North-south Component Research Articles

Interplanetary medium condition effects in the South Atlantic Magnetic Anomaly: A case study

One way to investigate the magnetosphere–ionosphere coupling is through the simultaneous observation of different parameters measured at different locations of the geospace environment and try to determine some relationships among them. The main objective of this work is to examine how the solar energetic particles and the interplanetary medium conditions may affect the space and time configuration of the ring current at low-latitudes and also to get a better understanding on how these particles interfere with the lower ionosphere in the South Atlantic Magnetic Anomaly region ( SAMA). To accomplish this, the cosmic noise absorption ( CNA) and the horizontal component of the Earth's magnetic field data measured from sites located in the SAMA region were compared with the proton and electron fluxes, interplanetary medium conditions (solar wind and the north–south component of the interplanetary magnetic field measured on board satellites), the SYM-H index and magnetometer data from Kakioka (KAK-Japan), located significantly outside the SAMA region. The time series analyzed correspond to the geomagnetic disturbance that occurred on August 25–30, 1998. The analysis was performed by implementing wavelet techniques, with particular attention to singularities detection, which highlights the presence of transient signals. The results are discussed in terms of the first three wavelet decomposition levels of the parameters. The magnitude of wavelet coefficients of the solar wind and proton flux at the two energy ranges analyzed is timely well correlated, indicating that these two signals are energetically linked. The larger wavelet coefficient amplitude of KAK and VSS magnetograms shows time delays that are compatible with an asymmetric configuration of the ring current, considering that at the storm time, VSS was at the dawn sector of the magnetosphere and KAK at the dusk side. The wavelet analysis of CNA signals reveals that the signal may be sensitive to the ionization produced by energetic electrons and protons as well. The time delays observed in wavelet coefficients may give an indication of the different accelerating process to which the particles are submitted when traveling along the magnetic field lines, from higher to lower latitudes, and the likely contribution of these particles to the ionization measured as an absorption of the cosmic noise in the lower ionosphere.

Anomalous Geomagnetic Variations Possibly Linked with the Taiwan Earthquake (Mw=6.4) on 19 December 2009

On 19 December 2009, the eastern part of Taiwan at approximate depth of 45 km was struck by a strong earthquake (Mw=6.4). The epicenter was located about 20 km away from the Hualien (HLN) station in Taiwan. By analyzing data from the HLN station and Amami Oshima (AMA) in Japan as a remote reference, the geomagnetic east-west (D) and vertical (Z) components recorded at the HLN station are showing no correlation with those at the AMA station in December 2009. Anomalous variations of ∼10–15 nT started about one week before the occurrence of the earthquake and lasted for about two weeks. Also, an enhanced ULF signal in the range of Pc 3 (10–40 s) was observed a few days before the onset of the earthquake. Moreover, the polarization ratio (Z/H (north-south component)) of the Pc 3 amplitude at the HLN station decreased a few days preceding the earthquake. The mechanism behind these anomalous variations is not fully understood. However, we expect that crustal stress perturbations and underground conductivity changes associated with the earthquake played an important role for generating such observed geomagnetic variations.

Mapping Three-Dimensional Surface Deformation by Combining Multiple-Aperture Interferometry and Conventional Interferometry: Application to the June 2007 Eruption of Kilauea Volcano, Hawaii

Surface deformation caused by an intrusion and small eruption during June 17-19, 2007, along the East Rift Zone of Kilauea Volcano, Hawaii, was three-dimensionally reconstructed from radar interferograms acquired by the Advanced Land Observing Satellite (ALOS) phased-array type L-band synthetic aperture radar (SAR) (PALSAR) instrument. To retrieve the 3-D surface deformation, a method that combines multiple-aperture interferometry (MAI) and conventional interferometric SAR (InSAR) techniques was applied to one ascending and one descending ALOS PALSAR interferometric pair. The maximum displacements as a result of the intrusion and eruption are about 0.8, 2, and 0.7 m in the east, north, and up components, respectively. The radar-measured 3-D surface deformation agrees with GPS data from 24 sites on the volcano, and the root-mean-square errors in the east, north, and up components of the displacement are 1.6, 3.6, and 2.1 cm, respectively. Since a horizontal deformation of more than 1 m was dominantly in the north-northwest-south-southeast direction, a significant improvement of the north-south component measurement was achieved by the inclusion of MAI measurements that can reach a standard deviation of 3.6 cm. A 3-D deformation reconstruction through the combination of conventional InSAR and MAI will allow for better modeling, and hence, a more comprehensive understanding, of the source geometry associated with volcanic, seismic, and other processes that are manifested by surface deformation.

