Frank, L. A., J. B. Sigwarth, J. D. Craven, C.-I. Meng, T. L. Killeen and W. E. Sharp, Global Views of Earth and its Auroras with the Visible Imaging System (VIS) on the Polar Spacecraft, 31st Scientific Assembly of COSPAR, Birmingham, United Kingdom, p. 175, 14-21 July 1996.
Abstract: The Visible System (VIS) that is to be launched with the Polar spacecraft is capable of providing complete global views of our planet along a large fraction of the spacecraft orbit. The VIS includes two telescopes for visible wavelengths and an Earth camera at far-ultraviolet wavelengths. The two telescopes are equipped with narrow-band filters for auroral emissions from OI at 557.7 and 630.0 nm, OII at 732.0 nm, and N2+ at 391.4 nm. In addition emissions from the proton auroras at H-alpha, 656.3 nm, are also viewed. With other filters the observing capabilities are extended to columnar ozone at 317.3 nm, NaI emissions at 589.0 nm in the atmospheric nightglow and in the lunar atmosphere, and OH emissions at 308.5 nm We are hopeful that we will be able to provide an overview of several imaging campaigns at this meeting.
Abstract: The Visible Imaging System (VIS) for the POLAR consists of three
cameras for investigating the spatial and temporal features of Earth's auroras. Two
of these cameras are equipped with twelve filters for studies of auroral emissions
at visible wavelengths, e.g., 391.4, 557.7, 630.0, 732.0, and the H-alpha proton
emissions at 656.3 nm The third camera has a sufficiently large field-of-view to
provide images of the entire Earth during most of the orbit without the mosaicing
that is employed by the visible cameras. These images are taken with one far-ultraviolet
filter that passes primarily the oxygen multiplets at 130.4 and 135.6 nm. The angular
resolution of this Earth Camera is 80 km from spacecraft apogee. Because the spacecraft
was launched after the winter viewing season at visible wavelengths for the Northern
Hemisphere the Earth Camera has been used for studies of auroral dynamics until the
next winter campaign. We present an overview of these results.
Abstract: The Visible Imaging System (VIS) for the POLAR spacecraft consists of three cameras for investigating the spatial and temporal features of Earth's auroras. The VIS co-investigators are identified above. Two of these cameras are equipped with twelve filters for studies of auroral emissions at visible wavelengths, e.g., 391.4, 557.7, 630.0, 732.0, and the H-alpha proton emissions at 656.3 nm. These two cameras, Low Resolution and Moderate Resolution, differ in their angular resolutions at auroral altitudes, 20 km and 10 km, respectively, as viewed from the spacecraft apogee altitude of 8 RE (Earth radii). The third camera has a sufficiently large field-of-view to provide images of the entire Earth during most of the orbit without the mosaicing that is employed by the visible cameras. These images are taken with one far-ultraviolet filter that passes primarily the oxygen multiplets at 130.4 and 135.6 nm. The angular resolution of this Earth Camera is 80 km from spacecraft apogee. The repetition rate for full image frames can be as fast as one frame each 12 seconds with the use of the instrument data compression software. Because the spacecraft was launched after the winter viewing season at visible wavelengths for the Northern Hemisphere the Earth Camera has been used for studies of auroral dynamics until the next winter campaign. We present an overview of these results.
Abstract: The Geotail spacecraft has provided a fabulous series of observations of plasma phenomena in the near and far reaches of Earth's magnetotail. Recently this long-lived spacecraft has been joined, among others, by the Polar and Wind spacecraft with the purpose of providing great insight into the global dynamical behavior of our planet's magnetosphere. It is our intent to provide an overview of several important plasma features of the magnetotail which have been observed with the Geotail spacecraft, e.g., plasma velocity distributions that exhibit "memories" of their past acceleration and transport, direct detection of currents associated with regions of weak magnetic fields, magnetically field-aligned currents during substorm onset, and nongyrotropic pressure tensors. We will then present our initial results of correlative studies of the behavior of plasmas as observed in the near-Earth plasma sheet with Geotail and the simultaneous records of global auroral activity as gained with the Earth Camera on board the Polar spacecraft.
Abstract: At about 0400 UT on May 10, 1996 a classic, isolated substorm was observed by a number of ISTP spacecraft including POLAR, GOES, and the Los Alamos geosynchronous satellites. Following this onset a sequence of periodic oscillations of the energetic particle flux was observed by all three of the Los Alamos geosynchronous satellites. The oscillations are particularly apparent at local times from noon to midnight in the electron fluxes between 50 and 105 keV. The oscillations persist for over 12 hours and flux maxima are separated in time by about 1.5 hours. They appear to be associated with similar oscillations observed in the magnetic field components measured by the GOES satellites. In this paper we further characterize these oscillations and we attempt to determine their source. The relationship of these periodic oscillations to periodic substorm activity, drift resonance, sources in the more distant plasma sheet, and driving by the solar wind will all be considered. This study uses coordinated ISTP observations and has also been chosen for study in the GEM substorm campaign.
Abstract: We present the first simultaneous, coordinated observations of auroral emissions using the three imaging camera systems aboard the GGS Polar satellite: the UV Earth Camera of the Visible Imaging System (VIS), the narrow-band and high-resolution UV Imager (UVI), and the x-ray imaging spectrometer (PIXIE). On 27 May Polar crossed the southern auroral zone during a period of significant auroral activity. All three of the Polar imaging systems provided excellent images of the aurora during this pass. The imaged region included the magnetic footprint of the satellite, which passed through the auroral emission region near midnight and near noon, local time. Polar particle instruments provided direct measurements of precipitating particles. Two DMSP satellites crossed the auroral zone within the Polar field of view during this pass and provided visible images of the aurora at this time. We will present images of the aurora from each of the imagers, comparing and contrasting the morphology of the auroral emissions across the spectrum and interpreting the images in terms of the auroral forms observed. Intensities of the UV and x-ray emissions will be intercalibrated and used to infer the intensity and energy distribution characteristics of the precipitating particles responsible for the observed emissions.
