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Bjoland L.M.,University of Tromsø | Chen X.,University Center in Svalbard | Chen X.,University of Oslo | Chen X.,University of Bergen | And 10 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

Joule heating in the ionosphere takes place through collisions between ions and neutrals. Statistical maps of F region Joule heating in the Northern Hemisphere polar ionosphere are derived from satellite measurements of thermospheric wind and radar measurements of ionospheric ion convection. Persistent mesoscale heating is observed near postnoon and postmidnight magnetic local time and centered around 70 magnetic latitude in regions of strong relative ion and neutral drift. The magnitude of the Joule heating is found to be largest during solar maximum and for a southeast oriented interplanetary magnetic field. These conditions are consistent with stronger ion convection producing a larger relative flow between ions and neutrals. The global-scale Joule heating maps quantify persistent (in location) regions of heating that may be used to provide a broader context compared to small-scale studies of the coupling between the thermosphere and ionosphere. ©2015. American Geophysical Union. All Rights Reserved.

Haaland S.,Max Planck Institute for Solar Systems Research | Haaland S.,University of Bergen | Eriksson A.,Swedish Institute of Space Physics | Engwall E.,Swedish Institute of Space Physics | And 10 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

[1] An important source of magnetospheric plasma is cold plasma from the terrestrial ionosphere. Low energy ions travel along the magnetic field lines and enter the magnetospheric lobes where they are convected toward the tail plasma sheet. Recent observations indicate that the field aligned ion outflow velocity is sometimes much higher than the convection toward the central plasma sheet. A substantial amount of plasma therefore escapes downtail without ever reaching the central plasma sheet. In this work, we use Cluster measurements of cold plasma outflow and lobe convection velocities combined with models of the magnetic field in an attempt to determine the fate of the outflowing ions and to quantify the amount of plasma lost downtail. The results show that both the circulation of plasma and the direct tailward escape of ions varies significantly with magnetospheric conditions. For strong solar wind driving with a southward interplanetary magnetic field, also typically associated with high geomagnetic activity, most of the outflowing plasma is convected to the plasma sheet and recirculated. For periods with northward interplanetary magnetic field, the convection is nearly stagnant, whereas the outflow, although limited, still persists. The dominant part of the outflowing ions escape downtail and are directly lost into the solar wind under such conditions. © 2012. American Geophysical Union. All Rights Reserved.

Haaland S.,University of Bergen | Haaland S.,Max Planck Institute for Solar Systems Research | Eriksson A.,Swedish Institute of Space Physics | Andre M.,Swedish Institute of Space Physics | And 12 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

Low-energy ions of ionospheric origin constitute a significant contributor to the magnetospheric plasma population. Measuring cold ions is difficult though. Observations have to be done at sufficiently high altitudes and typically in regions of space where spacecraft attain a positive charge due to solar illumination. Cold ions are therefore shielded from the satellite particle detectors. Furthermore, spacecraft can only cover key regions of ion outflow during segments of their orbit, so additional complications arise if continuous longtime observations, such as during a geomagnetic storm, are needed. In this paper we suggest a new approach, based on a combination of synoptic observations and a novel technique to estimate the flux and total outflow during the various phases of geomagnetic storms. Our results indicate large variations in both outflow rates and transport throughout the storm. Prior to the storm main phase, outflow rates are moderate, and the cold ions are mainly emanating from moderately sized polar cap regions. Throughout the main phase of the storm, outflow rates increase and the polar cap source regions expand. Furthermore, faster transport, resulting from enhanced convection, leads to a much larger supply of cold ions to the near-Earth region during geomagnetic storms. ©2015. The Authors.

Dorville N.,University Paris - Sud | Haaland S.,University of Bergen | Haaland S.,Max Planck Institute for Solar Systems Research | Anekallu C.,University College London | And 2 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

