inversion for seismic slip rate history and distribution with stabilizing constraints application to the 1986 andreanof islands earthquake we develop and present a method of inverting seismograms including their absolute amplitudes to obtain the complete seismic slip time history and distribution using the method of linear programming a rectangular fault is discretized into cells and the source duration into time steps the inversion for the slip rate distribution on the fault as a function of time reduces to the solution of a system of linear equations the influence on the solution of constraining different source parameters such as the sign of the slip rate and the seismic moment is investigated it is found that the constraint of positiveness of slip rate and the constraint that the seismic moment determined from the solution should be close to that obtained from the centroid moment tensor cmt solution are very strong constraints and are essential to obtaining a physically reasonable solution since the inverse problem is unstable instead of presenting only one particular solution we examine several solutions equally well fitting the data for all practical purposes we find that when both constraints are applied the solution becomes quite stable the method is applied to a data set consisting of the vertical component of available digitally recorded teleseismic p waves at stations within a chosen distance window for the 1986 andreanof islands earthquake mw 8 0 the preferred solution is the one in which the slip rate is constrained to be positive and the moment is set to the cmt value the average rupture speed in the 90 km segment to the east of the hypocenter was 3 2 km s and in the 190 km section to the west was 2 km s the maximum slip in the area of large moment release to the west was 5 m and the maximum slip rate which occurs in the same place as the maximum slip was 6 5 m s the slip distribution on the fault shows a corrugated pattern with the long axis in the direction of the plate convergence rather than normal to the arc which was the slip vector direction for the earthquake with most of the slip occurring pn a region of the fault to the west of the rupture nucleation zone this region continued to slip for about 55 s the total source duration being about 80 s the results of this analysis suggest that the long term motion on this portion of the aleutian arc is indeed in the direction of plate convergence

prompt penetration electric fields ppefs and their ionospheric effects during the great magnetic storm of 30 31 october 2003 1 we explore the ionospheric effects of prompt penetration electric fields ppefs for a variety of interplanetary magnetic field directions we use the great magnetic storm of 30 31 october as an example of ppef effects for intense southward interplanetary magnetic fields imfs inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm concurrent with the above positive phase ionospheric storms occur in the dayside and negative phase ionospheric storms occur on the nightside the topics of this paper the dayside ionospheric storms due to ppefs are characterized by transport of near equatorial plasma to higher altitudes and latitudes forming a giant plasma fountain these features are part of what is called the dayside ionospheric superfountain dis for these southward imfs dusk and dawn plasma are predicted to be transported toward the dayside for northward imfs negative phase ionospheric storms are expected on the dayside if the ppefs indeed reach that region of space imf by components are expected to have weak or neglible ionospheric effects on the basis of ppef arguments intervals of imf by should not be related to geomagnetic storms they are not imf by intervals should however cause a shearing of the magnetotail a feature that has been previously reported in the literature

very short term earthquake precursors from gps signal interference based on the 2013 nantou and rueisuei earthquakes taiwan abstract we set up a gps network with 17 continuous gps cgps stations in southwestern taiwan to monitor real time crustal deformation we found that systematic perturbations in gps signals occurred just a few minutes prior to the 2013 nantou ml 6 5 and rueisuei ml 6 4 earthquakes in taiwan the anomalous pseudorange readings were several millimeters higher or lower than those in the background time period these systematic anomalies were found as a result of interference of gps l band signals by electromagnetic emissions ems prior to the mainshocks the ems may occur in the form of harmonic or ultra wide band radiation and can be generated during the formation of mode i cracks at the final stage of earthquake nucleation we estimated the directivity of the likely em sources by calculating the inner product of the position vector from a gps station to a given satellite and the vector of anomalous ground motions recorded by the gps the results showed that the predominant inner product generally occurred when the satellite was in the direction either toward or away from the epicenter with respect to the gps network our findings suggest that the gps network may serve as a powerful tool to detect very short term earthquake precursors and presumably to locate a large earthquake before it occurs nevertheless a direct measurement of ems at the site of the gps array is required in future studies to confirm this hypothesis

equatorial plasma depletion precursor signatures and onset observed at 11 south of the magnetic equator coordinated radio and optical measurements of the structure and dynamics of the postsunset equatorial ionosphere were conducted on october 1 1994 from agua verde chile 11 3 s magnetic latitude mlat the measurements clearly show a north south aligned undulation or ripple on the bottomside of the f layer at 2000 lt appearing as an eastward propagating decrease in the 630 0 nm airglow resembling a traveling ionospheric disturbance in the digital portable ionosonde measurements and causing a total electron content decrease in the global positioning system gps satellite measurements the initial development of this feature toward the east and away from the magnetic equator took place in an otherwise smooth unstructured ionosphere spread f began to develop in the ionograms at 2020 lt and at this same time local onset of satellite signal scintillation was detected using the multiple ray paths throughout the sky available from the gps satellite constellation transmitting at l band frequencies uhf scintillation measurements from ancon peru along the same magnetic field line show that intense scintillation and ionospheric irregularities had developed over the magnetic equator almost 60 min prior to their development at 11 s mlat the observations suggest that the east west electric field expected to be present within the earlier developed depletion and scintillation region at the magnetic equator mapped along magnetic field lines to lower altitudes and higher latitudes resulting in an undulation or dome shaped structure before evolving into a fully developed depletion with associated ionospheric irregularities all along the magnetic flux tube

images of transequatorial f region bubbles in 630 and 777 nm emissions compared with satellite measurements images of transequatorial f region bubbles were obtained from magnetic field aligned airglow observations from haleakala hawaii for 9 nights in august 1988 bubbles of scale size 10 100 km were recorded with an intensified ccd detector attached to a filter wheel imager and sequential images were made in the plasma recombination emissions at 630 nm and 777 nm and in the background emissions the observations also yield information on the large scale structure of the ionosphere in the northern appleton anomaly region particularly on the latitude variations of plasma concentration and layer height measurements from the dmsp f8 and f9 satellites extend this to include the southern anomaly region the dmsp satellites were near 830 km in altitude and in near polar orbits at about 1800 and 2120 hours local time a comparison of the bubble images and the dmsp results with plasma concentration and drift velocities obtained from the san marco satellite allows us to put the measurements along the san marco track into the larger ionospheric context one to one correspondence is found between the presence of the optical bubbles and the presence of plasma depletions measured from the san marco satellite allowing identification on consecutive orbits of the same depletions this extends for up to 5 hours of the satellite measured information for individual depletions that is their vertical and horizontal drift velocities and the plasma concentration variations the images show the shapes of the depletions in apex height and longitude and their evolution horizontal drift velocities of the bubbles were determined by a correlation analysis bubble occurrence is compared with day to day changes in the equatorial fountain electric fields and transequatorial asymmetries caused by neutral winds and with measurements of radar backscatter from centimeter scale irregularities associated with bubbles in the kwajalein sector the development of 10 100 km scale size bubbles at a given time and location is clearly a consequence of the presence of even larger wavelike corrugations in the f layer provided there is also at least a moderately strong equatorial fountain