Periodic variations of geomagnetic activity indices

Geomagnetic activity is generated by the interaction of the solar wind with the magnetosphere in connection with energy and mass transfer. Most observations suggest that the solar wind energy is transferred to the magnetosphere by the reconnection process at the dayside magnetopause, where oppositely directed southward IMF and northward magnetospheric magnetic field lines merge. Yearly averages of geomagnetic activity indices Ap for the years 1965 to 2009 are compared to the respective averages of v and Bx, By, Bz, where v is the solar wind velocity and Bx, By, Bz are the southward, northward and north-south component of inter- planetary magnetic field (IMF). The correlation of these quantities is known to be rather good. Comparing the averages of Ap with v and Bx, By, Bz separately we find that, during the declining phase of the solar cycle, v and during the ascending phase Bx have more influence on Ap. Analysing the daily variation of ap in an analogue manner suggesting that during phases of the solar cycle, when ap depends more on the IMF- Bx, By, Bz, components, whereas during phases when ap increases as v increases.

Magnetic field structure of large-scale plasmoid generated by the fast reconnection mechanism in a sheared current sheet

Abstract. On the basis of the spontaneous fast reconnection model, three-dimensional magnetic field profiles associated with a large-scale plasmoid propagating along the antiparallel magnetic fields are studied in the general sheared current sheet system. The plasmoid is generated ahead of the fast reconnection jet as a result of distinct compression of the magnetized plasma. Inside the plasmoid, the sheared (east-west) field component has the peak value at the plasmoid center located at x=XC, where the north-south field component changes its sign. The plasmoid center corresponds to the so-called contact discontinuity that bounds the reconnected field lines in x<XC and the field lines without reconnection in x>XC. Hence, contray to the conventional prediction, the reconnected sheared field lines in x<XC are not spiral or helical, since they cannot be topologically connected to the field lines in x>XC. It is demonstrated that the resulting profiles of magnetic field components inside the plasmoid are, in principle, consistent with satellite observations. In the ambient magnetic field region outside the plasmoid too, the magnetic field profiles are in good agreement with the well-known observations of traveling compression regions (TCRs).

Geoeffectiveness of the interplanetary manifestations of coronal mass ejections and solar-wind stream–stream interactions

Coronal mass ejections and high-speed streams from the Sun, and related structures formed and evolved in interplanetary space, i.e. interplanetary manifestations of CMEs (ICMEs) and stream interaction regions (SIRs)/corotating interaction regions (CIRs), are mainly responsible for geomagnetic disturbances in the Earth’s magnetic environment. However, the presence or absence of associated/finer structures of ICMEs (e.g., shock/sheath, magnetic cloud) and SIRs/CIRs (forward and reverse shocks, stream interface) might influence their geoeffectiveness as these features within large-scale structures of ICMEs and SIRs display different and varying plasma and field characteristics. In this work, we analyze the solar-wind plasma and field parameters (plasma velocity, density and pressure, magnetic field, its north-south component and electric field) together with geomagnetic activity parameters (kp and Dst), applying the method of superposed epoch analysis. By systematically changing the time of passage of different features as epochs, e.g. discontinuities/shocks, CMEs/magnetic clouds in ICMEs and discontinuities/forward shocks in SIRs/CIRs, we study the relative geoeffectiveness of not only the large-scale structures (ICMEs/SIRs/CIRs), but of their finer features also. We critically analyze the differences in geoeffectiveness due to different structures and features, with distinct plasma/field characteristics, and we utilize these results to understand the mechanism during their interaction with geospace.

