climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

disturbance zonal and vertical plasma drifts in the peruvian sector during solar minimum phases in the present work we investigate the behavior of the equatorial f region zonal plasma drifts over the peruvian region under magnetically disturbed conditions during two solar minimum epochs one of them being the recent prolonged solar activity minimum the study utilizes the vertical and zonal components of the plasma drifts measured by the jicamarca 11 95 s 76 87 w incoherent scatter radar during two events that occurred on 10 april 1997 and 24 june 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the sheffield university plasmasphere ionosphere model inpe two main points are focused 1 the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and 2 anomalous behavior of daytime zonal drift in the absence of any magnetic storm a perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm for the first time based on a realistic low latitude ionosphere we will show on a detailed quantitative basis that this anticorrelation is driven mainly by a vertical hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime e region ionization it is shown that an increase in the field line integrated hall to pedersen conductivity ratio h p which can arise from precipitation of energetic particles in the region of the south american magnetic anomaly is capable of explaining the observed anticorrelation between the vertical and zonal plasma drifts evidence for the particle ionization is provided from the occurrence of anomalous sporadic e layers over the low latitude station cachoeira paulista 22 67 s 44 9 w brazil it will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind system during the prolonged solar minimum period

a numerical study of nighttime ionospheric variations in the american sector during 28 29 october 2003 variations of nighttime f2 peak height hmf2 over the american sector during the 28 29 october 2003 storm period were investigated using the national center for atmospheric research thermosphere ionosphere electrodynamics global circulation model the model was generally able to reproduce the ionospheric variations on 28 29 october 2003 observed by the ionosondes a series of controlled model simulations were subsequently undertaken to examine the effects of electric fields and neutral winds on the ionosphere the numerical experiments suggest that the dramatic nighttime increase of hmf2 on the storm day 29 october is mainly caused by traveling atmospheric disturbances tads from the high latitudes of the northern hemisphere however the electric field plays an important role in causing the elevation of hmf2 in the equatorial region the prompt penetration electric field ppef associated with the southward component of the interplanetary magnetic field bz is westward on the nightside whereas when bz reverses and becomes northward the ppef is westward in the premidnight and turns to eastward in the postmidnight these ppefs greatly affect the low latitude ionosphere during storm time on 28 october even though the bz disturbance was weak with a short duration of southward bz the tads from the southern hemisphere can propagate to the northern hemisphere and result in the corresponding oscillations in the nightside hmf2

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

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

equatorial and low latitude ionosphere thermosphere system response to the space weather event of august 2005 1 the response of the equatorial and low latitude ionosphere thermosphere system to the geomagnetic storm during 23 26 august 2005 is investigated the study is carried out using the vertical total electron content vtec measured by gps receivers along the 77 78 e longitude and the o n2 ratio obtained from the global ultraviolet imager instrument on board the timed satellite the equatorial ionization anomaly eia shows a poleward latitudinal expansion on 24 august probably associated with an eastward prompt penetration electric field the equatorial and low latitudes show an increase in vtec during the main phase of the storm on 24 august the prompt penetration eastward electric field along with an increase in the o n2 ratio could be responsible for this observed positive phase the vtec variations on 24 august also reveal the signature of a large scale acoustic gravity wave traveling atmospheric disturbance propagating with a horizontal velocity of 750 m s suppression of the eia is observed during the storm recovery phase on 25 august which probably is associated with the westward disturbance dynamo electric field and the equatorward expansion of the neutral composition changes o n2 depletion

changing climate states and stability from pliocene to present we present a recently developed method of potential analysis of time series data which comprises 1 derivation of the number of distinct global states of a system from time series data and 2 derivation of the potential coefficients describing the location and stability of these states using the unscented kalman filter ukf we test the method on artificial data and then apply it to climate records spanning progressively shorter time periods from 5 3 myr ago to the recent observational record we detect various changes in the number and stability of states in the climate system the onset of northern hemisphere glaciation roughly 3 myr bp is detected as the appearance of a second climate state during the last ice age in greenland there is a bifurcation representing the loss of stability of the warm interstadial state followed by the total loss of this state around 25 kyr bp the holocene is generally characterized by a single stable climate state especially at large scales however in the historical record at the regional scale the european monthly temperature anomaly temporarily exhibits a second highly degenerate unstable state during the latter half of the eighteenth century at the global scale temperature is currently undergoing a forced movement of a single stable state rather than a bifurcation the method can be applied to a wide range of geophysical systems with time series of sufficient length and temporal resolution to look for bifurcations and their precursors

sami3 rcm simulation of the 17 march 2015 geomagnetic storm we present a self consistent modeling study of the ionosphere plasmasphere system response to the 17 march 2015 geomagnetic storm using the coupled sami3 rcm code the novel feature of this work is that we capture the important storm time dynamics of the ionosphere on a global scale and its manifestation in the plasmasphere we find that the penetration electric fields associated with the magnetic storm lead to a storm time enhanced density in the low to middle latitude ionosphere we compare the modeled total electron content tec with gps measured tec in the american sector additionally we observe the development of polar cap tongues of ionization and the formation of subauroral plasma streams in the postsunset premidnight sector and its impact on the plasmasphere however we did not see the development of plasmaspheric plumes during this event which we attribute to the long main phase of the storm 18 h