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

threshold height h f c for the meridional wind to play a deterministic role in the bottom side equatorial spread f and its dependence on solar activity 1 detailed investigations have been carried out on the occurrence of bottom side equatorial spread f esf and the thermospheric meridional wind characteristics just before the former s initiation using ground based ionospheric data corresponding to the equinoctial periods of 1993 1998 from trivandrum 8 5 n 76 5 e dip 0 5 n and sriharikota 13 7 n 80 2 e dip 10 n in the indian longitudes critical analysis of the base height of the f region h f at the time of triggering of esf and the polarity of the meridional winds revealed that if the h f is above a certain level esf occurred under both equatorward and poleward wind conditions below that level esf occurred only when equatorward winds were present implying that the equatorward winds must somehow be able to offset the reduced growth rate of the plasma instability responsible for esf a plausible explanation linking equatorial ionization anomaly eia and the consequent equatorial temperature and wind anomaly etwa and the consequent neutral dynamics effectively enabling the instability even at lower height has been offered the threshold height h f c gleaned out on the basis of the polarity of the meridional winds has been shown to bear a linear relation to the solar activity and sheds light on the enigmatic short and long term variability of esf

onset conditions for equatorial spread f the problem of day to day variability in the occurrence of equatorial spread f esf is addressed using multidiagnostic observations and semiempirical modeling the observational results are derived from a two night case study of esf onset conditions observed at kwajalein atoll marshall islands using the altair incoherent scatter radar and all sky optical imaging techniques the major difference between nights when esf instabilities did not occur august 14 1988 and did occur august 15 1988 in the kwajalein sector was that the northern meridional gradient of 6300 a airglow was reduced on the night of limited esf activity modeling results suggest that this unusual airglow pattern is due to equatorward neutral winds previous researchers have shown that transequatorial thermospheric winds can exert a control over esf seasonal and longitudinal occurrence patterns by inhibiting rayleigh taylor instability growth rates we present evidence to suggest that this picture can be extended to far shorter time scales namely that surges in transequatorial winds acting over characteristic times of a few hours to a day can result in a stabilizing influence upon irregularity growth rates the seemingly capricious nature of esf onset may thus be controlled in part by the inherent variability of low latitude thermospheric winds

comment on temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw 7 1 hector mine earthquake by su et al 2013 we review the recent paper by su et al 2013 using global position system and global ionospheric maps data su et al claimed to have found ionospheric precursors a few days before the 16 october 1999 hector mine california earthquake they proposed that this type of analysis of ionospheric data may be useful for locating forthcoming large earthquakes in this comment we reexamine these data and show that ionospheric anomalies reported by su et al were not precursors to the hector mine earthquake therefore their proposed analysis is not useful in the context of earthquake prediction

scintillation producing fresnel scale irregularities associated with the regions of steepest tec gradients adjacent to the equatorial ionization anomaly 1 using ground based gps and digital ionosonde instruments we have built up at latitudes of the equatorial ionization anomaly eia in the brazilian sector a time evolving picture of total electron content tec l band amplitude scintillations and f region heights and we have investigated likely reasons for the occurrence or suppression of equatorial scintillations during the disturbed period of 18 23 november 2003 during the prestorm quiet nights scintillations are occurring postsunset as expected however during the storm time period their spatial temporal characteristics and intensity modify significantly owing to the dramatic changes in the ionospheric plasma density distribution and in the temporal evolution of tec the two dimensional maps showing both tec and amplitude scintillations revealed strong evidence of turbulences at the fresnel length causing scintillations concurrent with those regions of steepest tec gradients adjacent to the crests of the eia the largest density gradients have been found to occur in an environment of increased background electron density and their spatial distribution and location during the disturbed period may differ significantly from the magnetic quiet night pattern however in terms of magnitude the gradients at equatorial and low latitudes appear to not change during both magnetic quiet and disturbed conditions the scenarios for the formation or suppression of scintillation producing fresnel scale irregularities during the prestorm quiet nights and disturbed nights are discussed in view of different competing effects computed from numerical simulation techniques

are there new findings in the search for ulf magnetic precursors to earthquakes moore 1964 in a letter published in nature reported disturbances in geomagnetic field data prior to the 27 march 1964 alaska earthquake after the publication of this report many papers have shown magnetic changes preceding earthquakes however a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated as a consequence after 50 years magnetic disturbances in the geomagnetic field are still candidate precursory phenomena some researchers consider the investigation of ultra low frequency ulf 0 001 10 hz magnetic data the correct approach for identifying precursory signatures of earthquakes other researchers instead have recently reviewed many published ulf magnetic changes that preceded earthquakes and have shown that these are not actual precursors the recent studies by currie and waters 2014 and han et al 2014 aim to provide relevant new findings in the search for ulf magnetic precursory signals however in order to contribute to science alleged precursors must be shown to be valid and reproducible by objective testing here we will briefly discuss the state of the art in the search for ulf magnetic precursors paying special attention to the recent findings of currie and waters 2014 and han et al 2014 we do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ulf magnetic records

investigations of thermospheric ionospheric dynamics with 6300 a images from the arecibo observatory pilot observations were conducted at arecibo puerto rico using an all sky image intensified ccd camera system in conjunction with radar ionosonde and global positioning system gps diagnostic systems during the periods january 19 28 1993 and february 21 to august 22 1995 these represent the first use of campaign mode operations of an imager at arecibo for extended periods of f region observations the january 1993 period the so called 10 day run yielded a rich data set of gravity wave signatures perhaps the first case of direct imaging of thermospheric wave train properties in the f region the 6 month 1995 campaign revealed two additional optical signatures of f region dynamics a brightness wave in 6300 a passing rapidly through the field of view fov has been linked to meridional winds driven by the midnight temperature maximum mtm pressure bulge on may 3 1995 during a period of geomagnetic activity a 6300 a airglow depletion pattern entered the arecibo fov such effects represent the optical signatures of equatorial spread f instabilities that rise above the equator to heights near 2500 km thereby affecting arecibo s l 1 4 flux tube

on claimed ulf seismogenic fractal signatures in the geomagnetic field 1 during the last ten years fractal analysis of ultra low frequency ulf geomagnetic field components has been proposed as one of the most promising tools to highlight magnetic precursory signals possibly generated by the preparation processes of earthquakes several papers claim seismogenic changes in the fractal features of the geomagnetic field some months before earthquakes occur the target of the present paper is to put forth a qualitative investigation on the fractal characteristics of ulf magnetic signatures that previous authors have claimed to be related without doubt to strong earthquakes this analysis takes into account both the temporal evolution of the geomagnetic field fractal parameters reported in previous researches and the temporal evolution of global geomagnetic activity running averages of the geomagnetic indices kp and ap are plotted into the original figures from the previous publications this simple analysis shows that the fractal features of the ulf geomagnetic field are closely related to the geomagnetic activity both before and after the earthquake occurs the correlation between the geomagnetic field fractal parameters and geomagnetic activity is clearly shown over both long and short time scales in light of this the present paper shows that fractal behaviors of previously claimed seismogenic ulf magnetic signatures depend mainly on geomagnetic activity due to solar terrestrial interaction therefore previously reported association with the preparation process of the earthquake is dubious

ionospheric electron enhancement preceding the 2011 tohoku oki earthquake 1 the 2011 march 11 tohoku oki earthquake mw9 0 caused vast damages to the country large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics and here i report one such finding the japanese dense network of global positioning system gps detected clear precursory positive anomaly of ionospheric total electron content tec around the focal region it started 40 minutes before the earthquake and reached nearly ten percent of the background tec it lasted until atmospheric waves arrived at the ionosphere similar preseismic tec anomalies with amplitudes dependent on magnitudes were seen in the 2010 chile earthquake mw8 8 and possibly in the 2004 sumatra andaman mw9 2 and the 1994 hokkaido toho oki mw8 3 earthquakes but not in smaller earthquakes

the hector mine california earthquake of 16 october 1999 introduction to the special issue the hector mine california earthquake m w 7 1 struck the mojave desert at 09 46 utc 16 october 1999 the earthquake occurred approximately 55 km northwest of the town of twentynine palms california and about 200 km east northeast of los angeles fig 1 the shock was widely felt throughout southern california southern nevada western arizona and northernmost baja california mexico the hector mine earthquake like the m w 7 3 landers earthquake seven years earlier was associated with fault rupture in the eastern california shear zone ecsz fig 1 which is an approximately 80 km wide zone of deformation that accommodates about 24 of the relative pacific north american plate motion sauber et al 1986 1994 dokka and travis 1990 savage et al 1990 2001 gan et al 2000 miller et al 2001 a block diagram highlighting some of the basic aspects of the hector mine earthquake is presented in figure 2 a preliminary summary of the hector mine earthquake its effects and the response of the geoscience community is presented by scientists from the u s geological survey southern california earthquake center and california division of mines and geology usgs scec and cdmg 2000

