The polar wind: Recent observations

The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H⁺, He⁺ and O⁺ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to ∼50,500 km, and revealed several important features in the polar wind that are unexpected from “classical” polar wind theories. These include the day–night asymmetry in polar wind velocity, which is 1.5–2.0 times larger on the dayside; appreciable O⁺ flow at high altitudes, where the velocity at 5000–10,000 km is of 1–4 km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5–2. These features are attributable to a number of “non-classical” polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of ∼0.2–0.3 eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (<4000 km for H⁺). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H⁺ and smallest for O⁺. Near solar maximum, H⁺, He⁺, and O⁺ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000 km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized “non-polar-wind” ion such as a low-energy “cleft ion fountain” ion that has convected into a polar wind flux tube from an energized “polar-wind” ion that is accelerated locally by “non-classical” polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O⁺ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H⁺ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He⁺ and other minor ion species in the polar wind population.     

Crustal velocity structure in the southern edge of the Central Alborz (Iran)

Inversion of local earthquake travel times and joint inversion of receiver functions and Rayleigh wave group velocity measurements were used to derive a simple model for the velocity crustal structure beneath the southern edge of the Central Alborz (Iran), including the seismically active area around the megacity of Tehran. The P and S travel times from 115 well-located earthquakes recorded by a dense local seismic network, operated from June to November 2006, were inverted to determine a 1D velocity model of the upper crust. The limited range of earthquake depths (between 2 km and 26 km) prevents us determining any velocity interfaces deeper than 25 km. The velocity of the lower crust and the depth of the Moho were found by joint inversion of receiver functions and Rayleigh wave group velocity data. The resulting P-wave velocity model comprises an upper crust with 3 km and 4 km thick sedimentary layers with P wave velocities (V_p) of ～5.4 and ～5.8 km s^?1, respectively, above 9 km and 8 km thick layers of upper crystalline crust (V_p ～6.1 and ～6.25 km s^?1 respectively). The lower crystalline crust is ～34 km thick (V_p ～ 6.40 km s^?1). The total crustal thickness beneath this part of the Central Alborz is 58 ± 2 km.     

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.     

Crustal seismic structure and depth distribution of earthquakes in the Archean Kuusamo region,Fennoscandian Shield

Two-dimensional crustal velocity models are derived from passive seismic observations for the Archean Karelian bedrock of north-eastern Finland. In addition, an updated Moho depth map is constructed by integrating the results of this study with previous data sets. The structural models image a typical three-layer Archean crust, with thickness varying between 40 and 52 km. P wave velocities within the 12–20 km thick upper crust range from 6.1 to 6.4 km/s. The relatively high velocities are related to layered mafic intrusive and volcanic rocks. The middle crust is a fairly homogeneous layer associated with velocities of 6.5–6.8 km/s. The boundary between middle and lower crust is located at depths between 28 and 38 km. The thickness of the lower crust increases from 5–15 km in the Archean part to 15–22 km in the Archean–Proterozoic transition zone. In the lower crust and uppermost mantle, P wave velocities vary between 6.9–7.3 km/s and 7.9–8.2 km/s. The average V_p/V_s ratio increases from 1.71 in the upper crust to 1.76 in the lower crust.The crust attains its maximum thickness in the south-east, where the Archean crust is both over- and underthrust by the Proterozoic crust. A crustal depression bulging out from that zone to the N–NE towards Kuusamo is linked to a collision between major Archean blocks. Further north, crustal thickening under the Salla and Kittilä greenstone belts is tentatively associated with a NW–SE-oriented collision zone or major shear zone. Elevated Moho beneath the Pudasjärvi block is primarily explained with rift-related extension and crustal thinning at ∼2.4–2.1 Ga.The new crustal velocity models and synthetic waveform modelling are used to outline the thickness of the seismogenic layer beneath the temporary Kuusamo seismic network. Lack of seismic activity within the mafic high-velocity body in the uppermost 8 km of crust and relative abundance of mid-crustal, i.e., 14–30 km deep earthquakes are characteristic features of the Kuusamo seismicity. The upper limit of seismicity is attributed to the excess of strong mafic material in the uppermost crust. Comparison with the rheological profiles of the lithosphere, calculated at nearby locations, indicates that the base of the seismogenic layer correlates best with the onset of brittle to ductile transition at about 30 km depth.We found no evidence on microearthquake activity in the lower crust beneath the Archean Karelian craton. However, a data set of relatively well-constrained events extracted from the regional earthquake catalogue implies a deeper cut-off depth for earthquakes in the Norrbotten tectonic province of northern Sweden.     

