Description: We report the results of detailed mineralogical investigations by analytical scanning and transmission electron microscopy of particle RA-QD02-0115 recovered from the surface of asteroid 25143 Itokawa. We divided the 65 μm × 50 μm small particle into eight individual subsample slices via the focused ion beam method. The particle dominantly consists of olivine and contains inclusions of merrillite, tetrataenite/taenite, troilite, chromite, kamacite, and Cl-bearing apatite (in approx. decreasing order of frequency). The composition of olivine (fayalite 29.8 ± 1.1 mol% and molar Fe/Mn ratio of 57 ± 2) as well as the Ni-rich metal assemblage indicates an LL-type affinity in accord with previous classifications. The particle shows effects of solar wind irradiation on one of its principal faces. Olivine developed an approximately 34 nm wide rim composed of low-angle misoriented, nanometer-sized crystallites accompanied by a small amount of amorphous material. Exposed troilite developed a 4 to 8 nm wide polycrystalline rim with large-angle misorientations of the iron sulfide nanocrystallites. Merrilite shows marginally discernable surface damage but was too unstable under the electron beam for a detailed study. Cl-bearing apatite was found fully crystalline with no discernable rim structure. We discuss the unusual polycrystalline nature of the olivine rim in terms of possible annealing and recrystallization effects, which may have occurred during periods of time when Itokawa’s surface temperature may have been warmer due to closer perihelion distances. Model calculations show that the dynamical orbital evolution of near-Earth asteroids could lead to complex space weathering processes, arising from the competing interplay between irradiation-induced damaging and thermally driven annealing.

Description: No description available

Description: The ionosphere plays an important role in GNSS applications because it influences radio wave propagation. The ionospheric delay is the biggest error source for satellite navigation signals, but it can be directly measured and mitigated using dual-frequency GNSS receivers. However, the GNSS signal fades because of electron density gradients and irregularities in the ionosphere, decreasing the operational performance of navigation systems. Recently, several models were developed to reproduce the ionospheric fluctuations and scintillation activity under different geophysical conditions, but these models were calibrated with data sets without GNSS-derived experimental total electron content (TEC) data. There is a great demand for a proper model of ionospheric irregularity specification based on GNSS TEC measurements. In this work, we use data from the permanent GNSS network to develop the empirical model of the ionospheric irregularities over the Northern Hemisphere. As initial data, we used the daily dependences of the rate of TEC index (ROTI) as a function of geomagnetic local time on the specific grid. The ROTI maps allow us to estimate the overall fluctuation activity and the auroral oval evolution. The irregularities of the southern oval border were determined with the ROTI. This paper presents the correlation between the Kp geomagnetic index and parameters that characterized the activity of the ionosphere irregularities in 2010 to 2013.

Description: We report the results of detailed mineralogical investigations by analytical scanning and transmission electron microscopy of particle RA-QD02-0115 recovered from the surface of asteroid 25143 Itokawa. We divided the 65 ?m???50 ?m small particle into eight individual subsample slices via the focused ion beam method. The particle dominantly consists of olivine and contains inclusions of merrillite, tetrataenite/taenite, troilite, chromite, kamacite, and Cl-bearing apatite (in approx. decreasing order of frequency). The composition of olivine (fayalite 29.8???1.1 mol% and molar Fe/Mn ratio of 57???2) as well as the Ni-rich metal assemblage indicates an LL-type affinity in accord with previous classifications. The particle shows effects of solar wind irradiation on one of its principal faces. Olivine developed an approximately 34 nm wide rim composed of low-angle misoriented, nanometer-sized crystallites accompanied by a small amount of amorphous material. Exposed troilite developed a 4 to 8 nm wide polycrystalline rim with large-angle misorientations of the iron sulfide nanocrystallites. Merrilite shows marginally discernable surface damage but was too unstable under the electron beam for a detailed study. Cl-bearing apatite was found fully crystalline with no discernable rim structure. We discuss the unusual polycrystalline nature of the olivine rim in terms of possible annealing and recrystallization effects, which may have occurred during periods of time when Itokawa?s surface temperature may have been warmer due to closer perihelion distances. Model calculations show that the dynamical orbital evolution of near-Earth asteroids could lead to complex space weathering processes, arising from the competing interplay between irradiation-induced damaging and thermally driven annealing.

Description: The ionosphere plays an important role in GNSS applications because it influences radio wave propagation. The ionospheric delay is the biggest error source for satellite navigation signals, but it can be directly measured and mitigated using dual-frequency GNSS receivers. However, the GNSS signal fades because of electron density gradients and irregularities in the ionosphere, decreasing the operational performance of navigation systems. Recently, several models were developed to reproduce the ionospheric fluctuations and scintillation activity under different geophysical conditions, but these models were calibrated with data sets without GNSS-derived experimental total electron content (TEC) data. There is a great demand for a proper model of ionospheric irregularity specification based on GNSS TEC measurements. In this work, we use data from the permanent GNSS network to develop the empirical model of the ionospheric irregularities over the Northern Hemisphere. As initial data, we used the daily dependences of the rate of TEC index (ROTI) as a function of geomagnetic local time on the specific grid. The ROTI maps allow us to estimate the overall fluctuation activity and the auroral oval evolution. The irregularities of the southern oval border were determined with the ROTI. This paper presents the correlation between the Kp geomagnetic index and parameters that characterized the activity of the ionosphere irregularities in 2010 to 2013.

Description: Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 to 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10- to 12-year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 to 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53% of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 to 2013 and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100-km altitude and residual Sq amplitude showed an anti-correlation for about 71% of the geomagnetic stations. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.

Description: Being stimulated by the previously reported large amplitude (202 nT at Kakioka) geomagnetic sudden commencement (SC) on 24 March 1991, we searched larger amplitude SCs in the past. We tried to collect old magnetograms and used the list of SC observed at Kakioka (27.5? gm.lat.) for the period 1924 to 2013 and Colaba (10.5?)-Alibag (10.3?) for 1868 to 1967. We found that the largest amplitude SC occurred on 24 March (the same day as 1991 SC), 1940. The H-component amplitude is larger than 273 nT at Kakioka and 310 nT at Alibag. We could also obtain the copy of the magnetogram of Cape Town (?33.3?) which shows 164 nT amplitude. The statistical analysis shows that the occurrence rate of SCs is less than 5% for amplitude larger than 50 nT and less than 1% for amplitude larger than 100 nT at both Kakioka and Alibag. Large amplitude SCs tend to occur during the declining phase of the solar activity. Finally, we discussed the possible increase of the dynamic pressure associated with the interplanetary shock causing the largest SC.

Description: We investigate the aspect angle sensitivity of the pump-induced artificial optical emissions in the ionosphere over the European Incoherent Scatter Scientific Association (EISCAT) high-frequency transmitter facility at Ramfjord, Norway, as a function of the pump beam launch angle relative to the magnetic field line direction. The highest intensity optical emissions occur when the pump beam pointing direction is in the magnetic zenith (approximately 12? S of local zenith). For pump beam directions further north from field aligned, the optical emission intensity decreases for the same pump power. In addition, the primary photon-emitting region becomes displaced towards the magnetic zenith relative to the pump beam and for larger aspect angles, the brightest emissions were found to be outside the ?3-dB pump beam width. The Cooperative UK Twin-Located Auroral Sounding System (CUTLASS) coherent scatter high-frequency (HF) radar detected a quasi-constant level of backscatter power from the pumped ionosphere, indicating that saturated striations were formed for all pump beam directions. This indicates that the presence of upper-hybrid resonance is not sufficient to explain the angular sensitivity of the optical emissions.

Description: We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the aim of imaging 3-D distribution of fluids in the crust for its volcanic and seismogenic implications. The data were recorded at 77 sites in total: 30 sites are new and are arranged in an approximately 5???5 km grid whereas the remaining older sites constitute two separate east-west profiles. We ran a 3-D inversion using full components of impedance tensors in the period range between 0.13 and 400 s. The resulting model showed that a sub-vertical conductor exists a few kilometers below Naruko volcano. The conductor extends from the surface of the volcano and dips towards the south, away from the volcano towards the backbone range. High levels of seismicity are observed in the upper crust above and around the conductors. We suggest that the seismicity is fluid driven and that a fluid trap is created by the precipitation of quartz owing to a reduction in solubility at shallow depth. The Quaternary volcanic front is characterized by a sharp resistivity contrast and a high-resistivity zone and extends 10 to 15 km towards the east. A fore-arc conductor was observed at mid-crustal levels even farther towards the east. The sub-vertical conductors along the arc and the fore-arc conductor have resistivities of 1 to 10 ?m. Assuming a Hashin-Shtrikman model with saline fluids of 0.1-?m resistivity, a porosity of 1.5% to 15% is required to explain the observed conductive anomalies.

Description: The ionosonde observations made at 5-min intervals at the Indian dip equatorial station Tirunelveli (8.7?N, 77.8?E geographic; 1.1?N dip latitude) from March 2008 to February 2009 during the extended solar minimum period are used to study the interlink between equatorial spread F (ESF) and satellite traces (STs) which are assumed to represent tilts in the bottomside iso-electron density surfaces probably caused by large-scale wave-like structures (LSWS). The data show different patterns of ESF onset in the bottomside F region, which are illustrated through examples. In addition, the statistics of occurrence of ST and its relation to the formation of ESF are studied. The results indicate that (1) the zonally drifting ESF irregularities can be differentiated from those forming over the observing station. (2) Nearly half of the ESF events were preceded by ST. (3) In about 30% of the cases of occurrence of ST, ESF was not formed afterwards implying that LSWS may not always lead to ESF. (4) The percentage of ESF following ST was high in summer and increased with the time of the night. (5) Following the first occurrence of ST, the ESF onset was delayed by about 30 min on the average suggesting that ST may be used as a precursor of ESF. (6) Pre-reversal enhancement (PRE) of upward plasma drift was found insignificant during the period of study. The trapping of high-frequency radio waves between the E and F regions during intense sporadic E is also illustrated.