Determining the direction normal to the magnetopause layer is a key step for any study of this boundary. Various techniques have been developed for this purpose. We focus here on generic residue analysis (GRA) methods, which are based on conservation laws, and the new iterative BV method, where B represents the magnetic field and V refers to the ion velocity. This method relies on a fit of the magnetic field hodogram against a modeled geometrical shape and on the way this hodogram is described in time. These two methods have different underlying model assumptions and validity ranges. We compare here magnetopause normals predicted by BV and GRA methods to better understand the sensitivity of each method on small departures from its own physical hypotheses. This comparison is carried out first on artificial data with magnetopause-like noise. Then a statistical study is carried out using a list of 149 flank and dayside magnetopause crossings from Cluster data where the BV method is applicable, i.e., where the magnetopause involves a single-layer current sheet, with a crudely C-shaped magnetic hodogram. These two comparisons validate the quality of the BV method for all these cases where it is applicable. The method provides quite reliable normal directions in all these cases, even when the boundary is moving with a varying velocity, which distorts noticeably the results of most of the other methods. Key Points The BV technique is benchmarked with respect to other single-spacecraft methods It is less sensitive to noise than most of the other methods on simulated data A statistical study is made on 149 Cluster magnetopause crossings ©2015. American Geophysical Union. All Rights Reserved.

Biele J.,German Aerospace Center | Krause C.,German Aerospace Center | Blum J.,TU Braunschweig | Ulamec S.,German Aerospace Center | And 2 more authors.
Proceedings of the International Astronautical Congress, IAC | Year: 2012

Common to all comet landing / sampling missions is that the mechanical properties of the surface of a comet are an important design driver for landing, anchoring and sampling. Another issue is the outgassing flow perturbing the spacecraft/lander motion. In this paper, we continue previous work [1,2] on the estimation of surface strength and try to narrow the bounds on this on respective parameters. We also outline the rationale for our estimation on the min/max outgassing rates for 67P/Churyumov-Gerasimenko, the target of the Rosetta mission, from 4.5 AU to perihelion. In particular, we review the definitions of relevant mechanical parameters and their dependencies on scale and velocity and review laboratory and in-situ measurements on comet material analogs, comet-derived meteroids and actual comets. We also discuss a new hierarchical model for comet surface matter which is consistent with the putative formation of comets and the observed activity characteristics [2]. Emphasis is laid on the estimation of not only tensile, but also shear strengths and, in particular, compressive strength. Applications include landing and anchoring spacecraft as well as implications for surface penetration, e.g. , for anchoring, sampling or inserting measurement probes. Surface activity (gas release through the crust) is discussed in the framework of a new thermophysical model. For comet 67P/Churyumov-Gerasimenko in particular, we summarize our findings in an updated comet surface engineering model for the Rosetta mission and a table for bounds on the gas production rates as a function of heliocentric distance (pre-perihelion). Copyright © (2012) by the International Astronautical Federation.

Forster M.,Helmholtz Center Potsdam | Haaland S.,Max Planck Institute for Solar Systems Research | Haaland S.,University of Bergen
Journal of Geophysical Research A: Space Physics | Year: 2015

The interaction between the interplanetary magnetic field and the geomagnetic field sets up a large-scale circulation in the magnetosphere. This circulation is also reflected in the magnetically connected ionosphere. In this paper, we present a study of ionospheric convection based on Cluster Electron Drift Instrument (EDI) satellite measurements covering both hemispheres and obtained over a full solar cycle. The results from this study show that average flow patterns and polar cap potentials for a given orientation of the interplanetary magnetic field can be very different in the two hemispheres. In particular during southward directed interplanetary magnetic field conditions, and thus enhanced energy input from the solar wind, the measurements show that the southern polar cap has a higher cross polar cap potential. There are persistent north-south asymmetries, which cannot easily be explained by the influence of external drivers. These persistent asymmetries are primarily a result of the significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemispheres. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north-south asymmetries in large regions of geospace. ©2015. American Geophysical Union. All Rights Reserved.

Maes L.,Belgian Institute for Space Aeronomy | Maggiolo R.,Belgian Institute for Space Aeronomy | De Keyser J.,Belgian Institute for Space Aeronomy | Dandouras I.,CNRS Institute for research in astrophysics and planetology | And 5 more authors.
Geophysical Research Letters | Year: 2015

We measure the flux density, composition, and energy of outflowing ions above the polar cap, accelerated by quasi-static electric fields parallel to the magnetic field and associated with polar cap arcs, using Cluster. Mapping the spacecraft position to its ionospheric foot point, we analyze the dependence of these parameters on the solar zenith angle (SZA). We find a clear transition at SZA between ∼94° and ∼107°, with the O+ flux higher above the sunlit ionosphere. This dependence on the illumination of the local ionosphere indicates that significant O+ upflow occurs locally above the polar ionosphere. The same is found for H+, but to a lesser extent. This effect can result in a seasonal variation of the total ion upflow from the polar ionosphere. Furthermore, we show that low-magnitude field-aligned potential drops are preferentially observed above the sunlit ionosphere, suggesting a feedback effect of ionospheric conductivity. © 2015. The Authors.