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

disturbance dynamo effects over low latitude f region a study by network of vhf spaced receivers generation of equatorial spread f esf irregularities resulting from magnetic disturbance is known for past few decades however better prediction models for this phenomenon are still lacking magnetic storms also affects the f region plasma drifts in this work we examined variability in i occurrence of such freshly generated esf and ii low latitude f region zonal plasma drifts over indian longitude for this purpose simultaneous observations of amplitude scintillations on 251 mhz signal recorded by a network of spaced receivers located at low latitude stations are utilized observational stations are situated such that it longitudinally latitudinally covers an area of 5 6 13 here effect of disturbance dynamo dd electric field at low latitude f region and its variability are studied for three magnetic storms occurring in 2011 these magnetic storms are having nearly similar type characteristics except their start time we find that as time difference i e t between local sunset and start of magnetic activity decreases the dd effects seen at low latitude f region zonal irregularity drift around midnight becomes stronger for a given magnetic storm the dd effect on f region zonal irregularity drifts is found to be only marginally stronger at dip equator in comparison to off equatorial stations although effect of dd on f region zonal irregularity drifts are felt simultaneously generation of fresh esf is variable within a smaller longitudinal belt of 5 6 it is attributed to the presence of lsws at the bottomside of f region as initiation of esf is highly likely unlikely in the vicinity of crest trough of such lsws

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

multifractal detrended fluctuation analysis of the δ 18 o record of ngrip ice core the multifractal properties and scaling behaviors of the long term and recent 2000 year 18o records of ngrip ice core are investigated by the multifractal detrended fluctuation analysis method the generalized hurst exponents multifractal scaling exponents and singularity spectrums of two 18o records are derived to verify the multifractiality of two records and the multifractal behaviors of two records are obviously different which may reflect the climate change of the recent 2000 year time is quite different from one of the long term time in addition the probability distribution analysis of two 18o records is presented to manifest the different multifractality between two 18o records of ngrip ice core our results will be helpful to research the climate change

characterization of millennial scale climate variability the oxygen isotope time series from ice cores in central greenland the greenland ice sheet project 2 gisp2 and the greenland ice core project grip and west antarctica byrd provide a basis for evaluating the behavior of the climate system on millennial time scales these time series have been invoked as evidence for mechanisms such as an interhemispheric climate seesaw or a stochastic resonance process statistical analyses are used to evaluate the extent to which these mechanisms characterize the observed time series simple models in which the antarctic record reflects the greenland record or its integral are statistically superior to a model in which the two time series are unrelated however these statistics depend primarily on the large events in the earlier parts of the record between 80 and 50 kyr bp for the shorter millennial scale dansgaard oeschger events between 50 and 20 kyr bp a first order autoregressive ar 1 stochastic climate model with a physical time scale of t 5 600 6 300 yr is a self consistent explanation for the antarctic record for greenland ar 1 with t 5 400 6 200 yr plus a simple threshold rule provides a statistically comparable characterization to stochastic resonance though it cannot account for the strong 1500 yr spectral peak the similarity of the physical time scales underlying the millennial scale variability provides sufficient explanation for the similar appearance of the greenland and antarctic records during the 50 20 kyr bp interval however it cannot be ruled out that improved cross dating for these records may strengthen the case for an interhemispheric linkage on these shorter time scales additionally the characteristic time scales for the records are significantly shorter during the most recent 10 kyr overall these results suggest that millennial scale variability is determined largely by regional processes that change significantly between glacial and interglacial climate regimes with little influence between the southern and northern hemispheres except during those largest events that involve major reorganizations of the ocean thermohaline circulation

simulation of low latitude ionospheric response to 2015 st patrick s day super geomagnetic storm using ionosonde derived pre vertical drifts over indian region

ionospheric responses to the october 2003 superstorm longitude local time effects over equatorial low and middle latitudes 1 ionospheric responses to the major magnetic storm disturbances of october 2003 are investigated using database selected in the brazilian and japanese asian longitude sectors data obtained from latitudinally spaced digisondes in the equatorial and low latitude sites in brazil and from the asian and japanese ionosonde network the total electron content data from the extensive japanese gps receiver chain and magnetometer data from the pacific equatorial electrojet stations are analyzed during the period 28 31 october prompt penetrating pp dawn dusk polar cap electric fields produce large f region plasma uplift on the dayside and eveningside while the associated westward electric field on the nightside produces large downdraft of the f region plasma and causes development of westward electrojet current observed for the first time episodes of pp electric field effects appear to be of larger intensity over brazil than over asian longitudes equatorial anomaly development due to undershielding as well as overshielding electric fields was observed in the brazilian and in the asian sectors disturbance dynamo electric field causes large nighttime f layer uplifts that are modulated by strong meridional winds in both sectors the disturbance electric field local time variation patterns are compared with the results of recent global model mtiegcm simulation by richmond et al 2003 and validated in some cases transients of transequatorial winds flipping direction from southward to northward in the widely separated longitude sectors were diagnosed to be present toward the final recovery phase of the storm these results are presented and discussed in this paper

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

effects of interplanetary electric field on the development of an equatorial spread f event 1 on a geomagnetically disturbed night 7 january 2005 an equatorial spread f esf event was captured during premidnight hours by the indian mst radar operated in ionospheric mode at gadanki 13 5 n 79 2 e dip angle 12 5 n the base height of the ionospheric f region over dip equator and a low latitude station showed similar variation during most of the esf interval except mainly during 2145 2200 ist indian standard time ist universal time ut 5 5 hours the zonal electric field variation over dip equator responded to a prompt penetration event at 2000 ist by gradually changing its polarity from westward to eastward after 2015 ist leading to the initiation of esf at 2035 ist the linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the prompt penetration effect is taken into account the zonal electric field became westward again after 2100 ist however it ephemerally turned eastward shortly after 2145 ist 1615 ut that is believed to be associated with an overshielding condition a plasma plume got resurrected after 30 min indicating the association of the development of this plume structure with the overshielding electric field the oi 630 0 nm airglow intensity variations observed by a collocated airglow photometer simultaneously operated in a bidirectional zenith and east mode corroborated well with the esf structure and dynamics during the disturbed period these observations evince the active role of interplanetary electric field ief in the development of esf in the premidnight hours

