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[1] The Earth's outer radiation belt electrons increase when the magnetosphere is surrounded by the high-speed solar wind stream, while the southward interplanetary magnetic field (IMF) is also known as an important factor for the flux enhancement. In order to distinguish the two different kinds of solar wind parameter dependence statistically, we investigate the response of the outer belt to stream interaction regions (SIRs). A total of 179 SIR events are identified for the time period from 1994 to 2005. We classify the SIR events into two groups according to the so-called “spring-toward fall-away” rule: IMF sector polarity after the stream interface is toward in spring or away in fall (group A) and vice versa (group B). According to the Russell-McPherron effect, groups A and B have a significant negative and positive offset of the IMF Bz after the stream interface, respectively. Comparing groups A and B by superposing about the stream interface, only IMF Bz dependence can be obtained because the other solar wind parameters change in the same manner. As a result, the greatest flux enhancement is found in the highest-speed streams with a southward offset of the IMF Bz, indicating that only the solar wind speed by itself is not a sufficient condition for the large flux enhancement. It is also found that the large flux enhancement tends to be associated with weak geomagnetic activities with minimum Dst of about −50 nT on average, implying that the existence of intense magnetic storms is not essential for the flux enhancement.

[1] In the paper ‘‘Major geomagnetic storms (Dst 100 nT) generated by corotating interaction regions’’ by I. G. Richardson et al. (Journal of Geophysical Research, 111, A07S09, doi:10.1029/2005JA011476, 2006), there are several typographical errors. In Figures 1, 2, 3, 4, and 7, the y component of the solar wind electric field (Ey) is plotted with the incorrect sign. Signed values of Ey referred to in the text and given in Table 1 also have the incorrect sign. As stated in the second paragraph of section 2, the ‘‘Ey’’ panel shows the value of VxBz. However, this is equal to Ey, not Ey (assuming that VxBz VzBx in the solar wind). JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A12105, doi:10.1029/2007JA012332, 2007 Click Here for Full Article

From simultaneous observations of the European incoherent scatter Svalbard radar (ESR) and the Cooperative UK Twin Located Auroral Sounding System (CUTLASS) Finland radar on 9 March 1999, we have derived the height distributions of the thermospheric heating rate at the F region height in association with electromagnetic energy inputs into the dayside polar cap/cusp region. The ESR and CUTLASS radar observations provide the ionospheric parameters with fine time-resolutions of a few minutes. Although the geomagnetic activity was rather moderate (Kp=3+~4), the electric field obtained from the ESR data sometimes shows values exceeding 40 mV/m. The estimated passive energy deposition rates are also larger than 150 W/kg in the upper thermosphere over the ESR site during the period of the enhanced electric field. In addition, enhancements of the Pedersen conductivity also contribute to heating the upper thermosphere, while there is only a small contribution for thermospheric heating from the direct particle heating due to soft particle precipitation in the dayside polar cap/cusp region. In the same period, the CUTLASS observations of the ion drift show the signature of poleward moving pulsed ionospheric flows with a recurrence rate of about 10–20 min. The estimated electromagnetic energy deposition rate shows the existence of the strong heat source in the dayside polar cap/cusp region of the upper thermosphere in association with the dayside magnetospheric phenomena of reconnections and flux transfer events.

[1] The SuperDARN Hokkaido HF radar, capable of measuring the subauroral ionospheric plasma convection especially during storms, has been in continuous operation since the beginning of December 2006. We report the first two-dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 January 2007. The flow reversal region is extended over 20° in longitude and 5° in latitude, lasting for about 10–15 min, and the maximum flow speed is about 0.5–1.0 km/s. The flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere, suggesting that it is produced by the region 2 field-aligned current associated with the ring current enhancement during the storm main phase. The dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell, associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure. It is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought.

