ionospheric effects during the total solar eclipse over southeast asia pacific on 9 march 2016 part 1 vertical movement of plasma layer and reduction in electron plasma density

study of variation in the lower ionospheric reflection height with polar day length at antarctic station maitri estimated with tweek atmospherics 1 in the present paper investigations are made on the lower ionosphere with the help of observed tweek atmospherics at the indian antarctic research station maitri during the second half of austral summer january march of 2003 and 2005 the variations in the lower ionospheric reflection height are found to be in correspondence with the sunrise and sunset at maitri the results indicate that the tweek atmospherics are helpful in tracking the changes taking place in the lower ionospheric height through the day night boundary the ionospheric reflection height estimated using the cutoff frequency of fundamental first harmonic or first mode tweek atmospherics ranges from 64 to 79 km with a maximum calculated error of 2 7 km the recordings were carried out from 1800 to 0600 utc the analysis shows that the average cutoff frequency for the fundamental tweek atmospherics and hence the ionospheric reflection height varies from the months of january to march in accordance with the sunrise and sunset

flow to a heated borehole in porous thermoelastic rock analysis exact solutions are obtained for fluid flow induced by the heating of a borehole the rock is modeled as a fluid saturated porous thermoelastic medium the temperature and pore pressure fields are governed by a pair of diffusion equations which are coupled through a source term in the pressure equation proportional to the temperature rate the pressure profile exhibits a maximum that grows in magnitude and propagates away from the borehole for a constant heat flux applied as an instantaneous step the fluid flux to the borehole takes a finite initial value and decays monotonically when the heat flux exhibits a finite rise time the fluid flux is initially zero rises to a maximum and then decays at late time the inverse of the fluid flux is linear in ln t this observation can be exploited to estimate the permeability and fluid diffusivity of low permeability rock sample calculations are shown for westerly granite

influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from mt etna volcano subjected to elevated pressure abstract we report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from etna italy results were obtained for dry and saturated samples deformed under triaxial compression during each test the effective pressure was first increased up to 190 mpa to investigate the effect of pre existing crack closure on seismic properties then the effective pressure was unloaded down to 20 mpa a pressure which mirrors the stress field acting under a lava pile of approximately 1 5 2 km thick and deviatoric stress was increased until failure of the specimens using an effective medium model the measured elastic wave velocities were inverted in terms of two crack densities i the crack density of the pre existing thermal cracks and v the crack density of the stress induced cracks in addition a link was established between elastic properties elastic wave velocities vp and vs and permeability using a statistical permeability model our results show that the velocities increase with increasing hydrostatic pressure up to 190 mpa due to the closure of the pre existing thermal cracks this is interpreted by a decrease of the crack density i from 1 to 0 2 the effect of pre existing cracks closure is also highlighted by the permeability evolution which decreases of more than two orders of magnitude under deviatoric loading the velocities signature is interpreted in the first stage of the loading by the closure of the pre existing thermal cracks however with increasing deviatoric loading newly formed vertical cracks nucleate and propagate this is clearly seen from the velocity signature and its interpretation in term of crack density from the location of the acoustic emission sources and from microstructural observations this competition between pre existing cracks closure and propagation of vertical cracks is also seen from the permeability evolution and our study shows that mechanically induced cracks has lesser influence on permeability change than pre existing thermal cracks

field and laboratory resistivity monitoring of sediment consolidation in china s yellow river estuary traditional methods for in situ monitoring of the dynamic physical process within marine sediments are not efficient and effective enough and determination of the consolidation state of marine sediments in the yellow river estuary remains a challenging problem however the recent development of in situ testing technology for resistivity methodology creates new possibilities our combined analysis of laboratory and field experimental results demonstrates the consolidation process and the contemporaneous physical mechanical and electrical properties of marine sediments in the yellow river estuary and we discuss the feasibility of and that influence in situ monitoring of the sediment consolidation process using a multi electrode probe these results demonstrate that resistivity is a good indirect predictor of porosity which is the primary factor affecting resistivity behavior during the consolidation process values for empirical constants a and m for yellow river estuary sediment can be obtained based on archie s formula the relationship between resistivity and the geotechnical strength of silty sediments in the yellow river estuary shows that the penetration resistance determined by a light penetration test and undrained shear strength determined by a vane shear test are closely correlated to resistivity with a power function during the consolidation process of a uniform originated seabed this study confirms that resistivity monitoring using a multi electrode probe is a relevant method to estimate the degree and state of sediment consolidation in real time and in situ more work is needed to investigate the implications of this for the prediction and prevention of geological disasters in estuarine areas

analysis of experimentally validated trans ionospheric attenuation estimates of vlf signals 1 accurate models of trans ionospheric propagation are needed to assess the role of earth originating very low frequency vlf electromagnetic waves in radiation belt dynamics recent studies have called the relatively crude early trans ionospheric models into question finding that they underestimate the attenuation by 20 100 db a full wave model that includes all of the relevant physics has recently become available and experimentally verified to within a few decibels via comparison to more extensive satellite data using this model we discuss the importance of wave polarization incidence angle bearing ground conductivity horizontal distance from the source and the ionospheric profile all of which are demonstrated to play a significant role in the trans ionospheric propagation trans ionospheric attenuation estimates are provided both for the case of vertical incidence of a whistler mode wave and for the case of magnetospheric injection from a dipolar terrestrial vlf source these estimates agree with observation to within 6 db the remaining discrepancy may be attributable to ionospheric variation and or factors not captured by our horizontally stratified model on the basis of the full wave treatment presented herein we find that the earlier work showing a 20 db overestimation by traditional models results from the unrealistic simplifying assumption that the wave is vertically incident onto the ionosphere exacerbated by the fact that most of the satellite data used for comparison came at large horizontal distances hundreds of kilometers from the source