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

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

the storm time evolution of the ionospheric disturbance plasma drifts in this paper we use the c nofs and rocsat 1 satellites observations to analyze the storm time evolution of the disturbance plasma drifts in a 24 hour local time scale during three magnetic storms driven by long lasting southward imf bz the disturbance plasma drifts during the three storms present some common features in the periods dominated by the disturbance dynamo the newly formed disturbance plasma drifts are upward and westward at night and downward and eastward during daytime further the disturbance plasma drifts are gradually evolved to present significant local time shifts the westward disturbance plasma drifts gradually migrate from nightside to dayside meanwhile the dayside downward disturbance plasma drifts become enhanced and shift to later local time the local time shifts in disturbance plasma drifts are suggested to be mainly attributed to the evolution of the disturbance winds the strong disturbance winds arisen around midnight can constantly corotate to later local time at dayside the westward and equatorward disturbance winds can drive the f region dynamo to produce the poleward and westward polarization electric fields or the westward and downward disturbance drifts the present results indicate that the disturbance winds corotated to later local time can affect the local time features of the disturbance dynamo electric field

flood hydrology of the peace athabasca delta northern canada this study conducted a systematic examination of the flood hydrology of the peace athabasca delta pad a complex and internationally important freshwater ecosystem located in northwestern canada three distinct zones of floodwater origin within the pad were discerned on the basis of the dominant hydrology and the topography represented by a digital elevation model dem 1 perimeter peace delta 2 perimeter athabasca delta and 3 central delta lakes analysis of the satellite image and dem derived flood maps of historically significant events combined with field data of open water and ice influenced flood stages revealed that ice jamming was the most effective and likely the only mechanism capable of recharging the highly elevated perimeter areas in the athabasca and peace deltas this supports the conclusion of previous studies that used hydrometric data external to the delta to infer inter delta flood conditions by contrast even the record open water flow to the peace delta could not generate overbank flow hydraulic simulation of the naturalized system no dam no weirs suggests that overbanking of the lower peace river would have been a rare occurrence without the effects of regulation both ice jam induced and open water high waters were found to recharge perched basins in the athabasca delta enlargement of the central delta lakes beyond the shoreline was determined to be an effective flood mechanism for filling low to mid elevation wetlands comparison of the observed and naturalized lake levels indicates that flow regulation of the peace river and addition of the weirs on delta outflow channels has depending on the year led to an increase or a reduction in the annual maximum potential of inland flooding via lake expansion copyright 2006 crown in the right of canada published by john wiley sons ltd

ionogram recorded equatorial spread f and height changes at huancayo during sunspot maximum years the analyses presented here consider equatorial nighttime disturbance conditions as indicated by spread f traces on ionograms which record the presence of medium scale structures msss created by the passage of atmospheric gravity waves relationships between these msss and geomagnetic activity ga have been examined statistically particularly considering the ionospheric height h f changes increases and decreases associated with the presence or absence of these msss it is shown that for the postsunset height increases with spread f present the ga a few hours earlier has well defined low levels in contrast if these height increases are not accompanied by spread f the ga a few hours earlier is high when there are no height rises similar inverse associations with ga are recorded for both 1 spread f present and 2 spread f absent for the postsunset height decreases when no spread f occurs high ga levels are well defined at times about 7 h earlier thus all these results indicate an inverse relationship between the msss and ga the experimental evidence suggests that the presunrise height rises are produced by large scale traveling ionospheric disturbances generated in auroral zone regions by substorm onsets

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

local time dependent response of postsunset esf during geomagnetic storms 1 development or inhibition of esf during magnetically active periods has been an important space weather topic of interest during the recent past in view of its applications in the satellite based navigational systems particularly the postsunset period exhibits significant variability for storm time development of esf versus longitude in this paper we report the results of a multi instrumental ground based and space borne and multistation study on the development inhibition of postsunset esf during five moderate to intense geomagnetic storms occurred during the low and descending phase of the solar activity period 2004 2006 it has been observed that the prompt penetration of eastward electric fields into low latitudes and subsequent development of esf occurred in all longitudinal sectors where the local time corresponds to postsunset hours during the entire main phase of the storm in this paper we show the development of plasma bubble irregularities over a wide longitudinal extent of 92 owing to the dusk time penetration of eastward electric fields into low latitudes either the sudden increase in ae index and or a marked decrease in sym h index may be used as proxies to determine the occurrence as well as the time of penetration of electric fields into equatorial and low latitudes however in such cases where the ae index does not represent any sudden increase the dsymh dt seems to be the better index to determine the time of penetration in this paper is also presented an interesting case where the prompt penetration eastward electric fields dominated the existing strong westward electric fields and subsequently caused the onset of spread f and scintillations at both vhf 244 mhz as well as l band 1 5 ghz frequencies

nonlinearity and multifractality of climate change in the past 420 000 years 1 evidence of past climate variations are stored in polar ice caps and indicate glacial interglacial cycles of 100 kyr using advanced scaling techniques we study the long range correlation properties of temperature proxy records of four ice cores from antarctica and greenland these series are long range correlated in the time scales of 1 100 kyr we show that these time series are nonlinear for time scales of 1 100 kyr as expressed by temporal long range correlations of magnitudes of temperature increments and by a broad multifractal spectrum our results suggest that temperature increments appear in clusters of big and small increments a big positive or negative climate change is most likely followed by a big positive or negative climate change and a small climate change is most likely followed by a small climate change

