ionospheric disturbances during the magnetic storm of 15 july 2000 role of the fountain effect and plasma bubbles for the formation of large equatorial plasma density depletions 1 we investigate the role of the fountain effect and plasma bubbles for the formation of the large equatorial plasma depletions during the geomagnetic storm of 15 july 2000 the large equatorial plasma depletions are detected in the atlantic sector on the night of the 15th by the defense meteorological satellite program dmsp f15 and the first republic of china satellite rocsat 1 the observations show discontinuous drop of the plasma density at the walls of the depletions flat plasma density inside the depletions and persistence or growth of the depletions over night these properties are not consistent with the trough morphology induced by the fountain effect the coincident ionospheric observations of dmsp f15 and rocsat 1 demonstrate that the large depletions are created in the longitude regions where plasma bubbles are present the occurrence of the large depletions after sunset elongation in the north south direction formation of steep walls and colocation with plasma bubbles at lower altitudes or earlier times suggest that the large depletions are closely associated with plasma bubbles

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

two components of ionospheric plasma structuring at midlatitudes observed during the large magnetic storm of october 30 2003 1 we consider vhf amplitude scintillations gps phase fluctuations ionosonde measurements maps of gps total electron content tec observations of daytime aurora and timed guvi images during the large magnetic storms of october 29 31 2003 and find two distinct classes of plasma processes that produce midlatitude ionospheric irregularities one is associated with auroral plasma processes the other with storm enhanced density sed gradients a part of which occur in close proximity to sub auroral polarization stream saps electric fields as discussed by j c foster et al 2002 we analyze in detail the storm event of october 30 2003 the saps associated plasma structures may occur by an ion temperature gradient convective instability m j keskinen et al 2004 but structuring by auroral processes requires elucidation

analysis of manning coefficient for small depth flows on vegetated beds the limitations of manning s formula are analysed when it is in extreme conditions and more specifically with small depth flows on natural vegetation beds a thorough analysis is made of research carried out on macro rough beds placing particular emphasis on vegetated beds research carried out to date on the roughness of vegetated beds and macro roughness is commented on including that carried out at the laboratory of hydraulics and hydrology of the forestry engineering faculty polytechnic university of madrid the work was done in two phases the first in a laboratory channel with artificial vegetation and the second in natural beds the results of the experimental research allow the development of a new approximate method of determining manning coefficient according to the froude number this method may be applied in extreme conditions both in small depths and steep slopes it was proved that the manning coefficient depends not only on roughness height but also on depth and slope values thus it is advisable to choose the appropriate method for its calculation copyright 2005 john wiley sons ltd

substantial advective iron loss diminishes phytoplankton production in the antarctic zone 1 after 1 decade of research it is a well established fact that iron limits photosynthetic co2 fixation and phytoplankton growth in the southern ocean intense blooms are scarce however the input of iron to the southern ocean is considerable an important factor for diminished phytoplankton production refers to the meridional circulation of the southern ocean intense spatially relatively homogeneous upwelling of upper circumpolar deep water ucdw causes a large iron flux into the surface layer however the main entrainment of upwelled ucdw into the surface layer occurs in autumn and winter which strongly restricts the usefullness of iron supply for phytoplankton due to unfavorable light conditions moreover the meridional transport within the ekman layer is intense enough to export at least 25 of the iron input away from the antarctic zone before it can be used by phytoplankton this also depresses the potential phytoplankton primary production by at least 25 most iron that crosses the polar front unused probably leaves the surface ocean north of the polar front because the surface water participates in antarctic intermediate water mode water formation

physical anatomy of fronts and surface waters in the acc near the 6 w meridian during austral spring 1992 small scale features of the antarctic circumpolar current acc along a meridional section at 6 w between the polar front and the acc weddell gyre boundary front are discussed using data collected during the austral spring cruise ant x 6 of r v polarstern organized within the framework of the european igbp jgofs southern ocean the section covered three distinct fronts namely the polar front the southern polar front also southern acc front and the acc weddell gyre boundary front physical measurements during repeated transects over a period of 6 weeks in october november revealed a large variability in the polar frontal region indicating meandering and eddy shedding the positions of the southern polar front and the acc weddell gyre boundary front were observed to be far more stable than that of the polar front a possible reconstruction of the meandering flow field near the polar front based upon the physical observations is presented details in the flow field coincide with the spatial distribution of a number of biological parameters such as phytoplankton biomass and species and photosynthetic pigments although a causal relationship between them is likely biomass enhancement cannot be understood simply in terms of macronutrients from deeper layers entering the euphotic zone as substantiated for other oceanic frontal regions because macronutrients do not limit phytoplankton blooms this process however can be important for the micronutrient iron evidence is presented that the antarctic zone of the acc can be subdivided into a number of spheres of influence related to the fronts interleaving of water is apparent between positions within such a region but not between the regions