mapping lightning in the sky with a mini array mini arrays are commonly used for infrasonic and seismic studies here we report for the first time the detection and mapping of distant lightning discharges in the sky with a mini array the array has a baseline to wavelength ratio 4 2 10 2 to record very low frequency electromagnetic waves from 2 to 18 khz it is found that the mini array detects 69 lightning pulses per second from cloud to ground and in cloud discharges even though the parent thunderstorms are 900 1100 km away and a rigorous selection criterion based on the quality of the wavefront across the array is used in particular lightning pulses that exhibit a clockwise phase progression are found at larger elevation angles in the sky as the result of a birefringent subionospheric wave propagation attributed to ordinary and extraordinary waves these results imply that long range lightning detection networks might benefit from an exploration of the wave propagation conditions with mini arrays

very low frequency subionospheric remote sensing of thunderstorm driven acoustic waves in the lower ionosphere we present observations of narrowband subionospheric vlf transmitter signals on 20 march 2001 exhibiting coherent fluctuations of over 1 db peak to peak spectral analysis shows that the fluctuations have periods of 1 4 min and are largely coherent the subionospheric propagation path of the signal from puerto rico to colorado passes over two regions of convective and lightning activity as observed by goes satellite imagery and national lightning detection network lightning data we suggest that these fluctuations are evidence of acoustic waves launched by the convective activity below observed in the 80 90 km altitude range to which nighttime vlf subionospheric remote sensing is sensitive these observations show that vlf subionospheric remote sensing may provide a unique 24 h remote sensing technique for acoustic and gravity wave activity we reproduce this event in simulations using a fluid model of gravity and acoustic wave propagation to calculate the ionospheric disturbance followed by an electromagnetic propagation model to calculate the perturbation amplitude at the location of the vlf receiver simulation results show that a very large and coherent convective source is required to produce these amplitude perturbations

performance characteristics of the nldn for return strokes and pulses superimposed on steady currents based on rocket triggered lightning data acquired in florida in 2004 2012 we present a detailed evaluation of performance characteristics of the u s national lightning detection network nldn using as ground truth florida rocket triggered lightning data acquired in 2004 2012 the overall data set includes 78 flashes containing both the initial stage and leader return stroke sequences and 2 flashes composed of the initial stage only in these 80 flashes there are a total of 326 return strokes directly measured channel base currents are available for 290 of them and 173 kiloampere scale 1 ka superimposed pulses including 58 initial continuous current pulses and 115 m components all these events transported negative charge to the ground the nldn detected 245 return strokes and 9 superimposed pulses the resultant nldn flash detection efficiency is 94 return stroke detection efficiency is 75 and detection efficiency for superimposed pulses is 5 for peak currents 1 ka and 32 for peak currents 5 ka for return strokes the median location error is 334 m and the median value of absolute peak current estimation error is 14 the percentage of misclassified events is 4 all of them being return strokes the median value of absolute event time mismatch the difference in times at which the event is reported to occur by the nldn and recorded at the lightning triggering facility for return strokes is 2 8 s for two out of the nine superimposed pulses detected by the nldn we found optical evidence of a reilluminated branch recoil leader coming in contact with the existing grounded channel at an altitude of a few hundred meters above ground

more evidence for a one to one correlation between sprites and early vlf perturbations 1 past studies have shown a correlation between sprites and early vlf perturbations but the reported correlation varies widely from 50 to 100 the present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband vlf observations in which multiple transmitter receiver vlf pairs with great circle paths gcps passing near a sprite producing thunderstorm were available in this setup the multiple paths act in a complementary way that makes the detection of early vlf perturbations much more probable compared to a single vlf path that can miss several of them a fact that was overlooked in past studies the evidence shows that visible sprite occurrences are accompanied by early vlf perturbations in a one to one correspondence this implies that the sprite generation mechanism may cause also sub ionospheric conductivity disturbances that produce early vlf events however the one to one visible sprite to early vlf event correspondence if viewed conversely appears not to be always reciprocal this is because the number of early events detected in some case studies was considerably larger than the number of visible sprites since the great majority of the early events not accompanied by visible sprites appeared to be caused by positive cloud to ground cg lightning discharges it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite watch camera detection system in order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites sprite halos and elves

ice sheet load cycling and fluid underpressures in the eastern michigan basin ontario canada strong fluid underpressures have been detected in paleozoic strata in the eastern michigan basin with hydraulic heads reaching 400 m below land surface 4 mpa underpressure and 200 m below sea level in strata where unusually low permeabilities 10 20 10 23 m2 were measured in situ multiple glaciations including three with as much as 3 km of ice cover at the site in the last 120 ka suggest a causal link with the underpressures we examined this possibility using a one dimensional groundwater flow model incorporating mechanical loading from both ice weight and lithospheric flexure because hydrologic and mechanical changes during glaciation are not well characterized and subsurface properties are imperfectly known the model was used inversely to estimate flexural loads and loosely constrained permeabilities by matching observed pressures acceptable matches were obtained for a surprisingly wide range of scenarios with permeabilities close to measured values and plausible flexural loads matches were not obtained when too many parameters were preselected or when permeabilities were constrained to be significantly larger than measured values in successful model runs groundwater expulsion under glacial mechanical loads caused the underpressuring and flexural loads were important if aquifer and sub glacial pressures were significantly elevated during glaciation simulated fluid pressures in the low permeability strata fluctuated by 30 40 mpa during glacial cycles but resulted in advective transport of only tens of meters or less although other mechanisms cannot be ruled out we conclude that glacial mechanical forcing of a water saturated system can explain the observed underpressures

