Great Aurora Research Articles

The Great Aurora of 4 February 1872 observed by Angelo Secchi in Rome

Observation of auroras at low latitudes is an extremely rare event typically associated with major magnetic storms due to intense Earth-directed Coronal Mass Ejections. Since these energetic events represent one of the most important components of space weather, their study is of paramount importance to understand the Sun-Earth connection. Due to the rarity of these events, being able to access all available information for the few cases studied is equally important. Especially if we refer to historical periods in which current accurate observations from ground-based instruments or space were not available. Certainly, among these events, we must include the great aurora of February 4, 1872. An event whose effects have been observed in different regions of the Earth. What we could consider today a global event, especially for its effects on the communication systems of the time, such as the transatlantic cable that allowed a connection between the United States and Europe since 1866. In this paper, we describe the main results of the observations and studies carried out by Angelo Secchi at the Observatory of the Roman College and described in hisMemoria sull’Aurora Elettrica del 4 Febbraio 1872for the Notes of the Pontifical Academy of new Lincei. This note is extremely modern both in its multi-instrumental approach to the study of these phenomena and in its association between solar-terrestrial connection and technological infrastructures on the Earth. The Secchi’s note definitely represents the first example of analysis and study of an event on a global scale, such as the Atlantic cable, affecting the Earth. What we nowadays call an extreme space weather event.

An Analysis of Trouvelot's Auroral Drawing on 1/2 March 1872: Plausible Evidence for Recurrent Geomagnetic Storms

AbstractThis work examines Trouvelot's observations and drawing of an auroral display during the night of 1 March 1872. It is known that the auroral oval moves equatorward to midlatitude and even low latitude during large geomagnetic storms. Trouvelot's graphical record of the great aurora on 1 March 1872 has been often cited as a remarkable example of a midlatitude aurora, although it is puzzling that this apparently occurred on a geomagnetically quiet day. Kataoka et al. (2019, JSWSC, 9, A16) even criticised this as a dating error. Here, we investigate Trouvelot's descriptions and available geomagnetic measurements in detail. Our analysis shows that the original date of Trouvelot's auroral drawing is most probably accurate in local time. Moreover, Trouvelot's descriptions and the observational site show that the auroral visibility fell at the beginning of 2 March 1872 in Greenwich Mean Time (GMT). Consulting simultaneous variations of magnetograms at Helsinki and Greenwich, we found that the nightside aurora specifically coincides with the initial phase of the storm (substorm) and suggests a close association with a substorm triggered by sudden magnetospheric compression. This case study shows that short geomagnetic storms can be overlooked in a daily aa index and they can also cause midlatitude aurorae. Moreover, we found ≈27‐day intervals between this storm, the extreme storms on 4–6 February 1872, and another “bright aurora” that was reported on 6 January 1872. Based on their intervals, these midlatitude aurorae have probably resulted from recurrent solar activity.

Portuguese eyewitness accounts of the great space weather event of 1582

Newly discovered descriptions about the great aurora observed in March 1582 are presented in this work. These records were made by Portuguese observers from Lisbon. Both records described the aurora like a great fire in the northern part of the sky. It was observed during three consecutive nights, according to one of the sources. Thus, we present a discussion of these auroral records in order to complement other works that studied the aurora sighted in March 1582.

MID-LATITUDE AURORA IN SOLAR CYCLES 23–24 FROM OBSERVATIONS IN THE SOUTH OF EASTERN SIBERIA

The paper presents observations of mid-latitude aurora (MA) in the south of Eastern Siberia in solar cycles 23–24. Spectral composition and dominant emissions of MA, daily distribution of MA detection probability, dependence on the level of geomagnetic activity, and classification according to types of aurora are discussed. A close relationship is shown between the intensity of dominant emission at 630.0 nm and the Dst index during magnetic storms (MSs). It is pointed out that the most intense MA are recorded during MS main phases. The MA detected on November 20, 2003 can enlarge the list of great aurora. For the severe MSs (Dstmin< –200 nT) of March 24, 1991, April 6, 2000, October 30 and November 20, 2003, March 17, 2015, the observed dynamics of 557.7 and 630.0 nm auroral emissions is presented. Mechanisms of emission excitation during geomagnetic storms and a possible connection with magnetospheric structures are discussed.

