Andre Balogh | Imperial College London (original) (raw)

Papers by Andre Balogh

We study the 3-D spatial structure of a fast flow in the plasma sheet and its relationship to the... more We study the 3-D spatial structure of a fast flow in the plasma sheet and its relationship to the conjugate ionosphere during an isolated flow burst event during a period with moderate magnetic activity on September 1, 2002, around 2200 UT. Due to the relatively large separation distance (about 4000 km), Cluster could identify the different plasma and field signatures of an isolated plasma bubble. A similar ionospheric current pattern was found for this isolated non-substorm BBF as has been deduced earlier for a strong BBF within a substorm period, except for a smaller overall magnitude due to a lower average conductance. We compare the spatial scale (dawn-dusk) of the flow burst determined in space from multipoint measurement with the ionospheric electrodynamic signatures. The 3-D current system related to the localized signatures in the tail will be discussed.

ABSTRACT We have carried out two- and three-dimensional kinetic plasma simulation of the stabilit... more ABSTRACT We have carried out two- and three-dimensional kinetic plasma simulation of the stability and decay of thin current sheets. We demonstrate the consequences of their instability in both the current- and the reconnection direction. We found a number of cases when CLUSTER was well positioned for a multi-point investigation of current sheets. The constellation of four spacecraft allowed us to determine the sheet thickness and - dynamics independently. It appeared that thin current sheets can be found at substorm onsets as well as withoput substorms. The observed dynamics of the sheet evolution compares well with the simulation results. The observations allowed us to verify main theoretical predictions.

On 18 April 2002 the Cluster spacecraft crossed through a cusp-like region in the northern high a... more On 18 April 2002 the Cluster spacecraft crossed through a cusp-like region in the northern high altitude magnetosphere during 16:25-17:55 UT when the spacecraft co-ordinates ranged from X = 6.67 to 8.02 Re, Y = -2.5 to -3.98 Re and Z = 8.22 to 8.19 Re. The cusp crossing occurred when a moderate geomagnetic storm was in progress, solar wind

The Astrophysical Journal, 2011

We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data ... more We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. (1982, Phys. Rev. Lett. 48, 1256) by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-inflow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k ≈ 2 AU −1 (or frequency ν ≈ 2 µHz) at distances below 2.8 AU and at k ≈ 30 AU −1 (or ν ≈ 25 µHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10 45 Mx 2 /cycle at large scales and to a 3 times lower value at smaller scales.

From July to October 2001, the Cluster satellites were located within the magnetotail and crossin... more From July to October 2001, the Cluster satellites were located within the magnetotail and crossings of the neutral sheet were observed by the FGM instrument. The neutral sheet frequently appears to be mo ving relative to the spacecraft. Using measurements of four spacecraft, we are able to determine the neutral sheet normal direction and its speed along the normal, under certain assumptions. The general geometry of the neutral sheet is discussed and this g eometry is examined for selected cases.

Planetary and Space Science, 1993

The spacecraft Ul~ssc~s flew through the Jovian magnetosphere during February 1992. This paper co... more The spacecraft Ul~ssc~s flew through the Jovian magnetosphere during February 1992. This paper compares the magnetic field observations recorded during the inbound pass of the flyby with the electron density as derived from the URAP instrument. In general, it is expected that the density variations will anti-correlate with the magnetic field strength in order to maintain pressure balance, although there may be instances when a temperature or energy rise alone could balance the static stress. Furthermore, there is the possibility that a dynamic process could occur which would cause both the density and field magnitude to rise in unison. In the middle magnetosphere, anti-correlation is found to exist between the two data sets; however, in the outer magnetosphere (which was characterized by very disturbed fields) and in the transition region between the outer and middle magnetospheres, there is no simple relationship between the density and field. Examples of anti-correlation, temperature or energy increases and dynamic processes are found. Days 34/35 : the outer magnetosphere

The four Cluster spacecraft crossed an isolated Flux Transfer Event (FTE) on January 26 th., 2001... more The four Cluster spacecraft crossed an isolated Flux Transfer Event (FTE) on January 26 th., 2001, at about 11:31 UT. Data from the FGM (flux-gate) are used to determine: (i) the shape of the FTE structure, by reference to a model, and its velocity, and (ii) the profile of the current density inside the FTE, by using the tri-axial flux-gate magnetometer implemented on the four Cluster s/c to compute J via curlB**. The validity of the estimate is discussed. Then the FTE is shown to be a force-free "tubular" structure; the current is anti-parallel to B, and it is maximum near the boundary of the FTE (hence the tubular structure). Higher frequency fluctuations observed from the search-coil on STAFF are shown to be driven unstable by this current. **Balogh et al., Space Science Reviews, 79, 1997.

Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amp... more Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amplitude magnetic structures (SLAMS) which act to thermalise the plasma, giving rise to a spatially extended and time varying shock transition. With the launch of Cluster, new observations of the three-dimensional shape and size of shock structures are available. We present SLAMS observations made when the spacecraft were separated by about 100 km. The SLAMS enhancement in |B| is typically well correlated between spacecraft on this scale, consistent with previous observations showing that the overall SLAMS extent exceeded about 600 km, but small differences are still observed. The statistical characteristics of these differences contain information on the typical gradients of magnetic field changes within the SLAM structure which, in the cases studied here, occur on scales of 100-150 km.

Geophysical Research Letters, 2003

We present observations of very low frequency (VLF) waves (0.2 to 448 Hz) made by Ulysses during ... more We present observations of very low frequency (VLF) waves (0.2 to 448 Hz) made by Ulysses during the solar maximum and compare the observations with those obtained when the solar activity was approaching a minimum. The occurrences and properties of the waves are found to be similar during the solar maximum and solar minimum periods for slow and intermediate speed solar wind. The maximum intensities of the electromagnetic waves for the two solar cycle periods are comparable. These similarities suggest that the plasma conditions for the waves' excitation are similar for the slow and intermediate solar wind in both solar maximum and minimum phases. It is also found that the electric field noise detected in the low band channels, which are measuring less than 10 Hz signals, is contaminated by the spin modulation of the electric field caused by the photoelectron cloud around the spacecraft, especially when the ambient plasma density is low. This effect enhances with increasing solar ...

Annales Geophysicae, 2004

Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amp... more Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amplitude magnetic structures (SLAMS) which act to thermalise the plasma, giving rise to a spatially extended and time varying shock transition. With the launch of Cluster, new observations of the three-dimensional shape and size of shock structures are available. In this paper we present SLAMS observations made when the Cluster tetrahedron scale size was ∼100 km. The SLAMS magnetic field enhancement is typically well correlated between spacecraft on this scale, although small differences are observed. The statistical characteristics of these differences contain information on the typical gradients of magnetic field changes within the SLAM structure which, in the case studied here, occur on scales of 100-150 km, comparable with the upstream ion inertial length.

Space Sciences Series of ISSI, 2009

AIP Conference Proceedings, 2010

Fluctuations in the solar wind parameters and in the heliospheric magnetic field have been studie... more Fluctuations in the solar wind parameters and in the heliospheric magnetic field have been studied extensively. The nature of fluctuations has been shown to depend on the origin of the solar wind. However, the regions of transition between the high-speed and the slow speed streams have not been investigated with high resolution. In this work we use high resolution magnetic field measurements on the Ulysses spacecraft to calculate the variances of the fluctuations in the magnetic field components and its magnitude over several timescales, concentrating on intervals of rapid change in the solar wind parameters. At the same time, we computed the cross helicity to assess the Alfvénicity of the fluctuations and changes in it during transitions. The strong variability of all those parameters seems to indicate a filamentary nature of the heliospheric medium.

Chinese Journal of Geophysics, 2005

ABSTRACT

Planetary and Space Science, 1983

... Geos. Electronics GE-16, 176. Balogh, A., and Erdos, G. (1981) The evolution of low energy pr... more ... Geos. Electronics GE-16, 176. Balogh, A., and Erdos, G. (1981) The evolution of low energy proton pitch angle distributions through interplanetary shocks. 17th /C.RC (Paris), Conference Papers 3, 442. ... A. Balogh and G. Erdös, The evolution of low energy proton pitch ...

Planetary and Space Science, 2011

Hubert and Samsonov addressed our paper published in early 2010 (Bebesi et al., 2010) about a pla... more Hubert and Samsonov addressed our paper published in early 2010 (Bebesi et al., 2010) about a plasma event detected in the magnetosheath of Jupiter by the plasma instruments of the Cassini spacecraft. We proposed that the characteristics of the plasma parameter variations were consistent with a slow mode shock (SMS). As our title indicated, we claimed only that the event was a possible ''candidate'' for an SMS according to our data, which had some restrictions as discussed in the paper. As to the origin, we proposed the following: since there was a crossing of the then highly tilted Heliospheric Current Sheet in less than two days before the event, it might have played a role in initiating the shock front. We highly appreciate the opinion of the authors, but they do not point out any hard fact that would exclude the possibility of the scenario we suggested.

