Thomas Holzer - Academia.edu (original) (raw)

Papers by Thomas Holzer

The Cosmic and Heliospheric Branch proposes a bold new program for the years 1995 to 2010 that is... more The Cosmic and Heliospheric Branch proposes a bold new program for the years 1995 to 2010 that is centered on the following two themes: (1) the global heliosphere and interstellar space; and (2) cosmic particle acceleration and the evolution of matter. Within these major themes are more specific goals that have been studied and continue to be examined for a

The First Results from SOHO, 1997

After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange po... more After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located

The ultimate goal of this research is to develop an understanding which is sufficiently comprehen... more The ultimate goal of this research is to develop an understanding which is sufficiently comprehensive to allow realistic predictions of the behavior of the physical systems. Theory has a central role to play in the quest for this understanding. The level of theoretical description is dependent on three constraints: (1) the available computer hardware may limit both the number and

Swiss Political Science Review, 1998

The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs perihelion solar polar orbit ... more The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs perihelion solar polar orbit (with the first perihelion passage in 2004) to explore in situ one of the last frontiers in the solar system-the solar corona. This mission is both affordable and technologically feasible. Using a payload of 12 (predominantly particles and fields) scientific experiments, it

Stereotactic and Functional Neurosurgery, 1997

Forty-six patients with suspected brain tumors were investigated by positron emission tomography ... more Forty-six patients with suspected brain tumors were investigated by positron emission tomography (PET). Using 11C-methionine PET, the spatial extent of increased uptake in gliomas was larger than that of contrast enhancement on CT/ MR images in 67% or the same in 33%. Ten of 46 patients treated with brachytherapy for low-grade gliomas were also investigated with 18F-2-fIuorodeoxyglucose (FDG)-PET. One year after seed implantation, the glucose metabolism had not changed, but the decline of methionine uptake was significant. In conclusion, 11C-methionine PET may improve tumor delineation and, following brachytherapy, provides more information on the therapeutic effects than FDG.

On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid active region whi... more On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid active region which has been the target for a joint observation plan during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer corona (SOHO/LASCO).

The Astrophysical Journal, 2002

... Viggo H. Hansteen and Egil Leer 1 Institute of Theoretical Astrophysics, University of Oslo, ... more ... Viggo H. Hansteen and Egil Leer 1 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, NO-0315 Oslo, Norway; viggo.hansteen@astro ... we use f max = 1. A rapidly expanding geometry is simulated by choosing r g = 1.3 R , g = 0.5 R (Munro & Jackson ...

The Astrophysical Journal, 2002

Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejec... more Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal region's three-dimensional structure and how it evolves in relation to its eruptive dynamics. We use data taken during a recent study of a sigmoidal active region passing across the solar disk (an element of the third Whole Sun Month campaign). While S-shaped structures are generally observed in soft X-ray (SXR) emission, the observations that we present demonstrate their visibility at a range of wavelengths including those showing an associated sigmoidal filament. We examine the relationship between the S-shaped structures seen in SXR and those seen in cooler lines in order to probe the sigmoidal region's three-dimensional density and temperature structure. We also consider magnetic field observations and extrapolations in relation to these coronal structures. We present an interpretation of the disk passage of the sigmoidal region, in terms of a twisted magnetic flux rope that emerges into and equilibrates with overlying coronal magnetic field structures, which explains many of the key observed aspects of the region's structure and evolution. In particular, the evolving flux rope interpretation provides insight into why and how the region moves between active and quiescent phases, how the region's sigmoidicity is maintained during its evolution, and under what circumstances sigmoidal structures are apparent at a range of wavelengths.

The Astrophysical Journal, 2001

... across the magnetic field. As a result of thermal shielding, the hot plasma in the flux rope ... more ... across the magnetic field. As a result of thermal shielding, the hot plasma in the flux rope rapidly cools and condenses to form the prominence (Mason & Bassey 1983; Poland & Mariska 1986; Smith & Priest 1977). A low-density ...

