Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere

The relative timing of late Quaternary glacial advances in mid-latitude (40-55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand (NZ) and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glaciation in the temperate and hyperhumid Southern Alps of New Zealand can be generated with moderate cooling. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1-4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal)

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

Based on magnetic field measurements from the satellite CHAMP, a detailed picture could be obtained of the upstream wave (UW) distribution in the topside ionosphere. The low, near-polar orbit of CHAMP, covering all local times, allows the global distribution of this type of pulsation to be revealed. The observations from space are compared to recordings of the ground-based MM100 meridional array covering the latitude range 66° to 42° in magnetic coordinates. UWs show up very clearly in the compressional component of the satellite magnetic field data, whereas on the ground, their signature is found in the H component, but it is mixed with oscillations from field line resonant pulsations. Here we first introduce a procedure for an automated detection of UW signatures, both in ground and space data. Then a statistical analysis is presented of UW pulsations recorded during a 132-day period, centred on the autumn 2001 equinox. Observations in the top-side ionosphere reveal a clear latitudinal distribution of the amplitudes. Largest signals are observed at the equator. Minima show up at about 40° latitude. The coherence between ground and satellite wave signatures is high over wide latitude and longitude ranges. We make suggestions about the entry mechanism of UWs from the foreshock region into the magnetosphere. The clear UW signature in satellite recordings between −60° and 60° latitude allows for detailed investigations of the dependence on solar wind conditions. We test the control of solar wind speed, interplanetary magnetic field strength and cone angle on UWs. For the first time, it is possible to derive details of the Doppler-shift effect by modifying the UW frequency from direct observations. The results reconcile foreshock wave generation predictions with near-Earth observations

CHAMP observation of intense kilometer-scale field-aligned currents, evidence for an ionospheric Alfvén resonator

International audienceBursts of very intense kilometer-scale field-aligned currents (KSFACs) are observed quite frequently by the CHAMP satellite when passing through the auroral region. In extreme cases estimated current densities exceed 3 mA/m². Typical scale sizes of these KSFACs are 1 km. The low-Earth, polar orbiting satellite CHAMP allows one to assess KSFACs down to scales of a couple of 100 m based on its high-precision magnetic field vector data sampled at 50 Hz. Using data from 5 years (2001?2005) details of these currents can be investigated. In our statistical study we find that most of the KSFAC bursts and the strongest events are encountered in the cusp/cleft region. Significantly fewer events are found on the nightside. The affected region is typically 15°?20° wide in latitude. There seems to be some dependence of the current intensity on the level of magnetic activity, Kp. On the other hand, no dependence has been found on sunspot number, the solar flux level, F10.7 or the solar zenith angle. The latitude, at which KSFAC bursts are encountered, expands equatorward with increasing Kp. This trend follows well the auroral oval expansion during enhanced magnetic activity. These KSFACs are generally accompanying large-scale FAC sheets, and they are predominantly associated with Region 1 currents. We propose an explanation of the KSFACs in terms of Alfvén waves trapped in a ionospheric resonator, which is initiated when the convection electric field or current strength surpasses a critical value. Many properties of such a resonator are in agreement with our KSFAC results

Child’s play: Exposure to household pesticide use among children in rural, urban and informal areas of South Africa

Background. As part of a larger dermatological investigation undertaken in 1999 - 2001 involving the Department of Dermatology, Groote Schuur Hospital (Cape Town, South Africa) and Nottingham University (UK), household pesticide use was investigated among Xhosa-speaking families living in three areas in South Africa (a rural area, an urban township and an informal settlement).Objectives. The aim was to characterise pesticide use patternsand potential exposures through skin absorption, ingestion and inhalation for this group of South African children.Methods. A standardised questionnaire, which included a section investigating household pesticide use, was administered by four trained fieldworkers to the parents/guardians of the 740 children (25%) aged between 3 and 11 years identified as having atopic dermatitis either by clinical examination or according to the UK criteria (rural N=387,urban N=292, informal N=61).Results. Of the children with atopic dermatitis, 539 (73%) had been exposed to household pesticides. Most childhood exposure (89%) occurred in the informal settlements, followed by 78% in the urban area and 63% in the rural area.Conclusions. This research highlighted considerable home environment pesticide exposure of South African children in lower socio-economic groups in rural, urban and informal areas. As children are particularly vulnerable to the short- and long-term health effects of pesticide exposure, further indepth investigation is needed to ascertain and document the health effects associated with such exposure in the home

ClassCut for Unsupervised Class Segmentation

Abstract. We propose a novel method for unsupervised class segmentation on a set of images. It alternates between segmenting object instances and learning a class model. The method is based on a segmentation energy defined over all images at the same time, which can be optimized efficiently by techniques used before in interactive segmentation. Over iterations, our method progressively learns a class model by integrating observations over all images. In addition to appearance, this model captures the location and shape of the class with respect to an automatically determined coordinate frame common across images. This frame allows us to build stronger shape and location models, similar to those used in object class detection. Our method is inspired by interactive segmentation methods [1], but it is fully automatic and learns models characteristic for the object class rather than specific to one particular object/image. We experimentally demonstrate on the Caltech4, Caltech101, and Weizmann horses datasets that our method (a) transfers class knowledge across images and this improves results compared to segmenting every image independently; (b) outperforms Grabcut [1] for the task of unsupervised segmentation; (c) offers competitive performance compared to the state-of-the-art in unsupervised segmentation and in particular it outperforms the topic model [2].

Dynamical mean-field theory of indirect magnetic exchange

To analyze the physical properties arising from indirect magnetic exchange between several magnetic adatoms and between complex magnetic nanostructures on metallic surfaces, the real-space extension of dynamical mean-field theory (R-DMFT) appears attractive as it can be applied to systems of almost arbitrary geometry and complexity. While R-DMFT describes the Kondo effect of a single adatom exactly, indirect magnetic (RKKY) exchange is taken into account on an approximate level only. Here, we consider a simplified model system consisting of two magnetic Hubbard sites ("adatoms") hybridizing with a non-interacting tight-binding chain ("substrate surface"). This two-impurity Anderson model incorporates the competition between the Kondo effect and indirect exchange but is amenable to an exact numerical solution via the density-matrix renormalization group (DMRG). The particle-hole symmetric model at half-filling and zero temperature is used to benchmark R-DMFT results for the magnetic coupling between the two adatoms and for the magnetic properties induced in the substrate. In particular, the dependence of the local adatom and the nonlocal adatom-adatom static susceptibilities as well as the magnetic response of the substrate on the distance between the adatoms and on the strength of their coupling with the substrate is studied. We find both, excellent agreement with the DMRG data even on subtle details of the competition between RKKY exchange and the Kondo effect but also complete failure of the R-DMFT, depending on the parameter regime considered. R-DMFT calculations are performed using the Lanczos method as impurity solver. With the real-space extension of the two-site DMFT, we also benchmark a simplified R-DMFT variant.Comment: 14 pages, 8 figure