statistics of geomagnetic storms and ionospheric storms at low and mid latitudes in two solar cycles 1 the statistics of occurrence of the geomagnetic storms and ionospheric storms at kokubunji 35 7 n 139 5 e 26 8 n magnetic latitude in japan and boulder 40 0 n 254 7 e 47 4 n in america are presented using the dst and peak electron density nmax data in 1985 2005 covering two solar cycles 22 23 when 584 geomagnetic storms dst 50 nt occurred in addition to the known solar cycle and seasonal dependence of the storms the statistics reveal some new aspects 1 the geomagnetic storms show a preference for main phase mp onset at around ut midnight especially for major storms dst 100 nt over 100 excess mp onsets at ut midnight compared to a uniform distribution 2 the number of positive ionospheric storms at kokubunji about 250 is more than double that at boulder and 3 the occurrence of the positive storms at both stations shows a preference for the morning noon onset of the geomagnetic storms as expected from a physical mechanism of the positive storms 4 the occurrence of negative ionospheric storms at both stations follows the solar cycle phases most frequent at solar maximum better than the occurrence of positive storms which agrees with the mechanism of the negative storms

equatorial westward electrojet impacting equatorial ionization anomaly development during the 6 april 2000 superstorm we investigate the forward plasma fountain and the equatorial ionosphere in the topside region during the 6 april 2000 superstorm in the australian sector at 0900 lt space and ground based multi instrument measurements coupled thermosphere ionosphere plasmasphere electrodynamics ctipe simulations and field aligned observations comprise our results these reveal an unusual storm development during which the eastward prompt penetration electric e field ppef developed and operated under the continuous effects of the westward disturbance dynamo e field ddef while large scale traveling ionospheric disturbances tids traveled equatorward and generated strong equatorward wind surges we have identified the eastward ppef by the superfountain effect causing the equatorial ionization anomaly eia s development with crests situated at 28 n geomagnetic in the topside ionosphere at 840 km altitude the westward ddef s occurrence is confirmed by mapping the anti sq current system wherein the equatorial westward current created a weak long lasting westward electrojet event line plots of vertical drift data tracked large scale tids four scenarios covering 3 5 h in universal time demonstrate that the westward ddef became superimposed on the eastward ppef as these e fields of different origins became mapped into the f region they could interact consequently the eastward ppef related equatorial upward e b drift became locally reduced by up to 75 m s near the dip equator by the westward ddef related equatorial downward e b drift meanwhile the eia displayed a better development as equatorial wind surges reproduced by ctipe increased from 501 to 629 m s demonstrating the crucial role of mechanical wind effects keeping plasma density high key points 6 april 2000 superstorm produced some significant westward electrojet events ppef developed and operated under continuous ddef effects superimposed westward ddef on eastward ppef permitted eia development

the magnetic storms of 3 4 august 2010 and 5 6 august 2011 1 ground and space based observations we have used total electron content tec values from low middle and high latitudes recorded over the american continent and density and ion temperature measured in situ by the dmsp f15 and f17 satellites during the geomagnetic storms of 3 4 august 2010 and 5 6 august 2011 to study the formation and dynamics of plasma density enhancements that developed during these two storms common to both storms are the timing of the main phase that extends between 20 and 24 ut and their seasonality with both storms occurring near the end of the northern hemisphere summer solstice during both storms tec data show incipient equatorial anomalies lacking a poleward expansion beyond 20 magnetic latitude two large scale tec enhancements were observed at middle latitudes showing a complicated pattern of structuring and merging the first tec enhancement corresponds to a storm enhanced density sed seen between 21 and 01 ut on the following day the second tec enhancement was observed over central america located equatorward of the sed and apparently moving northward however careful analysis of the tec values indicates that this second tec enhancement is not transported from lower latitudes through a superfountain effect instead the enhanced plasma has a local origin and is driven by a southward directed meridional wind that moves plasma up the tilted magnetic field lines dmsp flights passing over the second tec enhancement show a reduction of the ion temperature confirming an adiabatic expansion of the plasma as it moves up the field lines it is concluded that the midlatitude tec enhancements do not arise from a low latitude ionospheric fountain effect

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

stratification of the f 2 layer observed in southeast asia this paper describes the latitudinal variation in f2 stratification balan and bailey 1995 as observed by a number of oblique and vertical ionosondes operating in southeast asia during 1997 stratification of the f2 layer was seen at dip latitudes from 4 s to 18 s on the southern side of the magnetic equator but did not occur at the closest reflection point to the magnetic equator dip latitude 2 3 n the observed transient cusp vertical ionosonde or additional nose oblique ionosonde was defined as an f3 layer or an f1 5 layer depending on whether it occurred above or below the layer which maintained continuity with the normal f2 layer peak within the zone of occurrence the transient layer was commonly seen as an f3 layer at reflection points closest to the magnetic equator but invariably as an f1 5 layer at reflection points farther from the magnetic equator these observations suggest that the distortion in the equatorial electron density profile associated with the phenomenon moved toward the base of the f2 layer as magnetic field lines descended with increasing latitude stratification of the f2 layer commenced at the same local time e g 0845 lt in november 1997 throughout the longitudinal range of coverage and was associated with a rapid rise in f2 layer height following sunrise the stratification ended at times varying from 1300 lt to sunset and was associated with a fall in the height of f2 peak electron density the region of maximum f2 layer stratification lay between the magnetic equator and the peak of the southern equatorial anomaly

an additional layer in the low latitude ionosphere in indian longitudes total electron content observations and modeling 1 the paper presents the observations and modeling of an additional layer in the low latitude ionosphere in indian longitudes the signatures of the additional layer are observed as ledges or humps between the equatorial ionization anomaly trough and crest eia in the latitudinal profiles of total electron content tec measured using a single ground based beacon receiver located at trivandrum 8 5 n 77 e dip 0 5 n in india the ground based ionograms also show the presence of the so called f 3 layer for a short duration corresponding to these signatures and the layer is found to drift upward to the topside ionosphere the study provides first observational evidence that the so called humps in the latitudinal variation of tec are nothing but the upward propagating f 3 layer this conclusion is supported by theoretical modeling using the sheffield university plasmasphere ionosphere model it is shown that upward exb drift and strong equatorward neutral wind perturbed by atmospheric waves can produce the humps in the latitudinal variation of tec through the reduction in the downward diffusion of ionization along geomagnetic field lines the model results also show that the f 3 layer drifts to the topside and forms topside ledges