Abstract: An observation of the sunlit aurora at FUV wavelengths
eliminates the nontrivial problem of underlying albedo radiation encountered when
imaging at visible wavelength. Unfortunately, it is replaced by the nontrivial problem
of overlying thermospheric FUV emissions arising from resonantly scattered sunlight
and emissions stimulated by solar-EUV-induced secondary electrons. The brightness
of the FUV emissions observed with a spacecraft at high altitudes is dependent on
geometry via solar and spacecraft zenith angles and is also dependent on properties
within the thermosphere, such as its composition and the radiation's wavelength-dependent
transmittance. The geometric effects can be removed, leaving for our attention, for
example, the effects of thermospheric composition that arise from Joule and particle
heating at auroral latitudes. What is more important here is that disturbances in
composition propagate to subauroral and polar cap latitudes, thereby inducing even
larger-scale changes in the thermosphere and the background FUV emissions.
These spatial and temporal alterations of thermospheric composition and their dependence
on IMF orientation are under investigation with FUV observations from the DE-1 spacecraft.
The techniques used there are now applied to the FUV observations of aurora and dayglow
with the Earth Camera on the POLAR visible imaging system. An empirically derived
FUV dayglow brightness model is created for magnetically quiet periods and is used
to identify areas in other FUV images where the thermospheric background has been
perturbed by auroral activity. The perturbed background, with interpolation over
the auroral region, is subtracted from the original auroral images to yield first-order
corrected images of the sunlit aurora in the absence of the dayglow. The corrected
FUV images from a single orbit of POLAR are shown in order to demonstrate the spatial
and temporal variations that can be observed with the Earth Camera in the absence
of the dayglow. A second set of simultaneous "images" illustrates the evolving
perturbations in thermospheric composition that are correlated with the time history
of IMF orientation and auroral activity. The time scales for variations in thermospheric
composition are different for the polar cap and subauroral latitudes.
Abstract: These initial studies of global magnetospheric dynamics are directed
toward the behavior of the near-Earth plasma sheet during the onsets of substorms.
The global auroral images at far-ultraviolet wavelengths with the Earth Camera of
the Visible Imaging System (VIS) on board the Polar spacecraft are used to determine
the Universal Time and the local time sector for the initial brightening of an auroral
arc during the nighttime. The next step in the investigation is the identification
of Geotail measurements in the near-Earth plasma sheet that are available at the
time of onset and are in the same local time sector. The third required data base
is simultaneous observations in the interplanetary medium with the Wind spacecraft.
The scientific objectives are directed toward assessing the roles of field-aligned
currents, impulsive plasma injection and triggering mechanisms in the plasma sheet
during the substorm onsets.
Abstract: In spite of the numerous earlier investigations, the details of the solar wind energy input to the magnetosphere and its release in the form of substorms remain poorly understood. The suite of satellites in the International Solar Terrestrial Program allows the study of these phenomena to an unprecedented accuracy. Here we study an isolated substorm event on May 15, 1996, where the interplanetary magnetic field and solar wind plasma properties were recorded by IMP 8 and WIND satellites, the near-Earth plasma environment was monitored by several geostationary satellites and GEOTAIL at about 10 RE radial distance, and POLAR passed through the dayside cusp to the high-latitude polar cap and was imaging the evolution of the auroral oval before and at the time of the substorm onset. The substorm event followed a prolonged period of northward IMF; we study the energy input into the magnetosphere and the growth phase evolution. Furthermore, the substorm expansion took place in several steps; we investigate the relative role of the solar wind variations and internal tail and/or ionospheric to the step-like evolution.
Abstract: Understanding the relationship of the particle
populations measured at low altitudes to the morphology of the high-altitude magnetosphere
is important, as we still lack the means to globally image the entire magnetosphere.
In this talk we investigate the relative locations of various particle boundaries
detected by several instruments: SAMPEX produces daily maps of the high-energy particle
environment ranging from the low-latitude inner radiation belts to the higher-latitude
magnetospheric trapping boundary. These maps are compared with averaged auroral images
taken by the FUV camera of the VIS imager onboard the POLAR satellite. This system
is mainly sensitive to electron precipitation in the keV range. Further information
about the precipitation boundaries are deduced from DMSP satellites. These spacecraft
provide the boundaries for the low-energy polar rain, as well as the auroral particles
(BPS and CPS precipitation) in one magnetic local time sector. The low-altitude boundaries
are then mapped to the magnetospheric equatorial plane, using the most recent version
of the Tsyganenko models. The results are used to discuss the various plasma regions
and the quiet time morphology of the magnetosphere, the definitions and significance
of open and closed field lines, and the physics of the transition region between
the trapped ring current particles and the plasma sheet particles.
Raeder, J., J. Berchem, M. Ashour-Abdalla, L. A. Frank, W. R. Paterson, K. L. Ackerson,
S. Kokubun, T. Yamamoto and R. P. Lepping, Global MHD Simulation of the May 19/20,
1996 Substorm Event and Comparisons with ISTP/GGS Observations, EOS, 77(46),
639, 1996.
Abstract: We present a global MHD simulation study of a substorm event that
occurred at about 0040 UT on May 20, 1996, and that was well covered by several ISTP
spacecraft and ground stations. On May 19 and 20, 1996 the Wind spacecraft monitored
the solar wind 110 RE upstream from earth. Between about 2100 UT on May 19 and 0100
UT on May 20 Wind observed a southward interplanetary magnetic field (IMF) with a
few, very brief northward excursions. At about 0040 UT on May 20, the Canopus magnetometer
chain observed a rapid decrease of the electrojet index, indicating the onset of
a substorm. Simultaneously, the UVI imager on the Polar spacecraft observed the development
of a substorm surge that expanded both westward and eastward. Using Wind data as
input to our three-dimensional global MHD model we simulated this event. We compare
the simulation results with the observations and discuss the onset mechanism of this
substorm. In particular we address the magnetic mapping of the auroral surge into
the tail and examine the effect of northward excursions of the IMF.
