a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

geomorphic controls on groundwater arsenic distribution in the mekong river delta cambodia natural arsenic contamination of groundwater is a severe public health crisis affecting nearly 60 million people in south asia and southeast asia alone contamination is spatially heterogeneous and results from the coupled microbial decomposition of organic matter and reductive dissolution of arsenic bearing iron minerals here we demonstrate that elevated arsenic concentrations arise in regions of recent organic matter deposition and thus are controlled by fluvial geomorphic processes arsenic contamination is best expressed within recent geomorphic features such as docked islands scroll bars and avulsions within these features the deposition of rapidly buried reactive organic matter facilitates microbial iron reduction and arsenic release ultimately the organic matter supply is exhausted and the conditions necessary for soluble arsenic to persist diminish

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

observations of highly correlated near simultaneous magnetic field perturbations at contraposed ground stations a merged data set from canadian auroral network for the open program unified study canopus and magnetometers ionospheric radars all sky cameras large experiment miracle magnetometer stations is used to study variations observed at widely separated locations three years of 10 s data are analyzed using canonical correlation techniques to determine the temporal offset of similar fluctuations observed at pairs of sites nearly simultaneous 10 min delay correlated episodes occur more often roughly 10 of the time when sites are in the dawn dusk sectors and less often 5 for noon midnight configurations

ionospheric response to the interplanetary magnetic field southward turning fast onset and slow reconfiguration 1 this paper presents a case study of ionospheric response to an interplanetary magnetic field imf southward turning it is based on a comprehensive set of observations including a global network of ground magnetometers global auroral images and a superdarn hf radar there is a clear evidence for a two stage ionospheric response to the imf southward turning namely fast initial onset and slow final reconfiguration the fast onset is manifested by nearly simultaneous within 2 min rise of ground magnetic perturbations at all local times corroborated by a sudden change in the direction of line of sight velocity near local midnight and by the simultaneous equatorward shift of the auroral oval the slow reconfiguration is characterized by the different rising rate of magnetic perturbations with latitudes faster at high latitude than at lower latitudes furthermore a cross correlation analysis of the magnetometer data shows that the maximum magnetic perturbation is reached first near local noon and then spread toward the nightside corresponding to a dayside to nightside propagation speed of 5 km s along the auroral oval global ionospheric convection patterns are derived based on ground magnetometer data along with auroral conductances inferred from the polar uv images using the assimilative mapping of ionospheric electrodynamics amie procedure the amie patterns especially the residual convection patterns clearly show a globally coherent development of two cell convection configuration following the imf southward turning while the foci of the convection patterns remain nearly steady the convection flow does intensify with time and the cross polar cap potential drop increases the overall changes as shown in the amie convection patterns therefore are fully consistent with the two stage ionospheric response to the imf southward turning

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

slickenside kinematic indicators abstract a new classification of slickenside kinematic indicators is presented based on 61 criteria these slickensides have been subdivided into eleven major groups v or crescentic markings steps fractures trains of inclined planar structures trailed material asymmetric elevations deformed elements mineralogical crystallographic orientations asymmetric plan view features asymmetric cavities and asymmetric folds this classification constitutes a useful tool for geologists interested in the determination of the shear sense in fault surfaces bearing slickensides examples of application of this classification to natural fault surfaces at different scales are presented

nucleation of ductile shear zones on dilatant fractures small shear zones in granitic rocks of the sierra nevada california and near roses rosas northeast spain display features which indicate that dilatant fracturing preceded the localization of ductile shear deformation many zones have sharp nearly planar boundaries between their highly deformed interiors and the undeformed wall rock the roses shear zones narrow continuously to hairline fractures at their ends mineralized microcracks oriented parallel to the shear zones cluster near the zone boundaries and are interpreted as relicts of the earlier fracturing episode dynamic recrystallization of minerals filling these microcracks demonstrates that fracturing predated the ductile deformation gradients in ductile strain suggest that deformation spread laterally into the wall rocks after nucleation of the shear zones we suggest that cracks enhance the wall rock ductility by increasing local fluid fluxes thereby promoting chemical alteration and or hydrolytic weakening

