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- ItemTesting the detectability of spatio-temporal climate transitions from paleoclimate networks with the start model(Göttingen : Copernicus, 2014) Rehfeld, K.; Molkenthin, N.; Kurths, J.A critical challenge in paleoclimate data analysis is the fact that the proxy data are heterogeneously distributed in space, which affects statistical methods that rely on spatial embedding of data. In the paleoclimate network approach nodes represent paleoclimate proxy time series, and links in the network are given by statistically significant similarities between them. Their location in space, proxy and archive type is coded in the node attributes. We develop a semi-empirical model for Spatio- Temporally AutocoRrelated Time series, inspired by the interplay of different Asian Summer Monsoon (ASM) systems. We use an ensemble of transition runs of this START model to test whether and how spatio-temporal climate transitions could be detectable from (paleo)climate networks. We sample model time series both on a grid and at locations at which paleoclimate data are available to investigate the effect of the spatially heterogeneous availability of data. Node betweenness centrality, averaged over the transition region, does not respond to the transition displayed by the START model, neither in the grid-based nor in the scattered sampling arrangement. The regionally defined measures of regional node degree and cross link ratio, however, are indicative of the changes in both scenarios, although the magnitude of the changes differs according to the sampling. We find that the START model is particularly suitable for pseudo-proxy experiments to test the technical reconstruction limits of paleoclimate data based on their location, and we conclude that (paleo)climate networks are suitable for investigating spatio-temporal transitions in the dependence structure of underlying climatic fields.
- ItemStatistical characteristics of surrogate data based on geophysical measurements(Göttingen : Copernicus, 2006) Venema, V.; Bachner, S.; Rust, H.W.; Simmer, C.In this study, the statistical properties of a range of measurements are compared with those of their surrogate time series. Seven different records are studied, amongst others, historical time series of mean daily temperature, daily rain sums and runoff from two rivers, and cloud measurements. Seven different algorithms are used to generate the surrogate time series. The best-known method is the iterative amplitude adjusted Fourier transform (IAAFT) algorithm, which is able to reproduce the measured distribution as well as the power spectrum. Using this setup, the measurements and their surrogates are compared with respect to their power spectrum, increment distribution, structure functions, annual percentiles and return values. It is found that the surrogates that reproduce the power spectrum and the distribution of the measurements are able to closely match the increment distributions and the structure functions of the measurements, but this often does not hold for surrogates that only mimic the power spectrum of the measurement. However, even the best performing surrogates do not have asymmetric increment distributions, i.e., they cannot reproduce nonlinear dynamical processes that are asymmetric in time. Furthermore, we have found deviations of the structure functions on small scales.
- ItemA propagation-separation approach to estimate the autocorrelation in a time-series(Göttingen : Copernicus, 2008) Divine, D.V.; Polzehl, J.; Godtliebsen, F.The paper presents an approach to estimate parameters of a local stationary AR(1) time series model by maximization of a local likelihood function. The method is based on a propagation-separation procedure that leads to data dependent weights defining the local model. Using free propagation of weights under homogeneity, the method is capable of separating the time series into intervals of approximate local stationarity. Parameters in different regions will be significantly different. Therefore the method also serves as a test for a stationary AR(1) model. The performance of the method is illustrated by applications to both synthetic data and real time-series of reconstructed NAO and ENSO indices and GRIP stable isotopes.
