Papers by Richard Vondrak
Journal of Geophysical Research: Space Physics, 2000
The recent occurrence of an interval (May 9-12, 1999) of abnormally low density solar wind has dr... more The recent occurrence of an interval (May 9-12, 1999) of abnormally low density solar wind has drawn attention to such events. The Solar Wind Experiment (SWE) instrument on the Wind spacecraft observed nine similar events between launch (November 1994) and August 1999: one in 1997, three in 1998, and five in January-August 1999. No such events were observed in 1996, the year of solar minimum. This already suggests a strong dependence upon solar activity. In this paper we discuss observations of the electron strahl, a strong anisotropy in the solar wind electrons above 60 eV directed along the magnetic field and observed continuously during the periods of low density in 1998 and 1999. When the solar wind density was less than 2 cm-3, the angular width of the strahl was below 3.5 ø and the temperature deduced from the slope of the electron strahl phase density (as a function of energy) in the energy range 200-800 eV was 100-150 eV, equivalent to a typical coronal electron temperature. Three examples of this phenomenon, observed on February 20-22, April 26-27, and May 9-12, 1999, are discussed to show their similarity to one another. These electron observations are interpreted to show that the strahl occurs as a result of the conservation of the first adiabatic invariant, combined with the lack of coulomb collisions as suggested by Fairfield and Scudder [1985].
MAXIE: a mechanical scanning auroral X-ray imaging experiment for flight on a TIROS satellite
IEEE Conference on Nuclear Science Symposium and Medical Imaging
Summary form only given, as follows. The satellite borne X-ray imager MAXIE (Magnetospheric Atmos... more Summary form only given, as follows. The satellite borne X-ray imager MAXIE (Magnetospheric Atmospheric X-ray Imaging Experiment) is planned for flight as the ONR-401 experiment on the NOAA-I/TIROS spacecraft to be launched into an 800-km polar orbit in late 1992/early 1993. The instrument maps intensities and energy spectra of X-rays from 4 keV to 100 keV produced by electrons that
The construction of a large radio telescope system has been proposed
The Energy Transport during Substorms Based on Solar Wind Measurements, Derived Auroral Electron Distributions and Magnetic Indices
Data from the Far Ultraviolet Instrument (FUV) on the IMAGE spacecraft and the Polar Ionospheric ... more Data from the Far Ultraviolet Instrument (FUV) on the IMAGE spacecraft and the Polar Ionospheric X-ray Imaging Experiment (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite are used to derive the energy distribution of precipitating particles during substorms. While the ultraviolet imagers can be used to estimate the distributions below ~30-50 keV the X-ray measurements provide information about the electrons up to 100 keV. We estimate the global energy deposition rate (UA) by auroral electrons in the northern hemisphere using data from the different imagers. By deriving the UA from ultraviolet emissions only we find that about 90-100 % of the total energy flux will be estimated during growth phase and expansion phase. However, due to the hard tail above 20-30 keV in the electron spectrum frequently observed during recovery phase only about 80% of the total energy flux will be estimated when only UV emissions are used to estimate UA. Using the time-shifted solar w...
Global Scale Electron Precipitation during Substorm Expansions
Astrophysics and Space Science Library, 1998
Recent Results and Plans for the Extended Science Mission for the Lunar Reconnaissance Orbiter Mission
Update of the Lunar Reconnaissance Orbiter Mission, including a description of the extended missi... more Update of the Lunar Reconnaissance Orbiter Mission, including a description of the extended mission and recent results.
Journal of Geophysical Research: Space Physics, 2004
Nitric oxide (NO) densities at heights between 96 and 150 km in the Earth's upper atmosphere ... more Nitric oxide (NO) densities at heights between 96 and 150 km in the Earth's upper atmosphere are directly compared with the energy deposition from precipitating energetic electrons. The comparisons are done for the beginning of a geomagnetic storm event on 2 May 1998. The electron energy is derived from X‐ray bremsstrahlung observations from the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) on board the Polar spacecraft. Measurements of the NO density are performed by the Student Nitric Oxide Explorer (SNOE) on the dayside by measuring airglow spectral features of the NO γ‐band. Since a significant part of the electron precipitation takes place during the night, and considering the long lifetime of NO, we have accumulated the X‐ray data in geographical boxes. This enables us to follow the development of the total energy deposition over a specific area during the night and morning hours. In agreement with theoretical predictions we find an increase in NO at higher latitudes ...
Auroral electron distributions derived from combined UV and X‐ray emissions
Journal of Geophysical Research: Space Physics, 2001
The Polar Ionospheric X‐ray Imaging Experiment and the Ultraviolet Imager on board the Polar sate... more The Polar Ionospheric X‐ray Imaging Experiment and the Ultraviolet Imager on board the Polar satellite provide the first simultaneous global scale views of the electron precipitation over a wide range of electron energies. By combining the results from these two remote sensing techniques we have developed a method to derive the electron energy distributions that reproduce the true electron spectra from 1 to 100 keV and that can be used to calculate the energy flux in the energy range from 100 eV to 100 keV. The electron energy spectra obtained by remote sensing techniques in three 5‐min time intervals on July 9 and July 31, 1997, are compared with the spectra measured by low‐altitude satellites in the conjugate hemisphere. In the energy range from 90 eV to 30 keV the derived energy flux is found to be 1.03±0.6 of the measured energy fluxes. The method enables us to present 5‐min time‐averaged global maps of precipitating electron energy fluxes with a spatial resolution of ∼700 km. T...
Global multispectral auroral imaging of an isolated substorm
Geophysical Research Letters, 2000
Bow shock protons in the lunar environment
The Moon, 1975
Journal of Geophysical Research: Space Physics, 2006
In this study we have derived height profiles of the ionospheric electron density Ne using remote... more In this study we have derived height profiles of the ionospheric electron density Ne using remote sensing of UV and X‐ray emissions from the Polar satellite and EISCAT radar data. The latter technique gives the most accurate determination of Ne providing a means to ground‐truthing the satellite imaging measurements. The UV‐emission data are taken from the Ultraviolet Imager (UVI) on Polar, while the X‐ray data are measured by the Polar Ionospheric X‐ray Imaging Experiment (PIXIE). As UVI yields a far better resolution in time and space than PIXIE, our primary approach involves UVI and EISCAT data. For a substorm event occurring on 24 March 1998, we derive Ne−UVI profiles valid in the E region above ∼105 km. By comparing with simultaneous Ne−EISCAT values, we find that the two techniques match fairly well in many cases. The altitude of maximum electron density is usually below 110 km. A few cases reveal Ne−EISCAT maxima in the upper E region (130–150 km), indicating a very soft preci...
Remote sensing of high-latitude ionization profiles by ground-based and spaceborne instrumentation
Ionospheric specification and modeling are now largely based on data provided by active remote se... more Ionospheric specification and modeling are now largely based on data provided by active remote sensing with radiowave techniques (ionosondes, incoherent-scatter radars, and satellite beacons). More recently, passive remote sensing techniques have been developed that can be used to monitor quantitatively the spatial distribution of high-latitude E-region ionization. These passive methods depend on the measurement, or inference, of the energy distribution of precipitating kilovolt electrons, the principal source of the nighttime E-region at high latitudes. To validate these techniques, coordinated measurements of the auroral ionosphere have been made with the Chatanika incoherent-scatter radar and a variety of ground-based and spaceborne sensors
Magnetospheric Modification by Gas Releases from Large Space Structures
Space Systems and Their Interactions with Earth's Space Environment, 1980
Terrae Incognitae, 2018
During his epic voyage through the North West Passage, Roald Amundsen's primary goal was to find ... more During his epic voyage through the North West Passage, Roald Amundsen's primary goal was to find the North Magnetic Pole, the point where the earth's magnetic field points vertically downward. In 1903, he interrupted his voyage, which he might have completed that year, to establish a camp at Gjøahavn in northern Canada. In 1904, he traveled to the vicinity of the North Magnetic Pole, establishing that it had moved northward since its discovery by James Clark Ross in 1831. For several weeks, Amundsen made magnetic measurements at different places, but was frustrated because he could not pinpoint the Pole's location. He remained another year at Gjøahavn to explore and to learn from the Inuit their skills for Arctic survival, which enabled the success of his future polar explorations. The modern understanding of geomagnetic variations solves the puzzle of why his search was so difficult and why he thought he was unsuccessful.
