in the subpolar North Atlantic. We also find that the anomalous surface buoyancy fluxes in the Arctic can efficiently weaken poleward heat transport in the North Atlantic on a basin scale (i.e., between 25oN and 50oN). We conclude that such remote control of the AMOC intensity and heat transport by the Arctic ocean is a robust feature of climate change on multi-decadal timescales.

North Atlantic Oscillation and moisture transport towards the Iberian Peninsula during winter

NASA Astrophysics Data System (ADS)

Ordóñez, Paulina; Liberato, Margarida L. R.; Gouveia, Célia; Trigo, Ricardo M.

2013-04-01

The North Atlantic Oscillation (NAO) is the major source of interannual variability in winter precipitation over the Iberian Peninsula (IP). Recent works have identified the most important sources of moisture that supply the IP during different seasons of the year, including the nearby western Mediterranean and the tropical-subtropical North Atlantic corridor that extends from the Gulf of Mexico to the IP, and the IP itself (Gimeno et al., 2010). However, although rainfall is directly related to the moisture supply, the relationship between the water vapor transported towards IP and the NAO phase remains unclear. In this work the moisture transport towards IP was analyzed using a Lagrangian diagnosis method, which relies on the Lagrangian particle dispersion model FLEXPART. This methodology computes budgets of evaporation minus precipitation (E-P) by evaluating changes in the specific humidity along back-trajectories. Here we have computed (for each day) the evolution of moisture of the particles bound for Iberia up to 10 days prior to their arrival. The analysis was constrained to the winter (DJF) season, responsible for the largest fraction of precipitation, for the 20 years of ECMWF Reanalyses ERA40 dataset from 1980 to 2000. The contribution of the NAO phase on the water budgets is examined using composites of the obtained (E - P) fields for the 5 most extreme positive and negative NAO years of the study period. Results confirm that the IP is dominated by positive (negative) E-P anomalies during positive (negative) NAO phase. Additionally an anomalous water vapor sink (source) region located approximately over the Gulf Stream is found during positive (negative) NAO phase. Gimeno L., Nieto R., Trigo R.M. , Vicente-Serrano S.M, Lopes-Moreno J.I., (2010) "Where does the Iberian Peninsula moisture come from? An answer based on a Lagrangian approach". J. Hydrometeorology, 11, 421-436 DOI: 10.1175/2009JHM1182.1.

Development of the Wintertime Sr/Ca-SST Record from Red Sea Corals as a Proxy for the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Bernstein, W. N.; Hughen, K. A.

2009-12-01

The North Atlantic Oscillation (NAO) is one of the most pronounced and influential patterns in winter atmospheric circulation variability. This meridional redistribution of atmospheric mass across the Atlantic Ocean produces large changes in the intensity, number and direction of storms generated within the basin, and the regional climate of surrounding continents. The NAO exerts a significant impact on society, through influences on agriculture, fisheries, water management, energy generation and coastal development. NAO effects on climate extend from eastern North America across Europe to the eastern Mediterranean and Middle East. Changes in NAO behavior during the late 20th century have been linked to global warming; yet despite its importance, the causes and long-term patterns of NAO variability in the past remain poorly understood. In order to better predict the influence of the NAO on climate in the future, it is critical to examine multi-century NAO variability. The Red Sea is an excellent location from which to generate long NAO records for two reasons. First, patterns of wintertime sea surface temperature (SST) and salinity (SSS) in the Red Sea are highly correlated with NAO variability (Visbeck et al. 2001; Hurrell et al. 2003). Second, the tropical/subtropical Red Sea region contains fast growing long-lived massive Porites spp. corals with annually banded skeletons. These corals are ideal for generating well-dated high-resolution paleoclimatic records that extend well beyond the instrumental period. Here we present a study of winter SST and NAO variability in the Red sea region based on coral Sr/Ca data. In 2008, we collected multiple drill cores ranging in length from 1 to 4.1 meters from Porites corals at six sites spanning a large SST gradient. Sr/Ca measurements from multiple corals will be regressed against 23 years of satellite SST data, expanding the SST range over which we calibrate. A sampling resolution of 0.5mm will yield greater than bi

The role of the North Atlantic Oscillation in controlling U.K. butterfly population size and phenology

PubMed Central

Westgarth-Smith, Angus R; Roy, David B; Scholze, Martin; Tucker, Allan; Sumpter, John P

2012-01-01

1. The North Atlantic Oscillation (NAO) exerts considerable control on U.K. weather. This study investigates the impact of the NAO on butterfly abundance and phenology using 34 years of data from the U.K. Butterfly Monitoring Scheme (UKBMS). 2. The study uses a multi-species indicator to show that the NAO does not affect overall U.K. butterfly population size. However, the abundance of bivoltine butterfly species, which have longer flight seasons, were found to be more likely to respond positively to the NAO compared with univoltine species, which show little or a negative response. 3. A positive winter NAO index is associated with warmer weather and earlier flight dates for Anthocharis cardamines (Lepidoptera: Pieridae), Melanargia galathea (Lepidoptera: Nymphalidae), Aphantopus hyperantus (Lepidoptera: Nymphalidae), Pyronia tithonus (Lepidoptera: Nymphalidae), Lasiommata megera (Lepidoptera: Nymphalidae) and Polyommatus icarus (Lepidoptera: Lycaenidae). In bivoltine species, the NAO affects the phenology of the first generation, the timing of which indirectly controls the timing of the second generation. 4. The NAO influences the timing of U.K. butterfly flight seasons more strongly than it influences population size. PMID:22879687

Sulfate Aerosol Control of Tropical Atlantic Climate over the Twentieth Century

NASA Technical Reports Server (NTRS)

Chang, C.-Y.; Chiang, J. C. H.; Wehner, M. F.; Friedman, A. R.; Ruedy, R.

2011-01-01

The tropical Atlantic interhemispheric gradient in sea surface temperature significantly influences the rainfall climate of the tropical Atlantic sector, including droughts over West Africa and Northeast Brazil. This gradient exhibits a secular trend from the beginning of the twentieth century until the 1980s, with stronger warming in the south relative to the north. This trend behavior is on top of a multi-decadal variation associated with the Atlantic multi-decadal oscillation. A similar long-term forced trend is found in a multimodel ensemble of forced twentieth-century climate simulations. Through examining the distribution of the trend slopes in the multimodel twentieth-century and preindustrial models, the authors conclude that the observed trend in the gradient is unlikely to arise purely from natural variations; this study suggests that at least half the observed trend is a forced response to twentieth-century climate forcings. Further analysis using twentieth-century single-forcing runs indicates that sulfate aerosol forcing is the predominant cause of the multimodel trend. The authors conclude that anthropogenic sulfate aerosol emissions, originating predominantly from the Northern Hemisphere, may have significantly altered the tropical Atlantic rainfall climate over the twentieth century

Role of the North Atlantic Oscillation in decadal temperature trends

NASA Astrophysics Data System (ADS)

Iles, Carley; Hegerl, Gabriele

2017-11-01

Global temperatures have undergone periods of enhanced warming and pauses over the last century, with greater variations at local scales due to internal variability of the climate system. Here we investigate the role of the North Atlantic Oscillation (NAO) in decadal temperature trends in the Northern Hemisphere for periods with large decadal NAO trends. Using a regression based technique we find a best estimate that trends in the NAO more than halved (reduced by 57%, 5%-95%: 47%-63%) the winter warming over the Northern Hemisphere extratropics (NH; 30N-90N) from 1920-1971 and account for 45% (±14%) of the warming there from 1963-1995, with larger impacts on regional scales. Over the period leading into the so-called warming hiatus, 1989-2013, the NAO reduced NH winter warming to around one quarter (24%; 19%-31%) of what it would have been, and caused large negative regional trends, for example, in Northern Eurasia. Warming is more spatially uniform across the Northern Hemisphere after removing the NAO influence in winter, and agreement with multi-model mean simulated trends improves. The impact of the summer NAO is much weaker, but still discernible over Europe, North America and Greenland, with the downward trend in the summer NAO from 1988-2012 reducing warming by about a third in Northern Europe and a half in North America. A composite analysis using CMIP5 control runs suggests that the ocean response to prolonged NAO trends may increase the influence of decadal NAO trends compared to estimates based on interannual regressions, particularly in the Arctic. Results imply that the long-term NAO trends over the 20th century alternately masked or enhanced anthropogenic warming, and will continue to temporarily offset or enhance its effects in the future.

Hierarchical Porous Carbon Spheres for High-Performance Na-O2 Batteries.

PubMed

Sun, Bing; Kretschmer, Katja; Xie, Xiuqiang; Munroe, Paul; Peng, Zhangquan; Wang, Guoxiu

2017-12-01

As a new family member of room-temperature aprotic metal-O 2 batteries, Na-O 2 batteries, are attracting growing attention because of their relatively high theoretical specific energy and particularly their uncompromised round-trip efficiency. Here, a hierarchical porous carbon sphere (PCS) electrode that has outstanding properties to realize Na-O 2 batteries with excellent electrochemical performances is reported. The controlled porosity of the PCS electrode, with macropores formed between PCSs and nanopores inside each PCS, enables effective formation/decomposition of NaO 2 by facilitating the electrolyte impregnation and oxygen diffusion to the inner part of the oxygen electrode. In addition, the discharge product of NaO 2 is deposited on the surface of individual PCSs with an unusual conformal film-like morphology, which can be more easily decomposed than the commonly observed microsized NaO 2 cubes in Na-O 2 batteries. A combination of coulometry, X-ray diffraction, and in situ differential electrochemical mass spectrometry provides compelling evidence that the operation of the PCS-based Na-O 2 battery is underpinned by the formation and decomposition of NaO 2 . This work demonstrates that employing nanostructured carbon materials to control the porosity, pore-size distribution of the oxygen electrodes, and the morphology of the discharged NaO 2 is a promising strategy to develop high-performance Na-O 2 batteries. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Breakdown of NAO reproducibility into internal versus externally-forced components: a two-tier pilot study

NASA Astrophysics Data System (ADS)

Douville, Hervé; Ribes, A.; Tyteca, S.

2018-03-01

Assessing the ability of atmospheric models to capture observed climate variations when driven by observed sea surface temperature (SST), sea ice concentration (SIC) and radiative forcings is a prerequisite for the feasibility of near term climate predictions. Here we achieve ensembles of global atmospheric simulations to assess and attribute the reproducibility of the boreal winter atmospheric circulation against the European Centre for Medium Range Forecasts (ECMWF) twentieth century reanalysis (ERA20C). Our control experiment is driven by the observed SST/SIC from the Atmospheric Model Intercomparison Project. It is compared to a similar ensemble performed with the ECMWF model as a first step toward ERA20C. Moreover, a two-tier methodology is used to disentangle externally-forced versus internal variations in the observed SST/SIC boundary conditions and run additional ensembles allowing us to attribute the observed atmospheric variability. The focus is mainly on the North Atlantic Oscillation (NAO) variability which is more reproducible in our model than in the ECMWF model. This result is partly due to the simulation of a positive NAO trend across the full 1920-2014 integration period. In line with former studies, this trend might be mediated by a circumglobal teleconnection mechanism triggered by increasing precipitation over the tropical Indian Ocean (TIO). Surprisingly, this response is mainly related to the internal SST variability and is not found in the ECMWF model driven by an alternative SST dataset showing a weaker TIO warming in the first half of the twentieth century. Our results may reconcile the twentieth century observations with the twenty-first century projections of the NAO. They should be however considered with caution given the limited size of our ensembles, the possible influence of other sources of NAO variability, and the uncertainties in the tropical SST trend and breakdown between internal versus externally-forced variability.

The evolution of the North Atlantic Oscillation for the last 700 years inferred from D/H isotopes in the sedimentary record of Lake Azul (Azores archipelago, Portugal).

NASA Astrophysics Data System (ADS)

Rubio de Ingles, Maria Jesus; Shanahan, Timothy M.; Sáez, Alberto; José Pueyo, Juan; Raposeiro, Pedro M.; Gonçalves, Vitor M.; Hernández, Armand; Trigo, Ricardo; Sánchez López, Guiomar; Francus, Pierre; Giralt, Santiago

2015-04-01

The δD plant leaf wax variations provide insights on precipitation and evaporation evolution through time. This proxy has been used to reconstruct the temporal evolution of the North Atlantic Oscillation (NAO) climate mode since this mode rules most of the climate variability in the central North Atlantic area. A total lipid extraction preparation and the correspondent analyses in the IRMS have been done for 100 samples from the uppermost 1.5 m of the sedimentary infill of Lake Azul (Azores archipelago, Portugal). According to the chronological model, established by 210Pb profile and 4 AMS 14C dates, this record contains the environmental history of the last 730 years. The reconstructed precipitation variations obtained from D/H isotope values, suggest that this area has suffered significant changes in its distribution and intensity rainfall patterns through time. The end of the Medieval Climate Anomaly (MCA, 1100- 1300 AD) is characterized by a progressive enrichmentof D/H isotope values which meant decreasing arid conditions. These rainfalls' increase might be interpreted by a shift from positive to negative dominance of the NAO. The Little Ice Age (LIA, 1300 - 1850 AD) was characterized by two humid periods (1300- 1550 AD and 1650 - 1850 AD) separated by a relatively dry period. These precipitation oscillations are clearly visible by marked changes in the D/H isotope values. The LIA was followed by the persistence of the positive NAO mode, exhibited by the depletion of the D/H isotope signal, which indicated an overall decrease of the precipitation in the central North Atlantic area. Surprisingly, the D/H of the last 100 years, characterized by the present global warming and a persistent positive NAO mode, display large fluctuations most possibly linked to an enhancement of the storminess which is in concordance with the data fluctuations observed in the instrumental record for the last 80 years in the archipelago. This climatic evolution is in accordance with

Potential links between the North Atlantic Oscillation and decreasing precipitation and runoff on Sardinia

NASA Astrophysics Data System (ADS)

Sarigu, A.; Montaldo, N.

2017-12-01

In the Mediterranean region, the reduction in precipitation and warmer temperatures is generating a desertification process, with dramatic consequences for both agriculture and the sustainability of water resources. On the island of Sardinia (Italy), the decrease in runoff impacts the management of water resources, resulting in water supply restrictions even for domestic consumption. In the 10 Sardinian basins with a longer database (at least 40 complete years of data, including data from the past 10 years), runoff decreased drastically over the 1975-2010 period, with mean yearly runoff reduced by more than 40% compared to the previous 1922-1974 period. Trends in yearly runoff are negative, with Mann-Kendall τ values ranging from -0.39 to -0.2. Decreasing winter precipitation over the 1975-2010 period everywhere on Sardinia island has led to these decreases in runoff, as most yearly runoff in the Sardinian basins (70% on average) is produced by winter precipitation due to the seasonality typical of the Mediterranean climate regime. The trend in winter precipitation is not homogenous; the negative trend is higher (around -0.25) on the west Sardinian coast, becoming lower across the island toward the east coast (around -0.14). Winter precipitation is highly correlated with the North Atlantic Oscillation (NAO), a weather phenomenon in the North Atlantic Ocean that controls the direction and strength of westerly winds and storm tracks into Europe. High negative correlations (up to -0.45) between winter NAO index and winter precipitation are estimated along the west coast. Meanwhile, these correlations decrease east across the island toward the high mountain in the center of Sardinia, reaching the lowest values along the east coast (about -0.25). The decreasing correlation between winter NAO index and winter precipitation in the longitudinal direction (from the North Atlantic dipole to the east) here accelerates due to local-scale orographic effects that overlap the

Winter North Atlantic Oscillation impact on European precipitation and drought under climate change

NASA Astrophysics Data System (ADS)

Tsanis, I.; Tapoglou, E.

2018-01-01

The North Atlantic Oscillation (NAO) is responsible for the climatic variability in the Northern Hemisphere, in particular, in Europe and is related to extreme events, such as droughts. The purpose of this paper is to study the correlation between precipitation and winter (December-January-February-March (DJFM)) NAO both for the historical period (1951-2000) and two future periods (2001-2050 and 2051-2100). NAO is calculated for these three periods by using sea level pressure, while precipitation data from seven climate models following the representative concentration pathway (RCP) 8.5 are also used in this study. An increasing trend in years with positive DJFM NAO values in the future is defined by this data, along with higher average DJFM NAO values. The correlation between precipitation and DJFM NAO is high, especially in the Northern (high positive) and Southern Europe (high negative). Therefore, higher precipitation in Northern Europe and lower precipitation in Southern Europe are expected in the future. Cross-spectral analysis between precipitation and DJFM NAO time series in three different locations in Europe revealed the best coherence in a dominant cycle between 3 and 4 years. Finally, the maximum drought period in terms of consecutive months with drought is examined in these three locations. The results can be used for strategic planning in a sustainable water resources management plan, since there is a link between drought events and NAO.

Sensitivity of proxies on non-linear interactions in the climate system

PubMed Central

Schultz, Johannes A.; Beck, Christoph; Menz, Gunter; Neuwirth, Burkhard; Ohlwein, Christian; Philipp, Andreas

2015-01-01

Recent climate change is affecting the earth system to an unprecedented extent and intensity and has the potential to cause severe ecological and socioeconomic consequences. To understand natural and anthropogenic induced processes, feedbacks, trends, and dynamics in the climate system, it is also essential to consider longer timescales. In this context, annually resolved tree-ring data are often used to reconstruct past temperature or precipitation variability as well as atmospheric or oceanic indices such as the North Atlantic Oscillation (NAO) or the Atlantic Multidecadal Oscillation (AMO). The aim of this study is to assess weather-type sensitivity across the Northern Atlantic region based on two tree-ring width networks. Our results indicate that nonstationarities in superordinate space and time scales of the climate system (here synoptic- to global scale, NAO, AMO) can affect the climate sensitivity of tree-rings in subordinate levels of the system (here meso- to synoptic scale, weather-types). This scale bias effect has the capability to impact even large multiproxy networks and the ability of these networks to provide information about past climate conditions. To avoid scale biases in climate reconstructions, interdependencies between the different scales in the climate system must be considered, especially internal ocean/atmosphere dynamics. PMID:26686001

On which timescales do gas transfer velocities control North Atlantic CO2 flux variability?

NASA Astrophysics Data System (ADS)

Couldrey, Matthew; Oliver, Kevin; Yool, Andrew; Halloran, Paul; Achterberg, Eric

2016-04-01

The North Atlantic is an important basin for the global ocean's uptake of anthropogenic and natural carbon dioxide (CO2), but the mechanisms controlling this carbon flux are not fully understood. The air-sea flux of CO2, F, is the product of a gas transfer velocity, k, the air-sea CO2concentration gradient, ΔpCO2, and the temperature and salinity-dependent solubility coefficient, α. k is difficult to constrain, representing the dominant uncertainty in F on short (instantaneous to interannual) timescales. Previous work shows that in the North Atlantic, ΔpCO2and k both contribute significantly to interannual F variability, but that k is unimportant for multidecadal variability. On some timescale between interannual and multidecadal, gas transfer velocity variability and its associated uncertainty become negligible. Here, we quantify this critical timescale for the first time. Using an ocean model, we determine the importance of k, ΔpCO2and α on a range of timescales. On interannual and shorter timescales, both ΔpCO2and k are important controls on F. In contrast, pentadal to multidecadal North Atlantic flux variability is driven almost entirely by ΔpCO2; k contributes less than 25%. Finally, we explore how accurately one can estimate North Atlantic F without a knowledge of non-seasonal k variability, finding it possible for interannual and longer timescales. These findings suggest that continued efforts to better constrain gas transfer velocities are necessary to quantify interannual variability in the North Atlantic carbon sink. However, uncertainty in k variability is unlikely to limit the accuracy of estimates of longer term flux variability.

On which timescales do gas transfer velocities control North Atlantic CO2 flux variability?

NASA Astrophysics Data System (ADS)

Couldrey, Matthew P.; Oliver, Kevin I. C.; Yool, Andrew; Halloran, Paul R.; Achterberg, Eric P.

2016-05-01

The North Atlantic is an important basin for the global ocean's uptake of anthropogenic and natural carbon dioxide (CO2), but the mechanisms controlling this carbon flux are not fully understood. The air-sea flux of CO2, F, is the product of a gas transfer velocity, k, the air-sea CO2 concentration gradient, ΔpCO2, and the temperature- and salinity-dependent solubility coefficient, α. k is difficult to constrain, representing the dominant uncertainty in F on short (instantaneous to interannual) timescales. Previous work shows that in the North Atlantic, ΔpCO2 and k both contribute significantly to interannual F variability but that k is unimportant for multidecadal variability. On some timescale between interannual and multidecadal, gas transfer velocity variability and its associated uncertainty become negligible. Here we quantify this critical timescale for the first time. Using an ocean model, we determine the importance of k, ΔpCO2, and α on a range of timescales. On interannual and shorter timescales, both ΔpCO2 and k are important controls on F. In contrast, pentadal to multidecadal North Atlantic flux variability is driven almost entirely by ΔpCO2; k contributes less than 25%. Finally, we explore how accurately one can estimate North Atlantic F without a knowledge of nonseasonal k variability, finding it possible for interannual and longer timescales. These findings suggest that continued efforts to better constrain gas transfer velocities are necessary to quantify interannual variability in the North Atlantic carbon sink. However, uncertainty in k variability is unlikely to limit the accuracy of estimates of longer-term flux variability.

On which timescales do gas transfer velocities control North Atlantic CO2 flux variability?

NASA Astrophysics Data System (ADS)

Couldrey, M.; Oliver, K. I. C.; Yool, A.; Halloran, P. R.; Achterberg, E. P.

2016-02-01

The North Atlantic is an important basin for the global ocean's uptake of anthropogenic and natural carbon dioxide (CO2), but the mechanisms controlling this carbon flux are not fully understood. The air-sea flux of CO2, F, is the product of a gas transfer velocity, k, the air-sea CO2 concentration gradient, ΔpCO2, and the temperature and salinity-dependent solubility coefficient, α. k is difficult to constrain, representing the dominant uncertainty in F on short (instantaneous to interannual) timescales. Previous work shows that in the North Atlantic, ΔpCO2 and k both contribute significantly to interannual F variability, but that k is unimportant for multidecadal variability. On some timescale between interannual and multidecadal, gas transfer velocity variability and its associated uncertainty become negligible. Here, we quantify this critical timescale for the first time. Using an ocean model, we determine the importance of k, ΔpCO2 and α on a range of timescales. On interannual and shorter timescales, both ΔpCO2 and k are important controls on F. In contrast, pentadal to multidecadal North Atlantic flux variability is driven almost entirely by ΔpCO2; k contributes less than 25%. Finally, we explore how accurately one can estimate North Atlantic F without a knowledge of non-seasonal k variability, finding it possible for interannual and longer timescales. These findings suggest that continued efforts to better constrain gas transfer velocities are necessary to quantify interannual variability in the North Atlantic carbon sink. However, uncertainty in k variability is unlikely to limit the accuracy of estimates of longer term flux variability.

Tropical Cyclones and Climate Controls in the Western Atlantic Basin during the First Half of the Nineteenth Century

NASA Astrophysics Data System (ADS)

Mock, C. J.; Dodds, S. F.; Rodgers, M. D.; Patwardhan, A.

2008-12-01

This study describes new comprehensive reconstructions of individual Western Atlantic Basin tropical cyclones for each year of the first half of the nineteenth century in the Western Atlantic Basin that are directly compatible and supplement the National Hurricane Center's HURDAT (Atlantic basin hurricane database). Data used for reconstructing tropical cyclones come from ship logbooks, ship protests, diaries, newspapers, and early instrumental records from more than 50 different archival repositories in the United States and the United Kingdom. Tropical cyclone strength was discriminated among tropical storms, hurricanes, major hurricanes, and non-tropical lows at least at tropical storm strength. The results detail the characteristics of several hundred storms, many of them being newly documented, and tracks for all storms were mapped. Overall, prominent active periods of tropical cyclones are evident along the western Atlantic Ocean in the 1830s but Caribbean and Gulf coasts exhibit active periods as being more evident in the 1810s and 1820s. Differences in decadal variations were even more pronounced when examining time series of activity at the statewide scale. High resolution paleoclimate and historical instrumental records of the AMO, NAO, ENSO, Atlantic SSTs, West African rainfall, and volcanic activity explain how different modes in these forcing mechanisms may explain some of the multidecadal and interannual variations. The early nineteenth century active hurricane activity appears to be particularly unique in corresponding with a low (negative index) AMO period, and as they relate to particular synoptic-scale patterns in the latter part of the Little Ice Age. Model simulations offer some hypotheses on such patterns, perhaps suggesting increased baroclinic-related storms and a slight later possible shift in the seasonal peak of tropical cyclones for some areas at times. Some years, such as 1806, 1837, 1838, 1842, and 1846 have particularly very active

Changes in aridity in response to the global warming hiatus

NASA Astrophysics Data System (ADS)

Guan, Xiaodan; Huang, Jianping; Guo, Ruixia

2017-02-01

The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in a global aridity index (AI) were analyzed by using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively forced aridity changes in the raw data. The AI and Palmer Drought Severity Index produced a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggested that this wetting zone occurred in response to the global warming hiatus. The dynamically induced AI (DAI) played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO) also indicated that different phases of the NAO, PDO, and AMO contributed to different performances of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high latitudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated global warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.

Regional Famine Patterns of The Last Millennium as Influenced by Aggregated Climate Teleconnections

NASA Astrophysics Data System (ADS)

Santoro, Michael Melton

Famine is the result of a complex set of environmental and social factors. Climate conditions are established as environmental factors contributing to famine occurrence, often through teleconnective patterns. This dissertation is designed to investigate the combined influence on world famine patterns of teleconnections, specifically the North Atlantic Oscillation (NAO), Southern Oscillation (SO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), or regional climate variations such as the South Asian Summer Monsoon (SASM). The investigation is three regional case studies of famine patterns specifically, Egypt, the British Isles, and India. The first study (published in Holocene) employs the results of a Principal Component Analysis (PCA) yielding a SO-NAO eigenvector to predict major Egyptian famines between AD 1049-1921. The SO-NAO eigenvector (1) successfully discriminates between the 5-10 years preceding a famine and the other years, (2) predicts eight of ten major famines, and (3) correctly identifies fifty out of eighty events (63%) of food availability decline leading up to major famines. The second study investigates the impact of the NAO, PDO, SO, and AMO on 63 British Isle famines between AD 1049 and 1914 attributed to climate causes in historical texts. Stepwise Regression Analysis demonstrates that the 5-year lagged NAO is the primary teleconnective influence on famine patterns; it successfully discriminates 73.8% of weather-related famines in the British Isles from 1049 to 1914. The final study identifies the aggregated influence of the NAO, SO, PDO, and SASM on 70 Indian famines from AD 1049 to 1955. PCA results in a NAO-SOI vector and SASM vector that predicts famine conditions with a positive NAO and negative SO, distinct from the secondary SASM influence. The NAO-famine relationship is consistently the strongest; 181 of 220 (82%) of all famines occurred during positive NAO years. Ultimately, the causes of famine are complex

How Does Mediterranean Basin's Atmosphere Become Weak Moisture Source During Negative Phase of NAO: Use of AIRS, AMSR, TOVS, & TRMM Satellite Datasets Over Last Two NAO Cycles to Examine Governing Controls on E-P

NASA Technical Reports Server (NTRS)

Smith, Eric A.; Mehta, Amita V.

2008-01-01

The Mediterranean Sea is a noted 'concentration" basin in that it almost continuously exhibits positive evaporation minus precipitation (E - P ) properties -- throughout the four seasons and from one year to the next. Nonetheless, according to the ECMWF Era-40 48-year (1958-2005) climate reanalysis dataset, for various phases of the North Atlantic Oscillation (NAO) when the pressure gradient between Portugal and Iceland becomes either very relaxed (large negative NAO-Index) or in transition (small positive or negative NAO-Index), the atmospheric moisture source properties of the basin become weak, at times even reversed for several months (i.e., negative E - P). This behavior poses numerous questions concerning how and why these events occur. Moreover, it begs the question of what it would take for the basin to reach its tipping point in which P would exceed E throughout the rainy season (some six months) on an annually persistent basis -- and the sea would possibly transform to a recurring "dilution" basin. This talk investigates these questions by: (1) establishing over a period from 1979 to present, based on detailed analyses of satellite retrieval products from a combination of NASA-AQUA, NOAA-LEO, NASA/JAXA Scatterometer, and NASA-TRMM platforms, plus additional specialized satellite data products and ancillary meteorological datasets, the actual observation-based behavior of E - P, (2) diagnosing the salient physical and meteorological mechanisms that lead to the weaker E - P events during the analysis period, partly based on analyzing surface and upper air data at discrete stations in the western and eastern Mediterranean -- while at the same time evaluating the quality of the ERA-40 data over this same time period, (3) conducting GCM and high-resolution regional modeling experiments to determine if perturbed but realistic meteorological background conditions could maintain Mediterranean as a "dilution" basin through the October to March rainy season on

Sensitivity of two Iberian lakes to North Atlantic atmospheric circulation modes

NASA Astrophysics Data System (ADS)

Hernández, Armand; Trigo, Ricardo M.; Pla-Rabes, Sergi; Valero-Garcés, Blas L.; Jerez, Sonia; Rico-Herrero, Mayte; Vega, José C.; Jambrina-Enríquez, Margarita; Giralt, Santiago

2015-12-01

The North Atlantic Oscillation (NAO) exerts a major influence on the climate of the North Atlantic region. However, other atmospheric circulation modes (ACMs), such as the East Atlantic (EA) and Scandinavian (SCAND) patterns, also play significant roles. The dynamics of lakes on the Iberian Peninsula are greatly controlled by climatic parameters, but their relationship with these various ACMs has not been investigated in detail. In this paper, we analyze monthly meteorological and limnological long-term datasets (1950-2011 and 1992-2011, respectively) from two lakes on the northern and central Iberian Peninsula (Sanabria and Las Madres) to develop an understanding of the seasonal sensitivity of these freshwater systems to the NAO, EA and SCAND circulation modes. The limnological variability within Lake Sanabria is primarily controlled by fluctuations in the seasonal precipitation and wind, and the primary ACMs associated with the winter limnological processes are the NAO and the SCAND modes, whereas only the EA mode appears to weakly influence processes during the summer. However, Lake Las Madres is affected by precipitation, wind and, to a lesser extent, temperature, whereas the ACMs have less influence. Therefore, we aim to show that the lakes of the Iberian Peninsula are sensitive to these ACMs. The results presented here indicate that the lake dynamics, in some cases, have a higher sensitivity to variations in the ACMs than single local meteorological variables. However, certain local features, such as geography, lake morphology and anthropic influences, are crucial to properly record the signals of these ACMs.

Long term changes in flooding and heavy rainfall associated with North Atlantic tropical cyclones: Roles of the North Atlantic Oscillation and El Niño-Southern Oscillation

NASA Astrophysics Data System (ADS)

Aryal, Yog N.; Villarini, Gabriele; Zhang, Wei; Vecchi, Gabriel A.

2018-04-01

The aim of this study is to examine the contribution of North Atlantic tropical cyclones (TCs) to flooding and heavy rainfall across the continental United States. Analyses highlight the spatial variability in these hazards, their temporal changes in terms of frequency and magnitude, and their connection to large-scale climate, in particular to the North Atlantic Oscillation (NAO) and El Niño-Southern Oscillation (ENSO). We use long-term stream and rain gage measurements, and our analyses are based on annual maxima (AMs) and peaks-over-threshold (POTs). TCs contribute to ∼20-30% of AMs and POTs over Florida and coastal areas of the eastern United States, and the contribution decreases as we move inland. We do not detect statistically significant trends in the magnitude or frequency of TC floods. Regarding the role of climate, NAO and ENSO do not play a large role in controlling the frequency and magnitude of TC flooding. The connection between heavy rainfall and TCs is comparable to what observed in terms of flooding. Unlike flooding, NAO plays a significant role in TC-related extreme rainfall along the U.S. East Coast, while ENSO is most strongly linked to the TC precipitation in Texas.

Mediterranean circulation perturbations over the last five centuries: Relevance to past Eastern Mediterranean Transient-type events

PubMed Central

Incarbona, Alessandro; Martrat, Belen; Mortyn, P. Graham; Sprovieri, Mario; Ziveri, Patrizia; Gogou, Alexandra; Jordà, Gabriel; Xoplaki, Elena; Luterbacher, Juerg; Langone, Leonardo; Marino, Gianluca; Rodríguez-Sanz, Laura; Triantaphyllou, Maria; Di Stefano, Enrico; Grimalt, Joan O.; Tranchida, Giorgio; Sprovieri, Rodolfo; Mazzola, Salvatore

2016-01-01

The Eastern Mediterranean Transient (EMT) occurred in the Aegean Sea from 1988 to 1995 and is the most significant intermediate-to-deep Mediterranean overturning perturbation reported by instrumental records. The EMT was likely caused by accumulation of high salinity waters in the Levantine and enhanced heat loss in the Aegean Sea, coupled with surface water freshening in the Sicily Channel. It is still unknown whether similar transients occurred in the past and, if so, what their forcing processes were. In this study, sediments from the Sicily Channel document surface water freshening (SCFR) at 1910 ± 12, 1812 ± 18, 1725 ± 25 and 1580 ± 30 CE. A regional ocean hindcast links SCFR to enhanced deep-water production and in turn to strengthened Mediterranean thermohaline circulation. Independent evidence collected in the Aegean Sea supports this reconstruction, showing that enhanced bottom water ventilation in the Eastern Mediterranean was associated with each SCFR event. Comparison between the records and multi-decadal atmospheric circulation patterns and climatic external forcings indicates that Mediterranean circulation destabilisation occurs during positive North Atlantic Oscillation (NAO) and negative Atlantic Multidecadal Oscillation (AMO) phases, reduced solar activity and strong tropical volcanic eruptions. They may have recurrently produced favourable deep-water formation conditions, both increasing salinity and reducing temperature on multi-decadal time scales. PMID:27412622

Baseflow response to climate variability induced droughts in the Apalachicola-Chattahoochee-Flint River Basin, U.S.A.

NASA Astrophysics Data System (ADS)

Singh, Sarmistha; Srivastava, Puneet; Abebe, Ash; Mitra, Subhasis

2015-09-01

Droughts have been a major factor leading to the Tri-State Water Wars in the southeastern United States. One of the primary issues related to the conflict is the reduction in baseflow levels in the Flint River during droughts. This affects the availability of freshwater resources to support the endangered mussel species in the Flint and Apalachicola Rivers and threatens the shellfish industry in the Apalachicola Bay. Study of large-scale climate phenomena as well as the interactions of interannual with decadal and multidecadal oceanic-atmospheric phenomena can provide valuable information regarding regional climatic conditions such as droughts and their impact on water resources. This study was conducted to quantify the impacts of climate variability cycles on baseflow levels in the Flint River. The individual and coupled impacts of the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO) on baseflow were quantified. The non-parametric Joint Rank Fit (JRFit) procedure was used to provide a robust test of the significance of interactions between the phases of ENSO-PDO, ENSO-AMO and ENSO-NAO baseflows. Simple-main effect comparisons were also performed using the JRFit model to estimate significant difference between the positive and negative phase baseflows of PDO, AMO and NAO associated with El Niño or La Niña phases. The results indicate that the phases of ENSO, AMO and NAO significantly affect baseflows in the Flint River. Interaction tests showed that the PDO and AMO phases modulate ENSO phase baseflows. La Niña associated with positive phases of PDO and AMO resulted in greater decrease in baseflow levels of approximately 28% and 33%, respectively. However, La Niña associated with negative phase of AMO showed above normal baseflows. The results illustrate the importance of coupled analyses of climate variability by providing a better understanding of the severity

Potential links between the North Atlantic Oscillation and decreasing precipitation and runoff on a Mediterranean area

NASA Astrophysics Data System (ADS)

Montaldo, Nicola; Sarigu, Alessio

2017-10-01

In the Mediterranean region, the reduction in precipitation and warmer temperatures is generating a desertification process, with dramatic consequences for both agriculture and the sustainability of water resources. On the island of Sardinia (Italy), the decrease in runoff impacts the management of water resources, resulting in water supply restrictions even for domestic consumption. In the 10 Sardinian basins with a longer database (at least 40 complete years of data, including data from the past 10 years), runoff decreased drastically over the 1975-2010 period, with mean yearly runoff reduced by more than 40% compared to the previous 1922-1974 period. Trends in yearly runoff are negative, with Mann-Kendall τ values ranging from -0.39 to -0.2. Decreasing winter precipitation over the 1975-2010 period everywhere on Sardinia island has led to these decreases in runoff, as most yearly runoff in the Sardinian basins (70% on average) is produced by winter precipitation due to the seasonality typical of the Mediterranean climate regime. The trend in winter precipitation is not homogenous; the negative trend is higher (around -0.25) on the west Sardinian coast, becoming lower across the island toward the east coast (around -0.14). Winter precipitation is highly correlated with the North Atlantic Oscillation (NAO), a weather phenomenon in the North Atlantic Ocean that controls the direction and strength of westerly winds and storm tracks into Europe. High negative correlations (up to -0.45) between winter NAO index and winter precipitation are estimated along the west coast. Meanwhile, these correlations decrease east across the island toward the high mountain in the center of Sardinia, reaching the lowest values along the east coast (about -0.25). The generally decreasing correlation between winter NAO index and winter precipitation in the longitudinal direction (from the North Atlantic dipole to the east) here accelerates due to local-scale orographic effects that

Decadal variability of the Tropical Atlantic Ocean Surface Temperature in shipboard measurements and in a Global Ocean-Atmosphere model

NASA Technical Reports Server (NTRS)

Mehta, Vikram M.; Delworth, Thomas

1995-01-01

Sea surface temperature (SST) variability was investigated in a 200-yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The second 100 yr of SST in the coupled model's tropical Atlantic region were analyzed with a variety of techniques. Analyses of SST time series, averaged over approximately the same subregions as the Global Ocean Surface Temperature Atlas (GOSTA) time series, showed that the GFDL SST anomalies also undergo pronounced quasi-oscillatory decadal and multidecadal variability but at somewhat shorter timescales than the GOSTA SST anomalies. Further analyses of the horizontal structures of the decadal timescale variability in the GFDL coupled model showed the existence of two types of variability in general agreement with results of the GOSTA SST time series analyses. One type, characterized by timescales between 8 and 11 yr, has high spatial coherence within each hemisphere but not between the two hemispheres of the tropical Atlantic. A second type, characterized by timescales between 12 and 20 yr, has high spatial coherence between the two hemispheres. The second type of variability is considerably weaker than the first. As in the GOSTA time series, the multidecadal variability in the GFDL SST time series has approximately opposite phases between the tropical North and South Atlantic Oceans. Empirical orthogonal function analyses of the tropical Atlantic SST anomalies revealed a north-south bipolar pattern as the dominant pattern of decadal variability. It is suggested that the bipolar pattern can be interpreted as decadal variability of the interhemispheric gradient of SST anomalies. The decadal and multidecadal timescale variability of the tropical Atlantic SST, both in the actual and in the GFDL model, stands out significantly above the background 'red noise' and is coherent within each of the time series, suggesting that specific sets of

Mechanistic origin of low polarization in aprotic Na-O2 batteries.

