sensitivity of extratropical cyclone characteristics to horizontal resolution in the ecmwf model the sensitivity to horizontal resolution of northern hemisphere extratropical cyclone characteristics during the wintertime december march is investigated using a set of seasonal forecasts 1982 2001 with the european centre for medium range weather forecasts ecmwf model three different horizontal resolutions tl95 tl159 and tl255 are employed in order to test the realism of the simulations the model results are compared with those obtained from era 40 re analysis data the cyclone tracking is accomplished by applying an automatic tracking scheme to six hourly mean sea level pressure data it is shown that many of the key characteristics of extratropical cyclones in the ecmwf model are highly sensitive to horizontal resolution with the low resolution version tl95 for example simulating only about 60 of the re analysed total number of extratropical cyclones regions found to be particularly sensitive include the northern pacific the arctic baffin bay and the labrador sea as well as the mediterranean sea for the latter region it is shown that even the relatively high resolution version of the model tl255 significantly underestimates the number of cases of genoa cyclogenesis furthermore it is shown that in some regions such as the entrance regions of the major northern hemisphere storm tracks model deficits are insensitive to increases in horizontal resolution the same analysis has been repeated for the high resolution operational ecmwf analysis 2000 2004 truncated at different total wave numbers tl95 tl159 tl255 and tl511 in order to separate dynamical effects of differences in resolution from those due to pure spectral truncation it is found that the dynamical effect of changing horizontal resolution dominates over the truncation effect for intense cyclones whereas the truncation effect dominates for shallow cyclones copyright 2006 royal meteorological society

disturbance zonal and vertical plasma drifts in the peruvian sector during solar minimum phases in the present work we investigate the behavior of the equatorial f region zonal plasma drifts over the peruvian region under magnetically disturbed conditions during two solar minimum epochs one of them being the recent prolonged solar activity minimum the study utilizes the vertical and zonal components of the plasma drifts measured by the jicamarca 11 95 s 76 87 w incoherent scatter radar during two events that occurred on 10 april 1997 and 24 june 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the sheffield university plasmasphere ionosphere model inpe two main points are focused 1 the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and 2 anomalous behavior of daytime zonal drift in the absence of any magnetic storm a perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm for the first time based on a realistic low latitude ionosphere we will show on a detailed quantitative basis that this anticorrelation is driven mainly by a vertical hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime e region ionization it is shown that an increase in the field line integrated hall to pedersen conductivity ratio h p which can arise from precipitation of energetic particles in the region of the south american magnetic anomaly is capable of explaining the observed anticorrelation between the vertical and zonal plasma drifts evidence for the particle ionization is provided from the occurrence of anomalous sporadic e layers over the low latitude station cachoeira paulista 22 67 s 44 9 w brazil it will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind system during the prolonged solar minimum period

observations of thermospheric horizontal neutral winds at watson lake yukon territory λ 65 n fabry perot interferometer observations of the thermospheric o i 6300 a emission have been conducted from an airglow observatory at a dark field site in the southeastern yukon territory canada for the period november 1991 to april 1993 the experiment operated in an unattended remote fashion has resulted in a substantial data set from which mean neutral winds have been determined dependent upon geomagnetic activity the nocturnal location of the site is either equatorward of the auroral oval or within the oval boundaries the data set is rich enough to permit hourly binning of neutral winds based upon the kp geomagnetic disturbance index as well as the season for cases of low geomagnetic activity the averaged vector horizontal neutral wind exhibits the characteristics of a midlatitude site displaying antisunward pressure gradient driven winds as the geomagnetic activity rises the late afternoon and evening winds slowly rotate sunward in an anticlockwise direction initially remaining near 100 m s in speed but eventually increasing to 300 m s for kp 5 for the higher levels of activity the observed neutral wind flow pattern resembles a higher latitude polar cap pattern characterized by ion drag forcing of thermospheric neutral gases in addition rotational coriolis forcing on the dusk side enhances the ion drag forcing resulting in dusk winds which trace out the clockwise dusk cell plasma flow on the dawn side the neutral winds also rotate in an anticlockwise direction as the strength of geomagnetic disturbances increase since the site is located at a transition latitude between the midlatitude and the polar cap the data set provides a sensitive test for general circulation models which attempt to parameterize the contribution of magnetospheric processes a comparison with the vector spherical harmonic vsh model indicates several regions of poor correspondence for december solstice conditions but reasonable agreement for the vernal equinox

