gps and glonass observations of large scale traveling ionospheric disturbances during the 2015 st patrick s day storm using a comprehensive database of 5300 ground based gnss stations we have investigated large scale traveling ionospheric disturbances lstids during 17 18 march 2015 st patrick s day storm for the first time the high resolution two dimensional maps of the total electron content tec perturbation were made using not only gps but also glonass measurements several lstids originated from the auroral regions in the northern and southern hemispheres were observed simultaneously over europe north america and south america this storm is considered as a two step main phase storm during the first main phase lstids propagated over the whole daytime european region and over high latitudes of north america during the second main phase we report 1 intense lstids propagated equatorward in north america and europe 2 convergence of several lstids originated from the opposite hemispheres in the interference zone over geomagnetic equator in south america 3 super lstids with the wavefront length of more than 10000 km observed simultaneously in north america and europe lstids observed in three sectors had wavelength of 1200 2500 km and wave periods of 50 80 min during the recovery phase on the background of the negative ionospheric storm developed over north america we detect signatures of the stream like structures alongated within the latitudinal range of 29 n 42 n across the usa these structures persisted through the nighttime to the early morning from 04 ut till 13 ut on 18 march 2015 and they were associated with the subauroral polarization streams saps induced nighttime ionospheric flows

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

gps phase scintillation at high latitudes during the geomagnetic storm of 17 18 march 2015 the geomagnetic storm of 17 18 march 2015 was caused by the impacts of a coronal mass ejection and a high speed plasma stream from a coronal hole the high latitude ionosphere dynamics is studied using arrays of ground based instruments including gps receivers hf radars ionosondes riometers and magnetometers the phase scintillation index is computed for signals sampled at a rate of up to 100 hz by specialized gps scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic quality gps data sampled at 1 hz in the context of solar wind coupling to the magnetosphere ionosphere system it is shown that gps phase scintillation is primarily enhanced in the cusp the tongue of ionization that is broken into patches drawn into the polar cap from the dayside storm enhanced plasma density and in the auroral oval in this paper we examine the relation between the scintillation and auroral electrojet currents observed by arrays of ground based magnetometers as well as energetic particle precipitation observed by the dmsp satellites equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique that has been applied over the ground magnetometer networks in north america and north europe the gps phase scintillation is mapped to the poleward side of strong westward electrojet and to the edge of the eastward electrojet region also the scintillation was generally collocated with fluxes of energetic electron precipitation observed by dmsp satellites with the exception of a period of pulsating aurora when only very weak currents were observed

middle and low latitude ionosphere response to 2015 st patrick s day geomagnetic storm this paper presents a study of the st patrick s day storm of 2015 with its ionospheric response at middle and low latitudes the effects of the storm in each longitudinal sector asian african american and pacific are characterized using global and regional electron content at the beginning of the storm one or two ionospheric positive storm effects are observed depending on the longitudinal zones after the main phase of the storm a strong decrease in ionization is observed at all longitudes lasting several days the american region exhibits the most remarkable increase in vertical total electron content vtec while in the asian sector the largest decrease in vtec is observed at low latitudes using spectral analysis we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field ppef and of the disturbance dynamo electric field ddef on the basis of ground magnetic data concerning the ppef earth s magnetic field oscillations occur simultaneously in the asian african and american sectors during southward magnetization of the b z component of the interplanetary magnetic field concerning the ddef diurnal magnetic oscillations in the horizontal component h of the earth s magnetic field exhibit a behavior that is opposed to the regular one these diurnal oscillations are recognized to last several days in all longitudinal sectors the observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models