an analysis of the quiet time day to day variability in the formation of postsunset equatorial plasma bubbles in the southeast asian region presented is an analysis of the occurrence of postsunset equatorial plasma bubbles epbs detected using a global positioning system gps receiver at vanimo the three year data set shows that the epb occurrence maximizes minimizes during the equinoxes solstices in good agreement with previous findings the vanimo ionosonde station is used with the gps receiver in an analysis of the day to day epb occurrence variability during the 2000 equinox period a superposed epoch analysis sea reveals that the altitude and the change in altitude of the f layer height is 1 standard deviation 1 larger on the days for which epbs were detected compared to non epb days these results are then compared to results from the thermosphere ionosphere electrodynamics general circulation model tiegcm which show strong similarities with the observations the tiegcm is used to calculate the flux tube integrated rayleigh taylor r t instability linear growth rate a sea reveals that the modeled r t growth rate is 1 higher on average for epb days compared to non epb days and that the upward plasma drift is the most dominant contributor it is further demonstrated that the tiegcm s success in describing the observed daily epb variability during the scintillation season resides in the variations caused by geomagnetic activity as parameterized by kp rather than solar euv flux as parameterized by f10 7 geomagnetic activity varies the modeled high latitude plasma convection and the associated joule heating that affects the low latitude f region dynamo and consequently the equatorial upward plasma drift key points day to day epb occurrence in southeast asia investigated using ground based gps tiegcm exhibits similiar daily variability to the epb observations small changes in kp strongly influence daily epb occurrence variability

on the seismogenic increase of the ratio of the ulf geomagnetic field components abstract following the paper by fraser smith et al 1990 many scientists have focused their research on the ulf geomagnetic field pulsations in the hope of finding possible anomalous signals caused by the seismic activity thereafter many papers have reported ulf geomagnetic field polarization ratio increases which have been claimed to be related to the occurrence of moderate and strong earthquakes even if there is no firm evidence of correlation between the polarization ratio increase and seismic events these publications maintain that these anomalous increases are without doubt precursors of pending earthquakes furthermore several researchers suggest that these seismogenic signals may be considered a promising approach towards the possibility of developing short term earthquake prediction capabilities based on electromagnetic precursory signatures on the contrary a part of the scientific community emphasizes the lack of validation of claimed seismogenic anomalies and doubt their association with the seismic activity since earthquake prediction is a very important topic of social importance the authenticity of earthquake precursors needs to be carefully checked the aim of this paper is to investigate the reliability of the ulf magnetic polarization ratio changes as an earthquakes precursor several polarization ratio increases of the geomagnetic field which previous researchers have claimed to have a seismogenic origin are put into question by a qualitative investigation the analysis takes into account both the temporal evolution of the geomagnetic field polarization ratio reported in previous papers and the global geomagnetic activity behaviour running averages of the geomagnetic index k p are plotted onto the original figures from previous publications moreover further quantitative analyses are also reported here nine cases are investigated which include 17 earthquakes in seven cases it is shown that the suggested association between the geomagnetic field polarization ratio increases and the earthquake preparation process seems to be rather doubtful more precisely the claimed seismogenic polarization ratio increases are actually closely related to decreases in the geomagnetic activity level furthermore the last two investigated cases seem to be doubtful as well although a close correspondence between polarization ratio and geomagnetic activity cannot be unambiguously demonstrated

iterative deconvolution of regional waveforms and a double event interpretation of the 2003 lefkada earthquake greece the moment tensor inversion for multiple point sources based on kikuchi and kanamori 1991 was extended to full waveform data at regional or local distances the new code proved to be efficient for retrieving major source contributions of the 2003 lefkada greece earthquake the source model was derived from five three component regional stations epicentral distances 140 km at periods 10 20 s two main events dominated the rupture process one at the lefkada island comprising three subevents of total moment 0 9 1018 n m and the other at the cephalonia island comprising one subevent of 0 5 1018 n m their spatial and temporal separation is 40 km and 14 s respectively they can be understood as two earthquakes the uncertainty estimate based on reduced data sets repeatedly excluding a station shows that the cephalonia subevent and the major lefkada subevent are very well resolved regarding their position time and focal mechanism the source model explains well the aftershock distribution characterized by two clusters at the lefkada and cephalonia islands respectively the focal mechanisms of the two main subevents are predominantly right lateral strike slip of south southwest north northeast orientation the cephalonia subevent occurred on a less steeply dipping fault with a small thrust component large deviations from pure double couple were found but interpreted as artifacts the new software developed in this article fortran code and matlab graphic user interface is freely available online material color graphics and 3d visualization of the 2003 lefkada earthquake sequence

on the reported magnetic precursor of the 1993 guam earthquake 1 using 1 second magnetometer data recorded 67 km from the epicenter of the 1993 mw 7 7 guam earthquake hayakawa et al 1996 and miyahara et al 1999 identify anomalous precursory changes in ultra low frequency magnetic polarization the ratio of vertical to horizontal field components in a check of their results we compare their data gam with 1 second data from the kakioka observatory kak in japan and the global magnetic activity index kp we also examine log books kept by usgs staff working on the guam magnetic observatory we find 1 analysis problems with both hayakawa et al and miyahara et al 2 significant correlation between the gam kak and kp data and 3 an absence of identifiable localized anomalous signals occurring prior to the earthquake the changes we do find in polarization are part of normal global magnetic activity they are unrelated to the earthquake

on the generation and growth of equatorial backscatter plumes 2 structuring of the west walls of upwellings the west wall of large scale upwellings that develop in the bottomside of the nighttime equatorial f layer becomes structured by the wind driven gradient drift instability the same process that leads to the formation of striations in barium ion clouds upwellings are initiated by wavelike perturbations with long spatial wavelengths 400 km and are amplified by the collisional rayleigh taylor instability and sometimes assisted by the gradient drift instability in the case of an upward moving f layer the west wall structuring process is driven by an eastward neutral wind enhanced by reduced drag during the postsunset hours and a velocity shear in east west bulk plasma drift in the bottomside f layer west wall structures evolve in a manner analogous to primary plasma bubbles i e secondary plasma bubbles grow from the west wall their characteristics are compared with those of the primary bubbles and discussed in the light of existing theories

measurement of the latitudinal distributions of total electron content during equatorial spread f events we have constructed latitudinal profiles of the total electron content tec using measurements from six gps receivers conducted during 1998 the tec profiles have been divided into two groups one corresponds to days when plumes or equatorial spread f esf develops and the second group portrays days of no esf condition the presence absence of esf is based on the signature of the coherent echoes measured by the jicamarca unattended long term investigation julia radar and records of scintillations from two sites spaced in latitude one scintillation station is located near the magnetic equator ancon and the other 12 southward antofagasta the tec profiles display the typical day to day and seasonal variability seen at low latitudes during the equinoxes we observed quite often the crests of the anomaly located between 12 and 20 away from the magnetic equator and a trough in between the monthly distribution of the appearance of the anomaly and the local time of their appearance are in very good agreement with the reported variability of the upward vertical drifts and the current theory of the equatorial fountain effect during the equinoxes and the december solstice the tec anomaly is observed almost every day sometimes when there is no esf activity nevertheless fine inspection of the tec latitudinal profiles suggests the existence of a close relationship between the temporal evolution of the tec profiles near sunset and the onset of esf we have examined the tec latitudinal distributions in two different ways first we calculated time difference profiles using the distributions corresponding to 1800 and 2000 lt second we used a parameterization of the tec distributions obtained at 2000 lt the first method indicates quite drastic increases of the crest values and sharp decreases near the trough during esf days in contrast during days of no esf there exist almost uniform tec decreases at all latitudes the second method displays a preferred high crest trough ratio 2 small tec values at the trough and large latitudinal integrated values during esf events

