Detection of large scale TIDs associated with the dayside cusp using SuperDARN data

Variations in the dayside ionosphere parameters as a result of a large-scale acoustic gravity wave (LS AGW) were studied for the 17 February 1998 substorm using the super dual auroral radar network (SuperDARN) measurements. This event was characterised by a sharp rise in the AE index with a maximum of ～900 nT. The source of the disturbance responsible for the LS AGW appears to have been located within the plasma convection throat and in the dayside cusp region. The location of the source was obtained from studies of a number of datasets including high-latitude convection maps, data from 4 DMSP satellites and networks of ground-based magnetometers. The propagation of the LS AGWs caused quasi-periodic variations in the skip distance (with an amplitude up to 220–260 km) of the ground backscatter measured by up to 6 SuperDARN radars, including Goose Bay and Kapuskasing, resulting in two large-scale travelling ionospheric disturbances (LS TIDs). The LS TIDs had wave periods of 1.5 and 2 h, a velocity of ～400 m/s for both, and wavelengths of 2200 and 2900 km, respectively. These quasi-periodic variations were also present in the peak electron density and height of the F2 layer measured by the Goose Bay ionosonde. The numerical simulation of the inverse problem show good agreement between Goose Bay radar and Goose Bay ionosonde measurements. But these LS TIDs would be difficult to deduce from the ground based ionospheric station data alone, because h_mF2 variations were 10–40 km only and f_OF2 variations between 10% and 20%. The results demonstrate how important SuperDARN radars can be, and that this is a more powerful technique than routine ground-based sounding for studies of weak quasi-periodic variations in the dayside subauroral ionosphere related to LS AGW.     

Relationship between the PC and AL indices during repetitive bay-like magnetic disturbances in the auroral zone

To study the relations of the polar cap (PC) magnetic activity (characterized by the PC index) to magnetic disturbances in the auroral zone (AL index) the behavior of 62 repetitive bay-like magnetic disturbances has been analyzed. It was found that the PC index, derived as a proxy of the geoeffective interplanetary electric field Em, starts to increase, on average, about 30 min ahead of the magnetic disturbance onset. Value of Em and PC～2 mV/m seems to be necessary for development of the repetitive bay-like disturbances with peak AL exceeding 400 nT. Growth phase duration (the time interval between the start of PC increase and AL sudden onset) and intensity of magnetic disturbances in the auroral zone (AL max) highly correlate with the PC growth rate. The growth phase reduces to a few minutes, if the PC index suddenly jumps above ～6–8 mV/m. The sharp development of Birkeland current wedge during expansion phase insignificantly influences the polar cap activity: the corresponding PC index increase does not exceed 10–20% of the PC value. It is concluded that the PC index may be considered as a convenient proxy of the solar wind energy input into the magnetosphere.     

Energy balance during intense and super-intense magnetic storms using an Akasofu ε parameter corrected by the solar wind dynamic pressure

