Red Auroras Research Articles

Extended magenta aurora as revealed by citizen science

During large geomagnetic storms, red auroras are typically observed from low-latitude countries such as Japan. The color arises from a specific emission line of oxygen atoms at high altitudes. However, during the May 10-11th 2024 superstorm, magenta auroras were observed above Japan instead of the typical red. In this study, we demonstrate that the magenta hue is created by a mixture of red (O) and a blue (N2+) aurora at extremely high altitudes. The blue color originates from the N2+ first negative emission band caused by both resonant scattering of the upwelling molecular ions and heavy particle precipitation during the storm. This study is primarily driven by observations from citizen scientists, and confirmed and quantified with observations from spacecraft and modeling techniques. Additionally, we show that high solar activity, terrestrial season, and the preheating of the atmosphere all contribute to the occurrence of magenta aurora. This study showcases the value and richness of citizen science, and we anticipate that such approaches will become increasingly important in the future.

Response of aurora candidates in the Chinese official histories to the space climate during 511–1876

Continuous observations at specified locations and chronicling of astronomical phenomena provide a good opportunity to study ancient space weather. There are 248 white, 125 red, and 44 blue color aurora-like descriptions, also known as aurora candidates, recorded in Chinese official historical records during the 1365-year period of 511–1876. Qualitative descriptions of the color, location, and appearance time of these candidates are quantitatively denoted. The red, white, and blue aurora candidates occurred most frequently 34% in autumn, 32% in summer, and 49% in summer, respectively. The white and red aurora as well as the overall candidates tend to appear during high solar activity periods. By contrast, the blue candidates frequently occur during low solar activity periods. Statistical results with 90% confidence intervals further show that the relationship between solar activities and overall/red (white/blue) aurora candidates is significant (insignificant). The red aurora candidates that frequently occurred in autumn during the periods of high solar activity agree well with those of low/middle latitude auroras, while the white aurora candidates might be confounded by noctilucent clouds or other atmospheric optical events, such as airglows, moon halo, etc. The study of ancient space weather/climate based on historical records shows that aurora occurrences are related to solar activities, and in particular, red auroras frequently appear in low/middle latitudes during high solar activity periods.Graphical

IpsDst of Dst Storms Applied to Ionosphere‐Thermosphere Storms and Low‐Latitude Aurora

AbstractConventionally, the minimum value of Dst (DstMin) and maximum values of Kp and AE (Kpmaxand AEmax) representing the geomagnetic storm intensities have been used for investigating space weather in Earth's environment. The present paper uses the derived parameters (IpsDst, IpsKp, and IpsAE) giving the mean values of Dst, Kp, and AE during the main phase (MP) of Dst storms for investigating ionosphere‐thermosphere storms and low‐latitude (630 nm) aurora. The derived parameters (IpsDst, IpsKp, and IpsAE) representing the impulsive strength of geomagnetic storms seem to have more systematic dependence among themselves than among the intensities (DstMin, Kpmax, and AEmax). The ionosphere‐thermosphere storms observed by the CHAMP (Challenging Minisatellite Payload) satellite and low‐latitude auroras observed by optical imagers are much more intense during high impulsive storms than high intensity storms. In a statistical sense, over 175 positive ionospheric storms (△NmF2) observed in 1985–2005 and the intensity of 20 red auroras observed in 1989–2004 at midlatitudes correlate better with the impulsive parameters than the intensity parameters, with the best correlation being with IpsDst. The mechanism of the impulsive action (high‐energy input over a short duration) leading to large IpsDst arises from the impact of fast solar storms (interplanetary coronal mass ejections) with large IMF Bz southward at their front (or shock). The impulsive action results in bright low‐latitude auroras and strong ionosphere‐thermosphere storms.

Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.