evolutionary phases of equatorial spread f including l band scintillations and plumes in the context of gps total electron content variability a case study 1 the evolution of large scale few kilometers medium scale few hundreds of meters and small scale meters size plasma density irregularities in the postsunset equatorial f region in the context of characteristic gps total electron content gtec variations are reported from indian longitudes the ionograms and gtec from a gps receiver installed as a part of the gps aided geo augmentation network gagan project for satellite based navigation are obtained from an equatorial station at trivandrum 8 5 n 76 91 e dip latitude 0 5 n the variations in the gtec with respect to tec are considered to represent the seed perturbations for the plasma instability that results in the equatorial spread f esf irregularities and are treated as a perturbation factor p the vhf radar at gadanki 13 5 n 79 17 e dip latitude 6 4 n provided the small scale structures of esf the background thermospheric conditions that affect the growth of the plasma instability through ion neutral collision frequency in are estimated using the f region base height h f and the representative scale height of the neutral atmosphere and are represented by a growth factor g the present case study reveals a close coupling between the background ionospheric conditions and the baseline perturbations in deciding the evolutionary phases of esf it has been shown that although large scale kilometer scale irregularities are formed without any constraints when the background ionospheric thermospheric conditions are favorable in the presence of fluctuations in gtec consistently the medium scale and small scale irregularities show remarkable similarity with the variations in the product of the perturbation and growth factors

reply to comment by f masci and j n thomas on temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw7 1 hector mine earthquake

de 2 observations of morningside and eveningside plasma density depletions in the equatorial ionosphere the occurrence of equatorial density depletions in the nightside f region ionosphere has been investigated by using observations gathered by the polar orbiting dynamics explorer 2 satellite from august 1981 to february 1983 a variety of electric field plasma drift patterns were observed within these depletions including updrafting downdrafting bifurcating converging subsonic and supersonic flows the depletions 116 events in total are distributed over two groups group i eveningside depletions consists of the events in the 1900 2300 mlt sector and group ii morningside depletions are the events in the 2300 0600 mlt sector a statistical analysis reveals clear differences in the density depletion occurrence rates between the two groups magnetic activity appears to suppress the generation of eveningside depletions with a delay of 2 3 hours in the morningside the probability of observing depletions increases instantly with increasing magnetic activity yet the best correlation is found with a 2 hour delay this indicates that in the premidnight sector the substorm induced dynamo and prompt penetration electric fields induce westward electric fields in the equatorial ionosphere 2 hours after the onset in the auroral region in the postmidnight sector high latitude ionospheric disturbances induce instantly equatorial eastward electric fields that move the f layer to higher altitudes where it can become unstable to the rayleigh taylor instability eveningside depletions were observed at all longitudes except those over the pacific ocean while the morningside depletions occurred mostly over the pacific and atlantic african sectors

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

on the reported ionospheric precursor of the 1999 hector mine california earthquake 1 using global positioning system gps data from sites near the 16 oct 1999 hector mine california earthquake pulinets et al 2007 identified anomalous changes in the ionospheric total electron content tec starting one week prior to the earthquake pulinets 2007 suggested that precursory phenomena of this type could be useful for predicting earthquakes on the other hand and in a separate analysis afraimovich et al 2004 concluded that tec variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake in an investigation of these very different results we examine tec time series of long duration from gps stations near and far from the epicenter of the hector mine earthquake and long before and long after the earthquake while we can reproduce the essential time series results of pulinets et al we find that the signal they identified as being anomalous is not actually anomalous instead it is just part of normal global scale tec variation we conclude that the tec anomaly reported by pulinets et al is unrelated to the hector mine earthquake

impact of meridional winds on equatorial spread f revisited 1 the impact of meridional winds on the onset and evolution of equatorial spread f esf is studied using the nrl ionosphere model sami3 esf the prevailing belief is that meridional winds have a stabilizing effect on the onset of esf in this letter it is shown that this is not necessarily the case and that meridional winds can be destabilizing we find that a wind profile with a positive gradient as a function of latitude v m 0 is a stabilizing influence on the generalized rayleigh taylor instability a wind profile with a negative gradient v m 0 is a destabilizing influence here a northward wind is positive and increases in the northward direction it is suggested that meridional wind profiles may account for in part the longitudinal and day to day variability of esf

the cephalonia transform fault and its extension to western lefkada island greece the central area of the ionian islands is dominated by the existence of a major tectonic structure called the cephalonia transform fault ctf its main part cephalonia segment has been identified by previous work based on the spatial distribution of earthquake foci fault plane solutions of strong earthquakes active tectonics structural studies and geodetic measurements this part cephalonia segment which exhibits strike slip motion with a thrust component strikes in a northeast direction dips to the southeast and has a length of 90 km in the present paper information concerning new fault plane solutions orientation of isoseismals sea bottom topography and recent gps results are used to further check the properties of this southern part of the ctf and to explore its northeastward prolongation to lefkada island it is shown that the ctf is extended to the western coast of lefkada this northern branch lefkada segment of the ctf which is also characterized by strike slip motion with a thrust component strikes in a north northeast direction dips to the east southeast and has a length of 40 km these two segments of the ctf form a major kinematic boundary where the slip rate is 2 3 cm yr

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

the ionospheric anomalies prior to the m9 0 tohoku oki earthquake the gps total electron content tec data were used to investigate the ionospheric abnormal behaviors prior to the 2011 tohoku oki earthquake the observations show a significant enhancement in tec on march 8 2011 and during the same period the solar activity also has a large increase both an empirical model and a theoretical model were used to check whether the tec anomalies were entirely contributed by the increase in solar radiation the comparison between the observations and the simulation results shows that only the solar radiation enhancement was not enough to produce the observed significant tec enhancement it means that some additional mechanisms such as the per earthquake ionospheric disturbance or the geomagnetic activities may play a significant role in the significant tec enhancement on march 8 the temporal spatial distribution of the extreme tec enhancement within 30 days before the earthquake was particularly pursued it is found that the extreme enhancement was persistently located in the region adjacent to the epicenter and the magnetic conjugate point for a long time of 16 h in addition a geomagnetic disturbance with kp 4 occurred on march 7 therefore the significant tec enhancement on march 8 might be related to the m9 0 tohoku oki earthquake and the geomagnetic disturbance

temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw7 1 hector mine earthquake 1 in this paper temporal and spatial analyses are employed to detect seismo ionospheric precursors sips in the ionospheric total electron content tec during the 16 october 1999 mw7 1 hector mine earthquake to discriminate anomalies caused by global effects such as solar radiations magnetic storms etc and local effects such as earthquake we cross examine the gps tecs and their gradients in the eastward and northward directions at epicenter centers of the hector mine area and the other two reference areas at similar magnetic latitudes in europe and japan temporal variations of the northward tec gradient suggest sips most likely appearing on days 6 5 before the earthquake a global search by using the tec of the global ionosphere map shows that the tec increase and decrease anomalies continuously and specifically appear around the epicenter on day 5 before the earthquake

the study of ionospheric anomalies in japan area during 1998 2010 by kon et al an inaccurate claim of earthquake related signatures abstract the problem of identifying precursory signals of earthquakes in the hope of mitigate the seismic hazard is a very important topic but inaccurate documentations of precursory signatures decrease the credibility of this field of research the statistical analysis by kon et al 2011 shows that there is tendency of positive total electron content tec anomalies to occur 1 5 days before 52 m 6 earthquakes which struck japan during 1998 2010 kon et al 2011 also report in detail three selected case studies claiming the occurrence of tec anomalies possibly related to large and destructive earthquakes this paper casts doubts on the possibility that in the three cases the tec disturbances were caused by seismic events suggesting that these tec changes could be induced by normal variations of the global geomagnetic activity as a consequence also the results of the superimposed epoch analysis performed by kon et al 2011 could be seriously influenced by global magnetospheric signals

