Hidehiko Suzuki

Historical space weather monitoring of prolonged aurora activities in Japan and in China

Great magnetic storms are recorded as aurora sightings in historical documents. The earliest known example of “prolonged” aurora sightings, with aurora persistent for two or more nights within a seven-day interval at low latitudes, in Japan was documented on February 21-23, 1204 in Meigetsuki, when a big sunspot was also recorded in China. We have searched for prolonged events over the 600-year interval since 620 in Japan based on the catalogue of Kanda (1933), and over the 700-year interval since 581 in China based on the catalogues of Tamazawa et al. (2017) and Hayakawa et al. (2015). Before the Meigetsuki event, a significant fraction of the 200 possible aurora sightings in Song dynasty (960-1279) of China was detected at least twice within a seven-day interval and sometimes recurred with approximately the solar rotation period of 27 days. The majority of prolonged aurora activity events occurred around the maximum phase of solar cycles rather than around the minimum, as estimated from the 14C analysis of tree rings. They were not reported during the Oort Minimum (1010-1050). We hypothesize that the prolonged aurora sightings are associated with great magnetic storms resulting from multiple coronal mass ejections from the same active region. The historical documents therefore provide useful information to support estimation of great magnetic storm frequency, which are often associated with power outages and other societal concerns.

Fast spectrometer for ground-based observations of OH rotational temperature

A sensitive spectrometer has been developed for observing the hydroxyl airglow in the polar region. This spectrometer is designed to acquire spectra of the Meinel OH 8-4 band, which has the advantage of being relatively free of contamination from auroral emissions. The spectrometer consists of a fast optical system, a transmission plane grating, and a cooled CCD image sensor. The spectrometer can acquire spectra between 900 and 987 nm, from which the OH rotational temperature can be derived with an accuracy of ± 1.9 to 2.5 K for a 1 min? exposure. The spectrometer specifications and initial measurement results for the OH rotational temperature and intensity at Syowa Station (69.0 °S, 39.6 °E) in Antarctica are presented.

Imaging-based observations of low-latitude auroras during 2001–2004 at Nayoro, Japan

Color images of six low-latitude auroral events observed using color digital cameras at Nayoro (142.5° E, 44.4° N), Hokkaido, Japan, from 2001 to 2004, were analyzed to determine the events’ locations and times of occurrence. Geographical azimuthal and elevation angles of the images’ pixels were determined precisely by using the positions of the stars captured in the images. Horizontal regions covered by these auroral events were directly indicated by mapping the color images onto geographical maps and assuming that the emission layer’s altitude is the lowest or highest value of a visible-level red aurora, as determined by the OI 630.0nm emission. The estimated geomagnetic latitudes and L values of these low-latitude auroral events were in the 39–50° range and below L < 2.5, respectively. This investigation indicates that four of the six auroral events were the same as those that were reported previously based on high-sensitivity optical observations at other sites on Hokkaido (Rikubetsu and Moshiri). Although the previous study is lacking information about the maximal brightness level of the red auroral events, the present investigation suggests that these four low-latitude auroral events reached the visible level. In addition, two new events were reported in this study. The present work provides essential information such as the morphology and appearance of visible auroras, which are extremely rare in mid- or low-latitude regions.

Rayleigh/Raman lidar observations of gravity wave activity from 15 to 70 km altitude over Syowa (69°S, 40°E), the Antarctic

The potential energy of gravity waves (GWs) per unit mass (Ep), at altitudes of 15–70 km, has been examined from temperature profiles obtained by a Rayleigh/Raman (RR) lidar at Syowa Station (69°S, 40°E) from May 2011 to October 2013, with the exception of the summer months. The GWs with ground-based wave periods longer than 2 h and vertical wavelengths between 1.8 and 16 km were extracted from the temperature profiles. Ep was larger in winter than in spring and fall, although in 2012, at altitudes below 30 km, Ep was larger in spring than in winter and fall. Ep increased with a mean scale height of 11.3 km. Ep profiles showed a local maximum at an altitude of 20 km and a minimum at 25 km in almost every month, which has not been reported by previous studies observed by radiosondes. The values of Ep in October of 2012 were smaller at 35–60 km and larger at 20–35 km than those in October of 2011 and 2013. This difference in the Ep profile is most probably caused by different seasonal variations of zonal winds. The larger and smaller Ep values seem to be observed both below and above the altitude at which the zonal wind speed reached 0 m s-1. This result suggests that wind filtering of gravity waves with small phase speeds is significantly important in early spring.

Atmospheric gravity waves excited by a fireball meteor: Observations and modeling

In a companion paper, Suzuki et al. (2013) studied an expanding circular train observed in the Na airglow for 9 min above Syowa Station, Antarctica, on 7 June 2008. This train was created by a southwestward moving fireball meteor. Here we report on “V”-shaped faint gravity waves (GWs) partially visible in many of the Na airglow images 8 to 43 min after the meteor. The GW phase lines appear to originate from the horizontal projection of the meteor path, with angles −42 to −52° south and 10 to 20° north of the path. The GWs south of the path propagated southwestward with a horizontal phase speed of cH∼80–100m/s, while those north of the path propagated northwestward with cH∼20–40m/s. Those south (north) of the path had horizontal wavelengths λH∼25–35km (λH∼18 km) and periods τr∼5–6 min (τr∼7–15 min). We then model the GWs excited by idealized horizontal and slanted heatings and body forces. We show that the GW phase lines form Vs when the heat/force is slanted vertically. If the central altitude of the heat/force is z0>92 km, the open ends of the Vs are mainly directed away from the meteor trajectory. If the heat/force is long enough, two oppositely directed Vs are created, forming an “X” at the center of the structure. We find that λH depends sensitively on the width of the heating. We obtain heating parameters which compare reasonably well with the Na observations: z0∼120 km, half-length half maximum of ∼25–35km, and half width half maximum of ∼2–3km.

Observation of cosmic rays and auroral X-rays in the Polar Patrol Balloon experiment

Abstract The Polar Patrol Balloon (PPB#6) aimed at studying the elemental and isotopic composition of galactic cosmic rays, solar energetic particles cosmic gamma ray bursts and auroral X-rays, and was launched from Syowa Station Antarctica, by the 34th Japanese Antarctic Research Expedition on 5 Jan 1993. The balloon moved westward by 1.5 circumpolar rounds over Antarctica covering 6–13g/cm 2 atmospheric depth and 63°S–70°S geographic latitude. A total of 584 hours of observations was obtained. The balloon trajectory, the observing system and preliminary results of spectra and global distribution of cosmic radiation and auroral X-rays were described.