Effects of Levitated Dust on Astronomical Observations from the Lunar Surface
It is believed that a substantial population of levitated dust is present in the terminator regio... more It is believed that a substantial population of levitated dust is present in the terminator region of the moon. Stray light scattered by this dust layer may contaminate astronomical observations made from the lunar surface using infrared, visible, and ultraviolet light. The evidence for dust levitation stems from: Surveyor vidicon images of horizon glow; anomalous brightness in photographs of the solar corona taken by Apollo astronauts while the spacecraft was just inside the moon's shadow; and observations by Apollo astronauts of streamers just prior to lunar orbital sunrise or just after lunar orbital sunset. It has been proposed that the differential charging of the lunar surface in the terminator region due to photoemission and the consequent strong local electric fields comprise the mechanism responsible for this levitation. Although quantitative data on the levitated lunar dust distribution are meager, it is possible to estimate column densities and sizes. In this paper we summarize the estimates of particulate sizes and number densities of previous authors, and construct a nominal terminator dust distribution, as a function of particulate radius and altitude above the lunar surface. Using the model we estimate the brightness of scattered sunshine for three wavelength bands. For the results in the visible wavelengths, we compare the estimated brightness with the known brightness of selected astronomical objects and discuss the implications for lunar-based astronomy.
Dispersal of Gases Released at the Lunar Surface
Lunar and Planetary Institute Science Conference Abstracts Supplement, 1976
Energetic particles and ion-composition experiment for crres. Interim technical report
The ONR-307 Energetic Particles and Ion Composition instrument payload will measure the energetic... more The ONR-307 Energetic Particles and Ion Composition instrument payload will measure the energetic particle and plasma environment of the Earth's radiation belts and inner plasma sheet. The payload has been successfully designed, built, and tested for flight on the Combined Release and Radiation Effects Satellite. The instruments were integrated with the spacecraft and tested with the integrated system. This mission, originally scheduled for shuttle launch in July 1987, will now be launched on an Atlas Centaur in June, 1990. The ONR-307 payload is currently undergoing final adjustments and calibration activities prior to re-integration with the spacecraft in May 1989. Procedures have been developed and documented for on-orbit operation of the payload and acquisition of the data on digital tapes.
The lunar environment: Atmosphere and radiation
AIP Conference Proceedings, 1990
The moon is an attractive location for astronomical observatories because of the absence of a sub... more The moon is an attractive location for astronomical observatories because of the absence of a substantial lunar atmosphere and the stability of the lunar surface. The present lunar atmosphere is sufficiently transparent that there is no significant image distortion due to absorption or refraction. This thin atmosphere results from a combination of small sources and prompt losses. The solar wind is the major source, with a total mass input into the lunar atmosphere of less than 50 gm/sec. The principal atmospheric loss mechanism for most gases is photoionization within a period of weeks to months, followed by immediate loss to the solar wind. Lunar base activities will add gases to the lunar atmosphere by rocket exhaust, processing of lunar materials, venting of pressurized volumes, and astronaut life support systems. Although these sources will substantially exceed natural sources, for modest lunar base activity the effects are expected to be localized and transient and not a significant impediment to lunar based astronomy.
Sunwatchers Across Time: Sun-Earth Day from Ancient and Modern Solar Observatories
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Papers by Richard Vondrak