Geomagnetic storms are large disturbances in the Earth's magnetosphere caused by enhanced solar wind–magnetosphere energy transfer. One of the main manifestations of a geomagnetic storm is the ring current enhancement. It is responsible for the decrease in the geomagnetic field observed at ground stations. In this work, we study the ring current dynamics during two different levels of magnetic storms. Thirty-three events are selected during the period 1981–2004. Eighteen out of 33 events are very intense (or super-intense) magnetic storms (Dst ⩽−250 nT) and the remaining are intense magnetic storms (−250<Dst ⩽−100 nT). Interplanetary data from spacecraft in the solar wind near Earth's orbit (ACE, IMP-8, ISEE-3) and geomagnetic indices (Dst and Sym-H) are analyzed. Our aim is to evaluate the interplanetary characteristics (interplanetary dawn–dusk electric field, interplanetary magnetic field component B_S), the ε parameter, and the total energy input into the magnetosphere (Wε) for these two classes of magnetic storms. Two corrections on the ε energy coupling function are made: the first one is an already known correction in the magnetopause radius to take into account the variation in the solar wind pressure. The second correction on the Akasofu parameter, first proposed in this work, accounts for the reconnection efficiency as a function of the solar wind ram pressure. Geomagnetic data/indices are also employed to study the ring current dynamics and to search for the differences in the storm evolution during these events. Our corrected ε parameter is shown to be more adequate to explain storm energy balance because the energy input and the energy dissipated in the ring current are in better agreement with modern estimates as compared with previous works. For super-intense storms, the correction of the Akasofu ε is on average a scaling factor of 3.7, whilst for intense events, this scaling factor is on average 3.4. The injected energy during the main phase using corrected ε can be considered a criterion to separate intense from very intense storms. Other possibilities of cutoff values based on the energy input are also investigated. A threshold value for the input energy is much more clear when a new classification on Dst=−165 nT is considered. It was found that the energy input during storms with Dst<−165 nT is double of the energy for storms with Dst>−165 nT.     

Interplanetary origins of November 2004 superstorms

The sun was very active in the declining phase of solar cycle 23. Large sunspot active regions gave origin to multiple flare and coronal mass ejection (CME) activity in the interval 2003–2005. On November 2004, the active region AR 10696 was the origin of dozens of flares and many CMEs. Some events of this solar activity region resulted in two large geomagnetic storms, or superstorms (Dst??250 nT) on November 8, peak Dst=?373 nT, and on November 10, peak Dst=?289 nT. It is the purpose of this article to identify the interplanetary origins of these two superstorms. The southward-directed interplanetary magnetic fields (IMF Bs) that caused the two superstorms were related to a magnetic cloud (MC) field for the first superstorm, and a combination of sheath and MC fields for the second superstorm. However, this simple, classic picture is complicated by the presence of multiple shocks and waves. Six fast-forward shocks and, at least, two reverse waves were observed in the period of the two superstorms. A detailed analysis of these complex interplanetary features is performed in this work.     

Asymmetric response of the topside ionosphere to large-scale IGW generated during the November 30, 1979, substorm

We used bottomside ground observations and topside sounding data from the Intercosmos-19 satellite to study a Travelling Ionospheric Disturbance (TID) that occurred in response to Large-Scale Internal Gravity Wave (LSIGW) propagation during a substorm on November 30, 1979. We built a global scheme for the wavelike ionospheric variations during this medium substorm (AE_max ～800 nT). The area where the TID was observed looks like a wedge since it covers the nighttime hours at subauroral latitudes but contracts to a ～02 h local sector at low latitudes. The ionospheric response is strongly asymmetric because the wedge area and the TID amplitude are larger in the winter hemisphere than in the summer hemisphere. Clear evidence was obtained indicating that the more powerful TID from the Northern (winter) hemisphere propagated across the equator into the low latitude Southern (summer) hemisphere. Intercosmos-19 observations show that the disturbance covers the entire thickness of the topside ionosphere, from h_mF2 up to at least the 1000 km satellite altitude at post-midnight local times. F-layer lifting reached ～200 km, N_e increases in the topside ionosphere by up to a factor of ～1.9 and variations in N_mF2 of both signs were observed. Assumptions are made concerning the reason for the IGW effect at high altitudes in the topside ionosphere. The relationship between TID parameters and source characteristics determined from a global network of magnetometers are studied. The role of the dayside cusp in the generation of the TID in the daytime ionosphere is discussed. The magnetospheric electric field effects are distinguished from IGW effects.     

