Arctic Oscillation and Antarctic Oscillation in internal atmospheric variability

n this study, we investigated the features of Arctic Oscillation (AO) and Antarctic Oscillation (AAO), that is, the annular modes in the extratropics, in the internal atmospheric variability attained through an ensemble of integrations by an atmospheric general circulation model (AGCM) forced with the global observed SSTs. We focused on the interannual variability of AO/AAO, which is dominated by internal atmospheric variability. In comparison with previous observed results, the AO/AAO in internal atmospheric variability bear some similar characteristics, but exhibit a much clearer spatial structure: significant correlation between the North Pacific and North Atlantic centers of action, much stronger and more significant associated precipitation anomalies, and the meridional displacement of upper-tropospheric westerly jet streams in the Northern/Southern Hemisphere. In addition, we examined the relationship between the North Atlantic Oscillation (NAO)/AO and East Asian winter monsoon (EAWM). It has been shown that in the internal atmospheric variability, the EAWM variation is significantly related to the NAO through upper-tropospheric atmospheric teleconnection patterns.

Evolving southwest African response to abrupt deglacial North Atlantic climate change events

Climate change during the last deglaciation was strongly influenced by the „bipolar seesaw‟, producing antiphase climate responses between the North and South Atlantic. However, mounting evidence demands refinements of this model, with the occurrence of abrupt events in southern low to mid latitudes occurring in-phase with North Atlantic climate. Improved constraints on the north-south phasing and spatial extent of these events are therefore critical to
understanding the mechanisms that propagate abrupt events within the climate system. We present a 19,400 year multi-proxy record of climate change obtained from a rock hyrax midden in southernmost Africa. Arid anomalies in phase with the Younger Dryas and 8.2 ka events are apparent, indicating a clear shift in the influence of the bipolar seesaw, which diminished as the Earth warmed, and was succeeded after ~14.6 ka by the emergence of a dominant interhemispheric atmospheric teleconnection.

Response of the Asian summer monsoon to a weakening of Atlantic thermohaline circulation

Various paleoclimate records have shown that the Asian monsoon was punctuated by numerous suborbital time-scale events, and these events were coeval with those that happened in the North Atlantic. This study investigates the Asian summer monsoon responses to the Atlantic Ocean forcing by applying an additional freshwater flux into the North Atlantic. The simulated results indicate that the cold North Atlantic and warm South Atlantic induced by the weakened Atlantic thermohaline circulation (THC) due to the freshwater flux lead to significantly suppressed Asian summer monsoon. The authors analyzed the detailed processes of the Atlantic Ocean forcing on the Asian summer monsoon, and found that the atmospheric teleconnection in the eastern and central North Pacific and the atmosphere-ocean interaction in the tropical North Pacific play the most crucial role. Enhanced precipitation in the subtropical North Pacific extends the effects of Atlantic Ocean forcing from the eastern Pacific into the western Pacific, and the atmosphere-ocean interaction in the tropical Pacific and Indian Ocean intensifies the circulation and precipitation anomalies in the Pacific and East Asia.

Twentieth Century Delta δC Variability in Surface Water Dissolved Inorganic Carbon Recorded by Coralline Algae in the Northern North Pacific Ocean and the Bering Sea

The oxygen isotopic composition and Mg/Ca ratios in the skeletons of long-lived coralline algae record ambient seawater temperature over time. Similarly, the carbon isotopic composition in the skeletons record delta(13)C values of ambient seawater dissolved inorganic carbon. Here, we measured delta(13)C in the coralline alga Clathromorphum nereostratum to test the feasibility of reconstructing the intrusion of anthropogenic CO(2) into the northern North Pacific Ocean and Bering Sea. The delta(13)C was measured in the high Mgcalcite skeleton of three C. nereostratum specimens from two islands 500 km apart in the Aleutian archipelago. In the records spanning 1887 to 2003, the average decadal rate of decline in delta(13)C values increased from 0.03% yr(-1) in the 1960s to 0.095% yr(-1) in the 1990s, which was higher than expected due to solely the delta(13)C-Suess effect. Deeper water in this region exhibits higher concentrations of CO(2) and low delta(13)C values. Transport of deeper water into surface water (i.e., upwelling) increases when the Aleutian Low is intensified. We hypothesized that the acceleration of the delta(13)C decline may result from increased upwelling from the 1960s to 1990s, which in turn was driven by increased intensity of the Aleutian Low. Detrended delta(13)C records also varied on 4-7 year and bidecadal timescales supporting an atmospheric teleconnection of tropical climate patterns to the northern North Pacific Ocean and Bering Sea manifested as changes in upwelling.

