Observations Of Aurora Research Articles

Comparison and significance of auroral studies during the Swedish and Russian bilateral expedition to Spitsbergen in 1899–1900

Abstract. Results of measurements and visual observations of aurora at Spitsbergen, carried out by the joint Swedish-Russian expedition during 1899–1900, are described. Auroral observations took place during the great bilateral Arc-of-Meridian expedition, which was patronized by the Swedish Royal Family and the Russian Imperial Family. The Russian-Swedish Arc-of-Meridian measurements were closely coordinated but auroral measurements from the two sites in the Spitsbergen Archipelago were almost independent of each other. The basic auroral data for our presentation are reports of the Russian astronomer Josef Sykora and the Swedish geophysicist Jonas Westman. Both scientists used similar types of photo cameras and spectrographs, which were the best at that time and were made in Potsdam by Toepfer. Detailed descriptions of the optical devices and the system of spectral calibration are presented. A Toepfer spectrograph, possibly the one used by Westman, is still kept at IRF in Kiruna. We present a comparative analysis of auroral data from the Russian and Swedish stations on three themes: visual observations of aurora, describing features of auroral forms and giving us statistical data on aurora occurrence and the heights of aurora, photos of aurora, and auroral spectra. It is shown that the observations contain enough data to construct an auroral oval and to determine the heights of aurora. The expedition obtained the first photographic observations of the aurora in the Arctic. The auroral spectra demonstrate a high spectral resolution and show not only the main auroral emissions in the blue-green spectral range but also some weak emissions in the violet and ultraviolet region. All data are interpreted from a modern point of view. The Russian-Swedish 1899–1900 expedition carried out the first complex auroral investigations in the Arctic using optical instruments and presented well documented data and new results.

Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude (magnetic latitude: 62°, L ∼ 4.6), using an all‐sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hβ) were often observed at latitudes separated equatorward from the main auroral oval. From a 1‐year observation (4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre‐ and post‐midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250–800 km, respectively. We found that as isolated arcs moved equatorward (poleward), the frequencies of the simultaneous Pc 1 pulsations increased (decreased). Using the Tsyganenko‐02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron (EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high‐energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low‐latitude auroral emissions away from the ordinary auroral oval.

Variations in the geomagnetic field and auroras during the main phase of a large magnetic storm of November 20, 2003

The substorm characteristics during the main phase of a large magnetic storm of November 20, 2003, are studied based on the data of TV observations of auroras and auroral absorption at Tixie Bay station and at the global network of magnetic stations. The contribution of auroral particles, responsible for the emission of discrete auroras, has been estimated based on an analysis of the spatial-time variations in the auroral luminosity intensity. This contribution accounted for ∼40% of the total luminous flux, which is approximately twice as large as was previously observed in substorm disturbances. Responses of the solar wind and IMF parameters in substorms and variations in the magnetic indices, characterizing geomagnetic activity in the northern polar cap and ring current (PCN, ASY-H and SYM-H), have been detected. The spatial-time distribution of the equivalent ionospheric currents has been constructed, and the total value of these currents along the meridian has been determined based on the [Popov et al., 2001] method and using the IMAGE magnetic data. It has been obtained that the maximal total equivalent ionospheric current in the premidnight sector (∼2000 MLT) leads the minimal value of the SYM-H index by ∼1.5 h.