PubMed

Ma, Shunchao; McKee, William C; Wang, Jiawei; Guo, Limin; Jansen, Martin; Xu, Ye; Peng, Zhangquan

2017-05-21

Research interest in aprotic sodium-air (Na-O 2 ) batteries is growing because of their considerably high theoretical specific energy and potentially better reversibility than lithium-air (Li-O 2 ) batteries. While Li 2 O 2 has been unequivocally identified as the major discharge product in Li-O 2 batteries containing relatively stable electrolytes, a multitude of discharge products, including NaO 2 , Na 2 O 2 and Na 2 O 2 ·2H 2 O, have been reported for Na-O 2 batteries and the corresponding cathodic electrochemistry remains incompletely understood. Herein, we provide molecular-level insights into the key mechanistic differences between Na-O 2 and Li-O 2 batteries based on gold electrodes in strictly dry, aprotic dimethyl sulfoxide electrolytes through a combination of in situ spectroelectrochemistry and density functional theory based modeling. While like Li-O 2 batteries, the formation of oxygen reduction products (i.e., O 2 - , NaO 2 and Na 2 O 2 ) in Na-O 2 batteries depends critically on the electrode potential, two factors lead to a better reversibility of Na-O 2 electrochemistry, and are therefore highly beneficial to a viable rechargeable metal-air battery design: (i) only O 2 - and NaO 2 , and no Na 2 O 2 , form down to as low as ∼1.5 V vs. Na/Na + during discharge; (ii) solid NaO 2 is quite soluble and its formation and oxidation can proceed through micro-reversible EC (a chemical reaction of the product after the electron transfer) and CE (a chemical reaction preceding the electron transfer) processes, respectively, with O 2 - as the key intermediate.

An atmospheric origin of the multi-decadal bipolar seesaw.

PubMed

Wang, Zhaomin; Zhang, Xiangdong; Guan, Zhaoyong; Sun, Bo; Yang, Xin; Liu, Chengyan

2015-03-10

A prominent feature of recent climatic change is the strong Arctic surface warming that is contemporaneous with broad cooling over much of Antarctica and the Southern Ocean. Longer global surface temperature observations suggest that this contrasting pole-to-pole change could be a manifestation of a multi-decadal interhemispheric or bipolar seesaw pattern, which is well correlated with the North Atlantic sea surface temperature variability, and thus generally hypothesized to originate from Atlantic meridional overturning circulation oscillations. Here, we show that there is an atmospheric origin for this seesaw pattern. The results indicate that the Southern Ocean surface cooling (warming) associated with the seesaw pattern is attributable to the strengthening (weakening) of the Southern Hemisphere westerlies, which can be traced to Northern Hemisphere and tropical tropospheric warming (cooling). Antarctic ozone depletion has been suggested to be an important driving force behind the recently observed increase in the Southern Hemisphere's summer westerly winds; our results imply that Northern Hemisphere and tropical warming may have played a triggering role at an stage earlier than the first detectable Antarctic ozone depletion, and enhanced Antarctic ozone depletion through decreasing the lower stratospheric temperature.

Subregional precipitation climate of the Caribbean and relationships with ENSO and NAO

NASA Astrophysics Data System (ADS)

Jury, Mark; Malmgren, BjöRn A.; Winter, Amos

2007-08-01

Thirty-five meteorological stations encompassing the Caribbean region (Cuba, Bahamas, Jamaica, Dominican Republic, Puerto Rico, US Virgin Islands, St. Maarten, and Barbados) were analyzed over the time interval 1951-1981 to assess regional precipitation patterns and their relationships with the North Atlantic Oscillation (NAO) and El Niño-Southern Oscillation (ENSO). Application of factor analysis to these series revealed the existence of four geographically distinct precipitation regions, (C1) western Cuba and northwestern Bahamas, (C2) Jamaica, eastern Cuba, and southeastern Bahamas, (C3) Dominican Republic and northwestern Puerto Rico, and (C4) eastern Puerto Rico, US Virgin Islands, St. Maarten, and Barbados. This regionalization is related to different annual cycles and interannual fluctuations of rainfall. The annual cycle is more unimodal and largest in the northwest Caribbean (C1) and becomes increasingly bimodal toward lower latitudes (C4) as expected. Year-to-year variations of precipitation are compared with two well-known climatic indices. The ENSO relationship, represented by Niño 3.4 sea surface temperatures (SST), is positive and stable at all lags, but tends to reverse over the SE Caribbean (C4) in late summer. The NAO influence is weak and seasonally dependent. Early summer rainfall in the northwest Caribbean (C1) increases under El Niño conditions. Clusters 2 and 3 are less influenced by the global predictors and more regional in character.

A propagating freshwater mode in the Arctic Ocean with multidecadal time scale

NASA Astrophysics Data System (ADS)

Schmith, Torben; Malskær Olsen, Steffen; Margrethe Ringgaard, Ida

2017-04-01

We apply Principal Oscillatory Pattern analysis to the Arctic Ocean fresh water content as simulated in a 500 year long control run with constant preindustrial forcing with the EC-Earth global climate model. Two modes emerge from this analysis. One mode is a standing mode with decadal time scale describing accumulation and release of fresh water in the Beaufort Gyre, known in the literature as the Beaufort Gyre flywheel. In addition, we identify a propagating mode with a time scale around 80 years, propagating along the rim of the Canadian Basin. This mode has maximum variability of the fresh water content in the Transpolar Drift and represents the bulk of the total variability of the fresh water content in the Arctic Ocean and also projects on the fresh water through the Fram Strait. Therefore, potentially, it can introduce a multidecadal variability to the Atlantic meridional overturning circulation. We will discuss the physical origin of this propagating mode. This include planetary-scale internal Rossby waves with multidecadal time scale, due to the slow variation of the Coriolis parameter at these high latitudes, as well as topographic steering of these Rossby waves.

Barents-Kara sea ice and the winter NAO in the DePreSys3 Met Office Seasonal forecast model

NASA Astrophysics Data System (ADS)

Warner, J.; Screen, J.

2017-12-01

Accurate seasonal forecasting leads to a wide range of socio-economic benefits and increases resilience to prolonged bouts of extreme weather. This work looks at how November Barents-Kara sea ice may affect the winter northern hemisphere atmospheric circulation, using various compositing methods in the DePreSys3 ensemble model, with lag to argue better a relationship between the two. In particular, the NAO (North Atlantic Oscillation) is focused on given its implications on European weather. Using this large hindcast dataset comprised of 35 years with 30 available ensemble members, it is found that low Barents-Kara sea ice leads to a negative NAO tendency in all composite methods, with increased mean sea level pressure in higher latitudes. The significance of this varies between composites. This is preliminary analysis of a larger PhD project to further understand how Arctic Sea ice may play a role in seasonal forecasting skill through its connection/influence on mid-latitude weather.

Hydroclimate of the northeastern United States is highly sensitive to solar forcing

NASA Astrophysics Data System (ADS)

Nichols, Jonathan E.; Huang, Yongsong

2012-02-01

Dramatic hydrological fluctuations strongly impact human society, but the driving mechanisms for these changes are unclear. One suggested driver is solar variability, but supporting paleoclimate evidence is lacking. Therefore, long, continuous, high-resolution records from strategic locations are crucial for resolving the scientific debate regarding sensitivity of climate to solar forcing. We present a 6800-year, decadally-resolved biomarker and multidecadally-resolved hydrogen isotope record of hydroclimate from a coastal Maine peatland, The Great Heath (TGH). Regional moisture balance responds strongly and consistently to solar forcing at centennial to millennial timescales, with solar minima concurrent with wet conditions. We propose that the Arctic/North Atlantic Oscillation (AO/NAO) can amplify small solar fluctuations, producing the reconstructed hydrological variations. The Sun may be entering a weak phase, analogous to the Maunder minimum, which could lead to more frequent flooding in the northeastern US at this multidecadal timescale.

Variability of sea surface height and circulation in the North Atlantic: Forcing mechanisms and linkages

NASA Astrophysics Data System (ADS)

Wang, Zeliang; Lu, Youyu; Dupont, Frederic; W. Loder, John; Hannah, Charles; G. Wright, Daniel

2015-03-01

Simulations with a coarse-resolution global ocean model during 1958-2004 are analyzed to understand the inter-annual and decadal variability of the North Atlantic. Analyses of Empirical Orthogonal Functions (EOFs) suggest relationships among basin-scale variations of sea surface height (SSH) and depth-integrated circulation, and the winter North Atlantic Oscillation (NAO) or the East Atlantic Pattern (EAP) indices. The linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability. In the subpolar region, variations of the gyre strength, SSH in the central Labrador Sea and the NAO index are highly correlated. Surface heat flux is important in driving variations of SSH and circulation in the upper ocean and decadal variations of the Atlantic Meridional Overturning Circulation (AMOC). Surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the AMOC. In the subtropical region, momentum flux plays a dominant role in driving variations of the gyre circulation and AMOC; there is a strong correlation between gyre strength and SSH at Bermuda.

North Atlantic Oscillation and pollutants variability in Europe: model analysis and measurements intercomparison

NASA Astrophysics Data System (ADS)

Pausata, F.; Pozzoli, L.; Van Dingenen, R.; Vignati, E.; Cavalli, F.; Dentener, F. J.

2013-12-01

Ozone pollution and particulate matter (PM) represent a serious health and environmental problem. While ozone pollution is mostly produced by photochemistry in summer, PM is of main concern during winter. Both pollutants can be influenced nt only by local scale processes but also by long range transport driven by the atmospheric circulation and stratospheric ozone intrusions. We analyze the role of large scale atmospheric circulation variability in the North Atlantic basin in determining surface ozone and PM concentrations over Europe. Here, we show, using ground station measurements and a coupled atmosphere-chemistry model simulation for the period 1980-2005, that with regard to ozone the North Atlantic Oscillation (NAO) does affect surface ozone concentrations - on a monthly timescale, over 10 ppbv in southwestern, central and northern Europe - during all seasons except fall. We find that the first Principal Component, computed from the time variation of the sea level pressure (SLP) field, detects the atmosphere circulation/ozone relationship not only in winter and spring but also during summer, when the atmospheric circulation weakens and regional photochemical processes peak. Given the NAO forecasting skill at intraseasonal time scale, the first Principal Component of the SLP field could be used as an indicator to identify areas more exposed to forthcoming ozone pollution events. Finally, our results suggest that the increasing baseline ozone in western and northern Europe during the 1990s could be related to the prevailing positive phase of the NAO in that period. With regard to PM, our study shows that in winter the NAO modulates surface PM concentrations accounting in average up to 30% of the total PM variability. During positive NAO phases, positive PM anomalies occur over southern Europe, and negative anomalies in central-northern Europe. A positve shift of the NAO mean states, hence, leads to an increase in cardiac and resipratory morbidity related to PM

Multi-Decadal Oscillations of the Ocean Active Upper-Layer Heat Content

NASA Astrophysics Data System (ADS)

Byshev, Vladimir I.; Neiman, Victor G.; Anisimov, Mikhail V.; Gusev, Anatoly V.; Serykh, Ilya V.; Sidorova, Alexandra N.; Figurkin, Alexander L.; Anisimov, Ivan M.

2017-07-01

Spatial patterns in multi-decadal variability in upper ocean heat content for the last 60 years are examined using a numerical model developed at the Institute of Numerical Mathematics of Russia (INM Model) and sea water temperature-salinity data from the World Ocean Database (in: Levitus, NOAA Atlas NESDIS 66, U.S. Wash.: Gov. Printing Office, 2009). Both the model and the observational data show that the heat content of the Active Upper Layer (AUL) in particular regions of the Atlantic, Pacific and Southern oceans have experienced prominent simultaneous variations on multi-decadal (25-35 years) time scales. These variations are compared earlier revealed climatic alternations in the Northern Atlantic region during the last century (Byshev et al. in Doklady Earth Sci 438(2):887-892, 2011). We found that from the middle of 1970s to the end of 1990s the AUL heat content decreased in several oceanic regions, while the mean surface temperature increased on Northern Hemisphere continents according to IPCC (in: Stocker et al. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, Cambridge University Press, Cambridge, 2013). This means that the climate-forcing effect of the ocean-atmosphere interaction in certain energy-active areas determines not only local climatic processes, but also have an influence on global-scale climate phenomena. Here we show that specific regional features of the AUL thermal structure are in a good agreement with climatic conditions on the adjacent continents. Further, the ocean AUL in the five distinctive regions identified in our study have resumed warming in the first decade of this century. By analogy inference from previous climate scenarios, this may signal the onset of more continental climate over mainlands.

Decadal modulation of the ENSO-East Asian winter monsoon relationship by the Atlantic Multidecadal Oscillation

NASA Astrophysics Data System (ADS)

Geng, Xin; Zhang, Wenjun; Stuecker, Malte F.; Liu, Peng; Jin, Fei-Fei; Tan, Guirong

2017-10-01

This work investigates the decadal modulation of the El Niño-Southern Oscillation (ENSO)-East Asian winter monsoon (EAWM) relationship by the Atlantic Multidecadal Oscillation (AMO). A stable ENSO-EAWM relationship is found during the positive AMO phase but not during the negative phase. While the impact of El Niño events on the EAWM does not depend on the AMO phase, a different picture is observed for La Niña events. The La Niña boreal winter season coincides with a strengthened EAWM during a positive AMO phase and a weakened EAWM during a negative AMO phase. We suggest that the AMO's modulating effect mainly comprises two pathways that influence ENSO's impact on the EAWM. On one hand, when La Niña coincides with a positive AMO, the warm SST anomalies over the western North Pacific (WNP) are amplified both in intensity and spatial extent, which favors strengthened WNP cyclonic anomalies and an enhanced EAWM. During La Niña with a negative AMO, only very weak SST anomalies occur over the WNP with reduced WNP cyclonic anomalies that are confined to the tropics, thus having little effect on the EAWM. On the other hand, an eastward-propagating Rossby wavetrain across the mid-high latitudes of Eurasia during a warm AMO phase strengthens the Siberian high and thus leads to a strengthened EAWM, while during a cold AMO phase the Siberian high is weakened, leading to a reduced EAWM. In contrast, El Niño and its associated atmospheric responses are relatively strong and stable, independent of the AMO phase. These results carry important implications to the seasonal-to-interannual predictability associated with ENSO.

Holocene multidecadal- to millennial-scale variations in Iceland-Scotland overflow and their relationship to climate

NASA Astrophysics Data System (ADS)

Mjell, Tor Lien; Ninnemann, Ulysses S.; Eldevik, Tor; Kleiven, Helga Kikki F.

2015-05-01

The Nordic Seas overflows are an important part of the Atlantic thermohaline circulation. While there is growing evidence that the overflow of dense water changed on orbital time scales during the Holocene, less is known about the variability on shorter time scales beyond the instrumental record. Here we reconstruct the relative changes in flow strength of Iceland-Scotland Overflow Water (ISOW), the eastern branch of the overflows, on multidecadal-millennial time scales. The reconstruction is based on mean sortable silt (SS>¯) from a sediment core on the Gardar Drift (60°19'N, 23°58'W, 2081 m). Our SS>¯ record reveals that the main variance in ISOW vigor occurred on millennial time scales (1-2 kyr) with particularly prominent fluctuations after 8 kyr. Superimposed on the millennial variability, there were multidecadal-centennial flow speed fluctuations during the early Holocene (10-9 kyr) and one prominent minimum at 0.9 kyr. We find a broad agreement between reconstructed ISOW and regional North Atlantic climate, where a strong (weak) ISOW is generally associated with warm (cold) climate. We further identify the possible contribution of anomalous heat and freshwater forcing, respectively, related to reconstructed overflow variability. We infer that ocean poleward heat transport can explain the relationship between regional climate and ISOW during the middle to late Holocene, whereas freshwater input provides a possible explanation for the reduced overflow during early Holocene (8-10 kyr).

North Atlantic early 20th century warming and impact on European summer: Mechanisms and Predictability

NASA Astrophysics Data System (ADS)

Müller, Wolfgang

2017-04-01

During the last century, substantial climate variations in the North Atlantic have occurred, such as the warmings in the 1920s and 1990s. Such variations are considered to be part of the variability known as the Atlantic Multidecadal Variations (AMV) and have a strong impact on local climates such as European summers. Here a synthesis of previous works is presented which describe the occurrence of the warming in the 1920s in the North Atlantic and its impact on the European summer climate (Müller et al. 2014, 2015). For this the 20th century reanalysis (20CR) and 20CR forced ocean experiments are evaluated. It can be shown that the North Atlantic Current and Sub-Polar Gyre are strengthened as a result of an increased pressure gradient over the North Atlantic. Concurrently, Labrador Sea convection and Atlantic meridional overturning circulation (AMOC) increase. The intensified NAC, SPG, and AMOC redistribute sub-tropical water into the North Atlantic and Nordic Seas, thereby increasing observed and modelled temperature and salinity during the 1920s. Further a mechanism is proposed by which North Atlantic heat fluxes associated with the AMV modulate European decadal summer climate (Ghosh et al. 2016). By using 20CR, it can be shown that multi-decadal variations in the European summer temperature are associated to a linear baroclinic atmospheric response to the AMV-related surface heat flux. This response induce a sea level pressure structure modulating meridional temperature advection over north-western Europe and Blocking statistics over central Europe. This structure is shown to be the leading mode of variability and is independent of the summer North Atlantic Oscillation. Ghosh, R., W.A. Müller, J. Bader, and J. Baehr, 2016: Impact of observed North Atlantic multidecadal variations to European summer climate: A linear baroclinic response to surface heating. Clim. Dyn. doi:10.10007/s00382-016-3283-4 Müller W. A., D. Matei, M. Bersch, J. H. Jungclaus, H. Haak, K

Impact of the North Atlantic Oscillation on the trans-Atlantic migrations of the European eel (Anguilla anguilla)

NASA Astrophysics Data System (ADS)

Kettle, A. James; Bakker, Dorothee C. E.; Haines, Keith

2008-09-01

Glass eel catches and FAO (Food and Agricultural Organization) landings of the European freshwater eel (Anguilla anguilla) show a decrease over the past 20 years. The long-term trends in the time series mask an interannual fluctuation, which becomes apparent on the application of a high-pass filter and autocorrelation analysis. Both the FAO landings and the glass eel catches show interannual fluctuations with a repeat period of 6-8 years, similar to the period of the North Atlantic Oscillation (NAO). Most glass eel catch monitoring stations are in phase. The glass eel catches show a significant negative correlation with the NAO lagged by 0-2 years, consistent with the hypothesis that the positive NAO phase has an adverse impact on the larval survival in and migration from the Sargasso Sea spawning location, one year prior to the arrival of the glass eels in Europe and North Africa. The FAO landings can be divided into two groups of different phase that have an approximate correspondence to the NAO dipole in winter rainfall in Europe and North Africa. One group (P) comprises Denmark, Ireland, Morocco, Netherlands, Norway, Sweden, Tunisia, and the United Kingdom, and the other group (N) comprises France, Germany, Italy, Poland, Portugal, Spain, and Turkey. At least for the interannual fluctuations, the success of the glass eel fishery (and eel recruitment) may be coupled with the number of migrating silver eels from the N group of countries and uncoupled with the P group of countries.

Mechanisms of decadal variability in the Labrador Sea and the wider North Atlantic in a high-resolution climate model

NASA Astrophysics Data System (ADS)

Ortega, Pablo; Robson, Jon; Sutton, Rowan; Andrews, Martin

2017-04-01

A necessary step before assessing the performance of decadal predictions is the evaluation of the processes that bring memory to the climate system, both in climate models and observations. These mechanisms are particularly relevant in the North Atlantic, where the ocean circulation, related to both the Subpolar Gyre and the Meridional Overturning Circulation (AMOC), is thought to be important for driving significant heat content anomalies. Recently, a rapid decline in observed densities in the deep Labrador Sea has pointed to an ongoing slowdown of the AMOC strength taking place since the mid 90s, a decline also hinted by in-situ observations from the RAPID array. This study explores the use of Labrador Sea densities as a precursor of the ocean circulation changes, by analysing a 300-year long simulation with the state-of-the-art coupled model HadGEM3-GC2. The major drivers of Labrador density variability are investigated, and are characterised by three major contributions. First, the integrated effect of local surface heat fluxes, mainly driven by year-to-year changes in the North Atlantic Oscillation, which accounts for 62% of the total variance. Additionally, two multidecadal-to-centennial contributions from the Arctic are quantified; the first associated with freshwater exports via the East Greenland Current, and the second with changes in the Denmark Strait Overflow. Finally, evidence is shown that decadal trends in Labrador Sea densities are followed by important atmospheric impacts. In particular, a delayed winter NAO response appears to be at play, providing a phase reversal mechanism for the Labrador Sea density changes.

Late Holocene forest dynamics in the Gulf of Gaeta (central Mediterranean) in relation to NAO variability and human impact

NASA Astrophysics Data System (ADS)

Di Rita, Federico; Lirer, Fabrizio; Bonomo, Sergio; Cascella, Antonio; Ferraro, Luciana; Florindo, Fabio; Insinga, Donatella Domenica; Lurcock, Pontus Conrad; Margaritelli, Giulia; Petrosino, Paola; Rettori, Roberto; Vallefuoco, Mattia; Magri, Donatella

2018-01-01

A new high-resolution pollen record, spanning the last five millennia, is presented from the Gulf of Gaeta (Tyrrhenian Sea, central Italy), with the aim of verifying if any vegetation change occurred in the central Mediterranean region in relation to specific well-known global and/or regional climate events, including the 4.2 ka event, the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), and to detect possible vegetation changes related to still under-investigated climate signals, for example the so-called "Bond 2" cold event around 2.8 ka BP. The vegetation dynamics of the Gaeta record shows a recurrent pattern of forest increase and decline punctuating the mid- and late Holocene. When the timing of these patterns is compared with the climate proxy data available from the same core (planktonic foraminifera assemblages and oxygen stable isotope record) and with the NAO (North Atlantic Oscillation) index, it clearly appears that the main driver for the forest fluctuations is climate, which may even overshadow the effects of human activity. We have found a clear correspondence between phases with negative NAO index and forest declines. In particular, around 4200 cal BP, a drop in AP (Arboreal Pollen) confirms the clearance recorded in many sites in Italy south of 43°N. Around 2800 cal BP, a vegetation change towards open conditions is found at a time when the NAO index clearly shows negative values. Between 800 and 1000 AD, a remarkable forest decline, coeval with a decrease in the frequencies of both Castanea and Olea, matches a shift in the oxygen isotope record towards positive values, indicating cooler temperatures, and a negative NAO. Between 1400-1850 AD, in the time period chronologically corresponding to the LIA (Little Ice Age), the Gaeta record shows a clear decline of the forest cover, particularly evident after 1550 AD, once again in correspondence with negative NAO index.

The role of Atlantic Multi-decadal Oscillation in the global mean temperature variability

DOE PAGES

Chylek, Petr; Klett, James D.; Dubey, Manvendra K.; ...

2016-11-01

We simulated the global mean 1900–2015 warming by 42 Coupled Models Inter-comparison Project, phase 5 (CMIP5) climate models varies between 0.58 and 1.70 °C. The observed warming according to the NASA GISS temperature analysis is 0.95 °C with a 1200 km smoothing radius, or 0.86 °C with a 250 km smoothing radius. The projection of the future 2015–2100 global warming under a moderate increase of anthropogenic radiative forcing (RCP4.5 scenario) by individual models is between 0.7 and 2.3 °C. The CMIP5 climate models agree that the future climate will be warmer; however, there is little consensus as to how largemore » the warming will be (reflected by an uncertainty of over a factor of three). Moreover, a parsimonious statistical regression model with just three explanatory variables [anthropogenic radiative forcing due to greenhouse gases and aerosols (GHGA), solar variability, and the Atlantic Multi-decadal Oscillation (AMO) index] accounts for over 95 % of the observed 1900–2015 temperature variance. This statistical regression model reproduces very accurately the past warming (0.96 °C compared to the observed 0.95 °C) and projects the future 2015–2100 warming to be around 0.95 °C (with the IPCC 2013 suggested RCP4.5 radiative forcing and an assumed cyclic AMO behavior). The AMO contribution to the 1970–2005 warming was between 0.13 and 0.20 °C (depending on which AMO index is used) compared to the GHGA contribution of 0.49–0.58 °C. During the twenty-first century AMO cycle the AMO contribution is projected to remain the same (0.13–0.20 °C), while the GHGA contribution is expected to decrease to 0.21–0.25 °C due to the levelling off of the GHGA radiative forcing that is assumed according to the RCP4.5 scenario. Therefore, the anthropogenic contribution and natural variability are expected to contribute about equally to the anticipated global warming during the second half of the twenty-first century for the RCP4.5 trajectory.« less

The role of Atlantic Multi-decadal Oscillation in the global mean temperature variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chylek, Petr; Klett, James D.; Dubey, Manvendra K.

We simulated the global mean 1900–2015 warming by 42 Coupled Models Inter-comparison Project, phase 5 (CMIP5) climate models varies between 0.58 and 1.70 °C. The observed warming according to the NASA GISS temperature analysis is 0.95 °C with a 1200 km smoothing radius, or 0.86 °C with a 250 km smoothing radius. The projection of the future 2015–2100 global warming under a moderate increase of anthropogenic radiative forcing (RCP4.5 scenario) by individual models is between 0.7 and 2.3 °C. The CMIP5 climate models agree that the future climate will be warmer; however, there is little consensus as to how largemore » the warming will be (reflected by an uncertainty of over a factor of three). Moreover, a parsimonious statistical regression model with just three explanatory variables [anthropogenic radiative forcing due to greenhouse gases and aerosols (GHGA), solar variability, and the Atlantic Multi-decadal Oscillation (AMO) index] accounts for over 95 % of the observed 1900–2015 temperature variance. This statistical regression model reproduces very accurately the past warming (0.96 °C compared to the observed 0.95 °C) and projects the future 2015–2100 warming to be around 0.95 °C (with the IPCC 2013 suggested RCP4.5 radiative forcing and an assumed cyclic AMO behavior). The AMO contribution to the 1970–2005 warming was between 0.13 and 0.20 °C (depending on which AMO index is used) compared to the GHGA contribution of 0.49–0.58 °C. During the twenty-first century AMO cycle the AMO contribution is projected to remain the same (0.13–0.20 °C), while the GHGA contribution is expected to decrease to 0.21–0.25 °C due to the levelling off of the GHGA radiative forcing that is assumed according to the RCP4.5 scenario. Therefore, the anthropogenic contribution and natural variability are expected to contribute about equally to the anticipated global warming during the second half of the twenty-first century for the RCP4.5 trajectory.« less

Spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean.

PubMed

Zhang, Min; Zhang, Yuanling; Shu, Qi; Zhao, Chang; Wang, Gang; Wu, Zhaohua; Qiao, Fangli

2018-01-15

Analyses of the chlorophyll a concentration (chla) from satellite ocean color products have suggested the decadal-scale variability of chla linked to the climate change. The decadal-scale variability in chla is both spatially and temporally non-uniform. We need to understand the spatiotemporal evolution of chla in decadal or multi-decadal timescales to better evaluate its linkage to climate variability. Here, the spatiotemporal evolution of the chla trend in the North Atlantic Ocean for the period 1997-2016 is analyzed using the multidimensional ensemble empirical mode decomposition method. We find that this variable trend signal of chla shows a dipole pattern between the subpolar gyre and along the Gulf Stream path, and propagation along the opposite direction of the North Atlantic Current. This propagation signal has an overlapping variability of approximately twenty years. Our findings suggest that the spatiotemporal evolution of chla during the two most recent decades is part of the multidecadal variations and possibly regulated by the changes of Atlantic Meridional Overturning Circulation, whereas the mechanisms of such evolution patterns still need to be explored. Copyright © 2017 Elsevier B.V. All rights reserved.

Response of North Atlantic Ocean Chlorophyll a to the Change of Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Zhang, Min; Zhang, Yuanling; Shu, Qi; Zhao, Chang; Wang, Gang; Wu, Zhaohua; Qiao, Fangli

2017-04-01

Changes in marine phytoplankton are a vital component in global carbon cycling. Despite this far-reaching importance, the variable trend in phytoplankton and its response to climate variability remain unclear. This work presents the spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean by using merged ocean color products for the period 1997-2016. We find a dipole pattern between the subpolar gyre and the Gulf Stream path,and chlorophyll a trend signal propagatedalong the opposite direction of the North Atlantic Current. Such a dipole pattern and opposite propagation of chlorophyll a signal are consistent with the recent distinctive signature of the slowdown of the Atlantic MeridionalOverturning Circulation (AMOC). It is suggested that the spatiotemporal evolution of chlorophyll a during the two most recent decades is a part of the multidecadal variation and regulated byAMOC, which could be used as an indicator of AMOC variations.

Effect of Qing Nao tablet on blood stasis model of mice

NASA Astrophysics Data System (ADS)

Kong, Xuejun; Hao, Shaojun; Wang, Hongyu; Liu, Xiaobin; Xie, Guoqi; Li, Wenjun; Zhang, Zhengchen

2018-04-01

To investigate the effect of Qing Nao tablet on mouse model of blood stasis syndrome, 60 mice, male and female, were randomly divided into 6 groups, were fed with large, small doses of Qing Nao tablet suspension, Naoluotong saline suspension and the same volume (group 2, 0.1ml/10g), administer 1 times daily, orally for 15 days. Intragastric administration for first days, in addition to the 1 group saline group every day in the hind leg intramuscular saline, the other 5 groups each rat day hind leg muscle injection of dexamethasone 0.8mg/kg intramuscular injection every day, 1 times, 15 days. 1 hour continuous intramuscular injection and intramuscular drug perfusion on the sixteenth day after mice. The eyeball blood, heparin after whole blood viscosity test. Compared with the control group, model group, high and low shear viscosity were significantly increased (P<0.01), indicating that the model was successful. Compared with the model group, high dose group and Qing Nao tablet Naoluotong group can significantly reduce the viscosity at high shear and (P<0.01), middle dose Qing Nao tablet group can significantly reduce high shear and shear viscosity (P<0.05); large, middle dose Qing Nao tablet group can significantly reduce the low shear viscosity (P<0.05), Naoluotong group can significantly reduce the low shear viscosity (P<0.01); low dose Qing Nao tablet group were lower high cut, low shear viscosity and trend The potential (P>0.05). The Qing Nao tablet has a good effect on the model of blood stasis in mice.

An interannual link between Arctic sea-ice cover and the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Caian, Mihaela; Koenigk, Torben; Döscher, Ralf; Devasthale, Abhay

2018-01-01

This work investigates links between Arctic surface variability and the phases of the winter (DJF) North Atlantic Oscillation (NAO) on interannual time-scales. The analysis is based on ERA-reanalysis and model data from the EC-Earth global climate model. Our study emphasizes a mode of sea-ice cover variability that leads the NAO index by 1 year. The mechanism of this leading is based on persistent surface forcing by quasi-stationary meridional thermal gradients. Associated thermal winds lead a slow adjustment of the pressure in the following winter, which in turn feeds-back on the propagation of sea-ice anomalies. The pattern of the sea-ice mode leading NAO has positive anomalies over key areas of South-Davis Strait-Labrador Sea, the Barents Sea and the Laptev-Ohkostsk seas, associated to a high pressure anomaly over the Canadian Archipelago-Baffin Bay and the Laptev-East-Siberian seas. These anomalies create a quasi-annular, quasi-steady, positive gradient of sea-ice anomalies about coastal line (when leading the positive NAO phase) and force a cyclonic vorticity anomaly over the Arctic in the following winter. During recent decades in spite of slight shifts in the modes' spectral properties, the same leading mechanism remains valid. Encouraging, actual models appear to reproduce the same mechanism leading model's NAO, relative to model areas of persistent surface forcing. This indicates that the link between sea-ice and NAO could be exploited as a potential skill-source for multi-year prediction by addressing the key problem of initializing the phase of the NAO/AO (Arctic Oscillation).

Combined Effect of El Nino Southern Oscillation and Atlantic Multidecadal Oscillation on Lake Chad Level Variability Region

NASA Technical Reports Server (NTRS)

Okonkwo, Churchill; Demoz, Belay; Sakai, Ricardo; Ichoku, Charles; Anarado, Chigozie; Adegoke, Jimmy; Amadou, Angelina; Abdullahi, Sanusu Imran

2015-01-01

In this study, the combined effect of the Atlantic Multidecadal Oscillation (AMO) and El Niño Southern Oscillation (ENSO) on the Lake Chad (LC) level variability is explored. Our results show that the lake level at the Bol monitoring station has a statistically significant correlation with precipitation (R2 = 0.6, at the 99.5% confidence level). The period between the late 1960s and early 1970s marked a turning point in the response of the regional rainfall to climatic drivers, thereby severely affecting the LC level. Our results also suggest that the negative impact of the cold phase of AMO on Sahel precipitation masks and supersedes the positive effect of La Niña in the early the 1970s. The drop in the size of LC level from 282.5 m in the early 1960s to about 278.1 m in 1983/1984 was the largest to occur within the period of study (1900-2010) and coincides with the combined cold phase of AMO and strong El Niño phase of ENSO. Further analyses show that the current warm phase of AMO and increasing La Niña episodes appear to be playing a major role in the increased precipitation in the Sahel region. The LC level is responding to this increase in precipitation by a gradual recovery, though it is still below the levels of the 1960s. This understanding of the AMO-ENSO-rainfall-LC level association will help in forecasting the impacts of similar combined episodes in the future. These findings also have implications for long-term water resources management in the LC region.

Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice.

PubMed

Li, Xichen; Holland, David M; Gerber, Edwin P; Yoo, Changhyun

2014-01-23

In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change.

Potential links between the North Atlantic Oscillation and decreasing precipitation and runoff on Sardinia

NASA Astrophysics Data System (ADS)

Montaldo, Nicola; Sarigu, Alessio

2017-04-01

Recently, climate change and human activities increased the desertification process in the Mediterranean regions, with dramatic consequences for agriculture and water resources. On the Sardinia island (Italy), runoff decreased significantly in the 1975-2010 period with a mean yearly runoff reduction of more than 50% compared to the previous 1922-1974 period. The decrease in runoff severely impacts the management of water resources on the Sardinia island, resulting in water supply restrictions even for domestic consumption. In the 10 Sardinian basins, with a longer database (at least 40 complete years of data, including data from the past 10 years), the trend of yearly runoff computed with the Mann-Kendall test is negative, with the Mann-Kendall τ values ranging from -0.39 to -0.2. The reason for the decrease in runoff is mainly the alarming decrease in the winter precipitation over the past few decades everywhere on the Sardinia island. Indeed, most of the yearly runoff of the Sardinian basins (on average, 70%) is produced by the winter precipitation due to the typical seasonality of the Mediterranean rainfall regime. Surprisingly, the winter precipitation trend is not homogenous; the negative trend is higher on the Sardinian west coast and becomes lower as one crosses the island toward the east coast. At the rain stations on the east coast, the τ Mann-Kendall values of the winter precipitation become almost half of the τ Mann-Kendall values on the west coast, which is exposed to the western European climate dynamics. In this sense, winter precipitation is highly correlated with the North Atlantic Oscillation (NAO), which is a weather phenomenon in the North Atlantic Ocean that controls the direction and strength of westerly winds and storm tracks into Europe. High negative correlations (up to -0.45) between winter NAO and winter precipitation are estimated along the west coast. Meanwhile, the correlations decrease as one crosses the island toward the east

Estimating Inflows to Lake Okeechobee Using Climate Indices: A Machine Learning Modeling Approach

NASA Astrophysics Data System (ADS)

Kalra, A.; Ahmad, S.

2008-12-01

The operation of regional water management systems that include lakes and storage reservoirs for flood control and water supply can be significantly improved by using climate indices. This research is focused on forecasting Lag 1 annual inflow to Lake Okeechobee, located in South Florida, using annual oceanic- atmospheric indices of Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), and El Nino-Southern Oscillations (ENSO). Support Vector Machine (SVM) and Least Square Support Vector Machine (LSSVM), belonging to the class of data driven models, are developed to forecast annual lake inflow using annual oceanic-atmospheric indices data from 1914 to 2003. The models were trained with 80 years of data and tested for 10 years of data. Based on Correlation Coefficient, Root Means Square Error, and Mean Absolute Error model predictions were in good agreement with measured inflow volumes. Sensitivity analysis, performed to evaluate the effect of individual and coupled oscillations, revealed a strong signal for AMO and ENSO indices compared to PDO and NAO indices for one year lead-time inflow forecast. Inflow predictions from the SVM models were better when compared with the predictions obtained from feed forward back propagation Artificial Neural Network (ANN) models.

Mechanisms of decadal variability in the Labrador Sea and the wider North Atlantic in a high-resolution climate model

NASA Astrophysics Data System (ADS)

Ortega, Pablo; Robson, Jon; Sutton, Rowan T.; Andrews, Martin B.

2017-10-01

A necessary step before assessing the performance of decadal predictions is the evaluation of the processes that bring memory to the climate system, both in climate models and observations. These mechanisms are particularly relevant in the North Atlantic, where the ocean circulation, related to both the Subpolar Gyre and the Meridional Overturning Circulation (AMOC), is thought to be important for driving significant heat content anomalies. Recently, a rapid decline in observed densities in the deep Labrador Sea has pointed to an ongoing slowdown of the AMOC strength taking place since the mid 90s, a decline also hinted by in-situ observations from the RAPID array. This study explores the use of Labrador Sea densities as a precursor of the ocean circulation changes, by analysing a 300-year long simulation with the state-of-the-art coupled model HadGEM3-GC2. The major drivers of Labrador Sea density variability are investigated, and are characterised by three major contributions. First, the integrated effect of local surface heat fluxes, mainly driven by year-to-year changes in the North Atlantic Oscillation, which accounts for 62% of the total variance. Additionally, two multidecadal-to-centennial contributions from the Greenland-Scotland Ridge outflows are quantified; the first associated with freshwater exports via the East Greenland Current, and the second with density changes in the Denmark Strait Overflow. Finally, evidence is shown that decadal trends in Labrador Sea densities are followed by important atmospheric impacts. In particular, a positive winter NAO response appears to follow the negative Labrador Sea density trends, and provides a phase reversal mechanism.