СРЕДНЕШИРОТНЫЕ СИЯНИЯ В 23–24-х СОЛНЕЧНЫХ ЦИКЛАХ ПО ДАННЫМ НАБЛЮДЕНИЙ НА ЮГЕ ВОСТОЧНОЙ СИБИРИ

The paper presents observations of mid-latitude aurora (MA) in the south of Eastern Siberia in solar cycles 23–24. Spectral composition and dominant emissions of MA, daily distribution of MA detection probability, dependence on the level of geomagnetic activity, and classification according to types of aurora are discussed. A close relationship is shown between the intensity of dominant emission at 630.0 nm and the Dst index during magnetic storms (MSs). It is pointed out that the most intense MA are recorded during MS main phases. The MA detected on November 20, 2003 can enlarge the list of great aurora. For the severe MSs (Dstmin< –200 nT) of March 24, 1991, April 6, 2000, October 30 and November 20, 2003, March 17, 2015, the observed dynamics of 557.7 and 630.0 nm auroral emissions is presented. Mechanisms of emission excitation during geomagnetic storms and a possible connection with magnetospheric structures are discussed.

The Great Aurora of January 1770 observed in Spain

Abstract. An analysis is made of the records made by Spanish observers of a notable aurora on 18 January 1770 in order to study the characteristics of this event. The records indicate that the phenomenon was observed in both continental and insular territories of Spain, in particular at San Cristóbal de la Laguna, Cádiz, Córdoba, Badajoz, Valencia, Castellón, Madrid, Barcelona, and Gerri de la Sal. The most equatorward observational site was San Cristóbal de la Laguna (28.48∘ N, 16.32∘ W) in the Canary Islands. In general, the descriptions put its duration from sunset to midnight, but the observers from Córdoba and Madrid report the aurora as being visible during the last hours of the night, and it was even observed the following day at Castellón. All the observers described the aurora as red in colour, while white and ash colours were also reported at Córdoba and Gerri de la Sal. The brightness and shape of auroral display changed over time. Calculations of the geomagnetic latitudes of the observation locations gave San Cristóbal de la Laguna as the southernmost (26∘ N) and Gerri de la Sal the northernmost (35∘ N) and indicate this aurora was observed over a wide range of abnormally low latitudes for such a phenomenon. Solar activity around the event was high, with the astronomer Horrebow registering 10 sunspot groups on that date (18 January 1770).

Spanish eyewitness accounts of the great space weather event of 1859

Exceptional geomagnetic storms were observed in late August and early September 1859. Auroras were observed around the world, and telegraph wires were damaged. Until now, there has been no evidence published of auroral observations in Spain during this famous space weather event. This paper presents Spanish observations that show the aspect of this great aurora from Spain, and the concurrent effects on European telegraph wires. We also computed the variation of the geomagnetic declination in Spain during recent centuries to put these records into context.

The development of the aurora of 18 January 1770

Abstract. The development of the great aurora of 18 January 1770 has been discussed in fundamental papers by Silberschlag, Behn and other authors. The aurora was observed in middle and low latitudes and in Northern latitude. In Central Europe it displayed all typical auroral forms, including the corona.

The great aurora of January 18, 1770

The development of the great aurora of January 18, 1770 has been discussed in a fundamental paper by Silberschlag (1770) and other authors. The aurora was observed in middle and low latitudes and in Northern latitude. In Central Europe it displayed all typical auroral forms, including the Corona.

Low-latitude auroras: The great aurora of 4 February 1872

The aurora of 4 February 1872 was comparable to, and perhaps even greater than, that of 1/2 September 1859. In this paper we show that the aurora of 4 February 1872 was seen worldwide, and that in the Caribbean, Egypt, Southern Africa, the Indian Ocean, the Indian subcontinent, and China these observations extended as low as 20° magnetic latitude. Observations are also available in the north to as far as the vicinity of the north magnetic pole. This aurora is then comparable to, or greater than, in geographical extent, and in equatorward closeness, to that of 2 September 1859. Both must now be included as the only known members in the class of greatest auroras of the past few hundred years. For the 1859 aurora, however, there is no accepted observation at a lower magnetic latitude than about 20°. By contrast, several observations for the aurora of 4 February 1872 are reported at magnetic latitudes of the order of 10°, and one probable observation at an even lower magnetic latitude of about 3°. This paper presents a survey and discussion of these observations.

Differences between CME‐driven storms and CIR‐driven storms

Twenty one differences between CME‐driven geomagnetic storms and CIR‐driven geomagnetic storms are tabulated. (CME‐driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR‐driven includes driving by the associated recurring high‐speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME‐driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR‐driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR‐driven storms than it is prior to CME‐driven storms. CME‐driven storms pose more of a problem for Earth‐based electrical systems; CIR‐driven storms pose more of a problem for space‐based assets.

Comparison of the aurora of September 1/2, 1859 with other great auroras

The maximum equatorward boundary of a number of visual auroral events for the period subsequent to that of the great storms of August and September 1859 are examined. These boundaries, in terms of dipole magnetic latitude, are related to the half-daily aa index. A least squares regression line, magnetic latitude = 55.86 − 0.056 aa, with a correlation coefficient of 0.84, adequately represents the data. The September 1859 event, in the context of these other storms, fits into the totality of the events examined as one of the two largest events of the sample, but is otherwise not unique. The discussion includes indications for further work in this area.

Changes in the interpretation of aurora and the example of the night of March 17, 1716

A new interpretation of celestial phenomena became apparent after the appearance of the great aurora of March 1716. The philosopher Wolff presented a general lecture to the public in which he explained the aurora as a normal celestial phenomenon.

Comments to the paper i lisac, "overview of scientific activites in geomagnetism and aeronomy in Croatia"

The auroral data from Croatia are of great interest as examples from middle latitude stations. The descriptions given by Lisac are not new; in general the development of auroras is well described from many observations in middle latitudes, e.g. from Germany (Schroder 1964). The auroral phenomenon of November 11, 1991 is also well-documented from other European parts. It is of more interest to have details on the earliest observations from Croatia after the so-called Maunder-Minimum (1645–1715). The indicated years in Lisac’s report are connected with times of solar maxima (1738.7 and 1750.3). Many auroras have been reported in the years 1737 and 1750 by European observers. During or near the solar minima (1734.0 and 1745.0) auroras were seldom observed in Central Europe, and consequently very seldom in the latitudes of Croatia and other places. It is known that after 1710 the interest in auroras increased in Europe. A key event was the great aurora of March 17, 1716 (see Schroder 2001). Following this event a general discussion started on the physical nature of these phenomena, and C Wolff (see Schroder 2001) and others pointed out their natural origin. Since this time auroras have been mostly well-documented from middle latitudes and interpreted as atmospheric phenomena.

Low-latitude auroras: the magnetic storm of 14–15 May 1921

We review solar/geophysical data relating to the great magnetic storm of 14–15 May 1921, with emphasis on observations of the low-latitude visual aurora. From the reports we have gathered for this event, the lowest geomagnetic latitude of definite overhead aurora (coronal form) was 40° and the lowest geomagnetic latitude from which auroras were observed on the poleward horizon in the northern hemisphere was 30°. For comparison, corresponding overhead/low-latitude values of 48°/32° and 41°/20° were reported for the great auroras on 28–29 August and 1–2 September 1859, respectively. However, for the 1921 event, there is a report of aurora from Apia, Samoa, in the southern hemisphere, within 13° of the geomagnetic equator. This report by professional observers appears to be credible, based on the aurora description and timing, but is puzzling because of the discrepancy with the lowest latitude of observation in the northern hemisphere and the great implied auroral height ( ∼2000 km , assuming overhead aurora at Auckland, New Zealand). We discuss various possibilities that might account for this observation.

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.

