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

cooling following large volcanic eruptions corrected for the effect of diffuse radiation on tree rings 1 the lack of a larger cooling in proxy records of climate change following large volcanic eruptions such as those of tambora in 1815 and krakatau in 1883 has long been a puzzle for climatologists these records however may have been biased by enhanced tree growth for several years following each eruption induced by additional diffuse radiation caused by the stratospheric volcanic aerosol clouds from the eruptions by comparing proxy reconstructions of climate with and without tree ring data this effect is demonstrated for the five largest eruptions for the period 1750 1980 when proxy records of northern hemisphere climate change are corrected for this proposed diffuse effect there is no impact on climate change for time scales longer than 20 years however it now appears that there was a hemispheric cooling of about 0 6 c for a decade following the unknown volcanic eruption of 1809 and tambora in 1815 and a cooling of 0 3 c for several years following the krakatau eruption of 1883

on relative timing in substorm onset signatures we investigate the timing of popular substorm onset signatures to understand their temporal relationship proxies for substorm onsets include auroral breakups high latitude magnetic bays low latitude pi2 bursts dispersionless injections at geostationary orbits and auroral kilometric radiation we use the auroral breakup identified with polar uvi images as a common reference time frame to calibrate the others results illustrated by two well defined auroral substorms unambiguously indicate that none of the four frequently used substorm onset proxies can provide a consistent timing of substorm onset this inconsistency in substorm onset timing is attributed as a consequence of temporal and spatial limitations on each observational technique a delay between the proxy identifiers and the auroral breakup is found to be typical it is therefore strongly suggested from this study result that a common reference time frame for substorm onset is necessary and we propose it should be auroral breakups we argue that there is a need for an intercalibration of magnetospheric substorm phenomenology by using a unified definition of the substorm onset

volcano induced regime shifts in millennial tree ring chronologies from northeastern north america the cooling effect on the earth s climate system of sulfate aerosols injected into the stratosphere by large volcanic eruptions remains a topic of debate while some simulation and field data show that these effects are short term less than about 10 years other evidence suggests that large and successive eruptions can lead to the onset of cooling episodes that can persist over several decades when sustained by consequent sea ice ocean feedbacks here we present a new network of millennial tree ring chronologies suitable for temperature reconstructions from northeastern north america where no similar records are available and we show that during the last millennium persistent shifts toward lower average temperatures in this region coincide with series of large eruptions

climate response to large high latitude and low latitude volcanic eruptions in the community climate system model 1 explosive volcanism is known to be a leading natural cause of climate change the second half of the 13th century was likely the most volcanically perturbed half century of the last 2000 years although none of the major 13th century eruptions have been clearly attributed to specific volcanoes this period was in general a time of transition from the relatively warm medieval period to the colder little ice age but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism this context motivates our investigation of the climate system sensitivity to high and low latitude volcanism using the fully coupled ncar community climate system model ccsm3 we evaluate two sets of ensemble simulations each containing four volcanic pulses with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid high latitudes of both the northern and southern hemispheres the short term direct radiative impacts of tropical and high latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea ice concentration in northern hemisphere nh winter a main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern eurasia furthermore both ensembles show significant reductions in global precipitation especially in the summer monsoon regions the most important long term impact is the cooling of the high latitude nh produced by multiple tropical eruptions suggesting that positive feedbacks associated with ice and snow cover could lead to long term climate cooling in the arctic

ground based studies of ionospheric convection associated with substorm expansion the instantaneous patterns of electric fields and currents in the high latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity along with ground based magnetometer observations for october 25 1981 for this purpose an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used these global patterns are unobtainable from any single data set the period under study was characterized by a relatively stable southward interplanetary magnetic field imf so that the obtained electric field patterns do reflect in general the state of sustained and enhanced plasma convection in the magnetosphere during one of the satellite passes however an intense westward electrojet caused by a substorm intruded into the satellite de 2 and radar chatanika alaska field of view in the premidnight sector providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields the distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern the changes in the convection pattern during the substorm indicate that the large scale potential distributions are indeed of general two cell patterns representing themore southward imf status but the night morning cell has two positive peaks one in the midnight sector and the other in the late morning hours corresponding to the substorm expansion and the convection enhancement respectively 40 refs 12 figs 1 tab less

climate response to the samalas volcanic eruption in 1257 revealed by proxy records the eruption of samalas in indonesia in 1257 ranks among the largest sulfur rich eruptions of the common era with sulfur deposition in ice cores reaching twice the volume of the tambora eruption in 1815 sedimentological analyses of deposits confirm the exceptional size of the event which had both an eruption magnitude and a volcanic explosivity index of 7 during the samalas eruption more than 40 km 3 of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km however the climatic response to the samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of northern hemisphere summers than inferred from tree ring based temperature reconstructions here we draw on historical archives ice core data and tree ring records to reconstruct the spatial and temporal climate response to the samalas eruption we find that 1258 and 1259 experienced some of the coldest northern hemisphere summers of the past millennium however cooling across the northern hemisphere was spatially heterogeneous western europe siberia and japan experienced strong cooling coinciding with warmer than average conditions over alaska and northern canada we suggest that in north america volcanic radiative forcing was modulated by a positive phase of the el nino southern oscillation contemporary records attest to severe famines in england and japan but these began prior to the eruption we conclude that the samalas eruption aggravated existing crises but did not trigger the famines

the global monsoon as seen through the divergent atmospheric circulation a comprehensive description is given of the global monsoon as seen through the large scale overturning in the atmosphere that changes with the seasons and it provides a basis for delimiting the monsoon regions of the world the analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions as given by the monthly mean fields for 1979 93 reanalyses from the national centers for environmental prediction national center for atmospheric research ncep ncar and european centre for medium range weather forecasts ecmwf which are able to reproduce the dominant modes a complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year the first mode which depicts the global monsoon has a simple vertical structure with a maximum in vertical motion at about 400 mb divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb and convergence in the lower troposphere with a maximum at 925 mb ecmwf or 850 mb ncep however this mode has a rich three dimensional spatial structure that evolves with the seasons it accounts for 60 of the annual cycle variance of the divergent mass circulation and dominates the hadley circulation as well as three overturning transverse cells these include the pacific walker circulation an americas atlantic walker circulation both of which comprise rising motion in the west and sinking in the east and a transverse cell over asia the middle east north africa and the indian ocean that has rising motion in the east and sinking toward the west these exist year round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak hadley cell the annual cycle of the two hadley cells reveals peak strength in early february and early august in both reanalyses a second monsoon mode which accounts for 20 of the variance features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb outflow from 750 to 350 mb and inflow peaking at 925 mb it is especially strong over africa where the shallow mostly meridional overturning migrates back and forth across the equator with the seasons it influences the middle east has a signature over australia and is also an important component of the overturning in the tropical eastern pacific and atlantic and thus of the convergence zones in these regions the relationship of the global monsoon to the regional monsoons is described over six zonal sectors africa australia asia north america south america and the pacific and atlantic oceans only the two ocean areas do not undergo a seasonal reversal required for monsoons although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large scale overturning the regional meridional cross sections highlight the importance of the shallow overturning cell in lower troposphere monsoon activity the steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations locations where this signal exceeds 60 of the daily noise correspond closely with the regional centers of the monsoon

substorm associated changes in large scale convection during the november 24 1996 geospace environment modeling event we have used data from the november 24 1996 geospace environment modeling program substorm event to investigate the critical question of substorm expansion phase triggering by interplanetary magnetic field imf changes that lead to a reduction in large scale convection coverage of ionospheric convection with the super dual auroral radar network superdarn radars was excellent during this period this has allowed us to investigate the changes in large scale convection associated with two expansion phase onsets that followed a 80 min period of strongly southward and quite steady imf we have found that reductions in global convection occurred in association with two observed northward turnings of the imf and to within observation uncertainty these reductions occurred at the same times that the two onsets were first observed in the magnetosphere the first smaller northward turning was found to give a small convection reduction and the onset of a small substorm while the second much larger northward turning was found to give a large reduction in global convection and the onset of a large substorm taken together with other more localized studies which also show convection reductions associated with expansion onsets our results imply that imf driven reductions in global convection may be generally associated with expansion onset our results also suggest that substorm expansions may represent an adjustment to conditions of reduced convection following a growth phase of enhanced convection and magnetotail energy storage under this suggestion for a given amount of energy stored in the tail a small reduction in convection would lead to a small substorm and a large reduction in convection would lead to a large substorm

a substorm onset signature at the auroral zone as observed with superdarn and equatorial magnetometers ionospheric convection enhancement with high westward velocities exceeding 1500 m s 1 was observed in association with the particle injection event by superdarn in the dusk sector of the auroral zone such a convection enhancement could be attributable to the enhanced sunward plasma flows in the dusk sector of the magnetosphere at the dip equator a ground pi2 onset was found to occur in association with these convection transients the onset of the pi2 lagged behind the convection enhancement by 4 11 min it is argued that the convection transient could be the earliest indicator of the substorm onset among energetic particle injection low latitude pi2 onset and perhaps the auroral breakup

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events 1 substorms cause significant disturbances in the ionosphere however it has not been well understood how the electric field and electrojet in the dayside equatorial ionosphere respond to substorm onset previous studies found that the equatorial electric field after substorm onset could be eastward or westward because the onset of isolated substorms is often related to a northward turning of the interplanetary magnetic field imf the measured total electric field is determined by contributions from both imf northward turning and substorm onset and is not necessarily the signature of the onset in order to exclude the effect of imf northward turning we analyze the variations of ionospheric electric field and electrojet during storm time substorms when the imf remains stable thus the ionospheric variations can be identified to be caused solely by substorms the electric field data are measured by the jicamarca radar and the electrojet is derived from magnetometers at jicamarca and piura it is found that substorm onset induces an eastward electric field and electrojet in the dayside equatorial ionosphere when the imf remains continuously southward across the onset the equatorial electrojet starts to increase at the onset reaches a maximum value 30 min after the onset and then decreases to the pre onset value 60 min after the onset westward electric field and counter electrojet occur only if the substorm onset is associated with a northward turning of the imf it is concluded that the effect of substorm onset on the dayside equatorial ionosphere without involvement of imf reorientations is an enhanced eastward electric field

substorm associated changes in the high latitude ionospheric convection 1 a study of polar cap dayside convection response to substorm intervals using canadian advanced digital ionosondes cadis situated well within the polar cap and superdarn radars during steady and prolonged southward imf bz conditions showed three distinct features 1 gradual prolonged decrease of dayside polar cap convection speed until the substorm onset 2 sudden decrease of convection following the onset of the substorm and 3 increase of convection during the recovery phase of the substorm we hypothesize that the observed features of the convection are due to the modulation of the region 1 current system associated with the substorm the ground magnetic response of magnetometers situated inside the polar cap is at least consistent with our postulate

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

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

polar equatorial ionospheric currents driven by the region 2 field aligned currents at the onset of substorms 1 the dawn to dusk convection electric field increases during the growth phase of substorms driving dp2 currents composed of two cell current vortices in high latitude and leading to an increase in the eastward electrojet at the dayside dip equator eej during the expansion phase of substorms electric field and currents are often reversed in direction to the normal dp2 currents at subauroral to equatorial latitudes when the convection electric field reduces abruptly the reversed current at the dayside dip equator appears as a counterelectrojet cej and causes an equatorial enhancement of the negative bay in the afternoon sector conversely the convection electric field increases during substorms as deduced from sawtooth events causing an increase in the eej in this study by analyzing isolated substorms with magnetometer array data and superdarn super dual auroral radar network convection maps we deduce that the reversed electric field and currents develop at the subauroral to equatorial latitudes at the onset of substorms while the convection electric field increases at auroral latitudes these observations imply that both the region 1 and region 2 field aligned currents r1 and r2 facs develop on the dayside concurrently with the current wedge responsible for the midlatitude positive bay at midnight the substorm associated r2 facs are strong enough to cause the reversed current at the subauroral latitude and the cej at the equator we also deduce that the dayside equatorial cej begins simultaneously with or even earlier than the midlatitude positive bay at midnight while the midlatitude positive bay onset is delayed by several minutes as the station departs from the midnight meridian these observations suggest that the substorm begins with the intensification of the r2 facs responsible for the equatorial cej

a superposed epoch study of superdarn convection observations during substorms 1 case studies of flow patterns during substorms have revealed characteristic patterns in the period leading to expansion onset velocities in the premidnight region have been observed to become strongly sheared and the premidnight convection reversal has been observed to extend across the midnight meridian at expansion onset the shear decreases and flow at midnight becomes meridional out of the polar cap the study presented here superposes flow patterns from 10 substorm intervals to determine the average flow patterns the study confirms the findings of the case studies and extends them to additional local time sectors in addition changes to the flow pattern after expansion onset are examined

bayesian multiproxy temperature reconstruction with black spruce ring widths and stable isotopes from the northern quebec taiga northeastern north america has very few millennium long high resolution climate proxy records however very recently a new tree ring dataset suitable for temperature reconstructions over the last millennium was developed in the northern quebec taiga this dataset is composed of one 18o and six ring width chronologies until now these chronologies have only been used in independent temperature reconstructions from 18o or ring width showing some differences here we added to the dataset a 13c chronology and developed a significantly improved millennium long multiproxy reconstruction 997 2006 ce accounting for uncertainties with a bayesian approach that evaluates the likelihood of each proxy model we also undertook a methodological sensitivity analysis to assess the different responses of each proxy to abrupt forcings such as strong volcanic eruptions ring width showed a larger response to single eruptions and a larger cumulative impact of multiple eruptions during active volcanic periods 18o showed intermediate responses and 13c was mostly insensitive to volcanic eruptions we conclude that all reconstructions based on a single proxy can be misleading because of the possible reduced or amplified responses to specific forcing agents

substorm convection patterns observed by the super dual auroral radar network a study of convection patterns during substorms observed by the super dual auroral radar network superdarn radar network is presented specific attention is given to the growth phase and the time immediately following expansion onset it is found that the growth phase is characterized by the enhancement of the velocity shear near midnight and its extension to low latitudes and to local times across the midnight meridian the velocity shear was observed to diminish at expansion onset in addition the ionospheric flow velocity magnitude was observed to be enhanced for some period of time prior to expansion onset and to decrease at expansion onset possible explanations for the establishment of the midnight velocity shear during growth phase and its subsequent disappearance at expansion onset are presented also arguments are presented regarding the decrease of ionospheric flow velocity at expansion onset

successive substorm expansions during a period of prolonged northward interplanetary magnetic field 1 we have studied successive substorm expansions that occurred in spite of a period of prolonged northward interplanetary magnetic field imf after the northward imf persisted for almost 19 h a series of 11 very weak to moderate substorm expansions occurred during the following 6 h interval of northward imf on 19 january 1998 separated from each other by a few tens of minutes most of these substorm expansions did not accompany significant changes of the solar wind and the imf as for typical substorms that occur under southward imf conditions spacecraft and ground based instruments observed auroral breakups and enhancements of the westward auroral electrojet and large scale convection in the ionosphere together with plasmoids and dipolarizations in the magnetotail in association with the substorm expansion onsets these signatures suggest that the mechanism of substorm expansion onsets is the same as for typical substorms even under prolonged northward imf conditions we suggest that the large imf by affects large scale convection and energy accumulation in the magnetotail and that the enhanced convection due to the large imf by effect and substorm expansions can be an important factor for the promotion of succeeding substorm expansion onsets

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

volcanic cooling signal in tree ring temperature records for the past millennium the authors acknowledge the national science foundation for funding much of the research presented herein rw s scottish work is currently funded through the uk leverhulme trust and natural environment research council nerc projects relic reconstructing 8000 years of environmental and landscape change in the cairngorms f 00 268 bg and scot2k reconstructing 2000 years of scottish climate from tree rings ne k003097 1

solar and volcanic fingerprints in tree ring chronologies over the past 2000 years abstract the sun is the main driver of earth s climate yet the sun s role in forcing decadal to centennial climate variations has remained controversial especially in the context of understanding contributions of natural climate forcings to continuing global warming to properly address long term fingerprints of solar forcing on climate long term very high resolution globally distributed climate proxy records are necessary in this study we compile and evaluate a near global collection of annually resolved tree ring based climate proxies spanning the past two millennia we statistically assess these records in both the time and frequency domains for solar forcing i e total solar irradiance tsi and climate variability with emphasis on centennial time scales analyses in the frequency domain indicate significant periodicities in the 208 year frequency band corresponding to the devries cycle of solar activity additionally results from superposed epoch analysis sea point toward a possible solar contribution in the temperature and precipitation series however solar climate associations remain weak with for example no clear linkage distinguishable in the southwestern united states drought records at centennial time scales other forcing factors namely volcanic activity appear to mask the solar signal in space and time to investigate this hypothesis we attempted to extract volcanic signals from the temperature proxies using a statistical modelling approach wavelet analysis of the volcanic contribution reveals significant periodicities near the devries frequency during the little ice age lia this remarkable and coincidental superposition of the signals makes it very difficult to separate volcanic and solar forcing during the lia nevertheless the volcano free temperature records show significant periodicities near the devries periodicity during the entire past 1500 years further pointing to solar mechanisms and emphasising the need for solar related studies in the absence of strong multi decadal volcanic forcing

time evolution of the subauroral electric fields a case study during a sequence of two substorms 1 the temporal evolution of the subauroral polarization stream saps is investigated using the doppler velocity observations by the unwin hf radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions the event under study of 14 december 2004 1000 1600 ut occurred during geomagnetically quiet conditions when a sequence of two substorms separated by 2 hours was observed by the image satellite it is shown that the saps appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59 63 s for 6 hours an unexpected exception occurred near the second substorm onset time when a narrow channel of weaker saps westward convection became embedded in the slow eastward drifting plasma for a short 25 min period which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm another remarkable plasma convection feature was observed in the same 25 min period 5 poleward of saps this was a narrow mirror channel of the eastward drifting plasma parallel to the main saps channel it is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the saps poleward edge a possible relationship between the saps intensity and its position relative to the auroral oval is also investigated the results suggest that the magnetosphere ionosphere feedback processes within saps become more effective as the equatorward edge of the eastward convection region retreats poleward with the saps position much less affected by the auroral dynamics

nightside ionospheric electrodynamics associated with substorms pfisr and themis asi observations 1 observations from the newly available poker flat incoherent scatter radar have been used to study the ionospheric electrodynamics during the substorm expansion phase substorm events selected have been divided into three categories based on onset location relative to the radar and repeatable features have been identified west of onset westward flows increased in response to the passage of the westward traveling surge wts poleward of them the enhanced flows occurred within the sub auroral polarization streams region of downward region 2 currents which extend equatorward from near the equatorward boundary of electron precipitation strong e region ionization increase associated with the wts occurred poleward of the enhanced westward flows suggesting that poleward pedersen currents fed by the downward region 2 field aligned current fac further equatorward contribute at least partially to closure of the upward fac of the wts an enhanced eastward flow channel developed east of onset e region ionization decreased poleward of this flow peak implying formation of downward fac and further increased equatorward of the flow peak suggesting strengthening of preexisting region 2 upward fac these observations indicate that the downward fac formed at onset at least partially closes via the upward region 2 currents the enhanced eastward flows decreased after passage of the auroral bulge and the reduced e region ionization increased again when onset occurred within the radar fov the thin breakup arc of onset occurred at the center of the harang reversal while if the optical onset was poleward of the radar fov the harang reversal was observed after the onset a 2 d picture of the evolution of ionospheric electrodynamics was generated by synthesizing observations from the three categories which provides a schematic description of the relationship between region 2 and substorm expansion electrodynamics

the response of high latitude convection to a sudden southward imf turning we describe the response of the high latitude convection to a sudden southward turning of the imf in this event bz recorded at the wind satellite switched from 6 nt to 6 nt in 2 minutes and effects in the ionosphere were observed by the superdarn hf radars in the vicinity of noon mlt the convection switched suddenly 2 min from sunward to antisunward with the velocity change reaching magnitudes as great as 1500 m s in about 6 minutes surprisingly the responses at the other mlts distributed from noon to midnight began at virtually the same time meridional flows near 22 mlt were observed to reverse direction in about 4 minutes with the velocity change reaching magnitudes as great as 750 m s in about 8 minutes this example shows that the convection can respond to a sudden imf change practically simultaneously 2 min over the entire high latitude zone and reconfigure from a pattern characteristic of bz to one characteristic of bz in a very short 2 4 min time

contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere this study tries to bring out the fact that storm time substorms can compete and at times significantly contribute to the geomagnetically disturbed time prompt penetration electric field effects on low and equatorial latitudes observations of unusual equatorial plasma drift data from jicamarca unattended long term investigations of the ionosphere and atmosphere during two space weather events show that substorms can induce both eastward and westward penetration electric fields under steady southward interplanetary magnetic field imf bz conditions during the first event on 2 january 2005 the enhancement of the daytime eastward electric field over jicamarca due to substorm is found to be comparable with the sq and interplanetary electric field iefy generated electric fields combined during the second event on 19 august 2006 the substorm is seen to weaken the daytime eastward field thereby inducing a westward field in spite of the absence of northward turning of imf bz overshielding the westward electric field perturbation in the absence of any overshielding events is observationally sparse and contrary to the earlier results further the substorm induced field is found to be strong enough to compete or almost nullify the effects of storm time iefy fields this study also shows quantitatively that at times substorm contribution to the disturbed time prompt electric fields can be significant and thus should be taken into consideration in evaluating penetration events over low latitudes

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