Response of the auroral electrojet indices to abrupt southward IMF turnings

Abstract. We present results from a study of the behavior of the auroral electrojet indices following abrupt southward turnings of the IMF Bz. The auroral electrojet indices are calculated from observations made by more than 100 ground based stations provided by the SuperMAG collaborators. Based on three simple criteria we selected 73 events. In each event the interval of analysis started at the time of the IMF Bz southward turning and ended 45 minutes later or at the onset of any abrupt energy unloading event in the magnetosphere, regardless of size. We refer to this period as the "pre-unloading phase". To isolate the dependence of the auroral electrojets on the solar induced ionospheric conductivity during this phase we separated the standard AU/AL indices into two new sets of indices defined by the upper and lower envelope of the north-south component for all sunlit stations (AUs/ALs) and for all stations in darkness (AUd/ALd). Based on events and statistical analyses we can conclude that following a southward turning of the IMF Bz the AUd/ALd indices show no measurable response while the AUs/ALs indices clearly intensify. The intensifications of AUs/ALs are dependent on the intensity of the solar wind driver (as measured by IMF Bz or the Akasofu ε parameter). The lack of AUd/ALd response does not depend on the intensity of any subsequent substorm. We find that during these isolated events the ionospheric current system is primarily confined to the sunlit ionosphere. This truncated version of the classical global DP-2 current system suggests that auroral electrojet continuity is not maintained across the terminator. Because of its conductivity dependence on the solar zenith angle, this truncated global current pattern is expected to be highly dependent on UT and season and thus can be asymmetric between hemispheres. Thus we argue that the global two-cell DP-2 current system is not a consequence only of a southward turning of the IMF but requires also the reduction of the conductivity gradient at the terminator.

Determination of the deflection of vertical components via GPS and leveling measurement: A case study of a GPS test network in Konya, Turkey

Deflection of the vertical is used in reducing geodetic measurements related to geoid networks (vertical and horizontal directions observations and length measurement, etc.) to ellipsoid plane and in geoid modeling processes. Generally, it is obtained by Astro-Geodetic and gravimetric techniques. These techniques are very complex and time-consuming. Ellipsoidal coordinates of points are easily obtained thanks to the widespread use of Satellite Positioning Techniques (GNNS) such as GPS in geodesy. When the orthometric heights of points are determined via geometric leveling, geoid height differences and deflection of the vertical components can be measured faster and much more easily by using GPS and leveling measurements than the other techniques. This study discusses the calculation of the deflection of vertical components via GPS and leveling measurements. The deflection of the vertical components obtained from GPS and leveling measurements were compared with global (EGM96 and CG03C) and local (TG03) geoid models. Deflection of the vertical components ξ (north-south) and η (east-west) were calculated as ξ = -4.15” ± 0.61”, η = 8.75” ± 0.69” via a GPS and leveling model; as ξ = -5.64”, η = 1.95” via the EGM96 geoid model; as ξ = -4.85”, η = 1.82” via the CG03C geoid model; as ξ = -7.47”, η = -0.51” via the TG03 model; and as ξ = -3.9”, η = 4.6” via Astro-Geodetic deflection of a vertical map of Turkey produced by Ayan (1976). When the values obtained from GPS and leveling measurements were compared with the values produced by the other techniques, the north-south component was found to be approximately consistent, while east-west component differed to same extent. Since very little data on the terrestrial gravity of Turkey was present in the EGM96 and CG03C global geoid models, it was not anticipated that the results obtained via these models would be comparable with other methods. Key words: Deflection of the vertical, deflection of the vertical components, GPS/Leveling, EGM96, CG03C.