Seismo-meteo-electromagnetic phenomena observed during a 5-year interval around the 2011 Tohoku earthquake

The purpose of the paper is to try to find ULF electromagnetic precursors to the 2011 Tohoku earthquake (EQ), on the basis of extensive investigation of radiations in vertical component of the magnetic field or with a large ratio of the vertical to full horizontal component. Nighttime records have been analyzed of three Japanese fluxgate magnetometers located in a distance from 300 to 1300 km from the epicenter of the main shock, and the frequency range from 10 to 150 mHz was used for the analysis. We have applied wavelet analyses to improve the detection of pulsed signals. All obtained scalograms have been averaged over the nighttime interval from 01 h to 05 h JST and flattened by means of multiplication by square of frequency. The sequence of spectra thus obtained has been compared with the evolution of seismicity, which has resulted in that the radiation in the vertical component has been detected. It exhibits seasonal variations with winter maxima, but it increases further by approaching the moment of the EQ and decreases after that. This radiation seems to be correlated with atmospheric parameters – air humidity, temperature, vapor pressure and rainfall. So, we consider that this radiation cannot be caused by subsurface sources, but its possible sources can be atmospheric discharges. The evolution of this phenomenon can be explained by a seasonal variation of atmospheric parameters and also its variations under the influence of injection of gas from the focal zone of a forthcoming EQ.     

Inferring land surface parameters from the diurnal variability of microwave and infrared temperatures

This study investigates the properties of the diurnal cycle of microwave brightness temperatures (TB), namely the phase and the amplitude, and their variability in time and space over the globe to infer information on key land surface parameters like changes in soil texture spatial distribution, soil moisture conditions, and vegetation density. The phase corresponds to the lag between Land Surface Temperature (LST) and TB diurnal cycles. The amplitude is determined as the difference between the maximum and the minimum of TB diurnal cycle. The diurnal cycle of TB was constructed using observations from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and the Special Sensor Microwave/Imager (SSM/I). The latter offer a series of sensors, namely, F13, F14, and F15 that were used in this study for a higher temporal coverage and more accurate diurnal cycle determination. LST estimates, which are available every 3 h from the International Satellite Cloud Climatology Project (ISCCP) database were used to build the LST diurnal cycle. ISCCP LST data is an infrared-based temperature with almost no penetration and is the representative of top skin temperature.The analyses of the diurnal cycles showed that the diurnal amplitude of TB decreases as the vegetation density increases, especially in the case of low frequencies which penetrate deeper into the canopy which makes them more sensitive to changes in vegetation density. The interannual variations of TB diurnal amplitudes were also in agreement with the seasonality of the vegetation cover. Over desert and rain forest regions where surface conditions do not vary significantly throughout the year, the changes in diurnal amplitudes were the lowest. A relationship between phase and amplitude values was established. It was found that the amplitude of TB diurnal cycle decreases when the phase lag increases. The spatial distribution of the determined diurnal properties, namely, phase and amplitude of TB, showed an agreement with lithology maps in desert areas. Lower TB amplitudes were observed over regions with loose siliceous rocks. Phase lag values between 1.5 and 3 h corresponded to 83% of the class “loose siliceous rocks” in the Sahara Desert, which corroborates the potential of using the diurnal properties of TB as an indicator of land surface parameters.     

Relation of PC index to the geomagnetic storm Dst variation

Relationships between the polar cap magnetic activity index PC and the magnetic storm Dst index have been studied for the magnetic storms with duration more 12 h and peak value Dst<?30 nT and, observed in 1998–2002 and 2004–2005. Along with PC index the geoeffective interplanetary electric field Em was also examined. It has been found that all examined storms, lying in range from ?30 to ?373 nT, started when the PC index and, correspondingly, the Em field firmly exceeded the threshold >2 mV/m. In particular, the “anomalous” magnetic storm on January 21–22, 2005 occurring under conditions of northward IMF B_Z (Du et al., 2008) is usual phenomena fitted well with the threshold restriction owing to the large IMF By component input. The maximal storm depression (the peak value of Dst) is linearly related to the quantities Em and PC, averaged for the time interval from the storm beginning to the storm maximum. The correlation between Dst and PC is more steady and larger than correlation between Dst and Em, the latter being dependent on Em value (effect of “Dst saturation”). The moment of the firm descent of the Em and PC quantities below the threshold level ～2 mV/m is indicative of the depression damping and transition to the recovery phase. The results are consistent with the similar peculiarities revealed for substorms development (Troshichev and Janzhura, 2009) and support the conclusion that the PC index is a reliable proxy characterizing the solar wind energy having been entered into the magnetosphere.     