[1] Evolution of energetic electron fluxes, related solar wind conditions, and relevant plasma waves in the inner magnetosphere are examined during the two corotating interaction region (CIR)-driven magnetic storms in November 1993. In this paper we focus on the fact that the flux of the outer radiation belt electrons increased significantly during the 3 November storm, while it did not increase above the prestorm level during the 18 November storm. The recovery phase of the 3 November storm is associated with the prolonged substorm activity; continuous injections of hot and subrelativistic electrons, and enhanced chorus wave activity which can accelerate subrelativistic electrons to MeV energies by means of wave-particle interactions. In contrast, the recovery phase of the 18 November storm is associated with reduced substorm activity, weak injections of hot and subrelativistic electrons, and low chorus wave activity. These differences in the recovery phase can be related to the southward offset of interplanetary magnetic field (IMF) in the high-speed coronal hole stream, which is influenced by the IMF sector polarity via the Russell-McPherron effect (dipole tilt effect associated with the IMF polarity).

We study the relation between strong and extreme geomagnetic storms and solar cycle characteristics. The analysis uses an extensive geomagnetic index AA data set spanning over 150 yr. complemented by the Kakioka magnetometer recordings. We apply Pearson correlation statistics and estimate the significance of the correlation with a bootstrapping technique. We show that the correlation between the storm occurrence and the strength of the solar cycle decreases from a clear positive correlation with increasing storm magnitude toward a negligible relationship. Hence, the quieter Sun can also launch superstorms that may lead to significant societal and economic impact. Our results show that while weaker storms occur most frequently in the declining phase, the stronger storms have the tendency to occur near solar maximum. Our analysis suggests that the most extreme solar eruptions do not have a direct connection between the solar large-scale dynamo-generated magnetic field, but are rather associated with smaller-scale dynamo and resulting turbulent magnetic fields. The phase distributions of sunspots and storms becoming increasingly in phase with increasing storm strength, on the other hand, may indicate that the extreme storms are related to the toroidal component of the solar large-scale field.

[1] A meteorological view of solar wind structures is useful for probability prediction of the flux enhancement of radiation belt electrons. We report the averaged variations of the solar wind parameters and radiation belt electrons during isolated geomagnetic storms driven by coronal mass ejections (CMEs) and corotating interaction regions (CIRs), using a superposed epoch analysis centered on interplanetary shocks and stream interfaces, respectively, whose arrival times can be used as a precursor for the flux enhancement. A total of 49 CME- and 6 CIR-associated storms with Dst 2 MeV electron flux alert with >103 pfu (pfu = particles cm−2 s−1 sr−1) at geosynchronous orbit 1 day after the shock is only 14% (7 of 49 events) and is smaller than the prestorm level, while the probability 4 days after the shock increases to 43% (21 of 49 events) and is larger than the prestorm level. In CIR-associated storms, the average flux recovers to the prestorm level about 1 day after a stream interface arrival. The probability of an electron flux alert is 83% (5 of 6 events) 1 day after the stream interface arrival and remains at that level for at least the next 4 days.

[1] Seventy-nine major geomagnetic storms (minimum Dst ≤ −100 nT) observed in 1996 to 2004 were the focus of a “Living with a Star” Coordinated Data Analysis Workshop (CDAW) in March 2005. In nine cases, the storm driver appears to have been purely a corotating interaction region (CIR) without any contribution from coronal mass ejection-related material (interplanetary coronal mass ejections (ICMEs)). These storms were generated by structures within CIRs located both before and/or after the stream interface that included persistently southward magnetic fields for intervals of several hours. We compare their geomagnetic effects with those of 159 CIRs observed during 1996–2005. The major storms form the extreme tail of a continuous distribution of CIR geoeffectiveness which peaks at Dst ∼ −40 nT but is subject to a prominent seasonal variation of ∼40 nT which is ordered by the spring and fall equinoxes and the solar wind magnetic field direction toward or away from the Sun. The O'Brien and McPherron (2000) equations, which estimate Dst by integrating the incident solar wind electric field and incorporating a ring current loss term, largely account for the variation in storm size. They tend to underestimate the size of the larger CIR-associated storms by Dst ∼ 20 nT. This suggests that injection into the ring current may be more efficient than expected in such storms. Four of the nine major storms in 1996–2004 occurred during a period of less than three solar rotations in September to November 2002, also the time of maximum mean IMF and solar magnetic field intensity during the current solar cycle. The maximum CIR-storm strength found in our sample of events, plus additional 23 probable CIR-associated Dst ≤ −100 nT storms in 1972–1995, is (Dst = −161 nT). This is consistent with the maximum storm strength (Dst ∼ −180 nT) expected from the O'Brien and McPherron equations for the typical range of solar wind electric fields associated with CIRs. This suggests that CIRs alone are unlikely to generate geomagnetic storms that exceed these levels.