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

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

the role of sex in the sedimentation of a marine diatom bloom a longitudinal transect in the atlantic sector of the southern ocean extending from the ice covered weddell sea across the antarctic circumpolar current and into the polar frontal zone was studied repeatedly during the austral spring the centric diatom corethron criophilum was found at most stations in variable numbers but in the polar frontal zone i encountered a large bloom undergoing a mass sexual phase this event apparently triggered downward transport of empty diatom cell walls in numbers that suggest the phenomenon is significant for the vertical silica flux and the formation of monospecific layers of this important diatom species in southern ocean sediments comparison of the cell wall dimensions of such a monospecific layer with those in the plankton in the sexual phase reveals a characteristic signature that may indicate the provenance of these layers

origin signature and palaeoclimatic influence of the antarctic circumpolar current the antarctic circumpolar current acc is today the strongest current in the world s ocean with a significant influence on global climate its assumed history and influence on palaeoclimate while almost certainly equally profound are here called into question in this paper we review 30 years of accumulated data interpretation and speculation about the acc deriving mainly from dsdp and odp drilling in the southern ocean for most of this time a conventional view of acc development signature and influence has held sway among palaeoceanographers and marine geologists in this view the acc began at about 34 ma close to the eocene oligocene boundary the time of onset of significant antarctic glaciation and the time of creation of a deep water gap tasmanian seaway between australia and antarctica as the south tasman rise separated from north victoria land this is the smoking gun of synchroneity the southern ocean sediment record shows a latest eocene development and subsequent geographic expansion of a siliceous biofacies its northern limit taken to indicate the palaeoposition of the acc axis in addition the acc was considered to have caused antarctic glaciation by isolating the continent within a cold water annulus reducing north south heat transport a different and later date for antarctic south american opening drake passage was proposed but the timing of acc onset there was disputed and the simple story survived recent developments however call it into question modern physical oceanography shows that all or most of present day acc transport is confined to narrow jets within deep reaching circumpolar fronts and numerical modelling has suggested that a steady reduction in greenhouse gas concentration through the cenozoic could cause antarctic glaciation with or without a contribution from ocean circulation change the rapidity of antarctic glacial onset at the eocene oligocene boundary and coeval creation of a deep water gap south of tasmania both survive but in light of the new information the presence of a siliceous biofacies cannot be claimed as evidence of the existence of a continuous deep reaching oceanic front and therefore of an acc and the possibility arises that cool and cold sea surface temperatures were effects of antarctic glaciation rather than evidence of a major contributor to its cause in considering future work we emphasise the importance of additional information from ancillary fields better definition of the necessary and sufficient properties of oceanic fronts additional determinations of cenozoic atmospheric pco2 and further developments in models of antarctic glaciation but also suggest the way forward in marine geology our knowledge of the development and palaeoclimatic significance of the acc will be best served by grainsize studies of bottom current strength at selected locations and geochemical or mineralogical studies of clays and ird as a way of examining provenance and therefore surface and bottom current directions and the existence of interocean connections

the propagation of traveling atmospheric disturbances observed during the april 6 7 2000 ionospheric storm 1 the great magnetic storm of april 6 7 2000 generated ionospheric disturbances in the west pacific region two ionosondes at wuhan 30 6degreesn 114 4degreese and chung li 24 9degreesn 121 e observed the ionosphere during this period the variations of the ionospheric parameters nmf 2 plasma density of the f peak hmf 2 height of the f peak and h f minimum virtual height of the f layer show that a traveling atmospheric disturbance tad affects the ionosphere at middle and low latitudes in this region the propagation velocities deduced from the time delay of hmf 2 and h f recorded at the two stations are about 655 and 164 m s respectively furthermore a method of deriving the vertical phase and group velocities is applied to the sequences of virtual heights at fixed sounding frequencies the vertical and associated meridional velocities demonstrate that the upward motions of the ionospheric plasma are caused by a tad