Spectral morphology of the X‐ray emission from Jupiter's aurorae

Simultaneous Chandra X‐ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re‐examined to investigate the spatial morphology of the X‐ray events in different energy bands. The data clearly show that in the Northern auroral region (in the main auroral oval and the polar cap) events with energy > 2 keV are located at the periphery of those with energy < 2 keV and coincide with FUV bright features. In addition, X‐ray spectra extracted from the areas where the two event distributions are concentrated possess different shapes. We associate the > 2 keV events (∼45 MW emitted power) with the electron bremsstrahlung component recently revealed by XMM‐Newton in the spectra of Jupiter's aurorae, and the < 2 keV emission (∼230 MW) with the product of ion charge exchange, now established as the likely mechanism responsible for the soft X‐ray Jovian aurora. We suggest that the same population of energetic electrons may be responsible for both, the X‐ray bremsstrahlung and the FUV emission of Jupiter's aurorae. Comparison of the > 2 keV X‐ray and FUV (340 GW) powers measured during the observations shows that they are broadly consistent with the predicted emissions from a population of energetic electrons precipitating in the planet's atmosphere, thus supporting our interpretation.

Extended SuperDARN and IMAGE observations for northward IMF: Evidence for dual lobe reconnection

We present observations of ionospheric convection in the Northern Hemisphere made by the SuperDARN radar network during a 3 h period on 3 December 2001. The interplanetary magnetic field (IMF) during the time of observations is predominately northward with the By component changing from positive to slightly negative. During this period Cluster is skimming the southern high latitude dusk magnetopause and reveals that reconnection is going on quasi‐continuously with the reconnection site being most of the time tailward of the southern cusp and always near the satellite location (Retinò, et al., 2005). Detailed analysis of the three dimensional distribution function indicates that Cluster samples magnetosheath lines connected with geomagnetic field lines tailward of the cusps in both hemispheres (Bavassano Cattaneo et al., 2006). The evolution of the ionospheric convection measured by SuperDARN, together with IMAGE FUV observations of aurorae and DMSP particle precipitation data, confirms Cluster observations and shows that simultaneous reconnection poleward of both the northern and southern cusps occurs at a variable rate on the dusk part of the magnetosphere when the IMF clock angle is small.

Variations in the polar precipitation equatorward boundary during the interaction between the Earth’s magnetosphere and solar wind streams from isolated solar sources

The position of the auroral luminosity equatorward boundary during the interaction between the Earth’s magnetosphere and isolated solar wind streams from different solar sources has been statistically studied based on the ground and satellite observations of auroras. These studies continue the series of the works performed in order to develop the technique for predicting auroras based on the characteristics of the interplanetary medium and auroral disturbances. The dependences of the minimal position of the auroral luminosity equatorward boundary (Φ′) on the values of the azimuthal component of the interplanetary electric field (Ey) and AL indices of magnetic activity, averaged over 6 and 24 h, are presented. The distribution limits for each type of isolated solar wind streams on the Φ′-Ey and Φ′-AL planes have been determined.

Simultaneous observations of fluctuating cusp aurora and low‐latitude magnetopause reconnection

The location and variability of magnetic reconnection are investigated using simultaneous in situ observations of boundary layer flows at the dayside magnetopause and remote sensing of proton cusp aurora in the ionosphere. Two events when the Geotail spacecraft was at the magnetopause and the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft was observing cusp proton precipitation are used in this investigation. The directions of high‐speed flows observed in the boundary layer by the Geotail spacecraft are compared to predicted directions from the antiparallel reconnection model and from two component reconnection models. The IMAGE cusp proton aurora observations provide additional information on the type of reconnection and on variability in the reconnection rate. For the first event, antiparallel reconnection may be occurring at the magnetopause and there is a long‐duration (10 s of minutes) decrease in the proton aurora intensity. For the second event, component reconnection is occurring and variability in the cusp emissions on a timescale of several minutes appears to indicate variability in the reconnection rate.

Comment on “Amateur observations of atmospheric phenomena during the IGY”

Following the article by Schröder [2007], we point out the key roles played by several Russian scientists in the planning and implementation of observations of aurorae during the International Geophysical Year (IGY).The leader of the program and the organizer of the visual observational network in the USSR was Nikolay V. Pushkov (1903–1981), director of the Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (IZMIRAN, Troitsk, Russia, now called the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation). As a member of the Comite Special de l'Annee Geophysique Internationale (CSAGI), Pushkov was actively involved in the inception of the international program of visual observations of aurorae that was accepted for the period of the IGY.