Laundal K.M.,University of Bergen | Laundal K.M.,Teknova AS | Cnossen I.,British Antarctic Survey | Milan S.E.,University of Bergen | And 7 more authors.
Space Science Reviews | Year: 2016

The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth’s magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere–thermosphere system. At ionospheric altitudes, the Earth’s field deviates significantly from a dipole. North–South asymmetries in the magnetic field imply that the magnetosphere–ionosphere–thermosphere (M–I–T) coupling is different in the two hemispheres. In this paper we review the primary differences in the magnetic field at polar latitudes, and the consequences that these have for the M–I–T coupling. We focus on two interhemispheric differences which are thought to have the strongest effects: 1) A difference in the offset between magnetic and geographic poles in the Northern and Southern Hemispheres, and 2) differences in the magnetic field strength at magnetically conjugate regions. These asymmetries lead to differences in plasma convection, neutral winds, total electron content, ion outflow, ionospheric currents and auroral precipitation. © 2016 The Author(s)

Haaland S.,Max Planck Institute for Solar Systems Research | Haaland S.,University of Bergen | Gjerloev J.,University of Bergen | Gjerloev J.,Johns Hopkins University
Journal of Geophysical Research: Space Physics | Year: 2013

Motion of charged particles in the Earth's magnetosphere sets up a system of currents. Current continuity requires that these currents are closed, either locally or via other current systems. In this paper, we have investigated whether magnetopause surface currents can contribute to ring current closure. Using measurements from the Cluster constellation of spacecraft, we calculated thickness and current density of the magnetopause current layer for a large number of flank magnetopause traversals. For each event, we consulted sectorial ring current indices, derived from SuperMAG - a large constellation of ground-based magnetometer stations. SuperMAG results show a significant and persistent dawn-dusk asymmetry in ground magnetic perturbations which indicates a more intense ring current on the duskside. The asymmetries become more pronounced during disturbed magnetospheric conditions, indicating an increased divergence of the current and closure through other current systems. A similar response to geomagnetic activity is also observed at the magnetopause. Duskside magnetopause current densities are generally higher than their dawnside counterparts, and also, the magnetopause asymmetry becomes more pronounced during disturbed conditions. Although the two current systems are related to different processes - gradient drift of energetic plasma sheet particles for the ring current and a surface current due to differential motion of ions and electrons inside the magnetopause interface for the magnetopause current - the results demonstrate a mutual relation between the two current systems. Key Points A dawn-dusk asymmetry in the current density of the magnetopause is reported. A relationship between RC and MP asymmetries is established. The RC and MP current show a similar response to geomagnetic activity ©2013. American Geophysical Union. All Rights Reserved.

Munteanu C.,Romanian Space Science Institute | Munteanu C.,University of Oulu | Munteanu C.,University of Bucharest | Haaland S.,University of Bergen | And 5 more authors.
Journal of Geophysical Research: Space Physics | Year: 2013

We present a statistical study of the performance of three methods used to predict the propagation delay of solar wind structures. These methods are based on boundary normal estimations between the Advanced Composition Explorer (ACE) spacecraft orbiting the L1 libration point and the Cluster spacecraft near the Earth's magnetopause. The boundary normal estimation methods tested are the cross product method (CP), the minimum variance analysis of the magnetic field (MVAB), and the constrained minimum variance analysis (MVAB0). The estimated delay times are compared with the observed ones to obtain a quantitative measure of each method's accuracy. Boundary normal estimations of magnetic field structures embedded in the solar wind are known to be sensitive to small-scale fluctuations. Our study uses wavelet denoising to reduce the effect of these fluctuations. The influence of wavelet denoising on the performance of the three methods is also analyzed. We find that the free parameters of the three methods have to be adapted to each event in order to obtain accurate propagation delays. We also find that by using denoising parameters optimized to each event, 88% of our database of 356 events are estimated to arrive within ±2 min from the observed time delay with MVAB, 74% with CP, and 69% with the MVAB0 method. Our results show that wavelet denoising significantly improves the predictions of the propagation time delay of solar wind discontinuities. © 2013. American Geophysical Union. All Rights Reserved.

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