Eva Bauer

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Matthew J. Brown

Southern Illinois University

Ian James Kidd

University of Nottingham

Marta Diaz-Guardamino

Durham University

Theodore Arabatzis

National & Kapodistrian University of Athens

Henry Tantaleán

Universidad Nacional Mayor de San Marcos

Julian Thomas

The University of Manchester

Katharina Rebay-Salisbury

University of Vienna

Marie Louise Stig Sørensen

University of Cambridge

Gary Feinman

Field Museum

Alexander Fantalkin

Tel Aviv University

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Papers by Eva Bauer

The WAM model - a third generation ocean wave prediction model. J Phys Oceanogr

by Eva Bauer and Luciana Bertotti

Journal of Physical Oceanography

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Global Operational Remote Sensing and Modelling of Ocean Waves

An overview is given of current operational methods for retrieving twodimensional ocean wave spec... more An overview is given of current operational methods for retrieving twodimensional ocean wave spectra from near real-time ERS-1 SAR wave mode (SWM) imagette spectra. The SWM data quality and performance of the WASAR algorithm are assessed. Sensitivity analyses and validation studies are performed using two-dimensional NOAA buoy data as well as TOPEX and ERS-1 altimeter-derived signi cant wave heights. An intercomparison between SWM-retrieved and WAM model spectral parameters shows a good overall agreement, however with a small but systematic overprediction of windseas and underprediction of swell by the WAM. While the former can be explained by to too strong forcing by the ECMWF wind elds, the latter is attributed to too strong damping of swell by the WAM. Some evidence is found of a misalignment between the wind speed vector and the wind stress in the presence of swell.

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Assessment of Climate Forcing Contributing to the Late Maunder Minimum

During the last millennium, variations of the solar luminosity, the volcanic activity, the land u... more During the last millennium, variations of the solar luminosity, the volcanic activity, the land use changes and the anthropogenic CO2 gas emissions constitute the major forcing functions of the Earth climate. Recent reconstructions of these forcing functions are employed to estimate the effect on the climate system by using CLIMBER-2, a coupled atmosphere-ocean-biosphere model of intermediate complexity. The forced CLIMBER-2 simulations involve changes in temperature and precipitation which are compared to simulations of comprehensive atmosphere-ocean general circulation models and to observational data. Volcanism is found to enhance decadal and interannual climate variability in the simulation. The solar-forced simulations capture satisfactorily the centennial climate variability reconstructed from paleoclimate data, and in particular, the long-term climate anomalies of the ``Medieval Warm Period'' and the ``Little Ice Age''. The climate of the Little Ice Age, and m...

Bauer etal Simulation8.2Cold Event P2004

1] The cold climate anomaly about 8200 years ago is investigated with CLIMBER-2, a coupled atmosp... more 1] The cold climate anomaly about 8200 years ago is investigated with CLIMBER-2, a coupled atmosphereocean-biosphere model of intermediate complexity. This climate model simulates a cooling of about 3.6 K over the North Atlantic induced by a meltwater pulse from Lake Agassiz routed through the Hudson strait. The meltwater pulse is assumed to have a volume of 1.6 Â 10 14 m 3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the Laurentide Ice Sheet (LIS). We present a possible mechanism which can explain the centennial duration of the 8.2 ka cold event. The mechanism is related to the existence of an additional equilibrium climate state with reduced North Atlantic Deep Water (NADW) formation and a southward shift of the NADW formation area. Hints at the additional climate state were obtained from the largely varying duration of the pulse-induced cold episode in response to overlaid random freshwater fluctuations in Monte Carlo simulations. The model equilibrium state was attained by releasing a weak multicentury freshwater flux through the St. Lawrence pathway completed by the meltwater pulse. The existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8.2 ka event. The results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance.

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Atmospheric Dust Burden for Last Glacial, Present and Doubled Carbon Dioxide Climate Conditions from CLIMBER2 Simulations

The atmospheric burden of mineral dust is controlled by processes of dust emission, transport and... more The atmospheric burden of mineral dust is controlled by processes of dust emission, transport and deposition. Changes in vegetation cover from natural or anthropogenic climate change are a key factor for changes in dust emission. Increases in surface temperature and precipitation imply a decrease of the land area with no or little vegetation cover and consequently the potential dust source area diminishes. Other factors controlling the strength of dust emission are surface wind speed and soil dryness which also depend on climate conditions. Our goal is to simulate with the CLIMBER-2 Earth system model the mineral dust cycle dynamically consistent with the climate system and to investigate the radiative impact of the dust cycle on the climate system. As an essential step towards this goal we demonstrate that the present-day distribution of dust optical thickness simulated with the dust cycle agrees reasonably with GCM simulations and satellite retrievals. Also, the simulated dust dep...

Comparison of assimilation results from an optimal interpolation and the Green's function method using ERS-1 SAR wave mode spectra

Sensitivity simulations with direct radiative forcing by aeolian dust during glacial cycles

Climate of the Past Discussions, 2014

Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first ... more Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first time with an Earth system model of intermediate complexity over the late Pleistocene period. Correlations between climate and dust deposition records suggest that aeolian dust potentially plays an important role for the evolution of glacial cycles. Here climatic effects from the dust direct radiative forcing (DRF) caused by absorption and scattering of solar radiation are investigated. Key elements controlling the dust DRF are the atmospheric dust distribution and the absorption-scattering efficiency of dust aerosols. Effective physical parameters in the description of these elements are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters can be reasonably constrained, the simulated dust DRF spans a wide uncertainty range related to the strong nonlinearity of the Earth system. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several watts per square metre in regions close to major dust sources and negligible values elsewhere. In the case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In the case of low absorption efficiency, the dust DRF can produce a significant global cooling in glacial periods, which leads to a doubling of the maximum glacial ice volume relative to the case with small dust DRF. DRF-induced temperature and precipitation changes can either be attenuated or amplified through a feedback loop involving the dust cycle. The sensitivity experiments suggest that depending on dust optical parameters, dust DRF has the potential to either damp or reinforce glacial-interglacial climate changes.

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An earth system model of intermediate complexity for studies of Quaternary climate variability

IOP Conference Series: Earth and Environmental Science, 2009

ABSTRACT This article was submitted without an abstract, please refer to the full-text PDF file.

Bauer etal Assessing climate forcings for past Millennium GRL2003

1] The effects of natural and anthropogenic forcings (solar activity, volcanism, atmospheric CO 2... more 1] The effects of natural and anthropogenic forcings (solar activity, volcanism, atmospheric CO 2 concentration, deforestation) on climate changes are estimated with the Earth system model of intermediate complexity, CLIMBER-2, for the past millennium. Simulated surface air temperatures for the Northern Hemisphere from the combined forcing correlate reasonably well with paleoclimatic data (r = 0.70). The largest negative anomalies occur when insolation minima coincide with volcanic eruptions. Anthropogenic forcings impose additional climate changes after 1850. The increasing warming from increasing CO 2 concentrations is attenuated by the cooling effect from deforestation. Results from differently combined forcings suggest that the relatively cool climate in the second half of 19th century is largely attributable to cooling from deforestation.

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Assessing climate forcings of the Earth system for the past millennium

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Final Report Of The European Space Agency Pilot Project

Introduction One of the major drivers of the first European Remote Sensing Satellite ERS-1, launc... more Introduction One of the major drivers of the first European Remote Sensing Satellite ERS-1, launched on 17 July 1991, was applications in wave research and wave forecasting. The Synthetic Aperture Radar (SAR) of ERS-1 provided for the first time detailed spectral information on the ocean surface waves. The SAR Wave Mode (SWM) data were available continuously and in quasi-real time from the global oceans. These spectral wave data opened up exciting new approaches to wave research and applications which reach far beyond the capabilities of the previous wave observation systems. In general, three different investigations are pursued using the ERS-1 wave and wind data. First, the improvement of the ocean wave models, second the assimilation of the remotely sensed data into operational wave forecast models, and third the elaboration of long-term spectral wave climatologies. These investigations are of considerable economic benefit for numerous activities, such as ship routing<F13.