Abstract: At about 0400 UT on May 10, 1996 a classic, isolated substorm was observed by a number of ISTP spacecraft including POLAR, GOES, and the Los Alamos geosynchronous satellites. Following this onset a sequence of periodic oscillations of the energetic particle flux was observed by all three of the Los Alamos geosynchronous satellites. The oscillations are particularly apparent at local times from noon to midnight in the electron fluxes between 50 and 105 keV. The oscillations persist for over 12 hours and flux maxima are separated in time by about 1.5 hours. They appear to be associated with similar oscillations observed in the magnetic field components measured by the GOES satellites. In this paper we further characterize these oscillations and we attempt to determine their source. The relationship of these periodic oscillations to periodic substorm activity, drift resonance, sources in the more distant plasma sheet, and driving by the solar wind will all be considered. This study uses coordinated ISTP observations and has also been chosen for study in the GEM substorm campaign.
Sigwarth, J. B. and L. A. Frank, Images of Earth's Auroras From the Visible Imaging
System (VIS) for the POLAR Spacecraft, EOS, 77(46), 623, 1996.
Abstract: The Visible Imaging System (VIS) for the Polar spacecraft consists of a set of three low-light-level cameras designed to obtain high-time and high-spatial resolution images of Earth's auroras. The two visible light cameras share a set of 12 filters for the observation of auroras at visible wavelengths of 391.4, 557.7, 630.0, and 732.0 nm, as well as the H-alpha proton emissions at 656.3 nm. The low-resolution and medium-resolution visible cameras have 5.4° x 6.3° and 2.8° x 3.3° instantaneous fields-of-view, respectively that can be selected anywhere within a full 20° x 20° rectangular field-of-view. Global images of the visible auroral emissions are obtained by the mosaicing of images from either of the visible cameras. The third camera or "Earth Camera" has a wide, 20° x 20° rectangular field-of-view that is capable of observing the entire Earth for most of the orbit without the need for mosaicing. The Earth Camera is predominantly sensitive to atomic oxygen multiplet emissions at 130.4 nm and 135.6 nm in the far ultraviolet. The VIS has been acquiring auroral images continuously since shortly after launch of the Polar spacecraft in February 1996. Both high-altitude northern auroral and low-altitude southern auroral image sequences have been used for studies of auroral dynamics. We present an overview of these results.
Abstract: A pair of substorms occurred around 08 UT on January 12, 1997, that were observed by numerous instruments that were a part of the ISTP mission. The GEOTAIL Plasma Wave Instrument (PWI) at 28 RE down the tail and the WIND WAVES experiment upstream at X=117 RE and Y=-54 RE detected enhanced auroral kilometric radiation (AKR) and a LF burst. POLAR was inbound at 7.5 RE near 07 MLT. The POLAR PWI detected the enhanced AKR that included expanded upper and lower frequency cutoffs. The POLAR HYDRA experiment observed plasma sheet ions and electrons that were of higher energy than normal. Many of the CANOPUS ground magnetometer stations were able to identify both substorms and track the movement. Negative bays near -1000 nT were observed. Large structured injections of protons and electrons were observed by GOES 8 and 9. Images from the POLAR VIS Earth Camera operating in the far-UV range showed a strong aurora with injections deep into the ring current. These images along with the other observations detail the dynamics of the plasma associated with these strong substorms.
Abstract: Several particle instruments onboard the Polar GGS spacecraft are used to document enhanced electron and ion fluxes appearing in the middle of the polar cap, isolated from the cusp/mantle and the auroral oval particles. These particles often associate with the transpolar arcs in the theta-auroral patterns at the ionosphere height, confirmed by the auroral images from the VIS Earth Camera. Such plasma measurements at a higher altitude pertaining to the theta-auroral pictures at a lower altitude occur on both northern and southern hemispheres. Particles observed by HYDRA in these regions have energies as high as a few keVs, above the typical values of the polar cap plasmas. The high energy components of these ions flow toward the Earth and the low energy components flow away from the Earth, whereas the electrons are more isotropic. In the same regions, energetic ions observed by CEPPAD IPS have energies extending to about 100 keV, but the energetic electrons (above 30 keV) are absent. Meanwhile, ion data from TIMAS shows ionospheric ion (O+, He+, etc.) outflows in these regions for some events, consistent with HYDRA measurements. Usually, the IMF By and/or Bz components (from Wind GGS MFI) change sign before the theta-auroral patterns develop. The energy and pitch angle distributions of the electrons and ions observed by HYDRA are analyzed to explain the possible source locations of these particles and the magnetic field configuration in the polar cap for the theta-auroral patterns. The ionospheric plasma convections are also examined from the ground-based radar data to verify the HYDRA measurements.
Abstract: Simultaneous optical observations of the aurora are presented from three vantage points in early 1997 as part of the POLAR and FAST missions. Long duration (many hours) global-scale images are provided at FUV and visible wavelengths with the VIS instrument on the POLAR spacecraft to properly place the local observations in the global context of auroral and magnetospheric dynamics. With clear skies the distribution of ground-based all-sky cameras provides high temporal and spatial resolution in the Alaskan sector in support of over flights by the FAST spacecraft. The aircraft flights provide optimum coverage under the flight path of FAST without concern for cloud cover as FAST provides outstanding high-resolution plasma and plasma-wave observations at spatial and temporal resolutions sufficient to identify individual discrete auroral features. The emphasis in this work is on the simultaneous optical observation combined in common formats from selected quiet and active periods. Simultaneous FAST plasma observations are compared with the optical observations to clearly delineate the plasma regimes and their magnetospheric source regions. Position of the auroral electrojet is determined simultaneously with the Alaskan-sector meridian chain of magnetometers.