spread f sporadic e coupling at chung li especially for postsunset periods of sunspot maximum years using ionogram recorded data the coupling between spread f occurrence and enhanced e blanketing frequencies fe indicative of fe changes has been investigated for an equatorial ionospheric anomaly crest station chung li for the postsunset periods of sunspot maximum years apart from the evidence for coupling from inspections of the f plots alone for the years analyzed 1981 1982 1988 and 1989 statistical results of more significance were found from superposed epoch analyses isolated spread f events of duration of 2 hours or less which started at or before 2200 lt were used as controls on time series these series were made up of comparisons between 15 min f plot fe values and interpolated monthly median fe values evidence for coupling was found for the analyses which involved 97 controls the evidence in the f plots for three events involving e patches which investigators have examined in some detail using the vhf radar at chung li suggests that these events are also coupled to isolated spread f occurrence copyright 2003 by the american geophysical union

the multi instrumented studies of equatorial thermosphere aeronomy scintillation system climatology of zonal drifts a spaced antenna scintillation system was installed at ancon peru in may 1994 to measure scintillation of 250 mhz signals from a geostationary satellite by three antennas spaced in the magnetic east west direction these measurements were used to establish the climatology of the zonal drift of the irregularities which cause equatorial scintillations the major objective of this study is to compare this drift climatology to the climatology of zonal neutral wind which is the driver of the equatorial electrodynamics a comparison of these two climatologies in conjunction with scintillation statistics may provide some clues regarding factors which help or hinder the formation of equatorial spread f esf with these objectives in mind the first year s drift and scintillation statistics have been presented as a function of local time season and magnetic activity and compared with the statistics of ion drift published earlier from incoherent scatter radar observations the scintillation drift is in good agreement with the jicamarca radar observations except for the fact that the local time dependence of our drift observations exhibit a broader maximum the broad maximum may be attributed to lower ion drag experienced in the presence of esf due to sustained uplifting of the ionosphere during magnetically active periods the scintillation drift often exhibits east to west reversals presumably because of the disturbance dynamo effects the westward drifts during such reversals may be as large as 100 m s we have also modeled the zonal drifts as a seasonal basis by using hedin s neutral wind model and anderson s fully analytical ionospheric model the modeled zonal drifts present good quantitative agreement with the drifts obtained with the scintillation technique

numerical study of explosively developing extratropical cyclones in the northwestern pacific region abstract numerical simulations of six explosively developing extratropical cyclones in the northwestern pacific ocean region are conducted using a regional mesoscale numerical model the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 cyclones are categorized according to the locations where they form and develop okhotsk japan sea oj cyclones originate over the eastern asian continent and develop over the sea of japan or the sea of okhotsk pacific ocean land po l cyclones also form over the asian continent and develop over the northwestern pacific ocean and pacific ocean ocean po o cyclones form and develop over the northwestern pacific ocean two cases the most extreme and normal deepening rate cases for each cyclone type are selected and simulated simulations show that the extreme cyclone of each type is characterized by a different mesoscale structure and evolutionary path which strongly reflect the larger scale environment a

a composite study of explosive cyclogenesis in different sectors of the north atlantic part i cyclone structure and evolution general characteristics of the dynamical and thermal structure and evolution of strong explosive cyclones in the northwestern atlantic near north america 18 cases and the extreme northeastern atlantic near iceland 19 cases are compared and contrasted through a composite study twice daily gridded analyses from the european centre for medium range weather forecasts at 2 58 resolution from january 1985 to march 1996 are used in the process of case selection it is found that the frequency of rapid cyclogenesis in the greenland iceland region is higher than previously thought and some of the events can be extremely violent many dynamically consistent differences are found when composite cyclones in the two sectors of the north atlantic are compared the upper level forcing that triggers the development in the northeast atlantic nea is no less intense at the onset of rapid deepening the nea cyclones are also associated with lower static stability and locally concentrated but shallower thermal gradient with less overall environmental baroclinicity these factors lead to rapid depletion of available potential energy and result in a faster evolution and a shorter life cycle therefore low level thermal gradient and upper level forcing components all weaken immediately after rapid deepening the low level incipient low in the nea composite is also stronger with a distinct potential vorticity pv anomaly visible at least 24 h prior to most rapid deepening and the development produces a more pronounced warm core seclusion explosive cyclones in the northwest atlantic on the other hand tend to have a higher stability and a greater amount of environmental baroclinicity with temperature gradients in a broader area and deeper layers these factors correspond to slower evolution and a longer life cycle for cases in the nea near iceland it appears that both upper level forcing and initial system strengths affect the maximum deepening rate the close proximity of this region to the high pv reservoir in the lower stratosphere is helpful in the generation of very strong forcing and a violent development under favorable synoptic conditions when a parent cyclone with appreciable strength exists to the north northeast of the incipient system