- ItemMulti-method study of the Middle Pleistocene loess-palaeosol sequence of Köndringen, SW Germany(Göttingen : Copernicus, 2023) Schwahn, Lea; Schulze, Tabea; Fülling, Alexander; Zeeden, Christian; Preusser, Frank; Sprafke, TobiasLoess-palaeosol sequences (LPSs) remain poorly investigated in the southern part of the Upper Rhine Graben but represent an important element to understand the environmental context controlling sediment dynamics in the area. A multi-method approach applied to the LPS at Köndringen reveals that its formation occurred during several glacial-interglacial cycles. Field observations, as well as colour, grain size, magnetic susceptibility, organic carbon, and carbonate content measured in three profiles at 5 cm resolution, provide detailed stratigraphical information. Only minor parts of the LPS are made up of loess sediment, whereas the major parts are polygenetic palaeosols and pedosediments of varying development that are partly intersected, testifying to a complex local geomorphic evolution. The geochronological framework is based on 10 cm resolution infrared-stimulated luminescence (IRSL) screening combined with 18 multi-elevated-temperature post-IR IRSL ages. The luminescence ages indicate that two polygenetic, truncated Luvisols formed during marine isotope stages (MISs) 9(-7?) and MIS 5e, whereas unaltered loess units correspond to the last glacial (MISs 5d-2) and MIS 8. The channel-like structure containing the two truncated Luvisols cuts into > 2 m thick pedosediments apparently deposited during MIS 12. At the bottom of the LPS, a horizon with massive carbonate concretions (loess dolls) occurs, which may correspond to at least one older interglacial.
- ItemFigures of merit of thermoelectric and bolometric thermal radiation sensors(Göttingen : Copernicus, 2013) Dillner, U.; Kessler, E.; Meyer, H.-G.Figures of merit condensing the performance parameters of radiation sensors such as responsivity, noise equivalent power, and time constant in a single number can be useful for rating the performance of a particular sensor in comparison to other ones or to fundamental performance limits. The classification system and the figures of merit of radiation sensors introduced by R. C. Jones are revisited for thermal radiation sensors with the focus on thermopiles and bolometers. As a result it is stated that radiation thermopiles and bolometers should be classified differently: type III detectors for thermopiles vs. type II detectors for bolometers. Modified figures of merit are suggested and relations between them given. The figures of merit are applied in an overview on state-of-the-art thermopiles and bolometers operated at room temperature.
- ItemThe HadGEM2-ES implementation of CMIP5 centennial simulations(Göttingen : Copernicus, 2011) Jones, C.D.; Hughes, J.K.; Bellouin, N.; Hardiman, S.C.; Jones, G.S.; Knight, J.; Liddicoat, S.; O'Connor, F.M.; Andres, R.J.; Bell, C.; Boo, K.-O.; Bozzo, A.; Butchart, N.; Cadule, P.; Corbin, K.D.; Doutriaux-Boucher, M.; Friedlingstein, P.; Gornall, J.; Gray, L.; Halloran, P.R.; Hurtt, G.; Ingram, W.J.; Lamarque, J.-F.; Law, R.M.; Meinshausen, M.; Osprey, S.; Palin, E.J.; Parsons, Chini, L.; Raddatz, T.; Sanderson, M.G.; Sellar, A.A.; Schurer, A.; Valdes, P.; Wood, N.; Woodward, S.; Yoshioka, M.; Zerroukat, M.The scientific understanding of the Earth's climate system, including thecentral question of how the climate system is likely to respond tohuman-induced perturbations, is comprehensively captured in GCMs and EarthSystem Models (ESM). Diagnosing the simulated climate response, andcomparing responses across different models, is crucially dependent ontransparent assumptions of how the GCM/ESM has been driven - especiallybecause the implementation can involve subjective decisions and may differbetween modelling groups performing the same experiment. This paper outlinesthe climate forcings and setup of the Met Office Hadley Centre ESM, HadGEM2-ES for the CMIP5 set of centennial experiments. We document theprescribed greenhouse gas concentrations, aerosol precursors, stratosphericand tropospheric ozone assumptions, as well as implementation of land-usechange and natural forcings for the HadGEM2-ES historical and futureexperiments following the Representative Concentration Pathways. Inaddition, we provide details of how HadGEM2-ES ensemble members wereinitialised from the control run and how the palaeoclimate and AMIPexperiments, as well as the "emission-driven" RCP experiments wereperformed.