Using machine learning to produce near surface soil moisture estimates from deeper in situ records at U.S. Climate Reference Network (USCRN) locations: Analysis and applications to AMSR-E satellite validation

Surface soil moisture is a critical parameter for understanding the energy flux at the land atmosphere boundary. Weather modeling, climate prediction, and remote sensing validation are some of the applications for surface soil moisture information. The most common in situ measurement for these purposes are sensors that are installed at depths of approximately 5 cm. There are however, sensor technologies and network designs that do not provide an estimate at this depth. If soil moisture estimates at deeper depths could be extrapolated to the near surface, in situ networks providing estimates at other depths would see their values enhanced. Soil moisture sensors from the U.S. Climate Reference Network (USCRN) were used to generate models of 5 cm soil moisture, with 10 cm soil moisture measurements and antecedent precipitation as inputs, via machine learning techniques. Validation was conducted with the available, in situ, 5 cm resources. It was shown that a 5 cm estimate, which was extrapolated from a 10 cm sensor and antecedent local precipitation, produced a root-mean-squared-error (RMSE) of 0.0215 m³/m³. Next, these machine-learning-generated 5 cm estimates were also compared to AMSR-E estimates at these locations. These results were then compared with the performance of the actual in situ readings against the AMSR-E data. The machine learning estimates at 5 cm produced an RMSE of approximately 0.03 m³/m³ when an optimized gain and offset were applied. This is necessary considering the performance of AMSR-E in locations characterized by high vegetation water contents, which are present across North Carolina. Lastly, the application of this extrapolation technique is applied to the ECONet in North Carolina, which provides a 10 cm depth measurement as its shallowest soil moisture estimate. A raw RMSE of 0.028 m³/m³ was achieved, and with a linear gain and offset applied at each ECONet site, an RMSE of 0.013 m³/m³ was possible.     

Magnetic susceptibility and Cs-137 inventory variability as influenced by land use change and slope positions in a hilly,semiarid region of west-central Iran

The objective of this study was to explore the slope position and land use change effects on the variability in magnetic susceptibility and ¹³⁷Cs inventory as the soil redistribution indicators in a hilly semiarid calcareous area in Iran. The selected study area is located in a hilly region with pasture and cultivation land use of Fereydunshahr, Isfahan Province in west-central Iran. In the two mentioned dominant ecosystems, four slope positions including summit, shoulder, backslope and footslope were identified and in each land use and slope position, three cores were selected to collect 72 soil samples from three depths (0–10, 10–20, 20–30 cm) in an area of 15 × 15 cm. Additional 28 soil samples were collected from the reference site for soil loss and deposition calculations by using the Cs-137 measurement. The results of the study with the use of the Cs-137 technique showed that the average soil loss in the pasture land (46.4 t ha^− 1 yr^− 1) was significantly (p < 0.05) lower than the average soil loss in the cultivated land (80.4 t ha^− 1 yr^− 1). The highest soil loss in both land uses was obtained in the shoulder position, 60.1 and 84.4 t ha^− 1 yr^− 1, respectively, for the pasture and cultivated lands. Moreover, the highest rates of soil deposition was observed in a footslope position in both land uses and they were 34 and 32.4 t ha^− 1 yr^− 1 for the pasture and cultivated lands, respectively. Magnetic susceptibility was significantly (p < 0.05) greater in pasture (χ_lf = 41.51 × 10^− 8 m³/kg) than in the cultivated land (χ_lf = 34.90 × 10^− 8 m³/kg). The pasture land with a lower soil loss rate, indicated significantly higher magnetic susceptibility in all landform positions as compared to that in the cultivated land. The results of the correlation analysis showed that among the studied soil physico-chemical properties, χ_lf (r = 0.83, p < 0.01) in the pasture land had the highest correlation with the Cs-137 inventory. Throughout the non-linear regression analysis, χ_lf was introduced for relating soil parameters and the cesium inventory explained 68% and 79% of the total variability of ¹³⁷Cs in the pasture and cultivated lands, respectively. The results implied that the variability in the magnetic susceptibility within the hillslope is consistent with the variation of the Cs-inventory; and the results thus demonstrate the slope and land use effects on soil redistribution.     