The summer North Atlantic Oscillation (SNAO) variability on decadal to paleoclimate time scales

NASA Astrophysics Data System (ADS)

Linderholm, H. W.; Folland, C. K.; Zhang, P.; Gunnarson, B. E.; Jeong, J. H.; Ren, H.

2017-12-01

The summer North Atlantic Oscillation (SNAO), strongly related to the latitude of the North Atlantic and European summer storm tracks, exerts a considerable influence on European summer climate variability and extremes. Here we extend the period covered by the SNAO from July and August to June, July and August (JJA). As well as marked interannual variability, the JJA SNAO has shown a large inter-decadal change since the 1970s. Decadally averaged, there has been a change from a very positive to a rather negative SNAO phase. This change in SNAO phase is opposite in sign from that expected by a number of climate models under enhanced greenhouse forcing by the late twenty first century. It has led to noticeably wetter summers in North West Europe in the last decade. On interannual to multidecadal timescales, SNAO variability is linked to variations in North Atlantic sea surface temperature (SST): observations and models indicate an association between the Atlantic Multi-decadal Oscillation (AMO) where the cold (warm) phase of the AMO corresponds a positive (negative) phase of the SNAO. Observations also indicate a link with SST in the Gulf Stream region of the North Atlantic where, particularly on decadal time scales, SST warming may favour a more positive phase of the SNAO. Influences of Arctic climate change on North Atlantic and European atmospheric circulation may also exist, particularly reduced sea ice coverage, perhaps favouring the negative phase of the SNAO. A new tree-ring data based JJA SNAO reconstruction extending over the last millennium, as well as climate model output for the same period, enables us to examine the influence of North Atlantic SST and Arctic sea-ice coverage, as well as SNAO impacts on European summer climate, in a long-term, pre-industrial context.

Enhanced biennial variability in the Pacific due to Atlantic capacitor effect.

PubMed

Wang, Lei; Yu, Jin-Yi; Paek, Houk

2017-03-20

The El Niño-Southern Oscillation (ENSO) and the variability in the Pacific subtropical highs (PSHs) have major impacts on social and ecological systems. Here we present an Atlantic capacitor effect mechanism to suggest that the Atlantic is a key pacemaker of the biennial variability in the Pacific including that in ENSO and the PSHs during recent decades. The 'charging' (that is, ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and 'discharging' (that is, the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) processes alternate, generating the biennial rhythmic changes in the Pacific. Since the early 1990s, a warmer Atlantic due to the positive phase of Atlantic multidecadal oscillation and global warming trend has provided more favourable background state for the Atlantic capacitor effect, giving rise to enhanced biennial variability in the Pacific that may increase the occurrence frequency of severe natural hazard events.

Enhanced biennial variability in the Pacific due to Atlantic capacitor effect

PubMed Central

Wang, Lei; Yu, Jin-Yi; Paek, Houk

2017-01-01

The El Niño-Southern Oscillation (ENSO) and the variability in the Pacific subtropical highs (PSHs) have major impacts on social and ecological systems. Here we present an Atlantic capacitor effect mechanism to suggest that the Atlantic is a key pacemaker of the biennial variability in the Pacific including that in ENSO and the PSHs during recent decades. The ‘charging' (that is, ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and ‘discharging' (that is, the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) processes alternate, generating the biennial rhythmic changes in the Pacific. Since the early 1990s, a warmer Atlantic due to the positive phase of Atlantic multidecadal oscillation and global warming trend has provided more favourable background state for the Atlantic capacitor effect, giving rise to enhanced biennial variability in the Pacific that may increase the occurrence frequency of severe natural hazard events. PMID:28317857

Enhanced biennial variability in the Pacific due to Atlantic capacitor effect

NASA Astrophysics Data System (ADS)

Wang, Lei; Yu, Jin-Yi; Paek, Houk

2017-03-01

The El Niño-Southern Oscillation (ENSO) and the variability in the Pacific subtropical highs (PSHs) have major impacts on social and ecological systems. Here we present an Atlantic capacitor effect mechanism to suggest that the Atlantic is a key pacemaker of the biennial variability in the Pacific including that in ENSO and the PSHs during recent decades. The `charging' (that is, ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and `discharging' (that is, the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) processes alternate, generating the biennial rhythmic changes in the Pacific. Since the early 1990s, a warmer Atlantic due to the positive phase of Atlantic multidecadal oscillation and global warming trend has provided more favourable background state for the Atlantic capacitor effect, giving rise to enhanced biennial variability in the Pacific that may increase the occurrence frequency of severe natural hazard events.

Decadal Air-Sea Interaction in the North Atlantic Based on Observations and Modeling Results

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa

1998-01-01

The decadal, 12-14 year, cycle observed in the North Atlantic SST and tide gauge data was examined using the NCEP/NCAR reanalyses, COADS data and an ocean model simulation. Besides this decadal mode, a shorter, subdecadal period of about 8 years exists in tide gauge data north of 40N, in the subpolar SST and in the winter North Atlantic Oscillation (NAO) index and in subpolar winter heat flux values. The decadal cycle is a well separated mode in a singular spectrum analysis (SSA) for a time series of SST EOF mode 1 with a center over the Gulf Stream extension. Tide gauge and SST data are consistent in that both show a significant subdecadal periodicity exclusively in the subpolar gyre, but in subtropics the 12-14 year period is the prominent, but nonstationary, decadal signal. The main finding of this study is that this 12-14 year cycle can be constructed based on the leading mode of the surface heat flux. This connection to the surface heat flux implicates the participation of the thermohaline circulation in the decadal cycle. During the cycle starting from the positive index phase of NAO, SST and oceanic heat content anomalies are created in subtropics due to local heat flux and intensification of the thermohaline circulation. The anomalies advect to the subpolar gyre where they are amplified by local heat flux and are part of the negative feedback of thermohaline circulation on itself. Consequently the oceanic thermohaline circulation slows down and the opposite cycle starts. The oscillatory nature would not be possible without the active atmospheric participation in the cycle, because it provides the unstable interaction through heat flux, without it, the oceanic mode would be damped. This analysis suggests that the two principal modes of heat flux variability, corresponding to patterns similar to North Atlantic Oscillation (NAO) and Western Atlantic (WA), are part of the same decadal cycle and an indirect measure of the north-south movement of the storm tracks.

Connections of Precipitable Water Vapor and Total Ozone Anomalies over European Russia with the North Atlantic Oscillation: Specific Features of Summer 2010

NASA Astrophysics Data System (ADS)

Sitnov, S. A.; Mokhov, I. I.; Bezverkhny, V. A.

2017-12-01

Based on the measurements of precipitable water vapor (PWV) and total column ozone (TCO) from the MODIS satellite instruments (Aqua/Terra platforms), the connections between the North Atlantic Oscillation (NAO) and the anomalies in PWV and TCO over European Russia (ER) in summer 2010 are analyzed. It is found that the PWV (TCO) anomalies over the northern ER in summer 2010 positively (negatively) correlated with the NAO, and the local correlations reached 0.68 (-0.55). The physical mechanisms of the correlations are discussed. A comparative analysis of the relationships between the NAO and the regional PWV and TCO anomalies over ER during the summer seasons of 2000-2015 is carried out.

Changes in North Atlantic Oscillation drove Population Migrations and the Collapse of the Western Roman Empire.

PubMed

Drake, B Lee

2017-04-27

Shifts in the North Atlantic Oscillation (NAO) from 1-2 to 0-1 in four episodes increased droughts on the Roman Empire's periphery and created push factors for migrations. These climatic events are associated with the movements of the Cimbri and Teutones from 113-101 B.C., the Marcomanni and Quadi from 164 to 180 A.D., the Goths in 376 A.D., and the broad population movements of the Migration Period from 500 to 600 A.D. Weakening of the NAO in the instrumental record of the NAO have been associated with a shift to drought in the areas of origin for the Cimbri, Quadi, Visigoths, Ostrogoths, Huns, and Slavs. While other climate indices indicate deteriorating climate after 200 A.D. and cooler conditions after 500 A.D., the NAO may indicate a specific cause for the punctuated history of migrations in Late Antiquity. Periodic weakening of the NAO caused drought in the regions of origin for tribes in antiquity, and may have created a powerful push factor for human migration. While climate change is frequently considered as a threat to sustainability, its role as a conflict amplifier in history may be one of its largest impacts on populations.

Life history tactics shape amphibians' demographic responses to the North Atlantic Oscillation.

PubMed

Cayuela, Hugo; Joly, Pierre; Schmidt, Benedikt R; Pichenot, Julian; Bonnaire, Eric; Priol, Pauline; Peyronel, Olivier; Laville, Mathias; Besnard, Aurélien

2017-11-01

Over the last three decades, climate abnormalities have been reported to be involved in biodiversity decline by affecting population dynamics. A growing number of studies have shown that the North Atlantic Oscillation (NAO) influences the demographic parameters of a wide range of plant and animal taxa in different ways. Life history theory could help to understand these different demographic responses to the NAO. Indeed, theory states that the impact of weather variation on a species' demographic traits should depend on its position along the fast-slow continuum. In particular, it is expected that NAO would have a higher impact on recruitment than on adult survival in slow species, while the opposite pattern is expected occur in fast species. To test these predictions, we used long-term capture-recapture datasets (more than 15,000 individuals marked from 1965 to 2015) on different surveyed populations of three amphibian species in Western Europe: Triturus cristatus, Bombina variegata, and Salamandra salamandra. Despite substantial intraspecific variation, our study revealed that these three species differ in their position on a slow-fast gradient of pace of life. Our results also suggest that the differences in life history tactics influence amphibian responses to NAO fluctuations: Adult survival was most affected by the NAO in the species with the fastest pace of life (T. cristatus), whereas recruitment was most impacted in species with a slower pace of life (B. variegata and S. salamandra). In the context of climate change, our findings suggest that the capacity of organisms to deal with future changes in NAO values could be closely linked to their position on the fast-slow continuum. © 2017 John Wiley & Sons Ltd.

Modest Little Ice Age cooling of the Western Tropical Atlantic inferred from Sr-U Coral Paleothermometry

NASA Astrophysics Data System (ADS)

Alpert, A.; Cohen, A. L.; Oppo, D.; Gaetani, G. A.

2016-12-01

Proxy records of the Little Ice Age (LIA; 1450-1850CE) at high latitude Northern Hemisphere indicate temperatures 1-2°C cooler relative to the mid-20th century. However, estimates of sea surface temperatures (SSTs) from the western tropical Atlantic (WTA) range widely, indicating SSTs from 0- 4°C cooler than the mid-20th century. The largest of these cooling estimates indicate that the LIA tropics were more sensitive than the high latitudes, inconsistent with model predictions. Here we apply a novel coral thermometer, Sr-U, that has been demonstrated to accurately capture spatial and temporal variability across coral genera in both the Pacific and Atlantic Oceans. A continuous section of reconstructed SSTs in the WTA (Puerto Rico) during the LIA (1465-1560CE) reveals a modest cooling relative to the late 20th century but no significant difference from the early 20th century prior. At this site sensitive to the modern Atlantic Multidecadal Oscillation (AMO) multidecadal variability was present during the LIA with amplitude comparable to the 20th century. Our record is consistent with weaker tropical sensitivity to external forcing than at higher latitudes during the LIA.

Linking the North Atlantic Oscillation to Rainfall Over Northern Lake Malawi

NASA Astrophysics Data System (ADS)

Johnson, T. C.; Powers, L. A.; Werne, J. P.; Brown, E. T.; Castaneda, I.; Schouten, S.; Sinninghe-Damste, J.

2005-12-01

Piston and multi-cores recovered from the north basin of Lake Malawi in 1998 by the International Decade for the East African Lakes (IDEAL) have provided a rich history of climate variability spanning the past 25,000 years. As we now begin to analyze the cores recovered by the Malawi Drilling Project in early 2005, we are considering the relationships among sedimentary signals of temperature (TEX86), northerly winds associated with a southward excursion of the Inter-Tropical Convergence Zone (per cent biogenic silica), and rainfall (terrigenous mass accumulation rate) in the well dated 1998 cores. A high-resolution record of the past 800 years suggests that rainfall in this region (10 - 12° S, 30 - 35° E) was relatively low during the Little Ice Age, when northerly winds were more prevalent, attributed to a more southerly position of the ITCZ during austral summers. The TEX86 signal of lake (surface?) temperature ranged mostly between 24 and 26°C during this period, with the coldest temperature of about 22°C around AD1680 and the warmest temperature, exceeding 27°C, in the youngest sediment sample. The cooler water temperatures coincide with periods of highest diatom productivity, consistent with the latter being due to relatively intense upwelling associated with the northerly winds. Our observation of low rainfall during periods of more southerly migration of the ITCZ is consistent with the results of McHugh and Rogers (2001), who linked rainfall in southeastern Africa to the North Atlantic Oscillation (NAO). During years of weak NAO, equatorial westerly transport of Atlantic moisture across Africa during austral summer is relatively intense, causing high rainfall in the East African Rift between the equator and 16° S. Conversely, when the NAO is positive, rainfall is higher south of 15° S than north of this latitude, which is consistent with a southward migration of the ITCZ. McHugh, M. J. and J. C. Rogers (2001). "North Atlantic Oscillation influence on

Sub-regional Precipitation Climate of the Caribbean and Relationships With ENSO and NAO

NASA Astrophysics Data System (ADS)

Winter, A.; Jury, M.; Malmgren, B.

2006-12-01

Thirty-five meteorological stations encompassing the Caribbean region (Cuba, Bahamas, Jamaica, Dominican Republic, Puerto Rico, U.S. Virgin Islands, St. Maarten, and Barbados) were analyzed over the time interval 1951-1981 to assess regional precipitation patterns and their relationships with the North Atlantic Oscillation (NAO) and El Niño-Southern Oscillation (ENSO). Application of factor analysis to these series revealed the existence of four geographically distinct precipitation regions: (1) western Cuba and northwestern Bahamas, (2) Jamaica, eastern Cuba, and southeastern Bahamas, (3) Dominican Republic and northwestern Puerto Rico, and (4) eastern Puerto Rico, U.S. Virgin Islands, St. Marteen, and Barbados. This regionalization is related to different annual cycles and interannual fluctuations of rainfall. The annual cycle is unimodal and largest in the northwest Caribbean (1), and becomes increasingly bimodal toward lower latitudes (4) as expected. Year-to-year variations of precipitation are compared with two well known climatic indices. The ENSO relationship, represented by Niño3.4 SST, is positive and stable at all lags, but tends to reverse over the SE Caribbean (4) in late summer. The NAO influence is weak and seasonally dependent. Early summer rainfall in the northwest Caribbean (1) increases under El Niño conditions. Clusters 2 and 3 are less influenced by the global predictors and more regional in character. Previous related work sub-divided the Caribbean into two to three regions. Our work also shows that the main Caribbean basin should be divided into two clusters and not one homogeneous region as has previously been reported.

Arctic sea-ice decline weakens the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Sévellec, Florian; Fedorov, Alexey V.; Liu, Wei

2017-08-01

The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study, we use an optimal flux perturbation framework and comprehensive climate model simulations to estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally to sea-ice decline. It is found that on decadal timescales, flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC, while on multi-decadal timescales (longer than 20 years), flux anomalies in the Arctic become more important. These positive buoyancy anomalies spread to the North Atlantic, weakening the AMOC and its poleward heat transport. Therefore, the Arctic sea-ice decline may explain the suggested slow-down of the AMOC and the `Warming Hole’ persisting in the subpolar North Atlantic.

Role of Tropical Atlantic SST Variability as a Modulator of El Nino Teleconnections

NASA Technical Reports Server (NTRS)

Ham, Yoo-Geun; Sung, Mi-Kyung; An, Soon-II; Schubert, Siegfried D.; Kug, Jong-Seong

2014-01-01

The present study suggests that the off-equatorial North Atlantic (NATL) SST warming plays a significant role in modulating El Niño teleconnection and its impact on the North Atlantic and European regions. The El Niño events accompanied by NATL SST warming exhibit south-north dipole pattern over the Western Europe to Atlantic, while the ENSO teleconnection pattern without NATL warming exhibits a Rossby wave-like pattern confined over the North Pacific and western Atlantic. Especially, the El Niño events with NATL warming show positive (negative) geopotential-height anomalies over the North Atlantic (Western Europe) which resemble the negative phase of the NAO. Consistently, it is shown using a simple statistical model that NATL SSTA in addition to the tropical Pacific SSTA leads to better prediction on regional climate variation over the North Atlantic and European regions. This role of NATL SST on ENSO teleconnection is also validated and discussed in a long term simulation of coupled global circulation model (CGCM).

A daily Azores-Iceland North Atlantic Oscillation index back to 1850.

PubMed

Cropper, Thomas; Hanna, Edward; Valente, Maria Antónia; Jónsson, Trausti

2015-07-01

We present the construction of a continuous, daily (09:00 UTC), station-based (Azores-Iceland) North Atlantic Oscillation (NAO) Index back to 1871 which is extended back to 1850 with additional daily mean data. The constructed index more than doubles the length of previously existing, widely available, daily NAO time series. The index is created using entirely observational sea-level pressure (SLP) data from Iceland and 73.5% of observational SLP data from the Azores - the remainder being filled in via reanalysis (Twentieth Century Reanalysis Project and European Mean Sea Level Pressure) SLP data. Icelandic data are taken from the Southwest Iceland pressure series. We construct and document a new Ponta Delgada SLP time series based on recently digitized and newly available data that extend back to 1872. The Ponta Delgada time series is created by splicing together several fractured records (from Ponta Delgada, Lajes, and Santa Maria) and filling in the major gaps (pre-1872, 1888-1905, and 1940-1941) and occasional days (145) with reanalysis data. Further homogeneity corrections are applied to the Azores record, and the daily (09:00 UTC) NAO index is then calculated. The resulting index, with its extended temporal length and daily resolution, is the first reconstruction of daily NAO back into the 19th Century and therefore is useful for researchers across multiple disciplines.

The influence of the winter North Atlantic Oscillation index on hospital admissions through diseases of the circulatory system in Lisbon, Portugal.

PubMed

Almendra, Ricardo; Santana, Paula; Vasconcelos, João; Silva, Giovani; Gonçalves, Fábio; Ambrizzi, Tércio

2017-02-01

The aim of this paper is to analyze the relationship between North Atlantic Oscillation (NAO), meteorological variables, air pollutants, and hospital admissions due to diseases of circulatory systems in Lisbon (Portugal) during winter months (2003-2012). This paper is one of the few studies analyzing the impact of NAO on health through its influence on thermal stress and air pollution and is the first to be conducted in Lisbon. This study uses meteorological data (synthetized into a thermal comfort index), air pollutant metrics, and the NAO index (all clustered in 10-day cycles to overcome daily variability of the NAO index). The relationship between morbidity, thermal comfort index, NAO index, and air pollutants was explored through several linear models adjusted to seasonality through a periodic function. The possible indirect effect between the NAO index and hospital admissions was tested, assuming that NAO (independent variable) is affecting hospital admissions (outcome variable) through thermal discomfort and/or pollution levels (tested as individual mediators). This test was conducted through causal mediation analysis and adjusted for seasonal variation. The results from this study suggest a possible indirect relationship between NAO index and hospital admissions. Although NAO is not significantly associated with hospital admissions, it is significantly associated with CO, PM 2.5 , NO, and SO 2 levels, which in turn increase the probability of hospitalization. The discomfort index (built with temperature and relative humidity) is significantly associated with hospital admissions, but its variability is not explained by the NAO index. This study highlights the impacts of the atmospheric circulation patterns on health. Furthermore, understanding the influence of the atmospheric circulation patterns can support the improvement of the existing contingency plans.

Indo-Pacific sea level variability at multidecadal time scales

NASA Astrophysics Data System (ADS)

Merrifield, M. A.; Thompson, P. R.

2016-12-01

Long tide gauge and atmospheric pressure measurements are used to infer multidecadal fluctuations in trade wind forcing and the associated Indo-Pacific sea level response along coastal and equatorial waveguides. The trade wind variations are marked by a weakening beginning with the late 1970s climate shift and a subsequent return to mean conditions since the early 1990s. These fluctuations covary with multidecadal wind changes at mid-latitudes, as measured by the Pacific Decadal Oscillation or the North Pacific indices; however, the mid-latitude multidecadal variations prior to 1970 or noticeably absent in the inferred trade wind record. The different behavior of tropical and mid-latitude winds support the notion that multidecadal climate variations in the Pacific result from a combination of processes and not a single coherent mode spanning the basin. In particular, the two-decade long satellite altimeter record represents a period of apparent connection between the two regions that was not exhibited earlier in the century.

Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes

NASA Astrophysics Data System (ADS)

Liu, Y.; Muhling, B.; Lee, S. K.; Muller-Karger, F. E.; Enfield, D. B.; Lamkin, J. T.; Roffer, M. A.

2016-02-01

Previous studies have shown that upper ocean circulations largely determine primary production in the euphotic layers, here the global ocean model with biogeochemistry (GFDL's Modular Ocean Model with TOPAZ biogeochemistry) forced with the ERA-Interim is used to simulate the natural variability of biogeochemical processes in global ocean during 1979-present. Preliminary results show that the surface chlorophyll is overall underestimated in MOM-TOPAZ, but its spatial pattern is fairly realistic. Relatively high chlorophyll variability is shown in the subpolar North Atlantic, northeastern tropical Atlantic, and equatorial Atlantic. Further analysis suggests that the chlorophyll variability in the North Atlantic Ocean is affected by long-term climate variability. For the subpolar North Atlantic region, the chlorophyll variability is light-limited and is significantly correlated with North Atlantic Oscillation. A dipole pattern of chlorophyll variability is found between the northeastern tropical Atlantic and equatorial Atlantic. For the northeastern North Atlantic, the chlorophyll variability is significantly correlated with Atlantic Meridional Mode (AMM) and Atlantic Multidecadal Oscillation (AMO). During the negative phase of AMM and AMO, the increased trade wind in the northeast North Atlantic can lead to increased upwelling of nutrients. In the equatorial Atlantic region, the chlorophyll variability is largely link to Atlantic-Niño and associated equatorial upwelling of nutrients. The potential impact of climate variability on the distribution of pelagic fishes (i.e. yellowfin tuna) are discussed.

Holocene Decadal to Multidecadal Hydrologic Variability in the Everglades: Climate and Implications for Ecosystem Management

NASA Astrophysics Data System (ADS)

Moses, C. S.; Anderson, W. T.; Saunders, C.; Rebenack, C.

2009-12-01

The Florida Everglades are a complex, unique ecosystem. Adding to the complexity, a system of canals and gates control the flow of waters from central Florida southward into the Everglades, and ultimately Florida Bay and the Gulf of Mexico. With south Florida’s distinct wet and dry seasons, the hydrology has driven ecosystem evolution over the last 4-5 kya. However, since the 1920s the water content of the Everglades has largely been anthropogenically modulated, with the exception of the natural variability of evaporation and precipitation over the large area south of the Tamiami Trail. Because of the incredibly flat nature of the Everglades, small changes in the freshwater balance have substantial impacts on the diversity and distribution of organisms. Decadal and multidecadal variability in precipitation, hurricane incidence, and sea level rise all have important effects on the ecosystem. During the instrumental record, the natural precipitation across south Florida has been strongly influenced by combinations of the Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation, and ENSO. Here we discuss evidence of natural climate variability impacts on the ecosystem beyond the anthropogenic hydrological controls. Proxy environmental data from seeds, charcoal, and trees, plus the sparse, but available, instrumental records provide evidence of changes in the ecosystem over the Holocene, and suggest considerations for future management.

Strong Dependence of U.S. Summertime Air Quality on the Decadal Variability of Atlantic Sea Surface Temperatures

NASA Astrophysics Data System (ADS)

Shen, Lu; Mickley, Loretta J.; Leibensperger, Eric M.; Li, Mingwei

2017-12-01

We find that summertime air quality in the eastern U.S. displays strong dependence on North Atlantic sea surface temperatures, resulting from large-scale ocean-atmosphere interactions. Using observations, reanalysis data sets, and climate model simulations, we further identify a multidecadal variability in surface air quality driven by the Atlantic Multidecadal Oscillation (AMO). In one-half cycle ( 35 years) of the AMO from cold to warm phase, summertime maximum daily 8 h ozone concentrations increase by 1-4 ppbv and PM2.5 concentrations increase by 0.3-1.0 μg m-3 over much of the east. These air quality changes are related to warmer, drier, and more stagnant weather in the AMO warm phase, together with anomalous circulation patterns at the surface and aloft. If the AMO shifts to the cold phase in future years, it could partly offset the climate penalty on U.S. air quality brought by global warming, an effect which should be considered in long-term air quality planning.

Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

PubMed Central

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-01-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean–atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region. PMID:28559341

Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-06-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.

A new approach developed to study variability in North African dust transport routes over the Atlantic during 2001-2015

NASA Astrophysics Data System (ADS)

Meng, L.; Gao, H. W.; Yu, Y.; Yao, X. H.; Gao, Y.; Zhang, C.; Fan, Lei

2017-10-01

We investigated the variability in the North African dust transport routes over the Atlantic (NAD routes) by extracting the dust transport central axis using Moderate Resolution Imaging Spectroradiometer aerosol data for 2001-2015. The results showed that the NAD routes can be classified into two regimes, a southern route centered at the southernmost position of 6.08 ± 1.12°N during November to March and a northern route centered at the northernmost position of 18.21 ± 1.04°N during April to October. In the southern route, large intervariation was correlated with the Intertropical Convergence Zone (ITCZ) and North Atlantic Oscillation (NAO), but the ITCZ and NAO jointly explained only 38% of the variation. In the northern route, the ITCZ alone explained 67% of the intervariation. The extracted trends during 2001-2015 exhibited a northward shift of 1.68° for the southern route and of 0.52° for the northern route. The causes for the shift were also examined.

SWH trends and links to large scale teleconnection patterns in the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Lionello, P.; Pino, C.; Galati, M. B.

2010-09-01

This study analyzes the SWH field in the Mediterranean Sea using a multidecadal simulations (1958-2001) carried out using the WAM (WAve Model) forced by the REMO-HIPOCAS wind fields. The simulations are validated against satellite altimeter data. Several mid-latitude patterns are linked to the SWH field in the Mediterranean. Considering the mean monthly SWH values, EA (Eastern Atlantic pattern) exerts the largest influence, while NAO and other patterns have a smaller but comparable effect. Severe SWH conditions have been characterized using the 95percentile of daily SWH maxima. NAO is important mainly for high SWH conditions in winter with significant correlation in December, January and March, but also EA, SCA (SCAndinavian) and EA-WR (Eastern Atlantic-Western Russia) play an important role. In general, both SWH high and mean values are modulated by several patterns, with an important variability in space and at monthly level so that no single pattern can be attributed a dominant role along the whole annual cycle and all the mentioned patterns are important for at least few months in the year. Significant trends of SWH are present only in sparse areas and suggest mostly a minor decrease of storm intensity, The statistics of extremes and high SWH values is substantially steady during the second half of the 20th century.

Revisiting Caveiro Lake sediment record: the Holocene NAO and AMO impact on Pico Island (Azores archipelago)

NASA Astrophysics Data System (ADS)

Hernandez, A.; Giralt, S.; Raposeiro, P. M.; Gonçalves, V. M.; Pueyo, J. J.; Trigo, R. M.; Bao, R.; Sáez, A.

2017-12-01

Northern Hemisphere climate is partly conditioned by a number of atmospheric and oceanic patterns which occur in the North Atlantic sector. The favourable location of the Azores Archipelago (37°-40° N, 25°-31° W) results in a privileged place to generate high-resolution Holocene climatic proxy data that can contribute to deep our understanding on the evolution of these atmospheric and oceanic patterns. In the frame of three research projects, namely PALEONAO (CGL2010-15767), RAPIDNAO (CGL2013-40608-R) and PALEOMODES (CGL2016-75281-C2), high-resolution proxy-based reconstructions from Azores Archipelago have recently shown a combined impact of atmospheric and oceanic patterns at multiannual and decadal time-scales (Rubio-Inglés et al. 2016; Hernández et al. 2017). However, the long-term evolution coupling/uncoupling of these patterns is not well-determined yet. Here, we present a new high-resolution climate reconstruction based on the Caveiro Lake sedimentary sequence in order to fill this gap. Previously, Björck et al. (2006) studied a section of this sequence (the uppermost 4.6 m covering last 6 Ka cal BP) concluding that changes in the thermohaline circulation and the SST were the main drivers in the long-term precipitation variability, whereas the NAO impact was the main atmospheric driver of short-term precipitation changes. However, they only distinguished the NAO impact for the last 600 years owing to the low resolution of the study for the lower portion of the core. The new studied sequence (8.40 m long, 8.2 Ka cal BP) has been analysed at decadal-to centennial time-scale resolution for X-ray diffraction (XRD), X-ray fluorescence (XRF) core scanning and elemental and isotope geochemistry on bulk organic matter. The statistical multivariate analysis of the data highlights the main drivers triggering the sedimentary infill of the lake would be the NAO and AMO by controlling the lacustrine productivity via nutrients input. This new high

Multi-Decadal to Millennial Scale Holocene Hydrologic Variation in the Southern Hemisphere Tropics of South America

NASA Astrophysics Data System (ADS)

Ekdahl, E. J.; Fritz, S. C.; Baker, P. A.; Burns, S. J.; Coley, K.; Rigsby, C. A.

2005-12-01

Numerous sites in the Northern Hemisphere show multi-decadal to millennial scale climate variation during the Holocene, many of which have been correlated with changes in atmospheric radiocarbon production or with changes in North Atlantic oceanic circulation. The manifestation of such climate variability in the hydrology of the Southern Hemisphere tropics of South America is unclear, because of the limited number of records at suitably high resolution. In the Lake Titicaca drainage basin of Bolivia and Peru, high-resolution lacustrine records reveal the overall pattern of Holocene lake-level change, the influence of precessional forcing of the South American Summer Monsoon, and the effects of high-frequency climate variability in records of lake productivity and lake ecology. Precessional forcing of regional precipitation is evident in the Lake Titicaca basin as a massive (ca. 85 m) mid-Holocene decline in lake level beginning about 7800 cal yr BP and a subsequent rise in lake level after 4000 cal yr BP. Here we show that multi-decadal to millennial-scale climate variability, superimposed upon the envelope of change at orbital time scales, is similar in timing and pattern to the ice-rafted debris record of Holocene Bond events in the North Atlantic. A high-resolution carbon isotopic record from Lake Titicaca that spans the entire Holocene suggests that cold intervals of Holocene Bond events are periods of increased precipitation, thus indicating an anti-phasing of precipitation variation on the Altiplano relative to the Northern Hemisphere tropics. A similar pattern of variation is also evident in high-resolution (2-30 yr spacing) diatom and geochemical records that span the last 7000 yr from two smaller lakes, Lagos Umayo and Lagunillas, in the Lake Titicaca drainage basin.

Simulated variability of the Atlantic meridional overturning circulation

NASA Astrophysics Data System (ADS)

Bentsen, M.; Drange, H.; Furevik, T.; Zhou, T.

To examine the multi-annual to decadal scale variability of the Atlantic Meridional Overturning Circulation (AMOC) we conducted a four-member ensemble with a daily reanalysis forced, medium-resolution global version of the isopycnic coordinate ocean model MICOM, and a 300-years integration with the fully coupled Bergen Climate Model (BCM). The simulations of the AMOC with both model systems yield a long-term mean value of 18 Sv and decadal variability with an amplitude of 1-3 Sv. The power spectrum of the inter-annual to decadal scale variability of the AMOC in BCM generally follows the theoretical red noise spectrum, with indications of increased power near the 20-years period. Comparison with observational proxy indices for the AMOC, e.g. the thickness of the Labrador Sea Water, the strength of the baroclinic gyre circulation in the North Atlantic Ocean, and the surface temperature anomalies along the mean path of the Gulf Stream, shows similar trends and phasing of the variability, indicating that the simulated AMOC variability is robust and real. Mixing indices have been constructed for the Labrador, the Irminger and the Greenland-Iceland-Norwegian (GIN) seas. While convective mixing in the Labrador and the GIN seas are in opposite phase, and linked to the NAO as observations suggest, the convective mixing in the Irminger Sea is in phase with or leads the Labrador Sea. Newly formed deep water is seen as a slow, anomalous cold and fresh, plume flowing southward along the western continental slope of the Atlantic Ocean, with a return flow of warm and saline water on the surface. In addition, fast-travelling topographically trapped waves propagate southward along the continental slope towards equator, where they go east and continue along the eastern rim of the Atlantic. For both types of experiments, the Northern Hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak AMOC

Climate influence on Vibrio and associated human diseases during the past half-century in the coastal North Atlantic

PubMed Central

Vezzulli, Luigi; Grande, Chiara; Reid, Philip C.; Hélaouët, Pierre; Edwards, Martin; Höfle, Manfred G.; Brettar, Ingrid; Colwell, Rita R.; Pruzzo, Carla

2016-01-01

Climate change is having a dramatic impact on marine animal and plant communities but little is known of its influence on marine prokaryotes, which represent the largest living biomass in the world oceans and play a fundamental role in maintaining life on our planet. In this study, for the first time to our knowledge, experimental evidence is provided on the link between multidecadal climatic variability in the temperate North Atlantic and the presence and spread of an important group of marine prokaryotes, the vibrios, which are responsible for several infections in both humans and animals. Using archived formalin-preserved plankton samples collected by the Continuous Plankton Recorder survey over the past half-century (1958–2011), we assessed retrospectively the relative abundance of vibrios, including human pathogens, in nine areas of the North Atlantic and North Sea and showed correlation with climate and plankton changes. Generalized additive models revealed that long-term increase in Vibrio abundance is promoted by increasing sea surface temperatures (up to ∼1.5 °C over the past 54 y) and is positively correlated with the Northern Hemisphere Temperature (NHT) and Atlantic Multidecadal Oscillation (AMO) climatic indices (P < 0.001). Such increases are associated with an unprecedented occurrence of environmentally acquired Vibrio infections in the human population of Northern Europe and the Atlantic coast of the United States in recent years. PMID:27503882

Sharpest Ever VLT Images at NAOS-CONICA "First Light"

NASA Astrophysics Data System (ADS)

2001-12-01

Very Promising Start-Up of New Adaptive Optics Instrument at Paranal Summary A team of astronomers and engineers from French and German research institutes and ESO at the Paranal Observatory is celebrating the successful accomplishment of "First Light" for the NAOS-CONICA Adaptive Optics facility . With this event, another important milestone for the Very Large Telescope (VLT) project has been passed. Normally, the achievable image sharpness of a ground-based telescope is limited by the effect of atmospheric turbulence. However, with the Adaptive Optics (AO) technique, this drawback can be overcome and the telescope produces images that are at the theoretical limit, i.e., as sharp as if it were in space . Adaptive Optics works by means of a computer-controlled, flexible mirror that counteracts the image distortion induced by atmospheric turbulence in real time. The larger the main mirror of the telescope is, and the shorter the wavelength of the observed light, the sharper will be the images recorded. During a preceding four-week period of hard and concentrated work, the expert team assembled and installed this major astronomical instrument at the 8.2-m VLT YEPUN Unit Telescope (UT4). On November 25, 2001, following careful adjustments of this complex apparatus, a steady stream of photons from a southern star bounced off the computer-controlled deformable mirror inside NAOS and proceeded to form in CONICA the sharpest image produced so far by one of the VLT telescopes. With a core angular diameter of only 0.07 arcsec, this image is near the theoretical limit possible for a telescope of this size and at the infrared wavelength used for this demonstration (the K-band at 2.2 µm). Subsequent tests reached the spectacular performance of 0.04 arcsec in the J-band (wavelength 1.2 µm). "I am proud of this impressive achievement", says ESO Director General Catherine Cesarsky. "It shows the true potential of European science and technology and it provides a fine

Novel synthesis approach for stable sodium superoxide (NaO2) nanoparticles for LPG sensing application

NASA Astrophysics Data System (ADS)

Nemade, Kailash; Waghuley, Sandeep

2017-05-01

The synthesis of stable superoxide is still great challenge for the researchers working in the field of materials science. Through this letter, we report the novel and simple synthesis approach for the preparation of stable sodium superoxide (NaO2) nanoparticles. NaO2 nanoparticles were prepared by a spray pyrolysis technique, under oxygen rich environment for gas sensing application. The texture characterizations show that as-obtained NaO2 nanoparticles have high structural purity. Most importantly, NaO2 nanoparticles exhibits higher sensing response, shorter response time and recovery time, low operating temperature and good stability during sensing of liquefied petroleum gas (LPG). The main accomplishment of present work is that as-fabricated sensor has low operating temperature (423 K), which is below auto-ignition temperature of LPG. The gas sensing mechanism of NaO2 nanoparticles was discussed without the conventional oxygen bridging mechanism. Through this short communication, LPG sensing application of stable sodium superoxide nanoparticle is explored.

A switch in the Atlantic Oscillation correlates with inter-annual changes in foraging location and food habits of Macaronesian shearwaters (Puffinus baroli) nesting on two islands of the sub-tropical Atlantic Ocean

NASA Astrophysics Data System (ADS)

Ramos, Jaime A.; Isabel Fagundes, Ana; Xavier, José C.; Fidalgo, Vera; Ceia, Filipe R.; Medeiros, Renata; Paiva, Vitor H.