Historical Auroras in the 990s: Evidence of Great Magnetic Storms

Recently, a significant carbon-14 enhancement in the year 994 in tree rings has been found, suggesting an extremely large cosmic ray flux event during a short period. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it is of solar origin. Contemporary historical records of low latitude auroras can be used as supporting evidence for intense solar activity around that time. We investigated the previously reported as well as the new records found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in the late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.

New historical records and relationships among 14C production rates, abundance and color of low latitude auroras and sunspot abundance

Incursions of high-energy particles from space, specifically solar energetic particles and galactic cosmic rays, have significant effects on the Earth, including disruption of the Earth’s magnetic field, generation of electric fields strong enough to damage electronic devices as well as the production of auroras at low-latitudes, within 45° of the magnetic equator. We examine the relationships among 14C production, auroral abundance, auroral color and sunspot abundance using existing data supplemented by a new dataset. The new dataset, based on Chinese and Korean records from A.D. 1100–1700, includes 46 new or revised records of sunspots and 279 records of low-latitude auroras. Low-latitude auroras are predominantly red (66%, 835 events) with lesser proportions of white (20%, 253 events) and black auroras (6%, 67 events). All other auroral colors (green, yellow, multicolored, blue and purple) aggregate to a total of 100 events (8%). Overall, white auroras are more frequent during times of higher 14C production. We use two empirical methods of evaluating the flux of high-energy particles: modeled peaks and lows in 14C production and peaks and lows in the 14C calibration curve. We find that comparison to modeled 14C production gives significant results. White auroras are significantly more abundant (98% probability) at times of high production of 14C. Red auroras are somewhat more abundant (88% probability) at times of low production of 14C. The abundances of black, multicolored, green, yellow, and blue auroras between times of low and high 14C production are not significantly different. Violet/purple auroras are significantly more abundant (98% probability) at times of low 14C production. The positive correlation of violet/purple auroras with times of low14C production rate and the lack of correlation of blue auroras with times of high14C production is surprising, for this portion of the visible spectrum contains strong emission lines and some lines with high energies of excitation. Observations of emissions in the blue to violet part of the spectrum may be biased towards time periods when the atmosphere is exceptionally clear, as these colors are more difficult for the human eye to perceive.

Ground and satellite observations of low‐latitude red auroras at the initial phase of magnetic storms

We report ground and satellite observations of unique low‐latitude red auroras that appear at the initial phase of geomagnetic storms. For two events on 21 October 2001, and 6 April 2000, the low‐latitude red auroras appeared at ~45° MLAT (L ∼ 2) ∼ 1.5 h after the storm sudden commencement in the postmidnight sector in Japan. Comprehensive satellite data were available for the former event. The energetic neutral atom images obtained by the Imager for Magnetopause‐to‐Aurora Global Exploration satellite show rapid enhancement of ring current hydrogen and oxygen fluxes at radial distances of ∼ 2–8 RE after the storm sudden commencement and associated with several storm‐time substorms. The hydrogen ring‐current enhancement occurred particularly in the postmidnight sector where the red aurora was observed. The timing of oxygen flux enhancement associated with a storm‐time substorm coincided with the red aurora appearance. This rapid and significant enhancement of energetic neutral atom flux was also confirmed by energetic ion data obtained by the NOAA/POES‐16 satellite. Extreme ultraviolet plasmaspheric images obtained by Magnetopause‐to‐Aurora Global Exploration indicate that the plasmapause was located at L = 2.3–2.5 in the postmidnight sector during the event, indicating that a spatial overlap occurs between the plasmasphere and the enhanced ring current ions at L ∼ 2. Based on these observations, we suggest that large energization of high‐energy ring‐current ions in the postmidnight inner magnetosphere caused the spatial overlap of these ring‐current ions with the low‐energy plasmaspheric plasmas at L ∼ 2, producing the low‐latitude red auroras at the very beginning of the storms.