Model simulation of the equatorial electrojet in the Peruvian and Philippine sectors

Between 100 and 120 km height at the Earth's magnetic equator, the equatorial electrojet (EEJ) flows as an enhanced eastward current in the daytime E region ionosphere, which can induce a magnetic perturbation on the ground. Calculating the difference between the horizontal components of magnetic perturbation (H) at magnetometers near the equator and about 6–9° away from the equator, ΔH, provides us with information about the strength of the EEJ. The NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM) is capable of simulating the EEJ current and its magnetic perturbation on the ground. The simulated diurnal, seasonal (March equinox, June solstice, December solstice), and solar activity (F_10.7=80, 140 and 200 units) variations of ΔH in the Peruvian (76°W) and Philippine (121°E) sectors, and the relation of ΔH to the ionospheric vertical drift velocity, are presented in this paper. Results show the diurnal, seasonal and solar activity variations are captured well by the model. Agreements between simulated and observed magnitudes of ΔH and its linear relationship to vertical drift are improved by modifying the standard daytime E region photoionization in the TIE-GCM in order to better simulate observed E region electron densities.     

Hydrological effects on gravity and correlations between gravitational variations and level of the Alzette River at the station of Walferdange,Luxembourg

The gravitational effects of water storage variations driven by local precipitation events are modeled for the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. A modified mass continuity model is implemented, which uses rainfall data from Walferdange as input. In the absence of soil moisture and groundwater level information, the model is empirically parameterized. Model outputs are compared to the gravity time series registered with the Observatory Superconducting Gravimeter CT040 located in the WULG. We find that the model explains 77% of the gravity residuals. In addition, a statistical analysis is carried out to determine the relationship between precipitation, gravity variations and water level changes in the nearby Alzette River. A time delay of 88 ± 34 min between the maximum variation rates of the water level and gravity signal has been calculated. The signals have an admittance of 45 ± 5 cm μGal^?1.     

Comparative study of top soil magnetic susceptibility variation based on some human activities

An investigation of the effect of some human activities on the magnetic susceptibility and frequency dependent susceptibility was conducted on top soil samples from, a commercial area, a motor park and a school environment in Jalingo, Taraba State, N-E Nigeria. The purpose was to assess the variation of magnetic susceptibility with different land use, detect pollution hotspots using magnetic proxy parameters and evaluate the contribution of superparamagnetic (SP) grain size contribution to the magnetic susceptibility from calculation of the frequency dependence of magnetic susceptibility (MS). The results of the mass specific low frequency magnetic susceptibility measurements showed significant enhancement with values ranging from 67.8 − 495.3 × 10⁻⁸ m³kg⁻¹ with a mean value of 191.61 × 10⁻⁸ × m³kg⁻¹ for the Jalingo College of Education (JCOE) data; 520.1 − 1612.8 × 10⁻⁸ m³kg⁻¹ with a mean value of 901.34 × 10⁻⁸ m³kg⁻¹ for the Jalingo main Market (JMM) and 188.5 − 1203.6 × 10⁻⁸m³kg⁻¹ with an average value of 574 92 × 10⁻⁶ m³kg⁻¹ for the Jalingo Motor Park (JMP). The significant magnetic enhancement indicates high concentration of ferrimagnetic minerals in the soil and hence increased pollution. The magnetic susceptibility of the different land use studied decreased in the order commercial area (market) > motor park > school premises. The results of the percentage frequency dependence susceptibility showed that most of the samples had a mixture of SP and coarse multi domain grains or SP grains < 0.05 µm. The value of χ_fd% range from 2.68 to 13.80% with an average value of 8.67% in the JCOE samples, 0.49 to 10.04% with an a-verage of 5.05% in the JMM samples and 0.56 to 13.04% with an average value of 5.86% in the JMP samples.     