erosion and physical transport via overland flow of arsenic and lead bound to silt sized particles understanding of the transport mechanisms of contaminated soils and sediment is essential for the sustainable management of contaminated lands in new england and elsewhere vast areas of agricultural lands are contaminated by the historical application of lead arsenate pesticides left undisturbed the physical and chemical mobility of as and pb in these soils is limited due to their strong affinity for adsorption onto solid phases however soil disturbance promotes erosion and overland flow during intense rainstorms here we investigate the event scale transport of disturbed as and pb contaminated soils through measurement of concentrations of as and pb in suspended sediment and changes in pb isotopic ratios in overland flow investigation of several rain events shows that where land disturbance has occurred physical transport of silt sized particles and aggregates is the primary transport vector of as and pb derived from pesticide contaminated soil although both as and pb are associated with similarly sized particles we find that solid phase as is more effectively mobilized and transported than pb our results demonstrate that anthropogenic land disturbance of historical lands contaminated with lead arsenate pesticides may redistribute through physical transport significant amounts of as and lesser amounts of pb to riparian and stream sediments where they are potentially more bioavailable

geologic framework and tectonic evolution in western victoria australia abstract the stawell zone is interpreted to be part of the eastern extension of the adelaide fold belt into victoria the cambro ordovician turbidite sequence of the stawell and glenelg zones rests on a pile of late proterozoic metavolcanic rocks rather than cambrian metavolcanic units that are characteristic of the lachlan fold belt early deformation events d 1 d 3 in the stawell zone pre date granite emplacement and were synchronous with regional fold forming events that accompany thrust movements along discrete detachment surfaces the thrust system follows a ne se trending strike with an e directed translation of the tectonic units the steep 60 predominantly w dipping thrusts represent high strain zones localised in relatively weak cambro ordovician quartz rich turbidites that are sandwiched along the boundaries of the late proterozoic metavolcanics overprinting the early thrust system are d 4 d 6 deformation events that include reverse strike slip and normal faults the grampians extensional basin overlying the late proterozoic to ordovician sequence records a significant change in the tectonic regime operating during the late silurian early devonian it has been subjected to a middle devonian compressional deformation event d 4 with the development of thrust and fold structures this deformation is also superimposed on the thrusted and folded d 1 to d 3 sequence to the east of the grampians half graben producing further thrusts a gradual change from a ne sw to a n s stress field produces oblique strike slip faults normal faults of probably early cretaceous age transect the entire sequence the proterozoic cambrian sequence has been affected by a low p high t mid greenschist facies regional metamorphic event peak metamorphic conditions have been inferred from metavolcanic rocks and mafic units derived from a strongly differentiated tholeiitic suite at stawell these have been calculated to be 1 7 0 7 2 kbar and 450 20 2 c the advective heat input necessary to create this low p high t metamorphic event is attributed to penetrative deformation and strain partitioning between the crust and the mantle lithosphere which in turn causes crustal thickening associated compression and the observed d 1 to d 3 structures on the surface

stepped fibres in sillimanite bearing veins valid shear sense indicators in high grade rocks abstract sillimanite bearing veins with striking lineated and stepped fibre surfaces occur in migmatitic amphibolite and granulite facies sillimanite bearing gneisses in the betic cordillera southern spain the quartz dominated and peraluminous leucogranite veins occupy brittle to semi brittle hydraulic fractures and shear fractures that cross cut the main foliation of the gneisses the shear sense suggested by fibre steps concurs with independent criteria where observed e g foliation deflection at vein margins petrographic study suggests that oriented quartz sillimanite fibres were formed during vein dilation and experienced later ductile and brittle strain with microboudinage and microfracturing of sillimanite aggregates perpendicular to the long axes of the fibres due to their pronounced anisotropy the geometry of the steps is thus controlled by the initial fibre orientations reflecting the original sense of shear during vein formation

the use of stream flow routing for direct channel precipitation with isotopically based hydrograph separations the role of new water in stormflow generation abstract understanding the pathways by which event water contributes to stream stormflow provides insight into stormflow generation mechanisms we analyze the impact of storm size on the relative contribution of event water to stormflow by using natural variations in the oxygen isotopic composition of precipitation and stream water to separate multiple stormflow hydrographs from a single fourth order 1212 ha catchment we extend previous isotope based hydrograph separations by independently accounting for the contribution of event water via direct channel precipitation to the stream hydrograph the direct channel precipitation contribution is determined using a numerical model of stream flow routing though the catchment taking precipitation and digital elevation data as input variables for the range of storm sizes sampled having recurrence intervals ranging from less than a week to 4 months essentially all the event water in stream stormflow can be attributed to direct channel precipitation event water not directly falling on the stream channel indirectly contributes to stormflow by increasing the subsurface discharge of pre event water to the stream neither the hydrograph separation data field observations during the precipitation events nor experimental observations of flow in a large scale natural soil column extracted from the watershed are consistent with macropore flow or groundwater ridging as the primary mechanism responsible for increasing subsurface discharge results from a series of artificial rain experiments using the unsaturated natural soil column are consistent with a preferential kinematic flow model and indicate that the discharge of pre event water to the stream during a storm event may be controlled by kinematic flow processes within the watershed soils

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

experimentally produced slickenside lineations in pyrophyllitic clay abstract during shearing of pyrophyllitic clay fault planes bearing slickenlines were generated on previously initiated c and c planes these slickenlines have excess lengths with respect to the measured slip displacement on the fault plane and are of the ridge in groove type with the hangingwall nesting into the footwall and vice versa these features cannot be explained in terms of either frictional asperity ploughing or dissolution reprecipitation but are produced during the development of a complex ductile shear zone that contains the fault plane this initial shear zone nucleates from localized shear bands that link up to form a throughgoing shear plane the nucleation and propagation of the fault post dates the formation of the shear plane and depends on the development of a zone of highly oriented layer silicates within the pyrophyllitic clay the fault is confined to this zone the lineations observed on the fault surfaces are produced while the material behaves plastically prior to the brittle faulting with increasing shear strain the brittle ductile transition is crossed and sliding continues under brittle conditions along the former shear zone

differences in trace metal concentrations among fluvial morphologic units and implications for sampling this study examines the segregation of trace metals within and between fluvial morphologic units in sand sized and finer bed sediments in a cobble bed stream the types of fluvial morphologic units sampled are low gradient riffles high gradient riffles glides eddy drop zones lateral scour pools attached bars and detached bars three to nine samples were collected from ten of each type of morphologic unit all 12 metals show significantly different concentrations between some morphologic units in sediments smaller than 2 mm eddy drop zones and attached bars consistently have the highest metal concentrations while low gradient riffles high gradient riffles and glides typically have the lowest concentrations metals showing the greatest between unit variability are al cr fe cu and ti followed by co mn and pb while mg mn v and zn display relatively few differences between units lateral and longitudinal variations of metals within units are not significant and there was no consistent predictable variation in metal concentrations with distance downstream results indicate that metal studies in other gravel and cobble bed streams should include a reconnaissance survey to determine variations between morphologic units stratify sampling by morphologic unit and analyze spatial autocorrelation to determine sample spacing

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

characterizing the ionospheric current pattern response to southward and northward imf turnings with dynamical supermag correlation networks we characterize the response of the quiet time no substorms or storms large scale ionospheric transient equivalent currents to north south and south north imf turnings by using a dynamical network of ground based magnetometers canonical correlation between all pairs of supermag magnetometer stations in the northern hemisphere magnetic latitude mlat 50 82 is used to establish the extent of near simultaneous magnetic response between regions of magnetic local time mlat parameters and maps that describe spatial temporal correlation are used to characterize the system and its response to the turnings aggregated over several hundred events we find that regions that experience large increases in correlation post turning coincide with typical locations of a two cell convection system and are influenced by the interplanetary magnetic field by the time between the turnings reaching the magnetopause and a network response is found to be 8 10 min and correlation in the dayside occurs 2 8 min before that in the nightside

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

timing of substorm signatures during the november 24 1996 geospace environment modeling event an excellent data set has been gathered for the november 24 1996 geospace environment modeling substorm interval that included an 95 min interval of strongly southward interplanetary magnetic field there were two expansion phase onsets and a pseudobreakup during this period for both onsets the classical signatures of onset in the auroral ionosphere ground magnetometer signatures of electrojet formation ground observations of pi2 pulsations and auroral brightening all occurred within less than a minute of each other indicating consistency between these onset indicators and giving reliable identification of onset times on the other hand low latitude positive bay observations that were most likely made near or within the longitude range of substorm onset did not provide accurate or consistent onset timing low latitude pi2s identified both onsets though one was delayed by l min from the auroral zone onset our most important and unexpected result is that particle injection at synchronous orbit was observed to initiate 2 5 min prior to both expansion onsets in the auroral ionosphere we suggest that the early detection of substorm onset at synchronous orbit was at least in part due to the unusually low latitude 63 magnetic of the auroral zone onsets which maps closer to synchronous orbit than usual onsets more often occur at somewhat higher latitudes which map to a few re beyond synchronous orbit as a result particle injections at synchronous orbit are generally delayed with respect to the time of current wedge initiation within the plasma sheet we do not currently know whether or not onset within the near earth plasma sheet generally occurs 2 5 min prior to expansion onset in the auroral ionosphere while we have no reason to believe that the timing we have observed is unique other studies of low latitude substorm onsets will be needed to ascertain the generality of this result

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

network analysis of geomagnetic substorms using the supermag database of ground based magnetometer stations the overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground based magnetometers this paper focuses on the quantitative characterization of substorm dynamics captured by ground based magnetometer stations we present the first analysis of substorms using dynamical networks obtained from the full available set of ground based magnetometer observations in the northern hemisphere the stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold dimensionless parameters can then be obtained that characterize the network and by extension the spatiotemporal dynamics of the substorm under observation we analyze four isolated substorm test cases as well as a steady magnetic convection smc event and a day in which no substorms occur these test case substorms are found to give a consistent characteristic network response at onset in terms of their spatial correlation such responses are differentiable from responses to the smc event and nonsubstorm times we present a method to optimize network parametrization with respect to the different individual station responses the spatial inhomogeneity of stations in the northern hemisphere and the choice of correlation window sizes our results suggest that dynamical network analysis has potential to quantitatively categorize substorms dimensionless parameters can then be obtained that characterise the network and by extension the spatio temporal dynamics of the substorm un der observation we analyse four isolated substorm test cases as well as a steady magnetic convection smc event and a day in which no substorms occur these test case substorms are found to give a consistent characteristic net work response at onset in terms of their spatial correlation such responses are differentiable from responses to the smc event and non substorm times we present a method to optimise network parametrisation with respect to the different individual station responses the spatial inhomogeneity of stations in the northern hemisphere and the choice of correlation window sizes our results suggest that dynamical network analysis has potential to quantitatively categorise substorms

motion of polar cap patches a statistical study with all sky airglow imager at resolute bay canada 1 a highly sensitive all sky airglow imager part of the optical mesosphere thermosphere imagers omtis has been operating for 3 years at resolute bay canada geographic latitude 74 7 n geomagnetic latitude 82 9 n since january 2005 one of its major applications is the observation of polar cap patches polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field imf conditions and they exhibit dynamic movement possibly in association with the changes in the imf orientation in order to determine how their motions are controlled by the upstream imf conditions we applied a motion tracking algorithm that was based on two dimensional cross correlation analysis to consecutive images obtained from january 2005 to december 2007 by the all sky airglow imager at resolute bay we identified and extracted 561 individual patches and then carried out a statistical study of their motion it is demonstrated that the speed of patches is primarily controlled by the imf bz furthermore the dawn dusk component of the patch drift velocities is well correlated with the imf by which is in good agreement with the published by dependence of the nightside polar cap convection this enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers

statistical maps of geomagnetic perturbations as a function of the interplanetary magnetic field 1 mappings of geomagnetic perturbations are shown for different combinations of the solar wind velocity interplanetary magnetic field imf and dipole tilt angle season average maps were derived separately for the northward eastward and vertical downward components of the geomagnetic disturbances using spherical cap harmonics in least error fits of sorted measurements the source data are obtained from 104 ground based magnetometer stations in the northern hemisphere at geomagnetic latitudes over 40 during the years 1998 through 2001 contour maps of statistical fits are shown along side scatter plots of individual measurements in corrected geomagnetic apex coordinates the patterns are consistent with previous mappings of ionospheric electric potential interestingly the vertical component of the magnetic perturbations closely resembles maps of the overhead field aligned currents including the northward imf configuration the maximum and minimum values from the statistical mappings are graphed to show their changes as a function of southward imf magnitude solar wind velocity and seasons it is expected that this work will lead to better advance predictions of the geomagnetic perturbations that are based on real time imf measurements

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

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

empirical high latitude electric field models electric field measurements from the dynamics explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn dusk ogo 6 measurements j p heppner 1977 the analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones paralleling the previous analysis the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the y component of the interplanetary magnetic field the objective which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns is met by deriving one pattern model bc for the northern hemisphere with a y interplanetary magnetic field imf and southern hemisphere with a y imf and two patterns models a and de for the northern hemisphere with a y imf and southern hemisphere with a y imf the most significant large scale revisions of the ogo 6 models are 1 on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the imf y component 2 on the nightside where a westward flow region poleward from the harang discontinuity appears under model bc conditions and 3 magnetic local time shifts in the positions of the convection cell foci the modeling above was followed by a detailed examination of cases where the imf z component was clearly positive northward neglecting the seasonally dependent cases where irregularities obscure pattern recognition the observations range from reasonable agreement with the new bc and de models to cases where different characteristics appeared primarily at dayside high latitudes the analysis of these differences for strong bz conditions using passes through different mlt zones led to finding that the deviations from both the bc and de models could be modeled by extending the evening cell foci toward and beyond noon with a deformation that roughly resembles a rotational twist of the extended evening cell the morning cell accommodation to the model bc deformation produces a narrow tongue of eastward convection near 75 invariant latitude on the dayside the model de deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 mlt sector in both cases the deformations of the two cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern thus the nightside dilemmas that plague three and four cell models designed to explain sunward convection in polar regions under bz conditions do not appear