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

comparison of penetration electric fields created by the solar wind with jicamarca data using swage 1 swage solar wind acting on the geophysical environment calculates the global ionospheric electric field generated by high latitude electrodynamics drivers determined from the time shifted solar wind data measured at l1 by joining the hill siscoe polar cap potential model with the n c ionospheric potential solver of particular interest are the conditions under which the eastward equatorial penetration electric field near twilight contributes to the pre reversal enhancement pre in the present model it is found that a steeper terminator conductance gradient leads to a more pronounced pre the model is statistically consistent with the jicamarca vertical drift data at twilight during quiet times for eighty two days in the years 1998 2005 the model is also consistent with the jicamarca vertical drift data during the november 2004 magnetic superstorms dst 250 nt and highlights the importance of including the lt dependence of the ionospheric response in this comparison disturbance dynamo dd effects are also included comparison is much better using the conductance model with a shallower terminator gradient and indicates that the conductance lt profile was relatively unchanged throughout the storms

early morning irregularities detected with spaceborne gps measurements in the topside ionosphere a multisatellite case study we present observations of the equatorial plasma bubbles epb in the topside ionosphere at early morning hours 05 08 lt in the recovery phase of the 18 19 february 2014 geomagnetic storm this rare type of irregularities was detected in the pacific sector using gps measurements on board several low earth orbit leo satellites we use a multisatellite constellation consisted of the three swarm and one terrasar x satellites that on 19 february flew in the same region and at similar altitudes 500 km the epb occurrence in the leo gps data was observed for several consecutive orbits from 11 ut to 16 17 ut on 19 february 2014 which suggests the following 1 rather long duration hours of favorable conditions for epb generation 2 formation and evolution of epb over wide longitude range of the pacific ocean and 3 possible movement of the epb region in the westward direction with dawn registration of the early morning epb in leo gps data was supported by concurrent in situ swarm and dmsp defense meteorological satellite program and ground based ionosonde and gps measurements leo based gps technique is found to be essential and promising data source to study the topside epb over regions with lack of the ground based facilities in addition we use the prompt penetration model and the thermosphere ionosphere electrodynamics global circulation model tie gcm to identify the possible mechanisms responsible for the observed phenomenon the model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift 40 45 m s owing to the disturbance dynamo action in the predawn dawn sector during 09 17 ut

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

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

measuring multifractality in seismic sequences abstract we investigated the multifractal structure of the interevent times between successive earthquakes that occurred in umbria marche which is one of the most seismically active areas of central italy we used the multifractal detrended fluctuation analysis mf dfa which permits detection of multifractality in nonstationary series analyzing the time evolution of the multifractal behaviour of the seismic sequence a loss of multifractality during the aftershocks is revealed

the glacial inception as recorded in the northgrip greenland ice core timing structure and associated abrupt temperature changes the mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross dated climate records at various locations using air isotopic measurements in the recently drilled northgrip ice core we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception 123 100 kyears bp encompassing dansgaard oeschger events do 25 24 and 23 even if we lack sufficient resolution to completely rule out disturbance over do 25 we quantify the rapid surface temperature variability over do 23 and 24 with associated warmings of 10 2 5 and 16 2 5 c amplitudes which mimic those observed in full glacial conditions we use records of 18o of o2 to propose a common timescale for the northgrip and the antarctic vostok ice cores with a maximum uncertainty of 2 500 years and to examine the interhemispheric sequence of events over this period after a synchronous north south temperature decrease the onset of rapid events is triggered in the north through do 25 as for later events do 24 and 23 have a clear antarctic counterpart which does not seem to be the case for the very first abrupt warming do 25 this information when added to intermediate levels of co2 and to the absence of clear ice rafting associated with do 25 highlights the uniqueness of this first event while do 24 and 23 appear similar to typical full glacial do events

contrasting atmospheric and climate dynamics of the last glacial and holocene periods our present climate is relatively stable compared to that of the last glacial maximum about 20 000 years ago palaeoclimate records obtained from ice cores1 2 and deep sea sediment cores3 for the last glacial period show abrupt temperature changes on timescales of a few hundred years which have been attributed to cycles of ice build up and release associated with large ice sheets dansgaard oeschger cycles and heinrich events 3 and their coupling to ocean circulation4 5 but little is known about the dynamics of the atmosphere during the last glaciation ice sheets influence atmospheric circulation and studies using general circulation models have suggested stormier more variable atmospheric dynamics during the last glacial maximum than today6 9 here we report the results of an analysis of temporal trends over the past 91 000 years in the oxygen isotope signatures of a high resolution ice core record from greenland1 2 this analysis provides direct evidence that atmospheric circulation during the last glaciation was more turbulent than it is today

response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000 the effects of the great magnetic storm of july 15 2000 on the equatorial ionosphere have been studied by ground based and satellite in situ measurements a large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo in that environment the imf bz turned southward and presumably caused penetration of e fields to low latitudes this e field initiated the onset of 250 mhz and l band scintillations at ascension island 15 w and precipitous tec decrease at fortaleza brazil 38 w bounding the narrow longitude region in the south atlantic these impulsive ionospheric effects were extremely well correlated with abrupt decreases of sym h 1 min resolution dst the dmsp in situ measurements showed the presence of severe ion density bite outs extending over 30 latitude in the south atlantic magnetic anomaly region the rocsat 1 satellite measured upward and large southward ion drifts in the same sector