Cave air ventilation and CO2 outgassing by radon-222 modeling: How fast do caves breathe?

In general, the rate and timing of calcite precipitation is in part affected by variations in cave air CO₂ concentrations. Knowledge of cave ventilation processes is required to quantify the effect variations in CO₂ concentrations have on speleothem deposition rates and thus paleoclimate records. In this study we use radon-222 (²²²Rn) as a proxy of ventilation to estimate CO₂ outgassing from the cave to the atmosphere, which can be used to infer relative speleothem deposition rates. Hollow Ridge Cave, a wild cave preserve in Marianna, Florida, is instrumented inside and out with multiple micro-meteorological sensor stations that record continuous physical and air chemistry time-series data. Our time series datasets indicate diurnal and seasonal variations in cave air ²²²Rn and CO₂ concentrations, punctuated by events that provide clues to ventilation and drip water degassing mechanisms. Average cave air ²²²Rn and CO₂ concentrations vary seasonally between winter (²²²Rn = 50 dpm L^? 1, where 1 dpm L^? 1 = 60 Bq m^? 3; CO₂ = 360 ppmv) and summer (²²²Rn = 1400 dpm L^? 1; CO₂ = 3900 ppmv). Large amplitude diurnal variations are observed during late summer and autumn (²²²Rn = 6 to 581 dpm L^? 1; CO₂ = 360 to 2500 ppmv).We employ a simple first-order ²²²Rn mass balance model to estimate cave air exchange rates with the outside atmosphere. Ventilation occurs via density driven flow and by winds across the entrances which create a ‘venturi’ effect. The most rapid ventilation occurs 25 m inside the cave near the entrance: 45 h^? 1 (1.33 min turnover time). Farther inside (175 m) exchange is slower and maximum ventilation rates are 3 h^? 1 (22 min turnover time). We estimate net CO₂ flux from the epikarst to the cave atmosphere using a CO₂ mass balance model tuned with the ²²²Rn model. Net CO₂ flux from the epikarst is highest in summer (72 mmol m^? 2 day^? 1) and lowest in late autumn and winter (12 mmol m^? 2 day^? 1). Modeled ventilation and net CO₂ fluxes are used to estimate net CO₂ outgassing from the cave to the atmosphere. Average net CO₂ outgassing is positive (net loss from the cave) and is highest in late summer and early autumn (about 4 mol h^? 1) and lowest in winter (about 0.5 mol h^? 1). Modeling of ventilation, net CO₂ flux from the epikarst, and CO₂ outgassing to the atmosphere from cave monitoring time-series can help better constrain paleoclimatic interpretations of speleothem geochemical records.     

