eof analysis and modeling of gps tec climatology over north america an empirical ionospheric model of the total electron content tec over north america 20 60 n 40 140 w is constructed using the gps tec data collected by massachusetts institute of technology mit haystack observatory during the years 2001 2012 this model is based on an analysis of quiet time monthly averages using the empirical orthogonal function eof decomposition technique allowing for separation of spatial and temporal variations the importance of different types of spatial temporal variations to the overall tec variability can be well represented by the characteristics of eof basis functions and associated principal components coefficients with various modes the mode one eof decomposition constitutes 97 5 of the total variance and therefore represents the essential feature of north america spatial and diurnal variation of the tec the mode two eof as reported in an earlier study reveals a large and significant symmetric longitudinal variation of the ionosphere organized with respect to magnetic declination the mode three eof decomposition shows midlatitude latitudinal structure that varies with season in a manner very similar to the so called winter anomaly because of the quick convergence of eof decomposition modes the first four eof modes are utilized for constructing a tec empirical model for each of the eof modes the temporal variations are expressed analytically in terms of local time season and solar activity and the spatial variations by cubic spline functions an analysis of accuracy and quality indicates that this regional empirical tec model can reflect the majority of the quiet time monthly means and represent characteristic temporal spatial variations in the north america

the geomagnetic storm time response of gps total electron content in the north american sector over the last two decades maps of gps total electron content tec have improved our understanding of the large perturbations in ionospheric electron density which occur during geomagnetic storms however previous regional and global studies of ionospheric storms have performed only a limited separation of storm time local time longitudinal and seasonal effects using 13 years of gps tec data we present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the north american sector where dense ground receiver coverage is available the rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer lasting negative phase across all latitudes and local times our results show clear seasonal variations in the storm time tec such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects we find no discernable difference between spring and fall equinox events with both being equivalent to the average storm time response across all seasons we also identify a prominent magnetic declination effect such that stronger dayside positive storm effects are observed in regions of negative declination i e eastern north america on the nightside asymmetries in the tec response are observed near the auroral oval and midlatitude trough which may be attributed to thermospheric zonal winds pushing plasma upward downward along field lines of opposite declination

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

east west differences in f region electron density at midlatitude evidence from the far east region the global configuration of the geomagnetic field shows that the maximum east west difference in geomagnetic declination of northern middle latitude lies in the us region similar to 32 degrees which produces the significant ionospheric east west coast difference in terms of total electron content first revealed by zhang et al 2011 for verification it is valuable to investigate this feature over the far east area which also shows significant geomagnetic declination east west gradient but smaller similar to 15 degrees than that of the us the current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density nmf2 electron density ne of different altitudes in the far east regions with a longitude separation of up to 40 60 degrees based on ground ionosonde and space based measurements although the east west difference r ew over the far east area displays a clear diurnal variation similar to the us feature that is negative r ew west ne east ne in the noon and positive at evening night the observational results reveal more differences including 1 the noontime negative r ew is most pronounced in april june while in the us during february march thus for the late spring and summer period negative r ew over the far east region is more significant than that of the us 2 the positive r ew at night is much less evident than in the us especially without winter enhancement 3 the magnitude of negative r ew tends to enhance toward solar maximum while in the us showing anticorrelation with the solar activity the altitude distribution of pronounced negative difference 300 400 km moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude the result in the paper is not simply a comparison corresponding to the us results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude citation zhao b m wang y wang z ren x yue j zhu w wan b ning j liu and b xiong 2013 east west differences in f region electron density at midlatitude evidence from the far east region j geophys res space physics 118 542 553 doi 10 1029 2012ja018235

horizontal convective rolls determining the environmental conditions supporting their existence and characteristics abstract data from the convection and precipitation electrification cape project as well as results from numerical simulations are used to study horizontal convective rolls the environmental conditions necessary for sustaining rolls and for influencing the aspect ratio ratio of roll wavelength to convective boundary layer cbl depth and orientation are examined observations and numerical model simulations both suggest that a moderate surface sensible heat flux and some vertical wind shear are necessary for roll existence unlike some previous studies however it is shown that rolls occurred within very low cbl shear conditions 2 10 3 s 1 in addition the low level i e 200 m shear seems to be more important than the shear through the depth of the cbl in roll sustenance the aspect ratio is shown to be proportional to the cbl instability measured in terms of the monin obukhov length the roll orientation is similar to the wind direction at 10 m agl the cbl wind direction the inversio