Stable isotope record of benthic foraminifera from the Gulf of California

A high-resolution, accelerator radiocarbon dated climate record of the interval 8,000-18,000 years B.P. from Deep Sea Drilling Project site 480 (Guaymas Basin, Gulf of California) shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation. Nonlaminated sediments are associated with cooler climatic conditions during the late glacial (up to 13,000 years B.P.), and from 10,300 to 10,800 years B.P., equivalent to the Younger Dryas event of the North Atlantic region. We propose that the changes from laminated (varved) to nonlaminated sediments resulted from increased oxygen content in Pacific intermediate waters during the glacial and the Younger Dryas episodes, and that the forcing for the latter event was global in scope. Prominent events of low delta18O are recorded in benthic foraminifera from 8,000 to 10,000 and at 12,000 years B.P.; evidence for an earlier event between 13,500 and 15,000 years B.P. is weaker. Maximum delta18O is found to have occurred 10,500, 13,500, and 15,000 years ago (and beyond). Oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of Pacific waters of intermediate depth during deglaciation or environmental changes within the Gulf of California region. Several lines of evidence suggest that during deglaciation the climate of the American southwest was marked by increased precipitation that could have lowered salinity in the Gulf of California. Recent modelling studies show that cooling of the Gulf of Mexico due to glacial meltwater injection, which is believed to have occurred at least twice during deglaciation, would have resulted in increased precipitation with respect to evaporation in the American southwest during summertime. The timing of deglacial events in the Gulf of Mexico and the Gulf of California supports such an atmospheric teleconnection.

Temperature variabilty in the southeastern Black-Sea during 64-20ka BP

The Eurasian inland propagation of temperature anomalies during glacial millennial-scale climate variability is poorly understood but this knowledge is crucial to understanding hemisphere-wide atmospheric teleconnection patterns and climate mechanisms. Based on biomarkers and geochemical paleothermometers, a pronounced continental temperature variability between 64,000 and 20,000 years ago, coinciding with the Greenland Dansgaard-Oeschger cycles, was determined in a well-dated sediment record from the formerly enclosed Black Sea. Cooling during Heinrich events was not stronger than during other stadials in the Black Sea. This is corroborated by modeling results showing that regular Dansgaard-Oeschger cycles penetrated deeper into the Eurasian continent than Heinrich events. The pattern of coastal ice-rafted detritus suggests a strong dependence on the climate background state, with significantly milder winters during periods of reduced Eurasian ice sheets and an intensified meridional atmospheric circulation.

Laminated sediment cores in the Bering Sea

During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin.We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bølling-Allerød and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling-Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and d18O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions.We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1ml/l and caused laminae preservation. Calculated benthic-planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bølling-Allerød and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730-990 yr during the Bølling-Allerød, 800-1100 yr in the Younger Dryas, and 765-775 yr for the Preboreal.

The role of the Indian Ocean sector and sea surface salinity for prediction of the coupled Indo-Pacific system

The purpose of this dissertation is to evaluate the potential downstream influence of the Indian Ocean (IO) on El Niño/Southern Oscillation (ENSO) forecasts through the oceanic pathway of the Indonesian Throughflow (ITF), atmospheric teleconnections between the IO and Pacific, and assimilation of IO observations. Also the impact of sea surface salinity (SSS) in the Indo-Pacific region is assessed to try to address known problems with operational coupled model precipitation forecasts. The ITF normally drains warm fresh water from the Pacific reducing the mixed layer depths (MLD). A shallower MLD amplifies large-scale oceanic Kelvin/Rossby waves thus giving ~10% larger response and more realistic ENSO sea surface temperature (SST) variability compared to observed when the ITF is open. In order to isolate the impact of the IO sector atmospheric teleconnections to ENSO, experiments are contrasted that selectively couple/decouple the interannual forcing in the IO. The interannual variability of IO SST forcing is responsible for 3 month lagged widespread downwelling in the Pacific, assisted by off-equatorial curl, leading to warmer NINO3 SST anomaly and improved ENSO validation (significant from 3-9 months). Isolating the impact of observations in the IO sector using regional assimilation identifies large-scale warming in the IO that acts to intensify the easterlies of the Walker circulation and increases pervasive upwelling across the Pacific, cooling the eastern Pacific, and improving ENSO validation (r ~ 0.05, RMS~0.08C). Lastly, the positive impact of more accurate fresh water forcing is demonstrated to address inadequate precipitation forecasts in operational coupled models. Aquarius SSS assimilation improves the mixed layer density and enhances mixing, setting off upwelling that eventually cools the eastern Pacific after 6 months, counteracting the pervasive warming of most coupled models and significantly improving ENSO validation from 5-11 months. In summary, the ITF oceanic pathway, the atmospheric teleconnection, the impact of observations in the IO, and improved Indo-Pacific SSS are all responsible for ENSO forecast improvements, and so each aspect of this study contributes to a better overall understanding of ENSO. Therefore, the upstream influence of the IO should be thought of as integral to the functioning of ENSO phenomenon.