three years of lightning impulse charge moment change measurements in the united states 1 we report and analyze 3 years of lightning impulse charge moment change icmc measurements obtained from an automated real time lightning charge moment change network cmcn the cmcn combines u s national lightning detection network nldn lightning event geolocations with extremely low frequency 1 khz data from two stations to provide icmc measurements across the entire united states almost 14 million lightning events were measured in the 3 year period we present the statistical distributions of icmc versus polarity and nldn measured peak current including corrections for the detection efficiency of the cmcn versus peak current we find a broad distribution of icmc for a given peak current implying that these parameters are at best only weakly correlated curiously the mean icmc does not monotonically increase with peak current and in fact drops for positive cg strokes above 150 ka for all positive strokes there is a boundary near 20 c km that separates seemingly distinct populations of high and low icmc strokes we also explore the geographic distribution of high icmc lightning strokes high icmc positive strokes occur predominantly in the northern midwest portion of the u s with a secondary peak over the gulf stream region just off the u s east coast high icmc negative strokes are also clustered in the midwest although somewhat south of most of the high icmc positive strokes this is a region far from the locations of maximum occurrence of high peak current negative strokes based on assumed icmc thresholds for sprite production we estimate that approximately 35 000 positive polarity and 350 negative polarity sprites occur per year over the u s land and near coastal areas among other applications this network is useful for the nowcasting of sprite producing storms and storm regions

radiated vlf energy differences of land and oceanic lightning 1 a global contrast between oceanic and continental lightning very low frequency energy is observed using the world wide lightning location network wwlln strokes over the ocean are found to be stronger on average than those over land with a sharp boundary along a majority of coastlines a linear regression method is developed to account for the spatial and temporal variation of wwlln in order to perform a multiyear and global analysis of stroke energy distributions the results are corroborated with data from the lightning imaging sensor the optical transient detector and the earth networks total lightning network these systematic comparisons lead to the conclusion that there exists a strong difference in the energetics between land and ocean thunderstorms that results in a higher fraction of more powerful strokes over the oceans

the north american lightning detection network naldn analysis of flash data 2001 09 abstractcloud to ground cg lightning data have been analyzed for the years 2001 09 for north america which includes alaska canada and the lower 48 u s states flashes recorded within the north american lightning detection network naldn are examined no corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising north america there were network changes in the naldn during the 9 yr but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 ka have been deleted thus the reader should be aware that secular changes are not just climatological in nature all data were analyzed with a spatial resolution of 20 km the analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in north america including the impacts of physical changes in the network dur

characteristics of long recovery early vlf events observed by the north african awesome network 1 lightning strokes are capable of initiating disturbances in the lower ionosphere whose recoveries persist for many minutes these events are remotely sensed via monitoring subionospherically propagating very low frequency vlf transmitter signals which are perturbed as they pass through the region above the lightning stroke in this paper we describe the properties and characteristics of the early vlf signal perturbations which exhibit long recovery times using subionospheric vlf transmitter data from three identical receivers located at algiers algeria tunis tunisia and sebha libya the results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties e g peak current and polarity or that of transient luminous events may be much less important the dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric vlf probe signal at the ionospheric disturbance where scattering occurs and the subsequent modal structure that propagates to the receiver location

why do oceanic negative cloud to ground lightning exhibit larger peak current values this study examines the temporal monthly and spatial climatology 2004 2010 of the first return stroke of the cloud to ground cg lightning flash peak current ip across various land water boundaries over the contiguous united states four regions are examined the gulf of mexico region 1 the florida peninsula region 2 lake michigan region 3 and part of the u s mid atlantic region 4 the crosss across the coastlines of regions 1 2 and 4 show a gradual oceanward increase in the mean negative polarity cg peak current values ip this transition along the respective land ocean boundaries is not sharp but gradual in direct contrast with ocean there is no consistent behavior in ip values as we move from land out across the fresh water of lake michigan region 3 meanwhile the positive cg flash peak current ip values do not exhibit a consistent variation across any coastal boundary for region 1 the ip values increase as we move toward the coast southwards especially during the wet season june october this finding is in direct contrast with studies that documented winter as the season of maximum ip values the zonal and seasonal variations of ip values across region 4 are not quite as pronounced but the oceanic ip values are still larger than over the adjoining landmass we explore in turn which up to date hypotheses pertinent to the oceanic ip enhancement are supported or refuted by our findings it is concluded that the oceanic ip enhancement is not an artifact related to cg detection or ip retrieval methods nor is it likely related to the cloud top heights or cg activity the study cannot refute the role of electrical conductivity and its contribution to cg leader attachment processes however given the observed blurred transition of the ip values across the coastlines this paper suggests that likely the main physical mechanism is acting on the thundercloud potential the recently suggested role of sodium chloride nacl but also the role of ice crystal size implicated herein as possible modulators of the thundercloud potential exhibit distinct pros and cons their candidacy is supported by their strong physical links to the electrostatic charging and thundercloud electric potential buildup but also by the exhibited blurred ip transition across the coastlines in contrast the suggested mechanisms cannot individually explain the observed ip enhancement in terms of season nacl concentrations and absence of similar behavior in the respective ip values

axial flow hydraulic pulse testing of an argillaceous limestone lindsay limestone is an argillaceous limestone encountered in southern ontario canada the lindsay formation is regarded as a suitable geologic medium for the construction of a deep geologic repository for storing low to intermediate level nuclear waste the lindsay limestone is a nodular argillaceous rock with very low permeability requiring the use of hydraulic pulse tests for the measurement of its permeability characteristics the paper describes the triaxial testing facility the theoretical basis for the test and the procedures used to analyze the experimental results for estimating the permeability of the lindsay limestone the results are compared with the data available in the literature

nighttime ionospheric d region parameters from vlf phase and amplitude 1 nighttime ionospheric d region heights and electron densities are determined from an extensive set of vlf radio phase and amplitude observations the d region parameters are characterized by the traditional h height in kilometers and sharpness in km 1 as used by wait and by the u s navy in their earth ionosphere waveguide programs the vlf measurements were made with several frequencies in the range 10 khz to 41 khz on long mainly all sea paths including omega la reunion and omega argentina to dunedin new zealand nau puerto rico and naa maine usa to cambridge uk and npm hawaii to san francisco because daytime vlf propagation on such paths is readily measured and predicted the differences between night and day amplitudes and phases were measured and compared with calculations for a range of nighttime ionospheric parameters this avoided the problem of uncertainties in the transmitter powers in this way the height h and the sharpness when averaged over periods of several days at least for the midlatitude d region near solar minimum were found to be 85 1 0 4 km and 0 63 0 04 km 1 respectively

