B. Klecker | TU Munich (original) (raw)

Papers by B. Klecker

AIP Conference Proceedings, 2000

During the period in which the ACE spacecraft has been operating, the Compton Gamma-Ray Observato... more During the period in which the ACE spacecraft has been operating, the Compton Gamma-Ray Observatory (CGRO) has continued monitoring hard X-ray and gamma-ray emission from the Sun, among other sources. The high-energy photons provide information about both the electrons, through bremsstrahlung continuum emission, and nuclei, through nuclear line emission, while they are still near the site of their acceleration. The question of the common origin of solar photons and particles is addressed through comparison of the photon observations with associated ACE events. Among many hard-X ray flares associated with particle events seen by ACE, three had particularly interesting spectra from the CGRO Burst and Transient Source Experiment (BATSE). Two, on 4 Nov. 1997 and 22 Nov. 1998, had very hard continuum spectra up to MeV energies. The third event, on 28 Nov. 1998, showed substantial 511-keV line emission, above the ever-present instrumental background; this could be due to the production either of short-lived positron emitters, such as 11C, or pions. .

We survey the occurrence of reconnection at the magnetopause and in the cusp using measurements f... more We survey the occurrence of reconnection at the magnetopause and in the cusp using measurements from the CIS and FGM experiments. We present evidence for recon- nection occurring both equatorward and poleward of the cusp for different IMF condi- tions. Contrasts between reconnection signatures detected at the magnetopause versus those observed in the cusp boundary will be discussed.

The CLUSTER spacecraft have crossed repeatedly the perpendicular Earth&amp;amp;amp;#39;s ... more The CLUSTER spacecraft have crossed repeatedly the perpendicular Earth&amp;amp;amp;#39;s bow shock and provided multi-spacecraft measurements. By means of data from the Cluster Ion Spectrometry experiment (CIS), which observes the 3D-ion distribution function of the major species (H+, He2+, He+, O+) in the energy range of 5 eV to 40 keV with 4- second resolution we have examined the evolution of

We present Cluster measurements from the dawnside magnetosphere. Using data from the Electron Dri... more We present Cluster measurements from the dawnside magnetosphere. Using data from the Electron Drift Instrument (EDI), the Fluxgate Magnetometer (FGM) and the Cluster Ion Spectrometry (CIS) instrument, we explore the plasma convection characteristics as the spacecraft passed through the outer magnetosphere and low-latitude boundary layer (LLBL). The main focus is on July 5, 2001, which was characterized by frequent high-shear

nationalacademies.org

... Lorentzen, KR, LMD, and BJB, Relativistic electron microbursts during the gem storms, Geophys... more ... Lorentzen, KR, LMD, and BJB, Relativistic electron microbursts during the gem storms, Geophys. Res. Lett., 28, 2573, 2001. Mason, GM, JE Mazur, MD Looper, and RA Mewaldt, Charge State Measurements of Solar Ener-getic Particles Observed with SAMPEX, Astrophys. ...

Advanced instrumentation onboard several spacecraft, e.g. WIND, SAMPEX, SOHO, and ACE, significan... more Advanced instrumentation onboard several spacecraft, e.g. WIND, SAMPEX, SOHO, and ACE, significantly extended our ability to explore energy spectra, elemental, isotopic, and ionic charge composition of solar energetic particle (SEP) events. Due to the much improved sensitivity of the instrumentation, spectral and compositional measurements are now available over a wide energy range from ≈ 10 keV/nuc to ≈ 100 MeV/nuc and for a large range of particle intensities. This provided over the last years detailed spectral and compositional information not only for large SEP events generally associated with coronal mass ejections (CMEs) and coronal / interplanetary shocks, but also for small, flare associated events. Originally, these 2 classes of events were assigned the labels "gradual" and "impulsive", based on the temporal profiles of the associated X-ray emission, but this 2-class paradigm of SEP events was also useful to distinguish differences in the accelerat...

Journal of Geophysical Research, 1977

ABSTRACT A set of parameters reproducing the quiet time spectra of He, O, N, and Ne as observed a... more ABSTRACT A set of parameters reproducing the quiet time spectra of He, O, N, and Ne as observed at 1 AU during the period 1973-1975 is constructed on the basis of current modulation theory for the transport of low-energy cosmic ray particles and Fisk's (1976) model for their acceleration by transit time damping large-scale field variations in the outer solar system. In this model, the relative abundances of singly ionized ions at injection are calculated from the known ionization rates and the calculated neutral particle distribution in the heliosphere, and the modulation theory includes the effects of diffusion, adiabatic deceleration, and convection. It is shown that both the spectral shapes and the relative intensities for He, O, N, and Ne can simultaneously be fitted remarkably well, where the set of parameters for the fit comprises the acceleration rate, the size of the heliosphere, and the fraction of accelerated singly-ionized particles.