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

explicit characteristics of evolutionary type plasma bubbles observed from equatorial atmosphere radar during the low to moderate solar activity years 2010 2012 using the fan sector backscatter maps of 47 mhz equatorial atmosphere radar ear at kototabang 0 2 s geographic latitude 100 3 e geographic longitude and 10 4 s geomagnetic latitude indonesia the spatial and temporal evolution of equatorial plasma bubbles epbs were examined to classify the evolutionary type epbs from those which formed elsewhere and drifted into the field of view of radar a total of 535 epbs were observed during the low to moderate solar activity years 2010 2012 out of which about 210 39 are of evolving type and the remaining 325 61 are drifting in epbs in general both the evolving type and drifting in epbs exhibit predominance during the postsunset hours of equinoxes and december solstices interestingly a large number of epbs were found to develop even a few minutes prior to the apex sunset during equinoxes further the occurrence of evolving type epbs exhibits a clear secondary peak around midnight 2300 0100 lt primarily due to higher rate of occurrence during the postmidnight hours of june solstices a significant number 33 of postmidnight epbs generated during june solstices did not exhibited any clear zonal drift while about 14 of epbs drifted westward also the westward drifting epbs are confined only to june solstices the responsible mechanisms for the genesis of fresh epbs during postmidnight hours were discussed in light of equatorward meridional winds in the presence of weak westward electric fields

recent progress in ionospheric earthquake precursor study in china a brief review abstract the study of ionospheric anomaly variation before large earthquakes has attracted the attention of geophysicists for many years this is primarily because ionospheric anomaly variation has been considered to constitute one possible method to identify earthquake precursors since china covers several major earthquake zones it is critical for chinese scientists to study possible ionospheric earthquake precursors in this report we provide a brief summary of recent progress in the study of ionospheric earthquake precursors mainly from chinese mainland researchers as well as some other scientists this report focuses on 1 some case studies of ionospheric abnormal behaviors before some great earthquakes around the world e g m7 9 wenchuan earthquake m9 0 tohoku oki earthquake m7 0 haiti earthquake and 2 some statistical characteristics of ionospheric anomalies before earthquakes including their temporal and spatial distributions and the relationship with the forthcoming earthquake the above mentioned studies may provide some new and beneficial insights for the future study of ionospheric earthquake precursors

challenges in the detection of ionospheric pre earthquake total electron content anomalies peta for earthquake forewarning various studies have investigated the link between seismic activity and ionospheric precursory phenomena many of these retrospective case studies have supported the existence of pre earthquake ionospheric anomalies by examining past earthquake events using a variety of analytical methods based on existing methodologies however the conversion of a retrospective analysis to a prospective forewarning scenario is not a straightforward process the obstacles to its potential adoption stem mainly from assumptions made during data analysis and interpretation in this study several parameters pertaining to existing approaches for the detection of these ionospheric anomalies are highlighted and discussed in particular ionosphere total electron content tec a detailed examination is conducted to understand the roles that each of these parameters play in the detection process and the consequent difficulties when adopting them in a prospective analysis these issues include accounting for variations in ionosphere characteristics owing to different measurement platforms e g ground and space based observations and statistical methods e g standard deviation envelopes used in detecting anomalies furthermore the necessity of excluding space weather contributions in the underlying tec fluctuations poses a challenge in determining the validity of observed ionospheric anomalies the notion of an earthquake preparation zone is also evaluated in the context of the ionosphere along with its implications in a forewarning scenario these issues need to be addressed in current research in order to enable its possible application in earthquake forewarning

relationship of the onset of equatorial f region irregularities with the sunset terminator observed with the equatorial atmosphere radar 1 the relationship between sunset terminators and the onset of radar backscatter plumes associated with equatorial spread f esf observed with the 47 mhz equatorial atmosphere radar from october 2002 to april 2004 is discussed almost all irregularity echoes began to appear at or before sunset time at the altitude of the apex of the geomagnetic field line connected with the observed area and the onset time of more than half of the events corresponded exactly to apex sunset time this tendency should be due to two causes 1 the rapid change of the evening zonal electric field and 2 damping of 3 m scale irregularities by the solar radiation before the apex sunset

on the generation and growth of equatorial backscatter plumes 1 wave structure in the bottomside f layer we examine the initial conditions that lead to backscatter plume development in the equatorial f region ionosphere by analyzing altair radar data we obtained the following principal results 1 prior to plume development an altitude modulation of electron density contours exists in the bottomside f layer these quasi periodic variations were mapped spatially over a 1200 km east west distance by using incoherent scatter measurements and found to consist of three cycles with an average spatial wavelength of 400 km 2 the wave structure observed in the bottomside electron density contours grew in amplitude at a rate consistent with that predicted by the generalized gradient drift instability 3 bottomside backscatter developed on the west walls of all three altitude modulated regions followed by plume development from near the crests of these regions

on the reported magnetic precursor of the 1989 loma prieta earthquake among the most frequently cited reports in the science of earthquake prediction is that by fraser smith et al 1990 and bernardi et al 1991 they found anomalous enhancement of magnetic field noise levels prior to the 18 october 1989 loma prieta earthquake in the ultra low frequency range 0 0110 10 001 hz from a ground based sensor at corralitos ca just 7 km from the earthquake epicenter in this analysis we re examine all of the available corralitos data 21 months from january 1989 to october 1990 and the logbook kept during this extended operational period we also examine 1 0 hz 1 s data collected from japan 0 0167 hz 1 min data collected from the fresno ca magnetic observatory and the global kp magnetic activity index the japanese data are of particular importance since their acquisition rate is sufficient to allow direct comparison with the lower frequency bands of the corralitos data we identify numerous problems in the corralitos data evident from both straightforward examination of the corralitos data on their own and by comparison with the japanese and fresno data sets the most notable problems are changes in the baseline noise levels occurring during both the reported precursory period and at other times long before and after the earthquake we conclude that the reported anomalous magnetic noise identified by fraser smith et al and bernardi et al is not related to the loma prieta earthquake but is an artifact of sensor system malfunction 2008 elsevier b v all rights reserved

evolution of equatorial irregularities under varying electrodynamical conditions a multitechnique case study from indian longitude zone 1 a comprehensive multitechnique study on the postsunset evolutions of equatorial ionization anomaly eia and equatorial plasma density irregularities in the context of the varying electrodynamical conditions under normal equatorial electrojet eej complete and partial counter electrojet cej events is presented from the indian longitude zone the study involves analysis of scintillation data at vhf 250 mhz and gps l1 1575 42 mhz frequency ionosonde data magnetometer data along with global ionospheric maps gims of total electron content tec for the vernal equinoctial months march april of 2011 the investigation reveals inefficiency of the noontime peak eej to dictate the day to day variability of postsunset irregularity phenomena intensification of eej after 1530 ist indian standard time on normal eej days and significantly enhanced residual fields presumably due to cej event after 1700 ist on complete and partial cej days are found to be associated with the resurgence of eia and evolution of postsunset irregularities the results are discussed in terms of superposition effects of electric fields arising from e and f region dynamos

a statistical study of global ionospheric map total electron content changes prior to occurrences of m 6 0 earthquakes during 2000 2014 there are many reports on the occurrence of anomalous changes in the ionosphere prior to large earthquakes however whether or not these changes are reliable precursors that could be useful for earthquake prediction is controversial within the scientific community to test a possible statistical relationship between ionospheric disturbances and earthquakes we compare changes in the total electron content tec of the ionosphere with occurrences of m 6 0 earthquakes globally for 2000 2014 we use tec data from the global ionosphere map gim and an earthquake list declustered for aftershocks for each earthquake we look for anomalous changes in gim tec within 2 5 latitude and 5 0 longitude of the earthquake location the spatial resolution of gim tec our analysis has not found any statistically significant changes in gim tec prior to earthquakes thus we have found no evidence that would suggest that monitoring changes in gim tec might be useful for predicting earthquakes