response of the equatorial ionosphere in the indian midnight sector to the severe magnetic storm of july 15 2000 1 during the severe magnetic storm of july 15 2000 an impulsive and remarkably large downward movement of f region occurred simultaneously at locations throughout the equatorial region dip 0 3 20 n in the indian sector in close association with episodes of rapid ring current intensification the abnormal midnight descent of equatorial f region maximum amplitude close to the magnetic equator 215 km hr indicative of a short lived westward electric field disturbance peak amplitude 4 6 mv m is interpreted as the signature of prompt penetration electric fields associated primarily with impulsive ring current injections the westward electric field disturbance in the indian midnight sector occurred near simultaneous with the eastward electric field disturbances in the dusk sector reported by basu et al 2001a moreover the prompt electric field penetration to the magnetic equator both in the dusk and midnight sectors occurred in an environment already under the influence of ionospheric disturbance dynamo idd electric fields illustrating the profound manner in which the equatorial f region plasma dynamics can get modified globally during the main phase of severe magnetic storms

unusual early morning development of the equatorial anomaly in the brazilian sector during the halloween magnetic storm 1 the solar events that occurred at the end of october 2003 gave rise to very strong geomagnetic disturbances that peaked twice with dst values reaching 345 nt around 0000 ut on 30 october and 400 nt around 2300 ut on the same day disturbances in several ionospheric parameters were observed over brazil this work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 october the f layer peak height over the equator first decreased under the strong prompt penetration westward electric field which was followed by significant height increase under eastward electric field we have used sheffield university plasmasphere ionosphere model supim with an intensified westward disturbed electric field in the presunrise hours presumably due to prompt penetration from the magnetosphere in order to study the effect of such a field in the ionosphere the simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial f layer height decreases the intensification of the equatorial ionization anomaly and the unusual enhancement on f layer peak density which was not modeled by the supim are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional transequatorial wind system as inferred from the f2 layer peak height variations the highly dynamic wind pattern with a short term response 2 4 hours is compatible with the predictions of some previous theoretical model calculations reported in the literature

spatial and temporal distribution of assemblages of the diatom corethron criophilum in the polar frontal region of the south atlantic morphometric data in the form of frequency distributions of valve widths transapical measurements of the diatom corethron criophilum have been plotted for stations between 50 and 47 s on transects 5 11 and 12 of cruise ant x 6 to the atlantic sector of the southern ocean the profiles largely confirm the picture of sharp differences between the waters as revealed by hydrological pigment and other biological data the assemblages to the north which lie in the southern part of the polar frontal zone water are more congruent with those in water to the south that is presumed to have eddied off the pfz water than with interlaying antarctic circumpolar current water the profiles also show how assemblages of this species can be recognised over space and time furthermore they reveal how a sexual event in the life cycle can lead to a rapid change in the character of the assemblage due to rapid loss of gametangial cell walls from the water column

biogeochemical dynamics and the silicon cycle in the atlantic sector of the southern ocean during austral spring 1992 high biogenic silica bsi concentrations maximum 11 7 moll 1 were recorded during late november at the southern border of the polar frontal region pfr position of the bsi maximum at depth suggested the occurrence of a sinking diatom population by contrast siliceous biomass was low bsi 0 6 mol l 1 in the marginal ice zone miz despite a sea ice retreat of 200 km during the study period diatoms released from the receding ice were not actively growing the permanently open ocean zone also showed very low bsi biomass 0 5 mol l 1 and appeared as an area where phytoplankton are not dominated by siliceous organisms especially in its middle part where bsi poc particulate organic carbon molar ratios ranged between 0 04 and 0 06 at 53 s from surface to 200 m depth at the southern border of the pfz the bloom coincided with an area of high lithogenic silica concentrations probably of aeolian origin in addition bsi poc molar ratios measured in the pfz were the highest ever recorded in the surface waters of the southern ocean maximum 1 75 this could be due to the presence of heavily silicified diatoms such as fragilariopsis kerguelensis or also could reflect the more rapid recycling of poc as compared to bsi within the bloom area bsi concentrations were positively correlated to pyrophaeophytin pigments possibly indicating the occurrence of a senescent diatom population high concentrations of bsi 1 5 mol si 1 1 extended to 200 m between 49 s and 51 s numerous empty frustules also were observed suggesting significant sedimentation of siliceous particles between 49 s and 51 s estimates of the bsi production of the polar frontal region are derived from 14c primary production and appropriate bsi poc ratios and implications for the total annual production of bsi for the southern ocean are discussed