synoptic activity in the seas around antarctica abstract the recent ncep department of energy doe reanalysis 2 update of the original ncep ncar dataset provides what is arguably the highest quality analyses spanning two decades available for the high southern latitudes it therefore offers an excellent starting point from which to assemble a modern comprehensive and reliable picture of synoptic activity in the subantarctic region this set covering the modern satellite era from january 1979 to february 2000 is used herein in addition the exploration in this study has been conducted with sophisticated feature tracking and trajectory analysis software it is shown that the high southern latitude cyclone system density is greatest in the indian ocean and to the south of australia near or to the south of 60 s the numbers in winter exceed those in summer except over a few but important regions such as the bellingshausen sea the antarctic coastal region is confirmed as one of high cyclonicity as is that in the northern part of the antarctic

characteristics of winter cyclone activity in the northern north atlantic insights from observations and regional modeling 1 fields from the ncep ncar reanalysis are used in conjunction with simulations from polar mm5 to examine regional processes contributing to cyclone development in the sub arctic arctic sector of the north atlantic strong deepening of systems 6 hpa 6 hours is especially common south of the tip of greenland and in the vicinity of the mean icelandic low il a secondary maximum is located just south of svalbard composite analyses of strongly deepening systems in these areas point to the influence of pronounced preexisting low level temperature gradients linked to ocean currents the sea ice margin and ocean land contrasts the area of preferred deepening near svalbard corresponds to the northernmost penetration of open water in the north atlantic impacts of greenland s orography are prominent in the synoptic complexity of the region typical synoptic situations examined as case studies include splitting or bifurcation of cyclones at the southern tip of greenland orographic cyclogenesis in the lee of greenland at the location of the mean il and deepening of preexisting systems near the il orographic influences are clearly captured in polar mm5 simulations for which control runs of the three cases are compared to runs for which the orography of greenland is removed

influence of wintertime large scale circulation on the explosively developing cyclones over the western north pacific and their downstream effects 1 the relationships between large scale wintertime circulation and extratropical cyclones that develop explosively the so called bomb cyclones over the western north pacific are investigated using japanese long term reanalysis project data on a monthly basis the east asian winter monsoon variability strongly modulates the bomb cyclone activity in terms of its geographical distribution when the monsoon is strong the bomb cyclone activity tends to concentrate in the vicinity of the kuroshio current and the kuroshio extension near japan while when the monsoon is weak it disperses over the broader areas the enhancement of the monsoon increases the heat and moisture supply from warm currents facilitating unstable conditions within the atmospheric boundary layer and intensifying baroclinicity in the lower troposphere these factors are believed to play a role in inducing bomb cyclones particularly along the warm currents on submonthly timescales the stationary rossby wave propagation along the south asian waveguide serves as a prominent trigger for the rapid reinforcement of synoptic scale disturbances around japan when a pronounced bomb cyclone comes to its mature stage northeast of japan it is capable of exciting stationary rossby waves downstream from the asian jet exit region as vorticity forcing the stationary wave packets developing southeastward across the north pacific ocean basin induce surface cyclogenesis in the vicinity of the hawaiian islands by leading to the equatorward advection of higher potential vorticity from the midlatitudes bringing about the occurrence of kona storms which cause weather hazards in hawaii

the spatial distribution and evolution characteristics of north atlantic cyclones a climatology of extratropical cyclones is produced using an objective method of identifying cyclones based on gradients of 1 km height wet bulb potential temperature cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods the north atlantic storm track is reproduced along with the major regions of genesis cyclones are grouped according to their genesis location and the corresponding lysis regions are identified most of the cyclones that cross western europe originate in the east atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west atlantic east atlantic cyclones also have higher 1 km height relative vorticity and lower mean sea level pressure at their genesis point than west atlantic cyclones this is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of preexisting parent cyclones the evolution characteristics of composite west and east atlantic cyclones have been compared the ratio of their upper to lower level forcing indicates that type b cyclones are predominant in both the west and east atlantic with strong upper and lower level features among the remaining cyclones there is a higher proportion of type c cyclones in the east atlantic whereas types a and c are equally frequent in the west atlantic