Other climate-change inputs

A vigorous round of correspondence appeared in Physics Today (October 2008, page 10) regarding the Opinion piece “Is Climate Sensitive to Solar Variability?” by Nicola Scafetta and Bruce West (Physics Today, March 2008, page 50). One letter writer, Peter Foukal, pointed out that neither total nor UV solar irradiance can account for most of the climate variance that correlates with solar activity. In view of the quantitative problems in using irradiance to account for the correlated climate variations, the question can be asked, Are the cosmic-ray variations, which are mostly due to solar activity, themselves drivers of climate change, or are they—as generally assumed—merely proxies for irradiance variations?Not mentioned in the discussion was observational evidence for greater long-term and short-term climate sensitivity to solar activity than irradiance can account for. Proxies for climate change on the centennial and millennial time scales—proxies such as glacier-carried debris and the oxygen-18 isotope—show strong correlations with the cosmic-ray-generated cosmogenic isotopes carbon-14 and beryllium-10 in stratified geological repositories. 1 1. G. Bond et al. , Science 294, 2130 (2001), and references therein. https://doi.org/10.1126/science.1065680 One little-known mechanism coupling solar activity to the atmosphere has been shown to respond to cosmic-ray changes as well as to other inputs, as documented and reviewed in recent publications. 2 2. G. B. Burns et al. , J. Geophys. Res. 113, D15112 (2008), https://doi.org/10.1029/2007JD009618 , 3 3. B. A. Tinsley, Rep. Prog. Phys. 71, 066801 (2008). https://doi.org/10.1088/0034–4885/71/6/066801 Clear evidence of meteorological responses, including changes in cloud cover, has been reported for five disparate short-term solar or terrestrial inputs that modulate the flow of the downward electric current density Jz of the global electric circuit through the atmosphere. For example, recent analysis of measurements in both the Antarctic and Arctic high-magnetic-latitude regions shows correlations between surface pressure and the north–south component of the interplanetary electric field. Changes in Jz due to low-latitude thunderstorms produce a similar effect on polar surface pressure. 2 2. G. B. Burns et al. , J. Geophys. Res. 113, D15112 (2008), https://doi.org/10.1029/2007JD009618 There are other consistent, statistically significant atmospheric responses to the effects of cosmic-ray, solar-proton, and relativistic-electron precipitation on J z. 3 3. B. A. Tinsley, Rep. Prog. Phys. 71, 066801 (2008). https://doi.org/10.1088/0034–4885/71/6/066801 The Jz flow deposits electric charge on droplets and aerosol particles in gradients of droplet concentration, humidity, and, therefore, resistivity in clouds in accordance with Ohm’s law and Gauss’s law. Such charges could affect clouds through the scavenging rates for cloud-condensation and ice-forming nuclei. Consequent changes in the concentration of such nuclei and in ice-nucleation rates can affect droplet concentration, precipitation rate, and cloud cover and can potentially explain the observations. But to model the effects of the cloud changes on global mean temperature on the century time scale, it will be necessary to separately evaluate the effects of solar-induced Jz changes on clouds at low and high altitudes, at high and low latitudes, over ocean and land, by day and night, and for stratus versus cumulus clouds. Such work has not been done, but uncertainties appear much larger than those shown for the solar irradiance effect in the reports of the Intergovernmental Panel on Climate Change, and can thus accommodate the observed changes in global temperature that correlate with solar activity. REFERENCESSection:ChooseTop of pageREFERENCES <<1. G. Bond et al. , Science 294, 2130 (2001), and references therein. https://doi.org/10.1126/science.1065680 , Google ScholarCrossref2. G. B. Burns et al. , J. Geophys. Res. 113, D15112 (2008), https://doi.org/10.1029/2007JD009618 , Google ScholarCrossref3. B. A. Tinsley, Rep. Prog. Phys. 71, 066801 (2008). https://doi.org/10.1088/0034–4885/71/6/066801 , Google ScholarCrossref© 2009 American Institute of Physics.

Impact of FORMOSAT-3/COSMIC GPS radio occultation and dropwindsonde data on regional model predictions during the 2007 Mei-yu season

A study of the impact of FORMOSAT-3/COSMIC GPS radio occultation (RO) and dropwindsonde data on regional model simulations for a 11-day period during the 2007 Mei-yu season is presented. The Weather Research and Forecasting (WRF) model and its three-dimensional variation component, WRF-Var, are used for regional model predictions of heavy rainfall events in Taiwan. Without the use of GPS RO and dropwindsonde data, pressure and relative humidity are, in general, underestimated by the model; temperature predictions have a warm bias at the low level and a cold bias at the high level; and the east–west and north–south component winds have positive and negative biases, respectively. Incorporating GPS RO data tends to improve the prediction for longer integration. The assimilation of dropwindsonde data improves the forecast at the earlier time and at higher levels, and the improvement decreases over time. The reason the dropwindsonde data produce a positive impact earlier and the GPS RO data later is that there are few GPS RO observations in the fine domain. The large-scale simulation is first improved using the GPS RO observations, and the resulting changes can have a positive impact on the mesoscale at the later time. The dropwindsonde observations were taken inside the fine domain such that their impact can be detected early in the simulation. With both types of observation included, the prediction shows even greater improvement. At the earlier forecast time, there is nearly no impact from GPS and dropwindsonde data on rainfall forecasts. However, at the later integration time, the GPS data start to significantly improve the rainfall forecast. The dropwindsonde data also provide a positive impact on rainfall forecasts, but it is not as significant as that of the GPS data.