Spectral characteristics of great auroras during two superstorms

The spectroscopic characteristics of great auroras during two superstorms of February 8–9, 1986, and March 13–14, 1989, are compared. The first storm occurred during the intensity minimum of solar activity, whilst the second one occurred at the time maximum activity phase of solar cycle 22. The storm of February 8–9, 1986, (min Dst = −312 nT) was produced by plasma fluxes generated by a series of solar flares of minor intensity, whereas the second storm on March 13–14, 1989, (min Dst = −600 nT) resulted from particle fluxes from an intense solar flare and exceptionally bright coronal mass ejection (CME). During these two superstorms there were great auroras observed, which were fundamentally different in their spectroscopic characteristics. In the first case, (Loparskaya obs.) intense green IBC 3 aurora were observed during the whole night in the auroral zone. The intensity of the green oxygen line λ 557.7 nm [0I] was > 100 kR, and the ratio of the emission intensity was I(557.7)/I(630.0) ≫ 1. In the second case (March 13–14, 1989), intense type A red auroras were observed. In the auroral zone (Loparskaya obs.), the intensity of the red oxygen line λ 630.0 nm [0I] reached 300 kR, whereas the ratio of emission intensity I (630.0)/I (557.7) ≫ 2 during the whole night. Such a difference in the spectral characteristics of the auroras may be determined either by different energetic spectra of the precipitating particles, or by different properties of the upper atmosphere during the years of low and high solar acivity.

A multievent study of broadband electrons observed by the DMSP satellites and their relation to red aurora observed at midlatitude stations

Broadband electrons during magnetic storms are characterized by an unusually intense flux of precipitating electrons in the broadband energy range from 30 eV to 30 keV near the equatorward edge of the auroral oval (47°–66° magnetic latitude). Broadband electrons were first reported by Shiokawa et al. [1996]. In this paper, we report a multievent study of broadband electrons, using particle data obtained by the Defense Meteorological Satellite Program (DMSP) satellites during 23 magnetic storms from January 1989 through May 1992. Twelve broadband electron events are identified. Most of them are observed in the night sector, but some are observed in the morning sector. Particle data for successive polar passes of the DMSP multisatellites are used to show that broadband electrons generally last for less than 30 min and that for some events, they precipitate over a wide range of local times simultaneously. On the basis of a quantitative calculation of optical emissions from electrons in the neutral atmosphere, we conclude that broadband electrons are a possible cause of red auroras observed at midlatitude ground stations. We suggest that broadband electrons are associated with certain substorms during the main phase of magnetic storms. This conjecture comes from observations of H component positive bays and Pi 2 pulsations observed at low‐latitude magnetic stations and from magnetic field variations observed at geosynchronous satellites. We conclude that the magnetospheric source of broadband electrons lies within the inner part of the plasma sheet. This conclusion is based on the facts that broadband electrons appear in latitudes where plasma sheet particles were observed before the event and that broadband electrons are observed poleward of the subauroral ion drifts, a position that corresponds to the inner edge of the injected particle layer during storms. High‐energy particle data obtained at geosynchronous satellites show that both strong magnetopause compressions in the dayside and decrease of the particle fluxes in the nightside occur in association with the broadband electron events. Possible mechanisms of broadband electron production are discussed.

IPDP Plasma Wave Events Observed in Association with Low Latitude Auroras.

A case study of IPDP (Intervals of Pulsations of Diminishing Period) observed in association with low-latitude auroras is reported. Visible red auroras were detected twice in the time intervals of 11h36m-12h30m UT and 14h10m-14h30m UT on October 21, 1989. Simultaneously there were two rapid northward excursions of the H-component magnetic perturbation with the magnitude of more than 150 nT. The IPDP plasma wave events were observed at Yonezawa during the low-latitude auroras. The energy source of the IPDP plasma wave event is inferred to be the wave-particle interaction involving the asymmetric ring current oxygen ions at the bulge region of the plasmapause during the expansive phase of substorms. The frequency increase is explained in terms of a decrease of energy of the oxygen ion stream while the asymmetric ring current decays.