Statistical observations of spatial characteristics of Pi1B pulsations

We have examined the spatial and temporal correlation of high-latitude Pi1B and Pi2 pulsations, mid-latitude Pi2 pulsations, and auroral substorm onsets identified in the IMAGE far ultraviolet imager (FUV) data. Numerous search coil and fluxgate magnetometers at high latitudes (65–80° in Antarctica and Greenland) and mid-latitude fluxgate magnetometers are used. We find that Pi1B onset times agree well with onset times of intense isolated auroral substorms identified by the IMAGE FUV instrument: Pi1B onsets occurred within the 2 min cadence of the imager. For any given event, we find that Pi1B are localized to approximately 4 h of local time and 7° of magnetic latitude relative to the initial auroral brightening location as observed by IMAGE FUV. Not surprisingly, we also find that Pi1B pulsations occur typically between 2100 and 0200 MLT. Comparison to Pi2 records from these and other lower-latitude stations shows that in almost all cases Pi1B activity coincides within ±2 min with Pi2 activity. Power law fits showed that Pi1B amplitude fell off with distance^−2.9 for two strong events (i.e., similar to the r⁻³ falloff of the signal from a dipolar source), and only slightly more rapidly than the falloff of Pi2 activity (d^−2.8). Given the global nature of Pi2 pulsations versus the localized nature of Pi1B events in this study, we conclude that the mechanism that drives Pi1B pulsations is likely different from that responsible for Pi2 pulsations.     

Magnetic survey of topsoils in Windsor–Essex County,Canada

Windsor–Essex County is a major cross-border truck and transportation route, with significant localized industrialization as well as rural and farming areas. Magnetic property measurements (in-field and laboratory susceptibility, frequency-dependent susceptibility, hysteresis properties, thermomagnetic and thermosusceptibility curves, anhysteretic and isothermal magnetizations) were made in order to determine the potential for using such variables to distinguish between natural and anthropogenic pollutants. In-field magnetic susceptibility measured on 324 soil sampling sites on a 0.5–2 km grid spacing through Windsor–Essex County ranged from 3.7 × 10^− 6 to 305.2 × 10^− 6 SI (average 36.2 ± 35.8 × 10^− 6 SI), and showed that high magnetic susceptibility values were obtained on soil sampling sites in and around the cities/towns of Windsor, Harrow, Olinda and Oakland and near the beaches of Point Pelee National Park (PPNP) and Deerbrook, whereas lower susceptibility values were observed in near the towns of Lakeshore and Essex. On this grid spacing, Highway 401 (the major truck route) did not show anomalous susceptibility values; however, closer (1–3 m) sampling on other roads did show anomalously high values, suggesting that the coarser grid spacing may have missed anomalies. Laboratory measurements indicated that the dominant magnetic mineral in the Windsor–Essex County soils is magnetite; however, the grain size is variable. Pseudo-single domain (PSD)–multidomain (MD) magnetite is generally found on beaches and in PPNP, whereas single domain (SD)–PSD magnetite has been found near the City of Windsor and other towns. While certain correlations exist between some anthropogenic activities and the measured magnetic susceptibility and magnetic property values, no overall correlation can be made. A variety of geologic and anthropogenic factors must be considered when interpreting the origin of the magnetic signal in a particular area.     

Vertical and horizontal distribution of magnetic susceptibility and metal contents in an industrial district of central Iran

This study was conducted to determine the vertical and horizontal distribution of selected metals and magnetic susceptibility (χlf) in an industrial site located in Isfahan province, central Iran. For this purpose, we used a grid sampling methodology and excavated 202 profiles. Soil samples were then collected from 0–30, 60–90, and 120–150 cm depths. The mass magnetic susceptibility (χ) of the soil samples was measured at both low and high frequencies (χlf and χhf) using the Bartington MS2 dual frequency sensor; and χfd was also calculated. Soil samples were also analyzed for iron (Fe), manganese (Mn), lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), chromium (Cr) and cobalt (Co) concentrations. The results showed that there were positive significant correlations among selected metals including Zn, Pb, Fe and Mn, which were mainly added through coal fly ash from an iron smelting factory at the studied site, while the concentration of Ni, Cr and Co was mainly controlled by the parent material of the soils. The trends in results at the site of study were similar in vertical and horizontal distribution for the industrial originated metals as judged by pollution load index (PLI) using χlf. The results of SEM/EDX also confirmed the presence of spheroid of magnetic particles in the surface soil samples taken in close proximity of the factory. Based on the results using the contamination factors (CF) determined for selected metals, the following order was observed: Pb > Zn > Mn > Fe > Cu > Ni ≥ Co > Cr. The results also suggested that magnetic methods could be used to estimate the metal contamination from anthropogenic sources in industrial soils.     