on the origins of mesospheric gravity waves 1 using hourly data from a three year simulation based on a gravity wave resolving general circulation model we have first inferred a global view of gravity wave sources and propagation affecting significantly the momentum balance in the mesosphere the meridional cross section of momentum fluxes suggests that there are a few dominant propagation paths originating from the subtropics in summer and the middle to high latitudes in winter these gravity waves are focused into the mesospheric jets in their respective seasons acting effectively to decelerate the jets the difference in the source latitudes likely contributes to the hemispheric asymmetries of the jets the horizontal distribution of the momentum fluxes indicates that the dominant sources are steep mountains and tropospheric westerly jets in winter and vigorous monsoon convection in summer the monsoon regions are the most important window to the middle atmosphere in summer because of the easterlies associated with the monsoon circulation

modeling of thermally driven hydrological processes in partially saturated fractured rock 1 this paper is a review of the research that led to an in depth understanding of flow and transport processes under strong heat stimulation in fractured porous rock it first describes the anticipated multiple processes that come into play in a partially saturated fractured porous volcanic tuff geological formation when it is subject to a heat source such as that originating from the decay of radionuclides the rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled the paper outlines how the conceptualization and the numerical modeling of the problem evolved progressing from the simplified to the more realistic examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last 2 decades the most recent model applied to in situ field thermal tests is characterized by 1 incorporation of a full set of thermal hydrological processes into a numerical simulator 2 realistic representation of the field test geometry in three dimensions and 3 use of site specific characterization data for model inputs model predictions were carried out prior to initiation of data collection and the model results were compared to diverse sets of measurements the approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock which affects local permeability values and subsequently the flow of liquid and gases the fluid flow in turn will change the temperature field we end with a note on future research opportunities specifically those incorporating chemical mechanical and microbiological factors into the study of thermal and hydrological processes

ionospheric d region parameters obtained using vlf measurements in the south pacific region the diurnal variations in the phase and amplitude of nwc npm and nlk very low frequency vlf transmissions received at suva fiji have been modeled using the long wave propagation capability lwpc v2 1 code to determine the ionospheric d region parameters h reference height and rate of increase of electron density with height for different daytime and nighttime conditions along the transmitter receiver great circle paths trgcps measured vlf signal amplitude and phase show explicit variation over the day and nighttime along the trgcp also revealing amplitude minima and phase steps during sunrise and sunset as the day night terminator traverses the trgcp while the daytime signal strength is reasonably smooth at nighttime the signal exhibits a great deal of variability for three signal paths the mean daytime h and were found to be 70 7 km and 0 40 km 1 respectively while nighttime mean values of these parameters were found to be 84 2 km and 0 68 km 1 respectively the temporal and day to day variability of the nighttime d region parameters shows that h and ranges in between 83 0 85 0 km and 0 58 0 80 km 1 respectively one of the possible sources of nighttime signal variability is increase in the number of modes propagating and relative complex interference between them along the trgcps whereby the weaker modes also become significant at night due to reduced attenuation in addition the variations in the nighttime d region itself may be a cause of high signal variability

modeling the geomagnetic effects caused by the solar eclipse of 11 august 1999 1 the solar eclipse of 11 august 1999 was total along a belt crossing central europe where there is a high density of magnetic observatories we studied the transient geomagnetic effects produced by the temporary cutoff of the ionizing solar radiations during the eclipse it is the first case in which the phenomenon has been analysed in a multisite context for observatories along the umbra path a model based on the equivalent electric current schema is proposed

the 22 july 2009 total solar eclipse modeling d region ionosphere using narrowband vlf observations we present d region ionospheric response to 22 july 2009 total solar eclipse by modeling 19 8 khz signal from nwc very low frequency vlf navigational transmitter located in the australia nwc vlf signal was received at five stations located in and around eclipse totality path in the indian east asian and pacific regions nwc signal great circle paths to five stations are unique having eclipse coverage from no eclipse to partiality to totality regions and the signal is exclusively confined in the low and equatorial regions eclipse induced modulations in nwc signal have been modeled by using long wave propagation capability code to obtain d region parameters of reflection height h and sharpness factor long wave propagation capability modeling showed an increase in h of about 2 3 km near central line of totality 3 0 km in the region near to totality fringe and 2 4 to 3 0 km in the region under partial eclipse using h and wait ionosphere electron density ne profile at the daytime altitude of 75 km showed a decrease in ne by about 58 at a station near totality central line whereas at totality fringe and in partial eclipse region decrease in the ne was between 63 and 71 with respect to normal time values the eclipse associated variations in the h and ne are less in low latitude region as compared to midlatitude the study contributes to explain observations of wave like signature in the d region during an eclipse and difference in the eclipse effect in the different latitude longitude sectors

evaluation of the gld360 performance characteristics using rocket and wire triggered lightning data we estimated the performance characteristics of the global lightning dataset gld360 using rocket and wire triggered lightning data acquired at camp blanding florida in 2011 2013 the data set consisted of 201 return strokes and 84 kiloampere scale 1 ka superimposed pulses initial continuous current pulses and m components in 43 flashes all the events transported negative charge to ground the gld360 detected 75 strokes and 4 superimposed pulses in 29 flashes the resultant detection efficiencies were 67 for flashes 37 for strokes and 4 8 for superimposed pulses out of 75 detected strokes one 1 3 was reported with incorrect polarity the median location error was 2 0 km and the median absolute current estimation error was 27 this is the first comprehensive evaluation of gld360 performance characteristics relative to absolute ground truth with all previous evaluations being at least in part relative to other locating systems the results presented in this work may be applicable to regions in and around florida