Application of wave spectra retrieved from ERS-1 SAR wave mode spectra in a wind- and wave-data assimilation system

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Climatic response to anthropogenic sulphate aerosols versus well-mixed greenhouse gases from 1850 to 2000 AD in CLIMBER-2

Tellus B, 2008

The Earth system model CLIMBER-2 is extended by a scheme for calculating the climatic response to... more The Earth system model CLIMBER-2 is extended by a scheme for calculating the climatic response to anthropogenic sulphur dioxide emissions. The scheme calculates the direct radiative forcing, the first indirect cloud albedo effect, and the second indirect cloud lifetime effect induced by geographically resolved sulphate aerosol burden. The simulated anthropogenic sulphate aerosol burden in the year 2000 amounts to 0.47 TgS. The best guesses for the radiative forcing due to the direct effect are −0.4 W m −2 and for the decrease in short-wave radiation due to all aerosol effects −0.8 Wm −2 . The simulated global warming by 1 K from 1850 to 2000 caused by anthropogenic greenhouse gases reduces to 0.6 K when the sulphate aerosol effects are included. The model's hydrological sensitivity of 4%/K is decreased by the second indirect effect to 0.8%/K. The quality of the geographically distributed climatic response to the historic emissions of sulphur dioxide and greenhouse gases makes the extended model relevant to computational efficient investigations of future climate change scenarios.

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Climate forcing due to the 8200 cal yr BP event observed at Early Neolithic sites in the eastern Mediterranean

by Gary Rollefson, Olaf Jöris, and Eva Bauer

Quaternary Research, 2006

We explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switc... more We explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switch of the North Atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on Neolithic civilisation in large parts of southeastern Europe, Anatolia, Cyprus, and the Near East. The event at 8200 cal yr BP is observed in a large number of high-resolution climate proxies in the Northern Hemisphere, and in many cases corresponds to markedly cold and arid conditions. We identify the relevant archaeological levels of major Neolithic settlements in Central Anatolia, Cyprus, Greece and Bulgaria, and examine published stratigraphic, architectural, cultural and geoarchaeological studies for these sites. The specific archaeological events and processes we observe at a number of these sites during the study interval 8400-8000 cal yr BP lead us to refine some previously established Neolithisation models. The introduction of farming to South-East Europe occurs in all study regions (Thrace, Macedonia, Thessaly, Bulgaria) near 8200 cal yr BP. We observe major disruptions of Neolithic cultures in the Levant, North Syria, South-East Anatolia, Central Anatolia and Cyprus, at the same time. We conclude that the 8200 cal yr BP aridity event triggered the spread of early farmers, by different routes, out of West Asia and the Near East into Greece and Bulgaria.

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Simulation of the cold climate event 8200 years ago by meltwater outburst from Lake Agassiz

Paleoceanography, 2004

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Some XBT-observations on the thermal structure of theWarmwassersphäre in equatorial and lower latitudes of the eastern Atlantic

by Michaela Knoll, Walter Zenk, and Eva Bauer

Deutsche Hydrographische Zeitschrift, 1982

Two megameter long XBT sections passing through the Atlantic between the Iberian Peninsula and th... more Two megameter long XBT sections passing through the Atlantic between the Iberian Peninsula and the equatorial Brazilian shelf, and between the Peninsula and the Cape region of South Africa were obtained during supply cruises to the antarctic in November 1980 and March 1981. Most of the individual probes reached an observation depth of nearly 800 m allowing statements on the thermal stratification and zonation of theWarmwassersphäre in the open ocean. Our new data are compared with a number of earlier long sections. As a general result we identify five zones dividing different hydrographic regions. Zone 1 is characterized by the clear influence of the Mediternean Undercurrent on the lower boundary of theWarmwasserphäre creating nearly thermostatic conditions below 300 m off Portugal. The adjacent zone 2 is identical with the Subtropical Convergence, where theWarmwassersphäre reaches its maximum depth (15°C isotherm at about 300 m). We call the equatorial region zone 3 and present an improved scheme of its current system and its thermal stratification. Zone 4 is marked by the Benguela Current and its northern extension. In a final zone 5 we show the influence of the Agulhas Current extension on the stratification.