Abstract:
Recent wave and particle measurements made by instruments onboard the POLAR and GEOTAIL spacecraft have been compared for times when both spacecraft are crossing the same magnetic field lines, GEOTAIL is skimming the magnetopause, and POLAR is at or near one of the northern or southern polar cap boundary layers. The data taken during these times suggest that POLAR instrumentation is observing the effects of high altitude heating of upflowing ionospheric ions, through wave-particle interactions. GEOTAIL observes these same ions after they have propagated into the magnetopause boundary layer through heating and acceleration. These observations, together with solar wind plasma and interplanetary magnetic field measurements from WIND, images of the footprints of the magnetic field from POLAR, and ground-based, remote sensing measurements, will be discussed in order to gain a further understanding of the magnetopause boundary layer and the transport and acceleration processes that take place in and near the magnetopause region.
Abstract:
On May 15, 1996, two sequential substorm onsets took place about 40 min apart following a southward turning of the IMF. The events were observed by several ISTP spacecraft in the upstream solar wind, by several spacecraft in the magnetotail, and by an extensive complement of ground-based instruments covering a wide range of latitudes and local times. The first event occurred during persistently negative IMF Bz, whereas the second onset occurred at the time when the IMF changed from southward to northward orientation. The two events had very different global evolution: The first onset led only to minor reconfiguration of the tail field and a short-lived auroral intensification. On the other hand, the second onset caused much stronger field dipolarization, global auroral expansion, and significant polar cap area reduction. Magnetic field modeling and field-aligned mappings are used to find the source regions of both the auroral brightenings and the substorm current wedge currents, which in this event were not colocated. The significance of the solar wind/IMF parameters and ionospheric conditions to the substorm evolution after the initial onset are discussed.
Abstract:
The Visible Imaging System (VIS) on the NASA/GSFC Polar spacecraft has been acquiring global auroral images since shortly after launch in February, 1996. These images were obtained with the Earth Camera that is sensitive predominately to the atomic oxygen emissions at 130.4 nm and 135.6 nm. Since the advent of the winter auroral viewing season in the northern hemisphere, the Low Resolution Camera of the VIS has been acquiring observations of the nighttime auroral oval at visible wavelengths. Extensive series of nearly simultaneous observations have been obtained using a sequence of narrowband transmission filters centered on the visible emissions of N2+ at 391.4 nm, of O1 at 557.7 nm, and of O1 at 630.0 nm. The visible images are acquired every 24 seconds. In addition a global auroral oval image from the Earth Camera has been obtained as part of each imaging sequence. The high inclination orbit and high apogee altitude of the Polar spacecraft allow auroral viewing for nearly 15 hours of the 17.6 hour orbital period. Examples of a number of auroral observations will be presented along with a comparison of the auroral intensities at the observed wavelengths.
Abstract: In conjunction with NASA's Polar satellite
program, we have conducted a campaign of auroral substorm observations using an all-sky
television camera with a fish-eye lens at Loparskaya (68.6° N, 33.3°
E geographic, 65.0° N, 114.2° E geomagnetic) during the Winter season
from October 1996 to April 1997. In this talk, we present local and global observations
of two nightside auroral intensifications on December 9, 1996 which were both triggered
by strong increases in the solar wind dynamic pressure during intervals of southward
IMF orientation. The first, a pseudo-breakup, took place at 2131 UT. In several tens
of seconds a very quiet diffuse arc transformed into a bright discrete rayed auroral
structure, but there was no expansion phase or appearance of pulsating aurora. The
second intensification began at 2251 UT westward of Loparskaya and manifested a very
active expansion phase in which activity moved symmetrically eastward and westward
from the point of initial intensification. We suggest that when breakup near midnight
produces both a westward and an eastward traveling surges.
Abstract:
The Polar and FAST satellites are frequently in magnetic conjunction in the polar cap. We have analyzed plasma and field data from conjunctions when energetic ions were observed on both FAST and Polar near the times of conjugacy. In these events boundary layer plasma was often, but not always, observed by only one of the satellites. We present an analysis of the ion, electron, DC electric field data, and global images that illustrate how the dawnside polar cap is often filled with filaments of boundary layer plasma. The locations of the conjugate satellites are used to put limits on the physical and/or temporal extent of the observed streams.Abstract: The Visible Imaging System (VIS) on the NASA/GSFC Polar spacecraft has been acquiring global auroral images since shortly after launch in February, 1996. These images were obtained with the Earth Camera that is sensitive predominately to the atomic oxygen emissions at 130.4 nm and 135.6 nm. Since the advent of the winter auroral viewing season in the northern hemisphere, the Low Resolution Camera of the VIS has been acquiring observations of the nighttime auroral oval at visible wavelengths. Extensive series of nearly simultaneous observations have been obtained using a sequence of narrowband transmission filters centered on the visible emissions of N2+ at 391,4 nm, of O1 at 557.7 nm, and of O1 at 630.0 nm. The visible images are acquired every 24 seconds. In addition a global auroral oval image from the Earth Camera has been obtained as part of each imaging sequence. The high inclination orbit and high apogee altitude of the Polar spacecraft allow auroral viewing for nearly 15 hours of the 17.6 hour orbital period. Examples of a number of auroral observations will be presented along with a comparison of the auroral intensities at the observed wavelengths.
Abstract:
Abstract: The POLAR satellite's plasma wave experiment detects intense broadband ELF and VLF waves near the spacecraft apogee (r/Re 7) about 100% of the time. It will be demonstrated that these waves are a permanent feature of the magnetosphere. The properties of these waves will be illustrated and a comparison will be made to waves previously observed within the low latitude boundary layer (LLBL). In addition, the evidence from POLAR particle instruments for high altitude heating of upflowing ionospheric ions, through wave-particle interactions, will be presented and discussed.