large scale traveling ionospheric disturbances impacting equatorial ionization anomaly development in the local morning hours of the halloween superstorms on 29 30 october 2003 this study investigates the development of eia like features during the halloween superstorms these features are similar to a well developed equatorial ionospheric anomaly eia and therefore suggest superfountain effects we tracked eia like features in the early morning sector of 29 30 october 2003 and at around midday on 30 october their plasma environment was studied with field aligned plasma density vertical plasma drift electron temperature and vertical plasma flow profiles coupled thermosphere ionosphere plasmasphere ctip simulations reproduced storm generated equatorward wind surges when these eia like features appeared early morning on 29 30 october there was no forward fountain circulation only large scale traveling ionospheric disturbances tids and strong equatorward winds were present these provide observational evidence that large scale tids created large plasma depletions over the dip equator and with the aid of equatorward winds some large enhancements at 30 n geomagnetic resulting in the development of early morning eia like features we identified tid signatures in the equatorial and midlatitude ionosonde and magnetometer data and studied eia like features at around midday on 30 october utilizing non field aligned topex tec 2000 ut and published champ tec 2030 ut 2200 ut line plots according to our analysis the eia like features seen in the tec data were created by large scale tids at 2000 and 2030 ut and by the combined effects of large scale tids and forward superfountain at 2200 ut ctip simulations demonstrate the crucial role of the neutral winds mechanical or direct effects in the development of high plasma densities at low midlatitudes

f region behavior in the sed plume during a geomagnetic superstorm a case study 1 we report observations from the gps total electron content tec ionosonde and millstone hill incoherent scatter radar showing some interesting features of the height profile of the ionospheric electron density that occurred during a passage of a storm enhanced density sed plume during the geomagnetic superstorm on 20 november 2003 first the tec increases to about 6 58 times the quiet day value while the f peak plasma density nmf2 only enhances by a factor of 1 37 second the f2 layer peak height hmf2 is dramatically lifted from the quiet time altitude of 250 km to an unusual altitude of 577 km furthermore the topside chapman scale height ht is larger by a factor of 6 25 compared to the quiet time value as a result the electron density content with an chapman function above 700 km contributes about 59 to the total content during the sed event our analysis shows that during a passage of the sed plume the enhancement of tec is mainly attributed to the great increase of ht with a very high hmf2

a statistical study on the characteristics of ionospheric storms in the equatorial ionization anomaly region gps tec observed over taiwan 1 positive and negative signatures of the ionospheric storms caused by the penetration electric field disturbance dynamo neutral wind neutral composition etc have been reported in this paper the ionospheric total electron content tec derived from the records of a network of ground based gps receivers in taiwan is used to statistically study the characteristics such as local time of appearance and duration of the storm signatures of various casuals in the equatorial ionization anomaly eia region during 1994 2003 a bias corrected accelerated bootstrap method and a z test are employed for the first time to detect each event and the overall storm signatures and characteristics respectively it is found that the positive signatures that appeared minutes to hours after the geomagnetic storm onset are pronounced on the storm day and the next day while the negative signatures that started hours after the geomagnetic storm onset can last for as long as the next 4 days the positive signature is statistically significant and most pronounced when the intense geomagnetic storm onset occurs during local afternoon which suggests that the signature may result from a combination of the prompt penetration electric field effect and mechanical effects of equatorward neutral wind additionally the negative signature that is statistically significant and most pronounced in the local afternoon of the storm onset day and or the next day may be produced by the disturbance dynamo or overshielding effects the long lasting negative signature occurred in local midnight noon period on days 2 4 after the storm onset may result from the neutral composition disturbances

volcanomagnetic evidence of the magmatic intrusion on 13thmay 2008 etna eruption 1 during the onset of 2008 volcanic crisis at mt etna the near real time magnetic data provided a continuous updating of the volcano activity state on the northern flank on the morning of 13th may 2008 significant local magnetic field changes marked the resumption of the eruptive activity characterized by the opening of a fracture field on the northern flank and an eruptive fissure in the valle del bove in agreement with the northward propagation of seismic events magnetic signals at 5 stations in the summit area revealed a nearly nnw sse oriented magmatic intrusion which started at about 9 00 gmt propagated northward for about 2 km and stopped at 14 00 gmt before reaching the north east rift magnetic variations with amplitude ranging between 1 8 nt and 6 5 nt are consistent with those calculated from piezomagnetic models where stress induced changes in rock magnetization are produced by the magmatic intrusion

super plasma fountain and equatorial ionization anomaly during penetration electric field 1 relative importance of diffusion electric field and neutral wind on equatorial plasma fountain and equatorial ionization anomaly eia during a strong daytime eastward prompt penetration electric field ppef event are evaluated using the sheffield university plasmasphere ionosphere model and the recorded ppef during the super geomagnetic storm of 9 november 2004 the fountain rapidly develops into a super fountain during the ppef event the super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces or stops the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss the eia crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the ppef event however the crests become stronger than normal only in the presence of an equatorward wind the results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during a daytime eastward ppef event the equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms

magnetic conjugate observation of the f3 layer using the sealion ionosonde network 1 results from the meridional ionosonde network located in southeast asia sealion demonstrate the interesting nature of the f3 layer showing its generation mechanism ionograms obtained on 16 november 2004 and 31 march 2005 at chiang mai cmu geographic latitude 18 8 n geographic longitude 98 9 e and magnetic latitude 13 2 n chumphon cpn 10 7 n 99 4 e and 3 2 n and kototabang ktb 0 2 s 100 3 e and 10 1 s showed significant differences between cpn near the magnetic equator and cmu and ktb in the magnetic low latitude region the simultaneous magnetic conjugate observations of the f3 layer achieved using the sealion ionosonde network data showed clear dependences of the f3 layer on the magnetic latitude it is suggested that these magnetic latitude dependences of the f3 layer can be explained by considering the plasma diffusion effects along the magnetic field lines in the magnetic low latitude region

ionosphere disturbances observed throughout southeast asia of the superstorm of 20 22 november 2003 1 ionospheric disturbances in the southeast asian region during the super magnetic storm of 20 22 november 2003 were investigated through an ionosonde chain and a gps network assisted by the space borne instruments at early stage of the storm in the postsunset sector large enhancements in the critical frequency of f2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly eia which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field ppe during the main phase of the storm when interplanetary magnetic field started a 12 h southward turning equatorial ionosphere was elevated to a very high level which should be most probably caused by a long duration ppe event meanwhile at mid low latitudes ionosphere witnessed an initial simultaneous decrease then followed by drastic increases which is very different from the past observations in this region reddy and nishida 1992 combined analysis of the data from the ionosonde and other space based measurement shows that for the present case the penetration efficiency of the interplanetary electric field ief to the equatorial ionosphere was larger at night than in the daytime which agrees with the results of fejer et al 2007 showing the ratios of ppe and ief changes were highly variable with the local time during the recovery phase eia was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field

f3 layer during penetration electric field 1 the occurrence of an additional layer called f3 layer in the equatorial ionosphere at american indian and australian longitudes during the super double geomagnetic storm of 7 11 november 2004 is presented using observations and modeling the observations show the occurrence reoccurrence and quick ascent to the topside ionosphere of unusually strong f3 layer in australian longitude during the first super storm 8 november and in indian longitude during the second super storm 10 november all with large reductions in peak electron density nmax and total electron content gps tec the unusual f3 layers can arise mainly from unusually strong fluctuations in the daytime vertical e b drift as indicated by the observations and modeling in american longitude the strongest upward e b drift or eastward prompt penetration electric field ppef ever recorded at jicamarca produces unusually strong f3 layer in the afternoon hours 1400 1600 lt of ppef with large reductions in nmax and tec the layer also reappears in the following evening 1700 1800 lt owing to an unusually large downward drift at night when the drift is unusually upward and strong the f region splits into two layers

investigating storm enhanced density and polar tongue of ionization development during the 22 october 1999 great storm we investigate large scale plasma density increases occurring during the 22 october 1999 great storm and focus on storm enhanced density sed and polar tongue of ionization toi development observations include two hourly global ionosphere map series coupled with multi instrument in situ space based and ground based data plots with super dual auroral radar network two cell convection maps and with model generated neutral wind vector maps results demonstrate the equatorial electrojet events occurring in the australian and american sectors the high density plasma features and their underlying plasma transportation processes during the main phase a series of four prompt penetration electric field ppef events occurred with subauroral polarization stream e field development forming a plasmaspheric drainage plume these e field events caused the repeated development of equatorial ionization anomaly eia sed bulge and sed plume during the local dusk midnight hours in those sectors that covered these local times showing a westward movement in accordance with their local time dependence the eia sed structure developed first in the american sector later on over the pacific and finally in the australian sector the sed plume plasma found its way into the polar cap through the dayside cusp region created in the north some large polar cap enhancements reaching up to seven times of the quiet time levels and evolved in each hemisphere into a polar toi we speculate that the enhanced growth of eia transporting high density solar produced plasma to the sed bulge via strong net eastward e field effects and the mechanical effects of equatorward neutral winds contributed to the polar toi s increasingly better development

infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007 1 long lived effusive volcanism at the pu u crater complex kilauea volcano hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years previous studies showed that this infrasonic tremor wavefield can be recorded at a range of 10 km however the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range in april 2007 we supplemented a broadband infrasound array at 12 5 km from pu u mene with a similar array at 2 4 km from the source kipu the additional closer range data enable further evaluation of tropospheric propagation effects and provide higher signal to noise ratios for studying volcanic source processes the infrasonic tremor source appears to consist of at least two separate physical processes we suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor low frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma air interface we further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle the infrasonic tremor arrives with a median azimuth of 67 at kipu additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex median azimuth 77 coincided with turbulent degassing activity at a new lava tube skylight our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at kilauea volcano

modeling of volcanic tremor as explosive point sources in a single layered elastic half space i investigate path effects on the waveform of a volcanic tremor using a model that consist of an impulsive dilatational point source embedded in a single layered elastic half space such a source may arise during a variety of volcanic conditions such as a sequence of rapid explosions at a volcanic vent as well as gas piston activity observed in basaltic lava lakes using acoustic signals recorded during the 1975 tolbachik eruption the 1983 klyuchevskoy eruption and the 1989 tokachi dake eruption i propose a general impulsive time function for the tremor source consisting either of a single impulse or a sequence of identical impulses computed seismograms illustrate the influence of a low velocity surface layer on the shape and spectra of the waveforms for the same layered model a single impulse produces a dispersive wave while a sequence of identical impulses produces a wave of multiple harmonics for a single impulse the peak in the seismograms shifts to higher frequencies when the surface layer is very thin for multiple impulses spectral peaks shift to higher frequencies as the time between successive impulses increases indicating an increasing importance of higher order harmonics

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

equatorial ionospheric electric fields during the november 2004 magnetic storm 1 we use radar measurements from the jicamarca radio observatory magnetometer observations from the pacific sector and ionosonde data from brazil to study equatorial ionospheric electric fields during the november 2004 geomagnetic storm our data show very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour indicative of undershielding and overshielding prompt penetration electric fields in the pacific equatorial region during the november 7 main phase of the storm when the southward imf the solar wind and reconnection electric fields and the polar cap potential drops had very large and nearly steady values this result is inconsistent with the recent suggestion that solar wind electric fields penetrate without attenuation into the equatorial ionosphere for several hours during storm main phase the largest daytime prompt penetration electric fields about 3 mv m ever observed over jicamarca occurred during the november 9 storm main phase when large equatorial electrojet current and drift perturbations were also present in the pacific and brazilian equatorial regions the rise and decay times of these equatorial electric fields were about 20 min longer than of the corresponding solar wind electric fields the ratios of prompt penetration electric fields and corresponding solar wind electric field changes were highly variable even during the day and had largest values near dawn also the prompt penetration electric fields did not show polar cap potential drop saturation effects our results clearly highlight that the relationships of prompt penetration and solar wind electric fields and polar cap potentials are far more complex than implied by simple proportionality factors

local time seasonal and solar cycle dependency of longitudinal variations of tec along the crest of eia over india 1 the global wave number 4 structure in the indian longitudinal region spanning from 70 to 95 e forming the upward slope of the peak in the total electron content tec are reported along the crest of equatorial ionization anomaly eia the continuous and simultaneous measurements from five gps stations of gps aided geo augmented navigation gagan network are used in this study the long term database 2004 2012 is utilized for examining the local time seasonal and solar cycle dependency on the longitudinal variations of tec our results confirm the existence of longitudinal variations of tec in accordance with wave number 4 longitudinal structure including its strength the results suggest that these variations in general start to develop at 09 lt achieve maximum strength at 12 15 lt and decay thereafter the decay rate depending on the season they are more pronounced in equinoctial season followed by summer and winter the longitudinal variations persist beyond midnight in equinox seasons whereas in winter they are conspicuously absent interestingly they also exhibit significant solar cycle dependence in the solstices whereas in the equinoxes they are independent of solar activity the comparison of crest to trough ratio ctr in the eastern 92 e and western 72 e extreme longitudes reveals higher ctr on the eastern side than over the western extreme suggesting the role of nonmigrating tides in modulating the exb vertical drift and the consequential eia crest formation

source location variability and volcanic vent mapping with a small aperture infrasound array at stromboli volcano italy stromboli volcano in italy is a persistently active complex volcanic system in may 2002 activity was confined to 3 major summit craters within which several active vents hosted multiple explosions each hour during a 5 day field campaign an array of 3 low frequency microphones was installed to investigate the coherent infrasound produced by degassing from these vents consistent phase lags across the 3 stations indicate distinct sources that are subsequently investigated to determine the associated vent location apparent depth and origin time the cross correlation routine allows for variations in comparison window length waveform filtering bandwidth and correlation and consistency thresholds allowing for improved detection of certain types of degassing sources identification of activity at the various vents could be subsequently corroborated with 3 channels of synchronously acquired thermal data and video during the may 2002 experiment persistent energetic infrasound was observed from a passive degassing source within the central crater cc and transient infrasound produced by discrete strombolian explosions was identified at 4 additional vents the continuous infrasound produced by the cc exhibits variable frequency dependent correlation lag times that are interpreted as a diffraction effect due to the acoustic radiator s recessed location within a steep walled crater such dispersion has important implications for accurate eruption source modeling because it indicates that infrasonic waveforms may be significantly filtered during propagation transient explosion signals from the northeast crater nec and southwest crater swc vents also exhibit dynamic correlation lag times but this scatter may be more reasonably attributed to variable epicentral locations explosions from the nec west vent for instance appear to emanate from a diffuse zone with a lateral extent in excess of 10 m

high speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008 1 to demonstrate high speed stream effects during the recent deep solar minimum year 2008 we have analyzed manually scaledfof2 and hmf2 at jicamarca and total electron content tec in the equatorial ionization anomaly eia region over the america longitudinal sector our results reveal that a prominent 9 day oscillation appears in the hmf2 and fof2 at the dip equator the 9 day oscillation amplitudes of fof2are not always positively correlated with tec in the equatorial ionosphere and they show nonlinear dependence on the intensity of geomagnetic disturbances with the outputs of fejer and scherliess s 1997 empirical model we found that this periodicity is also present in equatorial vertical drifts caused by disturbance dynamoelectric field ddef but absent in the drifts due to prompt penetration electric field ppef ddef effects on the equatorial periodic variations alone are not sufficient to explain the observed phenomena other mechanisms such as thermal expansion contraction and neutral composition changes are also the plausible causes of the periodic oscillation in the equatorial ionosphere further the complicated patterns appear in the 9 day band pass filtered tec perturbations in the eia region and they are quite different from the patterns of global coherent thermospheric oscillations triggered by high speed streams we also found that the latitudinal variations of band passed filtered tec present different behaviors involving tilt latitudinal configuration antiphased correlation between the crests and trough and south north asymmetry which vary as a function of season local time or even from event to event

formation and evolution of the ionospheric plasma density shoulder and its relationship to the superfountain effects investigated during the 6 november 2001 great storm this study investigates the 6 november 2001 great storm s impact on the topside ionosphere utilizing data from the onboard topex poseidon nasa altimeter defense meteorological satellite program special sensor ions electrons and scintillation instruments and ace interplanetary observatory a set of field aligned profiles demonstrate the storm evolution caused by the precursor and promptly penetrating interplanetary eastward electric e fields and strong equatorward winds reducing chemical loss during the long duration negative bz events at daytime evening the forward fountain experienced repeated strengthening as the net eastward e field suddenly increased the resultant symmetrical equatorial anomaly exhibited a continuous increase while the energy inputs at both auroral regions were similar in both hemispheres by progressing poleward a midlatitude shoulder exhibiting increased plasma densities a plasma density dropoff steep gradient and a plasma depletion appeared these features were maintained while the reverse fountain operated at the dropoff elevated temperatures indicated the plasmapause consequently the plasma depletion was the signature of plasmaspheric erosion in each hemisphere an isolated plasma flow supplying the minimum plasma was detected at the shoulder plasmaspheric compression due to the enhanced e fields could trigger this plasma flow exhibiting strong longitudinal variation at evening nighttime the shoulder increased 306 over the southeastern pacific where the nighttime weddell sea anomaly wsa appeared before the storm there the shoulder indicated the storm enhanced equatorward section of the quiet time wsa owing to the substantial equatorward plasmapause movement a larger poleward section of the quiet time wsa eroded away leaving a large depletion behind this study reports first these northern southern plasma flows and dramatic storm effects on a nighttime wsa

storm enhanced plasma density sed features auroral and polar plasma enhancements and rising topside bubbles of the 31 march 2001 superstorm 1 this study focuses on the 31 march 2001 superstorm s evening and nighttime sectors we specified forward fountain circulation and equatorial ionization anomaly eia storm enhanced density sed plume plasma flows auroral zones polar cap regions and traveling ionospheric disturbances tids these permitted analyzing low latitude plasma structures and middle and high latitude plasma buildups results reveal significant low latitude plasma structuring around ancon due to topside rising bubbles during the initial phase under disturbance conditions the deep equatorial plasma depletion appearing over the pacific during the main phase is an eia trough bubble structure topside bubbles and tid related drift perturbations structured sed plume plasma plasma distribution maximized when tids were in phase with fountain circulation and sed plume plasma flows and equatorward wind surges maintained high plasma densities plasma density and plasma flow measurements demonstrate the sed plume plasma s poleward migration through the auroral zone into the polar region and the maintenance and increase of auroral and polar enhancements forming a polar tongue of ionization toi our results contradict previous studies on this superstorm reporting the suppression of bubble formation over ancon and the absence of toi and explaining the development of equatorial depletion with no e b drift action our results oppose the current hypothesis that plasma enhancements are transported over many hours into the polar region indeed sed plume plasma produced by plasmaspheric detachment processes creates multiple downward plasma flows stretching from the midlatitude trough s equatorward edge to the polar cap region that in turn create plasma buildups at various latitudes where flow stagnates

neutral temperature anomaly in the equatorial thermosphere a source of vertical winds data obtained from the wats wind and temperature spectrometer instrument on de 2 dynamics explorer during high solar activity show new evidence for the presence of vertical winds of a significant magnitude in the equatorial thermosphere they reveal a latitudinal structure that can be related to the recently discovered phenomena of the equatorial temperature and wind anomaly etwa in the local evening hours the vertical winds usually are downward around the dip equator and collocated with the temperature minimum of etwa in general they are upward at about 24 dip latitude away from the dip equator and are collocated with the etwa temperature crests the magnitude of the vertical winds is in the 10 40 m s range it is proposed that the temperature and pressure ridges formed by the excess ion drag on the zonal winds around the two crests and ordered by the relatively lower ion drag at the trough of the well known equatorial ionization anomaly eia drive a new wind system in the meridional plane and that the measured vertical winds form part of this wind system

features of additional stratification in ionospheric f2 layer observed for half a solar cycle over indian low latitudes 1 the features of the additional stratification in the ionospheric f2 layer often referred to as the f3 layer observed over an indian low latitude station waltair 17 7 n 83 3 e magnetic latitude mag lat 8 2 n during the period 1997 2003 are presented along with the data from two other indian stations the observations grossly confirm those reported earlier in the occurrence and seasonal variability of the f3 layer from an analysis of half a solar cycle ionosonde data 1997 2003 it is observed that the layer appeared more frequently during the summer solstice months of low solar activity period and persisted for longer durations during this season compared with equinox and winter solstice the best stratification is seen between 10 12 hours ist the occurrence of the f3 layer does not seem to depend on magnetic activity but the percentage of occurrence decreased with increasing solar activity the solar activity dependence over waltair confirms the model predictions of balan et al 1998 that the layer becomes less distinct and less frequent as solar activity increases the ionosonde data for the same period 1997 2003 from an equatorial station trivandrum 8 4 n 76 9 e mag lat 0 47 n and another low latitude station shar 14 n 80 e mag lat 6 8 n are also analyzed with a view to examine the effect of the equatorial plasma dynamics on the occurrence of such events

an investigation of the northern hemisphere midlatitude nighttime plasma density enhancements and their relations to the midlatitude nighttime trough during summer this study has utilized regional surface maps and field aligned latitudinal profiles derived from multiinstrument dmsp f15 data it investigates northern midlatitude plasma enhancements in the nighttime topside ionosphere during summer and their relation to the midlatitude heavy ion stagnation trough the tracked midlatitude summer enhancements showed significant longitudinal variations their best development occurred in the 50 n 60 n 110 e 170 e geographic region proven by coupled thermosphere ionosphere plasmasphere wind velocity simulations equatorward winds were strongest there this region is the northern hemisphere equivalent of the weddell sea anomalys wsa locality there northern summer plasma enhancements resembled the nighttime wsa a southern summer equinoctial phenomenon and thus were named as wsa like feature their plasma density increased mainly owing to the mechanical or direct effects of the equatorward winds however as results show the wsa like feature was an ordinary northern midlatitude nighttime enhancement occurring in summer this was further confirmed by the wsa like features relation to the trough and by the troughs movement over the northern hemisphere the summer trough appeared at 62 461 2 93 n geomagnetic poleward of the wsa like feature and other midlatitude plasma enhancements and moved equatorward with a rate of 0 097 0 04 n nt when magnetic activity increased as our previous wsa investigation indicates the southern summer trough develops at lower latitudes at 47 1564 2 16 s equatorward of the nighttime wsa and moves poleward with a rate of 0 0497 0 003 s nt with increasing magnetic activity under the combined influence of the nighttime wsa and south atlantic magnetic anomaly copyright 2009 by the american geophysical union

a statistical study of the response of the dayside equatorial f2 layer to the main phase of intense geomagnetic storms as an indicator of penetration electric field 1 the response of the dayside equatorial f2 layer to the main phases of the 22 intense geomagnetic storms dst 150 nt in 1998 2008 is investigated using the digital ionosonde data from the equatorial stations in brazilian indian and australian longitudes together with equatorial electrojet strength and imf bz the storms include 15 superstorms dst 200 nt the observations show that there is a period during all mps when the f2 layer peak rises and falls rapidly with large peak electron density nmax reduction the rise velocity strongly correlates with the intensity dst of the storms and the duration of the nmax reduction corresponds to that of strong eastward electrojet when imf bz remains highly negative the observations indicate the occurrence of strong eastward prompt penetration electric fields ppef during the rapid f2 layer response the ppef drives the f2 layer peak rapidly upward which reduces nmax due to vertical expansion and diffusion the results therefore suggest that the rapid f2 layer response rapid rise and fall of peak height hmax with large nmax reduction observed by ionosondes can be used to detect the occurrence of the daytime eastward ppef during intense geomagnetic storms irrespective of season and level of solar activity the data also show two rare events of strong daytime westward electric fields due to disturbance dynamo and or prompt penetration the results are important when radars are not available to monitor the occurrence of the ppef

a physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 1 a physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi instrument observations theoretical modeling and basic principles according to the mechanism an equatorward neutral wind is required to produce positive ionospheric storms the mechanical effects of the wind 1 reduce or stop the downward diffusion of plasma along the geomagnetic field lines 2 raise the ionosphere to high altitudes of reduced chemical loss and hence 3 accumulate the plasma at altitudes near and above the ionospheric peak centered at around 30 magnetic latitudes daytime eastward prompt penetration electric field ppef if it occurs also shifts the equatorial ionization anomaly crests to higher than normal latitudes up to approximately 30 latitudes the positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind the mechanism agrees with the multi instrument observations made during the supergeomagnetic storm of 7 8 november 2004 with 18 h long initial phase ip and 10 h long main phase mp the observations which are mainly in the japanese australian longitudes where the mp onset was in the morning 0600 lt 2100 ut show 1 strong positive ionospheric storms in ne nmax hmax global positioning system total electron content gps tec and 630 nm airglow intensity in both northern and southern hemispheres started at the morning 0600 lt mp onset and lasted for a day 2 repeated occurrence of strong eastward ppef events penetrated after the mp onset and superposed with westward electric field started before the mp onset and 3 storm time equatorward neutral winds inferred from 1 and 2 repeated occurrence of an unusually strong f3 layer with large density depletions around the equator was also observed during the morning noon mp

insights into explosive activity at closely spaced eruptive vents using infrasound signals example of mt etna 2008 eruption abstract on 13 may 2008 an eruptive fissure opened on mount etna s eastern flank feeding both explosive activity and lava effusion from multiple vents for about 14 months during the investigated may september 2008 eruptive period infrasound recordings from a 4 station sparse network allowed tracking of the explosive activity in terms of location and dynamics in order to focus on activity from the eruptive fissure the infrasonic events generated by the summit craters were selected by using both spectral features and time delays between pairs of stations and excluded from our analysis then to accurately locate events from the fissure we used a composite method based on the semblance and brightness functions this enabled the study of the co existence of more than one infrasound source and or its migration along the eruptive fissure hence results permitted us to discriminate the number of active vents and their location along the fissure even when due to poor weather conditions it was not possible to access the vents or carry out direct observations the eruptive activity was characterised by variations in the number of active vents according to the overall intensity of the eruptive event variability of the infrasound waveforms highlighted either that distinct vents produced signals with different waveforms or that single vents generated different events during distinct periods of time or finally both the previous phenomena we applied the strombolian bubble vibration model to model waveform differences and attributed the signal variations to bubble radius changes

abnormal evening vertical plasma drift and effects on esf and eia over brazil south atlantic sector during the 30 october 2003 superstorm 1 equatorial f region vertical plasma drifts spread f and anomaly responses in the south american longitude sector during the superstorm of 30 october 2003 are analyzed using data from an array of instruments consisting of digisondes a vhf radar gps tec and scintillation receivers in brazil and a digisonde and a magnetometer in jicamarca peru prompt penetrating eastward electric field of abnormally large intensity drove the f layer plasma up at a velocity 1200 ms 1 during post dusk hours in the eastern sector over brazil the equatorial anomaly was intensified and expanded poleward while the development of spread f plasma bubble irregularities and gps signal scintillations were weaker than their quiet time intensity significantly weaker f region response over jicamarca presented a striking difference in the intensity of prompt penetration electric field between peru and eastern longitudes of brazil the enhanced post dusk sector vertical drift over brazil is attributed to electro dynamics effects arising energetic particle precipitation in the south atlantic magnetic anomaly sama these extraordinary results and their longitudinal differences are presented and discussed in this paper

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

storm enhanced plasma density features investigated during the bastille day superstorm field aligned passes track true profiles such defense meteorological satellite program passes permitted investigating storm enhanced plasma density sed feature development during the bastille day superstorm in a comprehensive way we tracked equatorial ionization anomaly eia and sed features and their underlying forward fountain circulation and downward sed plume plasma flows respectively northward subauroral polarization stream e fields detaching plasma and producing sed plumes were also detected we assessed the effects of south atlantic magnetic anomaly and summer towinter interhemispheric plasma flows on the eia and found a southward dipping gradient in drift flow when no storm evening related fountain strengthening occurred we investigated the relative importance of different plasma sources in sed development an extremely large plasma enhancement seen over florida at 2200 ut on 15 july 2000 was a sed feature that was tracked by many gps total electron content tec maps as a 200 tec unit tecu enhancement we tracked its equally large conjugate pair over trelew argentine patagonia and unraveled their development their underlying sed plume supplied most of the plasma appearing between these two sed features a small and highly asymmetrical eia offered on each side a low baseline upon which the downward streaming sed plume plasma piled up contradicting a currently accepted explanation there was no enhanced fountain action detected to contribute 150 tecu to the 200 tecu later 2400 ut there was enhanced fountain action but sed plume contribution still dominated proven by observational evidence sed development is a complex process of sed plume plasma flows and equatorward wind effects that cannot be described by one single explanation

traveling ionospheric disturbances and their relations to storm enhanced density features and plasma density irregularities in the local evening and nighttime hours of the halloween superstorms of 29 31 october 2003 1 this study focuses on the local evening or nighttime hours of the halloween superstorms its database containing multi instrument defense meteorological satellite program data plus ionosonde and magnetometer data allowed us to investigate the various plasma density features developed and the impact of traveling ionospheric disturbances tids drift perturbations and south atlantic magnetic anomaly sama effects on them we identified the midlatitude trough some topside bubbles the equatorial ionization anomaly eia and some storm enhanced density sed features results reveal that these features underlying vertical plasma flows became enhanced degraded when they were in the same opposite direction as the field aligned flows associated with a tid demonstrated with some coupled thermosphere ionosphere plasmasphere simulated wind vector maps high low plasma densities were maintained by equatorward poleward winds we observed some descending 600 m s bubbles with increased temperatures 4500 k due to their fast poleward movement 1 4 km s structuring some nearby sed features in the sama region and some low latitude plasma in the australian sector during the second superstorm s main phase 30 october 2003 a rising bubble with increased temperatures 5000 k due to the sama s energetic electrons further depleted the eia trough this observation contradicts a current interpretation of this depleted eia trough as bubble at the time of prereversal enhancement 2300 ut on 30 october some extremely large sed features 85 104 ions cm3 developed 30 n geomagnetic latitude around the symmetrical eia over brazil this scenario created a symmetrical plasma density profile contradicting some current speculations on the eia s asymmetry and its southern crest s displacement to higher latitudes over brazil indeed a sed feature appeared at higher latitudes 35 s geographic latitude

physical mechanism and statistics of occurrence of an additional layer in the equatorial ionosphere a physical mechanism and the location and latitudinal extent of an additional layer called the f3 layer that exists in the equatorial ionosphere are presented a statistical analysis of the occurrence of the layer recorded at the equatorial station fortaleza 4 s 38 w dip 9 s in brazil is also presented the f3 layer forms during the morning noon period in that equatorial region where the combined effect of the upward e b drift and neutral wind provides a vertically upward plasma drift velocity at altitudes near and above the f2 peak this velocity causes the f2 peak to drift upward and form the f3 layer while the normal f2 layer develops at lower altitudes through the usual photochemical and dynamical effects of the equatorial region the peak electron density of the f3 layer can exceed that of the f2 layer the f3 layer is predicted to be distinct on the summer side of the geomagnetic equator during periods of low solar activity and to become less distinct as the solar activity increases ionograms recorded at fortaleza in 1995 show the existence of an f3 layer on 49 of the days with the occurrence being most frequent 75 and distinct in summer as expected during summer the layer occurs earlier and lasts longer compared to the other seasons on the average the layer occurs at around 0930 lt and lasts for about 3 hours the altitude of the layer is also high in summer with the mean peak virtual height being about 570 km however the critical frequency of the layer f0f3 exceeds that of the f2 layer f0f2 by the largest amounts in winter and equinox f0f3 exceeds f0f2 by a yearly average of about 1 3 mhz

was magnetic storm the only driver of the long duration enhancements of daytime total electron content in the asian australian sector between 7 and 12 september 2017

observations and simulations of the ionospheric and thermospheric response to the december 2006 geomagnetic storm initial phase 1 we have investigated the thermospheric and ionospheric response to the 14 15 december 2006 geomagnetic storm using a coupled magnetosphere ionosphere thermosphere cmit 2 0 model simulation in this paper we focus on observations and simulations during the initial phase of the storm about 8 h when the shock was driving changes in geospace the global ionospheric maps of total electron content tec ionosonde data at four stations and millstone hill incoherent scatter radar isr observations are compared with the corresponding simulation results from the cmit model the observations showed significant positive storm effects occurred in the atlantic sector after the onset of this storm the cmit model is able to capture the temporal and spatial variations of the ionospheric storm effects seen in the gps tec observations although the model slightly underestimates the daytime positive ionospheric storm in the south american sector the simulations are also in agreement with the ionosonde and isr ionospheric measurements term analysis of the ion continuity equation demonstrates that changes in the electric fields play a dominant role in generating the observed ionospheric positive storm effect in the american sector during the initial phase although neutral winds and composition changes also contribute the difference in the strength of the enhancements over north and south america can be explained by the slope of the topside electron density profiles in the two hemispheres in the southern hemisphere electron densities decrease slowly with altitude whereas the decrease is much more rapid in the northern winter hemisphere the electric fields therefore cannot cause large increases in electron density by uplifting the plasma so positive storm effects are small in the southern hemisphere compared with the northern hemisphere even though the increase in hmf2 is greater in the southern hemisphere nighttime changes in electron density in other longitude sectors are small because the topside electron densities also decrease slowly with altitude at night

a multiparameter approach to volcano monitoring based on 4d analyses of seismo volcanic and acoustic signals the 2008 mt etna eruption 1 volcanic tremor and low frequency events together with infrasound signals can represent important precursory phenomena of eruptive activity because of their strict relationship with eruptive mechanisms and with fluid flows through the volcano s feeding system important variations of these seismo volcanic and infrasound signals recorded at mt etna volcano occurred both in the medium and short term before the eruption that took place on 13 may 2008 the most significant changes were observed in the frequency content and location of lp events as well as in volcanic tremor location that allowed us to track the magma pathway feeding the 2008 eruptive activity the infrasound showed three different families of events linked to the activity of the three active vents north east crater south east crater and the eruptive fissure the seismic and infrasonic variations reported corroborated by ground deformations variations help to develop a quantitative prediction and early warning system for effusive and or explosive eruptions

daytime ionospheric longitudinal gradients seen in the observations from a regional beidou geo receiver network many studies have devoted to the longitudinal variations of the ionosphere globally however the ionospheric longitudinal variations in a small region are rarely reported in this paper we for the first time use tec data from a beidou geostationary orbit geo receiver network to observe and investigate ionospheric longitudinal variations within the zonal scale of 1000 km over central china 112 122 e 27 31 n 20 24 n magnetic latitudes during june 2015 december 2016 the beidou geo tec provides a good dataset to study longitudinal variations compared with non geo tec without contaminating the spatial variations and elevation changes due to satellite motion pronounced daytime longitudinal gradients within the distance of 1000 km are present in beidou geo tec it was found that the tec is generally larger in the west than in the east in some cases the tec gradient magnitude is larger than 45 tecu for most events the obvious daytime longitudinal gradients are accompanied by the tec enhancement the occurrence rate of daytime longitudinal gradients under different geomagnetic activities is similar whereas strong daytime longitudinal gradients mainly occur under the moderate and strong disturbance geomagnetic activities these observations suggest that the electric field disturbances could have significant effects on producing the observed ionospheric longitudinal gradients

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

on the vertical drift of ionospheric f layer during disturbance time results from ionosondes the morphology of low latitude ionosphere is greatly affected by the zonal electric field especially at disturbance time in this study historical data from two low latitude ionosondes located at haikou and chongqing china are used to study the disturbance vertical drift properties of ionospheric f layer during the initial and main phases of 50 intense storms the disturbance drift from an empirical model is used as an indicator to denote the e x b disturbance magnitude it is found that the drifts both at the base and at the peak height are increased in magnitude when the disturbance becomes stronger for the same disturbance ionospheric vertical drifts at the base height are comparable with those at the peak height over haikou but they are larger than the latter over chongqing both drifts being smaller than those at the magnetic equator the drifts are larger in daytime than in nighttime but no rule is found on their seasonal dependence this indicates that low latitude storm time ionospheric vertical drift of the ionospheric layer exhibits both consistent and individual properties at different locations

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

buoyancy driven dissolution enhancement in rock fractures the structures of geological formations as well as flow and chemical transport patterns within them are profoundly affected by chemical dissolution and precipitation processes i e the interactions among flow chemical transport buoyancy and dissolution and precipitation reactions these processes are intrinsically hard to measure and therefore are not well understood nuclear magnetic resonance imaging is applied to study the dynamic behavior of coupled flow and dissolution in natural rock fractures our findings reveal that flow and transport in evolving fractures are far more unpredictable than commonly assumed due to complex interactions among fracture morphology flow dissolution and buoyancy this can explain physical processes causing catastrophic collapse and subsurface structural instabilities such as sinkholes and land subsidence

physical mechanisms of the ionospheric storms at equatorial and higher latitudes during the recovery phase of geomagnetic storms 1 the paper studies the physical mechanisms of the ionospheric storms at equatorial and higher latitudes which are generally opposite both during the main phase mp and recovery phase rp of geomagnetic storms the mechanisms are based on the natural tendency of physical systems to occupy minimum energy state which is most stable the paper first illustrates the recent developments in the understanding of the mechanisms during daytime mps when generally negative ionospheric storms in nmax and tec develop at equatorial latitudes and positive storms occur at higher latitudes including why the storms are severe only in some cases the paper then investigates the relative importance of the physical mechanisms of the positive ionospheric storms observed at equatorial latitudes within 15 during daytime rps when negative storms occur at higher latitudes using champ ne and gps tec data and sheffield university plasmasphere ionosphere model the results indicate that the mechanical effect of the storm time equatorward neutral winds that causes plasma convergence at equatorial f region could be a major source for the positive storms with the downwelling effect of the winds and zero or westward electric field if present acting as minor sources

patterns in the recent 2007 2008 activity of mount etna volcano investigated by integrated geophysical and geochemical observations 1 seismic deformation and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment in spite of their wide use there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques here we combine seismic volcanic tremor and long period seismicity deformation gps and geochemical volcanic gas plume co2 so2 ratios measurements in an attempt to interpret trends in the recent 2007 2008 activity of etna volcano we show that each eruptive episode occurring at the southeast crater sec was preceded by a cyclic phase of increase decrease of plume co2 so2 ratios and by inflation of the volcano s summit captured by the gps network these observations are interpreted as reflecting the persistent supply of co2 rich gas bubbles and eventually more primitive magmas to a shallow depth of 1 2 8 km asl magma storage zone below the volcano s central craters ccs overpressuring of the resident magma stored in the upper ccs conduit triggers further magma ascent and finally eruption at sec a process which we capture as an abrupt increase in tremor amplitude an upward 2800 m asl and eastward migration of the source location of seismic tremor and a rapid contraction of the volcano s summit resumption of volcanic activity at sec was also systematically anticipated by declining plume co2 so2 ratios consistent with magma degassing being diverted from the central conduit area toward sec

observations of the ionospheric response to the 15 december 2006 geomagnetic storm long duration positive storm effect 1 the long duration positive ionospheric storm effect that occurred on 15 december 2006 is investigated using a combination of ground based global positioning system gps total electron content tec topex and jason 1 tec and topside ionosphere plasmasphere tec gps radio occultation and tiny ionospheric photometer tip observations from the constellation observing system for meteorology ionosphere and climate cosmic satellites this multi instrument approach provides a unique view of the ionospheric positive storm effect by revealing the storm time response in different altitude regions the ground based gps tec topex jason 1 tec and topside ionosphere plasmasphere tec all reveal significant enhancements at low latitudes to midlatitudes over the pacific ocean region during the initial portions of the storm main phase from 0000 0400 universal time ut on 15 december at low latitudes the topside ionosphere plasmasphere tec increase represents greater than 50 of the tec enhancement that is observed by ground based gps receivers moreover electron density profiles obtained using the technique of gps radio occultation demonstrate that the f layer peak height increased by greater than 100 km during this time period the effects of soft particle precipitation are also apparent in the cosmic observations of topside ionosphere plasmasphere tec the positive storm effects over the pacific ocean region remain present in the equatorial ionization anomaly crest regions beyond 1200 ut on 15 december this long lasting positive storm effect is most apparent in ground based gps tec and cosmic tip observations while only a small increase in the topside ionosphere plasmasphere tec after 0400 ut is observed this indicates that the long lasting positive storm effect occurs predominantly at f region altitudes and furthermore that refilling of the topside ionosphere and plasmasphere is not the primary mechanism for producing the long lasting positive storm phase during this event the observations suggest that the enhanced eastward electric field and equatorward neutral wind are likely to play a significant role in the generation of long lasting positive storm effects

conditions for intense ionospheric storms expanding to lower midlatitudes 1 for studying conditions of intense ionospheric storms at lower midlatitudes several storms that occurred in march and april 2001 were compared in the two largest magnetic disturbances that occurred during this period the disturbance dst index reached 387 and 271 nt the two largest ionospheric storms occurred in response to other weaker magnetic disturbances in which dst reached 149 and 102 nt for the largest ionospheric storms on 21 march 2001 and 22 april 2001 a sequence of ionospheric and thermospheric disturbances was analyzed we found that a nighttime disturbance dynamo plays an important role in expanding ionospheric storms to lower latitudes when an eastward disturbance dynamo electric field forms after midnight the ionospheric layer is uplifted and the ion drag is reduced the storm time equatorward surge effectively reaches lower latitude regions without decaying under the condition of reduced ion drag the equatorward surge pushes up the ionosphere in turn and the ion drags might be further reduced the large event to event variation of ionospheric storms might be partly owing to such a positive feedback process in addition to the well known local time effect