[1] A novel time-frequency analysis method (S-transform) capable of handling noisy non-stationary signals is applied to study the properties of geomagnetically induced current (GIC) fluctuations in the Finnish natural gas pipeline. New local time- and storm phase-dependent S-transform spectral properties of auroral region GIC fluctuations during geomagnetic superstorms are reported. More specifically, the S-transform spectra have two distinct regions containing the most of the spectral power that persisted from storm to storm: main phase-related wide-band fluctuations driven possibly by a substorm-type ionospheric activity centered around the local midnight and recovery phase-related narrow-band fluctuations associated with Pc5 range geomagnetic pulsations in the local morning region. Based on this observed “stability”, a new S-transform-based statistical approach using, for example, an ensemble of different S-transform responses for known storms is proposed for GIC prediction.

[1] We investigate 17 coronal mass ejection (CME) events identified by the ACE spacecraft during solar cycle 23, focusing upon the fine structures of the sheath region between the CME and its associated shock to find their dependence on the shock parameters. We observe the planar magnetic structure (PMS) downstream of a quasi-perpendicular shock when the Alfven Mach number >2.0. Here, the PMS is characterized by the magnetic fields changing directions abruptly and intermittently within a plane parallel to the shock plane. The downstream PMS does not form when a magnetic cloud with β value 0.5 and the upstream is dominated by Alfvenic fluctuations.

[1] Superposed epoch analyses of ring current (RC) ions and radiation belt (RB) electrons are conducted for geomagnetic storms with Dst −130 nT associated with corotating interaction regions (CIRs), storms with Dst > −130 nT driven by coronal mass ejections (CMEs), and CME-driven great storms with Dst 3.5 during the recovery phase largely depend on the solar wind structures; CIRs are significantly more effective for the evolution of the outer belt than are CMEs because of the existence of a series of particle injections driven by Alfven waves within the fast coronal hole stream following the CIR. On the other hand, the flux enhancements of RB electrons and RC ions at L ≤ 3.0 largely depend on the strength of storms; only particular CMEs with a huge motional electric field and large dynamic pressure are effective in increasing the RB electrons and RC ions at L ≤ 3.0.

Accepted: 2004-08-18, 資料番号: SA1003826000

[1] Energy transfer from the solar wind into the magnetosphere and ionosphere is controlled by the southward magnetic field in the magnetosheath which under normal high Mach number conditions is about four times the solar wind southward field. In a low Mach number regime, however, the magnetosheath compression is diminished by a low solar wind density when the magnetic field remains steady. When magnetic clouds with extremely strong magnetic field cause severe geomagnetic storms under such low Mach number conditions, the density control of the energy transfer is expected to be important in understanding ring current evolution. Here we show evidence for such a density effect using in-situ observation by the GOES and Cluster spacecraft in the magnetosheath during the main phase of the super storm on 20 November 2003. Results from a global magnetohydrodynamic (MHD) simulation with an embedded ring current model also support this density effect. Citation: Kataoka, R., D. H. Fairfield, D. G. Sibeck

[1] In order to understand the response of the Jovian magnetosphere to solar wind dynamic pressure enhancements, we investigate magnetic field variations observed by the Galileo spacecraft. The lack of solar wind monitoring just upstream of the Jovian magnetosphere is overcome by simulating a one-dimensional magnetohydrodynamic (MHD) propagation of the solar wind from the Earth. We identify the events with an increase of the solar wind dynamic pressure >0.25 nPa at the Jovian orbit. Characteristic magnetic field variations are found in the Jovian magnetosphere for all of the nine events. The rectangular waveform due to the Jovian rotation disappears for eight of the nine events. Magnetic field disturbances in the frequency range from 0.3 to 10 mHz are enhanced simultaneously. The maximum amplitude of the disturbances is in proportional to the maximum amplitude of the solar wind dynamic pressure. We suggest that the current sheet is greatly deformed and reconnection bursts are induced under the compressed magnetosphere.

