Urban Brandstrom

Incoherent scatter radar spectrum distortions from intense auroral turbulence

We present EISCAT (European Incoherent Scatter Radar Facility) measurements of > 2000 K enhancements of the apparent ion temperature which occurred simultaneously over a latitude range of at least 100 km for brief periods (less than 1 min) in the auroral F region. One event occurred during a substorm onset and a second during passage of a westward-traveling surge. The apparent Ti increases showed significant anisotropy, with measurements oriented less parallel to B0 exhibiting the largest amount of apparent Ti increase. In these examples the vector electric fields measured by EISCAT were much too low to account for the temperature increases via frictional heating, and also too low to generate non-Maxwellian ion velocity distributions, which can cause errors in ion temperature estimates. We argue that the measured Ti increases are not real, and that both their magnitude and their anisotropy with respect to B0 can be satisfactorily explained by turbulent plasma flows with peak amplitudes of ∼ 2 km/s but which could not be directly resolved by EISCAT, because they varied with a time scale less than the 10-s integration period, or possibly because their scale size was smaller than the ∼ 3 - 5 km antenna beam width. While such unresolved but inferred turbulent flows can themselves cause ion frictional heating, we show that an equally important cause of high Ti estimates in our case was the distortion of the measured spectra by strongly varying Doppler shifts. We also present a counter example which shows a bright auroral arc in the radar common volume but with no large increases in the radar-measured Ti, indicating that not all auroral structures are associated with electric fields which vary with sufficient intensity to distort incoherent scatter radar spectra.

Optical and ionospheric phenomena at EISCAT under continuous X‐mode HF pumping

We present experimental results from multiinstrument observations in the high-latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X-polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458–548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave. Intensities at red and green lines varied in the range 110–950 R and 50–350 R, respectively, with a ratio of green to red line of 0.35–0.5. The results of optical observations are compared with behaviors of the HF-enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small-scale field-aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X-mode radio-induced optical emissions coexisted with HF-enhanced ion and plasma lines and strong artificial field-aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two-stream instabilities were not quenched by fully established small-scale field-aligned artificial irregularities excited by an X-mode HF pump wave.

Optical observations of water in Leonid meteor trails

[1] Two simultaneous filtered images (589 and 423 nm) of a meteor trail were recorded during the 2002 Leonid storm. The first image shows Na atoms and the second Ca and Fe atoms and signals at altitudes much higher than can give rise to ablation of metals, in agreement with other observations of high altitude visible trails [Spurný et al., 2000a; Spurný et al., 2000b]. Ablation models [McNeil et al., 1998] and analysis of the history of the 2002 Leonid meteoroids [McNaught and Asher, 1999] support the conclusion that the high altitude emissions are due to H 2 O + and H α,β,γ formed through the decomposition in the hyperthermal collision between H 2 O from meteoroid ice [Kresak, 1973] and atmospheric N 2 [Dressier et al., 1992].

The first daytime ground‐based optical image of the aurora

Aurorae, spectacular phenomena in the polar night sky, also provide a convenient projection of effects of complex and energetic plasma processes of the outer magnetosphere. Much has been learned about the ionosphere and magnetosphere from night-time auroral images. However, similar imaging is extraordinarily difficult by day, due to the overwhelming background of atmospherically-scattered sunlight. This is unfortunate, since many auroral plasma processes may be unique to the sunlit ionosphere. A visible-light image of the aurora at λ630-nm wavelength was obtained from Kiruna, Sweden, at sunset on May 2, 1999, by an imaging spectrometer featuring excellent spectral resolution and out-of-band rejection. We believe this to be the first such image obtained from the ground under near-daytime conditions. These observations were obtained as a test of principle during the development of a prototype instrument. We believe this technique holds great promise for future ground-based studies of the daylit ionosphere and magnetosphere.

First results of auroral tomography from ALIS-Japan multi-station observations in March, 1995

Auroral tomography observations have been carried out in March, 1995, as a joint international campaign between Sweden and Japan. Three unmanned Swedish ALIS stations (Kiruna, Merasjärvi, Tjautjas) and two Japanese JICCD sites (Abisko, Nikkaluokta), geographically separated by about 50 km at higher latitudes, were operated to capture multi-station monochromatic tomography images at 557.7 nm wavelength using CCD cameras. All cameras were pointing to one of the predetermined directions to secure a common field of view. Several images of auroral arcs, mostly for the core region right above Kiruna, have synchronously been taken by the multi-station imaging system. Tomographic inversion analysis for four-point images was carried out using the algebraic reconstruction technique. Reconstructions of a curved arc and of a double arc system suggest promising application of this technique to the retrieval of three-dimensional auroral luminosity.

VORTICITY IN THE MAGNETOSPHERIC PLASMA AND ITS SIGNATURES IN THE AURORA DYNAMICS

A review of both the theoretical and experimental data connected with the vorticity in the magnetospheric plasma and on its signatures in the auroral dynamics is presented. It is shown that the observed characteristics of the motion of auroral forms allow one to determine the distribution of the electric field and field-aligned currents in the magnetosphere; the shape of auroral vortices and their power spectra carry information on the nature of the MHD instabilities responsible for the excitation of the observed turbulence.The complex of experimental data necessary for a confident description of the electrodynamic state of the magnetosphere is discussed.

Fine structure of aurora

Fine structure is present in most types of aurora, but much of it has previously not been possible to study properly because of instrument limitations. However, recent advances in optical instrumentation have provided considerable improvements in temporal and spatial resolution. Optical measurement systems are able to use a higher resolution than other types of ground-based instruments used in auroral studies. New results have been obtained regarding, for example, elemental structures in discrete auroras, generation of flickering aurora, generation of Alfvén waves in shear regions, dynamic rayed aurora, fine structure of diffuse auroras and fine structure of auroral curls. Outstanding questions are highlighted and recommendations for future research are given. The importance of a coordinated infrastructure for ionospheric research, simultaneous measurements on different scales, optical calibration facilities and the development of time-dependent high-resolution models is stressed.

Alis, a state-of-the-art optical observation network for the exploration of polar atmospheric processes

Abstract An optical group at the Swedish Institute of Space Physics in Kiruna, Sweden has been developing the ALIS (Auroral Large Imaging System) multi-station optical observing network which makes it possible to obtain composite monochromatic 2-D images over a fairly wide field-of-view (FOV), and more interestingly, a CT (Computed Tomography) image set for the retrieval of 3-D structure of aurora by adjusting vergence angles of cameras to a common volume. National Institute of Polar Research, Japan is collaborating in observation and analysis. At the moment, the network has 6 stations separated from each other by about 50 km. Each station houses a monochromatic CCD (Charge Coupled Device) imaging system mounted on the steerable azimuth/elevation drive along with a house keeping unit and supervising computer linked to the control center via a telephone line. Altitude profiles of luminosity for stable arc and aurora vortex at 557.7nm and recently at 427.8nm are analysed by the algebraic reconstruction technique and compared with sophisticated numerical modelling of auroral emission rate. Conjunctions with satellites and radars are now intensively explored towards comprehensive understanding of the formation and electrodynamics of aurora. Imaging of polar stratospheric clouds is also attempted in relation to arctic environmental studies.

Electric Field Enhancement in an Auroral Arc according to the Simultaneous Radar (EISCAT) and Optical (ALIS) Observations

The character of a change in the ionospheric electric field when several auroral arcs crossed the region of radar measurements has been analyzed. In one case the plasma conductivity and electric field normal component in an arc increased as compared to their undisturbed values. In another case the field and conductivity changed traditionally (in antiphase). Arcs with an increased field were previously classified as correlating arcs, but their existence was subsequently open to question during optical observations. The usage of the ALIS system of digital cameras made it possible to decrease the errors introduced by optical equipment. The measurements in the vicinity of correlating arcs were performed when these arcs were generated, and a traditional arc was a completed formation. In an originating arc, the field value can depend not only on the ionospheric plasma conductivity but also on the processes in the magnetospheric-ionospheric system resulting in the field enhancement.

Project "Development of the Methodology of Experiment and Technical Support for Studies of the Flow Cyclotron Maser in the Earth's Magnetosphere by Creating an Artificial Ionization Cloud From a Geophysical Rocket"

Investigation of the wave particle interaction in the magnetosphere and ionosphere by controllable experiment in near Earth space is in focus of modern space geophysics. We propose to stimulate auroral precipitation by changing parameters of the Flow Cyclotron Maser (FCM) and test the FCM model itself. One of the main goals of the project is inducing of artificial pulsating aurora.