Validation and assimilation of Seasat altimeter wave heights using the WAM wave model

Journal of Geophysical Research, 1992

The mutual consistency of the Seasat global data sets of scatterometer winds and altimeter wave h... more The mutual consistency of the Seasat global data sets of scatterometer winds and altimeter wave heights is investigated for the complete Seasat period using the third-generation wave model WAM. The wave model was driven by surface (1000 hPa) wind and surface stress fields constructed by the Goddard Laboratory for Atmospheres (GLA) by assimilation of the scatterometer winds in an atmospheric model. For the 10-day period September 7-17 the intercomparison was extended to two further scatterometer wind fields: a 1000-hPa assimilated wind field from the European Centre for Medium-Range Weather Forecasts and a subjectively analyzed 19.5-m-height surface wind field from the Jet Propulsion Laboratory. On the global average, the modeled and observed wave heights agree reasonably well. Regional differences, however, can be large and sometimes exceed 40%. The errors are attributed mainly to deficiencies in the forcing wind fields. Low wind speeds are found to be overestimated and high wind speeds underestimated by the Seasat scatterometer algorithm. The friction velocities of the GLA model are found to be significantly underestimated in the high-wind belt of the southern hemisphere. The analysis demonstrates the diagnostic advantages of applying a wave model for the quality assessment of satellite wind and wave data. A preliminary wave data assimilation scheme is presented in which the wave field is updated without changing the forcing wind field. A considerable improvement of the computed wave field is achieved, particularly in regions in which the wave energy is dominated by swell. However, a more general assimilation scheme including modifications of the wind field is needed to upgrade wind sea forecasts.

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Assimilation of wave data into the wave model WAM using an impulse response function method

Journal of Geophysical Research, 1996

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Role of land cover changes for atmospheric CO 2 increase and climate change during the last 150 years

Global Change Biology, 2004

We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO 2 em... more We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO 2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2. We apply several datasets of historical land-use reconstructions: the cropland dataset by (R&F), the HYDE land cover dataset of Klein , and the land-use emissions data from . Comparison between the simulated and observed temporal evolution of atmospheric CO 2 and d 13 CO 2 are used to evaluate these datasets. To check model uncertainty, CLIMBER-2 was coupled to the more complex Lund-Potsdam-Jena (LPJ) dynamic global vegetation model.

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Aeolian dust modeling over the past four glacial cycles with CLIMBER-2

Global and Planetary Change, 2010

An integral aeolian dust cycle model for glacial-interglacial climate simulations with the Earth ... more An integral aeolian dust cycle model for glacial-interglacial climate simulations with the Earth system model of intermediate complexity CLIMBER-2 is introduced, to study the role of aeolian dust for the evolution of glacial cycles. Sources, transport and deposition of dust are modeled for the first time over the past four glacial cycles using internally consistent characteristics of the atmosphere, the terrestrial vegetation coupled to the carbon cycle, and the ice sheets. The space-time variability in the dust deposition reconstructed from ice cores, and marine and terrigenous sediments is reasonably reproduced on the coarse spatial grid of the CLIMBER-2 model for time scales from seasons to hundreds of millennia. Of prime importance for reproducing the variability in dust deposition are changes in dust source areas and dust emission, while changes in dust transport and dust deposition are of secondary importance. The dependence of the dust sources on characteristics of the biosphere and the cryosphere is pertinent for obtaining the strong 100-kyr cyclicity in aeolian dust.

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The WAM model - a third generation ocean wave prediction model. J Phys Oceanogr

by Eva Bauer and Luciana Bertotti

Journal of Physical Oceanography

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Global Operational Remote Sensing and Modelling of Ocean Waves

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Assessment of Climate Forcing Contributing to the Late Maunder Minimum