Journal of Geophysical Research: Space Physics, 2004

We report on the transient strong flow shear (large northward/southward electric field) events ac... more We report on the transient strong flow shear (large northward/southward electric field) events accompanied by energetic ion beams and localized field‐aligned currents observed at the boundary of the premidnight plasma sheet by Cluster in the Northern Hemisphere and Geotail in the Southern Hemisphere. The events took place associated with plasma sheet expansion during a substorm interval, with the main positive bay onset at 1155 UT on 10 October 2001. Typical timescales of these events were 1–5 minutes. Cluster multipoint analysis showed that the field‐aligned currents consist of upward and downward current layers, the latter located at the outermost edge of the plasma sheet and concentrated in a region with a thickness of 1600 km. Low‐energy proton flow suggested that the electric field was southward at the outer part and northward at the inner part, with a magnitude exceeding 10 mV/m. The electric field reversal region also corresponds to the boundary between beam‐like electrons an...

Journal of Geophysical Research: Space Physics, 2002

For solar cycle 22 the large‐scale interplanetary disturbances produced by the intense solar acti... more For solar cycle 22 the large‐scale interplanetary disturbances produced by the intense solar activity of March/June 1991 had a long‐term effect on the recovery of galactic cosmic rays throughout the heliosphere that persisted for almost 5 years. At 1 AU, the recovery of 13 MeV/nucleon anomalous cosmic ray oxygen (ACR O+) is much more rapid than that of 265 MeV/nucleon galactic cosmic ray helium (GCR He), consistent with previous observations in the distant heliosphere [McDonald et al., 2000] and strengthening the concept that the region of the heliosheath plays an important role in the modulation of galactic cosmic rays. A comparison of the time histories of GCR He and ACR O+ at 1 and 44 AU observations suggest the recovery moves from the distant heliosphere inward toward 1 AU for this particular phase of the heliomagnetic cycle. There is a very low relative modulation potential, Φ, between 1 and 70 AU of 116 ± 6 MV for GCR He at solar minimum using the force field approximation. Wh...

Astronomy and Astrophysics, 2009

Context. We present an investigation of the effects of solar magnetic field on the elemental abun... more Context. We present an investigation of the effects of solar magnetic field on the elemental abundance ratios of heavy ions in the solar wind. Aims. We compare the elemental abundance ratios Fe/O, Si/O, Mg/O, Ne/O, and C/O over the 23rd solar cycle, attention being given to the varying fraction of open magnetic flux on the visible side of the solar disc. Methods. We use ACE solar wind data, the current sheet source surface (CSSS) model of the corona, and SoHO/MDI data to relate solar wind compositional properties with the fraction of open magnetic flux on the Sun. We include both a quasi-stationary and intermittent solar wind. Results. For the six investigated solar wind speed ranges, the elemental composition shows a similar FIP-bias of the quasi-stationary solar wind composition with respect to the photosphere but with three plateaus separating low-, mid-, and high-FIP elements. The average enrichment factor for the low-FIP element group (Mg, Fe, Si) with respect to the photospheric values is between 1.67 and 2.47 when the fraction of open magnetic flux on the visible side of the solar disc is above 14%, and it ranges from 2.78 to 4.15 when this fraction is less than 7%. They are close to the enrichment of low-FIP elements with respect to the photospheric values in quasistationary fast-and slow-solar wind, which implies similar fractionation mechanisms for the stationary solar wind and the intermittent solar wind. In the low alpha (<7%) case (alpha is the fraction of open magnetic flux on the visible side of the solar disc), the enrichment of heavy elements for the fast solar wind is well correlated with the high fraction of CMEs. In addition, both the charge state ratios and the elemental abundance ratios exhibit a lower dependence on alpha in a slow solar wind than in a fast solar wind. The dependence of the charge state ratios on alpha is correlated with FIP, which implies that solar magnetic effects play a non-negligible role in the elemental fractionation of the solar wind. We suggest that lower hybrid waves play an important role in the possible linkage between solar magnetic field and elemental fractionation.

Advances in Space Research, 1999

A new component of quiet time cosmic ray flux with anomalous composition and energy spectra was d... more A new component of quiet time cosmic ray flux with anomalous composition and energy spectra was discovered-25 years ago, since then called Anomalous Cosmic Rays. We review the observed properties of Anomalous Cosmic Rays, concentrating on the recent key observations of the ionic charge composition and their implications. We discuss the processes by which they originate, in particular the ACR source, acceleration and loss time scales, and the questions of injection into the acceleration process and preacceleration in the inner heliosphere. We summarize the present status of our understanding and discuss open questions and possible future developments.

Advances in Space Research, 2005

The solar wind represents a uniquely accessible domain of space, where fundamental physical proce... more The solar wind represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasma can be studied in detail. Due to the unique orbit of Solar Orbiter one of the prime objectives are in situ measurements of different energetic particle populations in the inner heliosphere. These measurements include charged as well as neutral particles. Solar flares and coronal mass ejections occur when magnetic energy is suddenly released in the SunÕs atmosphere. In these eruptions, solar energetic particles including electrons, protons, and heavy nuclei are released. In extreme cases the energies exceed the nuclear binding limits and a particle zoo is created in high-energy collisions, accompanied by the emission of c-rays. In addition neutrons are released and escape due to charge-neutrality freely into space. Because neutrons decay after 15 min only a mission like Solar-Orbiter can observe neutrons below 100 MeV in sizable quantities. In this paper, we will review some aspects of our current understanding of energetic particles and emphasize the potential of Solar Orbiter to provide information on solar activity by means of measuring energetic charged and neutral particles.