Jupiter's Nightside Airglow and Aurora

Observations of Jupiter's nightside airglow (nightglow) and aurora obtained during the flyby of the New Horizons spacecraft show an unexpected lack of ultraviolet nightglow emissions, in contrast to the case during the Voyager flybys in 1979. The flux and average energy of precipitating electrons generally decrease with increasing local time across the nightside, consistent with a possible source region along the dusk flank of Jupiter's magnetosphere. Visible emissions associated with the interaction of Jupiter and its satellite Io extend to a surprisingly high altitude, indicating localized low-energy electron precipitation. These results indicate that the interaction between Jupiter's upper atmosphere and near-space environment is variable and poorly understood; extensive observations of the day side are no guide to what goes on at night.

Characteristics for the Occurrence of a High-Current $Z$-Pinch Aurora as Recorded in Antiquity Part II: Directionality and Source

The discovery that objects from the Neolithic or Early Bronze Age carry patterns associated with high-current Z-pinches provides a possible insight into the origin and meaning of these ancient symbols produced by humans. Part I deals with the comparison of graphical and radiation data from high-current -pinches to petroglyphs, geoglyphs, and megaliths. Part I focused primarily, but not exclusively, on petroglyphs of some 84 different morphologies: pictures found in laboratory experiments and carved on rock. These corresponded to mankind's visual observations of ancient aurora as might be produced if the solar wind had increased (T. Gold) at times between one and two orders of magnitude, millennia ago. Part II focuses on the source of light and its temporal change from a current-increasing Z-pinch or dense-plasma-focus aurora. Orientation and field-of-view data are given as surveyed and contributed from 139 countries, from sites and fields containing several millions of these objects. This information allows a reconstruction of the auroral form presumably associated with extreme geomagnetic storms and shows, based on existent geophysical evidence, plasma flow inward at Earth's south polar axis.

Auroral streamers and magnetic flux closure

On 7 December 2000 at 2200 UT an auroral streamer was observed to develop above Scandinavia with the IMAGE‐FUV global imagers. The ionospheric equivalent current deduced from the MIRACLE‐IMAGE Scandinavian ground‐based network of magnetometers is typical of a substorm‐time streamer. Observations of the proton aurora using the SI12 imager onboard the IMAGE satellite are combined with measurements of the ionospheric convection obtained by the SuperDARN radar network to compute the dayside merging and nightside flux closure rates. On the basis of this and other similar events, it is found that auroral streamers appear during the period of most intense flux closure in the magnetotail, most often shortly after substorm onset. The ionospheric convection velocity, as measured by SuperDARN, appears to be reduced in the vicinity of the streamer, suggesting de‐coupling of magnetospheric and ionospheric plasma flows in the region of enhanced ionospheric conductance.

Energetic proton precipitation related to ion–cyclotron waves

This brief review summarizes recent findings related to particle precipitation associated with electromagnetic ion–cyclotron (EMIC) waves seen on the ground as geomagnetic Pc1 and IPDP pulsations. Particle precipitation signatures of ion–cyclotron interaction are described as revealed from low-altitude satellite measurements of the energetic proton fluxes as well as from observations of the proton aurora. As a result, localized proton precipitation patterns situated equatorward of the isotropy boundary are disclosed. One of the patterns is a proton precipitation spot in the morning sector, presumably mapped onto plasmapause; another one is an elongated region of the precipitation, presumably mapped onto the plasmaspheric plume. Clear evidence of the pitch-angle scattering associated with the ion–cyclotron wave activity is found near the equatorial plane in the region conjugated with the localized proton precipitation at low altitude. Thus, the revealed precipitation patterns determine the location of the region of intense pitch-angle scattering of energetic protons, and, therefore, their observations can be used to monitor the region of the ion–cyclotron interaction and to study its origin and properties. Some examples of such application of the low-altitude observations of energetic particles are described.