solar heating of a stratified ocean in the presence of a static ice cover conductivity temperature and depth measurements were carried out in an isolated transverse lead in static shorefast ice in mould bay prince patrick island northwest territories during a 3 week period at the height of the melt season currents beneath the ice appeared to be weak and largely tidal in nature initially the water was vertically uniform and at the salinity determined freezing point down to a depth of at least 20 m by the end of the experiment the water column consisted of three distinct layers a well mixed nearly fresh surface meltwater layer a very stable half meter thick halocline centered somewhat below the bottom of the ice and a thermally stratified layer of constant salinity extending down to at least 25 m the halocline was characterized by a temperature maximum that was about 2 c warmer than the surrounding water this temperature maximum in the pycnocline effectively trapped shortwave energy absorbed in the lower layer and prevented it from melting the overlying ice theoretical calculations demonstrate that the thermal structure observed beneath the pycnocline was controlled by the input of shortwave radiation and that vertical heat transport was largely the result of diffusive processes the presence of leads drastically increases the amount of energy stored in the water in regions where leads are common it is likely that this energy will significantly accelerate the decay and removal of the ice once it becomes mobile and once the pycnocline is erased

theoretical estimates of light reflection and transmission by spatially complex and temporally varying sea ice covers the reflection absorption and transmission of light at visible and near infrared wavelengths by snow and ice covers is important for a number of geophysical problems the focus of this paper is on the reflection and transmission of light by spatially inhomogeneous and temporally varying sea ice covers this is investigated using a two stream multilayer radiative transfer model in the wavelength region from 400 to 1000 nm the model is computationally simple and utilizes the available experimental data on the optical properties of sea ice the ice cover is characterized as a layered medium composed of selections from nine distinct snow and ice types three case studies are presented illustrating values of spectral albedo transmittance and transmitted photosynthetically active radiation par for 1 a spatially inhomogeneous ice cover 2 a uniform ice cover as it undergoes a melt cycle and 3 a temporally changing spatially variable ice cover results indicate that small scale horizontal variations in snow depth and ice thickness can cause light transmission to change over 3 orders of magnitude dramatic changes in light reflection and transmission are predicted in the early part of the melt season as the ice cover evolves from an opaque snow covered medium to translucent bare or ponded ice

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

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

seasonality of southern ocean sea ice the sea ice cover of the southern ocean undergoes a rapid decrease from mid november to mid january the atmosphere to ocean heat flux is insufficient to account for this melting even in the presence of the high percentage of open water characteristic of the southern ocean sea ice it is estimated that sea air heat exchange in the 60 to 70 s zone can account for roughly 50 of the required spring heating the remainder must be supplied by the relatively warm deep water residing below the southern ocean pycnocline deep to surface water heat flux is accomplished by upwelling of the pycnocline due to the regional ekman divergence of the surface layer and by cross pycnocline mixing it is estimated that the required vertical mixing coefficient for the pycnocline is 1 5 cm2 s this value is considered as realistic in view of the relatively weak pycnocline which is a consequence of low levels of fresh water input to the surface layer it is suggested that the magnitude of fresh water input is a major factor in determining the degree of seasonality of southern ocean sea ice

equatorial broad plasma depletions associated with the evening prereversal enhancement and plasma bubbles during the 17 march 2015 storm broad plasma depletions bpds in the equatorial f region represent plasma depletions whose longitudinal and latitudinal scales are much greater than those of normal plasma bubbles this study investigates the characteristics and origin of bpds using the coincident ionospheric observations by the communication navigation outage forecasting system defense meteorological satellite program and swarm satellites during the 2015 st patrick s day 17 march storm two types of bpds were detected before midnight during the main phase of the storm one type of bpds showed a gradual plasma density variation type 1 and the other type of bpds showed a steep density gradient type 2 at the walls of bpds the type 1 bpds were detected with no signature of plasma bubbles nearby whereas the type 2 bpds were accompanied by bubbles the formation of the type 1 bpds is attributed to the uplift of the bottomside of the f region above the satellite altitude by the action of storm induced electric fields the steep walls of type 2 bpds are associated with the ionospheric uplift and the spatial discontinuity of the ionosphere produced by bubbles the detection of bpds that are more than 15 wide in latitude by the polar orbit swarm satellites arises from the elongation of bubbles along the magnetic field lines and the alignment of the elongation with the plane of the orbit