- ItemThe role of Antarctic overwintering teams and their significance for German polar research(Göttingen : Copernicus, 2022) Franke, Steven; Eckstaller, Alfons; Heitland, Tim; Schaefer, Thomas; Asseng, JölundGermany has been operating permanently crewed research stations in Antarctica for more than 45 years. The opening of the Georg Forster Station (1976) and Georg von Neumayer Station (1981) initiated a period of continuous environmental monitoring that allowed both the former East Germany and West Germany to become contracting parties in, and achieve consultative status with, the framework of the Antarctic Treaty. This marked a milestone in German polar research. Continuous research at the Neumayer Station III, its two predecessors, and the now-dismantled former German Democratic Republic (GDR) Georg Forster Station is undertaken by teams of so-called "overwinterers", presently with nine members, who stay at the base for longer than an entire Antarctic winter. Their long-Term stay in Antarctica is defined by isolation, separation from civilization, routine work to sustain long-Term scientific observations, and unique personal experiences. This article is dedicated to them and outlines their part and role in the German Antarctic research landscape.
- ItemSimultaneous observations of a Mesospheric Inversion Layer and turbulence during the ECOMA-2010 rocket campaign(Göttingen : Copernicus, 2013) Szewczyk, A.; Strelnikov, B.; Rapp, M.; Strelnikova, I.; Baumgarten, G.; Kaifler, N.; Dunker, T.; Hoppe, U.-P.From 19 November to 19 December 2010 the fourth and final ECOMA rocket campaign was conducted at Andøya Rocket Range (69 N, 16 E) in northern Norway. We present and discuss measurement results obtained during the last rocket launch labelled ECOMA09 when simultaneous and true common volume in situ measurements of temperature and turbulence supported by ground-based lidar observations reveal two Mesospheric Inversion Layers (MIL) at heights between 71 and 73 km and between 86 and 89 km. Strong turbulence was measured in the region of the upper inversion layer, with the turbulent energy dissipation rates maximising at 2 W kg-1. This upper MIL was observed by the ALOMAR Weber Na lidar over the period of several hours. The spatial extension of this MIL as observed by the MLS instrument onboard AURA satellite was found to be more than two thousand kilometres. Our analysis suggests that both observed MILs could possibly have been produced by neutral air turbulence.
- ItemClimatology of northern polar latitude MLT dynamics: Mean winds and tides(Göttingen : Copernicus, 2010) Kumar, G.K.; Hocking, W.K.Mean winds and tides in the northern polar Mesosphere and Lower Thermosphere (MLT) have been studied using meteor radars located at Resolute Bay (75° N, 95° W) and Yellowknife (62.5° N, 114.3° W). The measurements for Resolute Bay span almost 12 years from July 1997 to February 2009 and the Yellowknife data cover 7 years from June 2002 to October 2008. The analysis reveals similar wind flow over both sites with a difference in magnitude. The summer zonal flow is westward at lower heights, eastward at upper heights and the winter zonal flow is eastward at all heights. The winter meridional flow is poleward and sometimes weakly equatorward, while non winter months show equatorward flow, with a strong equatorward jet during mid-summer months. The zonal and meridional winds show strong interannual variation with a dominant annual variation as well as significant latitudinal variation. Year to year variability in both zonal and meridional winds exists, with a possible solar cycle dependence. The diurnal, semidiurnal and terdiurnal tides also show large interannual variability and latitudinal variation. The diurnal amplitudes are dominated by an annual variation. The climatological monthly mean winds are compared with CIRA 86, GEWM and HWM07 and the climatological monthly mean amplitudes and phases of diurnal and semidiurnal tides are compared with GSWM00 predictions. The GEWM shows better agreement with observations than the CIRA 86 and HWM07. The GSWM00 model predictions need to be modified above 90 km. The agreements and disagreements between observations and models are discussed. © 2010 Author(s).
- ItemLong-term trends in the ionospheric F2 region with different solar activity indices(Göttingen : Copernicus, 2013) Mielich, J.; Bremer, J.A new comprehensive data collection by Damboldt and Suessmann (2012a) with monthly foF2 and M(3000)F2 median values is an excellent basis for the derivation of long-term trends in the ionospheric F2 region. Ionospheric trends have been derived only for stations with data series of at least 22 years (124 stations with foF2 data and 113 stations with M(3000)F2 data) using a twofold regression analysis depending on solar and geomagnetic activity. Three main results have been derived: Firstly, it could be shown that the solar 10.7 cm radio flux F10.7 is a better index for the description of the solar activity than the relative solar sunspot number R as well as the solar EUV proxy E10.7. Secondly, the global mean foF2 and