anomalous occurrence features of the preliminary impulse of geomagnetic sudden commencement in the south atlantic anomaly region 1 occurrence features of the preliminary impulse pi of geomagnetic sudden commencement sc both in the pacific ocean and south atlantic anomaly saa regions were investigated using the long term magnetic field data obtained from the circum pan pacific magnetometer network cpmn and nict space weather monitoring nswm magnetometer networks the low latitude preliminary reverse impulse pri at okinawa oki dip latitude 37 97 in the pacific ocean region appeared in all the magnetic local time mlt sectors with the peak occurrence rate of 40 around noon on the other hand the pri occurrence rate at santa maria sma dip latitude 34 35 near the center of the saa region showed a significant enhancement in the daytime sector 0800 1600 h mlt with the peak value of 80 which resembles the occurrence feature of the equatorial pri moreover the pri amplitude around noon at sma was about 3 0 times larger than that at oki from the calculation of the ionospheric conductivity derived from the iri 2007 and nrlmsise 00 models it is shown that the height integrated conductivity was more enhanced in the saa region sma where the ambient magnetic field intensity is weak compared with that in the pacific ocean region oki therefore the anomalous increase of the pri occurrence and amplitude is caused by the significant enhancement of the ionospheric conductivity due to the weakness of the ambient magnetic field intensity in the saa region

ionospheric responses to the october 2003 superstorm longitude local time effects over equatorial low and middle latitudes 1 ionospheric responses to the major magnetic storm disturbances of october 2003 are investigated using database selected in the brazilian and japanese asian longitude sectors data obtained from latitudinally spaced digisondes in the equatorial and low latitude sites in brazil and from the asian and japanese ionosonde network the total electron content data from the extensive japanese gps receiver chain and magnetometer data from the pacific equatorial electrojet stations are analyzed during the period 28 31 october prompt penetrating pp dawn dusk polar cap electric fields produce large f region plasma uplift on the dayside and eveningside while the associated westward electric field on the nightside produces large downdraft of the f region plasma and causes development of westward electrojet current observed for the first time episodes of pp electric field effects appear to be of larger intensity over brazil than over asian longitudes equatorial anomaly development due to undershielding as well as overshielding electric fields was observed in the brazilian and in the asian sectors disturbance dynamo electric field causes large nighttime f layer uplifts that are modulated by strong meridional winds in both sectors the disturbance electric field local time variation patterns are compared with the results of recent global model mtiegcm simulation by richmond et al 2003 and validated in some cases transients of transequatorial winds flipping direction from southward to northward in the widely separated longitude sectors were diagnosed to be present toward the final recovery phase of the storm these results are presented and discussed in this paper

characterizing the 10 november 2004 storm time middle latitude plasma bubble event in southeast asia using multi instrument observations 1 the development and dynamics of ionospheric plasma bubble pb irregularity during the super storm of 7 11 november 2004 are investigated using the data from a multi instrument network operated in southeast asia analysis of fluctuations in global positioning system total electron content gps tec ionosonde gps scintillation and in situ satellite density data indicates a series of intense pb associated irregularities at equatorial low and middle latitudes in the japanese longitude on 10 november however in the chinese sector the scintillations and pb irregularities are confined within the range of 20 50 n in geographic latitude and 110 125 e in geographic longitude the absence of equatorial pb irregularities in this sector shows a major difference from that in the close by longitude japanese sector in the southern hemisphere australian sector the irregularities occurrence is present as a symmetrical distribution at conjugate latitudes combined analysis of the data from osan and wuhan ionosondes illustrates that the middle latitude spread f irregularities initially develop at the lower part of the f region and then distribute in the whole f region this initiation of spread f at lower altitudes indicates that the middle latitude pb associated irregularities are locally generated these results together with the irregularities occurrence sequence from higher to lower latitudes and the onset time delay of several hours implies that the presence of pb associated irregularities within a latitude range of 20 50 n in the chinese sector cannot be attributed to the effects of prompt penetration electric fields ppefs although the equatorial pbs in the close by longitude are seen to be associated with ppefs the possible mechanism is the f region plasma instabilities triggered by wave structures which act as an external driving force and seed active plasma dynamics and instability growth at middle latitude

effects of interplanetary electric field on the development of an equatorial spread f event 1 on a geomagnetically disturbed night 7 january 2005 an equatorial spread f esf event was captured during premidnight hours by the indian mst radar operated in ionospheric mode at gadanki 13 5 n 79 2 e dip angle 12 5 n the base height of the ionospheric f region over dip equator and a low latitude station showed similar variation during most of the esf interval except mainly during 2145 2200 ist indian standard time ist universal time ut 5 5 hours the zonal electric field variation over dip equator responded to a prompt penetration event at 2000 ist by gradually changing its polarity from westward to eastward after 2015 ist leading to the initiation of esf at 2035 ist the linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the prompt penetration effect is taken into account the zonal electric field became westward again after 2100 ist however it ephemerally turned eastward shortly after 2145 ist 1615 ut that is believed to be associated with an overshielding condition a plasma plume got resurrected after 30 min indicating the association of the development of this plume structure with the overshielding electric field the oi 630 0 nm airglow intensity variations observed by a collocated airglow photometer simultaneously operated in a bidirectional zenith and east mode corroborated well with the esf structure and dynamics during the disturbed period these observations evince the active role of interplanetary electric field ief in the development of esf in the premidnight hours

analysis of meteorological precursors to ordinary and explosive cyclogenesis in the western north pacific abstract thirty five cases of cyclogenesis that occurred during the cold seasons from 1975 to 1995 in the western north pacific ocean are studied to determine common and disparate dynamic and thermodynamic structures in both the ordinary and rapid developments an analysis of 1000 hpa height and 1000 500 hpa thickness anomalies with respect to the 20 yr climatology reveals the following results though each sample of cyclogenesis is characterized by a favorable appearing thickness trough ridge structure important differences are found both the upstream surface anticyclone and the downstream precedent cyclone are preferentially stronger at the beginning of the most rapid cyclogenesis in the strong sample because of the consequently stronger equatorward flow the 1000 500 hpa thickness anomaly in the strong sample is colder by approximately 40 m 2 c in the region of incipient cyclogenesis and eastward by 1500 km a harmonic time series analysis of ncep gridded fields partitions the geopotential height

interdecadal climate variability in the subpolar north atlantic the statistical relationships between various components of the subpolar north atlantic air sea ice climate system are reexamined in order to investigate potential processes involved in interdecadal climate variability it is found that sea surface temperature anomalies concentrated in the labrador sea region have a strong impact upon atmospheric sea level pressure anomalies over greenland which in turn influence the transport of freshwater and ice anomalies out of the arctic ocean via fram strait these freshwater and ice anomalies are advected around the subpolar gyre into the labrador sea affecting convection and the formation of labrador sea water this has an impact upon the transport of north atlantic current water into the subpolar gyre and thus also upon sea surface temperatures in the region an interdecadal negative feedback loop is therefore proposed as an internal source of climate variability within the subpolar north atlantic through the lags associated with the correlations between different climatic components observed horizontal advection time scales and the use of boolean delay equation models the time scale for one cycle of this feedback loop is determined to have a period of about 21 years

equatorial ionospheric plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions from polarimeter observations amplitude scintillation and faraday rotation angle fluctuations of satellite vhf beacons registered by electronic polarimeters operated at two stations spaced 110 km apart in the magnetic east west direction namely cachoeira paulista 22 41 s 45 w dip angle of 26 and sao jose dos campos 23 12 s 45 51 w dip angle of 26 in brazil are analyzed for equinoctial and summer months of 1982 1983 to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances the scintillation patch occurrences and total electron content fluctuations representing plasma depletion structures decrease during premidnight hours and are enhanced in the postmidnight period the occurrences often extend to morning hours with increasing magnetic activity index while the night events are associated with eastward irregularity patch motion the morning events have westward velocities the reversal occurring around 0400 lt reflecting the morning velocity reversal in the f region bulk plasma motion reported earlier from jicamarca radar measurements the westward plasma bubble motions reported here represent the first observation of this kind another important finding from the present investigation is a clear tendency for the zonal plasma motion namely the equatorial meridional electric field to become enhanced mainly in the premidnight hours immediately following strong magnetic activity

sensitivity of cyclogenesis to sea surface temperature in the northwestern atlantic during the intensive observation period 15 13 15 february 1997 of the fastex experiment a major cyclone crossed the atlantic ocean from the newfoundland basin to southern iceland its surface low center deepened by 17 hpa in 7 h when the perturbation crossed the north atlantic current nac from cold 38c to warm water 158c to elucidate the role of sea surface temperature sst and air sea fluxes in the dynamics of oceanic cyclones three nonhydrostatic mesoscale simulations were performed the first one is a control experiment with a realistic sst field describing in detail the oceanic front associated with the nac system the two following simulations are sensitivity experiments where the sst front is removed the first one uses a uniformly cold sst equal to 38c and the second one uses a uniformly warm sst equal to 158c the frontogenetic function and the vertical velocity sources in the lower atmospheric layers of the three simulations were diagnosed in the control simulation the surface heat fluxes were found to be negative in the perturbation warm sector and positive in the region behind the cold front as reported by numerous authors this pattern of surface heating and cooling did not intensify the cyclone except in the occlusion when the phasing with the sst front occurs this configuration enhances the horizontal gradient of surface buoyancy flux across the occlusion which increases the buoyancy flux source of vertical velocity w when the sst front is removed the surface heat fluxes are strongly affected in magnitude and in spatial variability the marine atmospheric boundary layer mabl stability the convective activity the warm advection in the core of the wave and the heating depth are strongly affected by the different surface flux fields there are several consequences i the uniform ssts tend to decrease the cold front intensity of the wave ii a weaker buoyancy flux source of vertical velocity is found above a uniform cold sst across the occlusion in comparison with the control case and iii surprisingly a weaker w buoyancy flux source is also found above a uniform warm sst because of a higher heating depth vertical velocity depends not only on the buoyancy flux forcing but also on the thermal wind the turbulent momentum and the thermal wind imbalance forcings the thermal wind forcing and the thermal wind imbalance forcing were the most sensitive to the sst compared to the turbulent momentum forcing this result means that i the feed back of the ageostrophic circulation induced by the surface is greater on the kinematic forcings than on the turbulent forcings and ii the turbulent momentum forcing does not play a crucial role in cyclogenesis above a uniform warm sst the strongest intensity of the occlusion is due to the strongest w thermal wind forcing and w thermal wind imbalance forcing in the mabl in spite of a weaker w buoyancy flux forcing than in the control case this result is explained by the convective activity that increases the low level convergence and vorticity spinup this point means that latent heat release and baroclinicity are in tight interaction in the first 12 h and at the scale of the simulation domain the three cyclones evolve similarly but at a small scale their internal structures diverge strongly and rapidly the scale at which the surface turbulent fluxes act on the dynamics of marine cyclones is therefore important finally the cyclone simulated in the warm sst case developed more rapidly than those simulated in the real and the cold sst cases this behavior is attributed to the strong positive surface heat fluxes because they preconditioned the mabl by moistening and heating the low levels during the incipient stage of the cyclone development