We study the 3-D spatial structure of a fast flow in the plasma sheet and its relationship to the... more We study the 3-D spatial structure of a fast flow in the plasma sheet and its relationship to the conjugate ionosphere during an isolated flow burst event during a period with moderate magnetic activity on September 1, 2002, around 2200 UT. Due to the relatively large separation distance (about 4000 km), Cluster could identify the different plasma and field signatures of an isolated plasma bubble. A similar ionospheric current pattern was found for this isolated non-substorm BBF as has been deduced earlier for a strong BBF within a substorm period, except for a smaller overall magnitude due to a lower average conductance. We compare the spatial scale (dawn-dusk) of the flow burst determined in space from multipoint measurement with the ionospheric electrodynamic signatures. The 3-D current system related to the localized signatures in the tail will be discussed.

ABSTRACT We have carried out two- and three-dimensional kinetic plasma simulation of the stabilit... more ABSTRACT We have carried out two- and three-dimensional kinetic plasma simulation of the stability and decay of thin current sheets. We demonstrate the consequences of their instability in both the current- and the reconnection direction. We found a number of cases when CLUSTER was well positioned for a multi-point investigation of current sheets. The constellation of four spacecraft allowed us to determine the sheet thickness and - dynamics independently. It appeared that thin current sheets can be found at substorm onsets as well as withoput substorms. The observed dynamics of the sheet evolution compares well with the simulation results. The observations allowed us to verify main theoretical predictions.

On 18 April 2002 the Cluster spacecraft crossed through a cusp-like region in the northern high a... more On 18 April 2002 the Cluster spacecraft crossed through a cusp-like region in the northern high altitude magnetosphere during 16:25-17:55 UT when the spacecraft co-ordinates ranged from X = 6.67 to 8.02 Re, Y = -2.5 to -3.98 Re and Z = 8.22 to 8.19 Re. The cusp crossing occurred when a moderate geomagnetic storm was in progress, solar wind

The Astrophysical Journal, 2011

We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data ... more We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. (1982, Phys. Rev. Lett. 48, 1256) by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-inflow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k ≈ 2 AU −1 (or frequency ν ≈ 2 µHz) at distances below 2.8 AU and at k ≈ 30 AU −1 (or ν ≈ 25 µHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10 45 Mx 2 /cycle at large scales and to a 3 times lower value at smaller scales.

From July to October 2001, the Cluster satellites were located within the magnetotail and crossin... more From July to October 2001, the Cluster satellites were located within the magnetotail and crossings of the neutral sheet were observed by the FGM instrument. The neutral sheet frequently appears to be mo ving relative to the spacecraft. Using measurements of four spacecraft, we are able to determine the neutral sheet normal direction and its speed along the normal, under certain assumptions. The general geometry of the neutral sheet is discussed and this g eometry is examined for selected cases.

Planetary and Space Science, 1993

The spacecraft Ul~ssc~s flew through the Jovian magnetosphere during February 1992. This paper co... more The spacecraft Ul~ssc~s flew through the Jovian magnetosphere during February 1992. This paper compares the magnetic field observations recorded during the inbound pass of the flyby with the electron density as derived from the URAP instrument. In general, it is expected that the density variations will anti-correlate with the magnetic field strength in order to maintain pressure balance, although there may be instances when a temperature or energy rise alone could balance the static stress. Furthermore, there is the possibility that a dynamic process could occur which would cause both the density and field magnitude to rise in unison. In the middle magnetosphere, anti-correlation is found to exist between the two data sets; however, in the outer magnetosphere (which was characterized by very disturbed fields) and in the transition region between the outer and middle magnetospheres, there is no simple relationship between the density and field. Examples of anti-correlation, temperature or energy increases and dynamic processes are found. Days 34/35 : the outer magnetosphere

The four Cluster spacecraft crossed an isolated Flux Transfer Event (FTE) on January 26 th., 2001... more The four Cluster spacecraft crossed an isolated Flux Transfer Event (FTE) on January 26 th., 2001, at about 11:31 UT. Data from the FGM (flux-gate) are used to determine: (i) the shape of the FTE structure, by reference to a model, and its velocity, and (ii) the profile of the current density inside the FTE, by using the tri-axial flux-gate magnetometer implemented on the four Cluster s/c to compute J via curlB**. The validity of the estimate is discussed. Then the FTE is shown to be a force-free "tubular" structure; the current is anti-parallel to B, and it is maximum near the boundary of the FTE (hence the tubular structure). Higher frequency fluctuations observed from the search-coil on STAFF are shown to be driven unstable by this current. **Balogh et al., Space Science Reviews, 79, 1997.

Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amp... more Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amplitude magnetic structures (SLAMS) which act to thermalise the plasma, giving rise to a spatially extended and time varying shock transition. With the launch of Cluster, new observations of the three-dimensional shape and size of shock structures are available. We present SLAMS observations made when the spacecraft were separated by about 100 km. The SLAMS enhancement in |B| is typically well correlated between spacecraft on this scale, consistent with previous observations showing that the overall SLAMS extent exceeded about 600 km, but small differences are still observed. The statistical characteristics of these differences contain information on the typical gradients of magnetic field changes within the SLAM structure which, in the cases studied here, occur on scales of 100-150 km.

Geophysical Research Letters, 2003

We present observations of very low frequency (VLF) waves (0.2 to 448 Hz) made by Ulysses during ... more We present observations of very low frequency (VLF) waves (0.2 to 448 Hz) made by Ulysses during the solar maximum and compare the observations with those obtained when the solar activity was approaching a minimum. The occurrences and properties of the waves are found to be similar during the solar maximum and solar minimum periods for slow and intermediate speed solar wind. The maximum intensities of the electromagnetic waves for the two solar cycle periods are comparable. These similarities suggest that the plasma conditions for the waves' excitation are similar for the slow and intermediate solar wind in both solar maximum and minimum phases. It is also found that the electric field noise detected in the low band channels, which are measuring less than 10 Hz signals, is contaminated by the spin modulation of the electric field caused by the photoelectron cloud around the spacecraft, especially when the ambient plasma density is low. This effect enhances with increasing solar ...

Annales Geophysicae, 2004

Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amp... more Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amplitude magnetic structures (SLAMS) which act to thermalise the plasma, giving rise to a spatially extended and time varying shock transition. With the launch of Cluster, new observations of the three-dimensional shape and size of shock structures are available. In this paper we present SLAMS observations made when the Cluster tetrahedron scale size was ∼100 km. The SLAMS magnetic field enhancement is typically well correlated between spacecraft on this scale, although small differences are observed. The statistical characteristics of these differences contain information on the typical gradients of magnetic field changes within the SLAM structure which, in the case studied here, occur on scales of 100-150 km, comparable with the upstream ion inertial length.

Space Sciences Series of ISSI, 2009

AIP Conference Proceedings, 2010

Fluctuations in the solar wind parameters and in the heliospheric magnetic field have been studie... more Fluctuations in the solar wind parameters and in the heliospheric magnetic field have been studied extensively. The nature of fluctuations has been shown to depend on the origin of the solar wind. However, the regions of transition between the high-speed and the slow speed streams have not been investigated with high resolution. In this work we use high resolution magnetic field measurements on the Ulysses spacecraft to calculate the variances of the fluctuations in the magnetic field components and its magnitude over several timescales, concentrating on intervals of rapid change in the solar wind parameters. At the same time, we computed the cross helicity to assess the Alfvénicity of the fluctuations and changes in it during transitions. The strong variability of all those parameters seems to indicate a filamentary nature of the heliospheric medium.

Chinese Journal of Geophysics, 2005

ABSTRACT

Planetary and Space Science, 1983

... Geos. Electronics GE-16, 176. Balogh, A., and Erdos, G. (1981) The evolution of low energy pr... more ... Geos. Electronics GE-16, 176. Balogh, A., and Erdos, G. (1981) The evolution of low energy proton pitch angle distributions through interplanetary shocks. 17th /C.RC (Paris), Conference Papers 3, 442. ... A. Balogh and G. Erdös, The evolution of low energy proton pitch ...

Planetary and Space Science, 2011

Hubert and Samsonov addressed our paper published in early 2010 (Bebesi et al., 2010) about a pla... more Hubert and Samsonov addressed our paper published in early 2010 (Bebesi et al., 2010) about a plasma event detected in the magnetosheath of Jupiter by the plasma instruments of the Cassini spacecraft. We proposed that the characteristics of the plasma parameter variations were consistent with a slow mode shock (SMS). As our title indicated, we claimed only that the event was a possible ''candidate'' for an SMS according to our data, which had some restrictions as discussed in the paper. As to the origin, we proposed the following: since there was a crossing of the then highly tilted Heliospheric Current Sheet in less than two days before the event, it might have played a role in initiating the shock front. We highly appreciate the opinion of the authors, but they do not point out any hard fact that would exclude the possibility of the scenario we suggested.