The instability of the M W and M L comparison for earthquakes in Greece for the period 1969 to 2007

We use 576 earthquakes of magnitude, M w, 3.3 to 6.8 that occurred within the region 33° N–42.5° N, 19° E–30° E in the time period 1969 to 2007 to investigate the stability of the relation between moment magnitude, M w, and local magnitude, M L, for earthquakes in Greece and the surrounding regions. We compare M w to M L as reported in the monthly bulletins of the National Observatory of Athens (NOA) and to M L as reported in the bulletins of the Seismological Station of the Aristotle University of Thessaloniki. All earthquakes have been analyzed through regional or teleseismic waveform inversion, to obtain M w, and have measured maximum trace amplitudes on the Wood–Anderson seismograph in Athens, which has been in operation since 1964. We show that the Athens Wood–Anderson seismograph performance has changed through time, affecting the computed by NOA M L by at least 0.1 magnitude units. Specifically, since the beginning of 1996, its east–west component has been recording systematically much larger amplitudes compared to the north–south component. From the comparison between M w and M L reported by Thessaloniki, we also show that the performance of the sensors has changed several times through time, affecting the calculated M L’s. We propose scaling relations to convert the M L values reported from the two centers to M w. The procedures followed here can be applied to other regions as well to examine the stability of magnitude calculations through time.

Investigation of linear and nonlinear of behaviours of reinforced concrete cantilever retaining walls according to the earthquake loads considering soil-structures interactions

It is known that retaining walls were severely damaged as well in the most recent earthquakes having occurred in the countries in the active seismic belts of the world. This damage can be ascribed to the calculation methods used for the designs of retaining walls in the event of their constructions and employment having been accurately carried out. Generally simplified pseudo-static methods are used in the analysis of retaining walls with analytical methods and soil-structure interaction are not considered. In view of these circumstances, in this article by taking soil interaction into consideration, linear and nonlinear behaviours of retaining walls are analyzed with the assistance of LUSAS which is one of the structural analysis programs. This investigations are carried out per LUSAS which employs the finite element method as to the Erzincan (1992) Earthquake North-South component and the obtained findings are compared with the ones obtained from the method suggested in Eurocode-8, which is still effective today, and Mononobe-Okabe method. Not only do the obtained results indicate the distribution and magnitude of soil pressures are depend on the filling soil but on the foundation soil as well and nonlinear effects should be considered in designs of these walls.

Geoeffectiveness of magnetic cloud, shock/sheath, interaction region, high-speed stream and their combined occurrence

A subset of CMEs, called interplanetary magnetic clouds (MCs), are observed to have systematic rotation [northward to southward (NS) or southward to northward (SN)] in their field structures. These MCs identified in the heliospheric plasma and field data at 1 AU may have different features associated with them. These structures (NS/SN) may be isolated MC moving with the ambient solar wind. MCs (NS/SN) may also be associated with shock/sheath region, formed due to compression of the ambient plasma/field ahead of them. A fraction from each of these four types of MCs have additional features, being ‘pushed’ by fast solar wind streams from coronal holes, forming interaction region (IR) between MCs and high-speed solar wind streams (HSS). Using these different sets of MCs, we have done a detailed study of the geoeffectiveness of NS and SN turning MCs and their associated features (shock/sheath, IR and HSS). To study the process that produces the geomagnetic disturbances and influences its amplitude/duration, we have utilized the interplanetary plasma and field parameters, namely, plasma velocity, density, temperature, pressure, field strength and its north–south component, during the passage of these structures with different associated properties. Differences in the geoeffectiveness of MCs with different structural and dynamical properties have been identified. The possible role of high-speed stream in influencing the recovery time (and hence duration) of geomagnetic disturbance has also been investigated. A best-fit equation representing the relation between level of the geomagnetic activity (due to MCs) and interplanetary plasma/field parameter has been obtained.

