global distribution of nighttime medium scale traveling ionospheric disturbances seen by swarm satellites the activity of nighttime medium scale traveling ionospheric disturbance mstid in middle latitudes 25 40 magnetic latitudes is investigated using the measurements of the electron density by swarm satellites fractional electron density fluctuation is used as a proxy for mstids and the mstid distribution is derived from the observations in december 2013 january 2017 the mstid activity shows a semi annual variation in most longitudes with the primary and secondary peaks during the june and december solstices respectively the distinguishing feature in the mstid distribution is the high occurrence rate of mstids around 150 e longitude in june august the longitudinal and annual distribution of mstids shows a hemispheric symmetry which we interpret as the demonstration of conjugacy in mstids

superdarn observations of daytime mstids in the auroral and mid latitudes possibility of long distance propagation 1 the propagation parameters of daytime medium scale traveling ionospheric disturbances mstids are investigated for the first time using near simultaneous superdarn radar data obtained at auroral and middle latitudes the observations suggest that mstids can propagate from auroral to mid latitudes with persistent propagation parameters if the dominant propagation direction is approximately equatorward however statistical analysis implies that a portion of mstids with higher horizontal phase velocity are unable to reach the mid latitude due to enhanced dissipation and the reduction of the ion drag effect

first simultaneous observations of daytime mstids over north america using gps tec and demeter satellite data 1 we present simultaneous observations of daytime medium scale traveling ionospheric disturbances mstids over north america using measurements of the total electron content tec by the us gps network and ionospheric plasma data from the demeter micro satellite several events show latitudinal variations of the plasma parameters at satellite altitude corresponding to the mstid structures revealed on 2d tec maps in a case study with a very well defined mstid quasi periodic variations of the plasma density and of the ion velocity parallel to the earth s magnetic field are observed along the satellite orbit that match the signature of the mstid on the tec maps we believe it is the first simultaneous observation of parallel plasma motion in the topside ionosphere and propagating mstid structures in the f region an initial analysis of this event is performed in the light of results from simple model of ionospheric disturbances associated with atmospheric gravity waves agws

geomagnetic conjugate observation of nighttime medium scale and large scale traveling ionospheric disturbances front3 campaign 1 the third front f region radio and optical measurement of nighttime tid campaign was carried out during the new moon period of may june 2003 in order to investigate the geomagnetic conjugacy of medium scale and large scale traveling ionospheric disturbances mstids lstids at midlatitudes seven all sky airglow imagers were operated in japan and australia for almost all clear sky nights we observed mstids in the 630 nm airglow images with horizontal wavelengths of 100 400 km propagating southwestward in japan and northwestward in australia all of them show a one to one correspondence of wave structures between the northern and southern hemispheres indicating strong electrodynamic coupling between the two hemispheres through the geomagnetic field line we also found that airglow intensity variations with a timescale longer than that of mstids often show a good correlation between the two hemispheres on 28 may we succeeded in detecting an equatorward propagating lstid spatial scale 1000 km as airglow enhancements at the conjugate stations the airglow peak of the lstid in the northern hemisphere was 20 min earlier than that in the southern hemisphere indicating that the observed lstid is caused by a wave in the neutral atmosphere rather than by an electric field structure

vertical structure of medium scale traveling ionospheric disturbances we develop an algorithm of computerized ionospheric tomography cit to infer information on the vertical and horizontal structuring of electron density during night time medium scale travelling ionospheric disturbances mstids to facilitate digital cit we have adopted total electron contents tec from a dense global positioning system gps receiver network geonet which contains more than 1000 receivers a multiplicative algebraic reconstruction technique mart was utilized with a calibrated iri 2012 model as an initial solution the reconstructed f2 peaklayer varied in altitude with average peak to peak amplitude of 52 km in addition the f2 peak layer anti correlated with tec variations this feature supports a theory in which night time mstid s comprise of oscillating electric fields due to conductivity variations moreover reconstructed tec variations over two stations was reasonably close to variations directly derived from the measured tec dataset our tomographic analysis may thus help understand three dimensional structure of mstids in a quantitative way

inertia gravity waves revealed in radiosonde data at jang bogo station antarctica 74 37 s 164 13 e 2 potential sources and their relation to inertia gravity waves

super medium scale traveling ionospheric disturbance observed at midlatitude during the geomagnetic storm on 10 november 2004 1 medium scale traveling ionospheric disturbances mstids whose peak to peak amplitude was larger than 20 tecu 1016el m2 were observed at midlatitude during the geomagnetic storm on 10 november 2004 this amplitude was more than 10 times larger than that of the average mstid high resolution data of the gps earth observation network geonet clarified the characteristic of the total electron content tec disturbances over japan on 10 november 2004 the disturbances started around 1000 ut in the central part of japan the maximum of tec temporal change was 7 2 tecu in 30 s the disturbances had several wave fronts which extended from northwest to southeast and propagated from northeast to southwest tec data around japan revealed that the disturbances were mainly observed from 18 n s to 34 n s of the geomagnetic latitude in the both hemispheres since those characteristics were similar to those of mstids in spite of the unusual large amplitude the mstids are referred as super mstids in this paper tec variations of the super mstids were also observed at 460 km altitude by the grace satellite the ion density fluctuations of the super mstids were observed in situ by the champ and dmsp f15 satellites which flew at 360 km and 850 km respectively it is found that the plasma density variations of the super mstids occurred mainly above 360 km altitude the characteristics that distinguish the event from plasma bubbles are its successive wave fronts constant northwest southeast direction along which the wave fronts stretched and late local time of the occurrence it is found that the uplift of the ionosphere around sunset excited the super mstids at midlatitudes the uplift was attributed to the strong eastward electric field during the geomagnetic storm

a statistical study of large scale traveling ionospheric disturbances observed by gps tec during major magnetic storms over the years 2003 2005 1 in this paper we plot two dimensional total electron content tec perturbation maps and investigate the statistical characteristics of large scale traveling ionospheric disturbances lstids during major magnetic storms from 2003 to 2005 the tec data were obtained from more than 600 gps receivers in north america within the geographical latitudes of 25 n 55 n we found a total of 135 cases of lstids with amplitudes of up to 3 5 tecu and a maximum front width of 4000 km the mean value of periods horizontal velocities and azimuths are 1 8 h 300 m s and 187 7 west of south respectively the mean velocity is obviously slower than that observed at lower latitudes such as japan of all the 135 lstid events 35 cases 26 occurred in the nighttime with their possible source within the region of north america according to the variation of magnetic h component observed in this region in addition the occurrence of lstids peaks at 1200 lt and at 1900 lt it is also pointed out that the ut dependence of the occurrence of auroral geomagnetic disturbances plays a major role in the forming of ut and lt dependence of the occurrence of lstids observed at midlatitudes

horizontal parameters of daytime thermospheric gravity waves and e region neutral winds over puerto rico we report on the electron density perturbation amplitudes periods up to 60 min horizontal and vertical wavelengths phase speeds and propagation directions of daytime traveling ionospheric disturbances tids from 115 to 300 km altitude using dual beam experiments at the arecibo observatory ao puerto rico as in previous studies we find a near continuum of waves above the ao while the tids propagate in nearly all directions except purely westward we find that most propagate southward southeastward we find that tid amplitudes increase nearly exponentially with increasing period although with a much smaller slope for periods 30 min tid amplitudes peak on the bottomside of the f region typical vertical wavelengths increase from less than 50 km at low altitudes to 100 300 km horizontal wavelengths increase from 70 100 km to 150 500 km over the same altitude range median vertical wavelengths horizontal wavelengths and periods increase with altitude up to z 100 150 m s we also measure the e region horizontal neutral winds and find that they peak at 150 m s near z 105 km in the middle of the day wave phase speeds are in general greater than these ambient winds in addition by tracing individual wave packets vertically in altitude we find that a packet s vertical wavelength generally peaks near the altitude where its inferred ion velocity amplitude is maximum the vertical wavelength generally decreases above this altitude an observation that is consistent with gravity wave packet theory

the 2009 samoa and 2010 chile tsunamis as observed in the ionosphere using gps total electron content 1 ground based global positioning system gps measurements of ionospheric total electron content tec show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events the samoa earthquake of 29 september 2009 and the chile earthquake of 27 february 2010 both earthquakes produced ocean tsunamis that were destructive to coastal communities near the epicenters and both were observed in tidal gauge and buoy measurements throughout the pacific ocean we observe fluctuations in tec correlated in time space and wave properties with these tsunamis using the jet propulsion laboratory s global ionospheric mapping software these tec measurements were band pass filtered to remove ionospheric tec variations with wavelengths and periods outside the typical range for tsunamis observable variations in tec appear correlated with the tsunamis in some locations hawaii and japan but not in others southern california or near the epicenters where variations are observed the typical amplitude tends to be 0 1 0 2 tec units for these events on the order of 1 of the background tec value these observations are compared to estimates of expected tsunami driven tec variations produced by embry riddle aeronautical university s spectral full wave model an atmosphere ionosphere coupled model and are found to be in good agreement significant tec variations are not always seen when a tsunami is present but in these two events the regions where a strong ocean tsunami was observed coincided with clear tec observations while a lack of clear tec observations coincided with smaller sea surface height amplitudes there exists the potential to apply these detection techniques to real time gps tec data providing estimates of tsunami speed and amplitude that may be useful for early warning systems

traveling ionospheric disturbances detected in the front campaign the f region radio and optical measurement of nighttime tid front campaign was conducted to clarify the non classical features of traveling ionospheric disturbances tids at mid latitudes in may 1998 and august 1999 a cluster of all sky ccd cameras and a gps receiver network observed a wide area of the ionosphere over japan to detect the spatial structure and temporal evolution of tids the propagation direction of the nighttime tid detected during the front campaign periods is restricted to the southwest the time evolution of their amplitude indicates that the tid structure is intensified as it travels from high latitudes to low latitudes the significant coincidence between the structures of 630 nm band airglow and total electron content indicates that the perturbations take place in the bottomside of the ionospheric f region coherent echoes from the field aligned irregularities were observed by the mu radar in the nights when the tid activity was high

geomagnetic conjugate observations of large scale traveling ionospheric disturbances using gps networks in japan and australia 1 the geomagnetic conjugacy of large scale traveling ionospheric disturbances lstids was studied using total electron content tec data derived from gps networks in japan and australia the number of simultaneous occurrences of lstids within 1 hour in both hemispheres was 5 out of 20 21 events in japan australia when kp 5 and 0 out of 15 10 when kp 4 as for the lstids observed simultaneously in both hemispheres the propagation velocities of equatorward lstid were comparable between the two hemispheres with differences of 10 40 the crossing times at 30 geomagnetic latitude of the simultaneous lstids over japan and australia were also different by several tens of minutes for all five events these observational results indicate that the lstids observed almost simultaneously in both hemispheres are not connected electromagnetically through the geomagnetic field but are generated by atmospheric gravity waves propagating to the equator independently in the two hemispheres

medium scale traveling ionospheric disturbances triggered by super typhoon nepartak 2016 two remarkable typhoon induced traveling ionospheric disturbances tids with concentric and northwest southeast nw se alignments respectively associated with concentric gravity waves cgws and ionosphere instabilities possibly seeded by cgws were observed in total electron content tec derived from ground based gnss networks in taiwan and japan when the category 5 super typhoon nepartak approached taiwan on 7 july 2016 the concentric tids ctids first appear with horizontal phase velocities of 161 200 m s horizontal wavelengths of 160 270 km and periods of 15 22 min during 08 00 11 20 ut following the ctids the nw se aligned nighttime medium scale tids mstids are formed on the west edge of the ctids over the taiwan strait during 11 30 14 00 ut it is suggested that the mstids are produced by the electrodynamical coupling of perkins instability and cgw induced polarization electric fields this study proposes connections of typhoon induced ctids and subsequently occurring mstids in the low latitude ionosphere

first satellite imaging observation of medium scale traveling ionospheric disturbances by formosat 2 isual on the night of may 16 2007 a satellite limb imager of formosat 2 isual observed wave like structures of the 630 nm airglow simultaneously with an all sky imager deployed at darwin in australia the height of the airglow layer was estimated as 220 km and the structures were aligned in the northeast southwest orientation with a wavelength of 300 km and propagated toward the northwest with a phase velocity of 100 m s 1 showing typical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids we conclude that isual for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by mstid from space such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level

continuous generation and two dimensional structure of equatorial plasma bubbles observed by high density gps receivers in southeast asia high density gps receivers located in southeast asia sea were utilized to study the two dimensional structure of ionospheric plasma irregularities in the equatorial region the longitudinal and latitudinal variations of tens of kilometer scale irregularities associated with equatorial plasma bubbles epbs were investigated using two dimensional maps of the rate of total electron content change index roti from 127 gps receivers with an average spacing of about 50 100 km the longitudinal variations of the two dimensional maps of gps roti measurement on 5 april 2011 revealed that 16 striations of epbs were generated continuously around the passage of the solar terminator the separation distance between the subsequent onset locations varied from 100 to 550 km with 10 min intervals the lifetimes of the epbs observed by gps roti measurement were between 50 min and over 7 h the epbs propagated 440 3000 km toward the east with velocities of 83 162 m s 1 the longitudinal variations of epbs by gps roti keogram coincided with the depletions of 630 nm emission observed using the airglow imager six epbs were observed by gps roti along the meridian of equatorial atmosphere radar ear while only three epbs were detected by the ear the high density gps receivers in sea have an advantage of providing time continuous descriptions of latitudinal longitudinal variations of epbs with both high spatial resolution and broad geographical coverage the spatial periodicity of the epbs could be associated with a wavelength of the quasiperiodic structures on the bottomside of the f region which initiate the rayleigh taylor instability

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

magnetic signatures of medium scale traveling ionospheric disturbances as observed by champ 1 in this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations mmfs as observed by the champ satellite from 2001 to 2002 solar maximum and from 2006 to 2007 solar minimum mmfs are defined as medium scale magnetic fluctuations perpendicular to the mean field which are not accompanied by plasma density irregularities at the champ altitude 400 km mmfs occur at 15 40 invariant latitude in the ionospheric f region the occurrence is rare above the southern atlantic ocean and bears little connection to geomagnetic activity the global mmf occurrence rate depends on season the occurrence is generally low in equinox maximizes around east asia oceania and europe northern atlantic ocean in june solstice and peaks above the american continents in december solstice as the solar cycle declines the detected mmf occurrence rate also decreases the mmf occurrence peaks around 2100 lt and slowly decreases toward midnight in the postmidnight sector events are practically absent the mmf occurrence is generally consistent with known features of nighttime medium scale traveling ionospheric disturbances mstids such as the conjugate climatology and premidnight occurrence peak in the east asia oceania region but differences in their distributions also exist implying that factors other than mstids e g ionospheric conductivity sporadic e layer or plasma instabilities may play a nonnegligible role in generating mmfs mmfs have a preferred direction of polarization which is consistent with that of mstids and again corroborates the close connection between these two phenomena we interpret the observed magnetic deflections in terms of field aligned currents facs the estimated wavelength range 200 500 km of associated fac pairs also agrees well with the size of mstid density structures

arecibo s thermospheric gravity waves and the case for an ocean source 1 wave like disturbances in electron density ne have been observed in the thermosphere above arecibo observatory puerto rico throughout its 45 year history however only recently has it become evident that these waves are continuously present in the arecibo thermosphere the wave characteristics are fairly constant between day and night and from season to season high resolution electron density measurements obtained by applying the coded long pulse radar technique to photoelectron enhanced langmuir waves are presented these new observations strongly suggest that the perturbations in electron density are the result of internal acoustic gravity waves agws propagating through the arecibo thermosphere the agws appear to be broadbanded in wave number space the downward phase trajectories of ne ne between 400 and 120 km combined with the low horizontal phase velocities obtained from airglow measurements support the idea that the agws are not ducted but rather are locally produced in addition the altitudes at which major peaks in ne ne are observed follow theoretical estimates for nonducted waves the nominal period of the agws is 60 min at 250 km altitude but periods of 20 min are also evident at lower attitudes classic sources of agws do not appear to be consistent with the arecibo observations of a continuous flux of background agws ray tracing of the agws combined with 630 0 nm airglow observations point to a source location in the atlantic ocean that is roughly 2100 km east northeast of arecibo internal ocean waves generated in response to the internal tide at the mid atlantic ridge are the most likely source of arecibo s thermospheric agws

nighttime medium scale traveling ionospheric disturbances detected by network gps receivers in taiwan 1 the nighttime medium scale traveling ionospheric disturbances mstids are detected by the network gps receivers in taiwan for the first time the two dimensional mapping technique a spatial resolution of 0 05 0 05 in latitude and longitude with 5 5 pixels smoothing is applied on the data of tec perturbations tecp and gps phase fluctuations tec min the results show that the mstids move southwestward to latitude of 20 5 n with a horizontal velocity between 100 and 160 m s and a wavelength of about 500 km the wavefronts of the mstids are aligned along the northwest southeast direction furthermore the greater tec min values are corresponding to the wave peak and trough of tecp this coincidence indicates that the mstids play an important role for the generation of f region irregularities in the low latitude ionosphere

ionospheric bow waves and perturbations induced by the 21 august 2017 solar eclipse u s national science foundation grant ags 1242204 nasa grant nnx17ah71g nasa lws muri grant onr15 foa 0011 onr n00014 17 1 2186

multievent analysis of oscillatory motion of medium scale traveling ionospheric disturbances observed by a 630 nm airglow imager over tromso

storm and substorm causes and effects at midlatitude location for the st patrick s 2013 and 2015 events midlatitude locations are unique regions exposed to both geomagnetic storm and substorm effects which may be superposed on specific events imposing an extra handicap for the analysis and identification of the sources and triggers we study space weather effects at the midlatitude location of the iberian peninsula for the st patrick s day events in 2013 and 2015 we have been able to identify and separate storm and substorm effects on ground magnetometer data from san pablo toledo observatory during storm time revealing important contributions of the substorm current wedge on both events the analysis of these substorm local signatures have shown to be related to the production of effective geomagnetically induced currents and ionospheric disturbances as measured from global navigation satellite systems data at mad2 igs permanent station and not directly related to the storm main phase the whole sun to earth chain has been analyzed in order to identify the solar and interplanetary triggers in both events a high speed stream hss and a coronal mass ejections cme are involved though for 2015 event the hss has merged with the cme increasing the storm geoeffectiveness the enhancement of substorm geoeffectiveness is justified by the effects of the inclined magnetic axes of the sun and of the earth during equinox period

traveling ionospheric disturbances over the united states induced by gravity waves from the 2011 tohoku tsunami and comparison with gravity wave dissipative theory

ionosonde observations of ionospheric disturbances due to the 15 february 2013 chelyabinsk meteor explosion we report the results of our investigations on ionospheric effects potentially caused by the 15 february 2013 chelyabinsk meteor explosion we used the observation data from a number of digisonde s

medium scale traveling ionospheric disturbances affecting gps measurements spatial and temporal analysis 1 in this work we present a simple technique to estimate the medium scale traveling ionospheric disturbances mstids characteristics such as occurrence velocity vertical propagation with periods lower than 20 min and its application to a set of gps data both temporally and spatially representative near one solar cycle and four local networks in the northern and southern hemispheres respectively some of the main results presented in this paper are the mstids which occur at daytime in local winter and nighttime in local summer related to the solar terminator and modulated by the solar cycle they present equatorward from 100 to 400 m s and westward 50 to 200 m s horizontal propagation velocities respectively the corresponding periods are compatible higher with the theoretical prediction which is given by the neutral atmosphere

comment on the night when the auroral and equatorial ionospheres converged by martinis c j baumgardner m mendillo j wroten a coster and l paxton intense oi 630 0 nm emission depletions were detected over mexico by an all sky imager during the main phase of the geomagnetic storm on 1 june 2013 minimum dst index 119 nt those emission depletions were interpreted to be associated with equatorial plasma bubbles martinis et al 2015 if bubbles were responsible for those middle latitude emission depletions they would have been extreme bubbles which extended over 40 magnetic latitudes and 7000 km in altitude at the magnetic equator however a few factors challenge this interpretation first the emission depletions detected over mexico showed westward drift whereas the equatorial ionosphere including bubbles drifted eastward on that night second the middle latitude emission depletions were tilted westward with respect to the geographic meridian but the westward tilt of bubbles was not identified third the growth of bubbles was not evident when the middle latitude emission depletions grew the westward tilt and westward propagation of the middle latitude emission depletions are consistent with the characteristics of medium scale traveling ionospheric disturbances mstids observed over the united states on that night thus the emission depletions over mexico can be interpreted to be the signature of mstids

analysis of the global ionospheric disturbances of the march 2015 great storm the global ionospheric storm in march 2015 was investigated using data from over 3000 gps stations worldwide in this study total electron content tec rate of tec rot and rot s standard deviation roti as well as the second order difference operator tect were considered as main characteristic methods to distinguish ionosphereic disturbances the results show that 1 based on the multiple methods above we all observed that for the first time there were three equatorward traveling ionospheric disturbances tids in the main phase of this storm in north america the disturbance zone expanded to 40 n the disturbance periods and ae peak stages were roughly synchronous we suggest that these three tids were induced by the propagation of agws to low latitudes under the action of ae 2 the most intense positive storm occurred over south america and the south atlantic over 300 enhancement 00 00 05 00 ut march 18 whereas a negative storm was observed in the corresponding region of the nh such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition the imf by component and the geomagnetic intensity 3 on march 18 a negative storm dominated globally except at certain low latitudes and tended to propagate equatorward and decay with time which could be largely attributed to the storm circulation theory and the evolution of the negative storm was further characterized by the fof2 variations of ionosondes

unusual nighttime impulsive fof2 enhancement below the southern anomaly crest under geomagnetically quiet conditions 1 an unusual nighttime impulsive electron density enhancement was observed on 6 march 2010 over a wide region of south america below the southern crest of the equatorial anomaly under low solar activity and quiet geomagnetic conditions the phenomenon was observed almost simultaneously by the f2 layer critical frequency fof2 recorded at three ionospheric stations which are widely distributed in space namely cachoeira paulista 22 4 s 44 6 w magnetic latitude 13 4 s sao jose dos campos 23 2 s 45 9 w magnetic latitude 14 1 s brazil and tucuman 26 9 s 65 4 w magnetic latitude 16 8 s argentina although in a more restricted region over tucuman the phenomenon was also observed by the total electron content tec maps computed by using measurements from 12 gps receivers the investigated phenomenon is very particular because besides being of brief duration it is characterized by a pronounced compression of the ionosphere this compression was clearly visible both by the virtual height of the base of the f region h f recorded at the aforementioned ionospheric stations and by both the vertical electron density profiles and the slab thickness computed over tucuman consequently neither an enhanced fountain effect nor plasma diffusion from the plasmasphere can be considered as the single cause of this unusual event a thorough analysis of isoheight and isofrequency ionosonde plots suggest that traveling ionospheric disturbances tids caused by gravity wave gw propagation could have likely played a significant role in causing the phenomenon

damping of large scale traveling ionospheric disturbances detected with gps networks during the geomagnetic storm 1 large scale traveling ionospheric disturbances lstids during the geomagnetic storm on 22 september 1999 were studied using total electron content tec data from the gps earth observation network geonet in japan international gps service igs and continuously operating reference stations cors in the united states the damping rates of the lstids were precisely derived in several local time sectors and were found to depend on values of the background tec this indicates that the dominant physical mechanism of the lstids damping is the ion drag effect by the background ionosphere the high resolution tec data from geonet revealed that two successive lstids were damped significantly as they traveled equatorward in the dawn sector the ratio of the perturbation component of tec to the background component i i0 decreased exponentially with the damping rate of 0 89 1000 km and 0 77 1000 km we studied also the amplitude of i i0 at high latitudes using igs data and found that the damping rates of lstids at high latitudes tended to be smaller than those at midlatitudes global tec observations during this geomagnetic storm by the igs and cors networks detected that several lstids propagated also equatorward in the afternoon sector and in the night sector the lstids in the afternoon sector were most damped with the damping rate of 1 04 1000 km which corresponds to the e folding length of 961 km the damping rate of lstids in the night sector was found to be small the lstids had a tendency to be damped rapidly in the regions where background tec was large this dependence of the damping rate on latitude and local time indicates that this intense damping of lstids was caused mainly by the ion drag effect that is proportional to the ion collision frequency the relation between the damping rates and the background tec derived from the observation are consistent with those estimated with a theoretical calculation of the gravity wave damping by the ion drag effect the worldwide distribution of gps receivers enabled us to estimate the longitudinal extent of these lstids the zonal width of lstids in the dawn sector was narrower than 45 in longitude 2 900 km around 55 n and wider than 20 in longitude 1 800 km around 40 n these widths were narrower than those reported in previous studies

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

medium scale traveling ionospheric disturbances detected with dense and wide tec maps over north america 1 nighttime and daytime medium scale traveling ionospheric disturbances mstids are detected with dense and wide detrended total electron content tec maps over north america using multiple gps receiver networks the tec maps cover a wide region of 60 130 w and 24 54 n 30 65 n in geomagnetic latitude and have a spatial resolution of 1 05 1 05 in latitude and longitude 0 15 0 15 with 7 7 pixel smoothing and a temporal resolution of 30 seconds the tec maps reveal for the first time that the nighttime mstids propagate southwestward with 200 500 km wavelengths over north america and have wavefronts longer than 2 000 km we also observe that daytime mstids with 300 1 000 km wavelengths propagate southeastward until mid afternoon and southwestward in the late afternoon in the mid to late afternoon these mstids propagating in the different directions are superimposed the tec maps can be a new powerful tool to investigate the mstids

nighttime medium scale traveling ionospheric disturbances at low geomagnetic latitudes 1 nighttime medium scale traveling ionospheric disturbances mstids are a commonly observed structure in the middle latitude ionosphere during the months surrounding the solstices and low solar flux conditions mstids consist of one or more narrow bands exhibiting uplift in f region electron density which are elongated from northwest to southeast in the northern hemisphere and southwest to northeast in the southern hemisphere these electrified structures propagate westward and toward the equator in a direction perpendicular to their long dimension previously this type of mstid was not thought to occur at magnetic latitudes equatorward of the equatorial anomalies or approximately 15 geomagnetic latitude here we present observational evidence from a field aligned narrowfield imaging system of mstids existing very close to the magnetic equator we discuss the implications of this observation in terms of the development and propagation of mstids