Active segment of the 12 November 2003 Mw 5.6 earthquake at Salsipuedes oceanic basin,Gulf of California. Mexico

We analyzed records of eight seismic stations of the autonomous broadband seismograph network of a joint project between Utrecht University (the Netherlands), California Institute of Technology, and Centro de Investigación Científica y de Estudios Superiores de Ensenada (CICESE). These stations recorded the Mw 5.6 earthquake that occurred on 12 November 2003 at Salsipuedes basin in the middle of the Gulf of California 2 km west of the island Angel de la Guarda. This event was located at 29.16º N and 113.37º W, 30 km northeast of Bahia de los Angeles. A foreshock and hundreds of aftershocks were recorded in the 48 hours after its origin time. With the location of 29 earthquakes we identified the active segment, perpendicular to the main transform fault NW–SE of Canal de Ballenas, representing the transtensional boundary between the Pacific and North American plates. The direction of the active fault described is consistent with the normal fault mechanism reported by the National Earthquake Information Center (strike=39º, dip=34º, slip=–44º).From the duration magnitude of 456 aftershocks, we calculated a b-value of 1.14±0.28; furthermore, we calculated a seismic moment of (3.5 ±3.3) X10¹⁷Nm, a source radius of 3.7 ± 2.63 km, and a static stress drop of 3.94 ± 1.15 MPa (39.4 ± 11.5 bar.).     

Mapping the spatial distribution of subsurface saline material in the Darling River valley

In the Australian landscape larg stores of soluble salt are present naturally. In many cases it is attributable to salts entrapped as marine sediment in earlier geological time. At the district level, the need for information on the presence of saline subsurface material is increasing, particularly for its application to salinity hazard assessment and environmental management. This is the case in irrigated areas, where changes in hydrology can result in secondary salinisation. To reduce the expense, environmental studies use a regression relationship to make use of more readily observed measurements (e.g. electromagnetic (EM) data) which are strongly correlated with the variable of interest. In this investigation a methodology is outlined for mapping the spatial distribution of average subsurface (6–12 m) salinity (EC_e — mS m^? 1) using an environmental correlation with EM34 survey data collected across the Bourke Irrigation District (BID) in the Darling River valley. The EM34 is used in the horizontal dipole mode at coil configurations of 10 (EM34-10), 20 (EM34-20), and 40 (EM34-40). A multiple-linear regression (MLR) relationship is established between average subsurface EC_e and the three EM34 signal data using a forward modeling stepwise linear modeling approach. The spatial distribution of average subsurface salinity generally reflects the known surface expression of point-source salinisation and provides information for future environmental monitoring and natural resource management. The generation of EM34 data on various contrived grids (i.e. 1, 1.5, 2. 2.5 and 3 km) indicates that in terms of accuracy, the data available on the 0.5 (RMSE = 188) and 1 km (RMSE = 283) grid are best, with the least biased predictions achieved using 1 (ME = ? 1) and 2 km (ME = 12) grids. Viewing the spatial distribution of subsurface saline material showed that the 0.5 km spacing is optimal, particularly in order to account for short-range spatial variation between various physiographic units. The Relative Improvement (RI) shows that increasing EM grids from 1, 1.5, 2, 2.5 to 3 km gave RI of ? 53, ? 100%, ? 107%, ? 128% and ? 140%, respectively. We conclude that at a minimum a 1 km grid is needed for reconnaissance EM34 surveying.     

Crustal structure variation along 30°N in the eastern Tibetan Plateau and its tectonic implications

We determined crustal structure along the latitude 30°N through the eastern Tibetan Plateau using a teleseismic receiver function analysis. The data came mostly from seismic stations deployed in eastern Tibet and western Sichuan region from 2004 to 2006. Crustal thickness and Vp/Vs ratio at each station were estimated by the H–k stacking method. On the profile, the mean crustal thickness and Vp/Vs ratio were found to be 62.3 km and 1.74 in the Lhasa block, 71.2 km and 1.79 near the Bangong–Nujiang suture, 66.3 km and 1.80 in the Qiangtang block, 59.8 km and 1.81 in the Songpan–Garze block, and 42.9 km and 1.76 in the Yangtze block, respectively. The estimated crustal thicknesses are consistent with predictions based on the topography and the Airy isostasy, except near the Bangong–Nujiang suture and in the Qiangtang block where the crust is 5–10 km thicker than predicted, indicating that the crust may be denser, possibly due to mafic underplating. We also inverted receiver functions for crustal velocity structure along the profile, which reveals a low S-wave velocity zone in the lower crust beneath the eastern Tibetan Plateau, although the extent of the low-velocity zone varies considerably. The low-velocity zone, together with previous results, suggests limited partial melting and localized crustal flow in the lower crust of the eastern Tibetan Plateau.     