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

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

a super bubble detected by dense gps network at east asian longitudes a post sunset bubble manifested by total electron content depletion was observed at midlatitudes similar to 30 degrees 34 degrees n similar to 130 degrees 134 degrees e during the main phase of a storm on 12 february 2000 with loss of lock and the rate of the total electron content index maps the bubble was seen to bifurcate at its early growth phase the upward drift speed was observed similar to 300 m s at similar to 2150 km and decreasing with increasing altitude and time the bubble had unusually large latitudinal extension reaching midlatitude of 36 5 degrees n 31 5 degrees n magnetic latitude indicating an apex height of similar to 2500 km in process of the evolution the bubble drifted eastward at a speed of similar to 50 m s the f region peak height and density obtained by a meridional ionosonde chain suggested a prompt penetrating magnetospheric electric field helped to trigger the super bubble

equatorial ionosphere responses to two magnetic storms of moderate intensity from conjugate point observations in brazil 1 equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated for the first time by conjugate point observations in brazil the study focuses on storm induced changes in the evening prereversal vertical drift thermospheric trans equatorial winds spread f plasma bubble irregularity development electron density plasma frequency heights the eia strength and zonal plasma drifts it is based on data obtained from five digisondes operated in brazil three of them being part of a conjugate point equatorial experiment copex involving a dip equatorial and two magnetic conjugate sites at 12 the other two were operated at the equatorial ionization anomaly eia trough and crest locations at nearby magnetic meridians the results bring out and clarify many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences during both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous an under shielding over shielding electric field occurring in the evening hours causes enhancement suppression of the prereversal vertical drift and post sunset spread f plasma bubble generation the same electric fields cause post sunset eia enhancement and suppression respectively post sunset post midnight spread f can develop from under shielding over shielding electric fields while it can be disrupted by over shielding under shielding electric field trans equatorial winds are found to be ineffective to stabilize the post sunset f region against the destabilizing effect of strong prereversal vertical drift storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields through their effect of inducing vertical hall electric fields rather than by a disturbance westward thermospheric wind during these storms

tropical plumes and extreme precipitation in subtropical and tropical west africa three cases of extreme precipitation in october january and march april over subtropical north western and tropical west africa have been selected in order to study the moisture transports precipitation generation mechanisms and large scale dynamics involved all cases show strong tropical extratropical interactions and elongated cloud bands extending from the tropics into the subtropics usually referred to as tropical plumes tps investigations are based on observational data and high resolution output from simulations using the university of wisconsin nonhydrostatic modeling system trajectory analyses show that moisture is transported from the tropical easterly mid level flow the monsoonal southerlies and the north easterly trade winds to provide precipitable water and potential instability at mid tropospheric levels the instability is released through ascent related both to weak quasi geostrophic forcing to the east of an upper level trough and to the strong inertially unstable and highly divergent upper level subtropical jet stj accompanying the tp in the january and march cases the passage of a precursor upper level trough over the same location precedes the development and initiates the moisture transport from the deep tropics the associated north westerly cold advection supports the generation of precipitation by triggering convection over the tropical atlantic ocean whose outflow feeds into the stj over africa and by enhancing the vertical mass transport within the intertropical discontinuity over and near west africa in october when the still active african monsoon facilitates the extraction of tropical moisture a wave in the tropical easterlies and strong trade winds from the southern hemisphere are dominant factors low level cyclogenesis and frontogenesis only play roles in the late stages of the developments the elongated mostly positively tilted potential vorticity pv streamers associated with the observed troughs form as a result of an equatorward transport of high pv air downstream of a large ridge over the north atlantic the rapid amplification of the ridge is achieved through a combination of negative horizontal pv advection and diabatic reduction of upper level pv through latent heating within a cloud band that forms in connection with an explosive baroclinic development near the east coast of north america copyright 2005 royal meteorological society