Particle precipitations during NEIAL events: simultaneous ground based observations at Svalbard

Abstract. In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs) observed with the EISCAT Svalbard Radar (ESR). For the first time, long sequences of NEIALs are recorded, with more than 50 events within an hour, ranging from 6.4 to 140 s in duration. The events took place from ~08:45 to 10:00 UT, 22 January 2004. We combine ESR data with observations of optical aurora by a meridian scanning photometer at wavelengths 557.7, 630.0, 427.8, and 844.6 nm, as well as records from a magnetometer and an imaging riometer. The large numbers of observed NEIALs together with these additional observations, enable us to characterise the particle precipitation during the NEIAL events. We find that the intensities in all optical lines studied must be above a certain level for the NEIALs to appear. We also find that the soft particle precipitation is associated with the down-shifted shoulder in the incoherent scatter spectrum, and that harder precipitation may play a role in the enhancement of the up-shifted shoulder. The minimum energy flux during NEIAL events found in this study was ~3.5 mW/m2 and minimum characteristic energy around 50 eV.

Amateur observations of atmospheric phenomena during the IGY

The fiftieth anniversary of the International Geophysical Year (IGY) provides an opportunity to look back at a scientific program which is now almost forgotten. Many of the research fields of the IGY required large numbers of observers around the world, far more than could be provided by the staffs of established institutions and university research groups. It became necessary to recruit men and women from outside the normal scientific net, but with an interest inastronomy and the physics of the planet.Sydney Chapman, L.V. Berkner, M. Nicolet, V.V. Beloussov, J. Coulomb, E. Larsen, and others took a leading role in the planning of the IGY. Chapman had a personal interest in luminous phenomena of the upper atmosphere. One focus of Chapman's research had been collecting historical observations of auroras at low and middle latitude areas such as the Indian subcontinent, Greece, and the Pacific Ocean. He therefore consulted specialists such as C.W. Gartlein (Cornell University), James Paton (Edinburgh), Cuno Hoffmeister (Sonneberg), and N. Grisin, V.V. Sharonov, I.A. Khvostikov, earlier from the USSR, and others to plan and coordinate an international program of observations of auroras and other luminous phenomena of the upper atmosphere. At about this time his interest in noctilucent clouds (NLCs) was also suddenly aroused by a review containing photographs by George Witt (Sweden) that appeared in the journal Tellus.

X-rays from solar system objects

During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies. At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1–2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles. This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun. Processes of production of solar system X-rays are discussed and an overview is provided of the main source mechanisms of X-ray production at each object. A brief account on recent development in the area of laboratory studies of X-ray production is also provided.

First terrestrial soft X-ray auroral observation by the Chandra X-ray Observatory

Northern auroral regions of Earth were imaged with energetic photons in the 0.1–10 keV range using the High-Resolution Camera (HRC-I) aboard the Chandra X-ray Observatory at 10 epochs (each ∼ 20 min duration) between mid-December 2003 and mid-April 2004. These observations aimed at searching for Earth's soft ( < 2 keV ) X-ray aurora in a comparative study with Jupiter's X-ray aurora, where a pulsating X-ray “hot-spot” has been previously observed by Chandra. The first Chandra soft X-ray observations of Earth's aurora show that it is highly variable (intense arcs, multiple arcs, diffuse patches, at times absent). In at least one of the observations an isolated blob of emission is observed near the expected cusp location. A fortuitous overflight of DMSP satellite F13 provided SSJ/4 energetic particle measurements above a bright arc seen by Chandra on 24 January 2004, 20:01–20:22 UT. A model of the emissions expected strongly suggests that the observed soft X-ray signal is bremsstrahlung and characteristic K-shell line emissions of nitrogen and oxygen in the atmosphere produced by electrons.

The presence of large sunspots near the central solar meridian at the times of modern Japanese auroral observations

Abstract. The validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories, is corroborated using more modern sunspot and auroral observations. Scientific observations of aurorae in Japan during the interval 1957–2004 are used to identify geomagnetic storms that are sufficiently intense to produce auroral displays at low geomagnetic latitudes. By examining white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory and the Solar and Heliospheric Observatory spacecraft, it is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian immediately before all but one of the 30 distinct Japanese auroral events, which represents a 97% success rate. Even an "average" observer would probably have been able to see a sunspot with the unaided eye before 24 of these 30 events, which represents an 80% success rate. This corroboration of the validity of the technique used to identify historical occurences of intense geomagnetic storms is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual historical geomagnetic storms during the greater part of the past two millennia.

Proton aurora observed from the ground

Auroral keV proton precipitation is a significant-energy particle input upon the high-latitude ionosphere, often dominating in the polar cusp and the dusk sector of the equatorward auroral oval. A unique signature of proton precipitation is the Doppler-shifted H Balmer lines (H α , H β ) observable from the ground. These lines are emitted by energetic H atoms produced within the proton beam through charge-exchange processes. Their observations allow one to assess the location, dynamic evolution especially during magnetospheric substorms, and spectral characteristics of the source regions of the energetic protons projected to the high-latitude ionosphere. They also allow to identify the associated magnetospheric processes and to evaluate ionospheric perturbations induced by the energetic protons. The source regions include the cusp, the low-latitude boundary layer, the mantle, and the plasma sheet, including its dayside extension. If qualitative studies of proton aurora morphology and time variability are possible with photometric observations of hydrogen lines, quantitative assessment of H-emission brightness, and incident proton mean energy and flux, requires spectroscopic measurements of the H-emission profile. In this review paper, we report on the tremendous progress made in the past 20 years in the observational capability applied to proton aurora and in the modeling of energetic proton transport in the upper atmosphere, which is needed for quantitative analysis of the spectroscopic measurements of H emission. The current issues in the field are also discussed and suggestions for future directions are proposed. They include the deployment of chains of instruments dedicated to proton aurora studies along magnetic local time and geomagnetic latitude, such as high-spectral-resolution-imaging spectrographs and spectral imagers. Such campaigns would improve our understanding of the topology and dynamics of the magnetosphere, and provide, at dayside, the azimuthal extent of the reconnection region. Magnetically conjugate experiments and optical instruments dedicated to proton aurora observations in Antarctica are greatly encouraged. The contribution of atmospheric scattering to the H-spectral profiles needs to be further assessed and additional laboratory measurements of differential cross sections are required for a comprehensive understanding of the physics of proton aurora.

Identification of Possible Intense Historical Solar Storms During the Years 1781–1788 Inferred from Aurorae and Geomagnetic Observations in Rio De Janeiro

The reconstruction of solar activity during the late 18th century is a puzzle for researchers due to the scarcity of sunspot observations in that epoch. In this work, we analyse some details of the solar activity during the years 1781–1788, inferred from geomagnetic measurements and visual observations of aurorae performed by the Portuguese scientist Bento Sanches Dorta from Rio de Janeiro. We describe in greater detail four large solar storms that induced large changes in daily values of geomagnetic declination and, simultaneously, correspond to visual observations of aurorae described by Sanches Dorta.

New observations of artificial aurora associated with TMA releases

An artificial aurora was generated during a trimethyl aluminum (TMA) release from the October 2000 TOMEX rocket launch. Cameras in several locations filmed the optical emissions, believed to be associated with small amounts of kerosene added to the TMA liquid. The geometry of the launch trajectory with respect to the magnetic field and camera viewing angles has provided new insight on the source of the emissions. Surprisingly, the aurora appears to be associated with the vertical footprint of the rocket, rather than the magnetic footprint of the rocket, as previously assumed. The new observations favor a generation mechanism involving large particles &gt;1 μm falling to 90 km altitude.