The POLAR wave and particle data for a few of these events have been correlated with similar measurements made on the GEOTAIL spacecraft as it was skimming the magnetopause and when both spacecraft were crossing the same magnetic field lines. GEOTAIL observes these same ions after they have propagated into the magnetopause boundary layer through heating and acceleration. These observations, together with other pertinent measurements, will be discussed in order to help gain a better understanding of the magnetopause boundary layer and the transport and acceleration processes that take place in and near the magnetopause region.
Abstract: Variability in the solar activity is manifested
in the near-Earth plasma environment in two distinct ways: The MeV electrons forming
the outer radiation belt are mainly driven by fast solar wind streams and vary in
a time scale of a day or less. On the other hand, the keV particles generating the
auroral emissions respond to changes in the interplanetary magnetic field north-south
component with a time scale of several hours. We examine a ten-day period (May 5-15,
1996), using particle precipitation measurements from SAMPEX and auroral oval images
acquired by the POLAR VIS imaging system. The global maps provided by SAMPEX and
POLAR are complemented by instantaneous measurements of the boundaries from the DMSP
spacecraft. We relate the variations in the radiation belt and auroral activity to
solar activity and solar wind and IMF characteristics. We investigate the relative
locations of the precipitation boundaries in order to study the various plasma regions
and magnetospheric morphology, the definitions and significance of open and closed
field lines, and the physics of the transition region between the trapped ring current
particles and the plasma sheet particles. Magnetic field models are used to map these
boundaries to the magnetosphere, which then provide a global image of the magnetospheric
plasmas that cannot be obtained by direct means.
Sigwarth, J. B. and L. A. Frank, Imaging of the Northern Auroral Oval With the Visible Imaging System on the Polar Spacecraft, 8th Scientific Assembly of International Association of Geomagnetism and Aeronomy (IAGA), Uppsala, Sweden, p. 181, 4-15 August 1997.
Abstract: The Visible Imaging System (VIS) on the NASA/GSFC Polar spacecraft has been acquiring global auroral images since shortly after launch in February, 1996. These images were obtained with the Earth Camera that is sensitive predominately to the atomic oxygen emissions at 130.4 nm and 135.6 nm. Since the advent of the winter auroral viewing season in the northern hemisphere, the Low Resolution Camera of the VIS has been acquiring observations of the nighttime auroral oval at visible wavelengths. Extensive series of nearly simultaneous observations have been obtained using a sequence of narrowband transmission filters centered on the visible emissions of N2+ at 391.4 nm, of O1 at 557.7 nm, and of O1 at 630.0 nm. The visible images are acquired every 24 seconds. In addition a global auroral oval image from the Earth Camera has been obtained as part of each imaging sequence. The high inclination orbit and high apogee altitude of the Polar spacecraft allow auroral viewing for nearly 15 hours of the 17.6 hour orbital period. Examples of a number of auroral observations will be presented along with a comparison of the auroral intensities at the observed wavelengths.
Abstract:
During the winter of 1996-97 four new digital all-sky cameras have started continuous observations of the auroras in Northern Finland, Sweden, and Svalbard. Simultaneously, the POLAR satellite has observed the global auroral oval both at visible and ultraviolet wavelengths during long continuous periods interrupted only by the satellite perigee passes.We have produced keograms--latitude vs. time plots--of the ground-based and satellite imager data, and compare the auroral activity with the auroral electrojet location as determined from the longitudinal IMAGE magnetometer chain. The mesoscale ground-based all-sky camera observations are compared with the global-scale spaceborne images: we compare and contrast the sensitivity of the instruments, the global and local view of the discrete auroral forms, and the emission intensities as seen from ground and space. Especially, we examine the differences in observations during all substorm phases, and use the results to discuss the changes in the auroral spectrum during the course of the substorm.
Abstract: An isolated substorm was recorded with the Earth Camera of the Visible Imaging System (VIS) on board the Polar spacecraft on 12 January 1997. During this substorm the Geotail spacecraft was positioned in the magnetotail at about 30 RE in the pre-midnight sector. Observations of the plasmas and magnetic fields were provided for the upstream interplanetary medium and the dusk magnetosheath by the Wind and IMP-8 spacecraft, respectively. These observations of an isolated substorm offer an excellent opportunity to test the effectiveness of global MHD models of Earth's magnetosphere. We provide an overview of the observations with the above spacecraft.
Abstract: Several plasma wave emissions observed by GEOTAIL, POLAR, and WIND are related to substorms. Comparison of the wave characteristics from the different ISTP spacecraft to other space and ground substorm monitors allows us to study both the sources of the waves and the plasma dynamics. AKR has long been known to be related to geomagnetic activity. Observations from multiple spacecraft aid us in separating differences in the AKR spectra due to generation or propagation effects. Low frequency (LF) bursts are a part of AKR observed during strong isolated substorms detected by the CANOPUS and other magnetometer networks. We have found that more high frequency AKR is detected by either GEOTAIL or WIND during LF burst events only if the path from the AKR source is not blocked by the earth or dense plasmasphere. POLAR observations from high over the AKR source region show that the AKR increases in intensity and its lower frequency limits when LF bursts are observed indicating that the AKR source region is expanding to higher altitudes. Frequently the upper frequency limit also increases indicating that the source region is then also expanding to lower altitudes. Wideband data from POLAR allow us to identify where in frequency the LF burst changes from being spin-modulated to being isotropic. Images from the POLAR VIS Earth Camera operating in the far-UV range usually feature a strong enhancement in the aurora at the time of the LF bursts. The high resolution ground magnetometer data show that the LF bursts occur when the expansive phase onset signatures are most intense. Magnetometer data from geosynchronous satellites usually show increased magnetic field dipolarization and the presence of field-aligned currents during LF burst events for the spacecraft closest to local midnight. Large injections of protons and electrons have also been detected by geosynchronous satellites. Observations from GEOTAIL, POLAR, and WIND of enhanced continuum and continuum storms produced by injected plasma impinging on the plasmasphere also help describe the plasma motion during substorms.
Abstract: Understanding the large-scale dynamics of the
magnetosphere is an important step to achieve the ISTP mission's broad objective
of assessing the global transport of plasma and energy through the geospace environment.
Three-dimensional numerical simulations of the interaction between the solar wind
and the magnetosphere-ionosphere system have now reached a level of sophistication
that allows these simulations to be used for correlative studies involving both local
and global observations. In this talk we present results from recent studies that
show how measurements from the GEOTAIL and POLAR spacecraft can be used with results
from global MHD simulations to obtain a multipoint assessment of the global dynamics
of the magnetosphere. Our approach consists of using the interplanetary magnetic
field and the plasma parameters measured by the WIND spacecraft upstream of the bow
shock as input to the numerical simulations. The validity of our predictions is tested
by comparing simulation results with both in-situ time series as measured by spacecraft
and global images of the auroral activity.
Chang, S. W., J. D. Scudder, J. B. Sigwarth, L. A. Frank, N. C. Maynard, W. J. Burke,
W. K. Peterson, E. G. Shelley, R. Friedel, J. B. Blake, C. T. Russell, R. A. Greenwald,
R. P. Lepping, G. J. Sofko, J.-P. Villain and M. Lester, Generation of the Theta
Aurora, EOS, 78(46), 586, 1997.
Abstract: A model is presented according to which theta auroral
arcs form after southward turnings of IMF Bz and/or large variations in By, following prolonged periods of northward
IMF or very small Bz, with
|By| greater than or comparable to
|Bz|. The arcs start on the dawn
(dusk) side of the auroral oval and drift duskward (dawnward) across the
polar cap for positive (negative) By in the northern hemisphere and conversely in
the southern hemisphere. After the theta aurora has formed, changes in
IMF By or Bz readjust the merging configuration and
continue the auroral pattern. The transpolar arcs are on closed magnetic
field lines that bifurcate two open sections of the polar cap and map to
the outer plasma sheet. Observations from the ISTP/GCS Polar and Wind
spacecraft and the ground-based SuperDARN radars that are consistent with
the predictions of the model include: (1) The formation and evolution of
the theta auroras observed by VIS are closely related to the IMF patterns
measured by the MFI. (2) Both electrons and ions in the transpolar arc
and poleward part of the nightside auroral oval exhibit similar spectral
characteristics, identified by Hydra and CEPPAD. The low energy electrons
show counter streaming distributions, consistent with their being on
closed field lines that magnetically connect to the boundary plasma sheet
in the magnetotail. (3) Ion composition measurements obtained from TIMAS
show cold plasma outflows from the ionosphere and hot, isotropic
magnetospheric ions in the two regions, also indicating transpolar arcs
are on closed field lines. (4) Large scale polar cap convection inferred
by SuperDARN observations is well anti-correlated with IMF Bz variations. (5) Plasma convection in the
transpolar arcs, inferred from EFI electric field and MFE magnetic field
measurements, is sunward. (6) Transpolar arcs are located in regions of
upward field-aligned currents with MFE.
Abstract:
Abstract:
Variations in Earth's far-ultraviolet (FUV) dayglow occur on a global scale after periods of strong geomagnetic activity, and are known to indicate changes in O column density due to heating by high-latitude sources. Within 6 hours of the onset of activity, significant decreases in O density below quiet-time levels may be observed at mid- subauroral-latitudes in the morning sector and throughout the polar cap. Depending on the time history of magnetic activity and the configuration of the neutral wind field, these decreases can expand to encompass the afternoon sector, or decrease in extent and/or degree of perturbation. Increases in brightness at mid-latitudes are also observed, though well after storm onset.Observations of the Earth's northern auroral oval an January 10, 1997 with the Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft recorded the arrival of the Coronal Mass Ejection (CME) that erupted from the Sun on January 6, 1997 and the large auroral substorms that followed. The VIS Earth Camera is sensitive predominantly to the atomic emissions at 130.4 nm and 135.6 nm and has been acquiring global auroral images since shortly after the launch of Polar in February 1996. The arrival of the CME at the magnetosphere at 0104 UT on January 10, 1997 was accompanied by the brightening of the local noon sector of the auroral oval. Subsequently the dawn and dusk sectors of the auroral oval brightened as the leading edge of the CME swept along the flanks of the magnetosphere. By 0125 UT the entire auroral oval had brightened in intensity. Dual bars of a theta aurora formed at 0209 UT and persisted until 0306 UT. From that time the diameter of the oval began to expand until the first substorm onset at 0346 UT. A series of auroral substorms with highly disturbed conditions followed for the next several days. These events will be discussed in detail and a movie produced from the sequence of images will be presented.
Abstract: During the winter of 1996-97, four new digital all-sky cameras started continuous observations of the aurora in northern Finland and Sweden, and at Svalbard. Simultaneously, the Visible Imaging System (VIS) on the POLAR satellite observed the auroral oval on a global scale at both visible and ultraviolet wavelengths during long, continuous periods interrupted only by the satellite's perigee passes. Additionally, high-resolution auroral images were obtained with the Swedish Auroral Large Imaging System (ALIS).The mesoscale observations obtained with this distributed network of ground-based all-sky cameras are compared in detail with the global scale auroral images from VIS in order to more fully investigate the two methods of observations during all substorm phases and to use the results to discuss the changes in the auroral spectrum during the course of a substorm. We also compare and contrast the responses of the different instruments to the same auroral features, including the effects of sensitivity, viewing geometry, and resolution.