observations and modeling of the coupled latitude altitude patterns of equatorial plasma depletions 1 the equatorial ionosphere is host to the most dramatic and enigmatic plasma instability mechanism in the geospace environment equatorial spread f esf was discovered in early ionosonde measurements and interpreted theoretically using rayleigh taylor theory subsequent diagnostic and modeling advances have improved substantially our understanding of esf onset and evolution and its associated effects on the ionosphere throughout the low latitude domain the degree to which esf mechanisms penetrate into the lower midlatitudes is a topic of current study a reverse of the familiar concept of high to low latitude coupling for space weather phenomena optical diagnostic systems first ground based and now space based reveal the presence of esf structures via images of airglow depletions that are aligned in the approximately north south direction spanning the geomagnetic equator ground based all sky camera systems used to capture the two dimensional horizontal patterns of airglow depletions are the main source of observations showing that esf processes intrude to midlatitudes in the l 1 5 domain in this paper we review the process of mapping airglow depletions along geomagnetic field lines to the equatorial plane hence defining the maximum apex heights achieved a case study comparison of simultaneous radar backscatter data from kwajalein with optical data from wake island sites that share common magnetic meridians in the pacific section confirms the utility of the approach and its applicability to sites at other longitudes modeling studies based on buoyancy arguments using flux tube integrated mean density values versus l shell apex heights show that instability induced plasma depletions starting at f layer bottomside heights easily reach altitudes above 2000 km in the equatorial plane implying that esf intrusions to lower midlatitudes should be a relatively frequent occurrence

coordinated measurements of f region dynamics related to the thermospheric midnight temperature maximum abstract as part of the nsf cedar program coupling energetics and dynamics of atmospheric regions in multi instrumented studies of equatorial thermospheric aeronomy miseta an all sky ccd airglow imaging system has been in operation in arequipa peru since october 1993 here we report on the first such use of a wide field imager to document the optical signature and variability of a brightness feature associated with the so called midnight temperature maximum mtm while the observational driver of this study is a rightness wave bw seen in 6300 a and 5577 airglow images detailed case studies are conducted during two campaign periods when fabry perot interferometer fpi and digital ionosonde data were also available during the passage of a bw the fpi observed enhancements in thermospheric temperatures reversals from equatorward to poleward of the meridional neutral winds and local minima in the zonal neutral winds the ionosonde recorded decreases in the height of the f layer during bw events this lends support to the concept that the poleward winds generated by the mtm pressure bulge cause the lowering of the f layer to regions of enhanced loss h 300 km and corresponding airglow production the two dimensional field of view of the imager allows identification of the geographical orientation of the bw pattern we use the orientation angle of the bw as an indicator of the geographical orientation of the mtm significant day to day variability in these patterns suggest a complex mix of tidal mode interactions that lead to the overall mtm phenomena

characteristics of large scale wave structure observed from african and southeast asian longitudinal sectors the spatial large scale wave structure lsws at the base of f layer is the earliest manifestation of seed perturbation for rayleigh taylor instability hence found to play a deterministic role in the development of equatorial plasma bubbles epbs except for a few case studies a comprehensive investigation has not been conducted on the characteristics of lsws because of the complexity involved in detecting the lsws particularly in spatial domain in this scenario a comprehensive study is carried out for the first time on the spatial and temporal characteristics of lsws observed in spatial domain over african and southeast asian longitudinal sectors during the year 2011 the observations indicate that these wave structures can be detected a few degrees west of e region sunset terminator and found to grow significantly at longitudes past the sunset terminator the phase fronts of these spatial structures are found to align with the geomagnetic field b lines over a latitudinal belt for at least 5 6 500 600 km centered on dip equator the zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports and the epbs were consistently observed when the amplitudes of lsws were grown to sufficient strengths these results would provide better insights on the underlying physical processes involved in excitation of lsws in terms of important roles being played by e region electrical loading and polarization electric fields induced via spatially varying dynamo current due to neutral wind perturbations associated with atmospheric gravity waves

lack of precursory slip to the 1999 hector mine california earthquake as constrained by insar we looked for evidence of interseismic strain occurring between the 1992 landers earthquake and the 1999 hector mine earthquake near the lavic lake and bullion faults by using interferometric synthetic aperture radar insar interferograms covering the hector mine epicentral region were studied for possible slip along the bullion and lavic lake faults by both visual inspection and a matched filter technique intended to emphasize slip located at the nucleation point some indications of possible deformation associated with the 5 july 1992 m l 5 4 pisgah event was observed but high decorrelation prevented a conclusive determination we have seen no evidence for precursory slip in the epicentral region up to 30 days before the hector mine event we estimated that the slip equivalent to a m w 4 5 event would have been observable in the months before the hector mine event and this places an upper bound on the long term precursory slip had it occurred we have noted that insar is well suited for detecting precursory slip in general due to the high spatial resolution and the lack of ground instrumentation required but that the detection level depends on the depth and orientation of the slip back

gradual reduction in ionospheric f 2 region before the 2013 lushan earthquake contributed to the forthcoming earthquake or solar activity ionospheric anomalies before earthquakes during geomagnetic quiet conditions have been extensively discussed due to the importance of earthquake prediction however because of the high variability of ionosphere a real caution should be adopted before attributing the observations to seismo ionospheric precursors sips in an investigation of contradictory results in ionospheric variation before 2013 lushan earthquake we examine the ionospheric variation versus solar activity in order to assess the influence of solar activity of 27 day periodicity on ionospheric variation a quadratic regression model is developed by using the data of f2 layer critical frequency fof2 in april of 2008 2014 using the model ionospheric variation before the 2013 lushan earthquake is analyzed the results show that fof2 was strongly correlated with solar activity index f10 7 and had a low correlation with the remaining by eliminating the contribution of solar radiation which indicates that the gradual reduction in fof2 before the earthquake was contributed to the variation of solar radiation rather than the forthcoming earthquake

the condor equatorial spread f campaign overview and results of the large scale measurements during the condor campaign a number of instruments were set up in peru to support the rocket experiments in this series of papers we report on the results of the experiments designed to study the equatorial f region in this overview paper we summarize the main results as well as report upon the macroscopic developments of spread f as evidenced by data from backscatter radas from scintillation observations and from digital ionosonde meaurements in this latter regard we argue here that at least two factors other than the classical gravitational rayleigh taylor plasma instability process must operate to yield the longest scale horizontal organization of spread f structures the horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow although detailed comparison with theory seems to require shear frequencies a bit higher than observa tions indicate on the other hand the largest scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions using simultaneous rocket and radar data we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over jicamarca are primarily spatial structures advecting overhead the detailed rocket radar compari son verified several other earlier results and speculations particularly those made in the plumex experiments in particular companion papers discuss and extend some of the plumex results to include the role of anomalous diffusion labelle et al this issue in the theory of equatorial spread f and to shed light upon the shallow spectral form often observed in the intermediate scale regime labelle and kelley this issue

global distribution of density irregularities in the equatorial ionosphere we analyzed measurements of ion number density made by the retarding potential analyzer aboard the atmosphere explorer e ae e satellite which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km large scale 60 km density measurements in the high altitude regions show large depletions of bubble like structures which are confined to narrow local time longitude and magnetic latitude ranges while those in the low altitude regions show relatively small depletions which are broadly distributed in space for this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation n n over a path length of 18 km as an indicator of overall irregularity intensity seasonal variations of irregularity occurrence probability are significant in the pacific regions while the occurrence probability is always high in the atlantic african regions and is always low in the indian regions we find that the high occurrence probability in the pacific regions is associated with isolated bubble structures while that near 0 longitude is produced by large depletions with bubble structures which are superimposed on a large scale wave like background considerations of longitude variations due to seeding mechanisms and due to f region winds and drifts are necessary to adequately explain the observations at low and high altitudes seeding effects are most obvious near 0 longitude while the most easily observed effect of the f region is the suppression of irregularity growth by interhemispheric neutral winds

a long term seismic quiescence before the 2004 sumatra mw 9 1 earthquake the 2004 sumatra m w 9 1 earthquake was preceded by a seismic quiescence that began 13 years before the mainshock an earthquake catalog created by the international seismological centre is analyzed in the study area 80 110 e 10 s 20 n between 1964 and 2004 including 1153 earthquakes shallower than 100 km with body wave magnitude of 5 0 m b 6 7 a detailed analysis of the earthquake catalog using a gridding technique zmap shows the quiescent area is located between 3 and 6 n which covers the southeastern part of the focal area including the rupture initiation point of the 2004 sumatra earthquake the observed spatial pattern of quiescence can be explained by stress perturbation due to a long term slow slip located on the deeper edge of the mainshock fault which is predicted by a numerical simulation based on a laboratory derived friction law although the quiescence is not significant statistically it may still be considered unlikely that such an anomalous quiescence would occur at almost the same time and location as other long term anomalies reported in the previous studies including decreases in b value and tidal triggering