2015-10-01

Changes in oceanographic conditions, shaped by changes in large-scale atmospheric phenomena such as the North Atlantic Oscillation (NAO), alters the structure and functioning of marine ecosystems. Such signals are readily captured by marine top predators, given that their use of foraging habitats and diets change when the NAO changes. In this study we assessed sexual, seasonal and annual (2010/11-2012/13) differences in diet, trophic and isotopic niche (using δ15N and δ13C values of whole blood, 1st primary, 8th secondary and breast feathers), foraging locations and oceanographic variation within foraging areas for Macaronesian shearwaters' (Puffinus baroli) during two years of contrasting NAO values, and between two sub-tropical islands 330 km apart in the North Atlantic Ocean, Cima Islet and Selvagem Grande. These two locations provide contrasting oceanographic foraging regimes for the birds, because the second colony is much closer to the African coast (375 vs 650 km), and, therefore, to the upwelling area of the Canary Current. There was a marked environmental perturbation in 2010/2011, related with a negative NAO Index and lower marine productivity (lower concentration of Chlorophyll a). This event corresponded to the Macaronesian shearwaters feeding farther north and west, which was readily seen in change of both δ15N and δ13C values, and in a higher intake of cephalopods. Diet and stable isotopes did not differ between sexes. Regurgitation analysis indicate a dominance of cephalopods in both islands, but prey fish were important for Selvagem Grande in 2012 and cephalopods for Cima Islet in 2011. Both δ15N and δ13C values were significantly higher for Cima Islet than for Selvagem Grande, irrespective of year, season and tissue sampled. SIBER analysis showed smaller isotopic niches for the breeding period. Our study suggests that during years of poor environmental conditions Macaronesian shearwaters shift their foraging location to more pelagic waters

Influence of winter NAO pattern on variable renewable energies potential in Europe over the 20th century

NASA Astrophysics Data System (ADS)

François, Baptiste; Raynaud, Damien; Hingray, Benoit; Creutin, Jean-Dominique

2017-04-01

Integration of Variable Renewable Energy (VRE) sources in the electricity system is a challenge because of temporal and spatial fluctuations of their power generation resulting from their driving weather variables (i.e. solar radiation wind speed, precipitation, and temperature). Very few attention was paid to low frequency variability (i.e. from annual to decades) even though it may have significant impact on energy system and energy market Following the current increase in electricity supplied by VRE generation, one could ask the question about the risk of ending up in a situation in which the level of production of one or more VRE is exceptionally low or exceptionally high for a long period of time and/or over a large area. What would be the risk for an investor if the return on investment has been calculated on a high energy production period? What would be the cost in term of carbon emission whether the system manager needs to turn on coal power plant to satisfy the demand? Such dramatic events would definitely impact future stakeholder decision to invest in a particular energy source or another. Weather low frequency variability is mainly governed by large-scale teleconnection patterns impacting the climate at global scale such as El Niño - Southern Oscillation (ENSO) in the tropics and in North America or the North Atlantic Oscillation (hereafter, NAO) in North America and Europe. Teleconnection pattern's influence on weather variability cascades to VRE variability and ends up by impacting electricity system. The aim of this study is to analysis the impact of the NAO on VRE generation in Europe during the winter season. The analysis is carried out over the twentieth century (i.e. from 1900 to 2010), in order to take into account climate low frequency variability, and for a set of 12 regions covering a large range of climates in Europe. Weather variable time series are obtained by using the ERA20C reanalysis and the SCAMP model (Sequential Constructive

Changing response of the North Atlantic/European winter climate to the 11 year solar cycle

NASA Astrophysics Data System (ADS)

Ma, Hedi; Chen, Haishan; Gray, Lesley; Zhou, Liming; Li, Xing; Wang, Ruili; Zhu, Siguang

2018-03-01

Recent studies have presented conflicting results regarding the 11 year solar cycle (SC) influences on winter climate over the North Atlantic/European region. Analyses of only the most recent decades suggest a synchronized North Atlantic Oscillation (NAO)-like response pattern to the SC. Analyses of long-term climate data sets dating back to the late 19th century, however, suggest a mean sea level pressure (mslp) response that lags the SC by 2-4 years in the southern node of the NAO (i.e. Azores region). To understand the conflicting nature and cause of these time dependencies in the SC surface response, the present study employs a lead/lag multi-linear regression technique with a sliding window of 44 years over the period 1751-2016. Results confirm previous analyses, in which the average response for the whole time period features a statistically significant 2-4 year lagged mslp response centered over the Azores region. Overall, the lagged nature of Azores mslp response is generally consistent in time. Stronger and statistically significant SC signals tend to appear in the periods when the SC forcing amplitudes are relatively larger. Individual month analysis indicates the consistent lagged response in December-January-February average arises primarily from early winter months (i.e. December and January), which has been associated with ocean feedback processes that involve reinforcement by anomalies from the previous winter. Additional analysis suggests that the synchronous NAO-like response in recent decades arises primarily from late winter (February), possibly reflecting a result of strong internal noise.

Northern North Atlantic Sea Surface Height and Ocean Heat Content Variability

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Rhines, Peter; Worthen, Denise L.

2013-01-01

The evolution of nearly 20 years of altimetric sea surface height (SSH) is investigated to understand its association with decadal to multidecadal variability of the North Atlantic heat content. Altimetric SSH is dominated by an increase of about 14 cm in the Labrador and Irminger seas from 1993 to 2011, while the opposite has occurred over the Gulf Stream region over the same time period. During the altimeter period the observed 0-700 m ocean heat content (OHC) in the subpolar gyre mirrors the increased SSH by its dominantly positive trend. Over a longer period, 1955-2011, fluctuations in the subpolar OHC reflect Atlantic multidecadal variability (AMV) and can be attributed to advection driven by the wind stress ''gyre mode'' bringing more subtropical waters into the subpolar gyre. The extended subpolar warming evident in SSH and OHC during the altimeter period represents transition of the AMV from cold to warm phase. In addition to the dominant trend, the first empirical orthogonal function SSH time series shows an abrupt change 2009-2010 reaching a new minimum in 2010. The change coincides with the change in the meridional overturning circulation at 26.5N as observed by the RAPID (Rapid Climate Change) project, and with extreme behavior of the wind stress gyre mode and of atmospheric blocking. While the general relationship between northern warming and Atlantic meridional overturning circulation (AMOC) volume transport remains undetermined, the meridional heat and salt transport carried by AMOC's arteries are rich with decade-to-century timescale variability.

Global Three-Dimensional Atmospheric Structure of the Atlantic Multidecadal Oscillation as Revealed by Two Reanalyses

NASA Astrophysics Data System (ADS)

Stuckman, Scott Seele

This study is a first documentation of the structure of the entire AMO life cycle, including extreme and transition phases, throughout the global troposphere. The extreme phase climate signature is constructed based on the strongest and most robust patterns identified by two methods (linear correlation and composite analyses), two reanalysis datasets (the National Centers for Environmental Prediction/National Center for Atmospheric Research and Twentieth Century Reanalysis, supplemented with precipitation data from the University of Delaware dataset) and data from two consecutive AMO cycles. The first characterization of the AMO transition phases uses a transition index based on the time derivative of AMO index. When trying to compare the zonal mean structure of AMO with the El Niño-Southern Oscillation (ENSO), a literature search showed the zonal mean structure of ENSO remained unpublished, despite the otherwise generally well-characterized horizontal structures. Therefore this study includes a seasonal analysis of the ENSO zonal mean structure during boreal winter (DJF) and summer (JJA). The AMO extreme phase is characterized by a blend of low and middle latitude centers of action, with the associated tilt of geopotential height anomaly patterns consistent with off-equatorial heating patterns generated by the Held idealized model. The surface climate signature is connected to the upper air with baroclinic vertical structure over the North Atlantic but barotropic structures elsewhere. The associated zonal mean circulation features three circulation cells globally with strong inter-hemispheric mixing that suggests the traditional view of the AMO involving a Northern-Southern Hemisphere asymmetry is accurate only near the surface. The AMO transition phase features a more equatorial-based climate signature and associated geopotential height anomaly patterns consistent with the Matsuno-Gill idealized model. The zonal mean circulation of the transition phases features

Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability.

PubMed

Booth, Ben B B; Dunstone, Nick J; Halloran, Paul R; Andrews, Timothy; Bellouin, Nicolas

2012-04-04

Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean. These links are extensive, influencing a range of climate processes such as hurricane activity and African Sahel and Amazonian droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures, but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear. Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860-2005 North Atlantic sea surface temperatures. After 1950, simulated variability is within observational estimates; our estimates for 1910-1940 capture twice the warming of previous generation models but do not explain the entire observed trend. Other processes, such as ocean circulation, may also have contributed to variability in the early twentieth century. Mechanistically, we find that inclusion of aerosol-cloud microphysical effects, which were included in few previous multimodel ensembles, dominates the magnitude (80 per cent) and the spatial pattern of the total surface aerosol forcing in the North Atlantic. Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol-cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.

Sea Surface Temperature Records Using Sr/Ca Ratios in a Siderastrea siderea Coral from SE Cuba

NASA Astrophysics Data System (ADS)

Fargher, H. A.; Hughen, K. A.; Ossolinski, J. E.; Bretos, F.; Siciliano, D.; Gonzalez, P.

2015-12-01

Sea surface temperature (SST) variability from Cuba remains relatively unknown compared to the rest of the Caribbean. Cuba sits near an inflection point in the spatial pattern of SST from the North Atlantic Oscillation (NAO), and long SST records from the region could reveal changes in the influence of this climate system through time. A Siderastrea siderea coral from the Jardínes de la Reina in southern Cuba was drilled to obtain a 220 year long archive of environmental change. The genus Siderastrea has not been extensively studied as an SST archive, yet Sr/Ca ratios in the Cuban core show a clear seasonal signal and strong correlation to instrumental SST data (r2 = 0.86 and 0.36 for monthly and interannual (winter season) timescales, respectively). Annual growth rates (linear extension) of the coral are observed to have a minor influence on Sr/Ca variability, but do not show a direct correlation to SST on timescales from annual to multidecadal. Sr/Ca measurements from the Cuban coral are used to reconstruct monthly and seasonal (winter, summer) SST extending back more than two centuries. Wintertime SST in southern Cuba is compared to other coral Sr/Ca records of winter-season SST from locations sensitive to the NAO in order to investigate the stationarity of the NAO SST 'fingerprint' through time.

Multidecadal oscillations in rainfall and hydrological extremes

NASA Astrophysics Data System (ADS)

Willems, Patrick

2013-04-01

Many studies have anticipated a worldwide increase in the frequency and intensity of precipitation extremes and floods since the last decade(s). Natural variability by climate oscillations partly determines the observed evolution of precipitation extremes. Based on a technique for the identification and analysis of changes in extreme quantiles, it is shown that hydrological extremes have oscillatory behaviour at multidecadal time scales. Results are based on nearly independent extremes extracted from long-term historical time series of precipitation intensities and river flows. Study regions include Belgium - The Netherlands (Meuse basin), Ethiopia (Blue Nile basin) and Ecuador (Paute basin). For Belgium - The Netherlands, the past 100 years showed larger and more hydrological extremes around the 1910s, 1950-1960s, and more recently during the 1990-2000s. Interestingly, the oscillations for southwestern Europe are anti-correlated with these of northwestern Europe, thus with oscillation highs in the 1930-1940s and 1970s. The precipitation oscillation peaks are explained by persistence in atmospheric circulation patterns over the North Atlantic during periods of 10 to 15 years. References: Ntegeka V., Willems P. (2008), 'Trends and multidecadal oscillations in rainfall extremes, based on a more than 100 years time series of 10 minutes rainfall intensities at Uccle, Belgium', Water Resources Research, 44, W07402, doi:10.1029/2007WR006471 Mora, D., Willems, P. (2012), 'Decadal oscillations in rainfall and air temperature in the Paute River Basin - Southern Andes of Ecuador', Theoretical and Applied Climatology, 108(1), 267-282, doi:0.1007/s00704-011-0527-4 Taye, M.T., Willems, P. (2011). 'Influence of climate variability on representative QDF predictions of the upper Blue Nile Basin', Journal of Hydrology, 411, 355-365, doi:10.1016/j.jhydrol.2011.10.019 Taye, M.T., Willems, P. (2012). 'Temporal variability of hydro-climatic extremes in the Blue Nile basin', Water

The bivalve Glycymeris longior as an environmental archive for the Mar Argentino, southern South Atlantic

NASA Astrophysics Data System (ADS)

del Socorro Doldan, María; Morsan, Enrique Mario; Giménez, Lucas; Zaidman, Paula Cecilia

2017-04-01

Southern Hemisphere lacks of suitable high-resolution long datasets for the marine environment. This is translated in poor understanding of climate dynamics and processes at regional and continental-scale. We assessed the potential of Glycymeris longior as an environmental indicator for the mid-latitudes of South Atlantic by applying sclerochronological techniques on sample sets collected from San Matías Gulf, Mar Argentino, southern South Atlantic. We present a reconstruction of marine environmental variability of SMG for the period 1890-2016, covering 125 years. The reconstruction is based on the growth increment series for the first absolutely-dated annually-resolved multi-decadal G. longior bivalve on Sothern Atlantic. Shells were collected in 1918, 1933, 1945, 1983, 1989, 2009, 2011, 2015 and 2016. Sample depth varies between collection years. Age of the individuals was estimated from the hinge region of the shell. G. longior forms an annual narrow growth line. Maximal longevity was 40 years old. A strong common environmental signal is apparent in the increment widths. Correlations between the growth increment indices and regional temperature series (sea surface temperatures, continental temperatures) and other proxies were made. Preliminary results indicate that G.longior sclerochronologies, combined with low-frequency proxies can facilitate reconstructions of oceanographic variability. We discuss multi-decadal climate variability. Given the ability to generate annually-resolved chronologies G. longior is likely to be used as a climate recorder in southern South America. Hence, G. longior shells from Pleistocene marine deposits from Patagonia, Argentina, have a considerable potential to contain information of past climate for mid-latitudes of South Atlantic.

North Atlantic Oscillation Drives Regional Greenland Glacier Volume During the 20th Century

NASA Astrophysics Data System (ADS)

Bjork, A. A.; Aagaard, S.; Hallander, A. M.; Khan, S. A.; Box, J. E.; Kjeldsen, K. K.; Larsen, N. K.; Korsgaard, N. J.; Cappelen, J.; Colgan, W. T.; Machguth, H.; Andresen, C. S.; Kjaer, K. H.

2016-12-01

While most areas of the Greenland ice sheet have undergone rapid mass loss since c. 1990, the central eastern section of the ice sheet has advanced and gained mass. This contrasting regional trend has been attributed to positive surface mass balance (SMB) in the absence of significant dynamic mass loss. To constrain the atypical behavior in this region, we mapped glacier length fluctuations of nearly 200 peripheral glaciers and ice caps (PGICs) over a 103-year period, and compare the results with c. 150 new glacier length records from central west Greenland. We demonstrate that the regional response in ice volume is closely correlated to changes in precipitation, governed by circulation patterns associated with the North Atlantic Oscillation (NAO) and secondarily influenced by temperature forcing in certain periods. More broadly, we find that the NAO contributes to contrasting precipitation variability in East and West Greenland, where it appears to be responsible for at least 10% and more than 25%, respectively, of the variability in ice sheet accumulation rate. This east-west asymmetry, which influences both LGICs and the ice sheet, illustrates how substantial uncertainty in NAO projections directly contributes to uncertainty in mass balance projections.

Northern tropical Atlantic climate since late Medieval times from Northern Caribbean coral geochemistry

NASA Astrophysics Data System (ADS)

Kilbourne, K. H.; Xu, Y.

2015-12-01

Paleoclimate reconstructions of different global climate modes over the last 1000 years provide the basis for testing the relative roles of forced and unforced variability climate system, which can help us improve projections of future climate change. The Medieval Climate Anomaly (MCA) has been characterized by a combination of persistent La Niña-like conditions, a positive North Atlantic Oscillation (+NAO), and increased Atlantic Meridional Overturning Circulation (AMOC). The northern tropical Atlantic is sensitive to each of these climate patterns, but not all of them have the same regional fingerprint in the modern northern tropical Atlantic. The relative influence of different processes related to these climate patterns can help us better understand regional responses to climate change. The regional response of the northern tropical Atlantic is important because the tropical Atlantic Ocean is a large source of heat and moisture to the global climate system that can feedback onto global climate patterns. This study presents new coral Sr/Ca and δ18O data from the northern tropical Atlantic (Anegada, British Virgin Islands). Comparison of the sub-fossil corals that grew during the 13th and 14th Centuries with modern coral geochemical data from this site indicates relatively cooler mean conditions with a decrease in the oxygen isotopic composition of the water consistent with lower salinities. Similar average annual cycles between modern and sub-fossil Sr/Ca indicate no change in seasonal temperature range, but a difference in the relative phasing of the δ18O seasonal cycles indicates that the fresher mean conditions may be due to a more northerly position of the regional salinity front. This localized response is consistent with some, but not all of the expected regional responses to a La Niña-like state, a +NAO state, and increased AMOC. Understanding these differences can provide insight into the relative importance of advection versus surface fluxes for

Sea level trends and NAO influences: The Bristol Channel/Severn Estuary

NASA Astrophysics Data System (ADS)

Phillips, M. R.; Crisp, S.

2010-09-01

Fifteen years, 1993 (earliest available) to 2007 inclusive of monthly mean and extreme (maximum and minimum) sea level data were assessed for four tide gauges located in the Bristol Channel (Mumbles and Ilfracombe) and Severn Estuary (Newport and Hinkley Point). Results showed decreasing maximum sea level trends and increasing minimum sea level trends, resulting in convergence. However, maximum extreme sea levels on the Welsh shoreline (Mumbles and Newport) were higher than corresponding locations on the English coast (Ilfracombe and Hinkley Point). Analysis showed that from 1995 to 1998 inclusive, maximum extreme sea levels were significantly higher at Mumbles (t = 2.342; df = 10; p < 0.05), Newport (t = 5.034; df = 13; p < 0.01) and Hinkley Point (t = 3.570; df = 13; p < 0.01) and were correlated to increased storm frequencies during these years. However, Ilfracombe (t = 1.472; df = 12; p > 0.05) did not demonstrate similar significance, possibly due to tide gauge location and coastal aspect, while tidal influences became more dominant as the tidal prism moved up the estuary. Actual mean sea levels (MSL) at Newport (t = 2.880; df = 14; p < 0.05) and Hinkley Point (t = 5.282; df = 14; p < 0.01) were significantly higher than predicted; at Mumbles (t = 2.673; df = 11; p < 0.05) they were significantly lower than predicted; while Ilfracombe (t = 1.989; df = 13; p > 0.05) once again showed no significant difference. Mumbles is the only location with off-shore sand waves and analysis suggested these as the cause of opposite trends. Sea level variation was strongly correlated to the North Atlantic Oscillation (NAO) Index, especially for maximum extreme sea levels during positive phases (R 2 = 86%), and higher positive or negative NAO Index values resulted in larger sea level ranges. Further analysis showed a rising Bristol Channel and Severn Estuary MSL trend of 2.4 mm yr - 1 and a 2050 MSL of 0.370 m is projected to inform future management. However, continuous

Late Holocene Hydroclimate Variability of West-Central Guatemala Driven by NAO and ENSO

NASA Astrophysics Data System (ADS)

Stansell, N.; Feller, J. R.; Steinman, B. A.; Lachniet, M. S.; Shea, C.; Avendaño, C.

2016-12-01

Finely-laminated sediments from Lake San Francisco in the Huehuetenango province of west-central Guatemala provide a sub-decadal resolution record of hydroclimate variability spanning the last 5200 years. Age control is based on 7 radiocarbon samples of charcoal and lead-210 dating of surface sediments. Modern water isotope samples indicate the lake is currently an open system, and variations of δ18O values of precipitation in the region are driven largely by the amount effect. In contrast, a strong covariance of δ18O and δ13C values combined with pollen evidence in the lower part of the record suggests the lake was a seasonally closed-basin from 5200 to 3200 BP, and was sensitive to evaporation under more arid conditions. There was an overall trend of increasingly wetter conditions during the late Holocene, and a lack of covariance between δ18O and δ13C indicates that the lake transitioned to an open-basin after 3200 BP. The Medieval Climate Anomaly was the wettest period of the late Holocene, and there was a shift to lower precipitation amounts during the Little Ice Age. Present conditions are more arid than most of the last millennium, but δ18O values in the modern sediments are intermediate compared to the full late Holocene. The Lake San Francisco record provides additional evidence that the hydroclimate of Central America is sensitive to both changes in North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO). Drier conditions at San Francisco over the length of the record were associated with more negative phases of NAO and vice versa. During the last 1500 years, drier conditions at San Francisco were also associated with warmer sea-surface temperatures (SSTs) in the Niño3 region, and it was wetter when SSTs were colder.

An abrupt slowdown of Atlantic Meridional Overturning Circulation during 1915-1935 induced by solar forcing in a coupled GCM

NASA Astrophysics Data System (ADS)

Lin, P.; Song, Y.; Yu, Y.; Liu, H.

2014-06-01

In this study, we explore an abrupt change of Atlantic Meridional Overturning Circulation (AMOC) apparent in the historical run simulated by the second version of the Flexible Global Ocean-Atmosphere-Land System model - Spectral Version 2 (FGOALS-s2). The abrupt change is noted during the period from 1915 to 1935, in which the maximal AMOC value is weakened beyond 6 Sv (1 Sv = 106 m3 s-1). The abrupt signal first occurs at high latitudes (north of 46° N), then shifts gradually to middle latitudes (∼35° N) three to seven years later. The weakened AMOC can be explained in the following. The weak total solar irradiance (TIS) during early twentieth century decreases pole-to-equator temperature gradient in the upper stratosphere. The North polar vortex is weakened, which forces a negative North Atlantic Oscillation (NAO) phase during 1905-1914. The negative phase of NAO induces anomalous easterly winds in 50-70° N belts, which decrease the release of heat fluxes from ocean to atmosphere and induce surface warming over these regions. Through the surface ice-albedo feedback, the warming may lead to continuously melting sea ice in Baffin Bay and Davis Strait, which results in freshwater accumulation. This can lead to salinity and density reductions and then an abrupt slowdown of AMOC. Moreover, due to increased TIS after 1914, the enhanced Atlantic northward ocean heat transport from low to high latitudes induces an abrupt warming of sea surface temperature or upper ocean temperature in mid-high latitudes, which can also weaken the AMOC. The abrupt change of AMOC also appears in the PiControl run, which is associated with the lasting negative NAO phases due to natural variability.

Influence of climate cycles on grapevine domestication and ancient migrations in Eurasia.

PubMed

Mariani, Luigi; Cola, Gabriele; Maghradze, David; Failla, Osvaldo; Zavatti, Franco

2018-09-01

The objective of this work is to investigate the Holocenic climate cycles that may have influenced the domestication of grapevine in the Subcaucasian area and its subsequent spread in Eurasia. The analysis covered the longitudinal belt ranging from the Iberian Peninsula to Japan, seen as the preferential pathway for the Holocenic spread of grapevine and many other crops in Eurasia. Spectral analysis was considered as the criterion of investigation and the Holocenic cycles were analyzed considering different geochemical and biological proxies, of which seven are directly referred to vine. In this context the relation of the abovementioned proxies with spectral peaks of possible causal factors like Solar activity (SA), North Atlantic oceanic factors (Atlantic Multidecadal Oscillation - AMO and North Atlantic Oscillation - NAO), and subtropical oceanic factors (El Nino Southern Oscillation - ENSO) was also analyzed. In order to acquire a sufficiently wide number of proxies sensitive to the causal factors, we referred to a latitudinal belt wider than the one colonized by vine, also acquiring proxy from the Scandinavian area, notoriously susceptible to North Atlantic forcings. The analysis of the proxy spectral peaks, considering 20 classes with a 50-years step in the 0-1000 years range, showed that the 50% of the classes have a higher frequency of peaks at East than West, the 20% a higher frequency at West than East and the 10% an equal frequency, showing the efficiency of the propagation of Western signals towards the center of Eurasia. The search of the causal factors spectral peaks in the proxy series showed that AMO, NAO and SA acted with a certain regularity on the entire belt investigated both latitudinally and longitudinally, while spectral peaks linked to ENSO underwent a considerable attenuation moving northward. Finally, the specific analysis on viticultural proxies showed common peaks with causal factors. Copyright © 2018 Elsevier B.V. All rights reserved.

Combined Effects of the North Atlantic Oscillation and the Arctic Oscillation on Sea Surface Temperature in the Alborán Sea

PubMed Central

Báez, José C.; Gimeno, Luis; Gómez-Gesteira, Moncho; Ferri-Yáñez, Francisco; Real, Raimundo

2013-01-01

We explored the possible effects of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) on interannual sea surface temperature (SST) variations in the Alborán Sea, both separately and combined. The probability of observing mean annual SST values higher than average was related to NAO and AO values of the previous year. The effect of NAO on SST was negative, while that of AO was positive. The pure effects of NAO and AO on SST are obscuring each other, due to the positive correlation between them. When decomposing SST, NAO and AO in seasonal values, we found that variation in mean annual SST and mean winter SST was significantly related to the mean autumn NAO of the previous year, while mean summer SST was related to mean autumn AO of the previous year. The one year delay in the effect of the NAO and AO on the SST could be partially related to the amount of accumulated snow, as we found a significant correlation between the total snow in the North Alborán watershed for a year with the annual average SST of the subsequent year. A positive AO implies a colder atmosphere in the Polar Regions, which could favour occasional cold waves over the Iberian Peninsula which, when coupled with precipitations favoured by a negative NAO, may result in snow precipitation. This snow may be accumulated in the high peaks and melt down in spring-summer of the following year, which consequently increases the runoff of freshwater to the sea, which in turn causes a diminution of sea surface salinity and density, and blocks the local upwelling of colder water, resulting in a higher SST. PMID:23638005

The Use of Oceanic Indices Variations Due to Climate Change to Predict Annual Discharge Variations in Northeastern United States

NASA Astrophysics Data System (ADS)

Berton, R.; Shaw, S. B.; Chandler, D. G.; Driscoll, C. T.

2014-12-01

Climatic change affects streamflow in watersheds with winter snowpack and an annual snowmelt hydrograph. In the northeastern US, changes in streamflow are driven by both the advanced timing of snowmelt and increasing summer precipitation. Projections of climate for the region in the 21st century is for warmer winters and wetter summers. Water planners need to understand future changes in flow metrics to determine if the current water resources are capable of fulfilling future demands or adapting to future changes in climate. The study of teleconnection patterns between oceanic indices variations and hydrologic variables may help improve the understanding of future water resources conditions in a watershed. The purpose of this study is to evaluate the correlation between oceanic indices and discharge variations in the Merrimack Watershed. The Merrimack Watershed is the fourth largest basin in New England which drains much of New Hampshire and northeastern portions of Massachusetts, USA. Variations in sea surface temperature (SST) and sea level pressure (SLP) are defined by the Atlantic Multi-decadal Oscillation (AMO) and the North Atlantic Oscillation (NAO), respectively. We hypothesize that temporal changes in discharge are related to AMO and NAO variations since precipitation and discharge are highly correlated in the Merrimack. The Merrimack Watershed consists of undisturbed (reference) catchments and disturbed (developed) basins with long stream gauge records (> 100 years). Developed basins provide an opportunity to evaluate the impacts of river regulation and land development on teleconnection patterns as well as changing climate. Time series of AMO and NAO indices over the past 150 years along with Merrimack annual precipitation and discharge time series have shown a 1 to 2-year watershed hydrologic memory; higher correlation between Merrimack‎ annual precipitation and discharge with AMO and NAO are observed when a 1 to 2-year lag is given to AMO and NAO

Multidecadal Scale Detection Time for Potentially Increasing Atlantic Storm Surges in a Warming Climate

NASA Astrophysics Data System (ADS)

Lee, Benjamin Seiyon; Haran, Murali; Keller, Klaus

2017-10-01

Storm surges are key drivers of coastal flooding, which generate considerable risks. Strategies to manage these risks can hinge on the ability to (i) project the return periods of extreme storm surges and (ii) detect potential changes in their statistical properties. There are several lines of evidence linking rising global average temperatures and increasingly frequent extreme storm surges. This conclusion is, however, subject to considerable structural uncertainty. This leads to two main questions: What are projections under various plausible statistical models? How long would it take to distinguish among these plausible statistical models? We address these questions by analyzing observed and simulated storm surge data. We find that (1) there is a positive correlation between global mean temperature rise and increasing frequencies of extreme storm surges; (2) there is considerable uncertainty underlying the strength of this relationship; and (3) if the frequency of storm surges is increasing, this increase can be detected within a multidecadal timescale (≈20 years from now).

Predicting the spatiotemporal distributions of marine fish species utilizing earth system data in a maximum entropy modeling framework

NASA Astrophysics Data System (ADS)

Wang, L.; Kerr, L. A.; Bridger, E.

2016-12-01

Changes in species distributions have been widely associated with climate change. Understanding how ocean conditions influence marine fish distributions is critical for elucidating the role of climate in ecosystem change and forecasting how fish may be distributed in the future. Species distribution models (SDMs) can enable estimation of the likelihood of encountering species in space or time as a function of environmental conditions. Traditional SDMs are applied to scientific-survey data that include both presences and absences. Maximum entropy (MaxEnt) models are promising tools as they can be applied to presence-only data, such as those collected from fisheries or citizen science programs. We used MaxEnt to relate the occurrence records of marine fish species (e.g. Atlantic herring, Atlantic mackerel, and butterfish) from NOAA Northeast Fisheries Observer Program to environmental conditions. Environmental variables from earth system data, such as sea surface temperature (SST), sea bottom temperature (SBT), Chlorophyll-a, bathymetry, North Atlantic oscillation (NAO), and Atlantic multidecadal oscillation (AMO), were matched with species occurrence for MaxEnt modeling the fish distributions in Northeast Shelf area. We developed habitat suitability maps for these species, and assessed the relative influence of environmental factors on their distributions. Overall, SST and Chlorophyll-a had greatest influence on their monthly distributions, with bathymetry and SBT having moderate influence and climate indices (NAO and AMO) having little influence. Across months, Atlantic herring distribution was most related to SST 10th percentile, and Atlantic mackerel and butterfish distributions were most related to previous month SST. The fish distributions were most affected by previous month Chlorophyll-a in summer months, which may indirectly indicate the accumulative impact of primary productivity. Results highlighted the importance of spatial and temporal scales when using

Annually resolved North Atlantic marine climate over the last millennium

NASA Astrophysics Data System (ADS)

Reynolds, D. J.; Scourse, J. D.; Halloran, P. R.; Nederbragt, A. J.; Wanamaker, A. D.; Butler, P. G.; Richardson, C. A.; Heinemeier, J.; Eiríksson, J.; Knudsen, K. L.; Hall, I. R.

2016-12-01

Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ18O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ18O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000-1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.

North Tropical Atlantic Climate Variability and Model Biases

NASA Astrophysics Data System (ADS)

Yang, Y.

2017-12-01

Remote forcing from El Niño-Southern Oscillation (ENSO) and local ocean-atmosphere feedback are important for climate variability over the North Tropical Atlantic. These two factors are extracted by the ensemble mean and inter-member difference of a 10-member Pacific Ocean-Global Atmosphere (POGA) experiment, in which sea surface temperatures (SSTs) are restored to the observed anomalies over the tropical Pacific but fully coupled to the atmosphere elsewhere. POGA reasonably captures main features of observed North Tropical Atlantic variability. ENSO forced and local North Tropical Atlantic modes (NTAMs) develop with wind-evaporation-SST feedback, explaining one third and two thirds of total variance respectively. Notable biases, however, exist. The seasonality of the simulated NTAM is delayed by one month, due to the late development of the North Atlantic Oscillation (NAO) in the model. A spurious band of enhanced sea surface temperature (SST) variance (SBEV) is identified over the northern equatorial Atlantic in POGA and 14 out of 23 CMIP5 models. The SBEV is especially pronounced in boreal spring and due to the combined effect of both anomalous atmospheric thermal forcing and oceanic vertical upwelling. While the tropical North Atlantic variability is only weakly correlated with the Atlantic Zonal Mode (AZM) in observations, the SBEV in CMIP5 produces conditions that drive and intensify the AZM variability via triggering the Bjerknes feedback. This partially explains why AZM is strong in some CMIP5 models even though the equatorial cold tongue and easterly trades are biased low.

Increasing Magnitude of Hurricane Rapid Intensification in the Central and Eastern Tropical Atlantic

NASA Astrophysics Data System (ADS)

Balaguru, Karthik; Foltz, Gregory R.; Leung, L. Ruby

2018-05-01

Rapid intensification (RI) of hurricanes is notoriously difficult to predict and can contribute to severe destruction and loss of life. While past studies examined the frequency of RI occurrence, changes in RI magnitude were not considered. Here we explore changes in RI magnitude over the 30-year satellite period of 1986-2015. In the central and eastern tropical Atlantic, which includes much of the main development region, the 95th percentile of 24-hr intensity changes increased at 3.8 knots per decade. In the western tropical Atlantic, encompassing the Caribbean Sea and the Gulf of Mexico, trends are insignificant. Our analysis reveals that warming of the upper ocean coinciding with the positive phase of Atlantic Multidecadal Oscillation, and associated changes in the large-scale environment, has predominantly favored RI magnitude increases in the central and eastern tropical Atlantic. These results have substantial implications for the eastern Caribbean Islands, some of which were devastated during the 2017 hurricane season.

North Atlantic explosive cyclones and large scale atmospheric variability modes

NASA Astrophysics Data System (ADS)

Liberato, Margarida L. R.

2015-04-01

Extreme windstorms are one of the major natural catastrophes in the extratropics, one of the most costly natural hazards in Europe and are responsible for substantial economic damages and even fatalities. During the last decades Europe witnessed major damage from winter storms such as Lothar (December 1999), Kyrill (January 2007), Klaus (January 2009), Xynthia (February 2010), Gong (January 2013) and Stephanie (February 2014) which exhibited uncommon characteristics. In fact, most of these storms crossed the Atlantic in direction of Europe experiencing an explosive development at unusual lower latitudes along the edge of the dominant North Atlantic storm track and reaching Iberia with an uncommon intensity (Liberato et al., 2011; 2013; Liberato 2014). Results show that the explosive cyclogenesis process of most of these storms at such low latitudes is driven by: (i) the southerly displacement of a very strong polar jet stream; and (ii) the presence of an atmospheric river (AR), that is, by a (sub)tropical moisture export over the western and central (sub)tropical Atlantic which converges into the cyclogenesis region and then moves along with the storm towards Iberia. Previous studies have pointed to a link between the North Atlantic Oscillation (NAO) and intense European windstorms. On the other hand, the NAO exerts a decisive control on the average latitudinal location of the jet stream over the North Atlantic basin (Woollings et al. 2010). In this work the link between North Atlantic explosive cyclogenesis, atmospheric rivers and large scale atmospheric variability modes is reviewed and discussed. Liberato MLR (2014) The 19 January 2013 windstorm over the north Atlantic: Large-scale dynamics and impacts on Iberia. Weather and Climate Extremes, 5-6, 16-28. doi: 10.1016/j.wace.2014.06.002 Liberato MRL, Pinto JG, Trigo IF, Trigo RM. (2011) Klaus - an exceptional winter storm over Northern Iberia and Southern France. Weather 66:330-334. doi:10.1002/wea.755 Liberato

Multi-decadal Decline of Southeast United States Streamflow

NASA Astrophysics Data System (ADS)

Tootle, G. A.; Lakshmi, V.; Therrell, M.; Huffaker, R.; Elliott, E. A.

2017-12-01

Unprecedented population growth combined with environmental and energy demands have led to water conflict in the Southeastern United States. The states of Florida, Georgia and Alabama have recently engaged in litigation on minimum in-stream flows to maintain ecosystems, fisheries and energy demands while satisfying a growing thirst in metropolitan Atlanta. A study of Southeastern United States (Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Tennessee) streamflow identified a declining pattern of flow over the past 25 years with increased dry periods being observed in the last decade. When evaluating calendar year streamflow for (56) unimpaired streamflow stations, a robust period of streamflow in the 1970's was followed by a consistent decline in streamflow from 1990 to present. In evaluating 20-year, 10-year and 5-year time periods of annual streamflow volume, the past decade reveals historic lows for each of these periods. When evaluating the influence of high frequency (e.g., El Nino-Southern Oscillation - ENSO) and low frequency (e.g., Atlantic Multi-decadal Oscillation - AMO) climatic phenomenon, the shift of the AMO from a cold phase to a warm phase in the 1990's combined with multiple La Nina events may be associated with the streamflow decline.

Broad-scale climate influences on spring-spawning herring (Clupea harengus, L.) recruitment in the Western Baltic Sea.

PubMed

Gröger, Joachim P; Hinrichsen, Hans-Harald; Polte, Patrick

2014-01-01

Climate forcing in complex ecosystems can have profound implications for ecosystem sustainability and may thus challenge a precautionary ecosystem management. Climatic influences documented to affect various ecological functions on a global scale, may themselves be observed on quantitative or qualitative scales including regime shifts in complex marine ecosystems. This study investigates the potential climatic impact on the reproduction success of spring-spawning herring (Clupea harengus) in the Western Baltic Sea (WBSS herring). To test for climate effects on reproduction success, the regionally determined and scientifically well-documented spawning grounds of WBSS herring represent an ideal model system. Climate effects on herring reproduction were investigated using two global indices of atmospheric variability and sea surface temperature, represented by the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO), respectively, and the Baltic Sea Index (BSI) which is a regional-scale atmospheric index for the Baltic Sea. Moreover, we combined a traditional approach with modern time series analysis based on a recruitment model connecting parental population components with reproduction success. Generalized transfer functions (ARIMAX models) allowed evaluating the dynamic nature of exogenous climate processes interacting with the endogenous recruitment process. Using different model selection criteria our results reveal that in contrast to NAO and AMO, the BSI shows a significant positive but delayed signal on the annual dynamics of herring recruitment. The westward influence of the Siberian high is considered strongly suppressing the influence of the NAO in this area leading to a higher explanatory power of the BSI reflecting the atmospheric pressure regime on a North-South transect between Oslo, Norway and Szczecin, Poland. We suggest incorporating climate-induced effects into stock and risk assessments and management strategies as part

Broad-Scale Climate Influences on Spring-Spawning Herring (Clupea harengus, L.) Recruitment in the Western Baltic Sea

PubMed Central

Gröger, Joachim P.; Hinrichsen, Hans-Harald; Polte, Patrick

2014-01-01

Climate forcing in complex ecosystems can have profound implications for ecosystem sustainability and may thus challenge a precautionary ecosystem management. Climatic influences documented to affect various ecological functions on a global scale, may themselves be observed on quantitative or qualitative scales including regime shifts in complex marine ecosystems. This study investigates the potential climatic impact on the reproduction success of spring-spawning herring (Clupea harengus) in the Western Baltic Sea (WBSS herring). To test for climate effects on reproduction success, the regionally determined and scientifically well-documented spawning grounds of WBSS herring represent an ideal model system. Climate effects on herring reproduction were investigated using two global indices of atmospheric variability and sea surface temperature, represented by the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO), respectively, and the Baltic Sea Index (BSI) which is a regional-scale atmospheric index for the Baltic Sea. Moreover, we combined a traditional approach with modern time series analysis based on a recruitment model connecting parental population components with reproduction success. Generalized transfer functions (ARIMAX models) allowed evaluating the dynamic nature of exogenous climate processes interacting with the endogenous recruitment process. Using different model selection criteria our results reveal that in contrast to NAO and AMO, the BSI shows a significant positive but delayed signal on the annual dynamics of herring recruitment. The westward influence of the Siberian high is considered strongly suppressing the influence of the NAO in this area leading to a higher explanatory power of the BSI reflecting the atmospheric pressure regime on a North-South transect between Oslo, Norway and Szczecin, Poland. We suggest incorporating climate-induced effects into stock and risk assessments and management strategies as part

Disentangling the relative role of climate change on tree growth in an extreme Mediterranean environment.