Diurnal variations of the total electron content under quiet helio-geomagnetic conditions

The morphology of averaged diurnal variations of total electron content (TEC) under quiet helio-geomagnetic conditions for all latitudinal bands and various longitudes has been studied using Global Ionospheric Maps (GIMs) datasets. The diurnal TEC variation maximum is generally registered at 14–15 LT. The maximum is 38±5, 14±2, 10±2 TECU (TECU is generally accepted TEC unit) at the equatorial, middle and high latitudes. The nighttime TEC minimum is within 5–7 TECU regardless of a season, latitude and longitude. At the equatorial latitudes TEC exhibits the most significant daily/season variations and the asymmetry of its behavior in the hemispheres near the equinox. Abnormal diurnal TEC variations (evening maximum, near-noon minimum) are observed at middle and high latitudes in summer due to atmospheric wind effects. The comparison of the averaged diurnal TEC variations with the behavior of the ionospheric F2-layer critical frequency indicated that GIMs describe daily/annual TEC variations reasonably well.     

Geoelectrical,strain and tilt investigations of hydrological processes at the broadband Geodynamical Observatory Moxa,Germany

The Geodynamic Observatory Moxa, located in Thuringia/Germany, is dedicated to studies of temporal deformations of the earth's crust and of variations of the gravity field. One of the essential issues with respect to these investigations is the reduction of the hydrological impact on the data of the gravimeters, strainmeters and tiltmeters. In order to optimise the reductions, we investigated the changes in the hydrological conditions in the woody mountain slope above the observatory with time-lapse electrical resistivity tomography (ERT), and analysed the strain and tilt measurements for prominent signatures of pore pressure induced subsurface deformations.Here we present the results for two profiles – parallel and perpendicular to the slope – measured with ERT during 33 campaigns between June 2007 and April 2010. Resistivity changes and variations of apparent soil moisture, inferred from ERT sections, were found to primarily occur in the first two metres of the subsurface. These variations can be related to subsurface flow in the upper two metres induced by precipitation events and snowmelts. Trees close to the profiles only show a minimum impact on the resistivity and soil moisture changes.Furthermore, systematic hydrologically induced deformations can be observed in hodographs of strain and tilt measurements for large precipitation events (> 80 mm) and snowmelts. In the strain data a short-term (< 3 days) dilatational signal is found with an amplitude of 20 nstrain to 60 nstrain and a long-term (> 7 days) compressional signal between 40 nstrain and 180 nstrain. The preferential N–S direction of long-term deformational signals (> 1 week) is also observed in the tilt data. The direction of tilt changes (25 nrad–120 nrad) is nearly parallel to the drainage direction of the nearby Silberleite creek indicating variations of pore pressure gradients during hydrological events.The results of these hydrological studies at the Geodynamic Observatory Moxa can be used for removing the time dependent hydrological signal in strain and tilt data and, thus, better correction algorithms for hydrological impacts can be developed to enhance the value of the data for geodynamic studies.     

Artificial earthquake test of gas supply networks

In this paper, seismic behavior of gas supply networks is investigated by constructing a 24 m×24 m buried network and conducting an artificial earthquake test by detonating TNT explosives. The pipe network consists of typical welded steel pipes used in gas supply networks. Ground motion is produced by detonating 30 kg of TNT explosives buried 5 m below ground surface and 15 m away from the network. The test preparations are presented, including site selection, network layout, ground motion generation, and arrangements of different sensors. The measured ground acceleration, strain, and acceleration of welded steel pipes, and pipe–soil relative slippage are discussed. The deformation patterns of welded steel pipes are also analyzed and explained, including axial and bending deformations, systematic network characteristics, deformation relationship between ground and pipes, and dynamic response of buried pipes.