Abstract:
Abstract: The Visible Imaging System (VIS) on board the
Polar spacecraft consists of two cameras for visible wavelengths and one camera for
far-ultraviolet emissions. With the use of the instrument computers and the spacecraft
timing signals, the large angular motions of the despun platform on which the cameras
are mounted for staring at the auroras are compensated in order to provide the good
spatial resolutions required for quantitative auroral and magnetospheric research.
Otherwise these large angular motions due to spacecraft imbalance smear the images
to the extent that their scientific content is highly degraded. With the high-resolution
images we discuss several topics of current interest. These topics include (1) the
determination of ionospheric conductivities with images taken with the visible filters,
(2) the correlation of the global responses of the auroral oval during substorm activity
with the plasma dynamics in the equatorial magnetosphere as observed with the Geotail
spacecraft, and (3) an example of the onset of an isolated substorm which was clearly
not
associated with the northward turning of the interplanetary magnetic field.
Abstract: An overview of recent observations of phenomena associated with the occurrence of auroral substorms is presented. Our knowledge of the substorms has increased dramatically over the past several years with the successful launches and operations of the ISTP spacecraft. These high-resolution in-situ fields and particles measurements in various regions of the magnetosphere and within the solar wind, together with global auroral imaging, offer the opportunity to determine the energy and mass transport prior to and during auroral storms. Ground-based observatories also provide similarly important inputs to these studies. Global MHD models must be necessarily employed in order to provide a framework for assimilating and interpreting the in-situ observations. An overview of the present status and capabilities of these models will be given, as well as recent observations which are relevant to assessing their viability in terms of plasma entry, magnetospheric topology, and dynamical responses to fluctuations in the interplanetary medium. A major arena for unanswered questions is centered on the mechanism(s) for the onset of auroral substorms and the details of the influence of interplanetary and solar wind parameters on stimulating this onset. The presenter will attempt to provide a reasonable overview of current ideas concerning the mechanisms for the onset and early expansion phases of auroral substorms.
Sigwarth, J. B., L. A. Frank and W. R. Paterson, Simultaneous Observations of
the Global Auroral Oval and the Magnetotail Plasma at Substorm Onset, presented
at the International Conference on Substorms, ICS-4, Lake Hamana, Japan, 9-13 March
1998.
Abstract: The combination of the Comprehensive Plasma Instrumentation (CPI) on the Geotail spacecraft and the Visible Imaging System (VIS) on the Polar spacecraft provides a unique opportunity to compare the changes in the plasma of the magnetotail with the changes in the global auroral oval just before, during, and after the substorm onset and into the expansion phase. The CPI measures the full three-dimensional, low-energy plasma distribution function in the magnetotail, while simultaneously, the VIS acquires global images of the Northern auroral oval. The global auroral images obtained with the VIS Earth Camera allow determination of the energy loading and unloading of the magnetotail lobes before the substorm onset through the determination of the polar cap area as well as changes in the auroral luminosities and the auroral area. Simultaneous observations from the CPI on Geotail reveal the changes of the distribution function and detailed information on the current flows in the magnetotail plasma. A discussion of the details of an isolated substorm onset and expansion on January 12, 1997 will be presented.
Abstract: This paper presents results from a comparison of global MHD simulation results with ground and multi-spacecraft measurements. Taken together, the data yield a multipoint assessment of the global dynamics of a magnetospheric substorm. Using the interplanetary magnetic field and the plasma parameters measured by the WIND spacecraft upstream of the bow shock on January 12, 1997, we simulated the substorm observed around 1928 UT. The time series from the simulation are in good agreement with the times series from 4 spacecraft (GOES 9, IMP 8, Interball Tail and Geotail) and with the ground-based measurements from Canopus. A good correlation also exists between the energy flux of precipitating electrons calculated from the simulation and the auroral activity imaged by the VIS experiment onboard the Polar spacecraft. The simulation results show that during the event Geotail is located in the reconnection region; in addition, they reveal that the expansion phase of the substorm is marked by the formation of small plasmoids in the near-Earth region (~12 RE).
Abstract:
The Low-Resolution Visible Camera which is a portion of the Visible Imaging System (VIS) on board the Polar spacecraft provides adequate spatial resolution and image repetition rates to investigate the possibility that auroral arcs are sometimes affected by the presence of coastlines as originally noted by the Russian explorer F. P. Wrangel during his polar expedition of 1820 to 1823. Our initial study is based upon the examination of images taken at OI 557.7 nm during January 1997. The frame repetition times varied in the range of about 1 to 2 minutes and the spatial resolution, dependent upon the spacecraft altitude, was typically 10 to 20 km. A careful methodology was applied to the analyses of these thousands of images in order to quantitatively evaluate the random identification of coastline effects. The study included tabulation of diffuse aurora and discrete arcs, whether or not a coastline was followed by auroral emission, whether or not discrete arcs which crossed shorelines at large angles of attack exhibited large changes in their intensities, and whether an arc which did follow a coastline was positioned inland or seaward from the shore. For a null test the coastline map was rotated by 15° about the geographic pole and the entire study as outlined above was repeated in order to provide a robust assessment of the occurrence of random events. In any case, the results should be of substantial interest to the audience.Abstract: On September 11, 1996 at approximately 21:54 UT, a magnetic conjunction occurred between the POLAR and AKEBONO spacecraft (77° invariant latitude). POLAR was in the high altitude dayside cusp and AKEBONO was in the low altitude dayside cusp. During this time and for the ~10 minutes following it, both spacecraft remained in the cusp as the POLAR CAMMICE instrument observed an energetic particle event (Chen et al, J. Geophys. Res. 103, p. 69, 1998) and the POLAR VIS instrument observed the beginning and expansion of a substorm (kp=4+). The GEOTAIL spacecraft was in a position to monitor the solar wind at ~27 RE dawnward of the Earth-Sun line. Magnetosheath-like particles and waves, together with a depressed and noisy magnetic field, were observed during this cusp pass at POLAR. These observations appear to be correlated with suprathermal ion measurements and consistent with other measurements made by AKEBONO. GEOTAIL observations show a noisy IMF with ~1-2 nT fluctuations about (-6, 8, -1) nT in GSM coordinates and a nearly steady solar wind speed of ~570 km/sec directed almost exclusively antisunward. These measurements will be discussed in terms of Earth's magnetospheric and auroral response. All of the observations will be used to draw some conclusions with respect to wave-particle interactions and to the reconnection process, which appears to be unsteady during this event.