Solar wind control of plasma number density in the near-Earth plasma sheet: three-dimensional structure

Abstract. The plasma number density in the near-Earth plasma sheet depends on the solar wind number density and the north-south component of interplanetary magnetic field (IMF Bz) with time lag and duration of several hours. We examined the three-dimensional structure of such dependences by fitting observations of plasma sheet and solar wind to an empirical model equation. Analyses were conducted separately for northward and southward IMF conditions. Effects of solar wind speed and IMF orientation were also examined by further subdivision of the dataset. Based on obtained results, we discuss (i) the relative contribution of the ionosphere and solar wind to plasma sheet mass supply, (ii) the entry mechanisms for magnetosheath particles, and (iii) the plasma transport in the plasma sheet. We found that solar wind number density dependence is weaker and IMF Bz dependence is stronger for faster solar wind with southward IMF, which suggests the contribution of ionospheric particles. Further from the Earth, different interplanetary conditions result in different structures of solar wind dependence, which indicate different solar wind entry mechanisms: (1) southward IMF results in a strong dependence on solar wind number density in the flank high-latitude region, (2) slow solar wind with northward IMF leads to lower-latitude peaks of solar wind number density dependence in the flank region, (3) fast solar wind with northward IMF results in a strong dependence on solar wind number density at the down-tail dusk flank equator, and (4) solar wind number density dependence is stronger in the downstream of quasi-parallel bow shock. These features are attributable to (1) low-latitude dayside reconnection entry, (2) high-latitude dayside reconnection entry, (3) entry due to decay of Kelvin-Helmholtz vortices, and (4) diffusive entry mediated by kinetic Alfven waves, respectively. Effect of IMF Bz and its time lags show plasma sheet reconfiguration associated with enhanced convective transport under southward IMF. Duration of IMF Bz effect under northward IMF is interpreted in terms of turbulent diffusive transport.

Localization of VLF ionospheric exit point by comparison of multipoint ground-based observation with full-wave analysis

In order to estimate the dynamic structure of the VLF ionospheric exit point, we conducted multipoint ground-based observation of the natural VLF emissions at three unmanned sites: West Ongul (69°01′ S, 39°30′ E), Skallen (69°40′ S, 39°24′ E), and H100 (69°18′ S, 41°19′ E) around Japanese Syowa station, Antarctica, during a whole year of 2006. In this observation, we developed three sets of unmanned autonomous observation systems for natural VLF emissions. Each observation system consists of two crossed vertical loop antennas to pick-up North–South (NS) and East–West (EW) magnetic components, a multi-channel analyzer, and a data logger. The intensity and polarization of NS and EW magnetic components are obtained in 4 spaced frequency (0.5, 1.0, 2.0, and 6.0 kHz) channels by the multi-channel analyzer. The VLF emissions observed at the three sites exhibit an interesting difference in the wave intensity as well as the polarization that allows important information about the locations of their ionospheric exit point to be determined. Firstly, to find the distinct exit point, we have theoretically calculated the spatial distributions of the wave intensity and the polarization on the Earth for VLF whistler mode waves coming down from the magnetized ionosphere, by using the full-wave analysis. Then, we have compared the calculated results with the observed data, to evaluate the possible locations of the ionospheric exit point for the auroral hiss events. As an example, the direction of the estimated ionospheric exit point for the auroral hiss event at 31 March 2006 was found to be consistent with a bright aurora region. However, in this case, the estimated ionospheric exit point was located a few hundred kilometers equatorward of the associated aurora. This would suggest that the ray paths for the auroral hiss could be different from the directions of the geomagnetic field lines for auroral precipitation.

Studying Specific Features of the Resonance Structure of the Background Noise Spectrum in the Frequency Range 1–10 Hz with Allowance for the Slope of the Earth’s Magnetic Field

We present new data on midlatitude features of the resonance structure of the magnetic ultralow-frequency noise spectrum in the frequency range 0.1–10 Hz, namely, the different frequency scale and frequency shift of the resonance-structure maxima for the East-West and North-South components. Resonance spectra of the magnetic components and polarization parameter of magnetic noise for the plane-stratified ionosphere model are numerically simulated with allowance for the inclination of the Earth's magnetic field on the basis of the International Reference Ionosphere IRI-2001 standard. Dependence of the calculated parameters of the resonance structure in the magnetic-component spectra on the source direction and inclination angle of the Earth's magnetic field is explored. The calculations make it possible to explain the different behavior of resonant oscillations in the linear-component spectra and the features of the resonance structure in the background-noise polarization parameter.