Time-Domain Moment Tensors for shallow (h ≤ 40 km) earthquakes in the broader Aegean Sea for the years 2006 and 2007: The database of the Aristotle University of Thessaloniki

We present a catalog of moment tensor (MT) solutions and moment magnitudes, M_w, for 119 shallow (h ≤ 40 km) earthquakes in Greece and its surrounding lands (34°N–42°N, 19°E–30°E) for the years 2006 and 2007, computed with the 1D Time-Domain Moment Tensor inversion method (TDMT_INV code of Dreger, 2003). Magnitudes range from 3.2 ≤ M_w ≤ 5.7. Green's functions (GF) have been pre-computed to build a library, for a number of velocity profiles applicable to the broader Aegean Sea region, to be used in the inversion of observed broad band waveforms (10–50 s). All MT solutions are the outcome of a long series of tests of different reported source locations and hypocenter depths. Quality factors have been assigned to each MT solution based on the number of stations used in the inversion and the goodness of fit between observed and synthetic waveforms. In general, the focal mechanisms are compatible with previous knowledge on the seismotectonics of the Aegean area. The new data provide evidence for strike-slip faulting along NW–SE trending structures at the lower part of Axios basin, close to the heavily industrialized, and presently subsiding, region of the city of Thessaloniki. Normal faulting along E–W trending planes is observed at the Strimon basin, and in Orfanou Gulf in northern Greece. A sequence of events in the east Aegean Sea close to the coastline with western Anatolia sheds light on an active structure bounding the north coastline of Psara–Chios Islands about 20–25 km in length exhibiting right lateral strike-slip faulting.     

Does the polar cap disappear under an extended strong northward IMF?

The suggestion that the polar cap can completely disappear under certain northward IMF conditions is still controversial. We know that the size of the polar cap is strongly controlled by the interplanetary magnetic field (IMF). Under a southward IMF, the polar cap is usually large and filled with weak diffuse polar rain electrons. The polar cap shrinks under a northward IMF. Here we use the global auroral images and coincident particle measurements on May 15, 2005 to show that the discrete arcs (due to precipitation of both electrons and ions) expanded from the dayside oval to the nightside oval and filled the whole polar ionosphere after a long (8 h) and strong (～5–30 nT) northward IMF B_z, The observations suggested that the polar cap disappeared under a closed magnetosphere.     

In-situ measurement of smoke particles in the wintertime polar mesosphere between 80 and 85 km altitude

The MAGIC sounding rocket, launched in January 2005 into the polar mesosphere, carried two detectors for charged aerosol particles. The detectors are graphite patch collectors mounted flush with the skin of the payload and are connected to sensitive electrometers. The measured signal is the net current deposited on the detectors by heavy aerosol particles. The collection of electrons and ions is prevented by magnetic shielding and a small positive bias, respectively. Both instruments detected a layer of heavy aerosol particles between 80 and 85 km with a number density approximately 10³ cm⁻³. Aerodynamic flow simulations imply that the collected particles are larger than ∼1 nm in radius. The particles are detected as a net positive charge deposited on the graphite collectors. It is suggested that the measured positive polarity is due to the electrification of the smoke particles upon impact on the graphite collectors.     

Observations of narrow bipolar events in East China

Narrow bipolar events (NBEs) are a distinct class of intra-cloud lightning discharge. In this paper we present observations of 10 negative and 67 positive such events in East China. Positive NBEs occurred at 7–12 km altitude above mean sea level (MSL) with a mean altitude of 9.5 km, and negative NBEs occurred at 14–16 km altitude. Electrical/channel characteristics of these events were derived from NBE pulse waveforms based on the transmission-line model. On average, the peak current moment and the charge moment change of a NBE event is 15 kA km, and 0.12 C km, respectively. The mean time for the propagation of current front along the channel is 2.2 μs. The upper limit on channel length for NBEs in this study is 510–1060 m, the lower limit on discharge current amplitude is 12.5–43.2 kA, and the minimum charge transfer is 0.1–0.3 C.     