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

analysis of ultralow frequency electromagnetic field measurements associated with the 1999 m 7 1 hector mine california earthquake sequence we installed two electromagnetic em monitoring systems in the im mediate aftermath of the 16 october 1999 hector mine earthquake to search for possible continuing ultralow frequency ulf em activity due to the mainshock as well as for any precursory or coseismic em signals that might be associated with large aftershocks we installed the first portable monitoring system 2 5 days after the m 7 1 hector mine earthquake at a location 16 km southeast of the epicenter and 2 km east of the surface rupture a second system was installed on 29 october 1999 10 km northwest of the epicenter and within 100 m of the surface rupture our continuous measurements of multiple component magnetic field electric field and ground motion span the low frequencies appropriate for recording possible em sig nals generated at seismogenic depths and were carried out during 3 months following the mainshock continuous magnetic field measurements at observatory em stations operating in california are used as remote reference sites to remove global atmo spheric signals which helps isolate local terrestrial sources of interest our analysis of preseismic ulf em variations the coseismic response the 2 month long magnetic field power spectra and electric field polarization shows no anomalous behavior clearly associated with seismic activity

a statistical analysis of equatorial plasma bubble structures based on an all sky airglow imager network in china this paper investigates the statistical features of equatorial plasma bubbles epbs using airglow images from 2012 to 2014 from a ground based network of four imagers in the equatorial region of china it is found that 1 epbs mainly occur during 21 00 00 00 local time lt in equinoxes there is an asymmetry in occurrence rates between march june and september equinoxes december solstices 2 most epbs occur in groups of two to six depletions the distance between adjacent epb depletions is 100 700 km and the average is 200 300 km the zonal extension of an epb group is usually less than 1500 km but can reach 3000 km 3 epbs usually have a maximum drift velocity near 100 m s at 21 00 22 00 lt in 9 5 1 5 geomagnetic latitude and then decrease to 50 70 m s toward sunrise 4 the averaged westward tilt angle of most epbs with respect to the geographic north south increased from 5 10 to 23 30 with lt between 20 00 and 03 00 lt then decreasing to 10 20 toward sunrise 5 when 90 140 the maximum pmle increases by 3 4 5 5 when f10 7 changes from 90 to 190 6 the epb occurrence patterns and zonal drift velocities are significantly different from those at kolhapur india which locates west to our stations by 20 0 32 0 in longitude

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

coupled interaction of earthquake nucleation with deep earth gases a possible mechanism for seismo electromagnetic phenomena summary the mechanisms of seismo electromagnetic phenomena remain largely unexplained to address this issue we introduce a fault model that takes account of a coupled interaction between earthquake nucleation and deep earth gases this interaction causes a negatively electrified gas flow due to an exo electron attachment reaction as the gases pass through fractured asperities this transient activity may be regarded to be a pressure impressed electric current generator in the model the current and frequency are formulated as functions of earthquake parameters the estimated current is sufficient to explain the seismic electromagnetic signals observed at ground level a physical model of how current generation is coupled with ionospheric electromagnetic disturbances is explained in terms of magnetic induction coupling for strong offshore earthquakes which may provide a plausible explanation of observed ionospheric electron enhancement prior to some recent offshore earthquakes the model also suggests that geomagnetic observations close to an epicentre of a strong offshore earthquake may provide an effective means of detecting clear and identifiable precursor signals

the egion june 15 1995 6 2m l earthquake western greece on june 15 1995 at 00 15 gmt a devastating earthquake 6 2m l occurred in the western end of the gulf of corinth this was followed 15 min later by the largest aftershock 5 4m l the main event was located by the university of patras seismological network patnet at the northern side of the gulf of corinth graben the second event 5 4m l was located also by patnet near the city of egion on a fault parallel to the eliki major fault that defines the south bound of the gulf of corinth graben a seismogenic volume that spans the villages of akrata se and rodini nw and extends to eratini ne was defined by the aftershock sequence which includes 858 aftershocks of magnitude greater than 2m l that occurred the first seventeen days the distribution of hypocentres in cross section does not immediately suggest a planar distribution but rather defines a volume about 15 km depth by 35 km nw se and by 20 km ne sw

an overview of the early november 1993 geomagnetic storm this paper describes the development of a major space storm during november 2 11 1993 we discuss the history of the contributing high speed stream the powerful combination of solar wind transients and a corotating interaction region which initiated the storm the high speed flow which prolonged the storm and the near earth manifestations of the storm the 8 day storm period was unusually long the result of a high speed stream maximum speed 800 km s emanating from a distended coronal hole storm onset was accompanied by a compression of the entire dayside magnetopause to within geosynchronous earth orbit geo for nearly 12 hours the near earth environment was in a state of tumult a super dense plasma sheet was observed at geo and severe spacecraft charging was reported the effects of electrons precipitating into the atmosphere penetrated into the stratosphere subauroral electron content varied by 100 and f layer heights oscillated by 200 km equatorial plasma irregularities extended in plumes to heights of 1400 km later energetic particle fluxes at geo recovered and rose by more than an order of magnitude a satellite anomaly was reported during the interval of high energetic electron flux model results indicate an upper atmospheric temperature increase of 200 k within 24 hours of storm onset joule heating for the first 24 hours of the storm was more than 3 times that for typical active geomagnetic conditions we estimate that total global ionospheric heating for the full storm interval was 190 pj with 30 of that generated within 24 hours of storm onset

onset conditions of equatorial range spread f at fortaleza brazil during the june solstice case studies are made of the ionospheric thermospheric and geomagnetic conditions associated with the occasional onset of range spread f at fortaleza 4 s 38 w dip latitude 1 8 and magnetic declination 21 w brazil in the june solstice a season in which frequency spread f is typically seen in the postsunset hours after 2000 lt it is found that the f layer experiences quite consistently a large vertical drift early in the evening hours 1815 1915 lt on days of range spread f in comparison to days of only frequency spread f the anomalously large dusk time vertical plasma drift occurs under both geomagnetically disturbed and quiet conditions there is no significant change in the pattern of meridional neutral winds at and prior to the time of onset of range spread f estimated from the data of f layer peak height hmax at the low latitude station cachoeira paulista 23 s 45 w and dip 26 5 s using a modified form of the servo model the results strongly suggest that though the meridional poleward wind is very effective in inhibiting the growth of rayleigh taylor r t instability and hence range spread f at fortaleza during the june solstice as shown by maruyama 1996 its variability does not play an important role in creating favorable conditions for r t instability on a day to day basis the prerequisite for the occasional occurrence of range spread f at fortaleza in the june solstice seems to be the presence of an impulsive and large f layer vertical plasma drift a condition favorable for destabilizing the bottomside f region through r t instability mechanism because of the high altitude of the layer