GPS measurements of postseismic deformation due to October 8, 2005 Kashmir earthquake

Relaxation of the coseismic stresses following an earthquake causes postseismic crustal deformation, which can last for days to years. Continuous monitoring of postseismic deformation facilitates the understanding of the mechanism of deformation and postseismic relaxation and viscous rheology. After the October 8, 2005 Kashmir earthquake, global positioning system data for 8 months, starting from October, 2005 have been analyzed from three continuous sites located at Gulmarg, Amritsar, and Jaipur. The average velocity during the observation period at Gulmarg (8.6 cm/year) is significantly higher than the Indian plate velocity exhibiting postseismic crustal deformation. The velocity at Amritsar (5.9 cm/year) and Jaipur (5.1 cm/year) is comparable to the Indian plate velocity. At Gulmarg, the logarithmic function fits well to the north–south component of postseismic transients (~in the coseismic slip direction). The nature of decay in these transients suggests that the deformation is mainly due to an afterslip, and the second possible contribution may be from the viscous relaxation process. This paper presents the characteristics of postseismic transients and possible contributions from various postseismic mechanisms subsequent to the Kashmir earthquake.

포항지역에 대한 바람권역 분석 -Part I : 기상관측자료를 토대로 분석한 성긴 바람권역 분석-

The air quality data is important for understanding and analyzing a surrounding influence. In that light, it is positively necessary for a propriety assessment to determine a location of the air quality monitoring sites. In this study, the climate analysis about temperature and wind, using the meteorological data in the Pohang, is conducted to do that. In the next stage, we distinguished the wind by east-west or north-south component, which has less correlation than temperature, analyzed and divided the wind sector. As the result, the wind circumstance of the Pohang is divided into major 5 wind sector; that is the urban area, the northeast coastal area, the east ocean and the west mountainous area. We think that an analysis on detailed wind sector by utilizing the numerical simulation is needed.

Effect of Surface Geology on Ground Motions: The Case of Station TAP056 - Chutzuhu Site

In the Tatun mountain area of northern Taiwan are two strong motion stations approximately 2.5 km apart, TAP056 and TAP066 of the TSMIP network. The accelerometer at station TAP056 is often triggered by earthquakes, but that at TAP066 station is not. Comparisons of vertical and horizontal peak ground accelerations reveal PGA in the vertical, east-west, and north-south components at TAP056 station to be 3.89, 7.57, and 5.45 times those at station TAP066, respectively. The PGA ratio does not seem to be related to earthquake source or path. Fourier spectra of earthquake records at station TAP056 always have approximately the same dominant frequency; however, those at station TAP066 are different due to different sources and paths of different events. This shows that spectra at TAP056 station are mainly controlled by local site effects. The spectral ratios of TAP056/TAP066 show the S-wave is amplified at around 8~10 Hz. The horizontal/vertical spectral ratios of station TAP056 also show a dominant frequency at about 6 and 8~10 Hz. After dense microtremor surveying and the addition of one accelerometer just 20 meters away from the original observation station, we can confirm that the top soft soil layer upon which the observation station is constructed generates the local site response at station TAP056.

Interplanetary magnetic clouds and cosmic ray modulation

We studied the cosmic ray intensity variation due to interplanetary magnetic clouds during an unusual class of low amplitude anisotropic wave train events. The low amplitude anisotropic wave train events in cosmic ray intensity have been identified using the data of ground based Deep River neutron monitor and studied during the period 1981–1994. Even though the occurrence of low amplitude anisotropic wave trains does not depend on the onset of interplanetary magnetic clouds, but the possibility of occurrence of these events cannot be overlooked during the periods of the interplanetary magnetic cloud events. It is observed that the solar wind velocity remains higher (> 300) than normal and the interplanetary magnetic field B remains lower than normal on the onset of the interplanetary magnetic cloud during the passage of low amplitude wave trains. It is also noted that the proton density remains significantly low during high solar wind velocity, which is expected. The north south component of interplanetary magnetic field Bz turns southward to one day before the arrival of cloud and remains in the southward direction after the arrival of a cloud. During these events the cosmic ray intensity is found to increase with increase of solar wind velocity. The superposed epoch analysis of cosmic ray intensity for these events during the onset of interplanetary magnetic clouds reveals that the decrease in cosmic ray intensity starts not at the onset of the cloud but after a few days. The cosmic ray intensity increases on arrival of the magnetic cloud and decreases gradually after the passage of the magnetic cloud.