the mean and annual cycle of upper layer temperature fields in relation to sverdrup dynamics within the gyres of the atlantic ocean using 28 years of expendable bathythermograph data 1967 1994 we describe the mean and annual cycle of the upper ocean temperature fields in the atlantic from 30 s to 50 n in the context of the basin scale wind driven gyres sverdrup stream function field which provide a framework for describing the oceanographic measurements we examine the circulation field implied by the temperature distributions which are used as a proxy for the field of mass similarities between the temperature and stream function fields increase with depth in the lower to subthermocline depths of the tropical and equatorial gyres the zonal currents form a closed circulation a southeastward boundary current is suggested near and below 150 m that provides closure for the tropical gyre and the equatorial gyre axis is southward of that suggested by the stream function field higher in the water column the north equatorial countercurrent necc may be a surface manifestation of the north equatorial undercurrent neuc where the latter can be interpreted as the southern limb of the tropical gyre because there are large vertical shears in the tropics the equatorial gyre is not clearly indicated in the vertically integrated temperature field but appears below about 200 m here the south equatorial undercurrent seuc can be interpreted as the eastward flowing northern limb of the equatorial gyre and is opposite in direction to the westward flowing south equatorial current above both the neuc and seuc are analagous to currents in the pacific that are governed by non sverdrup dynamics despite the shortcomings of the data the mean annual cycle appears to be relatively stable and we have discounted the possibility that in regions where it represents a significant percentage of the total variance it is changing slowly over the 28 years of record the wind forcing fields which undergo large meridional movements 5 6 of latitude during their annual cycle with some exceptions have essentially no counterpart in gyre movements between their seasonal extremes most of the variability associated with the annual cycle is confined to the upper 300 m greatest variability where ranges exceed 6 c occurs in the northwestern atlantic in late winter and early spring during this time of year south of the gulf stream and below about 100 m water temperatures exhibit a systematic phase lag with depth the next largest area of variability where ranges can also exceed 6 c resides in the tropical western basin between the equator and 10 n just below 100 m in the eastern basin ranges decrease and shoal additionally the phase fields are consistent with the intensification and relaxation of the tropical ridge trough system where the necc disappears in march in the west but the necc neuc complex is strongest in september

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

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

convective injection into stratospheric intrusions 1 stratospheric intrusions tropopause folds are known to be major contributors to stratosphere troposphere exchange the specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere however are not entirely understood this study presents direct observations of moist convection penetrating into stratospheric intrusions the characteristics of convective injection are shown by using in situ aircraft measurements radar reflectivities and model analyses convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion aircraft measurements from the stratosphere troposphere analyses of regional transport 2008 start08 experiment show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv trajectory analyses show that convective injection can impact transport in both directions from troposphere to stratosphere and from stratosphere to troposphere we present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions in particular convective injection is found to be associated with a split front where the upper level frontal boundary outruns the surface cold front

response of rapidly developing extratropical cyclones to sea surface temperature variations over the western kuroshio oyashio confluence region the dynamical response of rapidly developing extratropical cyclones to sea surface temperature sst variations over the western kuroshio oyashio confluence wkoc region was examined by using regional cloud resolving simulations this study specifically highlights an explosive cyclone that occurred in early february 2014 and includes a real sst experiment cntl run and two sensitivity experiments with warm and cool sst anomalies over the wkoc region warm and cool runs the results derived from the cntl run indicated that moisture supply from the ocean was enhanced when the dry air associated with the cold conveyor belt ccb overlapped with warm currents further the evaporated moisture contributed substantially to latent heat release over the bent back front with the aid of the ccb leading to cyclone intensification and strengthening of the asymmetric structure around the cyclone s center such successive processes were more active in the warm run than in the cool run the dominance of the zonally asymmetric structure resulted in a difference in sea level pressure around the bent back front between the two runs the wkoc sst variations have the potential to affect strong wind distributions along the ccb through modification of the cyclone s inner system additional experiments with two other cyclones showed that the cyclone response to the wkoc sst variations became evident when the ccb north of the cyclone s center overlapped with that region confirming that the dry nature of the ccb plays an important role in latent heat release by allowing for larger moisture supply from the ocean