Crustal structure of the Reykjanes Ridge near 62°N,on the basis of seismic refraction and gravity data

Explosion deep seismic sounding data sections of high quality had been obtained with RV Meteor in the Reykjanes Iceland Seismic Project (RRISP77 [Angenheister, G., Gebrande, H., Miller, H., Goldflam, P., Weigel, W., Jacoby, W.R., Pálmason, G., Björnsson, S., Einarsson, P., Pavlenkova, N.I., Zverev, S., Litvinenko, I.V., Loncarecic, B., Solomon, S., 1980. Reykjanes Ridge Iceland Seismic Experiment (RRISP 77). J. Geophys. 47, 228–238]) which close an information gap near 62°N. Preliminary results were presented by Weigel [Weigel, W., 1980. Aufbau des Reykjanes Rückens nach refraktionsseismischen Messungen. In: Weigel, W. (Ed.), Reykjanes Rücken, Island, Norwegischer Kontinentalrand. Abschlusskolloquium, Hamburg zur Meteor-Expedition, vol. 45. DFG, Bonn, pp. 53–61], and here we report on the data and results of interpretation. Clear refracted phases to 90 km distance permit crustal and uppermost mantle structure to be modelled by ray tracing. The apparent P-wave velocities are around 4.5, 6–6.5, 7–7.6 and 8.2–8.7 km/s, but no wide-angle reflections have been clearly seen. Accompanying sparker reflection data reveal thin sediment ponds in the axial zone and up to 400 m thick sediments at 10 Ma crustal age. Ray tracing reveals the following model below the sediments: (1) a distinct, 1–2 km thick upper crust (layer 2A) with Vp increasing with age (to 10 Ma) from <3.4 to 4.9 km/s and with a vertical gradient of 0.1–0.2 km/s/km, (2) a lower crust or layer 3 beginning at depths of 2 (axis) to 4 km (10 Ma age) below sea level with 6.1–6.8 km/s and similar vertical gradients as above, (3) the lower crust bottoms at 5.2–9.5 km depth below sea level (0–10 Ma) with a marked discontinuity, underneath which (4) Vp rises from about 7.5–7.8 km/s (0–10 Ma) with a positive vertical gradient of, again, 0.1–0.2 km/s/km such that 8 km/s would be reached at 12 km and deeper near the axis. Our preferred interpretation is that the mantle begins at the distinct discontinuity (“Moho”), but a deeper “Moho” of Vp ≈ 8 km/s cannot be excluded. From Iceland southward to 60°N several experiments show a decrease of crustal thickness from 14 to 8 km. Velocity trends with age across the ridge reflect cooling and filling of cracks, and thickness trends probably suggest volcanic productivity variations as previously suggested.Gravity inversion concentrates on a profile across the ridge with the above seismic a priori information; with 0.2–0.5 km depth uncertainty it leads to a good fit (±2.5 mGal where seismic data exist). Best fitting densities are (in kg/m³) for sediments, 2180; upper crust, 2450–2570; lower crust, 2850–2940; mantle lithosphere, 3215–3240 with a deficit for an asthenospheric wedge of no more than −100 kg/m³. The morphological ridges and troughs superimposed on the SE ridge flank are partly correlated, partly anti-correlated with the Bouguer anomaly and suggest that variable crustal density variations accompany the morphology variations.     

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.     

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.     

Global distribution and climatological features of the 5–6-day planetary waves seen in the SABER/TIMED temperatures (2002–2007)

The paper is focused on the global spatial structure, seasonal and interannual variability of the ～5-day Rossby (W1) and ～6-day Kelvin (E1) waves derived from the SABER/TIMED temperature measurements for 6 full years (January 2002–December 2007). The latitude structure of the ～5-day W1 wave is related to the gravest symmetric wave number 1 Rossby wave. The vertical structure of the ～5-day Rossby wave amplitude consists of double-peaked maxima centred at ～80–90 km and ～105–110 km. This wave has a vertically propagating phase structure from the stratosphere up to 120 km altitude with a mean vertical wavelength of ～50–60 km. The ～6-day E1 wave is an equatorially trapped wave symmetric about the equator and located between 20°N and 20°S. Its seasonal behaviour indicates some equinoctial and June solstice amplifications, while the vertical phase structure indicates that this is a vertically propagating wave between 20–100 km altitudes with a mean vertical wavelength of ～25 km.     

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.     

ELF transients associated with sprites and elves in eastern Mediterranean winter thunderstorms

During the northern hemisphere winter of 2005–2006, transient luminous events (TLEs) known as ‘sprites’ and ‘elves’ were imaged over thunderstorm cells in the eastern Mediterranean. Simultaneously, extremely low frequency (ELF) data (ELF: 3–3000 Hz) were recorded at two observation stations in Israel and Hungary in order to qualify and quantify parameters of the parent lightning discharge associated with the transient optical emissions in the upper atmosphere. In this study, we found that for 87% (Israel) and 77% (Hungary) of optically observed TLEs an intense ELF transient event was recorded. These stations are located some 500 and 2100 km, respectively, from the region of the TLEs. All ELF transients that were associated with TLEs were caused by lightning discharges with positive polarity. Calculation of the charge moment change showed values between 600 and 2800 C km with a peak around 1000 C km. Additionally, the time delay between the +CG and ensuing sprite was 76±34 ms and it was displaced up to 50 km from its parent CG.One of our objectives in the present study was to characterize, based on the ELF radiation from lightning, the electromagnetic (EM) waveforms of the lightning discharges which generate TLEs in the time and frequency domains, and to compare them with other lightning discharges occurring in the same thunderstorm cell at approximately the same time, but which did not produce TLEs. The survey for a typical EM waveform showed no unique ELF signature for lightning discharges associated with either sprites or elves.     