[1] We investigate the transient response of the Earth's magnetosphere-ionosphere system to a localized density pulse in the solar wind using a magnetohydrodynamic simulation. The simulated ionospheric disturbances exhibit many properties similar to those observed during traveling convection vortices (TCVs). The simulated TCVs are driven by pairs of field-aligned currents. The generation mechanisms of the field-aligned currents in the magnetosphere are evaluated in terms of a wave equation of field-aligned currents. The source current is the inertial current associated with in-out plasma acceleration in the magnetosphere near the impact region. The inertial current is converted into the field-aligned current off from the equatorial region via the curvilinear effect. The inhomogeneous effect also generates the field-aligned current near the inner equatorial region where the sharp gradient of Alfven speed exists.

[1] We have compiled a complete list of magnetic impulse events (MIEs) during the 8-year period of 1995–2002 covering solar minimum to solar maximum using fluxgate magnetometer data obtained at the South Pole. Wavelet analysis enables us to detect 825 distinct MIEs automatically with high confidence. Interplanetary magnetic field (IMF) discontinuities are also detected automatically for the same period from Wind and ACE satellite data. From an examination and comparison of the two lists, we find that monthly and seasonal variations in IMF discontinuity occurrences have a significant correlation (0.4–0.5) with those of MIEs. We also find that MIEs tend to occur during intervals of low density, high-speed solar wind streams, and/or radial IMF. No preferences for MIE occurrences are found for solar wind pressure jumps or IMF Bz southward turnings. From detailed minimum variance analysis of 36 IMF discontinuities with one-to-one correspondence to MIEs, ∼70% of the IMF discontinuities are found to be tangential discontinuities. The hot flow anomaly (HFA) mechanism can explain at most ∼50% of the MIEs; bursty reconnection and pressure pulses can explain the production of at most ∼30% and ∼20% of the MIEs, respectively. All of the observations and associations are consistent with HFAs or foreshock cavities being the main cause of MIEs.

Using ULF wave data measured by search coil and fluxgate magnetometers installed at six Automatic Geophysical Observatories (AGOs) locating from 70° to 87° in magnetic latitude and South Pole station at 74° magnetic latitude in Antarctica, the characteristics of ULF waves associated with magnetic impulse events (MIEs) in the cusp and LLBL region have been investigated in detail. It was found that transient, narrow-band Pc 1 waves with a falling tone spectral structure often occurred related to MIEs and that one event occurred simultaneously with the hot flow anomaly (HFA) event studied by Sibeck et al. (1999). These results suggest that the rapid outward motion of the magnetopause due to HFA may induce the falling-tone Pc 1 waves. If this speculation is correct, transient Pc 1 waves related to MIEs would be used as a practical diagnostic tool for monitoring magneotspheric boundary processes.

We investigate mass losses via stellar winds from sun-like main sequence stars with a wide range of activity levels. We perform forward-type magnetohydrodynamical numerical experiments for Alfven wave-driven stellar winds with a wide range of the input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with the Alfven waves, and the cool dense chromosphere is intermittently extended to 10 -- 20 % of the stellar radius. The dense atmospheres enhance the radiative losses and eventually most of the input Poynting energy from the stellar surface escapes by the radiation. As a result, there is no more sufficient energy remained for the kinetic energy of the wind; the stellar wind saturates in very active stars, as observed in Wood et al. The saturation level is positively correlated with B_{r,0}f_0, where B_{r,0} and f_0 are the magnetic field strength and the filling factor of open flux tubes at the photosphere. If B_{r,0}f_0 is relatively large >~ 5 G, the mass loss rate could be as high as 1000 times. If such a strong mass loss lasts for ~ 1 billion years, the stellar mass itself is affected, which could be a solution to the faint young sun paradox. We derive a Reimers-type scaling relation that estimates the mass loss rate from the energetics consideration of our simulations. Finally, we derive the evolution of the mass loss rates, \dot{M} t^{-1.23}, of our simulations, combining with an observed time evolution of X-ray flux from sun-like stars, which is shallower than \dot{M} t^{-2.33+/-0.55} in Wood et al.(2005)., 21 pages, 16 figures embedded, PASJ in press