Atmospheric Soluble Dust Records from a Tibetan Ice Core: Possible Climate Proxies and Teleconnection With the Pacific Decadal Oscillation

In autumn 2005, a joint expedition between the University of Maine and the Institute of Tibetan Plateau Research recovered three ice cores from Guoqu Glacier (33 degrees 34'37.80 '' N, 91 degrees 10'35.3 '' E, 5720 m above sea level) on the northern side of Mt. Geladaindong, central Tibetan Plateau. Isotopes ( delta(18)O), major soluble ions (Na(+), K(+), Mg(2+), Ca(2+), Cl(-), NO(3)(-), SO(4)(2-)), and radionuclide (beta-activity) measurements from one of the cores revealed a 70-year record (1935-2005). Statistical analysis of major ion time series suggests that atmospheric soluble dust species dominate the chemical signature and that background dust levels conceal marine ion species deposition. The soluble dust time series have interspecies relations and common structure (empirical orthogonal function (EOF) 1), suggesting a similar soluble dust source or transport route. Annual and seasonal correlations between the EOF 1 time series and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis climate variables (1948-2004) suggest that the Mt. Geladaindong ice core record provides a proxy for local and regional surface pressure. An approximately threefold decrease of soluble dust concentrations in the middle to late 1970s, accompanied by regional increases in pressure and temperature and decreases in wind velocity, coincides with the major 1976-1977 shift of the Pacific Decadal Oscillation (PDO) from a negative to a positive state. This is the first ice core evidence of a potential teleconnection between central Asian atmospheric soluble dust loading and the PDO. Analysis of temporally longer ice cores from Mt. Geladaindong may enhance understanding of the relationship between the PDO and central Asian atmospheric circulation and subsequent atmospheric soluble dust loading.

Pacific sea surface temperature associations with southwestern United States summer rainfall and atmospheric circulation

Pacific sea surface temperatures (SSTs) are examined for their associations with (1) summer rainfall, and (2) the latitude location of the mid-tropospheric subtropical high pressure ridge (STR) in the southwestern United States during 1945 to 1986. Extreme northward (southward) displacements of STR are associated with wet (dry) summers over Arizona and an enhanced (weakened) gradient of SST off the California and Baja coasts. These tend to follow winters marked by positive (negative) phases of the PNA, Pacific/North America, teleconnection pattern. Recent decadal variations of Arizona summer rainfall (1950s wet; 1970s dry) appear similarly related to southwestern United States synoptic circulation and eastern Pacific SSTs.

Southern Hemispheric Features and their Teleconnection with Indian Summer Monsoon

This thesis entitled southern hemispheric features and their Teleconnection with indian summer monsoon.Southern hemisphere is entirely distinct from the northern hemisphere in many aspects, which is well reflected in atmospheric and oceanic properties.The thesis consists of eight chapters, in which the first chapter contains an overview of southern hemisphere. In this chapter, variability in southern hemisphere is described along with Indian summer monsoon and its teleconnection. The different types of data sets used and various methodologies adopted in the present thesis were described in Chapter 2. The period of climate shift and the magnitude of anomalies after the climate shift, which extended from troposphere to stratopause level, were investigated in detail and presented in chapter 3. Chapter 4 depicts the recent trend and variability in southern stratosphere. The higher order variability during various months and the frequency of extremity is included in this chapter.Climatology of divergence and convergence after the documented shift is reported in chapter 5.Southern extratropical connection to Indian summer monsoon through the modulation of SAM is presented in Chapter 6.Chapter 7 deals with the modulation of SAM‐Monsoon link through North Atlantic Oscillation.

Summertime precipitation variability over europe and its links to atmospheric dynamics and evaporation

Gridded monthly precipitation data for 1979-2006 from the Global Precipitation Climatology Project are used to investigate interannual summer precipitation variability over Europe and its links to regional atmospheric circulation and evaporation. The first empirical orthogonal function (EOF) mode of European precipitation, explaining 17.2%-22.8% of its total variance, is stable during the summer season and is associated with the North Atlantic Oscillation. The spatialtemporal structure of the second EOF mode is less stable and shows monthtomonth variations during the summer season. This mode is linked to the Scandinavian teleconnection pattern. Analysis of links between leading EOF modes of regional precipitation and evaporation has revealed a significant link between precipitation and evaporation from the European land surface, thus, indicating an important role of the local processes in summertime precipitation variability over Europe. Weaker, but statistically significant links have been found for evaporation from the surface of the Mediterranean and Baltic Seas. Finally, in contrast to winter, no significant links have been revealed between European precipitation and evaporation in the North Atlantic during the summer season.