comparison of topside and bottomside irregularities in equatorial f region ionosphere numerical simulations have been carried out to study and compare the mechanisms of the formations of the topside and bottomside ionospheric irregularities as is well known the topside ionospheric irregularities have always originated from the bottomside ionosphere due to gravitational rayleigh taylor grt instability from the penetration process we found that the primary bubble with a horizontal scale of tens of kilometers always has a smooth shape in the bottomside ionosphere and breaks into much smaller scale structures after penetrating into deep topside ionosphere since the plasma bubble is unlikely to break into irregularities in the bottomside ionosphere the bottomside irregularities probably result from the turbulence in the neutral atmosphere examples of simulations are presented to demonstrate that bottomside irregularities may exist in a region with a strong neutral wind jet and seeding gravity wave motion a strong neutral jet stream always has a strong vertical wind shear which provides a broad height range of dynamic instability when the atmospheric gravity wave approaches its critical level its amplitude will continually grow to break into smaller scale waves and turbulence then all the waves of different scales as well as the turbulence will become the seeds of the bottomside irregularities

scintillations plasma drifts and neutral winds in the equatorial ionosphere after sunset an equatorial campaign was conducted during september 25 to october 7 1994 to investigate the neutral and plasma dynamics in the equatorial ionosphere after sunset in relation to the day to day variability of the occurrence of equatorial spread f esf the campaign was organized under the auspices of national science foundation s multi instrumented studies of the equatorial thermosphere aeronomy program miseta which included the jicamarca radar spaced antenna satellite scintillation digisonde all sky imager and fabry perot interferometer fpi measurements near the magnetic equator in peru during a part of the period september 27 to october 3 the geophysics directorate of phillips laboratory performed measurements away from the magnetic equator at aguaverde chile magnetic latitude 11 s located 800 km to the east of the jicamarca meridian using geostationary and gps satellite scintillation digisonde and all sky imager systems the incoherent scatter radar results indicate that the postsunset enhancement of upward plasma drift even though of the order of only 20 m s 1 during the solar minimum period is a necessary condition for the generation of esf in view of the extreme difficulty of determining the neutral wind speed during the early evening hours by the fpi due to low airglow intensity it was not possible to unequivocally associate the observed postsunset enhancements with strong eastward neutral winds however considering a few observations contiguous to the campaign period it appears that such a causal relationship may exist the scintillation drift measurements in peru and chile indicated that the zonal irregularity drift was smaller away from the magnetic equator implying a variation of neutral wind with latitude this is reproduced in the altitude variation of zonal drift observed by the jicamarca radar during a magnetic storm scintillation measurements indicated that eastward drifts near the magnetic equator are accompanied by westward drifts near the anomaly peak which is consistent with the effects of a disturbance dynamo the campaign results indicate that in order to resolve the variability of esf a careful probing of neutral dynamics as a function of latitude needs to be undertaken during the postsunset period

an equatorial bubble its evolution observed in relation to bottomside spread f and to the appleton anomaly this is a case study that undertakes the first comprehensive description of the concurrent evolutions of an isolated equatorial bubble bottomside spread f bssf and the enhanced appleton anomaly a principal focus is the dynamics of the intersection of the bubble with the anomaly crest which is the source of maximum scintillation on transionospheric rf propagation conditions are equinox at solar maximum measurements were by an array of eight ionospheric sounders in the western hemisphere with a collective field of view extending along the dip equator for about 1600 km and to 40 north dip latitude that resolved rapid changes in the phenomena yet encompassed their extent and duration viewed locally the bubble was triggered by an upwelling of the bottomside f layer during e b upward drift that accelerated upward for 15 20 min before the onset of irregularities seen as range spread f rsf viewed macroscopically this onset was part of continuous front of rsf onset that coincided with e b reversal and moved westward at the velocity of the terminator so as to remain at 1920 lt to the east of the bubble as bssf within the bubble during the upwelling of the bottomside crest at the west wall of the bubble at the onset of its eastward drift and west of the bubble as bssf the bubble drifted eastward at 185 m s and rose upward at 190 m s intersecting the maximum of the anomaly crest at 2100 lt 95 min after bubble onset during this entire period the bubble was in continuous contact with the anomaly profile which was simultaneously increasing but as a function of lt thus the intersection was a function of the upward and eastward velocities of the bubble and the westward motion of the anomaly at the velocity of the terminator the time and place of the intersection is thus dependent on the entire sequence of events and on the differing dependences on ut and lt and since each can vary the time and place of maximum scintillation is highly variable in light of this variability observations at least as comprehensive as those reported here appear to be necessary to describe the region adequately and therefore to study it further

electric and magnetic field perturbations recorded by demeter satellite before seismic events of the 17th july 2006 m 7 7 earthquake in indonesia abstract seismo electromagnetic phenomena refers to the electric and magnetic field perturbations that may be caused due to geophysical activities like earthquakes and volcanic eruptions due to the existence of such phenomena before earthquakes they may be regarded as short term precursors to earthquakes keeping in mind the in situ measurements for detection of such phenomena the satellite based techniques are of great interest because they keep a constant track of the seismically active zones globally with the objective of detecting the electromagnetic emissions in the ionosphere the demeter satellite has been launched on 29th june 2004 from baikonour in order to study the ionospheric perturbations associated with seismic activities in this paper we discuss some interesting results of electromagnetic emissions that are observed before a series of recent indonesian earthquakes in the jawa region with a major shock measuring 7 7 magnitude on richter scale which occurred on 17 july 2006 the emissions have been observed in the ultra low frequency ulf extremely low frequency elf range of electromagnetic spectra

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

spread f and the structure of equatorial ionization depletions in the southern anomaly region combined optical and radio sensors provide a unique characterization of the structure of equatorial emission depletion regions connected to rising bubbles over the magnetic equator in chile as part of the miseta campaign in fall 1994 a ccd enhanced all sky imaging photometer provided optical images of the postsunset appearance and motions of the depletion bands at a magnetic dip latitude of 11 s concurrently a digisonde collocated with the photometer monitored the appearance of spread f in between the ionograms the sounder operated as a doppler interferometer identifying the locations of f layer irregularities associated with the spread f they were found to lie inside the emission depletion regions the hf sounder requiring orthogonality with the field aligned f layer irregularities to generate the spread structure tracked these irregularities inside the emission depletion bands as they drifted eastward ray tracing simulations show that the radio waves become trapped within the depletion regions when the depletions are within 300 km of the sounder site model calculations indicate that the sounder rays encounter orthogonality with the earth s magnetic field within the depletion bubble southward from the site consistent with the local dip angle the combination of optical images with hf radio sounding demonstrated that radio imaging in the equatorial ionosphere can be done with a digital ionosonde that operates as a doppler interferometer the digisonde measurements and ray tracing show for the first time that the spread f signatures on ionograms are the result of coherent scatter from irregularities primarily within the walls of the depletion

investigation of ionospheric electron content variations before earthquakes in southern california 2003 2004 1 it has been proposed that earthquakes are preceded by electromagnetic signals detectable from ground and space based measurements ionospheric anomalies such as variations in the electron density a few days before earthquakes are one of the precursory signals proposed since global positioning system gps data can be used to measure the ionospheric total electron content tec the technique has received attention as a potential tool to detect ionospheric perturbations related to earthquakes here we analyze 2 years 2003 2004 of data from the southern california integrated gps network scign a dense network of 265 continuous gps stations centered on the los angeles basin for possible precursors this time period encompasses the december 2003 m6 6 san simeon and september 2004 m6 0 parkfield earthquakes we produce tec time series at all scign sites and apply three different statistical tests to detect anomalous tec signals preceding earthquakes we find anomalous tec signals but no statistically significant correlation in time or in space between these tec anomalies and the occurrence of earthquakes in southern california for the 2003 2004 period this result does not disprove the possibility of precursory phenomena but show the signal to noise ratio of a hypothetical tec precursor signature is too low to be detected by the analysis techniques employed here precursors may still be revealed for future large earthquakes in well instrumented areas such as california and japan if the tests can be developed into techniques that can better separate external influences from the actual tec signal

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz