The Carrington storm (September 1/2, 1859) is one of the largest magnetic storms ever observed and it has caused global auroral displays in low-latitude areas, together with a series of multiple magnetic storms during August 28 and September 4, 1859. In this study, we revisit contemporary auroral observation records to extract information on their elevation angle, color, and direction to investigate this stormy interval in detail.We first examine their equatorward boundary of "auroral emission with multiple colors" based on descriptions of elevation angle and color. We find that their locations were 36.5° ILAT on August 28/29 and 32.7° ILAT on September 1/2, suggesting that trapped electrons moved to, at least, L~1.55 and L~1.41, respectively. The equatorward boundary of "purely red emission" was likely located at 30.8° ILAT on September 1/2.If "purely red emission" was a stable auroral red arc, it would suggest that trapped protons moved to, at least, L ~ 1.36. This reconstruction with observed auroral emission regions provides conservative estimations of magnetic storm intensities. We compare the auroral records with magnetic observations. We confirm that multiple magnetic storms occurred during this stormy interval, and that the equatorward expansion of the auroral oval is consistent with the timing of magnetic disturbances. It is possible that the August 28/29 interplanetary coronal mass ejections (ICMEs) cleared out the interplanetary medium, making the ICMEs for the Carrington storm on September 1/2 more geoeffective.

While the Sun is generally more eruptive during its maximum and declining phases, observational evidence shows certain cases of powerful solar eruptions during the quiet phase of the solar activity. Occurring in the weak Solar Cycle 14 just after its minimum, the extreme space weather event in 1903 October -November was one of these cases.Here, we reconstruct the time series of geomagnetic activity based on contemporary observational records. With the mid-latitude magnetograms, the 1903 magnetic storm is thought to be caused by a fast coronal mass ejection (~1500 km/s) and is regarded as an intense event with an estimated minimum Dst' of ~−513 nT The reconstructed time series has been compared with the equatorward extension of auroral oval (~44.1° in invariant latitude) and the time series of telegraphic disturbances. This case study shows that potential threats posed by extreme space weather events exist even during weak solar cycles or near their minima.

Abstract. The diurnal variations in daytime airglow emission intensity measurements at three wavelengths OI 777.4 nm, OI 630.0 nm, and OI 557.7 nm made from a low-latitude location, Hyderabad (17.5 • N, 78.4 • E; 8.9 • N MLAT) in India have been investigated. The intensity patterns showed both symmetric and asymmetric behaviour in their respective diurnal emission variability with respect to local noon. The asymmetric diurnal behaviour is not expected considering the photochemical nature of the production mechanisms. The reason for this observed asymmetric diurnal behaviour has been found to be predominantly the temporal variation in the equatorial electrodynamics. The plasma that is transported across latitudes due to the action of varying electric field strengths over the magnetic equator in the daytime contributes to the asymmetric diurnal behaviour in the neutral daytime airglow emissions. Independent magnetic and radio measurements support this finding. It is also noted that this asymmetric diurnal behaviour in the neutral emission intensities has a solar cycle dependence with a greater number of days during high solar activity period showing asymmetric diurnal behaviour compared to those during a low solar activity epoch. These intensity variations over a long timescale demonstrate that the daytime neutral optical emissions are extremely sensitive to the changes in the eastward electric field over low and equatorial latitudes.

The geomagnetic storm (or "Carrington event") of 1-2 September 1859 is one of the largest geomagnetic disturbances on record. At the time, it caused widespread disruption to telegraph systems and was accompanied by aurorae seen overhead as far south as ∼29 • magnetic latitude. The magnitude of the Carrington event means it remains a popular subject of study in the field of space weather, despite the sparse magnetic measurements available from the time. One set of measurements that is available is from the Rome observatory ("Collegio Romano," magnetic latitude ∼38.6 • ). Here we transcribe these horizontal magnetic field data and convert them to nanoteslas. We find that the device used at Rome had an operational range of around 305 nT. Despite going off-scale during the storm, the magnetometer at Rome recorded changes of hundreds of nanoteslas per minute and tens of nanoteslas per second in the horizontal magnetic field. Apart from the tabulated data, we also examine the reported off-scale deviation of 3,000 nT at Rome during the storm. While we could not explicitly locate this reported deviation in the tabulated data, we find that this deviation is comparable to magnetic variations seen at auroral latitudes for modern large magnetic storms, indicating that Rome was in the auroral oval during the morning of 2 September 1859. By comparing this large off-scale deviation to modern geomagnetic data, we estimate that Rome may have experienced a maximum change of 420 nT min −1 .Geomagnetic storms can be characterized by the disturbance storm-time index (Dst), a proxy for the energy in the ring current during a storm (Gonzalez et al., 1994). This value is calculated as an hourly average of four

Irregular occurrence characteristics of the equatorial counter electrojet phenomena at different longitudinal zones are investigated using the magnetic data of the horizontal component 'H ' at the two equatorial stations Trivandrum and Addis Ababa, separated in longitude by about 40• . The limited longitudinal extent of the counter electrojet (CEJ) events are examined on the basis of the occurrence of the phenomenon at different local time intervals. Importance of the solar semi diurnal tides in modifying the equatorial counter electrojet phenomena at Trivandrum and Addis Ababa is discussed during these local time groups. Dominance of semi-diurnal tidal modes of varying magnitude is found to influence the local time occurrence behaviour of CEJ events over the equator. Peculiarities of both the change in amplitude and phase pattern of the diurnal variation of the 'H ' component within the narrow longitude sector, especially during the noon hours, indicate the modulation of the diurnal variation of the equatorial electrojet currents by vertical wind shears of highly localised nature.