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

variations in the low and middle latitude topside ion concentration observed by dmsp during superstorm events 1 observations of the topside ion number density by the dmsp satellites on the dayside near 0930 lt and near dusk describe a characteristic evolution during the course of three superstorm events in november 2001 november 2003 and november 2004 density enhancements at middle latitudes and at the equator may be identified as separate features that may appear together but can evolve independently these characteristics are consistent with the action of both upward outward e b drifts and equatorward neutral winds and it is suggested that both f region drivers are required to reproduce the observed behavior on these occasions upward excursions of the e b drift at the equator may be short lived compared to the satellite orbit period of about 100 min but may also exist for longer periods under the influence of penetration fields and modified dynamo fields upward drifts at middle latitudes may be induced by meridional winds and by the high latitude convection pattern as it expands to latitudes as low as 40 degrees magnetic

ionospheric response to 22 23 june 2015 storm as investigated using ground based ionosondes and gps receivers over india in this paper we present response of equatorial and low latitude ionosphere to 22 23 june 2015 geomagnetic storm using a chain of ground based ionosondes located at tirunelveli 8 73 n 77 70 e geomagnetic latitude 0 32 n hyderabad 17 36 n 78 47 e geomagnetic latitude 8 76 n and allahabad 25 45 n 81 85 e geomagnetic latitude 16 5 n along with a chain of gps receivers uniqueness of this storm is that in contrast to the equatorial plasma bubbles that were detected in the european sector we see suppression of plasma bubbles in the indian sector the observations suggest that westward penetration electric field during local midnight caused abrupt decrease of virtual height h f km to 200 km and suppressed plasma bubbles due to undershielding later the layer increased to 500 km simultaneously due to overshielding effect on 23 june we observed negative storm in the northern hemisphere while positive storm in the southern hemisphere in addition absence of equatorial es layers at tirunelveli and presence of f3 layer at tirunelveli hyderabad seem to be associated with equatorial electrojet eej counter electrojet cej variations however on 24 june we observed strong negative storm effects at allahabad hyderabad while positive storm effect at tirunelveli simultaneous enhancement of h f km at all three ionosonde stations at 20 30 ut on 23 june during recovery phase suggest eastward disturbance dynamo dd electric field that caused presunrise spread f at hyderabad allahabad but void of spread f at tirunelveli suggesting its midlatitude origin periodogram analysis of fof2 and h f km in the present analysis suggest the presence of shorter periods 2 h associated with dd electric field winds

dynamic response of ionospheric plasma density to the geomagnetic storm of 22 23 june 2015 on 21 22 june 2015 three consecutive interplanetary shocks slammed into the earth s magnetosphere immediately after the third shock at 18 36 ut on 22 june marked by an exceptional sudden storm commencement with an amplitude of delta sym h similar to 106 nt a major geomagnetic storm commenced in the present study a multi instrument approach comprising observations data analysis and modeling is used to examine the global ionospheric response results show that enhanced storm time processes produced major total electron content tec variations at different latitudes longitudes and phases of the storm a closer inspection of the tec observations reveals strong longitudinal and hemispherical asymmetry in addition multiple equatorward and poleward propagating traveling ionospheric disturbances tids were detected in the tec data equatorward propagating tids are consistent with vertical neutral winds simulated from thermosphere ionosphere electrodynamics general circulation model however poleward tids were not reproduced in the model we find that a combination of driving processes including enhanced high latitude injection prompt penetration electric fields disturbance dynamo effect neutral winds and composition changes were acting at different stages of the storm

estimation of gravel bed river flow resistance numerous formulations have been proposed linking friction factors to the gravel bed river downstream hydraulic geometry data from 280 rivers show that existing gravel bed power and semilogarithmic formulations fail to correctly predict the friction factors a new gravel bed semilogarithmic formulation is developed using nonlinear statistical tools it considers the influence of the relative roughness the froude number the sediment mobility parameter and a cross sectional form factor the best fit is achieved by modifying the adjustment parameter and the interior of the logarithmic term of the universal velocity distribution equation

ecology and biogeochemistry of the antarctic circumpolar current during austral spring a summary of southern ocean jgofs cruise ant x 6 of r v polarstern the r v polarstern cruise ant x 6 part of the international southern ocean jgofs programme investigated phytoplankton spring bloom development and its biogeochemical effects in different water masses of the atlantic sector of the southern ocean the polar frontal region pfr the southern antarctic circumpolar current zone sacc its boundary with the weddell gyre awb and the marginal ice zone miz the relative roles of physical stability iron limitation and grazing pressure in enhancing or constraining phytoplankton biomass accumulation were examined three sections were carried out between the pfr and the ice edge along the 6 w meridian from early october to late november 1992 this paper summarises the major findings of the cruise and discusses their implications for our understanding of southern ocean ecology and biogeochemistry a major finding was the negligible build up of plankton biomass and concomitant absence of co2 drawdown associated with seasonal retreat of the ice cover in striking contrast to this unexpected poverty of both the miz and the frontal region of the awb distinct phytoplankton blooms dominated by different diatom species accumulated in the pfr chlorophyll stocks in the sacc remained monotonously low throughout the study our findings confirm those of other studies that frontal regions are the major productive sites in the southern ocean and that input of meltwater and associated ice algae to the surface layer from a retreating ice edge is by itself an insufficient condition for induction of phytoplankton blooms the blooms in the pfr developed under conditions of shallow mixing layers high iron concentrations and relatively low grazing pressure however in all three blooms high biomass extended to deeper than 70 m which cannot be explained by either in situ growth or sinking out of a part of the population from the upper euphotic zone subduction of adjoining shallower layers to explain depth distribution is invoked despite a clear co2 drawdown in the polar frontal region the highly variable conditions encountered render reliable estimation of annual co2 fluxes in the southern ocean difficult

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

low latitude ionospheric thermospheric response to storm time electrodynamical coupling between high and low latitudes 1 using multi instrumental and multistation data we present low latitude ionospheric thermospheric behavior during the geomagnetic storm of 15 may 2005 the diurnal pattern of total electron content tec at a chain of equatorial to low latitude stations shows strong positive ionospheric storm on 15 may latitudinal variation of tec shows development of strong equatorial ionization anomaly eia on the same day evidence in terms of equatorial electrojet eej and magnetogram signatures is presented for the prompt penetration of interplanetary electric field ief as the cause of the positive ionospheric storm consequent to the storm time circulation resulting from the extra energy deposition via joule heating over high latitudes compositional changes occur in the global thermosphere tec enhancements on 16 may are attributed to enhancement of atomic oxygen at equatorial and low latitudes and the negative ionospheric storm on 17 may observed beyond certain low latitudes is explained in terms of enhancement of molecular species because of the storm time neutral composition changes strong esf plume structures on range time intensity rti map and l band scintillation and tec depletions in gps measurements are observed in the longitude sectors where the local time of sudden storm commencement ssc falls after the post sunset hours the ionospheric zonal electric fields are altered by the combined effects of eastward disturbance dynamo electric fields and direct prompt penetration of eastward electric fields associated with the northward turning of interplanetary magnetic field imf bz leading to subsequent development of esf after midnight

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

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

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

a biogeochemical study in the bellingshausen sea overview of the sterna 1992 expedition abstract a general overview and background of a two ship study to examine biogeochemical fluxes in the marginal ice zone of the bellingshausen sea 65 70 s 80 87 w se pacific sector of the southern ocean is presented the major feature studied was an intense band of chlorophyll that was found geographically close to a receding ice edge however the bloom appeared not to be a result of a shallow mixed layer caused by ice melt stabilisation but rather associated with an oceanic front that coincided with the ice edge details of the hydrographic conditions existing along the 85 w meridian from the ice edge to open water to the north and detailed surveys of surface hydrographic conditions are presented

effects of prolonged southward interplanetary magnetic field on low latitude ionospheric electron density the present work describes the low latitude ionospheric variability during an unusually prolonged 33 h geomagnetically disturbed condition that prevailed during 15 16 july 2012 the low latitude electron density in summer hemisphere investigated using ground and satellite based observations responded to this by generating strong negative ionospheric storm on 16 july the maximum electron density on 16 july over indian low latitudes was reduced by more than 50 compared to that on a geomagnetically quiet day 14 july 2012 in contrast to the extreme reduction in total electron content tec in the northern hemisphere tec from a winter hemispheric station revealed substantial 23 total electron content unit 1 tecu 1016 el m 2 enhancements on the same day this contrasting hemispherical response in tec is suggested to be due to the combined effects of strong interhemispheric and solar driven day night winds further very weak equatorial electrojet eej strength on 16 july indicated that the westward electric field perturbations in the low latitude ionosphere were possibly due to the disturbance dynamo effect associated with meridional circulation from polar to equatorial latitudes interestingly despite reduction in the integrated eej strength on 15 july the low latitude electron density showed substantial enhancement highlighting the significant effect of the positive ionospheric storm on the low latitude ionosphere the roles of electrodynamical neutral dynamical and compositional disturbances are discussed in view of these observations to understand low latitude ionospheric response when geomagnetic disturbance persists for longer duration

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

magnetic declination control of the equatorial f region dynamo electric field development and spread f we have carried out a comparative study of the evening prereversal enhancements in the equatorial f region vertical ionization drift velocities vz over fortaleza 4 s 38 w brazil and jicamarca 12 s 77 w peru two magnetic equatorial stations in the american zone the results show profound dissimilarities in the seasonal trends in the times and widths of the vz prereversal peak which reflect in the spread f characteristics as well at the two stations the dissimilarities are shown to be arising mainly from the difference in the magnetic field declination angles that causes differences in the conjugate e region sunset durations and hence in the f region polarization electric field development rates at the two stations

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

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

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

ionospheric storm of early november 1993 in the indian equatorial region an investigation is made of the response of equatorial ionosphere in the indian 75 e sector to the major magnetic storm of november 3 1993 using data from the ionosonde and magnetometer networks spanning the region 0 3 34 5 n dip some outstanding and new aspects of the storm time ionospheric behaviour are revealed an anomalous and striking positive gradient in 0f2 from the magnetic equator to 34 5 dip developed under counter electrojet cej condition in the morning on november 4 corresponding to the early stage of the storm main phase this storm effect is attributed to plasma transport by a poleward surge in transequatorial winds due to large scale atmospheric gravity waves agws launched by auroral heating remarkable wave like variations in hpf2 and 0f2 immediately followed at locations away from dip equator till local sunset with concomitant disruptions in the development of the equatorial ionization anomaly eia rapid variations in meridional neutral winds due to large scale agws are assessed as the cause of the oscillations in hpf2 and the associated cyclic sequence of development and inhibition of eia as the outcome of the combined effects of plasma transport due to meridional winds and the plasma fountain driven by e b drift just after the onset of the storm recovery phase at 1800 lt a sudden and anomalous drop 54 57 in 0f2 prevailed throughout the anomaly region over the interval 1915 2330 lt with an apparent time delay in occurrence toward the magnetic equator this premidnight collapse of equatorial f region is interpreted in terms of horizontal transport of plasma across the equator toward the opposite hemisphere by an equatorward surge in meridional winds the case study showed that besides disturbances in the zonal electric field due to prompt penetration and ionospheric disturbance dynamo effects perturbations in neutral meridional winds played a prominent role in the ionospheric storm of november 4 1993 in the indian equatorial region

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

onset conditions of equatorial range spread f at fortaleza brazil during the june solstice case studies are made of the ionospheric thermospheric and geomagnetic conditions associated with the occasional onset of range spread f at fortaleza 4 s 38 w dip latitude 1 8 and magnetic declination 21 w brazil in the june solstice a season in which frequency spread f is typically seen in the postsunset hours after 2000 lt it is found that the f layer experiences quite consistently a large vertical drift early in the evening hours 1815 1915 lt on days of range spread f in comparison to days of only frequency spread f the anomalously large dusk time vertical plasma drift occurs under both geomagnetically disturbed and quiet conditions there is no significant change in the pattern of meridional neutral winds at and prior to the time of onset of range spread f estimated from the data of f layer peak height hmax at the low latitude station cachoeira paulista 23 s 45 w and dip 26 5 s using a modified form of the servo model the results strongly suggest that though the meridional poleward wind is very effective in inhibiting the growth of rayleigh taylor r t instability and hence range spread f at fortaleza during the june solstice as shown by maruyama 1996 its variability does not play an important role in creating favorable conditions for r t instability on a day to day basis the prerequisite for the occasional occurrence of range spread f at fortaleza in the june solstice seems to be the presence of an impulsive and large f layer vertical plasma drift a condition favorable for destabilizing the bottomside f region through r t instability mechanism because of the high altitude of the layer

reply to comment on jarvela j and aberle j 2005 analysis of manning coefficient for small depth flows on vegetated beds hydrological processes 19 19 3221 3223

low latitude ionosphere response to super geomagnetic storm of 17 18 march 2015 results from a chain of ground based observations over indian sector in this paper we present unique results of equatorial and low latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17 18 march 2015 where dst reached its minimum of 228 nt here we utilized data from magnetometers chain of ionosondes located at tirunelveli 8 73 n 77 70 e geometry 0 32 n hyderabad 17 36 n 78 47 e geometry 8 76 n and allahabad 25 45 n 81 85 e geometry 16 5 n along with multistation gps receivers over indian sector the observations showed a remarkable increase of h f to as high as 560 km over tirunelveli magnetic equator with vertical drift of 70 m s at 13 30 ut due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre reversal enhancement pre and caused intense equatorial spread f irregularities in ionosondes and scintillations in gps receivers at wide latitudes plasma irregularities are so intense that their signatures are seen in allahabad lucknow storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of 2 h suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase in addition noteworthy observations are nighttime westward zonal drifts and pre related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase

day to day variability of the equatorial ionization anomaly and scintillations at dusk observed by guvi and modeling by sami3 1 the day to day variability in ionospheric irregularity generation giving rise to equatorial scintillation has remained an unresolved issue over many decades we take a fresh look at the problem utilizing the global imagery provided by the global ultraviolet imager guvi instrument on nasa s thermosphere ionosphere mesosphere energetics and dynamics satellite guvi has been acquiring images of 135 6 nm emission in the earth s ionosphere thermosphere system since 2001 these guvi disk images at dusk have been used to identify cases where the equatorial ionization anomaly eia crests lie near the magnetic equator over a relatively narrow longitude range so that the anomaly looks collapsed a 16 month period of guvi data collected during evening at solar maximum is used to study the morphology of these so called collapses since the eia collapse is shown to be linked to the suppression of equatorial plasma bubbles and scintillations in particular we look at the june solstice during which the atlantic and pacific show very different climatology and eia collapses are most frequent in the guvi data on the other hand eia collapses are a relatively rare occurrence during the equinox period when scintillations are most prevalent globally we obtained a few dramatic examples of day to day variability in eia behavior and scintillations over india the sami3 is also a model of the ionosphere sami3 model was used to investigate the conditions during the evening collapse of the anomaly in the indian longitude sector where measurements of total electron content tec and scintillations and estimates of the daytime vertical drifts and those at dusk were available results from sami3 show that the observed collapse of the anomaly at dusk can be simulated by a reversal of the upward vertical drift in midafternoon in agreement with the drift estimates from magnetometer observations such reversed vertical drifts at this time of the day are generally seen during counterelectrojet events introduction of neutral winds into sami3 better approximates the dusk behavior of tec at low latitude stations in india this study reveals that the longitudinally confined eia collapse may explain some of the differences in day to day variability of scintillations at different locations around the globe

meridional circulation across the antarctic circumpolar current serves as a double 231pa and 230th trap abstract upwelling of circumpolar deep water in the weddell gyre and low scavenging rates south of the antarctic circumpolar current acc cause an accumulation of particle reactive nuclides in the weddell gyre a ventilation reversible scavenging model that successfully described the accumulation of 230th in this area was tested with other particle reactive nuclides and failed to adequately describe the depth distributions of 231pa and 210pb we present here a modified model that includes a nutrient like accumulation south of the antarctic polar front in an upper meridional circulation cell as well as transport to a deep circulation cell in the weddell gyre by scavenging and subsequent release at depth the model also explains depletion of 231pa and 230th in weddell sea bottom water wsbw by ventilation of newly formed deep water on a timescale of 10 years but this water mass is too dense to leave the weddell gyre in order to quantify the processes responsible for the 231pa and 230th composition of newly formed antarctic bottom water aabw we present a mass balance of 231pa and 230th in the atlantic sector of the southern ocean based on new data from the geotraces program the acc receives 6 0 1 5 10 6 dpm s 1 of 230th from the weddell sea similar in magnitude to the net input of 4 2 3 0 10 6 dpm s 1 from the north for 231pa the relative contribution from the weddell sea is much smaller only 0 3 0 1 10 6 compared to 2 7 1 4 10 6 dpm s 1 from the north weddell sea deep water wsdw leaving the weddell gyre northward to form aabw is exposed in the acc to resuspended opal rich sediments that act as efficient scavengers with a th pa fractionation factor f 1 hydrothermal inputs may provide additional removal with low f scavenging in the full meridional circulation across the opal rich acc thus acts as a double 231pa and 230th trap that preconditions newly formed aabw