Interplanetary coronal mass ejections (ICMEs) are often observed to travel much faster than the ambient solar wind. If the relative speed between the two exceeds the fast magnetosonic velocity, then a shock wave will form. The Mach number and the shock standoff distance ahead of the ICME leading edge is measured to infer the vertical size of an ICME in a direction that is perpendicular to the solar wind flow. We analyze the shock standoff distance for 45 events varying between 0.5 AU and 5.5 AU in order to infer their physical dimensions. We find that the average ratio of the inferred vertical size to measured radial width, referred to as the aspect ratio, of an ICME is 2.8 ± 0.5. We also compare these results to the geometrical predictions from Paper I that forecast an aspect ratio between 3 and 6. The geometrical solution varies with heliocentric distance and appears to provide a theoretical maximum for the aspect ratio of ICMEs. The minimum aspect ratio appears to remain constant at 1 (i.e., a circular cross section) for all distances. These results suggest that possible distortions to the leading edge of ICMEs are frequent. But, these results may also indicate that the constants calculated in the empirical relationship correlating the different shock front need to be modified; or perhaps both distortions and a change in the empirical formulae are required.

At launch, coronal mass ejections (CMEs) are often approximated as locally cylindrical objects with circular cross sections. However, CMEs have long been known to propagate almost radially away from the Sun along with the bulk solar wind. This has important consequences for the structure of CMEs; an initially circular cross section will be severely flattened by this radial motion. Yet calculations of total flux and helicity transport by CMEs based on in situ observations still use the assumption of a locally cylindrical object. In this paper, we investigate the morphology of an interplanetary CME based upon geometric arguments. By radially propagating an initial cylindrical object that maintains a constant ratio between its expansion speed and bulk flow, A, we show that the flattening, or "pancaking," of the two-dimensional cross section effectively ceases; the aspect ratios of these CMEs converge to a fixed value as they propagate further into the heliosphere. Thereafter the CME morphology is scale invariant. We predict aspect ratios of 5 ± 1 at terrestrial distances. By correlating a planetary shock with an interplanetary shock linked to a CME, these aspect ratios are estimated using in situ measurements in Paper II. These estimates are made at various heliocentric distances.

[1] Two typical magnetic impulse events (MIEs) accompanied by traveling convection vortices (TCVs) are investigated. The analysis of their conjugate equivalent convection patterns is performed using magnetic field data obtained from high-latitude ground magnetometer networks in the Northern and Southern Hemispheres. A three-dimensional analysis of solar wind structures is also performed using solar wind data obtained from multiple International Solar-Terrestrial Physics satellites. In the first event observed at � 1310 UT on 22 May 1996, a westward moving TCV appeared simultaneously in the noon-to-dawn sector in the Northern and Southern Hemispheres. The solar wind source of this TCV is found to be a tangential discontinuity (TD), which causes a rapid northward turning of the interplanetary magnetic field (IMF) and abrupt dynamic pressure changes. In the second event observed at � 1610 UT on 27 May 1998, an eastward moving TCV appeared in the noon sector in the Northern and Southern Hemispheres, with a timing delay of 2 to 3 min in the Southern Hemisphere. The solar wind source of this TCV is found again to be a TD, which causes a rapid IMF By negative turning and an abrupt enhancement of dynamic pressure. Analyses show that the TDs driving these events have their motional electric fields pointing toward the TDs and their normal vectors with large cone angles from the sunward direction. These TDs satisfy the conditions for the formation of a hot flow anomaly (HFA) at the bow shock. The sweeping motion across the magnetosphere of the intersection of the TD and the bow shock is found to be consistent with the observed TCV motion in each event. Magnetopause deformations due to HFAs can explain all the observed morphological features and the triggering process of these two MIEs. It is suggested, however, that bursty merging and/or pressure pulses would reinforce the processes produced by the HFAs, since the TDs are usually accompanied by both abrupt IMF changes and pressure enhancements. Consequently, it seems reasonable to conclude that the integrated processes of HFA, bursty magnetic field merging, and pressure pulses produce the evolution of these MIEs and TCVs. INDEX TERMS: 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 2708 Magnetospheric Physics: Current systems (2409); 2463 Ionosphere: Plasma convection; KEYWORDS: traveling convection vortex, magnetic impulse event, interplanetary tangential discontinuity