an investigation of ionospheric responses and disturbance thermospheric winds during magnetic storms over south american sector 1 this paper presents the results of a study of the ionospheric and thermospheric response to magnetic storm disturbances for four stations covering a wide range of latitude in the south american region the study is based on the f layer critical frequency fof2 and the peak height hmf2 from fortaleza fz which is equatorial cachoeira paulista cp which is low latitude concepcion con a midlatitude site and king george island kgi a middle to high latitude site equivalent neutral winds are extracted from the measured hmf2 by employing the field line interhemispheric plasma flip model the equatorial ionization anomaly eia can undergo enhancement due to magnetospheric disturbance electric field that penetrates to low latitudes during the growth phase of a storm substorm whereas eia inhibition occurs more often under disturbance dynamo dd electric field season dependent meridional transequatorial winds can significantly alter the eia response to disturbance electric fields large amplitudes of dd electric field is observed during evening and morning hours in equinoctial but not in winter months over the brazilian low latitude of large westward magnetic declination angle large equatorward meridional wind surges seem to be helped by the presence of disturbance zonal westward winds the low latitude disturbance can in some cases be traced to specific disturbance fronts originating promptly from auroral activity enhancements this study confirms earlier studies that show that the quiet time meridional wind increases with increase of latitude and that over midlatitude it shows decreases with increase of solar flux due to the effect of the ion drag force this study further shows that the disturbance meridional wind and the intensity of dd electric field increase with increasing intensity of high latitude energy input the negative ionospheric storm phase over middle latitude observed in equinox and not in winter is also intensified with the increasing intensity of high latitude energy input

ionosonde observations of daytime spread f at low latitudes spread f on ionograms has been considered to be a phenomenon mainly occurred at nighttime this study presented a case study of daytime spread f observed by the ionosonde installed at puer pur 22 7 n 101 05 e dip latitude 12 9 n where daytime spread f that lasted for more than 2 h about 08 30 lt 10 45 lt was observed on 14 november 2015 to investigate the possible mechanism ionograms recorded at pur and chiang mai 18 76 n 98 93 e dip latitude 9 04 n were used in this study we found that traveling ionospheric disturbances were observed before the occurrence of daytime spread f meanwhile the movement of the peak height of the ionosphere was downward we suggested that downward vertical neutral winds excited by traveling atmospheric disturbances atmospheric gravity waves might play a significant role in forming daytime spread f over pur during geomagnetic storms

radar studies of mid latitude ionospheric plasma drifts we use incoherent scatter radar measurements from millstone hill and saint santin to study the midlatitude f region electrodynamic plasma drifts during geomagnetically quiet and active periods we present initially a local time season and solar flux dependent analytical model of the quiet time zonal and meridional exb drifts over these stations we discuss for the first time the saint santin drift patterns during solar maximum we have used these quiet time models to extract the geomagnetic perturbation drifts which were modeled s function of the time history of the auroral electrojet indices our results illustrate the evolution of the disturbance drifts driven by the combined effects of prompt penetration nd longer lasting perturbation electric fields the meridion l electrodynamic disturbance drifts have largest amplitudes in the midnight noon sector the zonal drifts re predominantly westward with largest amplitudes in the dusk midnight sector nd following a decrease in the high latitude convection they dec y more slowly th n the meridional drifts the prompt penetration nd steady state zonal disturbance drifts derived from radar measurements re in good agreement with results obtained from both the ion drift meter data on board the dynamics explorer 2 de 2 satellite nd f om the rice convection model

study of the equatorial and low latitude electrodynamic and ionospheric disturbances during the 22 23 june 2015 geomagnetic storm using ground based and spaceborne techniques we use a set of ground based instruments global positioning system receivers ionosondes magnetometers along with data of multiple satellite missions swarm c nofs dmsp guvi to analyze the equatorial and low latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22 23 june 2015 which is the second largest storm in the current solar cycle our results show that at the beginning of the storm the equatorial electrojet eej and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields ppef the ppef were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside and downward drift on the nightside furthermore about 45 min after the storm commencement the interplanetary magnetic field imf bz component turned northward leading to the eej changing sign to westward and to overall decrease of the vertical total electron content vtec and electron density on the dayside at the end of the main phase of the storm and with the second long term imf bz southward turn we observed several oscillations of the eej which led us to conclude that at this stage of the storm the disturbance dynamo effect was already in effect competing with the ppef and reducing it our analysis showed no significant upward or downward plasma motion during this period of time however the electron density and the vtec drastically increased on the dayside over the asian region we show that this second positive storm was largely influenced by the disturbed thermospheric conditions

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

ice core evidence of abrupt climate changes ice core records show that climate changes in the past have been large rapid and synchronous over broad areas extending into low latitudes with less variability over historical times these ice core records come from high mountain glaciers and the polar regions including small ice caps and the large ice sheets of greenland and antarctica

effect of magnetic activity on the dynamics of equatorial f region irregularities 1 two different aspects of the effect of magnetic activity on the dynamics of equatorial spread f esf irregularities are studied here using spaced receiver scintillation observations the first one deals with the question of how magnetic activity affects the generation of esf irregularities for this a parameter designated the random velocity which is a measure of random changes in the irregularity drift velocity is evaluated from the data in past studies this parameter has been found to have large values in the early phase of evolution of esf irregularities during the postsunset period with a steep decline to a low value by 22 lt this behavior is attributed to the decline in the height of the f region therefore a sudden increase in the random velocity in the postmidnight period is attributed to an increase in the height of the f region due to the ionospheric zonal electric field turning from westward to eastward due to the effect of magnetic activity which may also generate fresh irregularities that produce the observed scintillations this idea has been used to suggest that for two of the magnetically active days considered in the present study the irregularities may be freshly generated in the postmidnight period the second aspect is the identification of geomagnetically disturbed plasma drifts which is generally possible only after 22 lt when the estimated irregularity drift velocities are close to that of the background plasma the pattern of the estimated drift after 22 lt 3 ut is found to be well defined for magnetically quiet days with scintillations during a period of a month this allows the identification of a superimposed westward perturbation in the drift produced by a disturbance dynamo due to magnetic activity for all the three events studied here on 19 february and 1 march 1999 the eastward drift velocities show an identical decrease of about 50 m s from the undisturbed drift at 0440 ut on 1 march the decay phase of the storm sets in later and the eastward velocity continues to decrease until 0530 ut turning westward with a maximum decrease of about 80 m s from the undisturbed drift on 22 october 1999 which was more disturbed than these two days the westward perturbation was larger causing the drift velocity to turn westward around 5 ut and a decrease of nearly 150 m s from the quiet time drift at 8 ut the results are in broad agreement with some of the recent empirical models of the evolution with storm time of equatorial disturbance dynamo electric fields

equatorial ionospheric responses to high intensity long duration auroral electrojet activity hildcaa 1 the knowledge of the coupling processes between the magnetosphere and the equatorial ionosphere is of basic importance to the understanding of the near earth space weather this study focuses on observational results of such coupling processes based on data collected during the phenomenon defined as high intensity long duration continuous ae activity hildcaa which occurs outside the main phase of geomagnetic storms the fact that the responses of the equatorial low latitude ionosphere to hildcaa events have not been specifically focused so far is one of the motivations for this study ionosonde data on hmf2 h f and fof2 from three locations in brazil magnetic equatorial station sao luis sl subequatorial station fortaleza fz and low latitude station cachoeira paulista cp are analyzed together with ace satellite data on solar wind and interplanetary magnetic and electric fields during three hildcaa events that occurred in the years 2000 and 2001 the results did not indicate any presence of penetrating electric field disturbance during these events however they provided clear evidence of disturbance dynamo electric field and disturbance thermospheric winds through f layer height changes that were similar but generally less intense than those observed during a typical storm event the fof2 presented no particular disturbances that can be clearly attributed to the hildcaa event previous extensive studies carried out by the authors on ionospheric storm effects for these same three stations clearly illustrate the much more intense f layer storm disturbances compared with hildcaa events disturbances

strong longitudinal difference in ionospheric responses over fortaleza brazil and jicamarca peru during the january 2005 magnetic storm dominated by northward imf 1 in this study we investigate the response of the equatorial f layer to disturbance zonal electric field associated with imf interplanetary magnetic field variations dominated by a strong northward bz episode during the magnetic storm that occurred on 21 january 2005 we compared the results obtained from digisondes operated at fortaleza brazil geogr 3 9 s 38 45 w dip angle 11 7 and jicamarca peru geogr 12 0 s 76 8 w dip angle 0 64 a large auroral activity ae intensification that occurred at 1715 ut produced a large f layer peak height increase from 300 km to 600 km over jicamarca with no noticeable simultaneous effect over fortaleza then the bz turning northward at 1940 ut with a rapid change in ae that was accompanied by a large decrease of f layer height and total suppression of the pre over fortaleza with no simultaneous effect over jicamarca strong increase in the ae index from 400 to 1000 nt with superimposed oscillations under bz north that soon followed was associated with increases in both the f layer height and the vertical drift velocity over fortaleza at 2130 ut with no corresponding signatures over jicamarca these remarkable contrasting responses to prompt penetration electric field ppef as well as to disturbance wind dynamo electric field ddef and other effects observed at the two locations separated only by 2 h in lt in the south american sector are presented and discussed in this paper effects onspread f development and fof2 behavior during this storm event are also addressed in this work

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

greenland antarctic phase relations and millennial time scale climate fluctuations in the greenland ice cores abstract the greenland grip gisp2 and antarctic byrd ice cores are examined in the frequency domain with the data synchronized using common methane variations using conventional time series analysis a simple picture emerges there is low frequency periods longer than about 10 kyr coherence between the two records consistent with a simple time delay antarctica leading by 1 2 kyr two geographical data points are however inadequate to infer causality from the south to north time lag at higher frequencies in the millennial band there is no measurable average relationship between the records and they appear to represent different processes with a regional character a serious question concerns the extent to which the greenland cores reflect tracer concentration change without corresponding abrupt climate change the large abrupt shifts in ice 18 o can be rationalized as owing to wind trajectory shifts perhaps of rather modest size many different physical phenomena probably do however contribute to the record as a function of time and time scale

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

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

observation of a large density dropout across the magnetic field at 600 km altitude during the 6 7 april 2000 magnetic storm 1 the first republic of china satellite rocsat 1 at 600 km altitude observed two groups of equatorial spread f esf plasma depletion structures located in either side of the midnight meridian during the 6 7 april 2000 magnetic storm recovery phase in the group of postmidnight esf irregularities a large density dropout was observed in two consecutive rocsat orbits this large density dropout structure is similar to the density depletion event observed by defense meteorological satellite program dmsp f9 spacecraft during the 13 14 march 1989 magnetic storm greenspan et al 1991 except that the rocsat orbit traverses the magnetic field in the east west direction the postmidnight group of depletions together with the large density dropout was observed to drift westward with the background plasma at 170 m s 1 we examine the properties of the large density dropout through the plasma data taken from the drift meter dm and retarding potential analyzer rpa sensors in three consecutive orbits the apparent widening of the density depletion is explained by the different locations of the satellite within the depletion region the extreme low density level inside the upwelling depletion indicates that of the nighttime f peak passed over the rocsat orbit at 600 km the existence of no ions inside the dropout is consistent with such an elevation of the f peak

phase relationships between antarctic and greenland climate records comparison of climate records from antarctic and greenland ice cores shows that the two regions respond asynchronously during millennial scale climate changes the apparent out of phase relationship between the records has been described as a climate seesaw in which cooling in the northern hemisphere is balanced by warming in the southern hemisphere the same relationship has also been attributed to the initiation of climate change events in the southern hemisphere rather than the north atlantic as is conventionally assumed a simple statistical approach band pass filtering combined with lag correlation tests used to examine the phase relationships in more detail shows that neither an anti phase nor a phase lag relationship adequately describes the observations whereas antarctic and greenland climate records do exhibit approximate anti phase behavior about 50 of the time they are generally in phase during cooling a phase lead of southern hemisphere climate of 1000 1600 years is statistically indistinguishable from a lag of 400 800 years whether for dansgaard oeschger heinrich or longer duration events the seesaw or southern lead appearance of the data arises from the fundamentally different characteristics of the climate time series most importantly the absence of rapid warming events in antarctica comparable to those in greenland to be consistent with the observations climate models will need to capture these characteristics in addition to reproducing the correct phase relationships

equatorial disturbance dynamo electric fields f region vertical drift data from jicamarca peru show that equatorial east west electric fields are sometimes perturbed 16 24 hours after the onset of geomagnetic storms these disturbance dynamo electric fields which must be caused primarily by the action of neutral winds at low and middle latitudes decrease and sometimes even reverse the quiet time electric field pattern during both daytime and nighttime the long delay excludes the possibility that gravity waves are responsible and suggests that the thermospheric circulation is disturbed the data also show that after some storms there are no such delayed disturbances a fact which may be due to the longitudinal structure of the disturbances at high latitudes and or that only very strong storms can produce major thermospheric perturbations that extend to middle and low latitudes

comparison between nighttime ionosonde incoherent scatter radar ae e satellite and hf doppler observations of f region vertical electrodynamic plasma drifts in the vicinity of the magnetic equator 1 nighttime f region vertical drifts were made using an ionosonde for the equatorial station ibadan 7 4 n 3 9 e 6 s dip from 1 year of data during 1957 1958 international geophysical year igy that corresponds to a period of solar maximum for undisturbed condition we compare the seasonal vertical drifts with measurements made by incoherent scatter radar ae e satellite and hf doppler for equatorial f region vertical drifts we find a comparable variability pattern during periods of high f layer heights during equinox and the december solstice and the opposite behavior occurs during june solstice the drifts are predominantly downward between 2000 and 0500 lt intervals ionosonde drifts are smaller in values by either a factor of two or three than other methods except for consistent june solstice ionosonde and satellite magnitudes the equinoctial average prereversal enhancements measured by the four techniques are roughly comparable about 36 m s and occur at the same local time 1900 lt for all the seasons the evening reversal times are similar apart from june solstice that exhibits large variations the morning reversal times are also in accord except for the equinoctial jicamarca drift our observations indicate that ionosonde drifts measurements are in better agreement with vertical drifts results at other equatorial stations

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

observation and model comparisons of the traveling atmospheric disturbances over the western pacific region during the 6 7 april 2000 magnetic storm 1 the ionospheric features of traveling atmospheric disturbances tads over the western pacific region have been observed by the wuhan ncu dps and cebu ionosondes and the rocsat 1 satellite during the 6 7 april 2000 magnetic storm the nighttime observations are further compared with the simulation results of the thermosphere ionosphere electrodynamics general circulation model tiegcm both observation and model demonstrate that the tads propagate equatorward with a phase speed of 610 650 m s the observations and corresponding tiegcm simulations show a negative initial correlation between nmf2 and hmf2 caused by equatorward wind surges at various locations from midlatitudes to the equator these qualitative agreements reveal that the tiegcm is capable of simulating the tads the tiegcm simulations of two locations located in the downwind hemisphere further show decreases in nmf2 and hmf2 mainly due to the enhanced transequatorial winds after lowering the f2 layer at the two locations the hmf2 is raised for several hours and shows slightly enhanced nmf2 daytime values while the meridional wind is at background magnitude we propose that this effect is caused by accumulation of plasma transported from northern latitudes however we also find that the nmf2 hmf2 and the lifetimes of hmf2 uplift phase and equatorial vertical drift in the model results are quantitatively inconsistent with that in the observed data

observation of atmospheric and climate dynamics from a high resolution ice core record of a passive tracer over the last glaciation here we present a temporal analysis of diluted calcium from the greenland ice core project summit ice core over a length corresponding to the duration of the last glacial period 92 8 ka our analysis suggests that this signal can be split into two distinct temporal components whose dynamics are characterized by respective timescale regimes timescales longer than approximately 200 years show a strong negative correlation with the temperature proxy 18 o signal this we interpret as a result of the temperature dependence of processes governing source area efficiency at faster timescales 200 years correlation with the temperature proxy is significantly weakened while its variability or mean absolute deviation is negatively correlated with the 18 o this we believe is a sign of the turbulent nature or storminess of the atmosphere during the glacial climate furthermore this component of the signal displays intermittency and multifractality supporting our interpretation of an observation of atmospheric dynamics this then provides a signal of atmospheric and climate dynamics back to 92 ka

low latitude ionospheric disturbance electric field effects during the recovery phase of the 19 21 october 1998 magnetic storm 1 low latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity these perturbations can last for several hours after geomagnetic quieting we use incoherent scatter radar measurements from jicamarca and arecibo during 19 21 october 1998 to study for the first time the low latitude disturbance electric fields during the recovery phase of a large magnetic storm on 19 october the jicamarca data showed initially large and short lived time scale of about 10 20 min upward and westward drift perturbations in the early afternoon sector due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure following the decrease of auroral activity very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over jicamarca but surprisingly only small and sporadic perturbation drifts were present over arecibo the latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds the disturbance dynamo drifts also indicate significantly different local storm time and possibly latitudinal dependences for their vertical perpendicular and zonal drift components suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector in the next day during moderately disturbed conditions the daytime perturbation drifts were small but following transient increases in geomagnetic activity large upward perpendicular drifts were observed near dusk over jicamarca and arecibo where simultaneous westward perturbation drifts were also seen these perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator the measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models later at night under moderately disturbed conditions relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars our results illustrate the large variability of the low latitude perturbation electric fields relative to their climatological values after large storms probably due to the importance of additional disturbance processes they also indicate that a much deeper understanding of solar wind magnetospheric ionospheric processes is required for accurate predictions of these electric fields