the initiation and organization of convective cells atop a cold air outflow boundary abstract on 13 july 1986 a cold air outflow from thunderstorms over illinois and missouri propagated through the mist microburst and severe thunderstorm network over northern alabama the study of this outflow is important since the gust front was solely responsible for the initiation of numerous convective cells previous studies have documented the initiation of convection due to colliding gust fronts in addition there was a pronounced mesoscale organization of the cells atop the outflow boundary this was most likely due to a combination of kelvin helmholtz k h and internal gravity ig wave activity in contrast to previous cases the k h wave crests were oriented nearly perpendicular to the gust front within the analysis area the resulting intersections between the circulations associated with the k h waves and the gust front produced favorable locations for the initiation of convection subsequently the convective cells remained along the updraft side of the k h wave circulations as they pro

a case study of the ionospheric storm dusk effect the initial ionospheric storm positive phase often appears as a large enhancement in f region electron density at middle latitudes in the evening hours following a storm sudden commencement the cause of this dusk effect is still not well understood though several mechanisms have been proposed this phenomenon is studied using incoherent scatter radar data collected at millstone hill and total electron content data from a north south chain of stations during the may 26 27 1990 storm nine position millstone hill radar data allows estimation of gradients in electron density and in velocity components above the station from these the motion term in the continuity equation is calculated and used along with wind electric field data and modeling to assess the relative importance of the proposed mechanisms during this storm it is shown that a combination of mechanisms appear to have been involved including a traveling atmospheric disturbance advection of high density plasma from lower latitudes and neutral composition changes

thermodynamic variability within the convective boundary layer due to horizontal convective rolls abstract data from the convection and precipitation electrification cape experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer cbl potential temperature variations were only about 0 5 k while variations in water vapor mixing ratio values of 1 5 2 5 g kg 1 were observed throughout the cbl using radar aircraft and sounding data it is shown that horizontal convective rolls are the likely cause of these variabilities the enhanced moisture occurred within the roll updraft regions thus rolls were transporting moist air from the surface upward the observed cloud base heights obtained from cloud photogrammetry were produced from the highest moisture values within the roll updraft regions since the roll ascending branches contained moisture values that were most representative of the observed cloud base heights it is likely that measurements from within the roll updrafts would prov

observations of the sea breeze front during cape part i single doppler satellite and cloud photogrammetry analysis abstract an analysis of two sea breeze events on 6 august an onshore flow event and 12 august an offshore flow event 1991 is presented using single doppler observations satellite images and cloud pictures collected during the convection and precipitation electrification cape experiment documentation of the alongfrontal variability at the leading edge of the sea breeze circulation is presented for the first time the horizontal structure of the front was strongly modulated by the near perpendicular intersections of horizontal convective rolls developing in the ambient air out ahead of the sea breeze on 12 august these intersection points also appeared to be preferred locations for cloud development along the front horizontal convective rolls were also documented on 6 august however their orientation was nearly parallel to the sea breeze front as a result extended sections of these rolls appeared to have merged with the front as it propagated inland rather than having distinct intersection po

numerical simulation of the interaction between the sea breeze front and horizontal convective rolls part i offshore ambient flow abstract a three dimensional cloud resolving model is used to investigate the interaction between the sea breeze circulation and boundary layer roll convection horizontal convective rolls hcrs develop over land in response to strong daytime surface heating and tend to become aligned parallel to the vertical wind shear vector whereas the land sea heating contrast causes the formation of the sea breeze front sbf along the coastline the ability of hcrs to modulate the along frontal structure of the sbf is examined complementing and extending previous observational and numerical studies three simulations are discussed the first two demonstrating that the model can produce both phenomena independently the third is initialized with offshore mean flow and vertical shear perpendicular to the coastline and results in a sharply defined inland propagating sbf that encounters hcrs aligned perpendicular to it before the interaction takes place the sbf is nearly two dimensional and devoid of along front

on the effects of islands geometry and size on inducing sea breeze circulation abstract model scaling of the characteristics of the sea breeze circulation involved with circular and slab elongated symmetric midlatitude islands was performed larger horizontal and vertical velocities were indicated over the small circular islands as compared to those over corresponding elongated islands the circulation characteristics of both types of islands become similar when the half width of the island is about the same as the distance of inland penetration of the sea breeze in a nonisland case evaluation of the results through a wale analysis is presented

strike slip faults offshore southern taiwan implications for the oblique arc continent collision processes taiwan is the site of present day oblique arc continent collision between the luzon arc of the philippine sea plate and the chinese continental margin the major structural pattern revealed from marine geophysical studies in the area offshore southern taiwan is that of a doubly vergent orogenic belt bounded by significant zones of thrusting on the west and east of the submarine accretionary wedge due to the oblique collision process strike slip faults could play an important role in this convergent domain topographic lineaments revealed from new digital bathymetry data and seismic reflection profiles confirm the existence of three sets of strike slip faults in the collision subduction zone offshore southern taiwan the n s trending left lateral strike slip faults within the luzon volcanic arc the ne sw trending right lateral strike slip faults across the accretionary wedge and the nne ssw trending left lateral strike slip faults lie in the frontal portion of the accretionary wedge these strike slip faults overprint pre existing folds and thrusts and may convert into oblique thrusts or thrusts as the forearc blocks accrete to the mountain belt a bookshelf rotation model is used to explain the observed geometrical relationships of these strike slip fault systems based on this model the counter clockwise rotation of the forearc blocks in the area offshore southern taiwan could have caused extrusion of the accretionary wedge material into the forearc basin the originally continuous forearc basin is thus deformed into several closed and separate proto collisional basins such as the southern longitudinal trough and taitung trough a tectonic evolution model which emphasizes on the development of various structures at different stages of the oblique arc continent collision for the taiwan mountain belt is proposed

magnetic declination and zonal wind effects on longitudinal differences of ionospheric electron density at midlatitudes 1 a prominent ionospheric longitudinal variation at midlatitudes in particular over the continental us was found recently this variation is characterized as a higher east side electron density in the evening and a higher west side electron density in the morning and with clear seasonal and solar activity dependencies a combined effect of geomagnetic declination and changing zonal winds was proposed to explain it this paper represents a comprehensive investigation of this effect by examining climatology for both electron density longitudinal differences and the nighttime zonal winds in the eastern us electron density is from incoherent scatter radar extra wide coverage experiments during 1978 2011 over millstone hill for which the spatial separation of the data can be up to 50 in longitude the thermospheric zonal wind is from the on site fabry perot interferometer measurements during 1989 2001 the observed zonal wind climatology is found to be perfectly consistent with the expectation based on the east west electron density differences in terms of local time seasonal and solar cycle dependencies the correlation between the zonal wind and the east west differential ratio is extremely high with an overall correlation coefficient of 0 93 the observed time delay of 3 hours in the response of electron density differences to zonal winds is a marked feature thus these results confirm positively the declination zonal wind mechanism and provide new insight into longitudinal variations at midlatitudes for other geographic sectors

multiradar observations of the polar tongue of ionization 1 we present a global view of large scale ionospheric disturbances during the main phase of a major geomagnetic storm we find that the low latitude auroral and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system for the large geomagnetic storm on 20 november 2003 we examine data from the high latitude incoherent scatter radars at millstone hill sondrestrom and eiscat tromso with superdarn hf radar observations of the high latitude convection pattern and dmsp observations of in situ plasma parameters in the topside ionosphere we combine these with north polar maps of stormtime plumes of enhanced total electron content tec derived from a network of gps receivers the polar tongue of ionization toi is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern the dayside source of the toi is the plume of storm enhanced density sed transported from low latitudes in the postnoon sector by the subauroral disturbance electric field convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral f region is significantly enhanced by the sed material the three incoherent scatter radars provided full altitude profiles of plasma density temperatures and vertical velocity as the toi plume crossed their different positions under the cusp in the center of the polar cap and at the midnight oval polar cap boundary greatly elevated f peak density 1 5e12 m 3 and low electron and ion temperatures 2500 k at the f peak altitude characterize the sed toi plasma observed at all points along its high latitude trajectory for this event sed toi f region tec 150 1000 km was 50 tecu both in the cusp and in the center of the polar cap large upward directed fluxes of o 1 e14 m 2 s 1 were observed in the topside ionosphere

case study of a hailstorm in colorado part iii airflow from triple doppler measurements abstract triple doppler measurements are presented for a hailstorm of moderate intensity that occurred over the high plains of northeastern colorado and an airflow model is synthesized the storm had a number of persistent features similar to previous descriptions of supercells however its evolution is shown to be intermediate in a certain sense between classical multicell and supercell models a new model based on the doppler observations termed weak evolution emphasizes gradual changes in the structure of a long lived updraft the new airflow model explains the periodic echo intensifications noted for this storm and seems to apply well to other storms discussed in the literature

an investigation of convection behind the cape canaveral sea breeze front abstract a three dimensional numerical simulation of land water circulations near cape canaveral florida is performed using the advanced regional prediction system the role of kelvin helmholtz instability khi in determining the time and location of convection behind the sea breeze front is examined the model configuration attempts to improve upon limitations of previous work e g resolution surface characteristics initial state it provides a detailed and realistic simulation of the desired features the simulation exhibits a single precipitating storm that forms behind the sea breeze front this postfrontal storm develops when an outflow boundary intersects a deep layer of upward motion above the marine air the region of ascent initially is the remnant of a cell that formed along the sea breeze front but before the cell decays a portion of its upward motion is intensified and displaced the modification of the ascent is a product of khi that is occurring on top of the sea breeze interface i

dynamics of a thunderstorm outflow abstract the kinematic and thermodynamic structures of a thunderstorm outflow are examined by means of dual doppler radar analysis mesonet lower and sounding data the data were collected in the denver colorado area during june 1984 the dual doppler analysis shows that the cold outflow is ducted beneath the pbl inversion along the gust front there is a narrow quasi two dimensional updraft kelvin helmholtz instability khi developed along the top of the gust front head near the surface front and propagated backwards dissipating in the wake of the head region an isothermal layer aloft appears to have limited billow amplification to the quasi neutral layer below the gust front s leading edge had numerous inflections which are believed to result from barotrophic instabilities small vortices develop at some of the inflection points detailed analysis of one such circulation shows evidence of the formation of two enhanced updrafts separated by an occlusion downdraft these observations are the firs

spatial patterns of convection in south florida abstract although they are a fairly consistent feature the sea breeze and lake breeze convergence lines and the associated convection over south florida during the summer may vary considerably from one day to the next daily radar maps indicate a few basic recurring patterns analyses of radiosonde data show significant differences corresponding to the different patterns in the local thermodynamic parameters most notably the mixing ratio changes in the synoptic scale wind field correspond closely to changes in the observed radar patterns and the local thermodynamic conditions explanation of the formation and development of the different patterns of convection is given in terms of the complex interaction between the regional synoptic peninsular and local scale circulations

numerical simulation of thunderstorm outflow dynamics part i outflow sensitivity experiments and turbulence dynamics abstract in this first paper of a two part series a two dimensional numerical model is developed and used to investigate the dynamics of thunderstorm outflows by focusing only on the outflow and using essentially inviscid equations and high spatial resolution we are able to explicitly represent important physical processes such as turbulent mixing to simplify interpretation of the results the model atmosphere used in all experiments is calm and dry adiabatic this approach allows us to establish basic characteristics of modeled outflows in simple physical settings and provides a foundation for future studies using more realistic environments all simulated outflows are initialized by prescribing a controlled horizontal flux of cold air into the model domain through a lateral boundary in a series of sensitivity tests we examine three parameters of the cold air source region 1 the vertical temperature deficit profile 2 the magnitude of the temperature deficit and 3 the cold air depth by hol

direct observations of the role of convection electric field in the formation of a polar tongue of ionization from storm enhanced density 1 we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization toi from midlatitude plumes of storm enhanced density sed observations from the geomagnetic storm on 26 27 september 2011 are presented for two distinct sed events during an hour long period of geomagnetic activity driven by a coronal mass ejection a channel of high density f region plasma was transported from the dayside subauroral ionosphere and into the polar cap by enhanced convection electric fields extending to middle latitudes this toi feature was associated with enhanced hf backscatter indicating that it was the seat of active formation of small scale irregularities after the solar wind interplanetary magnetic field conditions quieted and the dayside convection electric fields retreated to higher latitudes an sed plume was observed extending to but not entering the dayside cusp region this prominent feature in the distribution of total electron content tec persisted for several hours and elongated in magnetic local time with the rotation of the earth no ionospheric scatter from superdarn radars was observed within this sed region the source mechanism enhanced electric fields previously drawing the plasma from midlatitudes and into the polar cap as a toi was no longer active resulting in a fossil feature we thus demonstrate the controlling role exercised by the convection electric field in generating a toi from midlatitude sed

the occurrence of ionospheric signatures of plasmaspheric plumes over different longitudinal sectors 1 plasmaspheric plumes have ionospheric signatures and are observed as storm enhanced density sed in global positioning system gps total electron content tec these ionospheric signatures have been primarily observed over the american sector and in a few limited examples over the european sector this study examines the longitudinal occurrence frequency of plasmaspheric plumes we analyzed all images from the imager for magnetopause to aurora global exploration image extreme ultraviolet imager euv databases for the first half of 2001 and identified a total of 31 distinct plume intervals observed during different storm events out of the total image euv plumes that we identified 12 were projected over north america 10 over asia and the remaining 9 were over europe and the atlantic ocean using ground based gps tec from mit s madrigal database we searched for corresponding sed tec plumes at different longitudinal sector and found 12 ionospheric sed plume signatures over north america 4 over europe and 2 over asia this indicates that the observation probability of an ionospheric sed plume when a plasmaspheric plume is seen is 100 in the american sector 50 in the european sector and 20 in the asian sector this could be due to the fact that the plumes may be either positioned beyond the limit of the ground based gps field of view which happens mainly when there is less plasmaspheric erosion or are too weak to be detected by the sparse number of gps receivers over asia the in situ plasma densities from the available coincident defense metrological satellite program dmsp satellites were also used to study the characteristics of sed tec plume at dmsp orbiting altitude i e 870 km the topographic explorer topex altimeter tec also is used to identify the conjugate sed plume signature over the southern hemisphere

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

effects of disturbed electric fields in the low latitude and equatorial ionosphere during the 2015 st patrick s day storm the 2015 st patrick s day geomagnetic storm with sym h value of 233 nt is an extreme space weather event in the current 24th solar cycle in this work we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the asian australian sector and the american sector during this super storm event the results reveal that the disturbed electric fields which comprise penetration electric fields pefs and disturbance dynamo electric fields ddefs play a decisive role in the ionospheric storm effects in low latitude and equatorial regions pefs occur on march 17 in both the american sector and the asian australian sector the effects of ddefs are also remarkable in the two longitudinal sectors both the ddefs and pefs show the notable local time dependence which causes the sector differences in the characteristics of the disturbed electric fields this differences would further lead to the sector differences in the low latitude ionospheric response during this storm the negative storm effects caused by the long duration ddefs are intense over the asian australian sector while the repeated elevations of hmf2 and the eia intensifications caused by the multiple strong pefs are more distinctive over the american sector especially the storm time f3 layer features are caught on march 17 in the american equatorial region proving the effects of the multiple strong eastward pefs

altitude adjusted corrected geomagnetic coordinates definition and functional approximations analysis of the functional approximations used to transform between geo graphic and altitude adjusted corrected geomagnetic aacgm coordinates reveals that errors of 50 km can occur in the auroral and polar regions these errors are the result of efforts to better approximate aacgm coordinates near the magnetic equator and the south atlantic anomaly in these regions aacgm coordinates are not defined and alternate coordinates have been used this augmentation and emphasis on the so lution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions in response a new set of spherical harmonic coefficients have been derived that better represent aacgm coordinates in these regions these new aacgm coefficients are limited to below 2000 km in altitude in order to ensure accuracy for altitudes above 2000 km a magnetic field line tracing solution is recommended a software package developed to take advantage of the new aacgm coefficients provides the capability of tracing magnetic field lines at any altitude for improved accuracy in addition linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 present the intent of this work is to provide a more accurate procedure for de termining aacgm coordinates in the auroral and polar regions for the study of mag netospheric and ionospheric processes

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

a numerical study of the convection triggering and propagation associated with sea breeze circulation over hainan island based on high resolution numerical simulations the effects of sea breeze circulation sbc on associated convective initiation and propagation over hainan island are investigated the results show that the blocking of synoptic wind on the windward side of the mountains inhibits the occurrence of windward side valley breeze and sea breeze in the context of low mountains weak synoptic wind not only favors the combination of the sbc with the valley breeze circulation on the leeward side of the mountains but also makes the convergence zone between the synoptic wind and the leeward side combined circulation stay near the tops of the mountains leading to the accumulation of large quantities of water vapor taking place over the mountaintops the combined effect of enhanced water vapor and high temperatures over the mountaintops can result in the generation of much larger convective available potential energy cape than the surrounding areas the coupling of the large cape with the considerable converging ascending motion and abundant water vapor near the tops of the mountains promotes the occurrence of a strong convection band cb over the mountaintops during the cb propagation under the steering of synoptic wind the flow across the cb continuously and strongly opposes the sbc front and the fronts of the kelvin helmholtz billows behind resulting in successive and strong lifting motion as well as large quantities of water vapor and high cape near these fronts these lead to an apparent downstream wave like propagation of the cb

ionospheric signatures of a plasmaspheric plume over europe 1 previously ionospheric signatures of plasmaspheric plumes were reported only at the north american longitude sector this led to the hypothesis that the geomagnetic field configuration at those longitudes played a vital role in the observation of plasmaspheric plume signatures only over the american continent combining ground based gps total electron content tec eiscat incoherent scattering radar isr and dmsp f15 ion drift meter observations we have observed greatly elevated density over the european continent during storm recovery phase on 12 september 2005 the tec seen over europe has a tongue of enhanced ionization extending to higher latitudes which is identical to the plasmaspheric plume signatures that have been often observed over north america therefore our observations clearly demonstrate that ionospheric signatures of plasmaspheric plumes are not limited to the north american sector and suggest that they may be observed at any longitude as long as a dense array of instruments are available to identify these signatures citation yizengaw e m b moldwin and d a galvan 2006 ionospheric signatures of a plasmaspheric plume over europe geophys res lett 33 l17103 doi 10 1029 2006gl026597

the formation of a multicell thunderstorm behind a sea breeze front idealized three dimensional numerical simulations are used to investigate the influence of sea breezes on the evolution of multicell thunderstorms in the tropics the study is motivated by a desire to understand a particular type of severe storm system that occurs occasionally over the top end region of northern australia but the results should have wider applicability the calculations are carried out using bryan s cloud model the simulations reproduce the main features of the evolution of an observed storm system new cells develop on the gust front of the initial updraught behind the sea breeze front and subsequently merge to form a multicell thunderstorm the propagation speed and direction the orientation and length of the line of updraught cells are all similar to those observed the sea breezes in the model play an important role in the evolution of the storm in general the low level convergence at the gust front produced by the initial cell needs to be strong enough and to persist for a sufficiently long time to allow new cells to develop near this front a strong cold pool occurs if the initial updraught is sufficiently tilted so that the downdraught does not fall into it but supplies cold air close to the gust front a generalized form of the rotunno klemp weisman criterion was used to test whether the new updraughts developed at locations where the cold pool circulation was largely opposed by that of the environmental shear the comparison of the shear components normal to the gust front showed that new cells develop even though this criterion is not fulfilled suggesting that the criterion is not applicable to the more complex flow configurations studied here copyright c

a numerical study on sea land breezes as a gravity current kelvin helmholtz billows and inland penetration of the sea breeze front abstract a two dimensional nonhydrostatic compressible and dry numerical model was developed by using high spatial resolution and an appropriate turbulence model fine structure and dynamics of the sea breeze head were investigated kelvin helmholtz kh instability was found to occur in the foremost part of the head consequently kh billows were generated there and grew in amplitude while travelling backward relative to the advancing front along the zero velocity boundary the kh billows entrained the upper air into the sea breeze the resultant turbulent mixing and wave perturbations induced a top friction force acting on the sea breeze head structure of the kh billow and the wavelike motion induced by it near the ground were also investigated and compared with the results obtained in laboratory density currents linear theories and observations the kh instability khi did not occur at all stages of the sea breeze and this resulted in a diurnal variation of the fine structure and dynamics of

a study on the nighttime midlatitude ionospheric trough constellation observing system for meteorology ionosphere and climate cosmic electron density profiles are used to investigate the nighttime midlatitudeionospheric trough mit we find that at midnight the longitudinally deepest mit occursto the west of the geomagnetic pole in both the northern and southern hemispheres duringthe equinox seasons and local summer the deepest mit could be ascribable to theenhanced depletion caused by horizontal neutral wind in the early evening the eastwardneutral wind prevails in the midlatitude f region which blows the plasma downwardwhere the declination is eastward in the northern hemisphere but westward in thesouthern hemisphere both lying to the west of the geomagnetic pole the downward driftwould enhance the plasma depletion for more molecular composition at lower altitude in addition we find for the first time that the location of nighttime mit minimumoscillated with a periodicity of 9 days and an amplitude of about 1 1 5 geomagneticlatitude during 2007 2008 associated with the recurrent high speed solar wind ourresults shed new light on the empirical description and numerical simulation of mit

possible ionosphere and atmosphere precursory analysis related to mw 6 0 earthquakes in japan abstract the attention towards possible link of earthquakes eqs and ionosphere in the form of seismo ionosphere anomalies sias has increased exponentially by utilizing new data and more accurate observations the integrated atmosphere and ionosphere monitoring satellites has played a decisive role in this development and provided detection and analysis of anomalies attributed to seismic processes in this paper we study eq anomalies in ionosphere from igs permanent global navigation satellite systems gnss based total electron content tec and fof2 parameter highest frequency reflected from the main ionospheric f2 layer on a vertical propagation path retrieved from stations operating within the seismogenic zone in japan for eqs of magnitude mw 6 0 furthermore spatial composite maps of geopotential height air temperature and outgoing long wave radiation olr from national oceanic and atmospheric administration national center for environmental prediction noaa ncep are analyzed to support the hypothesis of diffusion of sias through the atmosphere over the epicenter during the seismic preparation zone we find evidences of tec and fof2 anomalies in the analysis of nearby igs permanent stations within seismogenic zone on main shock day when geomagnetic activities remain quiet in addition atmospheric composite indices manifest anomalies attributed to the eq on the same day as tec and fof2 perturbations similarly differential ionosphere and atmosphere values indicate that eq abnormalities are significant on main shock day during ut 10 12 our results show that atmospheric and ionospheric measurements may play a role for the analysis and prediction of eqs

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

east west coast differences in total electron content over the continental us 1 total electron content tec measurements made by a network of dense gps receivers over the continental us are used to investigate ionospheric longitudinal differences we find that the evening tec is substantially higher on the us east coast than on the west and vice versa for the morning tec the longitudinal difference displays a clear diurnal variation through an analysis of morning evening variability in the east west tec difference minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental us we suggest that these new findings of longitudinal differences in ionospheric tec at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day this study indicates that longitudinal variations in tec measurements contain critical information on thermospheric zonal winds the proposed declination zonal wind mechanism may also provide a new insight into longitude ut changes at midlatitudes on a global scale as well as into some geospace disturbances

ionospheric redistribution during geomagnetic storms 1 the abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms recent reports suggest that the magnitude of the plasma density enhancement depends on the ut of storm onset this possibility is investigated over a 7year period using global maps of ionospheric total electron content tec produced at the jet propulsion laboratory the analysis confirms that the american sector exhibits on average larger storm time enhancement in ionospheric plasma content up to 50 in the afternoon middle latitude region and 30 in the vicinity of the high latitude auroral cusp with largest effect in the southern hemisphere we investigate whether this effect is related to the magnitude of the causative magnetic storms using the same advanced dst index employed to sort the tec maps into quiet and active dst 100 nt sets we find variation in storm strength that corresponds closely to the tec variation but follows it by 3 6h for this and other reasons detailed in this report we conclude that the ut dependent peak in storm time tec is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the south american region the large dst variation suggests a possible system level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current possibly connected through ut dependent modulation of ion outflow

a two dimensional numerical investigation of the interaction between sea breezes and deep convection over the florida peninsula abstract deep convection initiated by sea breezes over the florida peninsula is simulated using a two dimensional nonhydrostatic model reasonable agreement is obtained between model results and observations for the three types of undisturbed days classified by blanchard and lopez the convergence of the east and west coast sea breezes is the primary control on the timing and location of rapid convective development and this is mainly determined by the low level winds the simulated convection is spatially concentrated and does not produce an extensive stratiform region sensitivity tests are performed for a variety of wind and thermodynamic profiles and for different soil moisture contents during the early stages of these simulations small convective cells develop in between the sea breeze fronts as the outer cells at the sea breeze fronts deepen these smaller cells are suppressed typically during the midafternoon a new cell explosively develops in between the sea breeze fronts and the outer cells

sea breeze simulation over the malay peninsula in an intermonsoon period 1 this study presents a characteristic intermonsoon weather situation over the malay peninsula the coupled ocean atmosphere mesoscale prediction system coamps is used to investigate the mesoscale details of the simulated sea breeze circulations over the malay peninsula on 23 april 2002 the occurrence of sea breeze collisions occurring in the inland region of the southern malay peninsula is noted on the peninsula scale convection was first initiated along the low level convergence line that became established along the west coastal region of the malay peninsula in the early afternoon deep clouds that led to thunderstorms developed in the northwestern part of the malay peninsula after the sea breeze encountered the mountain wave induced under the ambient easterlies above the mountain ridge line the convective activity was further enhanced over the central malay peninsula because of the interaction between sea breeze front and gap winds from the mountains this case study suggests that the malay peninsula is a potentially fertile ground for many dynamically interesting case studies of land sea breeze circulations

non normal growth of kelvin helmholtz eddies in a sea breeze the generalized stability of a sea breeze front is analyzed using a two dimensional model the objective is to understand the mechanisms leading to the shedding of eddies behind the sea breeze front as seen in observations laboratory experiments and numerical models regions with ri 1 4 the energy source for optimal growth is the vertical shear of the mean horizontal wind the vertical shear in the upper part of the front and the horizontal shear in the lower part the growth begins with vertical advection by the perturbation velocity of the mean flow momentum located in the upper part of the front perturbations eventually propagate away from the localized shear area and a feedback mechanism is needed for this growth to be sustained this feedback occurs through temperature anomalies in the upper part of the front inducing pressure gradient anomalies in the lower part these gradients lead to a growing vertical wind component and this vertical wind component then enters the upper part of the front which reinforces the extraction of energy thereby closing the feedback loop and leading to both normal mode instability and in the stable regime large non normal growth we find that both the instability and the non normal growth are vulnerable to parameter changes that weaken this feedback loop

ionospheric symmetry caused by geomagnetic declination over north america 1 we describe variations in total electron content tec in the north american sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination patterns were uncovered by applying an empirical orthogonal function eof decomposition procedure to a 12 year ground based american longitude sector gps tec data set the first eof mode describes overall average tec while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second eof mode or the second most significant component we find a high degree of correlation between spatial variations in the second eof mode and vertical drifts driven by thermospheric zonal winds along with well organized temporal variation results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time season and solar cycle this study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined