experimental analysis of debris motion due the obstruction from fixed obstacles in tsunami like flow conditions abstract experimental research was conducted focusing on debris motion over a horizontal apron featuring vertical obstacles in the path of the debris propagation the apron was designed as a typical representation of a harbor threatened by an inundating tsunami the experimental setup idealized often complex harbor settings the debris was a scaled down 20 foot shipping container modelled at a 1 in 40 froude length scale offand onshore regions were separated by a vertical quay wall which allowed the incoming elongated solitary wave used to represent the first part of a tsunami to steepen break and propagate over the initially dry surface as a tsunami like bore in the path of propagation a varying number of debris were entrained within the inundating bore over the horizontal apron the entrained debris interacted with regularly spaced vertical obstacles representing infrastructure and houses within the propagation path varying debris and obstacle arrangements were tested to evaluate the effects the obstacles would have on the debris maximum longitudinal displacement and the spreading angle the main conclusion is that the spreading angle of the debris is not as significantly altered by the presence of obstacles on the harbor apron whereas the maximum longitudinal displacement of the debris was significantly affected

longitudinal development of low latitude ionospheric irregularities during the geomagnetic storms of july 2004 1 during the period 22 28 july 2004 three geomagnetic storms occurred due to a sequence of coronal mass ejections in this paper we present and discuss the ionospheric observations from a set of in situ satellites and ground based gps total electron content and scintillation receivers a vhf radar and two chains of ionosondes 300 e and 120 e respectively that provide the evolutionary characteristics of equatorial and low latitude ionospheric irregularities versus longitude during these storm periods it is found that the irregularities occurred over a wide longitudinal range extending from around 300 e to 120 e on storm days 25 and 27 july 2004 on 25 july plasma bubbles pbs began premidnight in america and postmidnight in southeast asia on 27 july the occurrence of irregularities followed the sunset terminator and was observed sequentially after sunset from american to southeast asian longitudes past studies have reported that storm time low latitude ionospheric irregularities are mostly confined to a narrower longitude range 90 after sunset hours and are associated with the prompt penetration of eastward electric fields ppefs into low latitudes in june solstice months the occurrence of range type spread f or pbs is very low in southeast asian and south american sectors in contrast the present results indicate that geomagnetic storms triggered the wide longitudinal development of pbs in the american sector this was probably due to the effects of ppefs on both storm days however in the southeast asian sector the pbs on the 2 days probably arose from disturbance dynamo electric field ddef ppef and gravity wave seeding effects this study further shows that under complex storm conditions besides the long duration or multiple penetrations the combined effects of ppefs and ddefs could result in a wide longitude extent of ionospheric irregularities at times

response of large scale ionospheric convection to substorm expansion onsets a case study 1 we have studied the response of large scale ionospheric convection to substorm expansion onsets on the basis of two weak substorms of 1 may 2001 during which a large part of the dawn cell of the two cell ionospheric convection pattern was monitored by the superdarn radars ionospheric convection began to enhance first in a localized region of the equatorward part of the dawn cell 2 minutes before the expansion onsets of both substorms and then enhanced in the entire dawn cell successively the enhanced convection persisted throughout their expansion phase possibly even near the footprint of a plasma sheet region without fast flows observed by geotail these observations suggest that ionospheric convection begins to enhance just before substorm expansion onset and then enhances in the entire cell possibly regardless of the presence of fast earthward flows in the corresponding plasma sheet region of the magnetotail the global enhancement of ionospheric convection is consistent with that of magnetotail convection which also begins just before onset

conjugate hemisphere ionospheric response to the st patrick s day storms of 2013 and 2015 in the 100 e longitude sector the effects of the st patrick s day geomagnetic storms of 2013 and 2015 in the equatorial and low latitude regions of both hemispheres in the 100 e longitude sector is investigated and compared with the response in the indian sector at 77 e the data from a chain of ionosondes and gps global navigation satellite systems receivers at magnetic conjugate locations in the 100 e sector have been used the perturbation in the equatorial zonal electric field due to the prompt penetration of the magnetospheric convective under shielded electric field and the over shielding electric field gives rise to rapid fluctuations in the f2 layer parameters the direction of imf bz and disturbance electric field perturbations in the sunset sunrise period is found to play a crucial role in deciding the extent of prereversal enhancement which in turn affect the irregularity formation equatorial spread f in the equatorial region the northward southward imf bz in the sunset period inhibited supported the irregularity formation in 2015 2013 in the 100 e sector large height increase hmf2 during sunrise produced short duration irregularities during both the storms the westward disturbance electric field on 18 march inhibited the equatorial ionization anomaly causing negative positive storm effect in low latitude equatorial region the negative effect was amplified in low midlatitude by disturbed thermospheric composition which produced severe density total electron content depletion the longitudinal and hemispheric asymmetry of storm response is observed and attributed to electrodynamic and thermospheric differences

nearshore tsunami inundation model validation toward sediment transport applications model predictions from a numerical model delft3d based on the nonlinear shallow water equations are compared with analytical results and laboratory observations from seven tsunami like benchmark experiments and with field observations from the 26 december 2004 indian ocean tsunami the model accurately predicts the magnitude and timing of the measured water levels and flow velocities as well as the magnitude of the maximum inundation distance and run up for both breaking and non breaking waves the shock capturing numerical scheme employed describes well the total decrease in wave height due to breaking but does not reproduce the observed shoaling near the break point the maximum water levels observed onshore near kuala meurisi sumatra following the 26 december 2004 tsunami are well predicted given the uncertainty in the model setup the good agreement between the model predictions and the analytical results and observations demonstrates that the numerical solution and wetting and drying methods employed are appropriate for modeling tsunami inundation for breaking and non breaking long waves extension of the model to include sediment transport may be appropriate for long non breaking tsunami waves using available sediment transport formulations the sediment deposit thickness at kuala meurisi is predicted generally within a factor of 2

estimating daytime vertical exb drift velocities in the equatorial f region using ground based magnetometer observations 1 the daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within 2 latitude of the dip equator a unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal h component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away the difference between these measured h values provides a direct measure of the daytime electrojet current and in turn the magnitude of the vertical exb drift velocity in the f region ionosphere this paper discusses a recent study that has established the quantitative relationship between the vertical exb drift velocity in the ionospheric f region and the daytime strength of the equatorial electrojet in the south american west coast longitude sector

empirical models of storm time equatorial zonal electric fields ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes we describe initially a methodology for the study of storm time dependent ionospheric electric fields we present empirical models of equatorial disturbance zonal electric fields obtained using extensive f region vertical plasma drift measurements from the jicamarca observatory and auroral electrojet indices these models determine the plasma drift perturbations due to the combined effects of short lived prompt penetration and longer lasting disturbance dynamo electric fields we show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the rice convection model for comparable changes in the polar cap potential drop we also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns when the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects the measured and modeled drift velocities are generally in good agreement however our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency and in the high latitude potential and energy deposition patterns which are not accounted for in the model these case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields

overshielding event of 28 29 july 2000 1 on 29 july 2000 image euv observed a shoulder like bulge on the plasmapause goldstein et al 2002 showed that plasmaspheric shoulders may be caused by a pre dawn concentration of eastward overshielding electric e field triggered by a decrease in magnetospheric convection a simulation by the magnetospheric specification model msm captures the shoulder formation reproducing its approximate size and location rocsat 1 ion drift meter data are consistent with the strength time development and local time variation of the msm eastward penetration e field and associated radial flows during the shoulder formation on 28 july

characteristics of penetration electric fields to the equatorial ionosphere during southward and northward imf turnings 1 the signatures of abrupt turnings of the vertical component of the interplanetary magnetic field imf bz can be seen at equatorial latitudes through the prompt transmission of high latitude electric fields to the lower latitudes called as prompt penetration electric field ppe the present work studies the signatures of ppe in daytime equatorial electrojet eej index derived in the indian sector during 2001 2005 the signatures are observed in polar pcn index and equatorial eej index ionosphere almost instantaneously 1 min the communication time of 12 6 min is observed between bow shock nose and the equatorial ionosphere and it is found to have inverse relationship with radial component of solar wind velocity during southward and northward bz turnings which might indicate magnetosphere crossing time scale by solar wind ionospheric reconfiguration time during southward turnings shows inverse relationship with solar wind flow in contrast to northward turnings with no relationship indicating differences in underlying physical mechanisms during both turnings we observe no local time dependence within 06 18 h in conductivity corrected eej signatures associated with bz turnings regression analysis between conductivity corrected eej and interplanetary electric field shows higher efficiency during northward turnings however further analysis investigating the effect of actual orientation of bz indicates that the magnitude of northward bz does not have influence on the ionospheric signatures it is noticed that the response signatures are mainly controlled by the magnitudes of southward bz thus the present study signifies the role of inner magnetospheric shielding electric field in addition to ceasing of convection during northward turnings

implications of the 26 december 2004 sumatra andaman earthquake on tsunami forecast and assessment models for great subduction zone earthquakes results from different tsunami forecasting and hazard assessment mod els are compared with observed tsunami wave heights from the 26 december 2004 indian ocean tsunami forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation an empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 indian ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern e g sri lanka thailand standard forecast models developed from subfault discretization of earthquake rupture in which deep ocean sea level observations are used to constrain slip are also tested forecast models of this type use tsunami time series measurements at points in the deep ocean as a proxy for the 2004 indian ocean tsunami a transect of deep ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the m 9 sumatra andaman earthquake this proxy model performs well in comparison to observed tsunami wave heights travel times and inundation patterns at banda aceh hypothetical tsunami hazard assessments models based on end member estimates for average slip and rupture length m w 9 0 9 3 are compared with tsunami observations using average slip low end member and rupture length high end member m w 9 14 consistent with many seismic geodetic and tsunami inversions adequately estimates tsunami runup in most regions except the extreme runup in the western aceh province the high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models in addition excess moment release 9 deduced from geodetic studies in comparison to seismic moment estimates may gen erate additional tsunami energy if the exponential time constant of slip is less than approximately 1 hr overall there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first order source parameters e g rupture length slip length scaling and spatiotemporal complexity of earthquake rupture

two dimensional observations of overshielding during a magnetic storm by the super dual auroral radar network superdarn hokkaido radar 1 two dimensional observations of ionospheric plasma flows possibly caused by overshielding are reported for the first time the observations were made by the midlatitude super dual auroral radar network hokkaido radar in japan during a major magnetic storm on 15 december 2006 the magnetosphere was exposed continuously to a southward interplanetary magnetic field imf for several hours during the main phase of the storm immediately following the subsequent northward turning of the imf an antisunward plasma flow was observed for about 14 min in the predusk sector at magnetic latitudes of 50 60 reaching a maximum line of sight speed of 70 80 m s these features are consistent with a simulation of coupling between the ring current and the ionosphere associated with an overshielding condition within 1 h of the first observation a similar antisunward flow was observed during a period of southward oriented imf however the simulation cannot account for the antisunward flow in this case it is suggested that the shielding overshielding condition is not simply caused by the northward turning of imf this second overshielding like condition is attributable to a sudden contraction of the polar cap associated with the substorm or to a sudden strengthening of the inertial current converted from the abrupt injection of magnetospheric ions however neither fully accounts for the observations

experimental observations of tsunami induced scour at onshore structures tsunami inundation of the coastal environment can induce scour at structure foundations leading to failure a series of experiments are made using a unique pneumatic long wave generator to generate tsunami wave periods of 25 147 s equating to 3 17 3 min at 1 50 froude scale the waves propagate over a sloping bathymetry and impinge upon a square structure founded onshore in a flat sediment bed flow velocity height and scour depth are recorded as a function of time during tsunami inundation the rate of scour is observed to be time dependent equilibrium which is not attained is argued to be an inappropriate measure for time dependent transient flows such as tsunami in which the flow velocity depth and direction are variable the maximum scour depth is recorded and critically is observed not to be equal to the final depth due to significant sediment slumping when flow velocities reduce in the latter stages of inundation current and wave scour predictor equations over predict the scour while the asce 7 16 method under predicts comparisons with available data in the literature show longer inundation durations increase the amount of scour

shoaling on steep continental slopes relating transmission and reflection coefficients to green s law the propagation of long waves onto a continental shelf is of great interest in tsunami modeling and other applications where understanding the amplification of waves during shoaling is important when the linearized shallow water equations are solved with the continental shelf modeled as a sharp discontinuity the ratio of the amplitudes is given by the transmission coefficient on the other hand when the slope is very broad relative to the wavelength of the incoming wave then amplification is governed by green s law which predicts a larger amplification than the transmission coefficient and a much smaller amplitude reflection than given by the reflection coefficient of a sharp interface we explore the relation between these results and elucidate the behavior in the intermediate case of a very steep continental shelf

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

dayside ionospheric response to the intense interplanetary shocks solar wind discontinuities observations from the digisonde global ionospheric radio observatory 1 the digisonde global ionospheric radio observatory giro has recorded strong ionospheric responses to two powerful interplanetary shock passages on 7 november 7 2004 and 21 january 2005 both events provide excellent opportunities to study geospace response processes to strong interplanetary forward shocks in great detail the angle between the normal of the 7 november 2004 shock front and the sun earth line was 3 0 degrees indicating that the shock hit the equatorial magnetosphere at 1200 lt local noon the subsequent dayside shock induced ionospheric phenomena were found to have marked longitudinal and latitudinal distributions comparative studies of the intense interplanetary shocks including the sheath associated with northward and southward interplanetary magnetic fields imf revealed their different geospace effects on the dayside ionospheric region the equatorial ionosphere responds to the interplanetary shock rather quickly and if the shock is associated with southward imf the plasma electrons in the equatorial ionosphere are rapidly uplifted during the 7 november 2004 event the averaged uplift velocity was close to 67 m s and the ionospheric total electron content tec increased from the original 16 tec units tecu to 38 tecu 1 tecu 1016 m 2 which may be due to the shock effect when the interplanetary shock including the magnetosheath is associated with northward imf the plasma in the equatorial ionosphere moves downward causing a sudden drop in the total electron content during the 21 january 2005 event the averaged downward velocity was 120 m s and the tec dropped from 75 tecu to 22 tecu at the time of maximum solar wind dynamic pressure and then recovered to 68 tecu in about 2 h after the shock passage the middle and high latitude ionospheric tec enhancements may be due to particle ion and electron precipitation ionization losses caused by the strong impacts of the interplanetary shocks