The Astrophysical Journal, 2005

It is presently unclear what role prominences play in the initiation and dynamics of coronal mass... more It is presently unclear what role prominences play in the initiation and dynamics of coronal mass ejections (CMEs), although erupting prominences are strongly correlated with CMEs. The masses of prominences involved in CMEs are not generally measured, but the accurate determination of such masses may help in assessing the dynamical importance of prominences in CME events. In the technique for

The Astrophysical Journal, 2006

In a previous study we developed a new technique for deriving prominence mass by observing how mu... more In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XII (19.5 nm) spectral line is absorbed by prominence material. In the present work we apply this new method, which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of different types of prominences (eruptive, quiescent, and surging) observed during the period 1999 July through 2004 July. The masses of prominences involved in CMEs are not generally measured, but the accurate determination of such masses may help in assessing the dynamical importance of prominences in CME events. In the present study, we find the average mass of our sample of quiescent prominences to be 4.18×1014 g, while the average mass of the eruptive prominences is 9.09×1014 g, and that of surges is 1.53×1014 g.

Space Science Reviews, 1982

In this review, we discuss critically recent research on the acceleration of the solar wind, givi... more In this review, we discuss critically recent research on the acceleration of the solar wind, giving emphasis to high-speed solar wind streams emanating from solar coronal holes. We first explain why thermally driven wind models constrained by solar and interplanetary observations encounter substantial difficulties in explaining high speed streams. Then, through a general discussion of energy addition to the solar wind above the coronal base, we indicate a possible resolution of these difficulties. Finally, we consider the question of what role MHD waves might play in transporting energy through the solar atmosphere and depositing it in the solar wind, and we conclude by examining, in a simple way, the specific mechanism of solar wind acceleration by Alfvén waves and the related problem of accelerating massive stellar winds with Alfvén waves.

Solar Physics, 1995

A b s t r a c t . On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument i... more A b s t r a c t . On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman a emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lyman a results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1 °, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman a line and other Lyman a emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed. K e y w o r d s : solar wind-interplanetary hydrogen-interstellar wind

Journal of Geophysical Research, 1973

The magnetosphere-ionosphere system associated with the nighttime auroral region is considered fo... more The magnetosphere-ionosphere system associated with the nighttime auroral region is considered for quiet conditions, and it is shown that in the presence of an electric field an ionospheric electron density perturbation that is narrow in latitude and broad in local time will grow ...

Journal of Geophysical Research, 1969

Journal of Geophysical Research, 1969

Journal of Geophysical Research, 1968

The Cosmic and Heliospheric Branch proposes a bold new program for the years 1995 to 2010 that is... more The Cosmic and Heliospheric Branch proposes a bold new program for the years 1995 to 2010 that is centered on the following two themes: (1) the global heliosphere and interstellar space; and (2) cosmic particle acceleration and the evolution of matter. Within these major themes are more specific goals that have been studied and continue to be examined for a

The First Results from SOHO, 1997

After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange po... more After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located

The ultimate goal of this research is to develop an understanding which is sufficiently comprehen... more The ultimate goal of this research is to develop an understanding which is sufficiently comprehensive to allow realistic predictions of the behavior of the physical systems. Theory has a central role to play in the quest for this understanding. The level of theoretical description is dependent on three constraints: (1) the available computer hardware may limit both the number and

Swiss Political Science Review, 1998

The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs perihelion solar polar orbit ... more The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs perihelion solar polar orbit (with the first perihelion passage in 2004) to explore in situ one of the last frontiers in the solar system-the solar corona. This mission is both affordable and technologically feasible. Using a payload of 12 (predominantly particles and fields) scientific experiments, it

Stereotactic and Functional Neurosurgery, 1997

Forty-six patients with suspected brain tumors were investigated by positron emission tomography ... more Forty-six patients with suspected brain tumors were investigated by positron emission tomography (PET). Using 11C-methionine PET, the spatial extent of increased uptake in gliomas was larger than that of contrast enhancement on CT/ MR images in 67% or the same in 33%. Ten of 46 patients treated with brachytherapy for low-grade gliomas were also investigated with 18F-2-fIuorodeoxyglucose (FDG)-PET. One year after seed implantation, the glucose metabolism had not changed, but the decline of methionine uptake was significant. In conclusion, 11C-methionine PET may improve tumor delineation and, following brachytherapy, provides more information on the therapeutic effects than FDG.

On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid active region whi... more On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid active region which has been the target for a joint observation plan during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer corona (SOHO/LASCO).

The Astrophysical Journal, 2002

... Viggo H. Hansteen and Egil Leer 1 Institute of Theoretical Astrophysics, University of Oslo, ... more ... Viggo H. Hansteen and Egil Leer 1 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, NO-0315 Oslo, Norway; viggo.hansteen@astro ... we use f max = 1. A rapidly expanding geometry is simulated by choosing r g = 1.3 R , g = 0.5 R (Munro & Jackson ...

The Astrophysical Journal, 2002

Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejec... more Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal region's three-dimensional structure and how it evolves in relation to its eruptive dynamics. We use data taken during a recent study of a sigmoidal active region passing across the solar disk (an element of the third Whole Sun Month campaign). While S-shaped structures are generally observed in soft X-ray (SXR) emission, the observations that we present demonstrate their visibility at a range of wavelengths including those showing an associated sigmoidal filament. We examine the relationship between the S-shaped structures seen in SXR and those seen in cooler lines in order to probe the sigmoidal region's three-dimensional density and temperature structure. We also consider magnetic field observations and extrapolations in relation to these coronal structures. We present an interpretation of the disk passage of the sigmoidal region, in terms of a twisted magnetic flux rope that emerges into and equilibrates with overlying coronal magnetic field structures, which explains many of the key observed aspects of the region's structure and evolution. In particular, the evolving flux rope interpretation provides insight into why and how the region moves between active and quiescent phases, how the region's sigmoidicity is maintained during its evolution, and under what circumstances sigmoidal structures are apparent at a range of wavelengths.

The Astrophysical Journal, 2001

... across the magnetic field. As a result of thermal shielding, the hot plasma in the flux rope ... more ... across the magnetic field. As a result of thermal shielding, the hot plasma in the flux rope rapidly cools and condenses to form the prominence (Mason & Bassey 1983; Poland & Mariska 1986; Smith & Priest 1977). A low-density ...

The Astrophysical Journal, 2005

It is presently unclear what role prominences play in the initiation and dynamics of coronal mass... more It is presently unclear what role prominences play in the initiation and dynamics of coronal mass ejections (CMEs), although erupting prominences are strongly correlated with CMEs. The masses of prominences involved in CMEs are not generally measured, but the accurate determination of such masses may help in assessing the dynamical importance of prominences in CME events. In the technique for

The Astrophysical Journal, 2006

In a previous study we developed a new technique for deriving prominence mass by observing how mu... more In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XII (19.5 nm) spectral line is absorbed by prominence material. In the present work we apply this new method, which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of different types of prominences (eruptive, quiescent, and surging) observed during the period 1999 July through 2004 July. The masses of prominences involved in CMEs are not generally measured, but the accurate determination of such masses may help in assessing the dynamical importance of prominences in CME events. In the present study, we find the average mass of our sample of quiescent prominences to be 4.18×1014 g, while the average mass of the eruptive prominences is 9.09×1014 g, and that of surges is 1.53×1014 g.

Space Science Reviews, 1982

In this review, we discuss critically recent research on the acceleration of the solar wind, givi... more In this review, we discuss critically recent research on the acceleration of the solar wind, giving emphasis to high-speed solar wind streams emanating from solar coronal holes. We first explain why thermally driven wind models constrained by solar and interplanetary observations encounter substantial difficulties in explaining high speed streams. Then, through a general discussion of energy addition to the solar wind above the coronal base, we indicate a possible resolution of these difficulties. Finally, we consider the question of what role MHD waves might play in transporting energy through the solar atmosphere and depositing it in the solar wind, and we conclude by examining, in a simple way, the specific mechanism of solar wind acceleration by Alfvén waves and the related problem of accelerating massive stellar winds with Alfvén waves.

Solar Physics, 1995

A b s t r a c t . On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument i... more A b s t r a c t . On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman a emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lyman a results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1 °, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman a line and other Lyman a emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed. K e y w o r d s : solar wind-interplanetary hydrogen-interstellar wind

Journal of Geophysical Research, 1973

The magnetosphere-ionosphere system associated with the nighttime auroral region is considered fo... more The magnetosphere-ionosphere system associated with the nighttime auroral region is considered for quiet conditions, and it is shown that in the presence of an electric field an ionospheric electron density perturbation that is narrow in latitude and broad in local time will grow ...

Journal of Geophysical Research, 1969

Journal of Geophysical Research, 1969

Journal of Geophysical Research, 1968