19th century auroral observations reveal solar activity patterns

Growing interest in the aurora in the early part of the eighteenth century, which resulted from the spectacular reappearance of the aurora in 1707 and 1716, followed a relative scarcity of great auroras during the Maunder minimum, a period of prolonged reduced solar activity from about 1645–1715. Observations in the early eighteenth century led to questions about the geographical extent, nature, and temporal variability of the auroras. Typically, such observations were included as part of recorded meteorological notations, though occasionally early astronomers, such as Tycho Brahe in the 1590s, included auroras in their observations. Meteorological observations were important because of the effects of weather and climate on agriculture, and, according to the belief at the time, on disease.

The polar onset and development of the November 8 and 9, 1991, global red aurora

On November 8, 1991, a major magnetic storm began with a sudden commencement at 0647 UT; it continued until about 1800 UT on November 9. Associated with this storm there was a great aurora which continued through November 8 and until at least 1200 UT on November 9. The first optical indication of this event was the appearance of bright sun‐aligned arcs over Eureka, North West Territories (89° corrected geomagnetic latitude (CGM)), Canada from 0750 UT until about 1230 UT on November 8. By that time, there was a gradual transformation to dominant 6300 Å emission over the central polar cap. Gradually, the major soft electron precipitation and associated red aurora moved equatorward. The aurora reached a low‐latitude limit of 40° CGM at 0600 UT on November 9. The polar arcs reached 22 kR intensity (5577 Å), while the red aurora seen later at low latitudes was at least 100 kR (6300 Å). The analysis of Defense Meteorological Satellite Program (DMSP) particle data from 83 passes during November 8 and 9 showed the extent and movement of precipitation from the polar region to midlatitudes. A comparison of this event was made with the earlier great auroral event of March 13–14, 1989. While the extent in low latitude and the duration of the two disturbances were similar, the November 8–9 event had approximately one half of the total energy input into the ionosphere. Its striking and unusual feature was the auroral onset and activity in the central polar region, a feature possibly related to the solar wind interplanetary magnetic field orientation.

Photometric studies of the great red aurora March 13 and 14, 1989

Extended photometric coverage of the great red aurora of March 13–14, 1989 was obtained at the Rabbit Lake observatory located in northern Saskatchewan, at an eccentric dipole latitude of 65.3°. The red aurora first appeared there about 0311 UT on March 13 and appeared to have run its course by about 0700 UT on March 14. During much of the two nights the observatory was near the poleward edge of the display; the aurora was active much of the time and its brightenings were accompanied by poleward expansions to as far north as the observatory. Combining these observations with those at low latitudes suggest a large auroral expanse from an equatorward edge of about 30° to a poleward edge of about 65° magnetic latitude. One key value of the optical data was the semicontinuous monitoring of major auroral emission intensities. The 01D emission at 630 nm reached 130 kR intensity shortly after onset, at about 0347 UT on March 13. Its intensity the following night was typically 35 kR or below. A HILAT satellite pass around 0415 UT March 14 indicated an electron influx of average energies varying between 150 and 800 eV. The excitation efficiency for the 630 nm emission, neglecting any collisional deactivation, was approximately 1 kR per erg cm−2 s−1 (1 erg = 10−7 J) of precipitating electron energy. These measurements along with related worldwide observations will assist in gaining a better understanding of the magnetospheric conditions producing such major widespread auroras.

Historical review of great auroras

Occurrences of great auroras of the past are discussed together with accounts of visual and instrumental observations. Earlier observations revealed the extraordinarily great heights and unusual spectral characteristics of such displays as well as documenting their penetration to low latitudes. Theoretical studies have led to an understanding of the observed unusual spectroscopic characteristics including their bright red colour and the abnormal vibrational and rotational structure in the molecular bands observed in high-altitude forms. As a result of the increasing sophistication of observing techniques, the phenomena associated with great auroras have passed beyond the characterization of optical and magnetic effects, to include information on associated changes in the composition of the neutral upper atmosphere and effects in the ionosphere. In more recent times, studies have led to increased understanding of the magnetospheric processes that produce these auroras.