vlf signal anomalies during cyclone activity in the atlantic ocean in this paper we present ionospheric disturbances during the simultaneous presence of two to three large meteorological systems classified as hurricanes and tropical storms in the atlantic ocean from august to november 2016 the ionospheric disturbances were detected by very low frequency 3 30 khz signals from two north american transmitters observed in algiers 36 75 n 03 47 e the results show clear anomalies in the amplitude both at nighttime and at daytime at nighttime the anomalies were observed in association with all large meteorological systems even at low stage of storm intensity tropical depression the anomalies showed periodicities between 2 and 3 hr with a strong decrease in the signal amplitude the wave like features were confirmed by the mother wavelet analysis of the normalized signal amplitude these signal anomalies may result from traveling ionospheric disturbances generated by tropical storms and hurricanes associated gravity waves

map of low frequency electromagnetic noise in the sky the earth s natural electromagnetic environment is disturbed by anthropogenic electromagnetic noise here we report the first results from an electromagnetic noise survey of the sky the locations of electromagnetic noise sources are mapped on the hemisphere above a distributed array of wideband receivers that operate in a small aperture configuration it is found that the noise sources can be localized at elevation angles up to 60 in the sky well above the horizon the sky also exhibits zones with little or no noise that are found toward the local zenith and the southwest of the array these results are obtained by a rigorous analysis of the residuals from the classic dispersion relation for electromagnetic waves using an array analysis of electric field measurements in the frequency range from 20 to 250 khz the observed locations of the noise sources enable detailed observations of ionospheric modification for example caused by particle precipitation and lightning discharges while the observed exclusion zones enable the detection of weak natural electromagnetic emissions for example from streamers in transient luminous events above thunderclouds

early slow events a new category of vlf perturbations observed in relation with sprites 1 analysis of subionospheric vlf transmissions observed in relation with sprites has led to the identification of a new category of vlf perturbations caused by the direct effects of tropospheric lightning on the overlying lower ionosphere they constitute a large subset of the so called early fast events where now the term fast which implies rapid onset durations less than 20 ms does not apply in contrast with early fast the perturbations have a gradual growth and thus slow onset durations ranging from about 0 5 to 2 5 s thus these events are labeled herein as early slow they are indicative of a new physical process at work which following a sprite causative cloud to ground discharge leads to a gradual buildup of conductivity changes in the lower ionosphere which must be responsible for the long onset durations of the observed perturbations analysis of broadband vlf sferic recordings made with a two channel receiver near the sprite producing storms shows that the growth phase of an early slow event coincides with the occurrence of complex and dynamic lightning action this is composed of a few sequential cloud to ground lightning strokes and clusters bursts of sferics which are attributable to intracloud lightning we postulate that the long onset durations are due to secondary ionization buildup in the upper d region below the nighttime vlf reflection heights caused mainly by the impact on sprite produced electrons of sequential electromagnetic pulses radiated upward from horizontal in cloud discharges

localization of individual lightning discharges via directional and temporal triangulation of sferic measurements at two distant sites 1 lightning discharges generate electromagnetic pulses known as sferics that propagate through the waveguide formed by the earth and the ionosphere the energy in the vlf band can propagate over great distances 10 000 km with low loss 3 db mm and can therefore be detected far from the source lightning location using sferic measurements from vlf receivers at palmer station antarctica and vieques island puerto rico the locations of lightning discharges from regions such as south america north america and africa are triangulated both sferic arrival azimuth at the two receivers and the time of arrival difference between the receivers are used to find the best estimate of the lightning discharge location owing to the extremely wide separation of the two receivers ambiguities sometimes result in pairing sferics detected at one site to their matching sferics detected at the other site in these cases a best best estimate scheme is used simulation results indicate that for the two receivers considered here the most accurate location performance is in south america with an expected median location error of 75 km the system has the worst performance due north of the vieques island site with an expected median location error of 2000 km triangulation results for south america are shown for the period 7 10 september 2001 results for 8 september 2001 are compared to cloud to ground lightning flashes detected by the national lightning detection network for this day 49 of flashes were detected with a median error of about 200 km results are also compared to lightning discharges detected by the lightning imaging sensor lis aboard the tropical rainfall measuring mission trmm satellite for a particular trmm pass over south america 20 of flashes detected by lis were correctly located using the described technique with a median error of 187 km the event rate for a localized south american storm is also monitored and documented for the same 4 day period

reflection height of daytime tweek atmospherics during the solar eclipse of 22 july 2009 1 we report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 july 2009 sixteen and sixty three tweek atmospherics were observed at moshiri and kagoshima japan where the magnitudes of the solar eclipse were 0 458 and 0 966 respectively this was the first observation of tweek atmospherics during a low magnitude eclipse 0 458 the average and standard deviation of the reflection height were 94 9 13 7 km at moshiri and 87 2 12 9 km at kagoshima the reflection height at moshiri was almost the same as that for normal nighttime conditions in july 96 7 12 6 km in spite of the low magnitude of the eclipse the reflection height at kagoshima seems be divided into two parts propagation across the total solar eclipse path and propagation in the partial solar eclipse path during the eclipse we also observed the phase variation in the lf transmitter signals the average change in the phase delay of the lf signals was 109 for the paths that crossed the eclipse path and 27 for the paths that did not cross the eclipse path assuming a normal daytime height for lf waves of 65 km a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5 6 km for the paths across the eclipse and 1 2 km for partial eclipse paths the wide range of estimated tweek reflection heights at kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses

low mid latitude d region ionospheric perturbations associated with 22 july 2009 total solar eclipse wave like signatures inferred from vlf observations we present first report on the periodic wave like signatures wls in the d region ionosphere during 22 july 2009 total solar eclipse using jji japan very low frequency vlf navigational transmitter signal 22 2 khz observations at stations allahabad varanasi and nainital in indian sector busan in korea and suva in fiji the signal amplitude increased on 22 july by about 6 and 7 db at allahabad and varanasi and decreased by about 2 7 3 5 and 0 5 db at nainital busan and suva respectively as compared to 24 july 2009 normal day the increase decrease in the amplitude can be understood in terms of modal interference at the sites of modes converted at the discontinuity created by the eclipse intercepting the different transmitter receiver great circle paths the wavelet analysis shows the presence of wls of period 16 40 min at stations under total eclipse and of period 30 80 min at stations under partial eclipse 85 54 totality with delay times between 50 and 100 min at different stations the intensity of wls was maximum for paths in the partially eclipsed region and minimum in the fully eclipsed region the features of wls on eclipse day seem almost similar to wls observed in the nighttime of normal days e g 24 july 2009 the wls could be generated by sudden cutoff of the photo ionization creating nighttime like conditions in the d region ionosphere and solar eclipse induced gravity waves coming to ionosphere from below and above the present observations shed additional light on the current understanding of gravity waves induced d region ionospheric perturbations

long range tracking of thunderstorms using sferic measurements 1 each lightning stroke launches an electromagnetic pulse known as a radio atmospheric or sferic that propagates in the waveguide between the earth and the ionosphere sferics with most of their energy contained in the frequency band from 3 hz to 30 khz can propagate with low loss to distances of tens of megameters using very low frequency vlf magnetic field measurements at palmer station antarctica the azimuths of sferics originating in north america 10 000 km range are found to be measurable to less than 1 degree accuracy analysis of the arrival azimuths at palmer station allows the assessment of lightning flash rates of storms occurring in diverse regions of the globe including north america and africa arrival azimuths are compared with flash level data from the national lightning detection network nldn and 83 6 of the sferics that could be matched to nldn flashes were within 2 degrees of the predicted azimuths for those flashes results are also compared with data from the satellite based optical transient detector otd and the arrival azimuths of sferics detected at palmer station are consistent with the location of lightning occurring elsewhere around the world the relative distribution of and the relationship between ground flashes and cloud flashes are discussed for a specific localized thunderstorm evidence that sferics generated by intracloud discharges were detected at palmer station is also presented

resistivity survey of the subsurface conditions in the estuary of the rio de la plata an electrical resistivity survey was performed at the estuary of the rio de la plata as part of more comprehensive geotechnical investigations of the subsurface conditions the studies were required for the emplacement of a 3 5 m diameter conduit proposed for the discharge of the treated wastewater of the city of buenos aires the soil profile at the site consists mainly of clays and silts underlain by a layer of dense sand the dense sand layer is a confined aquifer and the project required that the depth to the sand layer be perfectly determined previous geophysical surveys at the site and the general geotechnical conditions showed the inadequacy of seismic methods which are usually adopted in similar environments the resistivity method was determined to be a reliable alternative even though there has been little experience in surveying shallow depth water for geotechnical investigations the four electrode schlumberger electrode array was adopted for the resistivity survey some of the test devices were developed especially for the purpose of this project calibration of the method was achieved with data obtained from boreholes the results show that the resistivity technique performed satisfactorily to the 40 m depth required in this project as a result of the survey the next geotechnical investigation was focused on a more reduced area and the required number of boreholes was reduced substantially

scattering pattern of lightning induced ionospheric disturbances associated with early fast vlf events simultaneous observations of early fast very low frequency vlf events at nine closely spaced 65 km sites are used together with a numerical model of the propagation and scattering of vlf signals in the earth ionosphere waveguide to directly measure the scattering pat tern of associated ionospheric disturbances in cases when the causative lightning is within 700 km of the north south array of observing sites early fast vlf events are typically observed at no more than 2 or 3 sites which indicates a nar row beam of the scattered signal in the forward direction in the dierent cases studied forward scattering patterns exhibit 15 db beamwidths of less than 30 consistent with horizontal extent of 90 30 km

subionospheric early vlf signal perturbations observed in one to one association with sprites 1 observations on the night of 21 july 2003 of the ionospheric effects of a thunderstorm in central france are reported from 0200 to 0315 ut a camera system in the pyrenees mountains captured 28 sprites triggered by cg lightning as observed by the french meteorage lightning detection system a narrowband vlf receiver located on crete at 2200 km southeast of the storm observed subionospheric vlf signals from six ground based transmitters the amplitude of one of the vlf signals originating at a transmitter located 150 km west of the storm and passing through the storm region exhibited rapid onset perturbations occurring in a nearly one to one relationship with the optical sprites these early vlf events are consistent with a process of narrow angle forward scattering from a volume of enhanced ionization above the storm with lateral sizes larger than the vlf radio wavelength the many cg and cg discharges that did not produce sprites were also found to not be associated with detectable vlf amplitude perturbations even though some of these discharges reached relatively large peak currents the rapid onsets of several of the sprite related vlf perturbations were followed by relatively long onset durations ranging from 0 5 to 2 5 s indicating that these events were early but not fast these early slow events may suggest a slow process of ionization build up in the lower ionosphere following intense lightning discharges that also lead to sprites a limited number of early vlf perturbation events were also associated with whistler induced electron precipitation events or classic trimpi perturbations undoubtedly produced by the precipitation of electrons due to whistler mode waves injected into the magnetosphere by the same lightning flash that led to the production of the sprite

on the relationship between lightning peak current and early vlf perturbations 1 lightning strokes are known to cause direct heating and ionization of the d region some of which are detected via scattering of vlf transmitter signals and are known as early vlf events the disturbed ionosphere typically recovers in many tens of seconds new experimental evidence is presented demonstrating that the scattering pattern and onset amplitude of early vlf events are strongly related to both the magnitude and polarity of causative lightning peak current observations of early vlf events at nine stanford vlf receiver sites across the continental united states are combined with lightning geolocation data from the national lightning detection network nldn during january and march 2011 nldn recorded 7769 intense lightning discharges with high peak currents 100 ka generating 1250 detected early vlf events we show that the size of the scattered field due to the ionospheric disturbance increases with the peak current intensity of the causative lightning discharge the most intense peak currents of 200 and 250 ka disturb vlf transmitter signals as far as 400 km away from the lightning stroke early vlf event detection probability also increases rapidly with peak current intensity on the other hand the observed vlf amplitude change is not significantly dependent on the peak current intensity stroke polarity is also important with positive strokes being 5 times more likely to generate early vlf disturbances than negative strokes of the same intensity intense positive cloud to ground lightning discharges especially when occurring over the sea are also more likely to produce early vlf events with long recovery many minutes

d region ionosphere response to the total solar eclipse of 22 july 2009 deduced from elf vlf tweek observations in the indian sector 1 observations of tweeks with higher harmonics n 1 at low latitude stations allahabad and nainital in the indian sector during the total solar eclipse on 22 july 2009 are presented allahabad and nainital stations were in 100 and 85 of the totality paths observations suggest that about 30 40 obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in nighttime a total of 148 tweeks at allahabad and 20 tweeks at nainital were recorded with some of them up to 3rd harmonics the world wide lightning location network data indicated that tweeks observed were generated by lightning s located in the partial eclipse area of asia oceania region the changes in d region ionospheric vlf reflection height and electron density 22 23 cm 3 during eclipse have been estimated from the first cut off frequency of the tweeks the reflection height increased from 89 km from the first occurrence of tweek to about 91 92 km at the totality and then decreased to 87 km at the end of the eclipse suggesting a change of about 5 km in the reflection height during eclipse the reflection heights are lower by 2 3 km as compared to normal nighttime tweek reflection heights the above increase in the reflection height indicate that the partial nighttime condition is created during eclipse as the main d region ionizing radiation lyman is blocked but solar soft x ray and euv radiations originating from the limb solar corona are not totally blocked which produce some of ionization in the d region

recovery signatures and occurrence properties of lightning associated subionospheric vlf perturbations subionospheric vlf signatures of lightning associated ionospheric disturbances observed at multiple sites in the central united states are used to investigate the occurrence properties and recovery signatures of characteristic perturbations exhibiting rapid onset followed by slow recoveries the two different types of events so called early fast and lightning induced electron precipitation lep inan et al 1996a are distinguished by the lack of presence of a few hundred millisecond delay between vlf event onsets and causative lightning discharges respectively analysis of recovery signatures of the two types of events indicate subtle but distinct differences in the recovery rates a majority of early fast events were found to exhibit a more rapid initial recovery to preevent levels during the first 20 s of recovery when compared to lep events this experimental evidence indicates that the physical nature of the ionospheric disturbance involved in the two classes of events are different consistent with a recent theoretical suggestion inan et al 1996c the occurrence properties of early fast events observed by the holographic array for ionospheric lighting hail receivers indicate that ionospheric disturbances act primarily as forward scatterers

shipborne lf vlf oceanic lightning observations and modeling approximately 90 of natural lightning occurs over land but recent observations using global lightning detection gld360 geolocation peak current estimates and satellite optical data suggested that cloud to ground flashes are on average stronger over the ocean we present initial statistics from a novel experiment using a low frequency lf magnetic field receiver system installed aboard the national oceanic atmospheric agency noaa ronald w brown research vessel that allowed the detection of impulsive radio emissions from deep oceanic discharges at short distances thousands of lf waveforms were recorded facilitating the comparison of oceanic waveforms to their land counterparts a computationally efficient electromagnetic radiation model that accounts for propagation over lossy and curved ground is constructed and compared with previously published models we include the effects of earth curvature on lf ground wave propagation and quantify the effects of channel base current risetime channel base current falltime and return stroke speed on the radiated lf waveforms observed at a given distance we compare simulation results to data and conclude that previously reported larger gld360 peak current estimates over the ocean are unlikely to fully result from differences in channel base current risetime falltime or return stroke speed between ocean and land flashes

the thermo hydro mechanical behavior of the argillaceous cobourg limestone the cobourg limestone is a low permeability argillaceous rock that forms a part of the paleozoic sedimentary sequence found in southern ontario canada the limestone has a heterogeneous fabric consisting of nodular regions of calcite and dolomite and argillaceous partings of a similar composition but with a low clay content which gives the appearance of nominal stratifications the thermo hydro mechanical thm behavior of the rock is of interest to the proposals for using sedimentary formations as candidate rocks for siting deep geological repositories for the storage of heat emitting nuclear fuel waste the paper presents the results of experiments where thm processes were initiated in an intact cylindrical sample of the cobourg limestone containing a central cylindrical fluid filled cavity biot s classical theory of poroelasticity extended to include thermal effects is used to examine the thm response of the fluid cavity due to boundary heating of the cylinder the rise and decay of thermally induced cavity fluid pressure is used to examine the applicability of the thm modeling the experiments were conducted on cylindrical samples of the cobourg limestone with their axes either along or normal to the nominal planes of the argillaceous partings

subionospheric vlf signatures of oblique nonducted whistler induced precipitation subionospheric very low frequency vlf signal perturbations observed at multiple sites in association with individual lightning discharges exhibit onset delays which steadily increase with increasing l value the timing of the onsets and the inferred spatial extent 1000 km of the ionospheric disturbance are consistent with those expected for electron precipitation induced by obliquely propagating i e nonducted whistlers

exploiting lf mf signals of opportunity for lower ionospheric remote sensing we introduce a method to diagnose and track the d region ionosphere 60 100 km this region is important for long distance terrestrial communication and is impacted by a variety of geophysical phenomena but it is traditionally very difficult to detect modern remote sensing methods used to study the d region are predominately near the very low frequency vlf 3 30 khz band with some work also done in the high frequency and very high frequency bands hf vhf 3 300 mhz however the frequency band between vlf and hf has been largely ignored as a diagnostic tool for the ionosphere in this paper we evaluate the use of 300 khz radio reflections as a diagnostic tool for characterizing the d region of the ionosphere we present radio receiver data analyze diurnal trends in the signal from these transmitters and identify ionospheric disturbances impacting lf mf propagation we find that 300 khz remote sensing may allow a unique method for d region diagnostics compared to both the vlf and hf vhf frequency bands due to a more direct ionospheric reflection coefficient calculation method with high temporal resolution without the use of forward modeling