Abstract: The combination of the Comprehensive Plasma Instrumentation (CPI) on the Geotail spacecraft and the Visible Imaging System (VIS) on the Polar spacecraft provides a unique opportunity to compare the changes in the plasma of the magnetotail with the changes in the global auroral oval just before, during, and after the substorm onset and into the expansion phase. The CPI measures the full three-dimensional, low-energy plasma distribution function in the magnetotail, while simultaneously, the VIS acquires global images of the Northern auroral oval. The global auroral images obtained with the VIS Earth Camera allow determination of the energy loading and unloading of the magnetotail lobes prior to and after the substorm onset, respectively, through the determination of the polar cap area as well as changes in the auroral luminosities and the auroral area. Simultaneous observations from the CPI on Geotail reveal the changes of the distribution function and detailed information on the current flows in the magnetotail plasma. A discussion of the details of an isolated substorm onset and expansion of January 12, 1997 will be presented.
Abstract:
During northern winter auroral observation seasons, the Visible Imaging System (VIS) Low Resolution Camera on the Polar spacecraft is operated to obtain high-time and high-spatial resolution images of visible wavelength auroral emissions of the N2+ ions at 391.4 nm as well as the OI atomic emissions at 557.7 nm and 630.0 nm. The ratio of the observed auroral intensity at 630.0 nm to the intensity of the 391.4-nm emissions is used to obtain the characteristic energy of the precipitating electrons that generate the auroral emissions. The total electron energy flux can be obtained from the 391.4-nm intensity. Subsequently, the height integrated Hall and Pedersen conductivities are derived from the characteristic energy and total energy flux of the precipitating electrons. The derived characteristic energy and total energy flux are compared to direct measurements during auroral overflights by the FAST spacecraft.Abstract: The global imaging of Earth's auroras with the Visible Imaging System (VIS) on board the Polar spacecraft provides an effective monitor of magnetospheric activity. Our present study is directed toward the relationship of the dynamical behavior of the auroral features with simultaneous in-situ observations of plasmas and magnetic fields as observed with the Geotail spacecraft in the equatorial plasma sheet. The geocentric radial distances of perigee and apogee are about 10 RE and 30 RE (Earth radii), respectively, and are well-positioned to observe the plasma dynamics during magnetospheric substorms. We discuss our findings of the relationship of the large-scale images with the micro-physics of plasmas in the equatorial plane for several isolated substorms.
Abstract: The Visible Imaging System (VIS) on board the Polar spacecraft is providing a magnificent series of images of Earth's auroras at both far-ultraviolet and visible wavelengths. In order to take advantage of this auroral imaging, simultaneous observations of the plasmas and magnetic fields with the Geotail spacecraft in the equatorial plasma sheet, along with such observations in the solar wind, are presented. Two substorm events are examined, (1) the events associated with the arrival of a coronal mass ejection (CME) at Earth and (2) the occurrence of an isolated substorm with an onset which is clearly not associated with the northward turning of the interplanetary magnetic field. Also we report on the initial search for the legendary occurrence of auroral features which are clearly influenced by the presence of coastlines as first reported by a Russian polar explorer over a century ago. A series of high-resolution images with a camera at visible wavelengths during January 1997 is used in the search.
Abstract: On September 11, 1996 at approximately 21:54 UT, a magnetic conjunction occurred between the POLAR and AKEBONO spacecraft (77° invariant latitude). POLAR was in the high altitude dayside cusp and AKEBONO was in the low altitude dayside cusp. During this time and for the ~10 minutes following it, both spacecraft remained in the cusp as the POLAR CAMMICE instrument observed an energetic particle event (Chen et al, J. Geophys. Res. 103, p. 69, 1998) and the POLAR VIS instrument observed the beginning and expansion of a substorm (kp=4+). The GEOTAIL spacecraft was in a position to monitor the solar wind at ~27 RE dawnward of the Earth-Sun line. Magnetosheath-like particles and waves, together with a depressed and noisy magnetic field, were observed during this cusp pass at POLAR. These observations appear to be correlated with suprathermal ion measurements and consistent with other measurements made by AKEBONO. GEOTAIL observations show a noisy IMF with ~1-2 nT fluctuations about (-6, 8, -1) nT in GSM coordinates and a nearly steady solar wind speed of ~570 km/sec directed almost exclusively antisunward. These measurements will be discussed in terms of Earth's magnetospheric and auroral response. All of the observations will be used to draw some conclusions with respect to wave-particle interactions and to the reconnection process, which appears to be unsteady during this event.
Abstract: During northern winter auroral observation seasons, the Visible Imaging System (VIS) Low Resolution Camera on the Polar spacecraft is operated to obtain high-time and high-spatial resolution images of visible wavelength auroral emissions of the N2+ ions at 391.4 nm as well as the OI atomic emissions at 557.7 nm and 630.0 nm. The ratio of the observed auroral intensity at 630.0 nm to the intensity of the 391.4-nm emissions is used to obtain the characteristic energy of the precipitating electrons that generate the auroral emissions. The total electron energy flux can be obtained from the 391.4 nm intensity. Subsequently, the height integrated Hall and Pedersen conductivities are derived from the characteristic energy and total energy flux of the precipitating electrons. The derived characteristic energy and total energy flux are compared to direct measurements during auroral overflights by the FAST spacecraft.