Large geomagnetically induced currents (GICs) triggered by extreme space weather events are now regarded as one of the serious natural threats to the modern electrified society. The risk is described in detail in High-Impact, Low-Frequency Event Risk, A Jointly-Commissioned Summary Report of the North American Electric Reliability Corporation and the US Department of Energy's November 2009 Workshop, June 2010. For example, the March 13-14,1989 storm caused a large-scale blackout affecting about 6 million people in Quebec, Canada, and resulting in substantial economic losses in Canada and the USA (Bolduc 2002). Therefore, European and North American nations have invested in GIC research such as the Solar Shield project in the USA (Pulkkinen et al. 2009, 2015a). In 2015, the Japanese government (Ministry of Economy, Trade and Industry, METI) acknowledged the importance of GIC research in Japan. After reviewing the serious damages caused by the 2011 Tohoku-Oki earthquake, METI recognized the potential risk to the electric power grid posed by extreme space weather. During extreme events, GICs can be concerning even in mid- and low-latitude countries and have become a global issue.

Solar energetic particles (SEPs) are one of the extreme space weather phenomena. A huge SEP event increases the radiation dose received by aircrews, who should be warned of such events as early as possible. We developed a warning system for aviation exposure to SEPs. This article describes one component of the system, which calculates the temporal evolution of the SEP intensity and the spectrum immediately outside the terrestrial magnetosphere. To achieve this, we performed numerical simulations of SEP transport in interplanetary space, in which interplanetary SEP transport is described by the focused transport equation. We developed a new simulation code to solve the equation using a set of stochastic differential equations. In the code, the focused transport equation is expressed in a magnetic field line coordinate system, which is a non-orthogonal curvilinear coordinate system. An inverse Gaussian distribution is employed as the injection profile of SEPs at an inner boundary located near the Sun. We applied the simulation to observed SEP events as a validation test. The results show that our simulation can closely reproduce observational data for the temporal evolution of particle intensity. By employing the code, we developed the WArning System for AVIation Exposure to Solar energetic particles (WASAVIES)., 23 pages, 11 figures, accepted for publication in Earth, Planets and Space

The Tenth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper atmospheric sciences, Wed. 4 Dec. / Institute of Statistics and Mathematics (ISM) Seminar room 2 (D304) (3rd floor)

We propose an emergency alert framework for geomagnetically induced currents (GICs), based on the empirically extreme values and theoretical upper limits of the solar wind parameters and of dB/dt, the time derivative of magnetic field variations at ground. We expect this framework to be useful for preparing against extreme events. Our analysis is based on a review of various papers, including those presented during Extreme Space Weather Workshops held in Japan in 2011, 2012, 2013, and 2014. Large-amplitude dB/dt values are the major cause of hazards associated with three different types of GICs: (1) slow dB/dt with ring current evolution (RC-type), (2) fast dB/dt associated with auroral electrojet activity (AE-type), and (3) transient dB/dt of sudden commencements (SC-type). We set “caution,” “warning,” and “emergency” alert levels during the main phase of superstorms with the peak Dst index of less than −300 nT (once per 10 years), −600 nT (once per 60 years), or −900 nT (once per 100 years), respectively. The extreme dB/dt values of the AE-type GICs are 2000, 4000, and 6000 nT/min at caution, warning, and emergency levels, respectively. For the SC-type GICs, a “transient alert” is also proposed for dB/dt values of 40 nT/s at low latitudes and 110 nT/s at high latitudes, especially when the solar energetic particle flux is unusually high.

Auroral microphysics still remains partly unexplored. Cutting-edge ground-based optical observations using scientific complementary metal-oxide semiconductor (sCMOS) cameras recently enabled us to observe the fine-scale morphology of bright aurora at magnetic zenith for a variety of rapidly varying features for long uninterrupted periods. We report two interesting examples of combinations of fine-scale rapidly varying auroral features as observed by the sCMOS cameras installed at Poker Flat Research Range (PFRR), Alaska, in February 2014. The first example shows that flickering rays and pulsating modulation simultaneously appeared at the middle of a surge in the pre-midnight sector. The second example shows localized flickering aurora associated with growing eddies at the poleward edge of an arc in the midnight sector.