PubMed

Madrigal-González, Jaime; Andivia, Enrique; Zavala, Miguel A; Stoffel, Markus; Calatayud, Joaquín; Sánchez-Salguero, Raúl; Ballesteros-Cánovas, Juan

2018-06-14

Climate change can impair ecosystem functions and services in extensive dry forests worldwide. However, attribution of climate change impacts on tree growth and forest productivity is challenging due to multiple inter-annual patterns of climatic variability associated with atmospheric and oceanic circulations. Moreover, growth responses to rising atmospheric CO 2 , namely carbon fertilization, as well as size ontogenetic changes can obscure the climate change signature as well. Here we apply Structural Equation Models (SEM) to investigate the relative role of climate change on tree growth in an extreme Mediterranean environment (i.e., extreme in terms of the combination of sandy-unconsolidated soils and climatic aridity). Specifically, we analyzed potential direct and indirect pathways by which different sources of climatic variability (i.e. warming and precipitation trends, the North Atlantic Oscillation, [NAO]; the Mediterranean Oscillation, [MOI]; the Atlantic Mediterranean Oscillation, [AMO]) affect aridity through their control on local climate (in terms of mean annual temperature and total annual precipitation), and subsequently tree productivity, in terms of basal area increments (BAI). Our results support the predominant role of Diameter at Breast Height (DHB) as the main growth driver. In terms of climate, NAO and AMO are the most important drivers of tree growth through their control of aridity (via effects of precipitation and temperature, respectively). Furthermore and contrary to current expectations, our findings also support a net positive role of climate warming on growth over the last 50 years and suggest that impacts of climate warming should be evaluated considering multi-annual and multi-decadal periods of local climate defined by atmospheric and oceanic circulation in the North Atlantic. Copyright © 2018 Elsevier B.V. All rights reserved.

North Atlantic warming and the retreat of Greenland's outlet glaciers.

PubMed

Straneo, Fiammetta; Heimbach, Patrick

2013-12-05

Mass loss from the Greenland ice sheet quadrupled over the past two decades, contributing a quarter of the observed global sea-level rise. Increased submarine melting is thought to have triggered the retreat of Greenland's outlet glaciers, which is partly responsible for the ice loss. However, the chain of events and physical processes remain elusive. Recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes, multidecadal natural ocean variability and a long-term increase in the North Atlantic's upper ocean heat content since the 1950s all contributed to a warming of the subpolar North Atlantic. This led, in conjunction with increased runoff, to enhanced submarine glacier melting. Future climate projections raise the potential for continued increases in warming and ice-mass loss, with implications for sea level and climate.

Challenging a 15-year-old claim: The North Atlantic Oscillation index as a predictor of spring migration phenology of birds.

PubMed

Haest, Birgen; Hüppop, Ommo; Bairlein, Franz

2018-04-01

Many migrant bird species that breed in the Northern Hemisphere show advancement in spring arrival dates. The North Atlantic Oscillation (NAO) index is one of the climatic variables that have been most often investigated and shown to be correlated with these changes in spring arrival. Although the NAO is often claimed to be a good predictor or even to have a marked effect on interannual changes in spring migration phenology of Northern Hemisphere breeding birds, the results on relations between spring migration phenology and NAO show a large variety, ranging from no, over weak, to a strong association. Several factors, such as geographic location, migration phase, and the NAO index time window, have been suggested to partly explain these observed differences in association. A combination of a literature meta-analysis, and a meta-analysis and sliding time window analysis of a dataset of 23 short- and long-distance migrants from the constant-effort trapping garden at Helgoland, Germany, however, paints a completely different picture. We found a statistically significant overall effect size of the NAO on spring migration phenology (coefficient = -0.14, SE = 0.054), but this on average only explains 0%-6% of the variance in spring migration phenology across all species. As such, the value and biological meaning of the NAO as a general predictor or explanatory variable for climate change effects on migration phenology of birds, seems highly questionable. We found little to no definite support for previously suggested factors, such as geographic location, migration phenology phase, or the NAO time window, to explain the heterogeneity in correlation differences. We, however, did find compelling evidence that the lack of accounting for trends in both time series has led to strongly inflated (spurious) correlations in many studies (coefficient = -0.13, SE = 0.019). © 2017 John Wiley & Sons Ltd.

The East Atlantic - West Russia Teleconnection in the North Atlantic: Climate Impact and Relation to Rossby Wave Propagation

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon

2014-01-01

Large-scale winter teleconnection of the East Atlantic - West Russia (EA-WR) over the Atlantic and surrounding regions is examined in order to quantify its impacts on temperature and precipitation and identify the physical mechanisms responsible for its existence. A rotated empirical orthogonal function (REOF) analysis of the upper-tropospheric monthly height field captures successfully the EA-WR pattern and its interannual variation, with the North Atlantic Oscillation as the first mode. EA-WRs climate impact extends from eastern North America to Eurasia. The positive (negative) EA-WR produces positive (negative) temperature anomalies over the eastern US, western Europe and Russia east of Caspian Sea, with negative (positive) anomalies over eastern Canada, eastern Europe including Ural Mountains and the Middle East. These anomalies are largely explained by lower-tropospheric temperature advections. Positive (negative) precipitation anomalies are found over the mid-latitude Atlantic and central Russia around 60E, where lower-level cyclonic (anticyclonic) circulation anomaly is dominant. The eastern Canada and the western Europe are characterized by negative (positive) precipitation anomalies.The EA-WR is found to be closely associated with Rossby wave propagation. Wave activity fluxes show that it is strongly tied to large-scale stationary waves. Furthermore, a stationary wave model (SWM) forced with vorticity transients in the mid-latitude Atlantic (approximately 40N) or diabatic heat source over the subtropical Atlantic near the Caribbean Sea produces well-organized EA-WR-like wave patterns, respectively. Sensitivity tests with the SWM indicate improvement in the simulation of the EA-WR when the mean state is modified to have a positive NAO component that enhances upper-level westerlies between 40-60N.

Multi-scale approach to Euro-Atlantic climatic cycles based on phenological time series, air temperatures and circulation indexes.

PubMed

Mariani, Luigi; Zavatti, Franco

2017-09-01

The spectral periods in North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO) and El Nino Southern Oscillation (ENSO) were analyzed and has been verified how they imprint a time series of European temperature anomalies (ETA), two European temperature time series and some phenological series (dates of cherry flowering and grapevine harvest). Such work had as reference scenario the linear causal chain MCTP (Macroscale Circulation→Temperature→Phenology of crops) that links oceanic and atmospheric circulation to surface air temperature which in its turn determines the earliness of appearance of phenological phases of plants. Results show that in the three segments of the MCTP causal chain are present cycles with the following central period in years (the % of the 12 analyzed time series interested by these cycles are in brackets): 65 (58%), 24 (58%), 20.5 (58%), 13.5 (50%), 11.5 (58%), 7.7 (75%), 5.5 (58%), 4.1 (58%), 3 (50%), 2.4 (67%). A comparison with short term spectral peaks of the four El Niño regions (nino1+2, nino3, nino3.4 and nino4) show that 10 of the 12 series are imprinted by periods around 2.3-2.4yr while 50-58% of the series are imprinted by El Niño periods of 4-4.2, 3.8-3.9, 3-3.1years. The analysis highlights the links among physical and biological variables of the climate system at scales that range from macro to microscale whose knowledge is crucial to reach a suitable understanding of the ecosystem behavior. The spectral analysis was also applied to a time series of spring - summer precipitation in order to evaluate the presence of peaks common with other 12 selected series with result substantially negative which brings us to rule out the existence of a linear causal chain MCPP (Macroscale Circulation→Precipitation→Phenology). Copyright © 2017 Elsevier B.V. All rights reserved.

Differential modulation of eastern oyster ( Crassostrea virginica) disease parasites by the El-Niño-Southern Oscillation and the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Soniat, Thomas M.; Hofmann, Eileen E.; Klinck, John M.; Powell, Eric N.

2009-02-01

The eastern oyster ( Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time-frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico

Climate and ecosystem linkages explain widespread declines in North American Atlantic salmon populations.

PubMed

Mills, Katherine E; Pershing, Andrew J; Sheehan, Timothy F; Mountain, David

2013-10-01

North American Atlantic salmon (Salmo salar) populations experienced substantial declines in the early 1990s, and many populations have persisted at low abundances in recent years. Abundance and productivity declined in a coherent manner across major regions of North America, and this coherence points toward a potential shift in marine survivorship, rather than local, river-specific factors. The major declines in Atlantic salmon populations occurred against a backdrop of physical and biological shifts in Northwest Atlantic ecosystems. Analyses of changes in climate, physical, and lower trophic level biological factors provide substantial evidence that climate conditions directly and indirectly influence the abundance and productivity of North American Atlantic salmon populations. A major decline in salmon abundance after 1990 was preceded by a series of changes across multiple levels of the ecosystem, and a subsequent population change in 1997, primarily related to salmon productivity, followed an unusually low NAO event. Pairwise correlations further demonstrate that climate and physical conditions are associated with changes in plankton communities and prey availability, which are ultimately linked to Atlantic salmon populations. Results suggest that poor trophic conditions, likely due to climate-driven environmental factors, and warmer ocean temperatures throughout their marine habitat area are constraining the productivity and recovery of North American Atlantic salmon populations. © 2013 John Wiley & Sons Ltd.

Characterization of Bacillus subtilis strains in Thua nao, a traditional fermented soybean food in northern Thailand.

PubMed

Inatsu, Y; Nakamura, N; Yuriko, Y; Fushimi, T; Watanasiritum, L; Kawamoto, S

2006-09-01

To clarify the diversity of Bacillus subtilis strains in Thua nao that produce high concentrations of products useful in food manufacturing and in health-promoting compounds. Production of amylase, protease, subtilisin NAT (nattokinase), and gamma-polyglutamic acid (PGA) by the Bacillus subtilis strains in Thua nao was measured. Productivity of protease NAT by these strains tended to be higher than by Japanese commercial natto-producing strains. Molecular diversity of isolated strains was analysed via randomly amplified polymorphic DNA-PCR fingerprinting. The strains were divided into 19 types, including a type with the same pattern as a Japanese natto-producing strain. B. subtilis strains that could be a resource for effective production of protease, amylase, subtilisin NAT, or PGA were evident in Thua nao produced in various regions in northern Thailand. This study clearly demonstrated the value of Thua nao as a potential resource of food-processing enzymes and health-promoting compounds.

Linking the South Atlantic Meridional Overturning Circulation and the Global Monsoons

NASA Astrophysics Data System (ADS)

Lopez, H.; Dong, S.; Goni, G. J.; Lee, S. K.

2016-02-01

This study tested the hypothesis whether low frequency decadal variability of the South Atlantic meridional heat transport (SAMHT) influences decadal variability of the global monsoons. A multi-century run from a state-of-the-art coupled general circulation model is used as basis for the analysis. Our findings indicate that multi-decadal variability of the South Atlantic Ocean plays a key role in modulating atmospheric circulation via interhemispheric changes in Atlantic Ocean heat content. Weaker SAMHT produces anomalous ocean heat divergence over the South Atlantic resulting in negative ocean heat content anomaly about 15 years later. This, in turn, forces a thermally direct anomalous interhemispheric Hadley circulation in the atmosphere, transporting heat from the northern hemisphere (NH) to the southern hemisphere (SH) and moisture from the SH to the NH, thereby intensify (weaken) summer (winter) monsoon in the NH and winter (summer) monsoon in the SH. Results also show that anomalous atmospheric eddies, both transient and stationary, transport heat northward in both hemispheres producing eddy heat flux convergence (divergence) in the NH (SH) around 15-30°, reinforcing the anomalous Hadley circulation. Overall, SAMHT decadal variability leads its atmospheric response by about 15 years, suggesting that the South Atlantic is a potential predictor of global climate variability.

The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using Sr/Ca Ratios in Diploria labyrinthiformis (brain coral)

NASA Astrophysics Data System (ADS)

Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.

2006-12-01

The North Atlantic Oscillation (NAO) is a meridional oscillation in atmospheric mass measured by pressure anomalies between Iceland (65°N, 23°W) and the Azores (38°N, 26°W) (Hurrell, 1995). Changes between the positive and negative phase of the NAO strongly influence weather patterns across the US, Europe and the Middle East. A shift in recent decades toward a sustained positive NAO has raised questions about the influence of greenhouse gas emissions on this system. Unfortunately, instrumental records are too short to identify the natural baseline variability of the NAO, and NAO reconstructions generally encompass only land-based proxies, excluding ocean processes. Winter-time sea surface temperatures (SST) in the Sargasso Sea have previously been shown to correlate to the NAO (Visbeck et al., 2001), and thus a long winter SST record based on proxy data could be used to reconstruct NAO variability back in time. Here we present an annually resolved winter-time strontium to calcium ratio (Sr/Ca) record from a 220-year old brain coral (Diploria labyrinthiformis) collected from the south shore of Bermuda. Brain coral is prevalent in Bermuda and shows distinct annual banding in its skeleton providing precise age models. Winter-time coral Sr/Ca has previously been shown to accurately record winter SST free from growth rate influences (Goodkin et al., 2005), and that relationship is confirmed here. Cross-spectral analysis between winter-time coral Sr/Ca and four instrumental and proxy records of the NAO (Hurrell, 1995, Jones et al., 1997, Luterbacher et al., 2001, Cook et al., 2002) show two frequencies of coherence with >95% confidence. At periods greater than 20 years and between 3 and 5 years, the coral Sr/Ca effectively captures the NAO variability. Filtering the coral record to these frequencies and comparing to the instrumental and proxy records, including another marine-based NAO reconstruction from the North and Norwegian Seas (Schoene et al., 2003), show

Past and future impact of North Atlantic teleconnection patterns on the hydroclimate of the Caspian catchment area in CESM1.2.2 and observations

NASA Astrophysics Data System (ADS)

Nandini, Sri

2017-04-01

The Caspian Sea level has undergone dramatic variations of more than 3 m during the past century with important implications for the life of coastal people, economy and the ecosystem. The origin of these variations as well as future changes in the Caspian water budget are still a matter of debate. In this study, we examine the influence of the major seasonal North Atlantic teleconnection patterns, the North Atlantic Oscillation (NAO), the East Atlantic pattern (EA), the Scandinavian pattern (SCA), and the North Sea Caspian Pattern (NCP), on Caspian hydroclimate variability from 1850-2000 CE. Numerical experiments at different atmospheric grid resolutions (2° and 1°) are carried out with the coupled Community Earth System Model (CESM1.2.2). We test model skills under different resolutions through validation against observational data by various statistical methods (Empirical Orthogonal Functions, Taylor diagrams, linear regressions and Spearman rank correlation). Results reveal the strongest simulated signal in winter (DJF) with high explained variances for 1° CESM1.2.2 NAO (39%) and EA (15.7%), similar to observational data. The model is unable to reproduce the SCA pattern in the third EOF, which is found in the observations. The modelled NAO has a strong influence on winter temperature and rainfall over the Caspian catchment area. A strong winter NCP induces above-average 2-meter temperatures over north Caspian region and lower-than-normal precipitation over the eastern Caspian sea. Our study suggests that the 1° version of CESM1.2.2 (with CAM5 atmosphere physics) shows adequate performance with respect to teleconnection maps during the historical period. Lastly, 1° model climate projections (2005-2100 CE) are performed with different Representative Concentration Pathways (RCP 4.5 and RCP 8.5) to examine potential changes in the teleconnection patterns and their influence on the Caspian region.

The roles of static stability and tropical-extratropical interactions in the summer interannual variability of the North Atlantic sector

NASA Astrophysics Data System (ADS)

Mbengue, Cheikh Oumar; Woollings, Tim; Dacre, Helen F.; Hodges, Kevin I.

2018-04-01

Summer seasonal forecast skill in the North Atlantic sector is lower than winter skill. To identify potential controls on predictability, the sensitivity of North Atlantic baroclinicity to atmospheric drivers is quantified. Using ERA-INTERIM reanalysis data, North Atlantic storm-track baroclinicity is shown to be less sensitive to meridional temperature-gradient variability in summer. Static stability shapes the sector's interannual variability by modulating the sensitivity of baroclinicity to variations in meridional temperature gradients and tropopause height and by modifying the baroclinicity itself. High static stability anomalies at upper levels result in more zonal extratropical cyclone tracks and higher eddy kinetic energy over the British Isles in the summertime. These static stability anomalies are not strongly related to the summer NAO; but they are correlated with the suppression of convection over the tropical Atlantic and with a poleward-shifted subtropical jet. These results suggest a non-local driver of North Atlantic variability. Furthermore, they imply that improved representations of convection over the south-eastern part of North America and the tropical Atlantic might improve summer seasonal forecast skill.

Advancing decadal-scale climate prediction in the North Atlantic sector.

PubMed

Keenlyside, N S; Latif, M; Jungclaus, J; Kornblueh, L; Roeckner, E

2008-05-01

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa. Although these multidecadal variations are potentially predictable if the current state of the ocean is known, the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions. Here we apply a simple approach-that uses only sea surface temperature (SST) observations-to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.

Understanding the North Atlantic Oscillation and Its Effects in the Mediterranean

NASA Astrophysics Data System (ADS)

Trigo, Ricardo M.; Serrano, Sergio M. Vicente

2010-11-01

ESF-MedCLIVAR Workshop on Hydrological, Socioeconomic and Ecological Impacts of the North Atlantic Oscillation in the Mediterranean; Zaragoza, Spain, 24-27 May 2010; According to the latest Intergovernmental Panel on Climate Change report, the Mediterranean basin represents one of the most important hot spots of climate change in the world, with recent trends toward a hotter and drier climate being related to changes in atmospheric circulation patterns. Among these patterns the North Atlantic Oscillation (NAO) is the most important one and the only one that exerts a clear influence throughout the year, although with stronger intensity and extension during winter. In the framework of the European Science Foundation's Mediterranean Climate Variability and Predictability (MedCLIVAR) program (http://www.medclivar.eu/), a thematic workshop devoted to the hydrological, socioeconomic, and ecological impacts of the NAO in the Mediterranean area was held in Spain. The main objective of this 3-day workshop was to foster interaction in this increasingly interdisciplinary topic, in particular, among climatologists, hydrologists, geographers, agronomists, biologists, and other scientists. The workshop was attended by 62 participants from 15 different countries and included a mix of senior scientists and graduate students. The workshop was divided into five sessions focusing on (1) natural hazards, including droughts, severe precipitations, floods, heat waves, and cold spells; (2) vegetation activity and agriculture production; (3) natural ecosystems and environment, including forest dynamics, fisheries, dynamics of animal populations, and air quality; (4) geomorphology, including landslides and debris flows, erosivity mechanisms, and surface erosion processes; and (5) renewable energies production, including hydraulic, eolic, and solar.

Influence of the North Atlantic dipole on climate changes over Eurasia

NASA Astrophysics Data System (ADS)

Serykh, I. V.

2016-11-01

In this paper, some hydrophysical and meteorological characteristics of negative (1948-1976 and 1999-2015) and positive (1977-1998) phases of the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO) in the North Atlantic and Eurasia are constructed and investigated. Specifically, the near-surface temperature, sea-level atmospheric pressure, wind speed, heat content of the upper 700 m ocean layer, water temperature and salinity at various depths, the latent and sensible heat fluxes from the ocean to the atmosphere are analyzed. The fields obtained are in good agreement and complement each other. This gives important information about the hydrometeorological conditions in the region under study. Analysis of these data has shown that in the upper 1000 m North Atlantic layer there is a thermal dipole which can be interpreted as an oceanic analog of the atmospheric North Atlantic Oscillation (NAO). An index of the North Atlantic Dipole (NAD) as the difference between the mean heat contents in the upper 700 m oceanic layer between the regions (50°-70° N; 60°-10° W) and (20°-40° N; 80°-30° W) is proposed. A possible physical mechanism of the internal oscillations with a quasi-60-year period in the North Atlantics- Eurasia system of ocean-atmosphere interactions is discussed.

Intraseasonal to Interannual Variability of the Atlantic Meridional Overturning Circulation from Eddy-resolving Simulations and Observations

DTIC Science & Technology

2014-07-01

flow of warm, saline water in approximately the upper 1 km overlying a net southward flow of cold, fresh water [see Long- worth and Bryden, 2007 ...of the Arctic sea ice [Serreze et al., 2007 ] and Greenland glaciers [Holland et al., 2008; Straneo et al., 2010]. On a broader scale, fluctuations of...the AMOC are often linked to the Atlantic multidecadal oscillation [Knight et al., 2005; Delworth et al., 2007 ], the domi- nant pattern of

Using oceanic-atmospheric oscillations for long lead time streamflow forecasting

NASA Astrophysics Data System (ADS)

Kalra, Ajay; Ahmad, Sajjad

2009-03-01

We present a data-driven model, Support Vector Machine (SVM), for long lead time streamflow forecasting using oceanic-atmospheric oscillations. The SVM is based on statistical learning theory that uses a hypothesis space of linear functions based on Kernel approach and has been used to predict a quantity forward in time on the basis of training from past data. The strength of SVM lies in minimizing the empirical classification error and maximizing the geometric margin by solving inverse problem. The SVM model is applied to three gages, i.e., Cisco, Green River, and Lees Ferry in the Upper Colorado River Basin in the western United States. Annual oceanic-atmospheric indices, comprising Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), and El Nino-Southern Oscillations (ENSO) for a period of 1906-2001 are used to generate annual streamflow volumes with 3 years lead time. The SVM model is trained with 86 years of data (1906-1991) and tested with 10 years of data (1992-2001). On the basis of correlation coefficient, root means square error, and Nash Sutcliffe Efficiency Coefficient the model shows satisfactory results, and the predictions are in good agreement with measured streamflow volumes. Sensitivity analysis, performed to evaluate the effect of individual and coupled oscillations, reveals a strong signal for ENSO and NAO indices as compared to PDO and AMO indices for the long lead time streamflow forecast. Streamflow predictions from the SVM model are found to be better when compared with the predictions obtained from feedforward back propagation artificial neural network model and linear regression.

Long-Term Trends, Variability and Extremes of In Situ Sea Surface Temperature Measured Along the Eastern Adriatic Coast and its Relationship to Hemispheric Processes

NASA Astrophysics Data System (ADS)

Grbec, Branka; Matić, Frano; Beg Paklar, Gordana; Morović, Mira; Popović, Ružica; Vilibić, Ivica

2018-02-01

This paper examines long-term series of in situ sea surface temperature (SST) data measured at nine coastal and one open sea stations along the eastern Adriatic Sea for the period 1959-2015. Monthly and yearly averages were used to document SST trends and variability, while clustering and connections to hemispheric indices were achieved by applying the Principal Component Analysis (PCA) and Self-Organizing Maps (SOM) method. Both PCA and SOM revealed the dominance of temporal changes with respect to the effects of spatial differences in SST anomalies, indicating the prevalence of hemispheric processes over local dynamics, such as bora wind spatial inhomogeneity. SST extremes were connected with blocking atmospheric patterns. A substantial warming between 1979 and 2015, in total exceeding 1 °C, was preceded by a period with a negative SST trend, implying strong multidecadal variability in the Adriatic. The strongest connection was found between yearly SST and the East Atlantic (EA) pattern, while North Atlantic Oscillation (NAO) and East Atlantic/West Russia (EAWR) patterns were found to also affect February SST values. Quantification of the Adriatic SST and their connection to hemispheric indices allow for more precise projections of future SST, considered to be rather important for Adriatic thermohaline circulation, biogeochemistry and fisheries, and sensitive to ongoing climate change.

Decadal Variations in Eastern Canada's Taiga Wood Biomass Production Forced by Ocean-Atmosphere Interactions.

PubMed

Boucher, Etienne; Nicault, Antoine; Arseneault, Dominique; Bégin, Yves; Karami, Mehdi Pasha

2017-05-26

Across Eastern Canada (EC), taiga forests represent an important carbon reservoir, but the extent to which climate variability affects this ecosystem over decades remains uncertain. Here, we analyze an extensive network of black spruce (Picea mariana Mill.) ring width and wood density measurements and provide new evidence that wood biomass production is influenced by large-scale, internal ocean-atmosphere processes. We show that while black spruce wood biomass production is primarily governed by growing season temperatures, the Atlantic ocean conveys heat from the subtropics and influences the decadal persistence in taiga forests productivity. Indeed, we argue that 20-30 years periodicities in Sea Surface Temperatures (SSTs) as part of the the Atlantic Multi-decadal Oscillation (AMO) directly influence heat transfers to adjacent lands. Winter atmospheric conditions associated with the North Atlantic Oscillation (NAO) might also impact EC's taiga forests, albeit indirectly, through its effect on SSTs and sea ice conditions in surrounding seas. Our work emphasizes that taiga forests would benefit from the combined effects of a warmer atmosphere and stronger ocean-to-land heat transfers, whereas a weakening of these transfers could cancel out, for decades or longer, the positive effects of climate change on Eastern Canada's largest ecosystem.

Quantifying the impact of Teleconnections on Hydrologic Regimes in Texas

NASA Astrophysics Data System (ADS)

Bhatia, N.; Singh, V. P.; Srivastav, R. K.

2016-12-01

Climate change is being alleged to have led to the increased frequency of extreme flooding events and the resulting damages are severe, especially where the flood-plain population densities are higher. Much research in the field of hydroclimatology is focusing on improving real-time flood forecasting models. Recent studies show that, in the state of Texas, extreme regional floods are actually triggered by abruptly higher precipitation intensities. Such intensities are further driven by sea-surface temperature and pressure anomalies, defined by certain patterns of teleconnections. In this study, climate variability is defined on the basis of five major Atlantic and Pacific Ocean related teleconnections: (i) Atlantic Multidecadal Oscillation (AMO), (ii) North Atlantic Oscillation (NAO), (iii) Pacific Decadal Oscillation (PDO), (iv) Pacific North American Pattern (PNA), and (v) Southern Oscillation Index (SOI). Hydrologic extremes will be modeled using probabilistic distributions. Leave-One-Out-Test (LOOT) will be employed to address the outliers in the extremes, and to eventually obtain the robust correlation coefficient. The variation in the effect of most correlated teleconnection with respect to hydrologic attributes will be investigated for the entire state. This study will attempt to identify potential teleconnection inputs for data-driven hydrologic models under varying climatic conditions.

The Little Ice Age was 1.0-1.5 °C cooler than current warm period according to LOD and NAO

NASA Astrophysics Data System (ADS)

Mazzarella, Adriano; Scafetta, Nicola

2018-02-01

We study the yearly values of the length of day (LOD, 1623-2016) and its link to the zonal index (ZI, 1873-2003), the Northern Atlantic oscillation index (NAO, 1659-2000) and the global sea surface temperature (SST, 1850-2016). LOD is herein assumed to be mostly the result of the overall circulations occurring within the ocean-atmospheric system. We find that LOD is negatively correlated with the global SST and with both the integral function of ZI and NAO, which are labeled as IZI and INAO. A first result is that LOD must be driven by a climatic change induced by an external (e.g. solar/astronomical) forcing since internal variability alone would have likely induced a positive correlation among the same variables because of the conservation of the Earth's angular momentum. A second result is that the high correlation among the variables implies that the LOD and INAO records can be adopted as global proxies to reconstruct past climate change. Tentative global SST reconstructions since the seventeenth century suggest that around 1700, that is during the coolest period of the Little Ice Age (LIA), SST could have been about 1.0-1.5 °C cooler than the 1950-1980 period. This estimated LIA cooling is greater than what some multiproxy global climate reconstructions suggested, but it is in good agreement with other more recent climate reconstructions including those based on borehole temperature data.

Internally Generated and Externally Forced Multidecadal Oceanic Modes and their Influence on the Summer Rainfall over East Asia

NASA Astrophysics Data System (ADS)

Si, D.; Hu, A.

2017-12-01

The interdecadal oceanic variabilities can be generated from both internal and external processes, and these variabilities can significantly modulate our climate on global and regional scale, such as the warming slowdown in the early 21st century, and the rainfall in East Asia. By analyzing simulations from a unique Community Earth System Model (CESM) Large Ensemble (CESM_LE) project, we show that the Interdecadal Pacific Oscillation (IPO) is primarily an internally generated oceanic variability, while the Atlantic Multidecadal Oscillation (AMO) may be an oceanic variability generated by internal oceanic processes and modulated by external forcings in the 20th century. Although the observed relationship between IPO and the Yangtze-Huaihe River valley (YHRV) summer rainfall in China is well simulated in both the preindustrial control and 20th century ensemble, none of the 20th century ensemble members can reproduce the observed time evolution of both IPO and YHRV due to the unpredictable nature of IPO on multidecade timescale. On the other hand, although CESM_LE cannot reproduce the observed relationship between AMO and Huanghe River valley (HRV) summer rainfall of China in the preindustrial control simulation, this relationship in the 20th century simulations is well reproduced, and the chance to reproduce the observed time evolution of both AMO and HRV rainfall is about 30%, indicating the important role of the interaction between the internal processes and the external forcing to realistically simulate the AMO and HRV rainfall.

Can Arctic Sea Ice Decline Weaken the Atlantic Meridional Overturning Circulation?

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Sevellec, F.; Liu, W.

2017-12-01

The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study (detailed in Sevellec, Fedorov, Liu 2017, Nature Climate Change) we apply an optimal flux perturbation framework and comprehensive climate model simulations (using CESM) to estimate the sensitivity of the Atlantic meridional overturning circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally AMOC sensitivity to sea ice decline. We find that on decadal timescales flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC; however, on multi-decadal timescales (longer than 20 years), anomalies in the Arctic become more important. These positive buoyancy anomalies from the Arctic spread to the North Atlantic, weakening the AMOC and its poleward heat transport after several decades. Therefore, the Arctic sea ice decline may explain the suggested slow-down of the AMOC and the "Warming Hole" persisting in the subpolar North Atlantic. Further, we discuss how the proposed connection, i.e. Arctic sea ice contraction would lead to an AMOC slow-down, varies across different earth system models. Overall, this study demonstrates that Arctic sea ice decline can play an active role in ocean and climate change.

Groundwater level response to low-frequency (interannual to multidecadal) climate variability: an overview across Portugal

NASA Astrophysics Data System (ADS)

Neves, M. L.

2017-12-01

The impact of climate variability on groundwater systems is central to the successful management and sustainability of water resources. In Portugal, strong changes in the seasonal distribution of precipitation, with a concentration of rainfall during the winter season and an increase in the frequency and intensity of droughts, in conjunction with warming, are expected to have a profound impact on water resources. Nonetheless, there is still limited knowledge on the impact of climate variability on aquifer systems across the country. The primary goal of this study is to provide a national-scale assessment of the relative contribution of climate to the temporal and spatial variance of groundwater recharge across the four main hydrogeological units in which the country is divided. Monthly hydrological data sets spanning a common 30 year period include groundwater levels from the Portuguese National System for Water Research Information and precipitation data from both meteorological stations and ERA-Interim global atmospheric reanalysis. The links between large-scale climatic patterns, precipitation, and groundwater levels are explored using singular spectral analysis, wavelet coherence and lag correlation methods. Hydrologic time-series sampling diverse geographic regions and aquifer types have common non-stationary oscillatory components, which can be associated with the leading modes of atmospheric circulation in the western north Atlantic, namely the North Atlantic (NAO) and the Eastern Atlantic (EA) oscillations. Maps of the spatial distribution of the relative contribution of each mode of variability to the total variance of the groundwater levels illustrate which atmospheric mode impacts the most a particular aquifer. The results display the links between groundwater recharge and climate teleconnections but also emphasize the distinctive types of modulation of the climate signals among the several hydrogeological units and aquifer systems under consideration

On the Current Trend of Tropical Cyclone Activity and the Lengthening of the Tropical Cyclone Season in the North Atlantic Basin

NASA Technical Reports Server (NTRS)

Wilson, Robert M.

2013-01-01

In this TP, the trend in North Atlantic basin TC activity, especially as related to the determination of the length of season (LOS) and its possible association with warming surface-air and sea-surface temperature, is revisited. In particular, examined are: (1) the trend in TC activity for the yearly intervals 1945-1965, 1966-1994, and 1995-2012 for TCs having duration NSD greater or equal to 0.25 day, less than 2 days, greater than or equal to 2 days, greater than or equal to 4 days, and greater than or equal to 8 days; (2) the latitudinal and longitudinal genesis locations of the short-lived TC (defined herein as those TCs having duration NSD less than 2 days) for the three yearly intervals; (3) the first storm day (FSD), last storm day (LSD), and LOS based on TCs having duration NSD greater than or equal to 0.25 day and NSD greater than or equal to 2 days; (4) the relationship between FSD, LSD, and LOS for TCs having duration NSD greater than or equal to 0.25 day and NSD greater than or equal to 2 days; (5) the surface-air and sea-surface temperature, wind, and North Atlantic Oscillation (NAO) during the interval 1945-2012; (6) the relationship of FSD, LSD, and LOS against surface-air and sea-surface temperature, wind, and the NAO; (7) the relationship of TC activity against surface-air and sea-surface temperature, wind, and the NAO; and (8) the relationship of TC activity against FSD and LOS. This TP represents an update to an earlier study by Wilson concerning the length of the yearly hurricane season.

Impact of the North Atlantic Oscillation on winter precipitation totals in Slovakia

NASA Astrophysics Data System (ADS)

Leskova, Livia; Stastny, Pavel

2013-04-01

The North Atlantic Oscillation (NAO) is the most important circulation mode in the Northern Hemisphere, which impacts climate in Europe in various ways. The strongest impacts of oscillation on air temperature and precipitation regime are detected in Scandinavia and Mediterranean region, but impacts have opposite effect. Therefore, assessment of the relation between NAO and precipitation totals seems to be interesting in Slovakia, because of the country location in the centre between above mentioned regions. Our former research detected only the relation between NAO and a winter precipitation totals in Slovakia. More detailed aspects of this relation is analysed in this paper. A correlation method was used at two resolution levels, which detected opposite spatial impact of NAO on above mentioned seasonal precipitation. The first generalised level was based on the precipitation regions, which were distinguished on the base of characteristic precipitation regime of individual regions. The second level was more detailed and the correlation method was applied on data of every individual rain gauge station from the set of 202 rain gauge stations with complete data for period 1901 - 2010 in Slovakia. In the northern part of the country (Orava and Kysuce regions), there was found the positive correlation. Increase in the winter precipitation totals was recorded in the same regions and general precipitation trend in this area was similar to the trend in used Hurrell oscillation index. It means, following the increasing trend in oscillation course, we can also expect the increase in precipitation totals in these regions in the near future. In a southward direction, this correlation changed to the negative values and the most negative correlation coefficients were reached in the lowland regions (Podunajská and Východoslovenská nížina) and in the region of Juhoslovenská kotlina. This last mentioned region is located in multiple precipitation shadow of Carpathians

Interannual variability of cut-off low systems over the European sector: The role of blocking and the Northern Hemisphere circulation modes

NASA Astrophysics Data System (ADS)

Nieto, R.; Gimeno, L.; de La Torre, L.; Ribera, P.; Barriopedro, D.; García-Herrera, R.; Serrano, A.; Gordillo, A.; Redaño, A.; Lorente, J.

2007-04-01

An earlier developed multidecadal database of Northern Hemisphere cut-off low systems (COLs), covering a 41 years period (from 1958 to 1998) is used to study COLs interannual variability in the European sector (25°-47.5° N, 50° W-40° E) and the major factors controlling it. The study focus on the influence on COLs interannual variability, of larger scale phenomena such as blocking events and other main circulation modes defined over the Euro-Atlantic region. It is shown that there is a very large interannual variability in the COLs occurrence at the annual and seasonal scales, although without significant trends. The influence of larger scale phenomena is seasonal dependent, with the positive phase of the NAO favoring autumn COL development, while winter COL occurrence is mostly related to blocking events. During summer, the season when more COLs occur, no significant influences were found.

The Subpolar North Atlantic Ocean Heat Content Variability and its Decomposition.

PubMed

Zhang, Weiwei; Yan, Xiao-Hai

2017-10-23

The Subpolar North Atlantic (SPNA) is one of the most important areas to global climate because its ocean heat content (OHC) is highly correlated with the Atlantic Meridional Overturning Circulation (AMOC), and its circulation strength affects the salt transport by the AMOC, which in turn feeds and sustains the strength of the AMOC. Moreover, the recent global surface warming "hiatus" may be attributed to the SPNA as one of the major planetary heat sinks. Although almost synchronized before 1996, the OHC has greater spatial disparities afterwards, which cannot be explained as driven by the North Atlantic Oscillation (NAO). Temperature decomposition reveals that the western SPNA OHC is mainly determined by the along isopycnal changes, while in the eastern SPNA along isopycnal changes and isopycnal undulation are both important. Further analysis indicates that heat flux dominates the western SPNA OHC, but in the eastern SPNA wind forcing affects the OHC significantly. It is worth noting that the along isopycnal OHC changes can also induce heaving, thus the observed heaving domination in global oceans cannot mask the extra heat in the ocean during the recent "hiatus".

Ocean impact on decadal Atlantic climate variability revealed by sea-level observations.

PubMed

McCarthy, Gerard D; Haigh, Ivan D; Hirschi, Joël J-M; Grist, Jeremy P; Smeed, David A

2015-05-28

Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall, European summer precipitation, Atlantic hurricanes and variations in global temperatures. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres--the intergyre region. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States.

The relationship between Arctic sea ice and the Atlantic meridional overturning circulation in a warming climate

NASA Astrophysics Data System (ADS)

Liu, W.; Fedorov, A. V.

2017-12-01

A recent study (Sevellec, Fedorov, Liu 2017, Nature Climate Change) has suggested that Arctic sea ice decline can lead to a slow-down of the Atlantic meridional overturning circulation (AMOC). Here, we build on this previous work and explore the relationship between Arctic sea ice and the AMOC in climate models. We find that the current Arctic sea ice decline can contribute about 40% to the AMOC weakening over the next 60 years. This effect is related to the warming and freshening of the upper ocean in the Arctic, and the subsequent spread of generated buoyancy anomalies downstream where they affect the North Atlantic deep convection sites and hence the AMOC on multi-decadal timescales. The weakening of the AMOC and its poleward heat transport, in turn, sustains the "Warming Hole" - a region in the North Atlantic with anomalously weak (or even negative) warming trends. We discuss the key factors that control this robust AMOC response to changes in Arctic sea ice.

Long-Term Simulation of Dust Distribution with the GOCART Model: Correlation with the North Atlantic Oscillation

NASA Technical Reports Server (NTRS)

Ginoux, P.; Prospero, J.; Torres, O.; Chin, M.

2002-01-01

Global distribution of aeolian dust is simulated from 1981 to 1996 with the Goddard Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. The results are assessed with in-situ measurements and the Total Ozone Mapping Spectrometer (TOMS) aerosol products. The annual budget over the different continents and oceans are analyzed. It is found that there is a maximum of 25% difference of global annual emission from the minimum in 1996 to the maximum in 1988. There is a downward trend of dust emission over Africa and East Asia, of 6 and 2 Tg/yr, respectively. The inter-annual variability of dust distribution is analyzed over the North Atlantic and Africa. It is found that in winter most of the North Atlantic and Africa dust loading is correlated with the North Atlantic Oscillation. The GOCART model indicates that a controlling factor of such correlation can be attributed to dust emission from the Sahel. The Bodele depression is the major dust source in winter and its inter-annual variability is highly correlated with the NAO. However, it is not possible to conclude without further analysis that the North Atlantic Oscillation is forcing the inter-annual variability of dust emission and in-turn dust concentration over the North Atlantic.

North Atlantic simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II). Part II: Inter-annual to decadal variability

NASA Astrophysics Data System (ADS)

Danabasoglu, Gokhan; Yeager, Steve G.; Kim, Who M.; Behrens, Erik; Bentsen, Mats; Bi, Daohua; Biastoch, Arne; Bleck, Rainer; Böning, Claus; Bozec, Alexandra; Canuto, Vittorio M.; Cassou, Christophe; Chassignet, Eric; Coward, Andrew C.; Danilov, Sergey; Diansky, Nikolay; Drange, Helge; Farneti, Riccardo; Fernandez, Elodie; Fogli, Pier Giuseppe; Forget, Gael; Fujii, Yosuke; Griffies, Stephen M.; Gusev, Anatoly; Heimbach, Patrick; Howard, Armando; Ilicak, Mehmet; Jung, Thomas; Karspeck, Alicia R.; Kelley, Maxwell; Large, William G.; Leboissetier, Anthony; Lu, Jianhua; Madec, Gurvan; Marsland, Simon J.; Masina, Simona; Navarra, Antonio; Nurser, A. J. George; Pirani, Anna; Romanou, Anastasia; Salas y Mélia, David; Samuels, Bonita L.; Scheinert, Markus; Sidorenko, Dmitry; Sun, Shan; Treguier, Anne-Marie; Tsujino, Hiroyuki; Uotila, Petteri; Valcke, Sophie; Voldoire, Aurore; Wang, Qiang; Yashayaev, Igor

2016-01-01

Simulated inter-annual to decadal variability and trends in the North Atlantic for the 1958-2007 period from twenty global ocean - sea-ice coupled models are presented. These simulations are performed as contributions to the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II). The study is Part II of our companion paper (Danabasoglu et al., 2014) which documented the mean states in the North Atlantic from the same models. A major focus of the present study is the representation of Atlantic meridional overturning circulation (AMOC) variability in the participating models. Relationships between AMOC variability and those of some other related variables, such as subpolar mixed layer depths, the North Atlantic Oscillation (NAO), and the Labrador Sea upper-ocean hydrographic properties, are also investigated. In general, AMOC variability shows three distinct stages. During the first stage that lasts until the mid- to late-1970s, AMOC is relatively steady, remaining lower than its long-term (1958-2007) mean. Thereafter, AMOC intensifies with maximum transports achieved in the mid- to late-1990s. This enhancement is then followed by a weakening trend until the end of our integration period. This sequence of low frequency AMOC variability is consistent with previous studies. Regarding strengthening of AMOC between about the mid-1970s and the mid-1990s, our results support a previously identified variability mechanism where AMOC intensification is connected to increased deep water formation in the subpolar North Atlantic, driven by NAO-related surface fluxes. The simulations tend to show general agreement in their temporal representations of, for example, AMOC, sea surface temperature (SST), and subpolar mixed layer depth variabilities. In particular, the observed variability of the North Atlantic SSTs is captured well by all models. These findings indicate that simulated variability and trends are primarily dictated by the atmospheric datasets which

North Atlantic Simulations in Coordinated Ocean-Ice Reference Experiments Phase II (CORE-II) . Part II; Inter-Annual to Decadal Variability

NASA Technical Reports Server (NTRS)

Danabasoglu, Gokhan; Yeager, Steve G.; Kim, Who M.; Behrens, Erik; Bentsen, Mats; Bi, Daohua; Biastoch, Arne; Bleck, Rainer; Boening, Claus; Bozec, Alexandra;

Intraseasonal Characteristics Of North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Bojariu, R.; Gimeno, L..; de La Torre, L.; Nieto, R.

There is evidence of a temporal structure of regional response to the NAO variability in the cold season (e.g. NAO-related climate fluctuations reveal their strongest signal in January). To document the details of NAO intraseasonal characteristics we anal- ysed surface and upper air variables (air surface temperature, sea-ice concentration, sea surface temperature, and sea level pressure and geopotential heights at 700 hPa level) in individual months, from November to April. The data consist of 40 years of monthly reanalyses (1961-2000) extracted from the NCAR-NCEP data set. In ad- dition, snow cover data are used (monthly snow cover frequencies from the Climate Prediction Centre and number of days with snow cover from the Former Soviet Union Hydrological Snow Surveys available at the National Snow and Ice Data Centre). A NAO-related signal with predictive potential has been identified in November air surface temperature over Europe and SLP and geopotential heights over Eurasia. Neg- ative thermal anomalies over the Central Europe and positive geopotential anomalies at 700 hPa over a latitudinal belt from Arabic Peninsula to Pacific Ocean are associated with a high NAO index in the following winter. The November thermal anomalies that seem to be related to the NAO interannual persistence are also linked with the fluctu- ations of snow cover over Europe. Both tropical and high latitude influences may play a role in the onset of the November signal and in further NAO development.

New Insights into the Instability of Discharge Products in Na-O2 Batteries.

PubMed

Landa-Medrano, Imanol; Pinedo, Ricardo; Bi, Xuanxuan; Ruiz de Larramendi, Idoia; Lezama, Luis; Janek, Jürgen; Amine, Khalil; Lu, Jun; Rojo, Teófilo

2016-08-10

Sodium-oxygen batteries currently stimulate extensive research due to their high theoretical energy density and improved operational stability when compared to lithium-oxygen batteries. Cell stability, however, needs to be demonstrated also under resting conditions before future implementation of these batteries. In this work we analyze the effect of resting periods on the stability of the sodium superoxide (NaO2) discharge product. The instability of NaO2 in the cell environment is demonstrated leading to the evolution of oxygen during the resting period and the decrease of the cell efficiency. In addition, migration of the superoxide anion (O2(-)) in the electrolyte is observed and demonstrated to be an important factor affecting Coulombic efficiency.

Solar wind: A possible factor driving the interannual sea surface temperature tripolar mode over North Atlantic

NASA Astrophysics Data System (ADS)

Xiao, Ziniu; Li, Delin

2016-06-01

The effect of solar wind (SW) on the North Atlantic sea surface temperature (SST) in boreal winter is examined through an analysis of observational data during 1964-2013. The North Atlantic SSTs show a pronounced meridional tripolar pattern in response to solar wind speed (SWS) variations. This pattern is broadly similar to the leading empirical orthogonal function (EOF) mode of interannual variations in the wintertime SSTs over North Atlantic. The time series of this leading EOF mode of SST shows a significant interannual period, which is the same as that of wintertime SWS. This response also appears as a compact north-south seesaw of sea level pressure and a vertical tripolar structure of zonal wind, which simultaneously resembles the North Atlantic Oscillation (NAO) in the overlying atmosphere. As compared with the typical low SWS winters, during the typical high SWS winters, the stratospheric polar night jet (PNJ) is evidently enhanced and extends from the stratosphere to the troposphere, even down to the North Atlantic Ocean surface. Notably, the North Atlantic Ocean is an exclusive region in which the SW signal spreads downward from the stratosphere to the troposphere. Thus, it seems that the SW is a possible factor for this North Atlantic SST tripolar mode. The dynamical process of stratosphere-troposphere coupling, together with the global atmospheric electric circuit-cloud microphysical process, probably accounts for the particular downward propagation of the SW signal.

Interannual-to-multidecadal hydroclimate variability and its sectoral impacts in northeastern Argentina

NASA Astrophysics Data System (ADS)

Lovino, Miguel A.; Müller, Omar V.; Müller, Gabriela V.; Sgroi, Leandro C.; Baethgen, Walter E.

2018-06-01

This study examines the joint variability of precipitation, river streamflow and temperature over northeastern Argentina; advances the understanding of their links with global SST forcing; and discusses their impacts on water resources, agriculture and human settlements. The leading patterns of variability, and their nonlinear trends and cycles are identified by means of a principal component analysis (PCA) complemented with a singular spectrum analysis (SSA). Interannual hydroclimatic variability centers on two broad frequency bands: one of 2.5-6.5 years corresponding to El Niño Southern Oscillation (ENSO) periodicities and the second of about 9 years. The higher frequencies of the precipitation variability (2.5-4 years) favored extreme events after 2000, even during moderate extreme phases of the ENSO. Minimum temperature is correlated with ENSO with a main frequency close to 3 years. Maximum temperature time series correlate well with SST variability over the South Atlantic, Indian and Pacific oceans with a 9-year frequency. Interdecadal variability is characterized by low-frequency trends and multidecadal oscillations that have induced a transition from dryer and cooler climate to wetter and warmer decades starting in the mid-twentieth century. The Paraná River streamflow is influenced by North and South Atlantic SSTs with bidecadal periodicities. The hydroclimate variability at all timescales had significant sectoral impacts. Frequent wet events between 1970 and 2005 favored floods that affected agricultural and livestock productivity and forced population displacements. On the other hand, agricultural droughts resulted in soil moisture deficits that affected crops at critical growth stages. Hydrological droughts affected surface water resources, causing water and food scarcity and stressing the capacity for hydropower generation. Lastly, increases in minimum temperature reduced wheat and barley yields.

Intensified anticyclonic anomaly over the western North Pacific during El Niño decaying summer under a weakened Atlantic thermohaline circulation

NASA Astrophysics Data System (ADS)

Chen, Wei; Lu, Riyu; Dong, Buwen

2014-12-01

It has been well documented that there is an anticyclonic anomaly over the western North Pacific (WNPAC, hereafter) during El Niño decaying summer. This El Niño-WNPAC relationship is greatly useful for the seasonal prediction of summer climate in the WNP and East Asia. In this study, we investigate the modification of the El Niño-WNPAC relationship induced by a weakened Atlantic thermohaline circulation (THC) in a water-hosing experiment. The results suggest that the WNPAC during the El Niño decaying summer, as well as the associated precipitation anomaly over the WNP, is intensified under the weakened THC. On the one hand, this intensification is in response to the increased amplitude and frequency of El Niño events in the water-hosing experiment. On the other hand, this intensification is also because of greater climatological humidity over the western to central North Pacific under the weakened THC. We suggest that the increase of climatological humidity over the western to central North Pacific during summer under the weakened THC is favorable for enhanced interannual variability of precipitation, and therefore favorable for the intensification of the WNPAC during El Niño decaying summer. This study suggests a possible modulation of the El Niño-Southern Oscillation-WNP summer monsoon relationship by the low-frequency fluctuation of Atlantic sea surface temperature. The results offer an explanation for the observed modification of the multidecadal fluctuation of El Niño-WNPAC relationship by the Atlantic multidecadal oscillation.

Variability of Fram Strait Ice Flux and North Atlantic Oscillation

NASA Technical Reports Server (NTRS)

Kwok, Ron

1999-01-01

An important term in the mass balance of the Arctic Ocean sea ice is the ice export. We estimated the winter sea ice export through the Fram Strait using ice motion from satellite passive microwave data and ice thickness data from moored upward looking sonars. The average winter area flux over the 18-year record (1978-1996) is 670,000 square km, approximately 7% of the area of the Arctic Ocean. The winter area flux ranges from a minimum of 450,000 sq. km in 1984 to a maximum of 906,000 sq km in 1995. The daily, monthly and interannual variabilities of the ice area flux are high. There is an upward trend in the ice area flux over the 18-year record. The average winter volume flux over the winters of October 1990 through May 1995 is 1745 cubic km ranging from a low of 1375 cubic km in 1990 to a high of 2791 cubic km in 1994. The sea-level pressure gradient across the Fram Strait explains more than 80% of the variance in the ice flux over the 18-year record. We use the coefficients from the regression of the time-series of area flux versus pressure gradient across the Fram Strait and ice thickness data to estimate the summer area and volume flux. The average 12-month area flux and volume flux are 919,000 sq km and 2366 cubic km. We find a significant correlation (R =0.86) between the area flux and positive phases of the North Atlantic Oscillation (NAO) index over the months of December through March. Correlation between our six years of volume flux estimates and the NAO index gives R =0.56. During the high NAO years, a more intense Icelandic low increases the gradient in the sea-level pressure by almost 1 mbar across the Fram Strait thus increasing the atmospheric forcing on ice transport. Correlation is reduced during the negative NAO years because of decreased dominance of this large-scale atmospheric pattern on the sea-level pressure gradient across the Fram Strait. Additional information is contained in the original.

Intensified impact of tropical Atlantic SST on the western North Pacific summer climate under a weakened Atlantic thermohaline circulation

NASA Astrophysics Data System (ADS)

Chen, Wei; Lee, June-Yi; Lu, Riyu; Dong, Buwen; Ha, Kyung-Ja

2015-10-01

The tropical North Atlantic (TNA) sea surface temperature (SST) has been identified as one of regulators on the boreal summer climate over the western North Pacific (WNP), in addition to SSTs in the tropical Pacific and Indian Oceans. The major physical process proposed is that the TNA warming induces a pair of cyclonic circulation anomaly over the eastern Pacific and negative precipitation anomalies over the eastern to central tropical Pacific, which in turn lead to an anticyclonic circulation anomaly over the western to central North Pacific. This study further demonstrates that the modulation of the TNA warming to the WNP summer climate anomaly tends to be intensified under background of the weakened Atlantic thermohaline circulation (THC) by using a water-hosing experiment. The results suggest that the weakened THC induces a decrease in thermocline depth over the TNA region, resulting in the enhanced sensitivity of SST variability to wind anomalies and thus intensification of the interannual variation of TNA SST. Under the weakened THC, the atmospheric responses to the TNA warming are westward shifted, enhancing the anticyclonic circulation and negative precipitation anomaly over the WNP. This study supports the recent finding that the negative phase of the Atlantic multidecadal oscillation after the late 1960s has been favourable for the strengthening of the connection between TNA SST variability and WNP summer climate and has important implications for seasonal prediction and future projection of the WNP summer climate.

Enhanced Biennial Variability in the Pacific due to Atlantic Capacitor Effect after the Early 1990s

NASA Astrophysics Data System (ADS)

WANG, L.; Yu, J. Y.; Paek, H.

2016-12-01

The El Niño-Southern Oscillation (ENSO) and Pacific subtropical highs (PSHs) have major impacts on social and ecological systems through their influences on severe natural hazards including tropical storms, coastal erosions, droughts and floods. The ability to forecast ENSO and PSHs requires an understanding of the underlying physical mechanisms that drive their variability. Here we present an Atlantic capacitor effect mechanism to suggest the Atlantic as a key pacemaker of the biennial variability in the Pacific including ENSO and PSHs in recent decades, while the pacemaker was previously considered to be mainly lied within the Pacific or Indian Oceans. The "charging" (i.e., ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and "discharging" (i.e., the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) process works alternately, generating the biennial rhythmic changes in the Pacific. After the early-1990s, the positive phase of the Atlantic Multidecadal Oscillation and global warming provides more favorable background states over the NTA that enable the Atlantic capacitor effect to operate more efficiently, giving rise to enhanced biennial variability in the Pacific which may increase the occurrence frequency of severe natural hazard events. The results highlight the increasing important role of the Atlantic-Pacific coupling as an important pacemaker of the ENSO cycle in recent decades.

Linkages between atmospheric blocking, sea ice export through Fram Strait and the Atlantic Meridional Overturning Circulation

PubMed Central

Ionita, M.; Scholz, P.; Lohmann, G.; Dima, M.; Prange, M.

2016-01-01

As a key persistent component of the atmospheric dynamics, the North Atlantic blocking activity has been linked to extreme climatic phenomena in the European sector. It has also been linked to Atlantic multidecadal ocean variability, but its potential links to rapid oceanic changes have not been investigated. Using a global ocean-sea ice model forced with atmospheric reanalysis data, here it is shown that the 1962–1966 period of enhanced blocking activity over Greenland resulted in anomalous sea ice accumulation in the Arctic and ended with a sea ice flush from the Arctic into the North Atlantic Ocean through Fram Strait. This event induced a significant decrease of Labrador Sea water surface salinity and an abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC) during the 1970s. These results have implications for the prediction of rapid AMOC changes and indicate that an important part of the atmosphere-ocean dynamics at mid- and high latitudes requires a proper representation of the Fram Strait sea ice transport and of the synoptic scale variability such as atmospheric blocking, which is a challenge for current coupled climate models. PMID:27619955

Linkages between atmospheric blocking, sea ice export through Fram Strait and the Atlantic Meridional Overturning Circulation.

PubMed

Ionita, M; Scholz, P; Lohmann, G; Dima, M; Prange, M

2016-09-13

As a key persistent component of the atmospheric dynamics, the North Atlantic blocking activity has been linked to extreme climatic phenomena in the European sector. It has also been linked to Atlantic multidecadal ocean variability, but its potential links to rapid oceanic changes have not been investigated. Using a global ocean-sea ice model forced with atmospheric reanalysis data, here it is shown that the 1962-1966 period of enhanced blocking activity over Greenland resulted in anomalous sea ice accumulation in the Arctic and ended with a sea ice flush from the Arctic into the North Atlantic Ocean through Fram Strait. This event induced a significant decrease of Labrador Sea water surface salinity and an abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC) during the 1970s. These results have implications for the prediction of rapid AMOC changes and indicate that an important part of the atmosphere-ocean dynamics at mid- and high latitudes requires a proper representation of the Fram Strait sea ice transport and of the synoptic scale variability such as atmospheric blocking, which is a challenge for current coupled climate models.

Influence of Solar Variability on the North Atlantic / European Sector.

NASA Astrophysics Data System (ADS)

Gray, L. J.

2016-12-01

The 11year solar cycle signal in December-January-February averaged mean-sea-level pressure and Atlantic/European blocking frequency is examined using multilinear regression with indices to represent variability associated with the solar cycle, volcanic eruptions, the El Nino - Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). Results from a previous 11-year solar cycle signal study of the period 1870-2010 (140 years; 13 solar cycles) that suggested a 3-4 year lagged signal in SLP over the Atlantic are confirmed by analysis of a much longer reconstructed dataset for the period 1660-2010 (350 years; 32 solar cycles). Apparent discrepancies between earlier studies are resolved and stem primarily from the lagged nature of the response and differences between early- and late-winter responses. Analysis of the separate winter months provide supporting evidence for two mechanisms of influence, one operating via the atmosphere that maximises in late winter at 0-2 year lags and one via the mixd-layer ocean that maximises in early winter at 3-4 year lags. Corresponding analysis of DJF-averaged Atlantic / European blocking frequency shows a highly statistically significant signal at 1-year lag that originates promarily from the late winter response. The 11-year solar signal in DJF blocking frequency is compared with other known influences from ENSO and the AMO and found to be as large in amplitude and have a larger region of statistical significance.

Emerging European winter precipitation pattern linked to atmospheric circulation changes over the North Atlantic region in recent decades

NASA Astrophysics Data System (ADS)

Ummenhofer, Caroline C.; Seo, Hyodae; Kwon, Young-Oh; Parfitt, Rhys; Brands, Swen; Joyce, Terrence M.

2017-08-01

Dominant European winter precipitation patterns over the past century, along with their associated extratropical North Atlantic circulation changes, are evaluated using cluster analysis. Contrary to the four regimes traditionally identified based on daily wintertime atmospheric circulation patterns, five distinct seasonal precipitation regimes are detected here. Recurrent precipitation patterns in each regime are linked to changes in atmospheric blocking, storm track, and sea surface temperatures across the North Atlantic region. Multidecadal variability in the frequency of the precipitation patterns reveals more (fewer) winters with wet conditions in northern (southern) Europe in recent decades and an emerging distinct pattern of enhanced wintertime precipitation over the northern British Isles. This pattern has become unusually common since the 1980s and is associated with changes in moisture transport and more frequent atmospheric river events. The observed precipitation changes post-1950 coincide with changes in storm track activity over the central/eastern North Atlantic toward the northern British Isles.

Radio Meteors Observations Techniques at RI NAO

NASA Astrophysics Data System (ADS)

Vovk, Vasyl; Kaliuzhnyi, Mykola

2016-07-01

The Solar system is inhabited with large number of celestial bodies. Some of them are well studied, such as planets and vast majority of big asteroids and comets. There is one group of objects which has received little attention. That is meteoroids with related to them meteors. Nowadays enough low-technology high-efficiency radio-technical solutions are appeared which allow to observe meteors daily. At RI NAO three methodologies for meteor observation are developed: single-station method using FM-receiver, correlation method using FM-receiver and Internet resources, and single-station method using low-cost SDR-receiver.

High-Capacity Sodium Peroxide Based NaO 2 Batteries with Low Charge Overpotential via a Nanostructured Catalytic Cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Lu; Zhang, Dongzhou; Lei, Yu

The superoxide based Na-O-2 battery has circumvented the issue of large charge overpotential in Li-O-2 batteries; however, the one-electron process leads to limited capacity. Herein, a sodium peroxide based low-overpotential (similar to 0.5 V) Na-O-2 battery with a capacity as high as 7.5 mAh/cm(2) is developed with Pd nanoparticles as catalysts on the cathode.

Pharmacokinetics and efficiency of brain targeting of ginsenosides Rg1 and Rb1 given as Nao-Qing microemulsion.

PubMed

Li, Tao; Shu, Ya-Jun; Cheng, Jia-Yin; Liang, Run-Cheng; Dian, Shao-Na; Lv, Xiao-Xun; Yang, Meng-Qi; Huang, Shu-Ling; Chen, Gang; Yang, Fan

2015-02-01

Nao-Qing solution has been shown to be clinically effective in the treatment of acute ischemic stroke (AIS). The purpose of this study was to improve the pharmacokinetics and brain uptake of Nao-Qing, administered as an oil-in-water microemulsion. Sprague-Dawley (SD) rats were given Nao-Qing microemulsion by intranasal or intragastric routes. Samples of blood, brain, heart, liver, lung and kidney were collected at pre-determined time intervals, and the contents of ginsenosides Rg1 and Rb1 (active ingredients of the Nao-Qing microemulsion) were analyzed by high-performance liquid chromatography (HPLC). The results showed that contents of ginsenosides Rg1 and Rb1 in Nao-Qing microemulsion was 8475.13 ± 54.61 μg/ml and 6633.42 ± 527.27 μg/ml, respectively, and that the particle size, pH and viscosity of the microemulsion were 19.9 ± 5.07 nm, 6.1 and 3.056 × 10(-3 )Pas, respectively. Absorption of ginsenoside Rg1 was higher than that of ginsenoside Rb1, which was barely detectable after intragastric administration; furthermore, the concentration of ginsenoside Rg1 in blood and other tissues at each time point was lower for intragastric than for intranasal administration. Compared with intragastric administration, intranasal administration resulted in a shorter tmax (0.08 versus 1 h), a higher Cmax (16.65 versus 11.29 μg/ml), and a higher area under the concentration-time curve (AUC) (592.91 versus 101.70 μgċh/ml) in the brain. The relative rates of uptake (Re) and the ratio of peak concentration (Ce) in the brain were 126.31% and 147.48% for ginsenoside Rg1, respectively. These data illustrate that intranasal administration can promote the absorption of drugs in Nao-Qing microemulsion and achieve fast effect.

Evidence for multidecadal variability in US extreme sea level records

NASA Astrophysics Data System (ADS)

Wahl, Thomas; Chambers, Don P.

2015-03-01

We analyze a set of 20 tide gauge records covering the contiguous United States (US) coastline and the period from 1929 to 2013 to identify long-term trends and multidecadal variations in extreme sea levels (ESLs) relative to changes in mean sea level (MSL). Different data sampling and analysis techniques are applied to test the robustness of the results against the selected methodology. Significant but small long-term trends in ESLs above/below MSL are found at individual sites along most coastline stretches, but are mostly confined to the southeast coast and the winter season when storm surges are primarily driven by extratropical cyclones. We identify six regions with broadly coherent and considerable multidecadal ESL variations unrelated to MSL changes. Using a quasi-nonstationary extreme value analysis, we show that the latter would have caused variations in design relevant return water levels (50-200 year return periods) ranging from ˜10 cm to as much as 110 cm across the six regions. The results raise questions as to the applicability of the "MSL offset method," assuming that ESL changes are primarily driven by changes in MSL without allowing for distinct long-term trends or low-frequency variations. Identifying the coherent multidecadal ESL variability is crucial in order to understand the physical driving factors. Ultimately, this information must be included into coastal design and adaptation processes.

Increasing magnitude of Hurricane Rapid Intensification in the central-eastern Atlantic over the past 30 years

NASA Astrophysics Data System (ADS)

Leung, L. R.; Balaguru, K.; Foltz, G. R.

2017-12-01

During the 2017 Atlantic hurricane season, several hurricanes underwent rapid intensification (RI) in the central-eastern Atlantic. This motivates an analysis of trends in the strength of hurricane RI during the 30-year post-satellite period of 1986-2015. Our results show that in the eastern tropical Atlantic, to the east of 60W, the mean RI magnitude averaged during 2001-2015 was 3.8 kt per 24 hr higher than during 1986-2000. However, in the western tropical Atlantic, to the west of 60W, changes in RI magnitude over the same period were not statistically significant. We examined the large-scale environment to understand the causes behind these changes in RI magnitude and found that various oceanic and atmospheric parameters that play an important role in RI changed favorably in the eastern tropical Atlantic. More specifically, changes in SST, Potential Intensity, upper-ocean heat content, wind shear, relative humidity and upper-level divergence enhanced the ability for hurricanes to undergo RI in the eastern tropical Atlantic. In contrast, changes in the same factors are inconsistent in the western tropical Atlantic. While changes in SST and Potential Intensity were positive, changes in upper-ocean heat content, wind shear and upper-level divergence were either insignificant or unfavorable for RI. Finally, we examined the potential role of various climate phenomena, which are well-known to impact Atlantic hurricane activity, in causing the changes in the large-scale environment. Our analysis reveals that changes in the Atlantic Multidecadal Oscillation over the 30-year period are predominantly responsible. These results provide important aspects of the large-scale context to understand the Atlantic hurricane season of 2017.

Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America.

PubMed

Kitzberger, Thomas; Brown, Peter M; Heyerdahl, Emily K; Swetnam, Thomas W; Veblen, Thomas T

2007-01-09

Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies reconstructed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subcontinental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those regions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades.

Tropical rainforests dominate multi-decadal variability of the global carbon cycle

NASA Astrophysics Data System (ADS)

Zhang, X.; Wang, Y. P.; Peng, S.; Rayner, P. J.; Silver, J.; Ciais, P.; Piao, S.; Zhu, Z.; Lu, X.; Zheng, X.

2017-12-01

Recent studies find that inter-annual variability of global atmosphere-to-land CO2 uptake (NBP) is dominated by semi-arid ecosystems. However, the NBP variations at decadal to multi-decadal timescales are still not known. By developing a basic theory for the role of net primary production (NPP) and heterotrophic respiration (Rh) on NBP and applying it to 100-year simulations of terrestrial ecosystem models forced by observational climate, we find that tropical rainforests dominate the multi-decadal variability of global NBP (48%) rather than the semi-arid lands (35%). The NBP variation at inter-annual timescales is almost 90% contributed by NPP, but across longer timescales is progressively controlled by Rh that constitutes the response from the NPP-derived soil carbon input (40%) and the response of soil carbon turnover rates to climate variability (60%). The NBP variations of tropical rainforests is modulated by the ENSO and the PDO through their significant influences on temperature and precipitation at timescales of 2.5-7 and 25-50 years, respectively. This study highlights the importance of tropical rainforests on the multi-decadal variability of global carbon cycle, suggesting that we need to carefully differentiate the effect of NBP long-term fluctuations associated with ocean-related climate modes on the long-term trend in land sink.

Multidecadal climate variability in Brazil's Nordeste during the last 3000 years based on speleothem isotope records

NASA Astrophysics Data System (ADS)

Novello, Valdir F.; Cruz, Francisco W.; Karmann, Ivo; Burns, Stephen J.; Stríkis, Nicolás M.; Vuille, Mathias; Cheng, Hai; Lawrence Edwards, R.; Santos, Roberto V.; Frigo, Everton; Barreto, Eline A. S.

2012-12-01

We present the first high resolution, approximately ∼4 years sample spacing, precipitation record from northeastern Brazil (hereafter referred to as ‘Nordeste’) covering the last ∼3000 yrs from 230Th-dated stalagmites oxygen isotope records. Our record shows abrupt fluctuations in rainfall tied to variations in the intensity of the South American summer monsoon (SASM), including the periods corresponding to the Little Ice Age (LIA), the Medieval Climate Anomaly (MCA) and an event around 2800 yr B.P. Unlike other monsoon records in southern tropical South America, dry conditions prevailed during the LIA in the Nordeste. Our record suggests that the region is currently undergoing drought conditions that are unprecedented over the past 3 millennia, rivaled only by the LIA period. Using spectral, wavelet and cross-wavelet analyses we show that changes in SASM activity in the region are mainly associated with variations of the Atlantic Multidecadal Oscillation (AMO) and to a lesser degree caused by fluctuations in tropical Pacific SST. Our record also shows a distinct periodicity around 210 years, which has been linked to solar variability.

Harvesting Atlantic Cod under Climate Variability

NASA Astrophysics Data System (ADS)

Oremus, K. L.

2016-12-01

Previous literature links the growth of a fishery to climate variability. This study uses an age-structured bioeconomic model to compare optimal harvest in the Gulf of Maine Atlantic cod fishery under a variable climate versus a static climate. The optimal harvest path depends on the relationship between fishery growth and the interest rate, with higher interest rates dictating greater harvests now at the cost of long-term stock sustainability. Given the time horizon of a single generation of fishermen under assumptions of a static climate, the model finds that the economically optimal management strategy is to harvest the entire stock in the short term and allow the fishery to collapse. However, if the biological growth of the fishery is assumed to vary with climate conditions, such as the North Atlantic Oscillation, there will always be pulses of high growth in the stock. During some of these high-growth years, the growth of the stock and its economic yield can exceed the growth rate of the economy even under high interest rates. This implies that it is not economically optimal to exhaust the New England cod fishery if NAO is included in the biological growth function. This finding may have theoretical implications for the management of other renewable yet exhaustible resources whose growth rates are subject to climate variability.

Multi-decadal Variability of the Indian Monsoon Rainfall for the last 14 kyr

NASA Astrophysics Data System (ADS)

Panmei, C.; Pothuri, D.

2017-12-01

Precise reconstruction of Indian monsoon fluctuation events and variability trends over the last 14 kyr has great implications for understanding the dynamics and possible forcing/feedback mechanisms associated with it. We have carried out high-resolution Indian monsoon variability studies of multi-decadal to sub-centennial timescales for the past 14 kyr through oxygen isotopes and Mg/Ca-derived sea surface temperatures (SST) from a western Bay of Bengal sediment core MD 161/17, using planktonic foraminifera Globigerinoides ruber. Indian summer monsoon (ISM) intensity was low during the Younger Dryas (YD) as evidenced by enriched δ18Osw coincides with a striking warming of 1.5°C. We observed ISM intensification from 12-9 kyr, followed by a milder period from 9-7.2 kyr. ISM gradually weakened from 7.2-2.5 kyr, after which there were two very prominent shifts in both ISM and SST; abrupt decrease at 2.4 kyr and increase at 1.4 kyr for ISM, while SST exhibited opposite trend. The contrasting trend continued from 1.4 kyr to the present wherein ISM precipitation has been decreasing and SST has been increasing. In addition, spectral analysis was done using Redfit and the ISM precipitation records reveal statistically significant periodicities at 2118, 411, 344, 144, 101 and 90 yrs. Furthermore, we compared our results with other existing records from the Northern Indian Ocean and adjacent regions, and found that the records share similarities suggesting regional dynamics being expressed coherently. Our results suggest that ISM precipitation and warming/cooling of the Northern Indian Ocean is directly associated with the southward/northward shift of the Intertropical Convergence Zone, which in turn is influenced by Atlantic Meridional Overturning Circulation, North Atlantic climate, and solar insolation interplaying differently at different timescales.

Holocene Multi-Decadal to Millennial-Scale Hydrologic Variability on the South American Altiplano

NASA Astrophysics Data System (ADS)

Fritz, S. C.; Baker, P. A.; Ekdahl, E.; Burns, S.

2006-12-01

On orbital timescales, lacustrine sediment records in the tropical central Andes show massive changes in lake level due to mechanisms related to global-scale drivers, varying at precessional timescales. Here we use stable isotopic and diatom records from two lakes in the Lake Titicaca drainage basin to reconstruct multi- decadal to millennial scale precipitation variability during the last 7000 to 8000 years. The records are tightly coupled at multi-decadal to millennial scales with each other and with lake-level fluctuations in Lake Titicaca, indicating that the lakes are recording a regional climate signal. A quantitative reconstruction of precipitation from stable isotopic data indicates that the central Andes underwent significant wet to dry alternations at multi- centennial frequencies with an amplitude of 30 to 40% of total precipitation. A strong millennial-scale component, similar in duration to periods of increased ice rafted debris flux in the North Atlantic, is observed in both lake records, suggesting that tropical North Atlantic sea-surface temperature (SST) variability may partly control regional precipitation. No clear relationship is evident between these records and the inferred ENSO history from Lago Pallcacocha in the northern tropical Andes. In the instrumental period, regional precipitation variability on inter-annual timescales is clearly influenced by Pacific modes; for example, most El Ninos produce dry and warm conditions in this part of the central Andes. However, on longer timescales, the control of tropical Pacific modes is less clear. Our reconstructions suggest that the cold intervals of the Holocene Bond events are periods of increased precipitation in the central Andes, thus indicating an anti-phasing of precipitation variation in the southern tropics of South America relative to the Northern Hemisphere monsoon region.

Natural and anthropogenic forcing of North Atlantic tropical cyclone track position since 1550 A.D.

NASA Astrophysics Data System (ADS)

Baldini, Lisa; Baldini, James; McElwaine, Jim; Frappier, Amy; Asmerom, Yemane; Liu, Kam-biu; Prufer, Keith; Ridley, Harriet; Polyak, Victor; Kennett, Douglas; Macpherson, Colin; Aquino, Valorie; Awe, Jamie; Breitenbach, Sebastian

2016-04-01

Over the last 30 years, North Atlantic tropical cyclones (TC) have increased in frequency, intensity, and duration in response to rising North Atlantic sea surface temperatures (SST). Here we present a 450-year record of western Caribbean TC activity reconstructed using subannually-resolved carbon and oxygen isotope ratios in a stalagmite from Yok Balum Cave, southern Belize. Western Caribbean TC activity peaked at 1650 A.D. coincident with maximum Little Ice Age cooling and decreased gradually to 1983 A.D. (the end of the record). Comparison with existing basin-wide reconstructions reveals that the dominant TC tracks corridor migrated from the western Caribbean toward the North American east coast through time. A close link with Atlantic Multidecadal Oscillation (AMO) exists throughout the record but with a clear polarity shift in the TC-AMO relationship at 1870 A.D., coincident with industrialisation. We suggest that the cause of this reversal is Greenhouse gas and aerosol emission induced changes in the relationship between the Intertropical Convergence Zone and the Bermuda High between the modern warm period and the Pre-Industrial Era. The likely impact of continued anthropogenic forcing of TC track on population centres of the western North Atlantic and Caribbean will be addressed.

Intraseasonal variability of winter precipitation over central asia and the western tibetan plateau from 1979 to 2013 and its relationship with the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Liu, Heng; Liu, Xiaodong; Dong, Buwen

2017-09-01

Winter precipitation over Central Asia and the western Tibetan Plateau (CAWTP) is mainly a result of the interaction between the westerly circulation and the high mountains around the plateau. Empirical Orthogonal Functions (EOFs), Singular Value Decomposition (SVD), linear regression and composite analysis were used to analyze winter daily precipitation and other meteorological elements in this region from 1979 to 2013, in order to understand how interactions between the regional circulation and topography affect the intraseasonal variability in precipitation. The SVD analysis shows that the winter daily precipitation variability distribution is characterized by a dipole pattern with opposite signs over the northern Pamir Plateau and over the Karakoram Himalaya, similar to the second mode of EOF analysis. This dipole pattern of precipitation anomaly is associated with local anomalies in both the 700 hPa moisture transport and the 500 hPa geopotential height and is probably caused by oscillations in the regional and large-scale circulations, which can influence the westerly disturbance tracks and water vapor transport. The linear regression shows that the anomalous mid-tropospheric circulation over CAWTP corresponds to an anti-phase variation of the 500 hPa geopotential height anomalies over the southern and northern North Atlantic 10 days earlier (at 95% significance level), that bears a similarity to the North Atlantic Oscillation (NAO). The composite analysis reveals that the NAO impacts the downstream regions including CAWTP by controlling south-north two branches of the middle latitude westerly circulation around the Eurasian border. During the positive phases of the NAO, the northern branch of the westerly circulation goes around the northwest Tibetan Plateau, whereas the southern branch encounters the southwest Tibetan Plateau, which leads to reduced precipitation over the northern Pamir Plateau and increased precipitation over the Karakoram Himalaya, and

Local and Remote Influences on Vertical Wind Shear over the Northern Tropical Atlantic Region

NASA Astrophysics Data System (ADS)

Saravanan, R.; Zhu, X.

2009-12-01

Vertical wind shear is one of the most important parameters controlling the frequency and intensity of Atlantic hurricanes. It has been argued that in global warming scenarios, the mechanical effect of changing vertical wind shear may even trump the thermodynamic effect of increasing Atlantic sea surface temperatures, when it comes to projected trends in Atlantic hurricane activity. Despite its importance, little is known about the connection between vertical shear in the north Atlantic region and the global atmospheric circulation, apart from the well-known positive correlation with El Nino-Southern Oscillation (ENSO). In this study, we analyze the statistical relationship between vertical shear and features of the large-scale circulation such as the distribution of sea surface temperature and vertical motion. We examine whether this relationship is different on interannual timescales associated with ENSO as compared to the decadal timescales associated with the Atlantic Multidecadal Oscillation (AMO). We also investigate how well the global general circulation models manage to simulate the observed vertical shear in this region, and its relationship to the large-scale circulation. Our analyses reveal an interesting sensitivity to air-sea coupling in model simulations of vertical shear. Another interesting property of vertical shear, as defined in the context of hurricane studies, is that it is positive definite, rather like precipitation. This means that it has a very nongaussian probability distribution on short timescales. We analyze how this nongaussianity changes when averaged over longer timescales.

Connecting Atlantic temperature variability and biological cycling in two earth system models

NASA Astrophysics Data System (ADS)

Gnanadesikan, Anand; Dunne, John P.; Msadek, Rym

2014-05-01

Connections between the interdecadal variability in North Atlantic temperatures and biological cycling have been widely hypothesized. However, it is unclear whether such connections are due to small changes in basin-averaged temperatures indicated by the Atlantic Multidecadal Oscillation (AMO) Index, or whether both biological cycling and the AMO index are causally linked to changes in the Atlantic Meridional Overturning Circulation (AMOC). We examine interdecadal variability in the annual and month-by-month diatom biomass in two Earth System Models with the same formulations of atmospheric, land, sea ice and ocean biogeochemical dynamics but different formulations of ocean physics and thus different AMOC structures and variability. In the isopycnal-layered ESM2G, strong interdecadal changes in surface salinity associated with changes in AMOC produce spatially heterogeneous variability in convection, nutrient supply and thus diatom biomass. These changes also produce changes in ice cover, shortwave absorption and temperature and hence the AMO Index. Off West Greenland, these changes are consistent with observed changes in fisheries and support climate as a causal driver. In the level-coordinate ESM2M, nutrient supply is much higher and interdecadal changes in diatom biomass are much smaller in amplitude and not strongly linked to the AMO index.

The role of dynamically induced variability in the recent warming trend slowdown over the Northern Hemisphere

PubMed Central

Guan, Xiaodan; Huang, Jianping; Guo, Ruixia; Lin, Pu

2015-01-01

Since the slowing of the trend of increasing surface air temperature (SAT) in the late 1990 s, intense interest and debate have arisen concerning the contribution of human activities to the warming observed in previous decades. Although several explanations have been proposed for the warming-trend slowdown (WTS), none has been generally accepted. We investigate the WTS using a recently developed methodology that can successfully identify and separate the dynamically induced and radiatively forced SAT changes from raw SAT data. The dynamically induced SAT changes exhibited an obvious cooling effect relative to the warming effect of the adjusted SAT in the hiatus process. A correlation analysis suggests that the changes are dominated primarily by the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). Our results confirm that dynamically induced variability caused the WTS. The radiatively forced SAT changes are determined mainly by anthropogenic forcing, indicating the warming influence of greenhouse gases (GHGs), which reached levels of 400 ppm during the hiatus period. Therefore, the global SAT will not remain permanently neutral. The increased radiatively forced SAT will be amplified by increased dynamically induced SAT when the natural mode returns to a warming phase in the next period. PMID:26223491

Timing of squid migration reflects North Atlantic climate variability.

PubMed

Sims, D W; Genner, M J; Southward, A J; Hawkins, S J

2001-12-22

The environmental and biotic conditions affecting fisheries for cephalopods are only partially understood. A problem central to this is how climate change may influence population movements by altering the availability of thermal resources. In this study we investigate the links between climate and sea-temperature changes and squid arrival time off southwestern England over a 20-year period. We show that veined squid (Loligo forbesi) migrate eastward in the English Channel earlier when water in the preceding months is warmer, and that higher temperatures and early arrival correspond with warm (positive) phases of the North Atlantic oscillation (NAO). The timing of squid peak abundance advanced by 120-150 days in the warmest years ('early' years) compared with the coldest ('late' years). Furthermore, sea-bottom temperature was closely linked to the extent of squid movement. Temperature increases over the five months prior to and during the month of peak squid abundance did not differ between early and late years, indicating squid responded to temperature changes independently of time of year. We conclude that the temporal variation in peak abundance of squid seen off Plymouth represents temperature-dependent movement, which is in turn mediated by climatic changes associated with the NAO. Such climate-mediated movement may be a widespread characteristic of cephalopod populations worldwide, and may have implications for future fisheries management because global warming may alter both the timing and location of peak population abundance.

Characterizing the Seasonality and Spatiotemporal Evolution of the U.S. Warming Hole

NASA Astrophysics Data System (ADS)

Partridge, T.; Winter, J.; Osterberg, E. C.; Magilligan, F. J.; Hyndman, D. W.; Kendall, A. D.

2017-12-01

Regions of the Eastern United States have experienced periods of cooling during the last half of the twentieth century inconsistent with broader global warming trends. While there have been a variety of mechanisms proposed to explain this "warming hole", the spatial and temporal definitions of the warming hole often differ across studies, potentially obfuscating the physical drivers leading to its existence. Further, a broad consensus on the causality of the warming hole has yet to be reached. We use daily temperature data from the Global Historical Climate Network (GHCN) to conduct a thorough characterization of the spatiotemporal evolution and seasonality of regional cooling across the Eastern U.S., and define a dynamic warming hole as the region of most persistent cooling. We find that the location of the dynamic warming hole varies by season from the Midwestern U.S. during summer to the Southeastern U.S. during winter. In addition, the cool period associated with the warming hole is characterized by an abrupt decrease in maximum temperature (Tx) and a decline in minimum temperature (Tn) around 1957. While average Tn values in the warming hole recover after the decline and increase from the mid 1960's to present, Tx values for the second half of the 20th century remain below observed values from the first half of the century. To explore large-scale atmospheric drivers of the dynamic warming hole, we correlate SST teleconnection and regional atmospheric circulation indices with seasonal temperature values from 1901-1957 and 1958-2015. We show that 1957 marks a shift, where winter temperatures in the warming hole become more correlated with the Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO) and less correlated with the Atlantic Multidecadal Oscillation (AMO). Summer warming hole temperatures become less correlated with the NAO post 1957 and are strongly negatively correlated with precipitation.

Local and regional effects of large scale atmospheric circulation patterns on winter wind power output in Western Europe

NASA Astrophysics Data System (ADS)

Zubiate, Laura; McDermott, Frank; Sweeney, Conor; O'Malley, Mark

2014-05-01

Recent studies (Brayshaw, 2009, Garcia-Bustamante, 2010, Garcia-Bustamante, 2013) have drawn attention to the sensitivity of wind speed distributions and likely wind energy power output in Western Europe to changes in low-frequency, large scale atmospheric circulation patterns such as the North Atlantic Oscillation (NAO). Wind speed variations and directional shifts as a function of the NAO state can be larger or smaller depending on the North Atlantic region that is considered. Wind speeds in Ireland and the UK for example are approximately 20 % higher during NAO + phases, and up to 30 % lower during NAO - phases relative to the long-term (30 year) climatological means. By contrast, in southern Europe, wind speeds are 15 % lower than average during NAO + phases and 15 % higher than average during NAO - phases. Crucially however, some regions such as Brittany in N.W. France have been identified in which there is negligible variability in wind speeds as a function of the NAO phase, as observed in the ERA-Interim 0.5 degree gridded reanalysis database. However, the magnitude of these effects on wind conditions is temporally and spatially non-stationary. As described by Comas-Bru and McDermott (2013) for temperature and precipitation, such non-stationarity is caused by the influence of two other patterns, the East Atlantic pattern, (EA), and the Scandinavian pattern, (SCA), which modulate the position of the NAO dipole. This phenomenon has also implications for wind speeds and directions, which has been assessed using the ERA-Interim reanalysis dataset and the indices obtained from the PC analysis of sea level pressure over the Atlantic region. In order to study the implications for power production, the interaction of the NAO and the other teleconnection patterns with local topography was also analysed, as well as how these interactions ultimately translate into wind power output. The objective is to have a better defined relationship between wind speed and power

Subpolar Atlantic cooling and North American east coast warming linked to AMOC slowdown

NASA Astrophysics Data System (ADS)

Rahmstorf, Stefan; Caesar, Levke; Feulner, Georg; Saba, Vincent

2017-04-01

Reconstructing the history of the Atlantic Meridional Overturning Circulation (AMOC) is difficult due to the limited availability of data. One approach has been to use instrumental and proxy data for sea surface temperature (SST), taking multi-decadal and longer SST variations in the subpolar gyre region as indicator for AMOC changes [Rahmstorf et al., 2015]. Recent high-resolution global climate model results [Saba et al., 2016] as well as dynamical theory and conceptual modelling [Zhang and Vallis, 2007] suggest that an AMOC weakening will not only cool the subpolar Atlantic but simultaneously warm the Northwest Atlantic between Cape Hatteras and Nova Scotia, thus providing a characteristic SST pattern associated with AMOC variations. We analyse sea surface temperature (SST) observations from this region together with high-resolution climate model simulations to better understand the linkages of SST variations to AMOC variability and to provide further evidence for an ongoing AMOC slowdown. References Rahmstorf, S., J. E. Box, G. Feulner, M. E. Mann, A. Robinson, S. Rutherford, and E. J. Schaffernicht (2015), Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change, 5(5), 475-480, doi: 10.1038/nclimate2554. Saba, V. S., et al. (2016), Enhanced warming of the Northwest Atlantic Ocean under climate change, Journal of Geophysical Research-Oceans, 121(1), 118-132, doi: 10.1002/2015JC011346. Zhang, R., and G. K. Vallis (2007), The Role of Bottom Vortex Stretching on the Path of the North Atlantic Western Boundary Current and on the Northern Recirculation Gyre, Journal of Physical Oceanography, 37(8), 2053-2080, doi: 10.1175/jpo3102.1.

[The Spanish strategy for nutrition, physical activity and the prevention of obesity (NAOS Strategy)].

PubMed

Ballesteros Arribas, Juan Manuel; Dal-Re Saavedra, Marián; Pérez-Farinós, Napoleón; Villar Villalba, Carmen

2007-01-01

Obesity, the prevalence of which is still on the rise, is related to the main chronic diseases affecting the health of the population. Therefore, in 2004, the World Health Assembly approved the Global Strategy on Diet, Physical Activity and Health with the aim of reducing the risk factors of nontransmittable diseases related to unhealthy diets and physical inactivity. Along this same line, the Spanish Ministry of Health and Consumer Affairs began implementing the NAOS Strategy in 2005 as a platform from which to include and promote all those initiatives contributing to achieving the necessary social change in the promotion of healthy eating and the prevention of a sedentary lifestyle by meeting certain specific challenges within different scopes of action. The NAOS Strategy extends far beyond the healthcare and educational areas, by combining actions in all those sectors of society playing a role in preventing obesity. Informative campaigns, agreements with public and private institutions, voluntary working agreements, educational programs and supporting health promotion initiatives are some of the activities being carried out as part of the NAOS Strategy. Carrying out these activities and incorporating yet others, in conjunction with the work of evaluating and monitoring all of these activities, will be what is going to make it possible to maintain a high degree of effectiveness in preventing obesity.

Late Holocene sea level variability and Atlantic Meridional Overturning Circulation

USGS Publications Warehouse

Cronin, Thomas M.; Farmer, Jesse R.; Marzen, R. E.; Thomas, E.; Varekamp, J.C.

2014-01-01

Pre-twentieth century sea level (SL) variability remains poorly understood due to limits of tide gauge records, low temporal resolution of tidal marsh records, and regional anomalies caused by dynamic ocean processes, notably multidecadal changes in Atlantic Meridional Overturning Circulation (AMOC). We examined SL and AMOC variability along the eastern United States over the last 2000 years, using a SL curve constructed from proxy sea surface temperature (SST) records from Chesapeake Bay, and twentieth century SL-sea surface temperature (SST) relations derived from tide gauges and instrumental SST. The SL curve shows multidecadal-scale variability (20–30 years) during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), as well as the twentieth century. During these SL oscillations, short-term rates ranged from 2 to 4 mm yr−1, roughly similar to those of the last few decades. These oscillations likely represent internal modes of climate variability related to AMOC variability and originating at high latitudes, although the exact mechanisms remain unclear. Results imply that dynamic ocean changes, in addition to thermosteric, glacio-eustatic, or glacio-isostatic processes are an inherent part of SL variability in coastal regions, even during millennial-scale climate oscillations such as the MCA and LIA and should be factored into efforts that use tide gauges and tidal marsh sediments to understand global sea level rise.

Augmentation effect of acupuncture on Bi'nao for hypophasis in patients with Bell's palsy: study protocol for a randomized controlled trial.

PubMed

Li, Xiaoyan; Chen, Chunlan; Zhao, Chuang; Li, Zunyuan; Liang, Wei; Liu, Zhidan

2018-06-11

Hypophasis is one of the most frequently observed sequelae of patients with Bell's palsy, who have not recovered completely, creating a clinical difficulty for physicians. Acupuncture therapy has been widely used to treat Bell's palsy as a reasonable resolution for management of symptoms such as hypophasis. The number of acupuncture points (acu-points) is frequently selected in the approach of acupuncture therapy; however, whether these had high efficiency has not been proved. According to the literature review, Bi'nao was useful for treating eye and eye lipid diseases, which could be proved only by some successful cases. Thus, a randomized controlled trial was designed to evaluate the efficiency of the acu-point Bi'nao. Participants with hypophasis as the major symptom are selected among patients with Bell's palsy and randomly allocated into one of the three groups at a 1:1:1 allocation ratio. All participants receive conventional acupuncture therapy; however, those assigned to the real acupuncture group will be given added acupuncture therapy on the acu-point Bi'nao, while those assigned to the sham acupuncture group were given extra acupuncture therapy on the sham Bi'nao as a placebo. The efficacy of the acupuncture therapy on the acu-point Bi'nao for hypophasis will be evaluated by Eye Crack Width Measurement (ECWM) and Eyelid Strength Assessment (ESA) before and after therapy. This is the first study assessing the safety and efficiency of Bi'nao in treating the hypophasis of patients with Bell's palsy that might support the application of this acupuncture therapy. However, evaluating hypophasis is challenging, and, thus, ECWM and ESA were applied to measure the eyelid movement. Chinese Clinical Trials Registry, ChiCTR-INR-17012955 . Registered on 12 October 2017.

Improved Decadal Climate Prediction in the North Atlantic using EnOI-Assimilated Initial Condition

NASA Astrophysics Data System (ADS)

Li, Q.; Xin, X.; Wei, M.; Zhou, W.

2017-12-01

Decadal prediction experiments of Beijing Climate Center climate system model version 1.1(BCC-CSM1.1) participated in Coupled Model Intercomparison Project Phase 5 (CMIP5) had poor skill in extratropics of the North Atlantic, the initialization of which was done by relaxing modeled ocean temperature to the Simple Ocean Data Assimilation (SODA) reanalysis data. This study aims to improve the prediction skill of this model by using the assimilation technique in the initialization. New ocean data are firstly generated by assimilating the sea surface temperature (SST) of the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST) dataset to the ocean model of BCC-CSM1.1 via Ensemble Optimum Interpolation (EnOI). Then a suite of decadal re-forecasts launched annually over the period 1961-2005 is carried out with simulated ocean temperature restored to the assimilated ocean data. Comparisons between the re-forecasts and previous CMIP5 forecasts show that the re-forecasts are more skillful in mid-to-high latitude SST of the North Atlantic. Improved prediction skill is also found for the Atlantic multi-decadal Oscillation (AMO), which is consistent with the better skill of Atlantic meridional overturning circulation (AMOC) predicted by the re-forecasts. We conclude that the EnOI assimilation generates better ocean data than the SODA reanalysis for initializing decadal climate prediction of BCC-CSM1.1 model.

Interannual variability of the annual cycle of the surface temperature in the NCAR-NCEP reanalysis over the Northern Atlantic

NASA Astrophysics Data System (ADS)

Tesouro, M.; Gimeno, L.; Añel, J. A.; de La Torre, L.; Nieto, R.; Ribera, P.; García, R.; Hernández, E.

2003-04-01

The seasonal cycle of the surface temperature in the Northern Atlantic was investigated with the aim of studying interannual variability. To know how seasonal cycle is influenced by main climate modes could be a powerful tool to improve our seasonal prediction abilities. Data consist of daily temperatures at 2 metres taken from the Climate Research Unit (University of East Anglic_UK) (www.cru.uea.ac.uk) corresponding to the region from 90 W to 90 E longitude and from 88.5 N to 21.9 N latitude and for the last 44 years. Daily data were adjusted to the following expression for each year: y=a+b*sin(((2*PI)/d)x+c) The amplitude of the wave and the first inflexion point were used as indicators of the seasonal cycle. Results show a negative correlation between the NAO index and the amplitude over Northern Europe and over Mexico and a positive correlation over Northern United States and Canada. They also show a negative correlation between the NAO index and the first inflexion point over Northern Europe.

Multidecadal fCO2 Increase Along the United States Southeast Coastal Margin

NASA Astrophysics Data System (ADS)

Reimer, Janet J.; Wang, Hongjie; Vargas, Rodrigo; Cai, Wei-Jun

2017-12-01

Coastal margins could be hotspots for acidification due to terrestrial-influenced CO2 sources. Currently there are no long-term (>20 years) records from biologically important coastal environments that could demonstrate sea surface CO2 fugacity (fCO2) and pH trends. Here, multidecadal fCO2 trends are calculated from underway and moored time series observations along the United States southeast coastal margin, also referred to as the South Atlantic Bight (SAB). fCO2 trends across the SAB, derived from ˜26 years of cruises and ˜9.5 years from a moored time series, range from 3.0 to 4.5 µatm yr-1, and are greater than the open ocean increases. The pH decline related to the fCO2 increases could be as much as -0.004 yr-1; a rate greater than that expected from atmospheric-influenced pH alone. We provide evidence that fCO2 increases and pH decreases on an ocean margin can be faster than those predicted for the open ocean from atmospheric influence alone. We conclude that a substantial fCO2 increase across the marginal SAB is due to both increasing temperature on the middle and outer shelves, but to lateral land-ocean interactions in the coastal zone and on inner shelf.

Water Mass Variability at the Mid-Atlantic Ridge and in the Eastern North Atlantic

NASA Astrophysics Data System (ADS)

Köllner, Manuela; Klein, Birgit; Kieke, Dagmar; Klein, Holger; Roessler, Achim; Rhein, Monika

2017-04-01

The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the sub-polar gyre and stronger inflow of waters from the sub-tropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses. The North Atlantic Current (NAC) can be regarded as the southern border of the sub-polar gyre transporting water from the tropical regions northward. On its way towards the Mid Atlantic Ridge (MAR) the NAC has partly mixed with waters from the sub-polar gyre and crosses the MAR split into several branches. For the study we analyzed data of water mass variability and transport fluctuations from the RACE (Regional circulation and Global change) project (2012-2015) which provided time series of transports and hydrographic anomalies from moored instruments at the western flank of the MAR. The time depending positions of the NAC branches over the MAR were obtained from mooring time series and compared to sea surface velocities from altimeter data. The results show a high variability of NAC pathways over the MAR. Transition regimes with strong meandering and eddies could be observed as well as periods of strong NAC branches over the Fracture Zones affecting water mass exchange at all depth levels. A positive temperature trend at depths between 1000-2000 m was found at the Faraday Fracture Zone (FFZ). This warming trend was also detected by Argo floats crossing the MAR close to the FFZ region. During the second phase of RACE (RACE-II, 2016-2018) a mooring array across the eastern shelf break at Goban Spur was deployed to monitor the poleward Eastern Boundary

GIS-based Stress Field Modeling of the North Arm of Sulawesi (NAoS) and its application in mineral prospectivity assessment

NASA Astrophysics Data System (ADS)

Albert, Gáspár; Szentpéteri, Krisztián

2017-04-01

Remotely sensed and digital map data are useful sources for regional structural analysis, including stress calculations. If the type of a given fault is determined and is considered as Andersonian, and rather juvenile instead of a reactivated one, the tectonic stress can be calculated for each of the fault segments (Albert et al. 2016). The North Arm of Sulawesi, a west-east-trending land strip of the irregular shaped Sulawesi Island, is actively deforming and the upper plate tectonic setting is quite complex in this region since it is situated above a triple junction of the Eurasian, Pacific and Australian plates. The stress currently acting in this region not only creates neotectonics but triggers subduction-related volcanism shifting from west to east on the peninsula. The volcanic centers - adjacent to transfer faults and the colliding plates at depth - appear to be the most productive areas for epithermal-porphyry mineralization systems of economic potential (Szentpéteri et al. 2015). In this work we demonstrate how the derived stress field model helps to understand the location and clustering of various mineralization types in the NAoS. We examine if this method is applicable for mineral prospectively assessments. References Albert, G., Barancsuk, Á., and Szentpéteri, K., 2016, Stress field modelling from digital geological map data: Geophysical Research Abstracts, v. 18, EGU2016-14565. Szentpéteri, K., Albert, G., and Ungvári, Z., Plate tectonic - and stress field - modeling of the North Arm of Sulawesi, Indonesia, to better understand distribution of mineral deposits styles., in Proceedings SEG 2015 I World Class Ore Deposits: Discovery to Recovery, Wrest Point Convention Centre, Hobart, Australia, September 27 - 30. 2015.

Baroclinic wave configurations evolution at European scale in the period 1948-2013

NASA Astrophysics Data System (ADS)

Carbunaru, Daniel; Burcea, Sorin; Carbunaru, Felicia

2016-04-01

The main aim of the study was to investigate the dynamic characteristics of synoptic configurations at European scale and especially in south-eastern part of Europe for the period 1948-2013. Using the empirical orthogonal functions analysis, simultaneously applied to daily average geopotential field at different pressure levels (200 hPa, 300 hPa, 500 hPa and 850 hPa) during warm (April-September) and cold (October-March) seasons, on a synoptic spatial domain centered on Europe (-27.5o lon V to 45o lon E and 32.5o lat N to 72.5o lat N), the main mode of oscillation characteristic to vertical shift of mean baroclinic waves was obtained. The analysis independently applied on 66 years showed that the first eigenvectors in warms periods describe about 60% of the data and in cold season 40% of the data for each year. In comparison secondary eigenvectors describe up to 20% and 10% of the data. Thus, the analysis was focused on the complex evolution of the first eigenvector in 66 years, during the summer period. On average, this eigenvector describes a small vertical phase shift in the west part of the domain and a large one in the eastern part. Because the spatial extent of the considered synoptic domain incorporates in the west part AMO (Atlantic Multidecadal Oscillation) and NAO (North Atlantic Oscillation) oscillations, and in the north part being sensitive to AO (Arctic Oscillation) oscillation, these three oscillations were considered as modulating dynamic factors at hemispherical scale. The preliminary results show that in the summer seasons AMO and NAO oscillations modulated vertical phase shift of baroclinic wave in the west of the area (Northwestern Europe), and the relationship between AO and NAO oscillations modulated vertical phase shift in the southeast area (Southeast Europe). Second, it was shown the way in which this vertical phase shift modulates the overall behavior of cyclonic activity, particularly in Southeastern Europe. This work has been developed

Identifying Decadal to Multi-decadal Variability in the Pacific by Empirical Mode Decomposition

NASA Astrophysics Data System (ADS)

Sommers, L. A.; Hamlington, B.; Cheon, S. H.

2016-12-01

Large scale climate variability in the Pacific Ocean like that associated with ENSO and the Pacific Decadal Oscillation (PDO) has been shown to have a significant impact on climate and sea level across a range of timescales. The changes related to these climate signals have worldwide impacts on fisheries, weather, and precipitation patterns among others. Understanding these inter-annual to multi-decadal oscillations is imperative to longer term climate forecasts and understanding how climate will behave, and its effect on changes in sea level. With a 110-year reconstruction of sea level, we examine decadal to multi-decadal variability seen in the sea level fluctuations in the Pacific Ocean. Using empirical mode decomposition (EMD), we break down regional sea level into a series of intrinsic mode functions (IMFs) and attempt attribution of these IMFs to specific climate modes of variability. In particular, and not unexpectedly, we identify IMFs associated with the PDO, finding correlations between the PDO Index and IMFs in the Pacific Ocean upwards of 0.6-0.8 over the 110-year reconstructed record. Perhaps more significantly, we also find evidence of a longer multi-decadal signal ( 50-60 years) in the higher order IMFs. This lower frequency variability has been suggested in previous literature as influencing GMSL, but here we find a regional pattern associated with this multi-decadal signal. By identifying and separating these periodic climate signals, we can gain a better understanding of how the sea level variability associated with these modes can impact sea level on short timescales and serve to exacerbate the effects of long-term sea level change.

North Atlantic Oscillation drives the annual occurrence of an isolated, peripheral population of the brown seaweed Fucus guiryi in the Western Mediterranean Sea

PubMed Central

Melero-Jiménez, Ignacio J.; Salvo, A. Enrique; Báez, José C.; Bañares-España, Elena; Reul, Andreas

2017-01-01

The canopy-forming, intertidal brown (Phaeophyceae) seaweed Fucus guiryi is distributed along the cold-temperate and warm-temperate coasts of Europe and North Africa. Curiously, an isolated population develops at Punta Calaburras (Alboran Sea, Western Mediterranean) but thalli are not present in midsummer every year, unlike the closest (ca. 80 km), perennial populations at the Strait of Gibraltar. The persistence of the alga at Punta Calaburras could be due to the growth of resilient, microscopic stages as well as the arrival of few–celled stages originating from neighbouring localities, and transported by the permanent Atlantic Jet flowing from the Atlantic Ocean into the Mediterranean. A twenty-six year time series (from 1990 to 2015) of midsummer occurrence of F. guiryi thalli at Punta Calaburras has been analysed by correlating with oceanographic (sea surface temperature, an estimator of the Atlantic Jet power) and climatic factors (air temperature, rainfall, and North Atlantic Oscillation –NAO-, and Arctic Oscillation –AO- indexes). The midsummer occurrence of thalli clustered from 1990–1994 and 1999–2004, with sporadic occurrences in 2006 and 2011. Binary logistic regression showed that the occurrence of thalli at Punta Calaburras in midsummer is favoured under positive NAO index from April to June. It has been hypothesized that isolated population of F. guiryi should show greater stress than their congeners of permanent populations, and to this end, two approaches were used to evaluate stress: one based on the integrated response during ontogeny (developmental instability, based on measurements of the fractal branching pattern of algal thalli) and another based on the photosynthetic response. Although significant differences were detected in photosynthetic quantum yield and water loss under emersion conditions, with thalli from Punta Calaburras being more affected by emersion than those from Tarifa, the developmental instability showed that the

Influence of Climate Oscillations on Extreme Precipitation in Texas

NASA Astrophysics Data System (ADS)

Bhatia, N.; Singh, V. P.; Srivastav, R. K.

2016-12-01

Much research in the field of hydroclimatology is focusing on the impact of climate variability on hydrologic extremes. Recent studies show that the unique geographical location and the enormous areal extent, coupled with extensive variations in climate oscillations, have intensified the regional hydrologic cycle of Texas. The state-wide extreme precipitation events can actually be attributed to sea-surface pressure and temperature anomalies, such as Bermuda High and Jet Streams, which are further triggered by such climate oscillations. This study aims to quantify the impact of five major Atlantic and Pacific Ocean related climate oscillations: (i) Atlantic Multidecadal Oscillation (AMO), (ii) North Atlantic Oscillation (NAO), (iii) Pacific Decadal Oscillation (PDO), (iv) Pacific North American Pattern (PNA), and (v) Southern Oscillation Index (SOI), on extreme precipitation in Texas. Their respective effects will be determined for both climate divisions delineated by the National Climatic Data Centre (NCDC) and climate regions defined by the Köppen Climate Classification System. This study will adopt a weighted correlation approach to attain the robust correlation coefficients while addressing the regionally variable data outliers for extreme precipitation. Further, the variation of robust correlation coefficients across Texas is found to be related to the station elevation, historical average temperature, and total precipitation in the months of extremes. The research will shed light on the relationship between precipitation extremes and climate variability, thus aiding regional water boards in planning, designing, and managing the respective systems as per the future climate change.

Synchronous multi-decadal climate variability of the whole Pacific areas revealed in tree rings since 1567

NASA Astrophysics Data System (ADS)

Fang, Keyan; Cook, Edward; Guo, Zhengtang; Chen, Deliang; Ou, Tinghai; Zhao, Yan

2018-02-01

Oceanic and atmospheric patterns play a crucial role in modulating climate variability from interannual to multi-decadal timescales by causing large-scale co-varying climate changes. The brevity of the existing instrumental records hinders the ability to recognize climate patterns before the industrial era, which can be alleviated using proxies. Unfortunately, proxy based reconstructions of oceanic and atmospheric modes of the past millennia often have modest agreements with each other before the instrumental period, raising questions about the robustness of the reconstructions. To ensure the stability of climate signals in proxy data through time, we first identified tree-ring datasets from distant regions containing coherent variations in Asia and North America, and then interpreted their climate information. We found that the multi-decadal covarying climate patterns of the middle and high latitudinal regions around the northern Pacific Ocean agreed quite well with the climate reconstructions of the tropical and southern Pacific areas. This indicates a synchronous variability at the multi-decadal timescale of the past 430 years for the entire Pacific Ocean. This pattern is closely linked to the dominant mode of the Pacific sea surface temperature (SST) after removing the warming trend. This Pacific multi-decadal SST variability resembles the Interdecadal Pacific Oscillation.

Tree-ring reconstruction of streamflow in the Snare River Basin, Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Martin, J. P.; Pisaric, M. F.

2017-12-01

Drought is a component of many ecosystems in North America causing environmental and socioeconomical impacts. In the ongoing context of climatic and environmental changes, drought-related issues are becoming problematic in northern Canada, which have not been associated with drought-like conditions in the past. Dryer than average conditions threatens the energy security of northern canadian communities, since this region relies on the production of hydroelectricity as an energy source. In the North Slave Region of Northwest Territory (NWT), water levels and streamflows were significantly lower in 2014/2015. The Government of the NWT had to spend nearly $50 million to purchase diesel fuel to generate enough electricity to supplement the reduced power generation of the Snare River hydroelectric system, hence the need to better understand the multi-decadal variability in streamflow. The aims of this presentation are i) to present jack pine and white spruce tree-ring chronologies of Southern NWT; ii) to reconstruct past streamflow of the Snare River Basin; iii) to evaluate the frequency and magnitude of extreme drought conditions, and iv) to identify which large-scale atmospheric or oceanic patterns are teleconnected to regional hydraulic conditions. Preliminary results show that the growth of jack pine and white spruce populations is better correlated with precipitation and temperature, respectively, than hydraulic conditions. Nonetheless, we present a robust streamflow reconstruction of the Snare River that is well correlated with the summer North Atlantic Oscillation (NAO) index, albeit the strength of the correlation is non-stationary. Spectral analysis corroborate the synchronicity between negative NAO conditions and drought conditions. From an operational standpoint, considering that the general occurrence of positive/negative NAO can be predicted, it the hope of the authors that these results can facilitate energetic planning in the Northwest Territories through

Inability of CMIP5 Climate Models to Simulate Recent Multi-decadal Climate Change in the Tropical Pacific.

NASA Astrophysics Data System (ADS)

Power, S.; Delage, F.; Kociuba, G.; Wang, G.; Smith, I.

2017-12-01

Observed 15-year surface temperature trends beginning 1998 or later have attracted a great deal of interest because of an apparent slowdown in the rate of global warming, and contrasts between climate model simulations and observations of such trends. Many studies have addressed the statistical significance of these relatively short trends, whether they indicate a possible bias in models and the implications for global warming generally. Here we analyse historical and projected changes in 38 CMIP5 climate models. All of the models simulate multi-decadal warming in the Pacific over the past half-century that exceeds observed values. This stark difference cannot be fully explained by observed, internal multi-decadal climate variability, even if allowance is made for an apparent tendency for models to underestimate internal multi-decadal variability in the Pacific. We also show that CMIP5 models are not able to simulate the magnitude of the strengthening of the Walker Circulation over the past thirty years. Some of the reasons for these major shortcomings in the ability of models to simulate multi-decadal variability in the Pacific, and the impact these findings have on our confidence in global 21st century projections, will be discussed.

Coralline algal Barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability

PubMed Central

Hetzinger, S.; Halfar, J.; Zack, T.; Mecking, J. V.; Kunz, B. E.; Jacob, D. E.; Adey, W. H.

2013-01-01

During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes. Large-scale freshening episodes, related to polar freshwater pulses, have had a strong influence on ocean variability in this climatically important region. However, little is known about variability before 1950, mainly due to the lack of long-term high-resolution marine proxy archives. Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae. We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950. Both records capture episodical multi-year freshening events during the 20th century. Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification, which affect the transport of cold, Ba-enriched deep waters onto the shelf (highly stratified equals less Ba/Ca). Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes. PMID:23636135

Coralline algal barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability.

PubMed

Hetzinger, S; Halfar, J; Zack, T; Mecking, J V; Kunz, B E; Jacob, D E; Adey, W H

2013-01-01

During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes. Large-scale freshening episodes, related to polar freshwater pulses, have had a strong influence on ocean variability in this climatically important region. However, little is known about variability before 1950, mainly due to the lack of long-term high-resolution marine proxy archives. Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae. We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950. Both records capture episodical multi-year freshening events during the 20th century. Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification, which affect the transport of cold, Ba-enriched deep waters onto the shelf (highly stratified equals less Ba/Ca). Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes.

Dominant Role of Atlantic Multidecadal Oscillation in the Recent Decadal Changes in Western North Pacific Tropical Cyclone Activity

NASA Astrophysics Data System (ADS)

Zhang, Wei; Vecchi, Gabriel A.; Murakami, Hiroyuki; Villarini, Gabriele; Delworth, Thomas L.; Yang, Xiaosong; Jia, Liwei

2018-01-01

Over the 1997-2014 period, the mean frequency of western North Pacific (WNP) tropical cyclones (TCs) was markedly lower ( 18%) than the period 1980-1996. Here we show that these changes were driven by an intensification of the vertical wind shear in the southeastern/eastern WNP tied to the changes in the Walker circulation, which arose primarily in response to the enhanced sea surface temperature (SST) warming in the North Atlantic, while the SST anomalies associated with the negative phase of the Pacific Decadal Oscillation in the tropical Pacific and the anthropogenic forcing play only secondary roles. These results are based on observations and experiments using the Geophysical Fluid Dynamics Laboratory Forecast-oriented Low-ocean Resolution Coupled Climate Model coupled climate model. The present study suggests a crucial role of the North Atlantic SST in causing decadal changes to WNP TC frequency.

Understanding multidecadal variability in ENSO amplitude

NASA Astrophysics Data System (ADS)

Russell, A.; Gnanadesikan, A.

2013-12-01

Sea surface temperatures (SSTs) in the tropical Pacific vary as a result of the coupling between the ocean and atmosphere driven largely by the El Niño - Southern Oscillation (ENSO). ENSO has a large impact on the local climate and hydrology of the tropical Pacific, as well as broad-reaching effects on global climate. ENSO amplitude is known to vary on long timescales, which makes it very difficult to quantify its response to climate change and constrain the physical processes that drive it. In order to assess the extent of unforced multidecadal changes in ENSO variability, a linear regression of local SST changes is applied to the GFDL CM2.1 model 4000-yr pre-industrial control run. The resulting regression coefficient strengths, which represent the sensitivity of SST changes to thermocline depth and zonal wind stress, vary by up to a factor of 2 on multi-decadal time scales. This long-term modulation in ocean-atmosphere coupling is highly correlated with ENSO variability, but do not explain the reasons for such variability. Variation in the relationship between SST changes and wind stress points to a role for changing stratification in the central equatorial Pacific in modulating ENSO amplitudes with stronger stratification reducing the response to winds. The main driving mechanism we have identified for higher ENSO variance are changes in the response of zonal winds to SST anomalies. The shifting convection and precipitation patterns associated with the changing state of the atmosphere also contribute to the variability of the regression coefficients. These mechanisms drive much of the variability in ENSO amplitude and hence ocean-atmosphere coupling in the tropical Pacific.

Interhemispheric Changes in Atlantic Ocean Heat Content and Their Link to Global Monsoons

NASA Astrophysics Data System (ADS)

Lopez, H.; Lee, S. K.; Dong, S.; Goni, G. J.

2015-12-01

This study tested the hypothesis whether low frequency decadal variability of the South Atlantic meridional heat transport (SAMHT) influences decadal variability of the global monsoons. A multi-century run from a state-of-the-art coupled general circulation model is used as basis for the analysis. Our findings indicate that multi-decadal variability of the South Atlantic Ocean plays a key role in modulating atmospheric circulation via interhemispheric changes in Atlantic Ocean heat content. Weaker SAMHT produces anomalous ocean heat divergence over the South Atlantic resulting in negative ocean heat content anomaly about 15 years later. This, in turn, forces a thermally direct anomalous interhemispheric Hadley circulation in the atmosphere, transporting heat from the northern hemisphere (NH) to the southern hemisphere (SH) and moisture from the SH to the NH, thereby intensify (weaken) summer (winter) monsoon in the NH and winter (summer) monsoon in the SH. Results also show that anomalous atmospheric eddies, both transient and stationary, transport heat northward in both hemispheres producing eddy heat flux convergence (divergence) in the NH (SH) around 15-30°, reinforcing the anomalous Hadley circulation. The effect of eddies on the NH (SH) poleward of 30° is opposite with heat flux divergence (convergence), which must be balanced by sinking (rising) motion, consistent with a poleward (equatorward) displacement of the jet stream and mean storm track. The mechanism described here could easily be interpreted for the case of strong SAMHT, with the reverse influence on the interhemispheric atmospheric circulation and monsoons. Overall, SAMHT decadal variability leads its atmospheric response by about 15 years, suggesting that the South Atlantic is a potential predictor of global climate variability.