the midlatitude f2 layer during solar eclipses observations and modeling national natural science foundation of china 40725014 40674090 40636032 national important basic research project 2006cb806306

resistivity of partially saturated carbonate rocks with microporosity simple archie s relations relate average conductivity to average porosity and average saturation and seem to work when the fluctuations of local porosity and local saturation are small in general carbonates are extremely inhomogeneous and archie s relations fail the saturation exponent n can depend on saturation itself and n can be anomalously large or small the resistivity of rocks with a mixture of micropores macropores and vugs is computed using effective medium theories quantitative mathematical modeling is used to study the influence of textural details geometries that lead to an anomalously high value of saturation exponent are contrasted with those with an anomalously low value of saturation exponent the resistivity becomes anomalously large when the conducting water phase is trapped in isolated regions the resistivity becomes insensitive to the volume fraction of water if the configuration of the major current carrying paths changes little with saturation simple examples with differenc

long range lightning geolocation using a vlf radio atmospheric waveform bank 1 lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency vlf 3 30 khz range vlf waves propagate through the earth ionosphere waveguide with relatively low attenuation enabling the detection of these radio atmospherics at great distances from the lightning discharge a new technique of long range 6000 km global lightning geolocation via sferic detection is presented this new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks which are then used to estimate the propagation distance and accurately determine the arrival time using three sensors in a trial network this new technique is used to demonstrate a median accuracy of 1 4 km depending on the time of day an overall cloud to ground cg stroke detection efficiency between 40 and 60 is estimated by correlating individual lightning stroke events to data from the national lightning detection network nldn additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by nldn suggesting that many of the unmatched events correspond to weak cloud to ground strokes m components or cloud pulses exploiting an empirical correlation between peak vlf field strength and peak current values reported by nldn we also provide unvalidated estimates of the peak current and lightning channel polarity the trial network does not distinguish between cloud and ground discharges so these peak current estimates only relate to an earth referenced channel current for the subset of reported events that are return strokes

classifying onset durations of early vlf events scattered field analysis and new insights the physical processes responsible for a variety of early vlf scattering events have not yet been satisfactorily identified properly categorizing the early vlf event type is imperative to understand the causative physical processes involved in this paper the onset durations of 26 exceptionally high signal to noise ratio early vlf scattering events are analyzed using scattered fields to classify events new observations of events that exhibit slow amplitude changes but fast scattered field changes are presented which call into question previous analyses of early slow events we separately identify and analyze three early vlf events that definitively exhibit slow scattered field behavior additionally we identify a significant number of events which have onset durations between the current definitions of fast and slow four events are observed which unambiguously exhibit a rapid initial rotation of the scattered field phasor during the first few seconds of the recovery stage possible physical mechanisms are discussed

perturbations of midlatitude subionospheric vlf signals associated with lower ionospheric disturbances during major geomagnetic storms 1 we examine the effects on the midlatitude ionospheric d region of the 7 april 2000 storm and the halloween storm of late october 2003 by means of the associated perturbations of several subionospheric vlf signals propagating in both the northern and southern hemispheres we use vlf nighttime data from the holographic array for ionospheric lightning research hail located in the united states l 2 3 as well as data from palmer station antarctica l 2 4 on 7 april 2000 a 5 db depression in vlf amplitudes is observed at multiple hail stations with a depression onset that occurs later for vlf signal paths at lower latitudes on both 7 april 2000 and 31 october 2003 fluctuations in the amplitude of the vlf signals are first observed in the premidnight sector and persist through the end of the data recording period dawn the frequency content of the fluctuations is predominantly in the 0 01 to 0 02 hz range but extends up to 0 03 hz increases in the energetic electron flux in the loss cone as measured by the noaa poes satellites are observed on both 7 april 2000 and 31 october 2003 we suggest that both the signal depressions and subsequent fluctuations are associated with variations in the precipitation flux of energetic electrons onto the upper atmosphere auroral activity patterns based on data from the noaa poes satellites show that the equatorward edge of the auroral oval expanded equatorward to lower l shells l 3 during both geomagnetic storms using the auoral activity patterns and multiple vlf lf signal paths we provide evidence that the fluctuations and the signal depression coincide with the equatorward edge of the auroral oval extending over the perturbed vlf lf great circle paths quantitative modeling of subionospheric vlf wave propagation incorporating energetic electron flux measurements and the associated altitude profiles of secondary ionization yields results consistent with the variations in the vlf signal amplitude observed

the vlf fingerprint of elves step like and long recovery early vlf perturbations caused by powerful cg lightning em pulses 1 subionospheric vlf recordings are investigated in relation with intense cloud to ground cg lightning data lightning impacts the lower ionosphere via heating and ionization changes which produce vlf signal perturbations known as early vlf events typically early events recover in about 100 s but a small subclass does not recover for many minutes known as long recovery early events lore in this study we identify lore as a distinct category of early vlf events whose signature may occur either on its own or alongside the short lived typical early vlf event since lore onsets coincide with powerful lightning strokes of either polarity we infer that they are due to long lasting ionization changes in the uppermost d region ionosphere caused by electromagnetic pulses emitted by strong cg lightning peak currents of typically 250 ka which are also known to generate elves the lore perturbations are detected when the discharge is located within 250 km from the great circle path of a vlf transmitter receiver link the probability of occurrence increases with stroke intensity and approaches unity for discharges with peak currents 300 ka lores are nighttime phenomena that occur preferentially at least in the present regional data set during winter when strong cg discharges are more frequent and intense the evidence suggests lore as a distinct signature representing the vlf fingerprint of elves a fact which although was predicted by theory it escaped identification in the long going vlf research of lightning effects in the lower ionosphere