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

observations of ion neutral coupling associated with strong electrodynamic disturbances during the 2015 st patrick s day storm we use incoherent scatter radar observations at millstone hill mho and arecibo ao and topside ionosphere in situ dmsp observations during the great geomagnetic storm on 17 18 march 2015 to conduct a focused study on ion neutral coupling and storm time ionosphere and thermosphere dynamics some of these observations were made around the time of large ionospheric drifts within a sub auroral polarization stream saps during the storm main phase we identify multiple disturbance characteristics in the north american late afternoon and dusk sector 1 strong sub auroral westward drifts occurred between 20 24 ut near mho accompanied by a storm enhanced density plume passage over mho in the afternoon with a poleward upward ion drift the strongly westward flow reached 2000 m s speed near the poleward plume edge 2 prompt penetration electric field signatures appearing as poleward upward ion drifts on the dayside over both mho and ao were consistent with dmsp vertical drift data and contributed to plume development 3 meridional wind equatorward surges occurred during daytime hours at mho followed by 2 3 hr period oscillations at both mho and ao the zonal electric field at ao was strongly correlated with the wind oscillation 4 large ion temperature enhancements as well as 50 m s upward ion drifts throughout the e and f regions were observed during the saps period these were presumably caused by strong frictional heating due to large plasma drifts the heating effects appeared to drive significant atmospheric upwelling and corresponding ion upflow was also observed briefly this study highlights some of the important effects of fast plasma transport as well as other disturbance dynamics on ion neutral coupling during a single intensification period within a great geomagnetic storm

disposition of solar radiation in sea ice and the upper ocean a one dimensional sea ice model with an ice thickness distribution is presented to examine the disposition of the incoming surface shortwave radiation within the sea ice and the upper ocean the sea ice model consists of 15 different ice thickness categories and an open water leads category ice growth melting on horizontal and vertical surfaces meltwater pond growth and drainage and snow accumulation evolve independently for each of the ice categories leads melt ponds and thinner ice categories are of particular interest as these features account for nearly all of the solar energy that is transmitted into the upper ocean beneath the ice pack also examined is the surface reflection and absorption internal ice absorption and lateral melting for ponded and pond free ice area averaged results show that 69 of the total annual solar energy is reflected 15 is absorbed by the snow cover 12 is absorbed by the ice and 4 is transmitted to the ocean mixed layer through thin ice and leads

seasonal and longitudinal dependence of equatorial disturbance vertical plasma drifts 1 we used equatorial measurements from the rocsat 1 satellite to determine the seasonal and longitudinal dependent equatorial f region disturbance vertical plasma drifts following sudden increases in geomagnetic activity the prompt penetration vertical drifts are upward during the day and downward at night and have strong local time dependence at all seasons the largest prompt penetration drifts near dusk and dawn occur during june solstice the daytime disturbance dynamo drifts are small at all seasons they are downward near dusk with largest smallest values during equinox june solstice the nighttime drifts are upward with the largest magnitudes in the postmidnight sector during december solstice during equinox the downward disturbance dynamo drifts near sunset are largest in the eastern hemisphere while the late night upward drifts are largest in the western hemisphere the longitudinal dependence of the disturbance dynamo drifts is in good agreement with results from simulation studies

responses in the polar and equatorial ionosphere to the march 2015 st patrick day storm the st patrick day storm of 2015 17 march 2015 occurred at a unique time when there were multiple spacecraft observing the earth s ionosphere between 350 and 885 km observations of the plasma flows and densities from the five operational polar orbiting dmsp spacecraft combined with those from the equatorial orbiting c nofs spacecraft provided a comprehensive global record of the both the polar and equatorial ionosphere regions responses to the storm this paper presents an overview of the data from this suite of spacecraft focusing on the following aspects 1 the polar cap ionosphere s reaction to the storm 2 the change in the penetration electric field in the midlatitude region as a function of time and the solar local time during the storm 3 the equatorial ionosphere s response of the meridional vertical flows to the penetration electric field and the disturbance dynamo during the storm and 4 the creation of a predawn ionospheric bubble system near the equator during the storm s main phase that was observed at low altitudes by c nofs and later at high altitudes by several dmsp examining these phenomenon enable us to trace the dynamic flow of energy from the solar wind input in the polar ionosphere all the way to the equatorial ionosphere

observations of polar ice from the holocene and the glacial period using the scanning electron microscope samples taken from the dome c ice core antarctica and the grip ice core greenland are examined using the scanning electron microscope to determine their microstructure in both cores samples are taken from two differing climatic periods the holocene and the last glacial period many of the usual features observed in similar samples under the light microscope are observed including bubbles grain boundaries and clathrate hydrates features not resolvable using the light microscope are also found dust particles are found in situ eighty five per cent of those observed contained silicon which was generally associated with aluminium and magnesium an estimation is made of the relative proportions of dust particles located at grain boundaries and in the bulk of the ice grain at dome c a higher proportion than expected from a random distribution of particles was found located at grain boundaries although in greenland this was not found to be the case for most samples direct evidence is also presented indicating the role of dust particles and microscopical inclusions in impeding or pinning grain boundary migration soluble impurities are also detected at some triple junctions and grain boundaries

small scale structure of the midlatitude storm enhanced density plume during the 17 march 2015 st patrick s day storm kilometer scale density irregularities in the ionosphere can cause ionospheric scintillation a phenomenon that degrades space based navigation and communication signals during strong geomagnetic storms the midlatitude ionosphere is primed to produce these 1 10 km small scale irregularities along the steep gradients between midlatitude storm enhanced density sed plumes and the adjacent low density trough the length scales of irregularities on the order of 1 10 km are determined from a combination of spatial temporal and frequency analyses using single station ground based global positioning system total electron content tec combined with radar plasma velocity measurements kilometer scale irregularities are detected along the boundaries of the sed plume and depleted density trough during the 17 march 2015 geomagnetic storm but not equatorward of the plume or within the plume itself analysis using the fast fourier transform of high pass filtered slant tec suggests that the kilometer scale irregularities formed near the poleward gradients of sed plumes can have similar intensity and length scales to those typically found in the aurora but are shown to be distinct phenomena in spacecraft electron precipitation measurements

ocean to ice heat flux at the north pole environmental observatory 1 data from drifting buoys deployed in april 2002 as part of the north pole environmental observatory project have been analysed to estimate ocean heat flux in the time period from 1 may 2002 to 11 mar 2003 prior to late january the observatory remained in deep water but subsequently drifted directly over the yermak plateau a relatively shallow feature north of svalbard while over deep water heat flux was dominated by storage and release of solar energy in the ocean boundary layer during summer the most likely annual average value for 2002 was 2 6 w m 2 less than previous determinations in the western arctic over yermak plateau heat flux at the interface came from mixing of warmer water into the boundary layer from below when the observatory was in water with depths less than 1200 m the average heat flux was around 22 w m 2

topside ionospheric irregularities as seen from multisatellite observations we use in situ data from champ and dmsp satellites along with data of gps receiver onboard champ satellite and ground based gps receivers to study the occurrence and global distribution of ionospheric irregularities during the main phase of the geomagnetic storm of 29 31 august 2004 minimum dst excursion of a128 nt using the champ gps measurements we created maps of gps phase fluctuation activity and found two specific zones of the most intense irregularities 1 the region of the auroral oval at high latitudes of both hemispheres and 2 the low latitudes equatorial region between africa and south america at high latitudes the topside ionospheric irregularities appeared to be more intensive in the southern hemisphere which is most likely due to seasonal variations in the interhemispheric field aligned currents system an analysis of multi instrumental observations reveals reinforcement of the equatorial ionization anomaly after sunset in atlantic sector on 30 august and formation of the significant plasma depletions and irregularities over a large longitudinal range equatorial irregularities were also found in the morning sector at the recovery phase of the storm in addition to low earth orbit leo gps measurements we analyze the leo in situ measurements and we show that these two techniques cannot be interchangeable in all cases because of the altitudinal extent of plasma irregularities overall we demonstrate that the leo gps technique can serve a useful tool for detection of the topside ionospheric irregularities during space weather events and may essentially contribute to other methods based on various instruments

global equatorial plasma bubble occurrence during the 2015 st patrick s day storm an analysis of the occurrence of equatorial plasma bubbles epbs around the world during the 2015 st patrick s day geomagnetic storm is presented a network of 12 global positioning system receivers spanning from south america to southeast asia was used in addition to colocated vhf receivers at three stations and four nearby ionosondes the suppression of postsunset epbs was observed across most longitudes over 2 days the epb observations were compared to calculations of the linear rayleigh taylor growth rate using coupled thermosphere ionosphere modeling which successfully modeled the transition of favorable epb growth from postsunset to postmidnight hours during the storm the mechanisms behind the growth of postmidnight epbs during this storm were investigated while the latter stages of postmidnight epb growth were found to be dominated by disturbance dynamo effects the initial stages of postmidnight epb growth close to local midnight were found to be controlled by the higher altitudes of the plasma i e the gravity term modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low latitude region which made the plasma more susceptible to rayleigh taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight epbs

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

on the occurrence of postmidnight equatorial f region irregularities during the june solstice 1 postmidnight equatorial f region irregularities efis are known to develop mainly during the solstitial months however it is not well understood whether they occur at all longitudes and what process causes their occurrence at different longitude sectors in this study we use the gps total electron content tec fluctuations obtained from a global gps network and spread f in ionograms from jicamarca 283 e 12 s dip 1 n in the american longitude sector and kwajalein 167 e 9 n dip 4 n bac lieu 106 e 9 n dip 2 n and chumphon 99 e 11 n dip 3 n in the pacific and asian longitude sectors during 2000 2009 to investigate the efi characteristics during june solstice results from global tec fluctuations show that at solar maximum the occurrence rate of postmidnight efis is high in african and pacific regions moderate in the southeast asian region and low in the peruvian region and that most postmidnight efis are the continuation of postsunset efis during solar minimum the postmidnight efis were rarely observed in tec but were very frequent in ionograms the latter had more frequent postmidnight onsets over peru whereas they were initiated during late postsunset hours in pacific and southeast asian longitudes in both longitudes the postsunset layer rise occurred with some delay the layer rise was more prominent on spread f nights over jicamarca and less so over pacific longitudes the results showing different degrees of association at the different longitudes between the postsunset postmidnight efis and f layer heights highlight the influence of other factors in the late night efi development perturbation seeds and plasma drifts neutral winds in particular are discussed as strong candidates for causing these irregularities in the june solstitial months of solar minimum years

analysis of the global ionospheric disturbances of the march 2015 great storm the global ionospheric storm in march 2015 was investigated using data from over 3000 gps stations worldwide in this study total electron content tec rate of tec rot and rot s standard deviation roti as well as the second order difference operator tect were considered as main characteristic methods to distinguish ionosphereic disturbances the results show that 1 based on the multiple methods above we all observed that for the first time there were three equatorward traveling ionospheric disturbances tids in the main phase of this storm in north america the disturbance zone expanded to 40 n the disturbance periods and ae peak stages were roughly synchronous we suggest that these three tids were induced by the propagation of agws to low latitudes under the action of ae 2 the most intense positive storm occurred over south america and the south atlantic over 300 enhancement 00 00 05 00 ut march 18 whereas a negative storm was observed in the corresponding region of the nh such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition the imf by component and the geomagnetic intensity 3 on march 18 a negative storm dominated globally except at certain low latitudes and tended to propagate equatorward and decay with time which could be largely attributed to the storm circulation theory and the evolution of the negative storm was further characterized by the fof2 variations of ionosondes

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

the role of shortwave radiation in the summer decay of a sea ice cover heat balance models of ice leads and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean particular emphasis was given to the treatment of heat transfer and lateral melting in leads the rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the greenland sea during the 1984 marginal ice zone experiment and in the static ice of mould bay northwest territories field coefficients were found to be considerably larger than those previously obtained in the laboratory suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases thus although very wide leads transmit considerable energy to the underlying ocean they have relatively little effect on lateral melting other results provide information on the relative importance of horizontal heat transfer rates ice thickness floe perimeter atmospheric forcing and oceanic heat flux in general the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting this suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation

the inferred formation of a subice platelet layer below the multiyear landfast sea ice in the wandel sea ne greenland induced by meltwater drainage

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

a wintertime temperature inversion in kootenay lake british columbia we describe the wintertime development and persistence of an anomalous temperature inversion layer in a deep temperate lake with emphasis on the roles of convective mixing and river induced circulation the layer is about 20 m thick 100 km long and lies at a depth of 60 80 m the destabilizing temperature distribution is compensated by a very weak 0 015 ppt salinity increase across the inversion layer we observe that neither the energy available from the wind nor the buoyancy extracted at the surface via a negative heat flux are sufficient to penetrate the depth of the inversion calculations of a thermal diffusion coefficient for this layer indicate a weak turbulent exchange below the halocline lake overturn does not follow the classical pattern of surface processes driving complete winter mixing rather full circulation is made possible only by the input of relatively saline river water

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

processes and imagery of first year fast sea ice during the melt season an analysis of first year fast sea ice during the melt season has been made by using surface measurements and aircraft radar and photographic imagery obtained during a field study near prince patrick island in the canadian archipelago from june 13 to july 13 1982 and satellite imagery from landsat and seasat distinct changes observed in the properties of the snow layer and the sea ice were a temporary increase in small scale surface roughness caused by formation of nodules of ice at the snow ice interface extensive snow melt and surface flooding development of surface water drainage networks and low topography around fractures and seal breathing holes and a rapid draining of much of the surface water from the extensive salinity profiles obtained two zones of rapid desalination in the first year ice were observed one zone extending from the air ice interface downward toward the center of the ice sheet that resulted from surface warming and drainage of the surface melt water through the ice and the other zone extending from the sea ice interface upward toward the center of the ice sheet that resulted from heating and separation of seawater and ice caused by a layer of low salinity meltwater beneath the ice formed from surface meltwater runoff aircraft radar imagery detected changes in the amount of surface water and in the development of topography surrounding drainage features similar changes were detected in coincident landsat multispectral scanner mss imagery of the study area and in seasat radar imagery and landsat mss imagery of the prince of wales strait from july 1978

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

coastal landfast sea ice decay and breakup in northern alaska key processes and seasonal prediction 1 seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay the breakup process of landfast sea ice in the chukchi sea at barrow alaska was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions weather records image sequences obtained from cameras coastal x band marine radar and satellite imagery we investigated the relation of breakup to winds tides and nearshore current measurements from a moored acoustic doppler current profiler two breakup modes are distinguished at barrow on the basis of the degree of ice decay mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice thermal breakup is the result of ice disintegration under melt ponds requiring little force to induce dispersion grounded pressure ridges are pivotal in determining the breakup mode the timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in june and july this linkage allows for the development of an operational forecast of landfast ice breakup results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance the cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill

modeling the thermodynamics of a sea ice thickness distribution 2 sea ice ocean interactions in this paper we examine the coupling of an ice thickness distribution model with an ocean mixed layer model the annual cycle of the modeled mixed layer temperature salinity and depth are compared to observations from the drifting ice stations of the arctic ice dynamics joint experiment aidjex the role of the ice thickness distribution in determining the ice ocean coupling is examined we find that the ice thickness distribution is important for the exchange of heat salt and fresh water between the ice and the ocean especially with regard to the effects of thin first year ice several different parameterizations of the ice ocean turbulent heat exchange are compared the results indicate that the storage of heat in the ocean mixed layer is an important physical process for determining the annual average ice thickness double diffusion and the stabilizing effects of meltwater also impact the exchange of heat between the ocean and ice cover questions remain as to the relative importance of these processes and their accurate parameterization in ice ocean coupled models