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.     

Validation of temperature measurements from MIPAS-ENVISAT with balloon observations obtained by MIPAS-B

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a limb sounding Fourier transform interferometer in the mid-infrared band, on board the polar-orbiting ENVIronmental SATellite (ENVISAT) was launched in March 2002 by the European Space Agency (ESA). For the MIPAS data validation, three balloon flights with MIPAS-B, a balloon version of MIPAS, were carried out on the 24th and 25th of September 2002 from Aire sur l’Adour (France 44°N, 0°E), on the 20th and 21th of March, and on the 2nd and 3rd of July 2003 from Esrange, Kiruna (Sweden 68°N, 21°E). The MIPAS operational data version 4.61 for the temperature vertical profiles were compared with the correlative MIPAS-B measurements via the coincident comparison and the trajectory comparison approaches, respectively. The precision of the MIPAS temperature was estimated to be 1.04–2.48 K in the region 123–8 hPa (15–33 km) and beyond the expectation. The systematic difference shows that the absolute accuracy of the MIPAS temperature is within the total combined errors between 356 and 3 hPa (8–39 km). The agreements in the middle stratosphere are better than in the lower stratosphere and upper troposphere. The maximum difference of 1.9 K (0.9%) was found at 228 hPa (11 km). The biases of MIPAS measurements are ?0.39 K (?0.19%) and +0.25 K (+0.12%) (“+” positive bias, “?” negative bias) corresponding to the altitude regions 143–31 hPa (14–24 km) and 31–5 hPa (24–37 km), respectively.     

Seismicity and fluid geochemistry at Lassen Volcanic National Park,California: Evidence for two circulation cells in the hydrothermal system

Seismic analysis and geochemical interpretations provide evidence that two separate hydrothermal cells circulate within the greater Lassen hydrothermal system. One cell originates south to SW of Lassen Peak and within the Brokeoff Volcano depression where it forms a reservoir of hot fluid (235–270 °C) that boils to feed steam to the high-temperature fumarolic areas, and has a plume of degassed reservoir liquid that flows southward to emerge at Growler and Morgan Hot Springs. The second cell originates SSE to SE of Lassen Peak and flows southeastward along inferred faults of the Walker Lane belt (WLB) where it forms a reservoir of hot fluid (220–240 °C) that boils beneath Devils Kitchen and Boiling Springs Lake, and has an outflow plume of degassed liquid that boils again beneath Terminal Geyser. Three distinct seismogenic zones (identified as the West, Middle, and East seismic clusters) occur at shallow depths (< 6 km) in Lassen Volcanic National Park, SW to SSE of Lassen Peak and adjacent to areas of high-temperature (≤ 161 °C) fumarolic activity (Sulphur Works, Pilot Pinnacle, Little Hot Springs Valley, and Bumpass Hell) and an area of cold, weak gas emissions (Cold Boiling Lake). The three zones are located within the inferred Rockland caldera in response to interactions between deeply circulating meteoric water and hot brittle rock that overlies residual magma associated with the Lassen Volcanic Center. Earthquake focal mechanisms and stress inversions indicate primarily N–S oriented normal faulting and E–W extension, with some oblique faulting and right lateral shear in the East cluster. The different focal mechanisms as well as spatial and temporal earthquake patterns for the East cluster indicate a greater influence by regional tectonics and inferred faults within the WLB. A fourth, deeper (5–10 km) seismogenic zone (the Devils Kitchen seismic cluster) occurs SE of the East cluster and trends NNW from Sifford Mountain toward the Devils Kitchen thermal area where fumarolic temperatures are ≤ 123 °C. Lassen fumaroles discharge geothermal gases that indicate mixing between a N₂-rich, arc-type component and gases derived from air-saturated meteoric recharge water. Most gases have relatively weak isotopic indicators of upper mantle or volcanic components, except for gas from Sulphur Works where δ¹³C–CO₂, δ³⁴S–H₂S, and δ¹⁵N–N₂ values indicate a contribution from the mantle and a subducted sediment source in an arc volcanic setting.