Enhancement of OI 630.0 nm emission at mid-latitudes during an intense magnetic storm

All-sky camera (ASC), Global Positioning System (GPS), and ionosonde measurements were used to investigate the upper atmospheric variations at mid-latitude during the strong geomagnetic storm on October 29–31, 2003. An arc-shaped 630.0 nm emission was observed in the northern sky on all-sky images taken at Mt. Bohyun (36.2°N, 128.9°E, GMLAT=29°N) in Korea during 17:48–8:58 UT in the main phase of the geomagnetic storm on October 29. The NmF₂ and hmF₂ from the ionosonde show strong disturbances at that time. The vertical profiles of electron densities, calculated by the ionospheric tomographic method using ground-based GPS slant total electron contents measurements, show the largest value at ∼440 km height at 18:30 UT on October 29 when the enhancements of OI 630.0 nm emission were observed. The arc-shaped red emission observed during the main phase of the magnetic storm is likely a low-latitude red aurora due to its short duration of ∼1 h. The result implies that the plasmapause was at L=1.4–1.6 during the geomagnetic storm. The fact that the arc did not follow a constant L-value appears to suggest that neutral precipitation and a traveling ionospheric disturbance could also be the cause of the arc.     

On the electric field at the tip of dart leaders in lightning flashes

The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to values larger than the critical electric field necessary for the initiation of cold electron runaway in low-density air comprising the channel. These results are in support of the hypothesis that cold runaway electron breakdown may play a role in the emission of X-ray bursts by dart leaders. The calculations also show that the peak power dissipated by a typical dart leader is about 300–500 MW/m and the energy dissipated within the first 10 μs or so is about 500–600 J/m. Furthermore, the minimum resistance and the maximum radius of the core of a typical dart leader are estimated to be about 3 Ω/m and 0.003 m, respectively.     

Variations in the near-surface atmospheric electric field at high latitudes and ionospheric potential during geomagnetic perturbations

We have analyzed variations in the near-surface atmospheric electric field (Ez) normalized to their daily averages that were simultaneously observed in different high-latitude regions at moderate geomagnetic activity (Kp ∼ 3). The Ez data were measured under fair weather conditions at the Vostok Antarctic research station (Φ′ = −83.5°) in the southern polar cap and at the Hornsund Arctic observatory (Φ′ = 74.0°) on Svalbard close to the polar boundary of the auroral oval in the Northern Hemisphere. It is established that variations in the atmospheric electric field in the polar cap region at the Vostok station are controlled (the correlation coefficient R ∼ 0.7–0.9) by variations in the overhead ionospheric potential. The situation at the Hornsund observatory is more complicated. During intervals when Hornsund occurred below the westward electrojet, the correlation was typically positive with R ∼ 0.60–0.85; however, while this observatory was in the region of the eastern electrojet, the correlation could be negative with R ∼ 0.7–0.8. Normally, during such periods, the westward electrojet was detected polarwards of Hornsund while, according to the SuperDARN radar data, the observatory was located below the negative vortex of the polar ionospheric convection.     

Age estimation of the deposition of the cretaceous Upper Sandstones and a later remagnetization event,from Hirna area,SE Ethiopia

Outcrops of the Cretaceous Upper sandstone formation some 375 km to the East of Addis Ababa on the motor Highway to Harar was paleomagnetically investigated. About seventy core samples were collected at various stratigraphic levels from 250–300 meters thick sedimentary formation. After standard sample preparations in the laboratory the resulting specimens were subjected to routine paleomagnetic demagnetization protocol. In the first steps of demagnetizations process the recent and viscous magnetizations were removed by heating until a temperature of level of 300 °C. Further demagnetization of the samples resulted in the isolation of the final magnetization with stable line segments that is directed towards the origin, which is interpreted as Characteristic Remanent Magnetization (ChRM). Rock – magnetic experiments have identified goethite (αFeOOH), hematite (αFe₂O₃), detritial hematite, and magnetite as the magnetic mineral phases carrying the remanence. The ChRM identified resulted in an average value of (D_s = 0.5°, I_s = ?0.7°, α₉₅ = 4.3°, N = 34) for the red sandstones while an average value of (D_s = 335.8°, I_s = ?31.8°, α₉₅ = 4.7°, N = 14) for the limestone intercalations. The former ChRM in the red sandstone is determined to be secondary while the latter ChRM is known to be primary. Comparison of these directional results and their pole equivalents with the African plate Apparent Polar Wander Path curve established by Besse and Courtillot (2003) give ages of between 115–130 Million years for the limestone intercalation and ages of 30 million years for red sandstone unit. These are interpreted respectively as estimates of the age of deposition and a later remagnetization respectively.     

Nighttime E region plasma irregularities over an equatorial station Trivandrum

In situ measurements of electron density were made over Trivandrum (8.5°N, 76.9°E) during nighttime to study E-region plasma density irregularities. Irregularities, with vertical scale sizes from a few km to 15 cm, were detected during rocket ascent and descent. Electron density profiles during ascent and descent of an earlier nighttime rocket flight from Trivandrum are also presented. Some of the important results are as follows: (i) horizontal gradients in electron density exist in 110–120 km region with horizontal scale size of at least 40 km, (ii) based on the presence/absence of electron density structures during ascent and descent of both flights, the horizontal distance over which the gradient drift instability operates is found to be at least 80 km and 90 km, for both the flights, (iii) observed irregularities in regions of negative density gradient are suggested to be produced through the gradient drift instability (GDI) driven by vertical polarization electric field as well as by electric field produced through wind shears and those in positive gradient regions by wind driven GDI, (iv) largest irregularity amplitude (≈30%) was associated with steepest gradients and so was the presence of smallest vertical scale sizes (12 m to 15 cm), which were absent at other altitudes, (v) the spectral index of irregularities was in the range of ?2.2±0.2 for large scales (few kilometers>λ>50 m), ?3.25±0.25 for medium scales (50 m>λ>10 m) and ?2.6±0.1 for smaller scales (10 m>λ>1 m) and (vi) irregularities in large and medium scales are expected to be produced directly through GDI and the small and sum-meter scales through non-linear GDI.     

Thunderstorm-associated responses in the vertical motion of the mid-latitude F-region ionosphere

Mid-latitude Digisonde Doppler velocities, auroral electrojet (AE) indices and cloud-to-ground (CG) lightning strokes during August 2003–2004 were used to study the perturbations in the F-region vertical drift associated with terrestrial thunderstorms. A superposed epoch analysis (SEA) showed that the F-region vertical drifts V_z had a net descent of ～0.6 m s^?1 peaking ～3 h after lightning. Stronger downward perturbations of up to ～0.9 m s^?1 were observed in the afternoon on the day prior to lightning days. The perturbations were less significant on the day after and insignificant during the remaining intervals up to 144 h on either side of the lightning. The stronger responses on the day before are consistent with causality because the lightning times were merely proxies for the physical mechanisms involved. The actual causes are unclear, but we discuss the possible roles of lightning-induced ionisation enhancements, intense electric fields penetrating upward from electrified clouds, and atmospheric gravity waves (AGWs) radiated from thunderstorms or from the accompanying tropospheric fronts. There is no doubt that the behaviour of the mid-latitude F-region is controlled by the thermospheric winds and the solar wind-magnetosphere electrical generators, but our results suggest that electrified clouds also account for a significant, albeit relatively small component of the ionospheric variability.     

Paleomagnetism of the Late Cretaceous ignimbrite from the Okhotsk-Chukotka Volcanic Belt,Kolyma-Omolon Composite Terrane: Tectonic implications

New Late Cretaceous paleomagnetic results from the Okhotsk-Chukotka Volcanic Belt in the Kolyma-Omolon Composite Terrane yield stable and consistent remanent directions. The Late Cretaceous (86–81 Ma) ignimbrites from the Kholchan and Ola suites were sampled at 19 sites in the Magadan area (60.4° N, 151.0° E). We isolated the characteristic paleomagnetic directions from 16 sampled sites using an alternating field demagnetization procedure. The primary nature of these directions is ascertained by dual polarities and positive fold tests. A tilt-corrected mean direction (D = 42.8°, I = 84.7°, k = 46.0, α₉₅ = 10.0°) yields a paleomagnetic pole of 66.7° N, 168.5° E (A₉₅ = 18.8°) which appears almost identical to the 90–67 Ma pole reported from the Lake El’gygytgyn area of the Okhotsk-Chukotka Volcanic Belt (Chukotka Terrane). This consistency suggests that the Kolyma-Omolon Composite Terrane and Chukotka Terrane has acted as a single tectonic unit since 80 Ma without any significant internal deformation. Accordingly, we calculate a combined 80 Ma characteristic paleomagnetic pole (Long. = 164.7° E, Lat. = 68.0°, A₉₅ = 10.9°, N = 12) for the Kolyma-Omolon-Chukotka Block which falls 16.5–17.5° south of the same age poles from Europe and East Asia. We ascribe this discrepancy in pole positions to tectonic activity in the area and infer a southward displacement of 1640 ± 1380 km for the Kolyma-Omolon-Chukotka Block with respect to the North American and Eurasian blocks since 80 Ma; more than 260 km of it is attributed to tectonic displacement in the Arctic Ocean due to the opening of the Canadian Basin.     

The effects of thunderstorm-generated atmospheric gravity waves on mid-latitude F-region drifts

Superposed epoch analysis (SEA) was used to examine ionospheric drift velocities measured by a digital ionosonde located at the mid-latitude station Bundoora (145.1°E, 37.7°S geographic), near Melbourne. The control times for the SEA were the times of cloud-to-ground (CG) lightning strokes measured from August 2003 to August 2004 by the World Wide Lightning Location Network (WWLLN). Statistically, regions of concentrated lightning activity migrated from west to east across Bundoora, and the stroke frequency was higher the day prior the activity reached the station, and lower on the day after it passed to the east. For the SEA, CG strokes were separated into four directional quadrants centred on north, south, east and west. No SEA results are shown for the south quadrant due to the relatively low detection frequency of strokes across the Southern Ocean (6% of all events). The strongest downward vertical perturbations in F-region drifts, ?4.5 m s^?1, were found for lightning located towards the west during ?30 to ?16 h (i.e., the afternoon prior the activity passed near the station at t=0 h). The downward perturbation decreased in amplitude to ?1.5 m s^?1 for lightning located towards the north during ?6–+6 h, and was weakest (?0.7 m s^?1) for lightning located towards the east during +16–+28 h (i.e., the next afternoon). There were directionally consistent perturbations in the drift azimuths associated with the lightning located in their respective quadrants; lightning located to the west of the station caused eastward azimuth enhancements, northward lightning caused southward enhancements, and eastward lightning caused westward enhancements. Velocity magnitudes and fluctuations tended to increase during the passage of lightning. The observed responses were stronger when the SEA was performed with data selected using time windows of <2 min on either side of each lightning stroke. However, they persisted at longer time scales and were strong when thunderstorm onsets (instead of lightning times) were used as controls. Our results can be explained by thunderstorm-generated atmospheric gravity waves (AGWs) which subsequently gave rise to medium-scale travelling ionospheric disturbances (MSTIDs), with the lightning strokes acting merely as a proxy for this coupling. The prevailing thermospheric winds were flowing from east to west across the study region, and may have acted as a directional ‘filter’ for the MSTIDs, allowing waves generated in the west quadrant to reach the station and preventing those generated in other quadrants. Displacement of the MSTIDs in the direction anti-parallel to mean neutral wind flow has been observed by (Waldock, J.A., Jones, T.B., 1986. HF Doppler observations of medium-scale travelling ionospheric disturbances at mid-latitudes. Journal of atmospheric and terrestrial physics 48(3), 245–260).     

The coherence between the IMF and high-latitude ionospheric flows: The dayside magnetosphere–ionosphere low-pass filter

This study seeks to establish a new system characteristic describing dayside convective flows in the coupled magnetosphere–ionosphere: the low-pass filter function through which interplanetary magnetic field (IMF) fluctuations are processed as they are communicated from the magnetopause to the high-latitude ionosphere near local noon. In doing so, this study confirms that variations in the ionospheric flows at high-latitudes near local noon are well correlated with variations in the IMF orientation and magnitude on short timescales. We construct the filter function by comparing time series of the ionospheric equivalent flows at a fixed location at magnetic local noon and 80° latitude with time series of the IMF. The coherence spectra of these two parameters—averaged over 330 h of comparison—indicate that there is a low-pass cutoff in the ionospheric response to IMF driving at a periods shorter than 20 min (frequencies higher than 0.8 mHz). When there is sufficient power in the IMF fluctuations, this cutoff is relatively sharp—the coherence drops by roughly a factor of three between the periods 32 and 21 min (0.5 and 0.8 mHz). The results also show that on average the coherence between the east–west component of the equivalent flows and IMF B_y tends to be less than the coherence between the north–south component of the equivalent flows and IMF B_z.     

Whistlers observed at low-latitude ground-based VLF facility in Fiji

The propagation features of nighttime whistlers to low-latitude station, Suva (−18.2°, 178.3°, geomag. lat. −22.1°, geomag. long. 253.5°, L=1.15), Fiji, from preliminary observations made during the period from September 2003–2005, are reported. The observations of ELF–VLF signals commenced in September 2003 using the VLF set-up of World Wide Lightning Location Network at our station. The whistlers were observed during the severe magnetic storm of 20–22 November 2003 and moderate magnetic storm of 17–19 July 2005. A whistler with dispersion D=12.7 s^1/2 occurred on 22 November at 00:11 h LT. On 20 July at 01:00 h LT, a short whistler with dispersion D=20.9 s^1/2 and two whistler events having two-component whistlers with D=15.8, 16.7 s^1/2 and 16.7, 17.3 s^1/2 were observed. Non-ducted pro-longitudinal mode of the whistler propagation supported by negative latitudinal electron density gradients in the ionosphere that are enhanced by magnetic storms, seems most likely mode of propagation for the whistlers with dispersion of 12.7–17.3 s^1/2 to this low-latitude station.     

The November 2004 superstorm: Comparison of low-latitude TEC observations with LLIONS model results

We investigate the effects of penetration electric fields, meridional thermospheric neutral winds, and composition perturbation zones (CPZs) on the distribution of low-latitude plasma during the 7–11 November 2004 geomagnetic superstorm. The impact on low-latitude plasma was assessed using total electron content (TEC) measurements from a latitudinally distributed array of ground-based GPS receivers in South America. Jicamarca Radio Observatory incoherent scatter radar measurements of vertical E×B drift are used in combination with the Low-Latitude IONospheric Sector (LLIONS) model to examine how penetration electric fields and meridional neutral winds shape low-latitude TEC. It is found that superfountain conditions pertain between ～1900 and 2100 UT on 9 November, creating enhanced equatorial ionization anomaly (EIA) crests at ±20° geomagnetic latitude. Large-amplitude and/or long-duration changes in the electric field were found to produce significant changes in EIA plasma density and latitudinal location, with a delay time of ～2–2.5 h. Superfountain drifts were primarily responsible for EIA TEC levels; meridional winds were needed only to create hemispherical crest TEC asymmetries. The [O/N₂] density ratio (derived from the GUVI instrument, flown on the TIMED satellite) and measurements of total atmospheric density (from the GRACE satellites), combined with TEC measurements, yield information regarding a likely CPZ that appeared on 10 November, suppressing TEC for over 16 h.     

Spectacular low- and mid-latitude electrical fields and neutral winds during a superstorm

In November 2004, a major magnetic storm occurred, a lengthy portion of which was recorded by the Upper Atmospheric Radar Chain. On the 9th and 10th, the Jicamarca Radar detected the highest magnitude penetrating electric fields (±3 mV/m) and vertical drifts (±120 m/s) ever seen at this premiere facility. These large and variable drifts were highly correlated with the interplanetary magnetic and electric fields and created a double F layer on the dayside and unusual TEC behavior throughout the low-latitude zone. These solar wind-induced drifts both suppressed and generated irregularities at the magnetic equator at different times. Large-scale thermospheric disturbances were generated by high-latitude heating and tracked through the middle- to low-latitude zones where both parallel and perpendicular plasma drifts created major ionospheric changes. The auroral oval was located at a magnetic L shell of about three for many hours.     

The current performance of the in situ 14C extraction line at ETH

We present the new ¹⁴C extraction line at ETH Zürich. This system is designed to extract in situ-produced cosmogenic ¹⁴C from terrestrial quartz samples, and to obtain pure CO₂ gas for analysis with a gas ion source Accelerator Mass Spectrometry (AMS) system. Samples are degassed at 1550–1600 °C without the use of a fluxing agent. Gas purification is achieved by a series of cryogenic traps and passage through hot Ag and Cu wool/mesh. Graphitization and, thus, sample dilution is not required. Tests to determine the CO₂ recovery after gas extraction and cleaning yielded consistently good recovery rates of >99.8% (n = 7). The ¹⁴C blank contribution from the all-metal tubing system is negligible. Our preliminary procedural blank estimate – deriving mostly from the hot extraction furnace – is <5 × 10^{5 14}C atoms. Extraction tests on two quartz samples by stepped-heating show a quantitative separation of atmospheric ¹⁴C at ≤500 °C from the in situ component above 1200 °C. Based on these data, we estimate to achieve a complete ¹⁴C extraction from a quartz sample.     

Variability of total electron content near the crest of the equatorial anomaly during moderate geomagnetic storms

The ionospheric responses to a large number (116) of moderate (?50≥D_st>?100 nT) geomagnetic storms distributed over the period (1980–1990) are investigated using total electron content (TEC) data recorded at Calcutta (88.38°E, 22.58°N geographic, dip: 32°N). TEC perturbations exhibit a prominent dependence on the local times of main phase occurrence (MPO). The storms with MPO during daytime hours are more effective in producing larger deviations and smaller time delays for maximum positive deviations compared to those with nighttime MPO. Though the perturbations in the equinoctial and winter solstitial months more or less follow the reported climatology, remarkable deviations are detected for the summer solstitial storms. Depending on the local times of MPO, the sunrise enhancement in TEC is greatly perturbed. The TEC variability patterns are interpreted in terms of the storm time modifications of equatorial electric field, wind system and neutral composition.     

Ionospheric activity and possible connection with seismicity: Contribution from the analysis of long time series of GNSS signals

The modifications of some atmospheric physical properties prior to a high magnitude earthquake were debated in the frame of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) model. In this work, among the variety of involved phenomena, the ionisation of air at the ionospheric levels triggered by the leaking of gases from the Earth’s crust was investigated through the analysis of GNSS (Global Navigation Satellite System) signals. In particular, the authors analysed a 5 year (2008–2012) long series of GNSS based ionospheric TEC to produce maps over an area surrounding the epicentre of the L’Aquila (Italy, M_w = 6.3) earthquake of April 6th, 2009. The series was used to detect and quantify amplitude and duration of episodes of ionospheric disturbances by a statistical approach and to discriminate local and global effects on the ionosphere comparing these series with TEC values provided by the analysis of GNSS data from international permanent trackers distributed over a wider region. The study found that during this time interval only three statistically meaningful episodes of ionospheric disturbances were observed. One of them, occurring during the night of 16th of March 2009, anticipated the main shock by 3 weeks and could be connected with the strong earthquake of 6th of April. The other two significant episodes were detected within periods that were not close to the main seismic events and are more likely due to various and global reasons.     

Testing Taylor’s hypothesis in Amazonian rainfall fields during the WETAMC/LBA experiment

Taylor’s hypothesis (TH) for rainfall fields states that the spatial correlation of rainfall intensity at two points at the same instant of time can be equated with the temporal correlation at two instants of time at some fixed location. The validity of TH is tested in a set of 12 storms developed in Rondonia, southwestern Amazonia, Brazil, during the January–February 1999 Wet Season Atmospheric Meso-scale Campaign. The time Eulerian and Lagrangian Autocorrelation Functions (ACF) are estimated, as well as the time-averaged space ACF, using radar rainfall rates of storms spanning between 3.2 and 23 h, measured at 7–10-min time resolution, over a circle of 100 km radius, at 2 km spatial resolution. TH does not hold in 9 out of the 12 studied storms, due to their erratic trajectories and very low values of zonal wind velocity at 700 hPa, independently from underlying atmospheric stability conditions. TH was shown to hold for 3 storms, up to a cutoff time scale of 10–15 min, which is closely related to observed features of the life cycle of convective cells in the region. Such cutoff time scale in Amazonian storms is much shorter than the 40 min identified in mid-latitude convective storms, due to much higher values of CAPE and smaller values of storm speed in Amazonian storms as compared to mid-latitude ones, which in turn contribute to a faster destruction of the rainfall field isotropy. Storms satisfying TH undergo smooth linear trajectories over space, and exhibit the highest negative values of maximum, mean and minimum zonal wind velocity at 700 hPa, within narrow ranges of atmospheric stability conditions. Non-dimensional parameters involving CAPE (maximum, mean and minimum) and CINE (mean) are identified during the storms life cycle, for which TH holds: CAPE mean/CINE mean = [30–35], CAPE max/CINE mean = [32–40], and CAPE min/CINE mean = [22–28]. These findings are independent upon the timing of storms within the diurnal cycle. Also, the estimated Eulerian time ACF’s decay faster than the time-averaged space and the Lagrangian time ACF’s, irrespectively of TH validity. The Eulerian ACF’s exhibit shorter e-folding times, reflecting smaller correlations over short time scales, but also shorter scale of fluctuation, reflecting less persistence in time than over space. No significant associations (linear, exponential or power law) were found between estimated e-folding times and scale of fluctuation, with all estimates of CAPE and CINE. Secondary correlation maxima appear between 50 and 70 min in the Lagrangian time ACF’s for storms satisfying TH. No differences were found in the behavior of each of the three ACF’s for storms developed during either the Easterly or Westerly zonal wind regimes which characterize the development of meso-scale convective systems over the region. These results have important implications for modelling and downscaling rainfall fields over tropical land areas.     