mid latitude ionospheric irregularities persisting into late morning during the magnetic storm on 19 march 2001 1 post sunrise intense ionospheric irregularities at low to mid latitudes are reported for the first time a method based on spaced receiver technique is proposed to estimate the apparent drift velocity of the irregularities by using the correlation of the slant total electron content tec from 3 gps receivers the irregularities were detected at 23 45 n by the gps earth observation network geonet of japan from 0455 lt to 1051 lt on 21 march 2001 during the recovery phase of the magnetic storm at the corresponding time spread f was observed with 3 ionosondes located meridionally at okinawa 127 8 e 26 3 n 20 7 n magnetic latitude kokubunji 139 5 e 35 7 n 30 0 n magnetic latitude and wakkanai 141 7 e 45 4 n 40 5 n magnetic latitude while an intense negative ionospheric storm was processing and propagating from mid to lower latitudes the irregularities were seen as plasma bubbles by the defense meteorological satellite program dmsp in situ measurements westward drift with the speed of 100 m s was estimated by spaced receivers from geonet and confirmed by dmsp during the evolution of the irregularities the plasma bubbles at mid latitude sustained 1 5 hour after sunrise and at the lower latitudes they survived more than 4 hours after sunrise the observations suggested that the irregularities were generated by an eastward electric field associated with the disturbance dynamo and the long time existence of the irregularities after sunrise seemed to be related to the daytime intense negative ionospheric storm on 21 march

large density depletions in the nighttime upper ionosphere during the magnetic storm of july 15 2000 1 we measured electron density and temperature of the nighttime upper ionosphere for the several key intervals during the progress of the magnetic storm on 15 july 2000 with the langmuir probe on korea multipurpose satellite 1 kompsat 1 during the main phase of the storm kompsat 1 detected near 0 e a very deep and extensive trough of electron density centered around the geomagnetic equator the electron density dropped sharply from 4 105cm 3 to less than 2 104cm 3 with the trough region extended over 1400 km along the satellite track later in the recovery phase kompsat 1 observed severe distortion still persisted near 230 e with enhanced density in the southern hemisphere together with dmsp observations we estimate the size of the observed trough to be at least 5500 km in the longitudinal direction dmsp data indicates that the trough was caused by the enhanced eastward electric field which lifted the equatorial f region ionosphere upward

magnetospheric convection near a drainage plume 1 we report on equatorial convection associated with a plasmaspheric drainage plume using simultaneous observations from five satellites during the early recovery phase of the july 2000 bastille day magnetic storm the extreme ultraviolet sensor on the magnetopause to aurora global exploration satellite detected the plume near 16 00 17 00 magnetic local time extending outward to l 2 8 the plasmaspheric boundary was near l 2 at other local times we mapped simultaneously measured ionospheric plasma drifts from rocsat 1 and three defense meteorological satellite program dmsp spacecraft along magnetic field lines to infer equatorial convection velocities in the inner magnetosphere the zonal component of convection derived from rocsat 1 ion drift measurements had a sharp positive azimuthal gradient near the plume s boundaries reversing direction from westward to eastward the meridional profile of horizontal velocities deduced from dmsp measurements shows a large westward flowing subauroral polarization stream saps located outside the plasmapause the peak velocity of the saps centered at a radial distance of l 2 8 with a full width of 1 re in the inertial frame of reference equatorial plasmas flowed toward the plume from both its day and evening sides suggesting a negative gradient in the equatorial azimuthal velocity that was largest near the plume s outermost boundary these observations provide new evidence about diversion of saps plasma flows and distinctive azimuthal velocity patterns in the vicinity of plasmaspheric plumes

storm time plasma irregularities in the pre dawn hours observed by the low latitude rocsat 1 satellite at 600 km altitude large scale ion density depletions were detected in the nighttime sector by rocsat 1 for over 10 hours during the 22 october 1999 geomagnetic storm prominent depletion structures bubbles that are characterized by large amplitude density decrease n no 1 with rapid horizontal ion drift 600 800 m s are found to cluster in the 03 00 04 30 local time sector and at magnetic latitudes 14 20 s when the storm was in its early recovery phase these presunrise bubbles are positively correlated to the enhanced eastward electric fields of greater than 1 2 mv m which were in response to the storm time disturbances resulting from the in phase contributions of the prompt penetration magnetospheric and the long lasting ionospheric disturbance dynamo electric fields further analyses of the field aligned and cross field ion drifts within the depletions reveal that bubble plasma were driven by the eastward polarization electric fields to move upward but these upward velocities were compensated by large downward field aligned diffusive motions these features confirm that the disturbance electric fields produced during a great magnetic storm can significantly affect the occurrence timing and spatial extent of severe plasma irregularities in low latitude ionosphere the spatial dimensions of the pre sunrise irregularities may exceed the large region observed by the 35 inclined circular orbiting rocsat 1

radar studies of midlatitude ionospheric plasma drifts we use incoherent scatter radar measurements from millstone hill and saint santin to study the midlatitude f region electrodynamic plasma drifts during geomagnetically quiet and active periods we present initially a local time season and solar flux dependent analytical model of the quiet time zonal and meridional exb drifts over these stations we discuss for the first time the saint santin drift patterns during solar maximum we have used these quiet time models to extract the geomagnetic perturbation drifts which were modeledsfunction of the time history of the auroral electrojet indices our results illustrate the evolution of the disturbance drifts driven by the combined effects of prompt penetrationnd longer lasting perturbation electric fields the meridionl electrodynamic disturbance drifts have largest amplitudes in the midnight noon sector the zonal driftsre predominantly westward with largest amplitudes in the dusk midnight sectornd following a decrease in the high latitude convection they decy more slowly thn the meridional drifts the prompt penetrationnd steady state zonal disturbance drifts derived from radar measurementsre in good agreement with results obtained from both the ion drift meter data on board the dynamics explorer 2 de 2 satellite nd f om the rice convection model