Dayside red auroras at very high latitudes: The importance of thermal excitation

Extensive radar observations have been made from Sondrestrom of the F region in the daytime sector between 70 and 79° Λ. Regions of enhanced electron temperature and electron density are found in close association with the velocity reversal in the morning and afternoon convection cells. From the radar measurements, calculations are made of the contributions to the atomic oxygen emission at 6300A from dissociative recombination and thermal excitation. The latter mechanism, in particular, in the enhancement regions gives rise to intensities that are comparable to those observed at very high latitudes during the past decade.

The solar terrestrial event of 14–21 December 1971: The pattern of 6300 Å emission over the polar cap

An exceptional solar terrestrial event was initiated by the ejection of plasma from the Sun on 14 December 1971 and was followed by a spectacular pattern of soft particle precipitation into the polar cap, which evolved in a slowly changing sequence until 21 December. The storm was characterized by high proton fluxes in space and near the Earth, an extended interval of northward B z , a highly developed ring current and widespread polar cap particle fluxes. These varied from a dayside “butterfly pattern” early in the event, to highly structured Sun-aligned polar cap patterns late in recovery. A number of polar cap ground-based measurements were compiled and are reported upon. The storm seems reminiscent of the great red auroras of the IGY and some common features are noted. The 6300 Å emission is shown to result largely from direct excitation by low energy electrons, of a few hundred eV. Since the emission covered the Earth's high-latitude dayside region nearly to the invariant pole it indicates a magnetospheric topology that permits entry of low energy plasma over this region or of mechanisms which allow the generation or penetration of the plasma.

Red auroras in the morning sector

The distribution, orientations, and substorm behaviors of red auroras in the morning sector, which were observed during the NASA airborne auroral observation in December 1969, are reported. Combining earlier and present observations, we confirm that red arcs are present in the polar cap along the entire section of the midday part of the oval and along the poleward edge of the oval in the dark sector. It is suggested that red arcs along the poleward boundary of the oval are caused by precipitation of a few hundred electron volt electrons that are present in the upper (northern) and lower (southern) boundary layers of the plasma sheet.

Very Small Intensity of the Red OI Triplet during the Auroral Displays of September 14–16

IT has been shown in previous papers1,2 that the red aurora of type A owes its redness to the enhancement of the red OI-triplet (1D2 − 3P0,1,2) and that the relative intensity of this triplet and the frequency of the red auroras of type A seem to follow the sunspot frequency2,3. This rule was found to hold for spectrograms obtained since 1923 and up to the winter season 1937–38.

Altitude Effects in the Red Part of the Auroral Spectrum and the Two Types of Red Auroras

IN a previous note in NATURE1, I described observations made at Oslo of an auroral display which showed red upper limits, while the lower part had the ordinary greenish-yellow colour. Spectroscopic observations gave an enormous enhancement of the red oxygen line 6300 with increasing height. In a later paper2, I described quantitative measurements of spectrograms corresponding to auroras of ordinary colour, which also gave a considerable enhancement of the red line 6300 with increasing altitude. It became a matter of importance to make further measurements in order to see if the altitude effect on the red line was a general occurrence.

Points from Foregoing Letters

A DESCRIPTION of the spectra of ‘northern lights’, both red and the ‘sun-lit’, usually feeble, grey-violet auroras, simultaneously photographed from several Norwegian stations, is supplied by Prof. Carl Stormer. The height of the red auroras was mainly between 100 km. and 500 km., whilst some of the c sun-lit’ auroras had their summit above 800 km. and in one case reached 1,100 km. above sea-level.

Red and Sunlit Auroras and the State of the Upper Atmosphere

ON October 16 this year, a strong auroral display was observed at Oslo. It commenced as an arc fairly low on the northern sky, but at intervals it took the form of a drapery-shaped band with pronounced ray structure, and sometimes—for example, between 22h and 23h in the evening—rays of quite unusual length (several hundred kilometres) were observed.