Correlations between electrical and elastic properties of solid–liquid composites with interfacial energy-controlled equilibrium microstructures

Electrical conductivity and seismic velocity are studied for plausible pore geometries in the Earth's interior for reliable quantitative analysis of experimental data such as seismic tomography and magnetotelluric explorations. Electrical conductivity of a two-phase system with equilibrium, interfacial energy-controlled phase geometry is calculated for the dihedral angles θ = 40°–100° that are typical for rock–aqueous fluid and θ = 20°–60° for rock–melt systems of lower crust and upper mantle for the case of tetrakaidecahedral grains. Electrical conductivity vs. seismic velocity correlations are acquired by combining of the simulated electrical conductivities with the seismic velocity calculated with the help of equilibrium geometry model Takei [Takei, Y., Effect of pore geometry on V_P/V_S: From equilibrium geometry to crack. J. Geophys. Res. 107 (2002): 10.1029/2001JB000522.] for the same pore geometries. The results show that electrical conductivity gradually decreases reaching zero when seismic velocities reach seismic velocities of intact rock for rock–melt systems, while for rock–aqueous fluid systems with θ ≥ 60° conductivity drops to zero at velocities up to 10% smaller. This can explain the seeming discrepancy of the low seismic velocity region, attributed to the high fluid fraction, and the low electrical conductivity of the same region, which is sometimes faced at collocated electromagnetic and seismic experiments.     

Inferred fault geometry and slip distribution of the 2010 Jiashian,Taiwan, earthquake is consistent with a thick-skinned deformation model

We invert measurements of coseismic displacements from 139 continuously recorded GPS sites from the 2010, Jiashian, Taiwan earthquake to solve for fault geometry and slip distribution using an elastic uniform stress drop inversion. The earthquake occurred at a depth of ~ 23 km in an area between the Western Foothills fold-and-thrust belt and the crystalline high mountains of the Central Range, providing an opportunity to examine the deep fault structure under Taiwan. The inferred rupture plane is oblique to the prominent orientation of thrust faults and parallel to several previously recognized NW-striking transfer zones that appear to connect stepping thrusts. We find that a fault striking 318°–344° with dip of 26°–41° fits the observations well with oblique reverse-sinistral slip under a low stress drop of about 0.5 MPa. The derived geodetic moment of 2.92 × 10¹⁸ N-m is equivalent to a M_w = 6.24 earthquake. Coseismic slip is largely concentrated within a circular patch with a 10-km radius at the depth between 10 and 24 km and maximum slip of 190 mm. We suggest this earthquake ruptured the NW-striking Chishan transfer fault zone, which we interpret as a listric NE-dipping lateral ramp with oblique slip connecting stepping thrust faults (ramps). The inferred slip on the lateral ramp is considerably deeper than the 7–15 km deep detachment identified in previous studies of western Taiwan. We infer an active basal detachment under western Taiwan at a depth of at least ~ 20–23 km based on these inversion results. The earthquake may have nucleated at the base of the lateral ramp near the intersection with the basal detachment. Coulomb stress change calculations suggest that this earthquake moved several NE-striking active thrust faults in western Taiwan nearer to failure.     

Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes

This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5–10 min were observed about 10–24 min after the earthquakes and have horizontal propagation velocities of 922–1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4–5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11–13 min after the earthquake.     

Numerical modeling of the light ion trough and heat balance of the topside ionosphere in quiet geomagnetic conditions

The results from the numerical calculations of the global distribution of topside ionospheric parameters such as H⁺ ions and ion and electron temperatures up to 1500 km height are presented for equinoctial conditions at solar minimum. Calculations are carried out using the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN, and using a new calculation block for electric fields due to dynamo and of magnetospheric origin. A comparison of two sets of calculations of magnetospheric convection electric field for a given potential difference is carried out, one through polar caps and other through field aligned currents of first zone. It is shown that the distribution of the electric potential obtained through field aligned currents of first zone is more self-consistent than that through polar caps. The light ion trough in H⁺ ions is deeper and occupies larger region for the potential difference through polar cap. For a given potential difference through field aligned current, at 1500 km, the maximum ion temperature is 150 K higher, minimum ion temperature is 200 K lower and maximum electron temperature is 100 K higher than those obtained for the same potential difference through polar caps. It is concluded that for modeling the electric field of magnetospheric origin, it is necessary to use the potential difference through field aligned current of first zone instead of through polar caps.