Jaejin Lee

Analysis of GEO spacecraft anomalies: Space weather relationships

[1]xa0While numerous anomalies and failures of spacecraft have been reported since the beginning of the space age, space weather effects on modern spacecraft systems have been emphasized more and more with the increase of their complexity and capability. However, the relationship between space weather and commercial satellite anomalies has not been studied extensively. In this paper, we investigate the geostationary Earth orbit (GEO) satellite anomalies archived by Satellite News Digest during 1997–2009 in order to search for possible influences of space weather on the anomaly occurrences. We analyze spacecraft anomalies for the Kp index, local time, and season and then compare them with the tendencies of charged particles observed by Los Alamos National Laboratory (LANL) satellites. We obtain the following results: (1) there are good relationships between geomagnetic activity (as measured by the Kp index) and anomaly occurrences of the GEO satellites; (2) the satellite anomalies occurred mainly in the midnight to morning sector; and (3) the anomalies are found more frequently in spring and fall than summer and winter. While we cannot fully explain how space weather is involved in producing such anomalies, our analysis of LANL data shows that low-energy (<100 keV) electrons have similar behaviors with spacecraft anomalies and implies the spacecraft charging might dominantly contribute to the GEO spacecraft anomalies reported in Satellite News Digest.

Magnetic signatures and conjugate features of low‐latitude plasma blobs as observed by the CHAMP satellite

[1]xa0We investigated the magnetic signatures of plasma blobs, as observed by the CHAMP satellite. In total, we have identified 52 blobs with clear density enhancements and magnetic signatures. In each blob the magnetic field strength was depressed, and the components perpendicular to the main magnetic field direction showed fluctuations. The variation in magnetic field strength implies that the enhanced plasma pressure is balanced by a magnetic pressure reduction, and the deflection in the perpendicular components indicates the presence of field-aligned currents. Both characteristics are consistent with bubble magnetic signatures. Concurrent observations of CHAMP (at ∼350 km altitude) with ROCSAT-1 (∼600 km), STSAT-1 (∼680 km), and DMSP F15 (∼840 km) strongly suggest that the blobs have a field-aligned structure spanning several hundred kilometers. We also investigated the seasonal/longitudinal distribution of the detected blob events. From that a rough coincidence with the bubble occurrence distribution is found, although the blob distribution is biased heavily toward the winter hemisphere. Plasma blob encounters at CHAMP altitude are quite frequent, even after local midnight. We believe that our results corroborate the close relationship between equatorial plasma bubbles and blobs.

The 27‐day modulation of the low‐latitude ionosphere during a solar maximum

[1]xa0The 27-day solar modulation of the low-latitude ionosphere is investigated for the solar maximum period using in situ satellite measurement data and the total electron contents (TEC) estimated from the satellite signals of the global positioning system (GPS). Whereas the density and temperature of the topside ionosphere observed at an altitude of 685 km manifest delayed responses to the 27-day variations in the daily F10.7 values, similar to those previously reported for an altitude of 840 km, the nighttime-scale height, obtained by comparing the densities observed at altitudes of 685 and 840 km at similar local times, was shown to vary in accordance with the changes in F10.7 with the same time delay. The oxygen ion fraction measured at an altitude of 840 km shows a similar response regardless of the local time. Moreover, the GPS TEC values, most of which come from the F peak region, also exhibit similar delayed modulations in accordance with solar rotation. The TEC value correlates well with the thermospheric neutral density, and both are observed to be modulated with the solar rotation with time delay, especially when a long-term variation is filtered out. The present result confirms that the whole thermospheric and ionospheric system is modulated with solar rotation.

Local time‐dependent Pi2 frequencies confirmed by simultaneous observations from THEMIS probes in the inner magnetosphere and at low‐latitude ground stations

[1]xa0Using electric and magnetic field data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) fast mode waves away from midnight. probes (TH-A, TH-D, and TH-E) acquired in the inner magnetosphere (Lu2009 0.6) with BOH Pi2s and radially standing fast mode structures. Thus, these fast mode waves are explained by plasmaspheric resonance. On the duskside, however, few events at THEMIS probes had high coherence with BOH Pi2s. Furthermore, the THEMIS probe data showed no evidence of Pi2 signals at 9.0–18.0 MLT, which is consistent with previous studies. Most of the high-coherence events were detected when the local time separation between the THEMIS probes and BOH was less than 3xa0h. These observations suggest that Pi2 wave energy is lost as it propagates azimuthally from a source region localized in longitude. From longitudinally separated simultaneous multipoint observations at THEMIS probes and BOH and HER stations, we found that the Pi2 frequency varies with longitude both in space and on the ground. This implies that although plasmaspheric fast mode waves establish a standing wave structure on a given meridional plane, their frequency changes with longitude if the plasmasphere is not axisymmetric. Finally, we show that a low-latitude daytime Pi2 is not a fast mode wave propagating to the dayside through the magnetosphere.

Characteristics of ground-level enhancement–associated solar flares, coronal mass ejections, and solar energetic particles

[1]xa0Ground-level enhancements (GLEs) are sudden, sharp, and short-lived increases in cosmic ray intensities registered by neutron monitors. These enhancements are known to take place during powerful solar eruptions. In the present investigation, the cosmic ray intensities registered by the Oulu neutron monitor have been studied for the period between January 1979 and July 2009. Over this span of time, increase rates of 32 GLEs have been deduced. In addition, we have studied characteristics of the 32 event-associated solar flares, coronal mass ejections (CMEs), and solar energetic particle (SEP) fluxes. We found that all of the 32 GLEs were associated with solar flares, CMEs, and SEP fluxes. Approximately 82% of the events were associated with X-class flares. Most of the flares that were associated with GLEs of increase rates >10% originated from the active regions located on the southwest hemisphere of the Sun. The average speed (1726.17 km/s) of GLE-associated CMEs was much faster than the average speed (423.39 km/s) of non-GLE-associated CMEs. It also became evident that ∼67% GLEs were associated with very fast (>1500 km/s) CMEs. Although a GLE event is often associated with a fast CME, this alone does not necessarily cause the enhancement. Solar flares with strong optical signatures may sometimes cause GLE. High SEP fluxes often seem to be responsible for causing GLEs as the correlation with SEP fluxes implies.

Equatorial plasma bubbles with enhanced ion and electron temperatures

[1]xa0While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period between 2000 and 2001. The oxygen ion fraction inside the BETs, which was no lower than that of the ambient ionosphere, was similar to the case of ordinary low-temperature EPBs. These observations indicate that the BETs and low-temperature EPBs detected on the topside were produced by the upward drift of low-density plasma from lower altitudes. The feature that distinguishes BETs from normal EPBs is the occurrence of an unusually fast poleward field-aligned plasma flow relative to the ambient plasma. The BETs occurred preferentially around geomagnetic latitudes of 10° in the summer hemisphere, where the ambient ion and electron temperatures are lower than those in the conjugate winter hemisphere. The occurrence of BETs did not show any notable dependence on geomagnetic activities. The characteristics of the BETs suggest that the BETs were produced by adiabatic plasma heating associated with a fast poleward oxygen ion transport along magnetic flux tubes.

SIMULTANEOUS OBSERVATION OF A HOT EXPLOSION BY NST AND IRIS

We present the first simultaneous observations of so-called “hot explosions” in the cool atmosphere of the Sun made by the New Solar Telescope (NST) of Big Bear Solar Observatory and the Interface Region Imaging Spectrograph (IRIS) in space. The data were obtained during the joint IRIS-NST observations on 2014 July 30. The explosion of interest started around 19:20 UT and lasted for about 10 minutes. Our findings are as follows: (1) the IRIS brightening was observed in three channels of slit-jaw images, which cover the temperature range from 4000 to 80,000 K; (2) during the brightening, the Si iv emission profile showed a double-peaked shape with highly blue and redshifted components ( and 80 km s−1); (3) wing brightening occurred in Hα and Ca ii 8542 Å bands and related surges were observed in both bands of the NST Fast Imaging Solar Spectrograph (FISS) instrument; (4) the elongated granule, seen in NST TiO data, is clear evidence of the emergence of positive flux to trigger the hot explosion; (5) the brightening in Solar Dynamics Observatory/Atmospheric Imaging Assembly 1600 Å images is quite consistent with the IRIS brightening. These observations suggest that our event is a hot explosion that occurred in the cool atmosphere of the Sun. In addition, our event appeared as an Ellerman bomb (EB) in the wing of Hα, although its intensity is weak and the vertical extent of the brightening seems to be relatively high compared with the typical EBs.

Van Allen Probes Observations of Electromagnetic Ion Cyclotron Waves Triggered by Enhanced Solar Wind Dynamic Pressure

Magnetospheric compression due to impact of enhanced solar wind dynamic pressure Pdyn has long been considered as one of the generation mechanisms of electromagnetic ion cyclotron (EMIC) waves. With the Van Allen Probe-A observations, we identify three EMIC wave events that are triggered by Pdyn enhancements under prolonged northward IMF quiet time preconditions. They are in contrast to one another in a few aspects. Event 1 occurs in the middle of continuously increasing Pdyn while Van Allen Probe-A is located outside the plasmapause at post-midnight and near the equator (magnetic latitude (MLAT)u2009~u2009-3o). Event 2 occurs by a sharp Pdyn pulse impact while Van Allen Probe-A is located inside the plasmapause in the dawn sector and rather away from the equator (MLATu2009~u200912o). Event 3 is characterized by amplification of a pre-existing EMIC wave by a sharp Pdyn pulse impact while Van Allen Probe-A is located outside the plasmapause at noon and rather away from the equator (MLATu2009~u2009-15o). These three events represent various situations where EMIC waves can be triggered by Pdyn increases. Several common features are also found among the three events. (i) The strongest wave is found just above the He+ gyrofrequency. (ii) The waves are nearly linearly polarized with a rather oblique propagation direction (~28o to ~39o on average). (iii) The proton fluxes increase in immediate response to the Pdyn impact, most significantly in tens of keV energy, corresponding to the proton resonant energy. (iv) The temperature anisotropy with T⊥u2009>u2009T|| is seen in the resonant energy for all the events, although its increase by the Pdyn impact is not necessarily always significant. The last two points (iii) and (iv) may imply that, in addition to the temperature anisotropy, the increase of the resonant protons must have played a critical role in triggering the EMIC waves by the enhanced Pdyn impact.

The global context of the 14 November 2012 storm event

From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ∼20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

Spectral observations of FUV auroral arcs and comparison with inverted-V precipitating electrons

[1] This paper presents first simultaneous observations of far ultraviolet (FUV) spectra of discrete and diffuse auroras, together with precipitating electrons measured on the same spacecraft, to emphasize the importance of high-resolution FUV images for accurate estimation of precipitating energy flux in the auroral region. An FUV spectrograph image with ∼2 km × 3 km resolution show small-scale features were embedded in the auroral arcs. Comparison of peak energies of inverted-V events with the corresponding FUV spectra shows that the observed long band N 2 Lyman-Birge-Hopfield (LBH) emission (long LBH band (LBHL): 160.0-171.5 nm) varied more sensitively to the peak energies compared to the short band. Comparison of the inverted-V structures and their energy fluxes with the LBHL irradiance for ∼10 km × 10 km regions show they are well correlated for peak energy >2 keV. When the data are averaged over a larger area (70 km × ∼140 km), on the other hand, the LBHL irradiance becomes less bright for the corresponding electron energy flux due to the contribution from the low-intensity background diffuse aurora produced by secondary electrons. This study demonstrates a reliable relationship between precipitating electron energy flux and LBHL intensity is obtained only if the precipitating region and FUV intensity are locally matched with a scale of less than 10 km corresponding to the size of discrete auroras.