the long duration positive storm effects in the equatorial ionosphere over jicamarca the long duration positive storm lps in the equatorial regions is relatively poorly understood in this report we conducted a statistical analysis of the lps effects in the equatorial ionosphere over jicamarca 12 0 s 283 2 e in 1998 2010 there are 250 geomagnetic storms minimum dst 50 nt in 1998 2010 but the ionosonde observations at jicamarca are available only for 204 storms a total of 46 lpss are identified in terms of the criterion that the storm time relative deviation of peak density of f2 layer nmf2 exceeds 25 for more than 6 h a salient feature is that the occurrence of lpss tends to decay approximately exponentially on the following days after the main phase of geomagnetic storms the ratios of the number of equatorial lpss to that of geomagnetic storms have no obvious dependence on season and solar activity during the daytime lpss the disturbed zonal electric field is mostly westward as indicated from the geomagnetic field changes in the equatorial american region for the nighttime lpss the significant uplifting of f2 layer caused by an eastward electric field is the most important feature therefore the disturbed electric field should play an essential role in forming the equatorial lpss

formation of undular bores and solitary waves in the strait of malacca caused by the 26 december 2004 indian ocean tsunami 1 deformation of the indian ocean tsunami moving into the shallow strait of malacca and formation of undular bores and solitary waves in the strait are simulated in a model study using the fully nonlinear dispersive method fndm and the korteweg devries kdv equation two different versions of the incoming wave are studied where the waveshape is the same but the amplitude is varied full amplitude and half amplitude while moving across three shallow bottom ridges the back face of the leading depression wave steepens until the wave slope reaches a level of 0 0036 0 0038 when short waves form resembling an undular bore for both full and half amplitude the group of short waves has very small amplitude in the beginning behaving like a linear dispersive wave train the front moving with the shallow water speed and the tail moving with the linear group velocity energy transfer from long to short modes is similar for the two input waves indicating the fundamental role of the bottom topography to the formation of short waves the dominant period becomes about 20 s in both cases the train of short waves emerging earlier for the larger input wave than for the smaller one eventually develops into a sequence of rank ordered solitary waves moving faster than the leading depression wave and resembles a fission of the mother wave the kdv equation has limited capacity in resolving dispersion compared to fndm

equatorial electrojet responses to intense solar flares under geomagnetic disturbance time electric fields large enhancement in the equatorial electrojet eej current can occur due to sudden increase in the e layer density arising from solar flare associated ionizing radiations as also from background electric fields modified by magnetospheric disturbances when present before or during a solar flare we investigate the eej responses at widely separated longitudes during two x class flares that occurred at different activity phases surrounding the magnetic super storm sequences of 28 29 october 2003 during the 28 october flare we observed intense reverse electrojet under strong westward electric field in the sunrise sector over jicamarca sources of westward disturbance electric fields driving large eej current are identified for the first time model calculations on the e layer density with and without flare and comparison of the results between jicamarca and sao luis suggested enhanced westward electric field due to the flare occurring close to sunrise over jicamarca during the flare on 29 october which occurred during a rapid ae recovery a strong overshielding electric field of westward polarity over jicamarca delayed an expected eej eastward growth due to flare induced ionization enhancement in the afternoon this eej response yielded a measure of the overshielding decay time determined by the storm time region 2 field aligned current this paper will present a detailed analysis of the eej responses during the two flares including a quantitative evaluation of the flare induced electron density enhancements and identification of electric field sources that played dominant roles in the large westward eej at the sunrise sector over jicamarca

numerical simulation of nonlinear long waves in the presence of discontinuous coastal vegetation abstract we presented numerical simulations of long waves interacting with arrays of emergent cylinders inside regularly spaced patches representing tsunamis interacting with discontinuous patchy coastal vegetation we employed the fully nonlinear and weakly dispersive serre green naghdi equations sgn until the breaking process starts while we changed the governing equations to nonlinear shallow water equations nsw at the vicinity of the breaking wave peak and during the run up stage we modeled the cylinders as physical boundaries rather than approximating them as macro roughness friction our results show that the cylinders provide protection for the areas behind them however they might also cause amplification in local water depth in those areas the presented results are extensively validated against the existing numerical and experimental data our results demonstrate the capability and reliability of our model in simulating wave interaction with emergent cylinders

characterizing the 10 november 2004 storm time middle latitude plasma bubble event in southeast asia using multi instrument observations 1 the development and dynamics of ionospheric plasma bubble pb irregularity during the super storm of 7 11 november 2004 are investigated using the data from a multi instrument network operated in southeast asia analysis of fluctuations in global positioning system total electron content gps tec ionosonde gps scintillation and in situ satellite density data indicates a series of intense pb associated irregularities at equatorial low and middle latitudes in the japanese longitude on 10 november however in the chinese sector the scintillations and pb irregularities are confined within the range of 20 50 n in geographic latitude and 110 125 e in geographic longitude the absence of equatorial pb irregularities in this sector shows a major difference from that in the close by longitude japanese sector in the southern hemisphere australian sector the irregularities occurrence is present as a symmetrical distribution at conjugate latitudes combined analysis of the data from osan and wuhan ionosondes illustrates that the middle latitude spread f irregularities initially develop at the lower part of the f region and then distribute in the whole f region this initiation of spread f at lower altitudes indicates that the middle latitude pb associated irregularities are locally generated these results together with the irregularities occurrence sequence from higher to lower latitudes and the onset time delay of several hours implies that the presence of pb associated irregularities within a latitude range of 20 50 n in the chinese sector cannot be attributed to the effects of prompt penetration electric fields ppefs although the equatorial pbs in the close by longitude are seen to be associated with ppefs the possible mechanism is the f region plasma instabilities triggered by wave structures which act as an external driving force and seed active plasma dynamics and instability growth at middle latitude

a case study of ionospheric storm effects during long lasting southward imf bz driven geomagnetic storm multiple instrumental observations including gps total electron content tec fof2 and hmf2 from ionosondes vertical ion drift measurements from communication navigation outage forecasting system magnetometer data and far ultraviolet airglow measured by thermosphere ionosphere mesosphere energetics and dynamics global ultraviolet imager timed guvi are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14 17 july 2012 geomagnetic storm event which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below 10 nt in the east asian australian sector latitudinal profile of tec variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly eia crest regions which were caused by the combined effects of disturbance dynamo electric fields ddef and equatorward neutral winds in the recovery phase strong inhibition of eia occurred and the summer crest of eia disappeared on 16 july due to the combined effects of intrusion of neutral composition disturbance zone as shown by the timed guvi o n2 measurements and long lasting daytime westward ddef inferred from the equatorial electrojet observations the transit time of ddef over the dip equator from westward to eastward is around 2200 lt in the american longitude the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase preceded by storm enhanced density plume in the initial phase in addition multiple short lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field imf bz in the recovery phase and were responsible for enhanced the eia and equatorial ionospheric uplift around sunset

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

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

debris flow generated tsunamis and their dependence on debris flow dynamics abstract debris flow generated tsunamis can be extremely dangerous for lakeside settlements and infrastructure debris flow composition strongly affects debris flow thickness and velocity and therefore also the generated tsunami this interaction is however poorly understood we investigate the effects of debris flow volume composition gravel sand clay water and subaerial outflow slope on wave celerity and amplitude in a small scale physical model consisting of an inclined outflow channel which transits into a three dimensional water reservoir we find that upon debouching a debris flow pushes the water forward until wave celerity exceeds subaqueous debris flow velocity i e froude number wave celerity has the strongest relation with debris flow velocity debris flow velocity increases with increasing water and clay content up to 22 which both lubricate the flow far field leading wave amplitude has the strongest relation with debris flow momentum velocity times effective mass which is mostly a function of debris flow thickness water and clay content we test the applicability of published semi empirical equations for predicting tsunami amplitude generated by dry landslides and show that they are to some extent also applicable to debris flow potential scale effects especially considering the smallest waves and water depths could influence the applicability of these predictors and translation of the results to the field scale our results demonstrate the importance of debris flow composition on tsunami generation and evolution and thus the necessity of including flow composition in predictive simulation models

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

a review of volcanic island evolution and magma production rate an example from a cenozoic island arc in the caribbean different stages of volcanic island evolution are evident in the cenozoic lesser antilles arc developed near the eastern edge of the caribbean plate the early stage of seamount evolution is represented by the kick em jenny submarine volcano near the southern end of the arc the volcanically active islands known as the volcanic caribbees are composed of a series of composite volcanoes and are examples of an emergent volcanic island stage those islands that were formerly active known as the limestone caribbees provide evidence that an erosional to submergent stage occurred in the northern part of the island arc during the oligocene and miocene epochs growth of the islands and underlying crust is dependent upon the magma production rate along the arc which has for the last 100 ka ranged from less than 1 km 3 to 40 km 3 these differences in magma production and volcanic rock composition along the arc are attributed to the obliquity of plate convergence and the plate convergence rates

wave characteristic and morphologic effects on the onshore hydrodynamic response of tsunamis abstract while the destruction caused by a tsunami can vary significantly owing to near and onshore controls we have only a limited quantitative understanding of how different local parameters influence the onshore response of tsunamis here a numerical model based on the non linear shallow water equations is first shown to agree well with analytical expressions developed for periodic long waves inundating over planar slopes more than 13 000 simulations are then conducted to examine the effects variations in the wave characteristics bed slopes and bottom roughness have on maximum tsunami run up and water velocity at the still water shoreline while deviations from periodic waves and planar slopes affect the onshore dynamics the details of these effects depend on a combination of factors in general the effects differ for breaking and non breaking waves and are related to the relative shift of the waves along the breaking non breaking wave continuum variations that shift waves toward increased breaking such as steeper wave fronts tend to increase the onshore impact of non breaking waves but decrease the impact of already breaking waves the onshore impact of a tsunami composed of multiple waves can be different from that of a single wave tsunami with the largest difference occurring on long shallow onshore topographies these results demonstrate that the onshore response of a tsunami is complex and that using analytical expressions derived from simplified conditions may not always be appropriate

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

effects of disturbed electric fields in the low latitude and equatorial ionosphere during the 2015 st patrick s day storm the 2015 st patrick s day geomagnetic storm with sym h value of 233 nt is an extreme space weather event in the current 24th solar cycle in this work we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the asian australian sector and the american sector during this super storm event the results reveal that the disturbed electric fields which comprise penetration electric fields pefs and disturbance dynamo electric fields ddefs play a decisive role in the ionospheric storm effects in low latitude and equatorial regions pefs occur on march 17 in both the american sector and the asian australian sector the effects of ddefs are also remarkable in the two longitudinal sectors both the ddefs and pefs show the notable local time dependence which causes the sector differences in the characteristics of the disturbed electric fields this differences would further lead to the sector differences in the low latitude ionospheric response during this storm the negative storm effects caused by the long duration ddefs are intense over the asian australian sector while the repeated elevations of hmf2 and the eia intensifications caused by the multiple strong pefs are more distinctive over the american sector especially the storm time f3 layer features are caught on march 17 in the american equatorial region proving the effects of the multiple strong eastward pefs

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

tsunami run up and draw down on a plane beach tsunami run up and draw down motions on a uniformly sloping beach are evaluated based on fully nonlinear shallow water wave theory the nonlinear equations of mass conservation and linear momentum are first transformed to a single linear hyperbolic equation to solve the problem with arbitrary initial conditions we apply the fourier bessel transform and inversion of the transform leads to the green function representation the solutions in the physical time and space domains are then obtained by numerical integration with this semi analytic solution technique several examples of tsunami run up and draw down motions are presented in particular detailed shoreline motion velocity field and inundation depth on the shore are closely examined it was found that the maximum flow velocity occurs at the moving shoreline and the maximum momentum flux occurs in the vicinity of the extreme draw down location the direction of both the maximum flow velocity and the maximum momentum flux depend on the initial waveform it is in the inshore direction when the initial waveform is predominantly depression and in the offshore direction when the initial waves have a dominant elevation characteristic

tsunami source of the 2004 sumatra andaman earthquake inferred from tide gauge and satellite data tsunami source of the 2004 sumatra andaman earthquake was esti mated from a joint inversion of tsunami waveforms recorded on tide gauges and sea surface heights captured by satellite altimetry measurements the earthquake the largest in the past 40 years caused devastating tsunami damage to countries around the indian ocean but the tsunami source in particular its northern end was not well resolved although aftershocks and crustal deformation extended from off north western sumatra island through the nicobar islands to the andaman islands some seismic wave analyses indicated a shorter source length several hundred kilometers we used tsunami waveforms recorded at 12 tide gauge stations around the source and the sea surface heights measured by three satellites jason1 topex poseidon and envisat we numerically computed tsunami propagation using realistic bathym etry more than 66 000 depth points were digitized from nautical charts and combined with the etopo2 data inversion of satellite data indicates that the tsunami source extended to the andaman islands with a total length of 1 400 km but such a model produces much larger tsunami waveforms than observed at indian tide gauge stations inversion of tide gauge records and the joint inversion indicate that the tsunami source was about 900 km long the largest slip about 13 to 25 m was located off sumatra island and the second largest slip up to 7 m near the nicobar islands the slip distribution is similar for different rupture velocities and rise times with a slow velocity of 1 km sec and a rise time of 3 min yielding the largest variance reduction

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

cross shore sediment transport under breaking solitary waves 1 laboratory experiments were performed to examine the cross shore sediment transport processes under breaking solitary waves on a fine sand beach the initial beach slope of 1 12 was exposed to a positive solitary wave eight times the beach was rebuilt and exposed to a negative solitary wave eight times the wave motion and sediment transport were not affected much by the beach profile change from the initial profile the positive solitary wave plunged violently near the shoreline and suspended a considerable volume of sand the plunging wave with no seaward flow impeding its run up caused large run up on the foreshore the strong downrush following the large run up resulted in erosion on the foreshore and deposition seaward of wave run down on the other hand the negative solitary wave collapsed against the seaward flow induced by the free surface slope of the negative wave and caused less sediment suspension the wave run up against the seaward flow was much smaller the weak downrush following the small run up resulted in deposition on the foreshore and erosion near the wave collapsing point these limited laboratory experiments indicate the importance of the initial wave profile for swash sediment dynamics and the capacity of a single wave in causing noticeable beach profile changes

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

propagation and amplification of tsunamis at coastal boundaries when tsunamis hit a coastal area they often cause substantial damage and loss of life at locations otherwise well protected from normal even severe wind generated waves an example of such a catastrophe took place on 12 december 1992 when an earthquake of magnitude ms 7 5 occurred in the eastern region of flores island indonesia1 2 one of the areas hardest hit by the resulting tsunamis was babi a small coastal island two villages on the island were completely destroyed even though both were located in sheltered areas where wave conditions are normally calm here we describe the results of numerical and laboratory experiments that show how unlike wind generated waves tsunamis are capable of penetrating into sheltered coastal areas without significantly losing their energy for the case of babi island the original tsunami wave was split into two with one wave propagating around each side of the island the two waves met in the sheltered region and the subsequent amplification of wave amplitude resulted in the destructive flow onto the beach

an idealized model for tsunami study 1 an idealized mathematical model of tsunami evolution in deep sea and across the continental shelf is proposed the initial value problem in deep sea is related to the well known cauchy poisson problem and the tsunami propagation across the continental shelf is derived using the linearized shallow water equations when analyzing different cases of tsunamis in deep sea it was found that tsunamis evolve into two basic wave types one resembles a single wave and the other a wave packet the analysis of different cases of tsunamis at the shoreline reveals that the continental shelf due to its geometrical properties serves as a tsunami amplifier producing tsunami amplitudes up to 20 times larger than those at the edge of the continental shelf a comparison with tsunami measurements suggests that the idealized model may be used for a reliable assessment of the principle hydrodynamic properties of the tsunami such as the tsunami amplitude and its half period

westward ionospheric electric field perturbations on the dayside associated with substorm processes 1 a controversy has risen in the direction of ionospheric electric field perturbation on the dayside caused by substorm expansion phase in recent years i e eastward or westward to exclude the effect of interplanetary magnetic field northward turning the substorms without interplanetary field imf trigger are required to investigate this issue previous works such as that by huang et al 2004 showed that the eastward electric field perturbations caused by substorms can be observed however our case suggests that some substorms can produce strong westward electric field perturbations and drive westward equatorial electrojets on the dayside ionosphere this westward electric field is created by an overshielding like imbalance state of field aligned currents facs region 2 r2 fac greater than region 1 r1 fac which is built up through r2 fac enhancement rather than r1 fac reduction due to imf northward turning the substorm processes should be responsible for the westward electric field especially through polar cap shrinkage and magnetic field dipolarization

laboratory experiments of tsunami runup on a circular island laboratory experiments of a 7 2 m diameter conical island were conducted to study three dimensional tsunami runup the 62 5 cm tall island had 1 on 4 side slopes and was positioned in the center of a 30 m wide by 25 m long flat bottom basin solitary waves with height to depth ratios ranging from 0 05 to 0 20 and source lengths ranging from 0 30 to 7 14 island diameters were tested in water depths of 32 and 42 cm twenty seven capacitance wave gages were used to measure surface wave elevations at incident and four radial transects on the island slope maximum vertical runup measurements were made at 20 locations around the perimeter of the island using rod and transit a new runup gage was located on the back or lee side of the island to record runup time series

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

the 26 december 2004 sumatra tsunami analysis of tide gauge data from the world ocean part 1 indian ocean and south africa the m w 9 3 megathrust earthquake of december 26 2004 off the northwest coast of sumatra in the indian ocean generated a catastrophic tsunami that was recorded by a large number of tide gauges throughout the world ocean part 1 of our study of this event examines tide gauge measurements from the indian ocean region at sites located from a few hundred to several thousand kilometers from the source area statistical characteristics of the tsunami waves including wave height duration and arrival time are determined along with spectral properties of the tsunami records

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

quiet zone within a seismic gap near western nicaragua possible location of a future large earthquake a 5700 square kilometer quiet zone occurs in the midst of the locations of more than 4000 earthquakes off the pacific coast of nicaragua the region is indicated by the seismic gap technique to be a likely location for an earthquake of magnitude larger than 7 the quiet zone has existed since at least 1950 the last large earthquake originating from this area occurred in 1898 and was of magnitude 7 5 a rough estimate indicates that the magnitude of an earthquake rupturing the entire quiet zone could be as large as that of the 1898 event it is not yet possible to forecast a time frame for the occurrence of such an earthquake in the quiet zone

recovering water wave elevation from pressure measurements the reconstruction of water wave elevation from bottom pressure measurements is an important issue for coastal applications but corresponds to a difficult mathematical problem in this paper we present the derivation of a method which allows the elevation reconstruction of water waves in intermediate and shallow waters from comparisons with numerical euler solutions and wave tank experiments we show that our nonlinear method provides much better results for the surface elevation reconstruction compared to the linear transfer function approach commonly used in coastal applications more specifically our method accurately reproduces the peaked and skewed shape of nonlinear wave fields therefore it is particularly relevant for applications on extreme waves and wave induced sediment transport

an experimental study of wave run up at a steep beach this paper presents experiments on run up of strongly nonlinear waves on a beach of 10 54 inclination velocity fields are obtained by the piv particle image velocimetry technique acceleration measurements are also attempted but it is difficult to obtain useful results in every case in addition free surface profiles are extracted from digital images and wave resistance probes the investigation focuses on the dynamics of the early stages of the run up when steep fronts evolve in the vicinity of the equilibrium shoreline but maximum run up heights are also reported measurements on moderately nonlinear waves are compared to results from long wave theories including a numerical boussinesq model and analytic shallow water results from the literature in particular the applicability of the long wave theories is addressed however most attention is given to run up of high incident solitary waves that are on the brink of breaking at the shoreline in one case a temporarily slightly overturning wave front is found that neither develops into a plunger or displays appreciable spilling this feature is discussed in view of measured velocity and acceleration patterns and with reference to the dam break problem effects of scaling as well as viscous damping are also briefly discussed

monte carlo slip inversion in the frequency domain application to the 1992 nicaragua slow earthquake the spatio temporal complexity of moment release of the 1992 nicaragua slow earthquake mw 7 7 is estimated by simulated annealing contrary to linearized inversions monte carlo techniques do not make assumptions about a priori features of the model in particular large variations in rupture velocities can be imaged relative spectra between the main shock and an empirical green s function were obtained from 4 44 mhz using first and second orbit fundamental mode rayleigh waves the spectra were inverted for the moment distribution on a 2d horizontal fault under the physical constraints of slip positivity and causality the non linear inversion revealed two main regions of slip one centered 20 km to the nw of the epicenter the other 160 km to the se but delayed by 70 s rupture velocities in the slipping patches were found to be low around 1 km s large amount of slip occurred trench ward of the epicenter accounting for the large tsunami excitation analysis of the slip distribution suggests that the slow and smooth nature of the 1992 nicaragua event may be related to the frictional properties at the plate interface

flow and sediment transport induced by a plunging solitary wave 1 two parallel experiments involving the evolution and runup of plunging solitary waves on a sloping bed were conducted 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures and for observation of the morphological changes the two experimental conditions were kept as similar as possible the experiments showed that the complete sequence of the plunging solitary wave involves the following processes shoaling and wave breaking runup rundown and hydraulic jump and trailing wave the bed shear stress measurements showed that the mean bed shear stress increases tremendously with respect to that in the approaching wave boundary layer by as much as a factor of 8 in the runup and rundown stages and that the rms value of the fluctuating component of the bed shear stress is also affected by as much as a factor of 2 in the runup and hydraulic jump stages the pore water pressure measurements showed that the sediment at or near the surface of the bed experiences upward directed pressure gradient forces during the down rush phase the magnitude of this force can reach values as much as approximately 30 of the submerged weight of the sediment the experiments further showed that the sediment transport occurs in the sheet flow regime for a substantial portion of the beach covering the area where the entire sequence of the wave breaking takes place the bed morphology is explained qualitatively in terms of the measured bed shear stress and the pressure gradient forces

the transition to overshielding after sharp and gradual interplanetary magnetic field northward turning overshielding is referred to a shielding status during which the dawnward shielding electric field dominates over the duskward penetration electric field in the inner magnetosphere typically appearing when the interplanetary magnetic field imf suddenly turns northward after a prolonged southward orientation it is expected that the transition to overshielding after imf northward turning can be affected by the shape of northward turning sharp or gradual moreover the initial shielding status undershielding or goodshielding prior to the transition may also have influence on the transition here we analyze two groups of cases in which the transitions appear after sharp duration less than 5 min and gradual duration more than 30 min northward turning each group includes two cases in which the transition initiated from undershielding and goodshielding these cases show that 1 the beginning of the transition to overshielding coincides with sharp imf northward turning but appears in the midst of gradual imf northward turning 2 the transition from goodshielding to overshielding is always associated with convection electric field drop and or polar cap shrinkage regardless of the shape of imf northward turning and 3 the typical solar wind condition in which the imf suddenly turns northward after a prolonged southward orientation is neither a necessary condition nor a sufficient condition for overshielding furthermore we will discuss the effect of substorm processes on overshielding

eastward electric field enhancement and geomagnetic positive bay in the dayside low latitude ionosphere caused by magnetospheric substorms during sawtooth events 1 substorms cause significant disturbances in the magnetosphere and ionosphere although many substorm induced phenomena have been relatively well understood a serious controversy arises as to how the magnetospheric and ionospheric convection responds to the expansion onset in this paper we present the observations of the low latitude ionospheric electric field and geomagnetic field at substorm onsets during sawtooth events when the interplanetary magnetic field imf remains steady southward so the ionospheric disturbances are attributed solely to the substorm effects in the substorm events we have analyzed the dayside equatorial ionospheric electric field shows an eastward enhancement at the onset and the geomagnetic field northward component at middle and low latitudes shows an increase positive bay on both the dayside and nightside we suggest that the magnetospheric convection is enhanced at substorm onset and that the enhanced magnetospheric convection electric field penetrates to the low latitude ionosphere the penetration electric field driven by substorm onset causes the eastward ionospheric electric field enhancement and geomagnetic positive bay on the dayside and the substorm current wedge causes the geomagnetic positive bay on the nightside our findings are significantly different from the results of most previous studies and provide new insight into the substorm dynamic process