Surveys in Geophysics, 2005

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014

This is the second in a pair of papers discussing a statistical study of electromagnetic ion cycl... more This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10 years (2001-2010) of Cluster observations. In the first paper, an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)-distance as well as magnetic local time (MLT)-L frames. This paper focuses on the distribution of EMIC wave-associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H + anisotropy, electron and hot H + density measurements, hot H + parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well-known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off-equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere. Previous studies have investigated the distribution of the hot H + thermal anisotropy in MLT [e.g., Denton et al., 2005; Min et al., 2012]. These studies found that the magnetospheric ion populations become more anisotropic from dusk, through noon, to dawn [

ABSTRACT Recent observations at the Earth's bow shock with Cluster spacecraft provide new... more ABSTRACT Recent observations at the Earth's bow shock with Cluster spacecraft provide new insights into time evolution of particle distributions and the reflection properties of the oblique Earth's bow shock. Field-aligned ion beams appear to emerge from the gyrating ions in the shock ramp created by the same reflection process. In fact, effective scattering in pitch angle within the shock ramp during the reflection seems to be the basic production mechanism of field-aligned ion beams. The efficiency of reflection, transmission and scattering depends on shock parameters, such as Mach number, plasma beta and shock angle. Therefore, these parameters appear to control the relative intensity of these ion beams. Meanwhile the Cluster spacecraft have crossed the Earth's bow shock many times under different interplanetary conditions. A database of shock crossings for a wide range of plasma conditions such as shock normal angle, Mach number, and plasma beta has been compiled. In a statistical study this data set is used to investigate the ion reflection and the ion beam properties at the oblique Earth bow shock in detail. The results will be compared on an event-by-event basis with results of numerical simulations and predictions from theoretical models.

In the summer of 2002, the orbital planes of CLUSTER (apogee at ~20 Re) and POLAR (apogee at ~9 R... more In the summer of 2002, the orbital planes of CLUSTER (apogee at ~20 Re) and POLAR (apogee at ~9 Re) were closely aligned in MLT with both missions having apogee in the tail. This provided a unique opportunity to study the relation between the inner magnetotail at near-Earth distances (POLAR) and the mid-tail region (CLUSTER) during substorm onsets. A considerable number of events have been identified for which CLUSTER observations suggest that an X-line was formed in the mid-tail region while high speed flows were observed at POLAR altitude. In particular, for this study we will focus in the August 21st, 2001 substorm event. The near-earth energetic particles (from POLAR/CEPPAD) will be analyzed for signatures of westward drift-Alfven wave propagation, a signature of the kinetic ballooning instability. Predictions of substorm theories that involve reconnection and the ballooning instability will be tested.

The polar orbit of the CLUSTER satellite is ideal for observing ion outflow from the cusp, and ho... more The polar orbit of the CLUSTER satellite is ideal for observing ion outflow from the cusp, and how those ions are transported across the polar cap, and into the lobe. Using the CODIF/CIS instrument, which measures the 3D distributions of the major magnetospheric ion species over the energy range 40 eV to 40 keV, we have developed an automated procedure to identify when tailward streaming O+ are observed on CLUSTER. The database gives the occurrence frequency of the O+ beams, and their flux and energy, density and temperature as a function of position for geomagnetically quiet and storm times. The CLUSTER satellites were launched in 2000, the maximum of solar cycle 23, and have continued to operate as the solar activity has declined to its current deep minimum. In our previous work, we have concentrated on the early years, close to solar maximum, to show how the O+ flux and transport paths depend on the IMF magnitude and orientation, solar wind pressure, and geomagnetic activity. By ...

Auroral arcs are typically described in terms of an upward field-aligned current (FAC) sheet abov... more Auroral arcs are typically described in terms of an upward field-aligned current (FAC) sheet above the arc, connected by ionospheric Pedersen currents to a downward current sheet near the arc, while a divergence free Hall current electrojet (EJ) flows along the arc. A similar current topology is realized also on oval scale, where the arc associated FACs are replaced, in the morning and evening sectors, by the Region 1 and Region 2 currents, and the arc electrojet by the large scale convection electrojet. In the Harang region (HR), which makes the transition between the evening and morning sectors, the current configuration is often believed to consist of three FAC sheets, two downward FACs on the sides that feed a central upward FAC, again via ionospheric Pedersen currents. We show FAST observations indicating that in the HR the ionospheric current closure is sometimes dominated by the coupling between FAC sheets and electrojet currents, both on arc and oval scale. The FAC-EJ coupli...

IEEE Transactions on Geoscience and Remote Sensing, 1985

In this presentation, we use Cluster data to compare predictions from various methods for determi... more In this presentation, we use Cluster data to compare predictions from various methods for determination of the velocity, orientation, and thickness of the magnetopause current layer. We employ established as well as new multi-spacecraft techniques, in which time differences between the crossings by the four spacecraft, along with the duration of each crossing, are used to calculate magnetopause speed, normal