Linking The Atlantic Gyres: Warm, Saline Intrusions From Subtropical Atlantic to the Nordic Seas

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa M.; Rhines, P. B.

2010-01-01

Ocean state estimates from SODA assimilation are analyzed to understand how major shifts in the North Atlantic Current path relate to AMOC, and how these shifts are related to large scale ocean circulation and surface forcing. These complement surface-drifter and altimetry data showing the same events. SODA data indicate that the warm water limb of AMOC, reaching to at least 600m depth, expanded in density/salinity space greatly after 1995, and that Similar events occurred in the late 1960s and around 1980. While there were large changes in the upper limb, there was no immediate response in the dense return flow, at least not in SODA, however one would expect a delayed response of increasing AMOC due to the positive feedback from increased salt transport. These upper limb changes are winddriven, involving changes in the eastern subpolar gyre, visible in the subduction of low potential vorticity waters. The subtropical gyre has been weak during the times of the northward intrusions of the highly saline subtropical waters, while the NAO index has been neutral or in a negative phase. The image of subtropical/subpolar gyre exchange through teleconnections within the AMOC overturning cell will be described.

Statistical Relationships between the El Niño Southern Oscillation, the North Atlantic Oscillation, and Winter Tornado Outbreaks in the U.S

NASA Astrophysics Data System (ADS)

Robinson Cook, A. D.; Schaefer, J. T.

2009-12-01

Winter tornado activity (January-March) between 1950 and 2003 was analyzed to determine the possible effects of the El Niño Southern Oscillation and the North Atlantic Oscillation on the frequency, location, and strength of tornado outbreaks in the United States. Outbreaks were gauged through analyses of tornadoes occurring on tornado days (a calendar day featuring six or more tornadoes within the contiguous United States) and then stratified according to warm (37 tornado days), cold (51 tornado days), and neutral (74 tornado days) winter ENSO phase. Tornado days were also stratified according to NAO phase (positive, negative, and neutral) as well. Although significant changes in the frequency of tornado outbreaks were not observed, spatial shifts in tornado activity are observed, primarily as a function of ENSO phase. Historically, the neutral ENSO phase features tornado outbreaks from central Oklahoma and Kansas eastward through the Carolinas. During cold ENSO phases (La Niña), tornado outbreaks typically occur in a zone stretching from southeastern Texas northeastward into Illinois, Indiana, and Michigan. Winter tornado activity was mainly limited to areas near the Gulf Coast, including central Florida, during anomalously warm phases (El Niño). Shifts in the intensity of tornado activity were also found as a function of ENSO and particularly NAO phase. Stronger tornadoes with longer path lengths were observed during La Niña and Neutral ENSO events, as well as Positive and Neutral NAO events.

Causes and Consequences of Exceptional North Atlantic Heat Loss in Recent Winters

NASA Astrophysics Data System (ADS)

Josey, Simon; Grist, Jeremy; Duchez, Aurelie; Frajka-Williams, Eleanor; Hirschi, Joel; Marsh, Robert; Sinha, Bablu

2016-04-01

The mid-high latitude North Atlantic loses large amounts of heat to the atmosphere in winter leading to dense water formation. An examination of reanalysis datasets (ERA-Interim, NCEP/NCAR) reveals that heat loss in the recent winters 2013-14 and 2014-15 was exceptionally strong. The causes and consequences of this extraordinary ocean heat loss will be discussed. In 2013-2014, the net air-sea heat flux anomaly averaged over the whole winter exceeded 100 Wm-2 in the eastern subpolar gyre (the most extreme in the period since 1979 spanned by ERA-Interim). The causes of this extreme heat loss will be shown to be severe latent and sensible heat fluxes driven primarily by anomalously strong westerly airflows from North America and northerly airflows originating in the Nordic Seas. The associated sea level pressure anomaly field reflects the dominance of the second mode of atmospheric variability, the East Atlantic Pattern (EAP) over the North Atlantic Oscillation (NAO) in this winter. The extreme winter heat loss had a significant impact on the ocean extending from the sea surface into the deeper layers and a re-emergent cold Sea Surface Temperature (SST) anomaly is evident in November 2014. The following winter 2014-15 experienced further extreme heat loss that served to amplify the strength of the re-emergent SST anomaly. By summer 2015, an unprecedented cold mid-latitude North Atlantic Ocean surface temperature anomaly is evident in observations and has been widely referred to as the 'big blue blob'. The role played by the extreme surface heat loss in the preceding winters in generating this feature and it subsequent evolution through winter 2015-16 will be explored.

A new collective view of oceanography of the Arctic and North Atlantic basins

NASA Astrophysics Data System (ADS)

Yashayaev, Igor; Seidov, Dan; Demirov, Entcho

2015-03-01

We review some historical aspects of the major observational programs in the North Atlantic and adjacent regions that contributed to establishing and maintaining the global ocean climate monitoring network. The paper also presents the oceanic perspectives of climate change and touches the important issues of ocean climate variability on time scales from years to decades. Some elements of the improved understanding of the causes and mechanisms of variability in the subpolar North Atlantic and adjacent seas are discussed in detail. The sophistication of current oceanographic analysis, especially in connection with the most recent technological breakthroughs - notably the launch of the global array of profiling Argo floats - allows us to approach new challenges in ocean research. We demonstrate how the ocean-climate changes in the subpolar basins and polar seas correlate with variations in the major climate indices such as the North Atlantic Oscillation and Atlantic Multidecadal Oscillation, and discuss possible connections between the unprecedented changes in the Arctic and Greenland ice-melt rates observed over the past decade and variability of hydrographic conditions in the Labrador Sea. Furthermore, a synthesis of shipboard and Argo measurements in the Labrador Sea reveals the effects of the regional climate trends such as freshening of the upper layer - possible causes of which are also discussed - on the winter convection in the Labrador Sea including its strength, duration and spatial extent. These changes could have a profound impact on the regional and planetary climates. A section with the highlights of all papers comprising the Special Issue concludes the Preface.

Silver hake tracks changes in Northwest Atlantic circulation.

PubMed

Nye, Janet A; Joyce, Terrence M; Kwon, Young-Oh; Link, Jason S

2011-08-02

Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales. Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake, Merluccius bilinearis, a commercially important fish in the Northeast US shelf region. Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream. These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the Gulf Stream path, namely changes in the Atlantic meridional overturning circulation (AMOC). If the AMOC weakens, as is suggested by global climate models, silver hake distribution will remain in a poleward position, the extent to which could be forecast at both decadal and multidecadal scales.

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Vizy, Edward K.; Sun, Xiaoming

2018-03-01

Distributions of ocean mixed layer temperature trends and trends in the net heat flux from the atmosphere differ, indicating the important role of the transport of heat within the ocean for determining temperature trends. Annual-mean, linear trends in the components of the tropical ocean mixed layer heat budget for 1980-2015 are diagnosed in 4 ocean reanalyses to improve our physical understanding of multidecadal-scale SST trends. The well-known temperature trend in the tropical Pacific, with cooling in the east and warming in the west, is reproduced in each reanalysis with high statistical significance. Cooling in the east is associated with negative trends in the net heat flux from the atmosphere and enhanced equatorial upwelling related to a strengthening of the subtropical cells. Negative trends in the net heat flux also occur in the western tropical Pacific, but advective warming associated with a strengthening and shoaling of the equatorial undercurrent overwhelms these negative trends. The strengthening of the equatorial undercurrent is consistent with enhanced easterly wind stress, which is applied to the ocean reanalyses, and differential sea level trends that enhance the negative zonal height gradient across the Pacific. The Pacific North Equatorial countercurrent is also strengthening in all 4 reanalyses in association with a strengthening of the sea level trough at 10°N in the central and eastern Pacific. All 4 ocean reanalyses produce warming of 0.1-0.3 K/decade in the North Atlantic with statistical significance levels ranging from below 90-99%. The Atlantic is similar to the Pacific in having the equatorial undercurrent strengthening, but indications of shoaling are less consistent in the reanalyses and the North Equatorial Countercurrent in the Atlantic is not strengthening. Large-scale ocean mixed layer warming trends in the Indian Ocean in the reanalyses are interrupted by some regional cooling close to the equator. Net surface heat flux trends

A Skilful Marine Sclerochronological Network Based Reconstruction of North Atlantic Subpolar Gyre Dynamics

NASA Astrophysics Data System (ADS)

Reynolds, D.; Hall, I. R.; Slater, S. M.; Scourse, J. D.; Wanamaker, A. D.; Halloran, P. R.; Garry, F. K.

2017-12-01

Spatial network analyses of precisely dated, and annually resolved, tree-ring proxy records have facilitated robust reconstructions of past atmospheric climate variability and the associated mechanisms and forcings that drive it. In contrast, a lack of similarly dated marine archives has constrained the use of such techniques in the marine realm, despite the potential for developing a more robust understanding of the role basin scale ocean dynamics play in the global climate system. Here we show that a spatial network of marine molluscan sclerochronological oxygen isotope (δ18Oshell) series spanning the North Atlantic region provides a skilful reconstruction of basin scale North Atlantic sea surface temperatures (SSTs). Our analyses demonstrate that the composite marine series (referred to as δ18Oproxy_PC1) is significantly sensitive to inter-annual variability in North Atlantic SSTs (R=-0.61 P<0.01) and surface air temperatures (SATs; R=-0.67, P<0.01) over the 20th century. Subpolar gyre (SPG) SSTs dominates variability in the δ18Oproxy_PC1 series at sub-centennial frequencies (R=-0.51, P<0.01). Comparison of the δ18Oproxy_PC1 series against variability in the strength of the European Slope Current and maximum North Atlantic meridional overturning circulation derived from numeric climate models (CMIP5), indicates that variability in the SPG region, associated with the strength of the surface currents of the North Atlantic, are playing a significant role in shaping the multi-decadal scale SST variability over the industrial era. These analyses demonstrate that spatial networks developed from sclerochronological archives can provide powerful baseline archives of past ocean variability that can facilitate the development of a quantitative understanding for the role the oceans play in the global climate systems and constraining uncertainties in numeric climate models.

Vadose zone controls on damping of climate-induced transient recharge fluxes in U.S. agroecosystems

NASA Astrophysics Data System (ADS)

Gurdak, Jason

2017-04-01

Understanding the physical processes in the vadose zone that link climate variability with transient recharge fluxes has particular relevance for the sustainability of groundwater-supported irrigated agriculture and other groundwater-dependent ecosystems. Natural climate variability on interannual to multidecadal timescales has well-documented influence on precipitation, evapotranspiration, soil moisture, infiltration flux, and can augment or diminish human stresses on water resources. Here the behavior and damping depth of climate-induced transient water flux in the vadose zone is explored. The damping depth is the depth in the vadose zone that the flux variation damps to 5% of the land surface variation. Steady-state recharge occurs when the damping depth is above the water table, and transient recharge occurs when the damping depth is below the water table. Findings are presented from major agroecosystems of the United States (U.S.), including the High Plains, Central Valley, California Coastal Basin, and Mississippi Embayment aquifer systems. Singular spectrum analysis (SSA) is used to identify quasi-periodic signals in precipitation and groundwater time series that are coincident with the Arctic Oscillation (AO) (6-12 mo cycle), Pacific/North American oscillation (PNA) (<1-4 yr cycle), El Niño/Southern Oscillation (ENSO) (2-7 yr cycle), North Atlantic Oscillation (NAO) (3-6 yr cycle), Pacific Decadal Oscillation (PDO) (15-30 yr cycle), and Atlantic Multidecadal Oscillation (AMO) (50-70 yr cycle). SSA results indicate that nearly all of the quasi-periodic signals in the precipitation and groundwater levels have a statistically significant lag correlation (95% confidence interval) with the AO, PNA, ENSO, NAO, PDO, and AMO indices. Results from HYDRUS-1D simulations indicate that transient water flux through the vadose zone are controlled by highly nonlinear interactions between mean infiltration flux and infiltration period related to the modes of climate

Implications of multi-scale sea level and climate variability for coastal resources

USGS Publications Warehouse

Karamperidou, Christina; Engel, Victor; Lall, Upmanu; Stabenau, Erik; Smith, Thomas J.

2013-01-01

While secular changes in regional sea levels and their implications for coastal zone management have been studied extensively, less attention is being paid to natural fluctuations in sea levels, whose interaction with a higher mean level could have significant impacts on low-lying areas, such as wetlands. Here, the long record of sea level at Key West, FL is studied in terms of both the secular trend and the multi-scale sea level variations. This analysis is then used to explore implications for the Everglades National Park (ENP), which is recognized internationally for its ecological significance, and is the site of the largest wetland restoration project in the world. Very shallow topographic gradients (3–6 cm per km) make the region susceptible to small changes in sea level. Observations of surface water levels from a monitoring network within ENP exhibit both the long-term trends and the interannual-to-(multi)decadal variability that are observed in the Key West record. Water levels recorded at four long-term monitoring stations within ENP exhibit increasing trends approximately equal to or larger than the long-term trend at Key West. Time- and frequency-domain analyses highlight the potential influence of climate mechanisms, such as the El Niño/Southern Oscillation and the North Atlantic Oscillation (NAO), on Key West sea levels and marsh water levels, and the potential modulation of their influence by the background state of the North Atlantic Sea Surface Temperatures. In particular, the Key West sea levels are found to be positively correlated with the NAO index, while the two series exhibit high spectral power during the transition to a cold Atlantic Multidecadal Oscillation (AMO). The correlation between the Key West sea levels and the NINO3 Index reverses its sign in coincidence with a reversal of the AMO phase. Water levels in ENP are also influenced by precipitation and freshwater releases from the northern boundary of the Park. The analysis of both

The 11-year solar radiation rhythm and the North Atlantic Oscillation during the last two centuries

NASA Astrophysics Data System (ADS)

Brunck, Heiko; Sirocko, Frank

2016-04-01

The study is based on a historical chronology of freezing events in central Europe during the last 230 years (river Rhine (Sirocko et al. 2012), Baltic Sea (Koslowski and Glaser, 1999) and Lake Constance (Dobras, 1983)). These regions display both significant similarities with extremely cold winters in central Germany for the years 1799, 1830, 1895, 1929, 1940, 1942, 1947, 1956 and 1963, as well as regional differences in timing and severity of cold winters. The statistical analysis of all 92 historical freezing events showed that 80 events occurred during a negative NAOwinter phase. The bootstrap test defined the results as extremely significant. To understand the climatic forcing behind the freezing chronology the NAO data set was smoothed by a three point running mean filter and compared with the 11- year cyclicity of the sunspot numbers. A complete NAO cycle can be observed within each solar cycle back to 1960 and from 1820 to 1900. From 1900 to 1960 the correlation between the Sun and NAO was weak. This on/off mode becomes visible only in the smoothed NAO data, when time intervals longer than "normal" weather observations are analysed. Statistical test for the coherence of the entire 230 years are insignificant. However, the relation is highly significant, if only the intervals from 1960 to 2010 and 1830 to 1900 are analysed. The phase correlation can be explained by temperature variations up to +-2.5°C in time series of stratospheric air temperature at 40 km height, where ozone is formed by ultraviolet solar radiation. Advanced analysis of sea surface temperatures from reanalysis data (ECMWF Data Archiv, 2013) between 30° - 40°N and 65° - 75°N indicate similar temperature variations in phase with the solar activity. Consequently, the 11 year solar periodicity is related to various parts of the Earth/Ocean/Atmosphere system and not only to the stratospheric signal. However, the NAO is the dominating mediator to implement a solar component into the

Decadal variability in the Northern Hemisphere winter circulation: Role of internal and external drivers

NASA Astrophysics Data System (ADS)

Maliniemi, V.; Asikainen, T.; Mursula, K.

2017-12-01

Northern Hemisphere winter circulation is known to be affected by both internal and external (solar-related) forcings. Earlier studies have shown ENSO and volcanic activity to produce negative and positive North Atlantic Oscillation (NAO) type responses, respectively. In addition, recent studies have shown a positive NAO response related to both geomagnetic activity (proxy for solar wind driven particle precipitation) and sunspot activity (proxy for solar irradiance). These solar-related signals have been suggested to be due to the changes in the polar vortex. Here the relative role of these four internal and external drivers on wintertime circulation in the Northern Hemisphere is studied. The phase of the quasi-biennial oscillation (QBO) is used to study the driver responses for different stratospheric conditions. Moreover, the effects are separated for early (Dec/Jan) and late (Feb/Mar) winter. The global pattern of ENSO is very similar (negative NAO) otherwise, but in early winter and westerly QBO the pattern is changed in the Atlantic sector to a weakly positive NAO. The positive NAO pattern due to volcanic activity is more pronounced for westerly QBO in both early and late winter. The positive NAO pattern produced by geomagnetic activity is obtained during easterly QBO phase in both early and late winter. Sunspot related NAO response in late winter is also strongly modulated by the QBO phase. These results imply that the stratospheric conditions expressed by QBO significantly modulate the way the internal and external drivers affect the Northern Hemisphere winter climate.

Slow Adaptation in the Face of Rapid Warming Leads to the Collapse of Atlantic Cod in the Gulf of Maine

NASA Astrophysics Data System (ADS)

Pershing, A. J.; Alexander, M. A.; Hernandez, C.; Kerr, L. A.; Le Bris, A.; Mills, K.; Nye, J. A.; Record, N.; Scannell, H. A.; Scott, J. D.; Sherwood, G. D.; Thomas, A. C.

2016-02-01

Climate change is altering conditions in all marine ecosystems, but the pace of change is not uniform. Rapid changes in environmental conditions pose a challenge for resource management, especially when available tools or policies assume the environment is stationary. Between 2004 and 2013, the Gulf of Maine and northwest Atlantic Shelf warmed at a rate that few large marine ecosystems have ever experienced. This warming was associated with a northward shift in the Gulf Stream and with Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation. The unprecedented warming led to reduced recruitment and enhanced mortality of Atlantic cod. Fisheries management has built-in feedbacks designed to reduce quotas as populations decline, but the management process could not keep pace with the rapid temperature-related changes in the Gulf of Maine cod stock. Future recovery of this fishery now depends on both sound management and favorable temperatures. The experience in the Gulf of Maine highlights the need to incorporate environmental factors into resource management and to build resiliency in coupled social-ecological systems. It also highlights a need for scientific and policy guidance for managing species threatened by future warming.

Impact of the North Atlantic dipole on climate changes over Eurasia

NASA Astrophysics Data System (ADS)

Serykh, Ilya

2017-04-01

Hydrophysical and meteorological characteristics of negative (1948-1976, 1999-2015) and positive (1977-1998) phases of the Pacific Decadal Oscillation (PDO) / Interdecadal Pacific Oscillation (IPO) in the North Atlantic and Eurasia are constructed and investigated. Specifically, the near-surface temperature, sea-level atmospheric pressure, wind speed, heat content of the upper 700 m ocean layer, water temperature and salinity at various depths, the latent and sensible heat fluxes from the ocean to the atmosphere are analyzed. The fields obtained from different sources (20thC_ReanV2c, ERA-20C, JRA-55, NCEP/NCAR, HadCRUT4, HadSLP2, NODC, Ishii, SODA, OAFlux, HadSST3, COBE2, ERSSTv4) are in good agreement and complement each other. This gives important information about the hydrometeorological conditions in the region under study. Analysis of these data has shown that in the upper 1000 m North Atlantic layer there is a thermal dipole which can be interpreted as an oceanic analog of the atmospheric North Atlantic Oscillation (NAO). An index of the North Atlantic Dipole (NAD) as the difference between the mean heat contents in the upper 700 m oceanic layer between the regions (50°-70° N; 60°-10° W) and (20°-40° N; 80°-30° W) is proposed. A possible physical mechanism of the internal oscillations with a quasi-60-year period in the North Atlantics-Eurasia system of ocean-atmosphere interactions is discussed. Dipole spatial structure from observations datasets and re-analyses were compared with the results of the Historical Experiment from the climate models of the CMIP5 project. It is found that several climate models reproduce dipole spatial structure of the near-surface temperature and sea level pressure anomalies similarly to these fields in the re-analyses considered. However, the phase diagrams of the gradient of near-surface temperature and sea level pressure between the Azores High and Island Low from climate models do not separate on subsets as the

A conditional stochastic weather generator for seasonal to multi-decadal simulations

NASA Astrophysics Data System (ADS)

Verdin, Andrew; Rajagopalan, Balaji; Kleiber, William; Podestá, Guillermo; Bert, Federico

2018-01-01

We present the application of a parametric stochastic weather generator within a nonstationary context, enabling simulations of weather sequences conditioned on interannual and multi-decadal trends. The generalized linear model framework of the weather generator allows any number of covariates to be included, such as large-scale climate indices, local climate information, seasonal precipitation and temperature, among others. Here we focus on the Salado A basin of the Argentine Pampas as a case study, but the methodology is portable to any region. We include domain-averaged (e.g., areal) seasonal total precipitation and mean maximum and minimum temperatures as covariates for conditional simulation. Areal covariates are motivated by a principal component analysis that indicates the seasonal spatial average is the dominant mode of variability across the domain. We find this modification to be effective in capturing the nonstationarity prevalent in interseasonal precipitation and temperature data. We further illustrate the ability of this weather generator to act as a spatiotemporal downscaler of seasonal forecasts and multidecadal projections, both of which are generally of coarse resolution.

North Atlantic Oscillation influence and weather types associated with winter total and extreme precipitation events in Spain

NASA Astrophysics Data System (ADS)

Queralt, S.; Hernández, E.; Barriopedro, D.; Gallego, D.; Ribera, P.; Casanova, C.

2009-12-01

An analysis of winter intensity and frequency of precipitation is presented, based on 102 daily precipitation stations over Spain and the Balearic Islands for the 1997-2006 decade. Precipitation stations have been merged in the eight different regions which compose the analyzed area by the use of an EOF analysis. NAO influence on the intensity and frequency of precipitation of each region is described in terms of mean precipitation, mean rain frequency, the number of extreme events, changes in the precipitation distribution and the prevalent synoptic configuration. Results indicate a non-stationary response; NAO signal being more evident in mid-late winter. Strong regional differences in the response to NAO are also found, which vary according to the specific character of the precipitation under analysis. Thus, NAO exerts a clear effect on the intensity of total and extreme precipitation rates in northern and westernmost Spanish regions, whereas the frequency of precipitation is clearly affected by NAO in central and southwestern areas. While the correlation between NAO and precipitation is negative for most of the analyzed area, two regions reveal positive responses to NAO in total precipitation occurrence and intensity for specific months. Further analyses reveal asymmetric responses to opposite phases of NAO in the precipitation distributions of some regions. The complex regional relationship between NAO and precipitation is also revealed through the modulation of the former in the preferred Circulation Weather Types associated to precipitation in each region. This spatially non-homogeneous NAO signal stresses the need of caution when employing Iberian precipitation as a proxy for NAO.

The Global Land-Ocean Temperature Index in Relation to Sunspot Number, the Atlantic Multidecadal Oscillation Index, the Mauna Loa Atmospheric Concentration of CO2, and Anthropogenic Carbon Emissions

NASA Technical Reports Server (NTRS)

Wilson, Robert M.

2013-01-01

Global warming/climate change has been a subject of scientific interest since the early 19th century. In particular, increases in the atmospheric concentration of carbon dioxide (CO2) have long been thought to account for Earth's increased warming, although the lack of a dependable set of observational data was apparent as late as the mid 1950s. However, beginning in the late 1950s, being associated with the International Geophysical Year, the opportunity arose to begin accurate continuous monitoring of the Earth's atmospheric concentration of CO2. Consequently, it is now well established that the atmospheric concentration of CO2, while varying seasonally within any particular year, has steadily increased over time. Associated with this rising trend in the atmospheric concentration of CO2 is a rising trend in the surface-air and sea-surface temperatures (SSTs). This Technical Publication (TP) examines the statistical relationships between 10-year moving averages (10-yma) of the Global Land-Ocean Temperature Index (GLOTI), sunspot number (SSN), the Atlantic Multidecadal Oscillation (AMO) index, and the Mauna Loa CO2 (MLCO2) index for the common interval 1964-2006, where the 10-yma values are used to indicate trends in the data. Scatter plots using the 10-yma values between GLOTI and each of the other parameters are determined, both as single-variate and multivariate fits. Scatter plots are also determined for MLCO2 using single-variate and bivariate (BV) fits, based on the GLOTI alone and the GLOTI in combination with the AMO index. On the basis of the inferred preferential fits for MLCO2, estimates for MLCO2 are determined for the interval 1885-1964, thereby yielding an estimate of the preindustrial level of atmospheric concentration of CO2. Lastly, 10-yma values of MLCO2 are compared against 10-yma estimates of the total carbon emissions (TCE) to determine the likelihood that manmade sources of carbon emissions are indeed responsible for the recent warming now

Influence of climate variability versus change at multi-decadal time scales on hydrological extremes

NASA Astrophysics Data System (ADS)

Willems, Patrick

2014-05-01

Recent studies have shown that rainfall and hydrological extremes do not randomly occur in time, but are subject to multidecadal oscillations. In addition to these oscillations, there are temporal trends due to climate change. Design statistics, such as intensity-duration-frequency (IDF) for extreme rainfall or flow-duration-frequency (QDF) relationships, are affected by both types of temporal changes (short term and long term). This presentation discusses these changes, how they influence water engineering design and decision making, and how this influence can be assessed and taken into account in practice. The multidecadal oscillations in rainfall and hydrological extremes were studied based on a technique for the identification and analysis of changes in extreme quantiles. The statistical significance of the oscillations was evaluated by means of a non-parametric bootstrapping method. Oscillations in large scale atmospheric circulation were identified as the main drivers for the temporal oscillations in rainfall and hydrological extremes. They also explain why spatial phase shifts (e.g. north-south variations in Europe) exist between the oscillation highs and lows. Next to the multidecadal climate oscillations, several stations show trends during the most recent decades, which may be attributed to climate change as a result of anthropogenic global warming. Such attribution to anthropogenic global warming is, however, uncertain. It can be done based on simulation results with climate models, but it is shown that the climate model results are too uncertain to enable a clear attribution. Water engineering design statistics, such as extreme rainfall IDF or peak or low flow QDF statistics, obviously are influenced by these temporal variations (oscillations, trends). It is shown in the paper, based on the Brussels 10-minutes rainfall data, that rainfall design values may be about 20% biased or different when based on short rainfall series of 10 to 15 years length, and

The effects of climate change on harp seals (Pagophilus groenlandicus).

PubMed

Johnston, David W; Bowers, Matthew T; Friedlaender, Ari S; Lavigne, David M

2012-01-01

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data.

The Effects of Climate Change on Harp Seals (Pagophilus groenlandicus)

PubMed Central

Johnston, David W.; Bowers, Matthew T.; Friedlaender, Ari S.; Lavigne, David M.

2012-01-01

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data. PMID:22238591

Joint spatiotemporal variability of global sea surface temperatures and global Palmer drought severity index values

USGS Publications Warehouse

Apipattanavis, S.; McCabe, G.J.; Rajagopalan, B.; Gangopadhyay, S.

2009-01-01

Dominant modes of individual and joint variability in global sea surface temperatures (SST) and global Palmer drought severity index (PDSI) values for the twentieth century are identified through a multivariate frequency domain singular value decomposition. This analysis indicates that a secular trend and variability related to the El Niño–Southern Oscillation (ENSO) are the dominant modes of variance shared among the global datasets. For the SST data the secular trend corresponds to a positive trend in Indian Ocean and South Atlantic SSTs, and a negative trend in North Pacific and North Atlantic SSTs. The ENSO reconstruction shows a strong signal in the tropical Pacific, North Pacific, and Indian Ocean regions. For the PDSI data, the secular trend reconstruction shows high amplitudes over central Africa including the Sahel, whereas the regions with strong ENSO amplitudes in PDSI are the southwestern and northwestern United States, South Africa, northeastern Brazil, central Africa, the Indian subcontinent, and Australia. An additional significant frequency, multidecadal variability, is identified for the Northern Hemisphere. This multidecadal frequency appears to be related to the Atlantic multidecadal oscillation (AMO). The multidecadal frequency is statistically significant in the Northern Hemisphere SST data, but is statistically nonsignificant in the PDSI data.

Improving Streamflow Forecasts Using Predefined Sea Surface Temperature

NASA Astrophysics Data System (ADS)

Kalra, A.; Ahmad, S.

2011-12-01

With the increasing evidence of climate variability, water resources managers in the western United States are faced with greater challenges of developing long range streamflow forecast. This is further aggravated by the increases in climate extremes such as floods and drought caused by climate variability. Over the years, climatologists have identified several modes of climatic variability and their relationship with streamflow. These climate modes have the potential of being used as predictor in models for improving the streamflow lead time. With this as the motivation, the current research focuses on increasing the streamflow lead time using predefine climate indices. A data driven model i.e. Support Vector Machine (SVM) based on the statistical learning theory is used to predict annual streamflow volume 3-year in advance. The SVM model is a learning system that uses a hypothesis space of linear functions in a Kernel induced higher dimensional feature space, and is trained with a learning algorithm from the optimization theory. Annual oceanic-atmospheric indices, comprising of Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), El Niño-Southern Oscillations (ENSO), and a new Sea Surface Temperature (SST) data set of "Hondo" Region for a period of 1906-2005 are used to generate annual streamflow volumes. The SVM model is applied to three gages i.e. Cisco, Green River, and Lees Ferry in the Upper Colorado River Basin in the western United States. Based on the performance measures the model shows very good forecasts, and the forecast are in good agreement with measured streamflow volumes. Previous research has identified NAO and ENSO as main drivers for extending streamflow forecast lead-time in the UCRB. Inclusion of "Hondo Region" SST information further improve the model's forecasting ability. The overall results of this study revealed that the annual streamflow of the UCRB is significantly influenced by

Covariability of seasonal temperature and precipitation over the Iberian Peninsula in high-resolution regional climate simulations (1001-2099)

NASA Astrophysics Data System (ADS)

Fernández-Montes, S.; Gómez-Navarro, J. J.; Rodrigo, F. S.; García-Valero, J. A.; Montávez, J. P.

2017-04-01

Precipitation and surface temperature are interdependent variables, both as a response to atmospheric dynamics and due to intrinsic thermodynamic relationships and feedbacks between them. This study analyzes the covariability of seasonal temperature (T) and precipitation (P) across the Iberian Peninsula (IP) using regional climate paleosimulations for the period 1001-1990, driven by reconstructions of external forcings. Future climate (1990-2099) was simulated according to SRES scenarios A2 and B2. These simulations enable exploring, at high spatial resolution, robust and physically consistent relationships. In winter, positive P-T correlations dominate west-central IP (Pearson correlation coefficient ρ = + 0.43, for 1001-1990), due to prevalent cold-dry and warm-wet conditions, while this relationship weakens and become negative towards mountainous, northern and eastern regions. In autumn, negative correlations appear in similar regions as in winter, whereas for summer they extend also to the N/NW of the IP. In spring, the whole IP depicts significant negative correlations, strongest for eastern regions (ρ = - 0.51). This is due to prevalent frequency of warm-dry and cold-wet modes in these regions and seasons. At the temporal scale, regional correlation series between seasonal anomalies of temperature and precipitation (assessed in 31 years running windows in 1001-1990) show very large multidecadal variability. For winter and spring, periodicities of about 50-60 years arise. The frequency of warm-dry and cold-wet modes appears correlated with the North Atlantic Oscillation (NAO), explaining mainly co-variability changes in spring. For winter and some regions in autumn, maximum and minimum P-T correlations appear in periods with enhanced meridional or easterly circulation (low or high pressure anomalies in the Mediterranean and Europe). In spring and summer, the Atlantic Multidecadal Oscillation shows some fingerprint on the frequency of warm/cold modes. For

Impact of fluctuation of hydro-physical regime in the North Atlantic on the climate of Eurasia

NASA Astrophysics Data System (ADS)

Serykh, Ilya; Anisimov, Mikhail; Byshev, Vladimir; Neiman, Victor; Romanov, Juri

2015-04-01

In the mid-1970s a heat content in the North Atlantic Ocean has substantially changed. Because of its high energy value the event appears to have a significant impact on the regional environment. To verify this suggestion we analyzed the global ocean-atmosphere data related to the negative (1950-1970) and positive (1980-1999) phases of the North Atlantic Oscillation (NAO). The analysis of these data have shown the existence of a thermal dipole in the North Atlantic upper layer which can be interpreted in a sense as an oceanic counterpart of atmospheric NAO. To identify this North Atlantic Dipole (NAD) its index was considered as the ocean 0-100-m layer temperature difference between regions (20°-40°N; 80°-30°W) and (50°-70°N; 60°-10°W). Then the NAD index was suggested a possible physical mechanism factor of the regional ocean-atmosphere system variability which in turn could produce a draw effect on the recent climate of Eurasia. The study showed that the current phase (2000-2013) of the climate in the North Atlantic region becomes qualitatively similar to the situation, typical for period 1950-1970, when the index of continentality in the Eurasian region was a very high. There is a reason to believe that in the coming decades this index is likely to increase, that would be primarily manifested by relatively cold weather in winters and by hot-dry summer seasons. To assess the variability of ocean heat content it was used a General Ocean Circulation model developed at the Institute of numerical mathematics, Russian Academy of Sciences. This model belongs to the class of σ-models, and its distinguishing feature is the splitting of the physical processes and spatial coordinates. By using the model there were performed numerical experiments for the evolution of hydrophysical regime of the North Atlantic Ocean at the period of 1958-2006, with a spatial resolution of 0.25°x0.25° for 25 horizons with time window of 1 hour. As initial conditions for the

Sensitivity of marine protected area network connectivity to atmospheric variability

NASA Astrophysics Data System (ADS)

Fox, Alan D.; Henry, Lea-Anne; Corne, David W.; Roberts, J. Murray

2016-11-01

International efforts are underway to establish well-connected systems of marine protected areas (MPAs) covering at least 10% of the ocean by 2020. But the nature and dynamics of ocean ecosystem connectivity are poorly understood, with unresolved effects of climate variability. We used 40-year runs of a particle tracking model to examine the sensitivity of an MPA network for habitat-forming cold-water corals in the northeast Atlantic to changes in larval dispersal driven by atmospheric cycles and larval behaviour. Trajectories of Lophelia pertusa larvae were strongly correlated to the North Atlantic Oscillation (NAO), the dominant pattern of interannual atmospheric circulation variability over the northeast Atlantic. Variability in trajectories significantly altered network connectivity and source-sink dynamics, with positive phase NAO conditions producing a well-connected but asymmetrical network connected from west to east. Negative phase NAO produced reduced connectivity, but notably some larvae tracked westward-flowing currents towards coral populations on the mid-Atlantic ridge. Graph theoretical metrics demonstrate critical roles played by seamounts and offshore banks in larval supply and maintaining connectivity across the network. Larval longevity and behaviour mediated dispersal and connectivity, with shorter lived and passive larvae associated with reduced connectivity. We conclude that the existing MPA network is vulnerable to atmospheric-driven changes in ocean circulation.

Seasonal to multi-decadal trends in apparent optical properties in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Allen, James G.; Nelson, Norman B.; Siegel, David A.

2017-01-01

Multi-decadal, monthly observations of optical and biogeochemical properties, made as part of the Bermuda Bio-Optics Project (BBOP) at the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea, allow for the examination of temporal trends in vertical light attenuation and their potential controls. Trends in the magnitude of the diffuse attenuation coefficient, Kd(λ), and a proxy for its spectral shape reflect changes in phytoplankton and chromophoric dissolved organic matter (CDOM) characteristics. The length and methodological consistency of this time series provide an excellent opportunity to extend analyses of seasonal cycles of apparent optical properties to interannual and decadal time scales. Here, we characterize changes in the magnitude and spectral shape proxy of diffuse attenuation coefficient spectra and compare them to available biological and optical data from the BATS time series program. The time series analyses reveal a 1.01%±0.18% annual increase of the magnitude of the diffuse attenuation coefficient at 443 nm over the upper 75 m of the water column while showing no significant change in selected spectral characteristics over the study period. These and other observations indicate that changes in phytoplankton rather than changes in CDOM abundance are the primary driver for the diffuse attenuation trends on multi-year timescales for this region. Our findings are inconsistent with previous decadal-scale global ocean water clarity and global satellite ocean color analyses yet are consistent with recent analyses of the BATS time series and highlight the value of long-term consistent observation at ocean time series sites.

Multi-Decadal Change of Atmospheric Aerosols and Their Effect on Surface Radiation

NASA Technical Reports Server (NTRS)

Chin, Mian; Diehl, Thomas; Tan, Qian; Wild, Martin; Qian, Yun; Yu, Hongbin; Bian, Huisheng; Wang, Weiguo

2012-01-01

We present an investigation on multi-decadal changes of atmospheric aerosols and their effects on surface radiation using a global chemistry transport model along with the near-term to long-term data records. We focus on a 28-year time period of satellite era from 1980 to 2007, during which a suite of aerosol data from satellite observations and ground-based remote sensing and in-situ measurements have become available. We analyze the long-term global and regional aerosol optical depth and concentration trends and their relationship to the changes of emissions" and assess the role aerosols play in the multi-decadal change of solar radiation reaching the surface (known as "dimming" or "brightening") at different regions of the world, including the major anthropogenic source regions (North America, Europe, Asia) that have been experiencing considerable changes of emissions, dust and biomass burning regions that have large interannual variabilities, downwind regions that are directly affected by the changes in the source area, and remote regions that are considered to representing "background" conditions.

Pronounced differences between observed and CMIP5-simulated multidecadal climate variability in the twentieth century

NASA Astrophysics Data System (ADS)

Kravtsov, Sergey

2017-06-01

Identification and dynamical attribution of multidecadal climate undulations to either variations in external forcings or to internal sources is one of the most important topics of modern climate science, especially in conjunction with the issue of human-induced global warming. Here we utilize ensembles of twentieth century climate simulations to isolate the forced signal and residual internal variability in a network of observed and modeled climate indices. The observed internal variability so estimated exhibits a pronounced multidecadal mode with a distinctive spatiotemporal signature, which is altogether absent in model simulations. This single mode explains a major fraction of model-data differences over the entire climate index network considered; it may reflect either biases in the models' forced response or models' lack of requisite internal dynamics, or a combination of both.