Interactions between mass balance, atmospheric circulation, and recent climate change on the Djankuat Glacier, Caucasus Mountains, Russia

This paper reports recent changes in the mass balance record from the Djankuat Glacier, central greater Caucasus, Russia, and investigates possible relationships between the components of mass balance, local climate, and distant atmospheric forcing. The results clearly show that a strong warming signal has emerged in the central greater Caucasus, particularly since the 1993/1994 mass balance year, and this has led to a significant increase in the summer ablation of Djankuat. At the same time, there has been no compensating consistent increase in winter precipitation and accumulation leading to the strong net loss of mass and increase in glacier runoff. Interannual variability in ablation and accumulation is partly associated with certain major patterns of Northern Hemisphere climatic variability. The positive phase of the North Pacific (NP) teleconnection pattern forces negative geopotential height and temperature anomalies over the Caucasus in summer and results in reduced summer melt, such as in the early 1990s, when positive NP extremes resulted in a temporary decline in ablation rates. The positive phase of the NP is related to El Nino-Southern Oscillation, and it is possible that a teleconnection between the tropical Pacific sea surface temperatures and summer air temperatures in the Caucasus is bridged through the NP pattern. More recently, the NP pattern was predominantly negative, and this distant moderating forcing on summer ablation in the Caucasus was absent. Statistically significant correlations are observed between accumulation and the Scandinavian (SCA) teleconnection pattern. The frequent occurrence of the positive SCA phase at the beginning of accumulation season results in lower than average snowfall and reduced accumulation. The relationship between the North Atlantic Oscillation (NAO), Arctic Oscillation, and accumulation is weak, although positive precipitation anomalies in the winter months are associated with the negative phase of the NAO. A stronger positive correlation is observed between accumulation on Djankuat and geopotential height over the Bay of Biscay unrelated to the established modes of the Northern Hemisphere climatic variability. These results imply that the mass balance of Djankuat is sensitive to the natural variability in the climate system. Distant forcing, however, explains only 16% of the variance in the ablation record and cannot fully explain the recent increase in ablation and negative mass balance.

Do High-Frequency Eddies Contribute to Low-Frequency Teleconnection Tendencies?*

An isentropic potential vorticity (PV) budget analysis is employed to examine the role of synoptic transients, advection, and nonconservative processes as forcings for the evolution of the low-frequency PV anomalies locally and those associated with the North Atlantic Oscillation (NAO) and the Pacific–North American (PNA) pattern. Specifically, the rate of change of the low-frequency PV is expressed as a sum of tendencies due to divergence of eddy transport, advection by the low-frequency flow (hereafter referred to as advection), and the residual nonconservative processes. The balance between the variances and covariances of these terms is illustrated using a novel vector representation. It is shown that for most locations, as well as for the PNA pattern, the PV variability is dominantly driven by advection. The eddy forcing explains a small amount of the tendency variance. For the NAO, the role of synoptic eddy fluxes is found to be stronger, explaining on average 15% of the NAO tendency variance. Previous studies have not assessed quantitively how the various forcings balance the tendency. Thus, such studies may have overestimated the role of eddy fluxes for the evolution of teleconnections by examining, for example, composites and regressions that indicate maintenance, rather than evolution driven by the eddies. The authors confirm this contrasting view by showing that during persistent blocking (negative NAO) episodes the eddy driving is relatively stronger.

Transient teleconnection event at the onset of a planet-encircling dust storm on Mars

We use proper orthogonal decomposition (POD) to study a transient teleconnection event at the onset of the 2001 planet-encircling dust storm on Mars, in terms of empirical orthogonal functions (EOFs). There are several differences between this and previous studies of atmospheric events using EOFs. First, instead of using a single variable such as surface pressure or geopotential height on a given pressure surface, we use a dataset describing the evolution in time of global and fully three-dimensional atmospheric fields such as horizontal velocity and temperature. These fields are produced by assimilating Thermal Emission Spectrometer observations from NASA's Mars Global Surveyor spacecraft into a Mars general circulation model. We use total atmospheric energy (TE) as a physically meaningful quantity which weights the state variables. Second, instead of adopting the EOFs to define teleconnection patterns as planetary-scale correlations that explain a large portion of long time-scale variability, we use EOFs to understand transient processes due to localised heating perturbations that have implications for the atmospheric circulation over distant regions. The localised perturbation is given by anomalous heating due to the enhanced presence of dust around the northern edge of the Hellas Planitia basin on Mars. We show that the localised disturbance is seemingly restricted to a small number (a few tens) of EOFs. These can be classified as low-order, transitional, or high-order EOFs according to the TE amount they explain throughout the event. Despite the global character of the EOFs, they show the capability of accounting for the localised effects of the perturbation via the presence of specific centres of action. We finally discuss possible applications for the study of terrestrial phenomena with similar characteristics.