synoptic and dynamic aspects of an extreme springtime saharan dust outbreak in march 2004 a large scale strong and persistent outbreak of saharan dust on to the adjacent tropical and subtropical atlantic ocean was observed in satellite imagery surface observations show that the event was accompanied by unusual weather conditions across large parts of north africa including low temperatures and strong winds over the sahara extreme precipitation in libya and a heat wave on the guinea coast the dust outbreak was associated with an unseasonally southerly position of the intertropical convergence zone and a delayed northward progression of the african monsoon the dust front was initially related to a density current caused by strong evaporational cooling along a precipitating cloud band that penetrated into the northern sahara ahead of an upper level trough at later stages massive upper level convergence sinking low level divergence and an explosive anticyclogenesis over northwest africa caused strong northerly flow and a quick spreading of the dust front to the south and west the strong pressure gradients over north africa were further enhanced by the formation of a cyclone ahead of the upper trough a dynamical analysis based on potential vorticity pv theory provides new insights into the generation of north african harmattan surges using a pv inversion it is shown that the explosive anticyclogenesis was caused largely by unbalanced dynamics related to the density current divergent outflow from the precipitation over libya and inertial instability in the entrance region of the strong subtropical jet and tropical plume along the eastern side of the upper trough these processes enhanced the effects of the balanced advection of negative vorticity and cold air by the large scale wave moreover we show the importance of an explosive cyclogenesis event over the central north atlantic for the amplification of the downstream wave associated with the penetration of the cold front into north africa copyright 2006 royal meteorological society

response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000 the effects of the great magnetic storm of july 15 2000 on the equatorial ionosphere have been studied by ground based and satellite in situ measurements a large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo in that environment the imf bz turned southward and presumably caused penetration of e fields to low latitudes this e field initiated the onset of 250 mhz and l band scintillations at ascension island 15 w and precipitous tec decrease at fortaleza brazil 38 w bounding the narrow longitude region in the south atlantic these impulsive ionospheric effects were extremely well correlated with abrupt decreases of sym h 1 min resolution dst the dmsp in situ measurements showed the presence of severe ion density bite outs extending over 30 latitude in the south atlantic magnetic anomaly region the rocsat 1 satellite measured upward and large southward ion drifts in the same sector

an investigation of ionospheric responses and disturbance thermospheric winds during magnetic storms over south american sector 1 this paper presents the results of a study of the ionospheric and thermospheric response to magnetic storm disturbances for four stations covering a wide range of latitude in the south american region the study is based on the f layer critical frequency fof2 and the peak height hmf2 from fortaleza fz which is equatorial cachoeira paulista cp which is low latitude concepcion con a midlatitude site and king george island kgi a middle to high latitude site equivalent neutral winds are extracted from the measured hmf2 by employing the field line interhemispheric plasma flip model the equatorial ionization anomaly eia can undergo enhancement due to magnetospheric disturbance electric field that penetrates to low latitudes during the growth phase of a storm substorm whereas eia inhibition occurs more often under disturbance dynamo dd electric field season dependent meridional transequatorial winds can significantly alter the eia response to disturbance electric fields large amplitudes of dd electric field is observed during evening and morning hours in equinoctial but not in winter months over the brazilian low latitude of large westward magnetic declination angle large equatorward meridional wind surges seem to be helped by the presence of disturbance zonal westward winds the low latitude disturbance can in some cases be traced to specific disturbance fronts originating promptly from auroral activity enhancements this study confirms earlier studies that show that the quiet time meridional wind increases with increase of latitude and that over midlatitude it shows decreases with increase of solar flux due to the effect of the ion drag force this study further shows that the disturbance meridional wind and the intensity of dd electric field increase with increasing intensity of high latitude energy input the negative ionospheric storm phase over middle latitude observed in equinox and not in winter is also intensified with the increasing intensity of high latitude energy input

evolution of equatorial ionospheric bubbles during a large auroral electrojet index increase in the recovery phase of a magnetic storm 1 we present a model and observations of the evolution of equatorial ionospheric bubbles during a large auroral electrojet ae index increase in the recovery phase of a geomagnetic storm using a three dimensional time dependent numerical simulation model we find for the 19 21 october 1998 storm that the equatorial bubble evolution is different during storm time as compared to quiet time conditions we have found that the storm time vertical drift in conjunction with reduced off equatorial e region shorting is the primary mechanism that distinguishes the large ae increase recovery phase storm time evolution from the quiet time case comparison of the simulation model with ground based storm time radar observations is made

subseasonal variations in warm season moisture transport and precipitation over the central and eastern united states abstract subseasonal variations in warm season may august precipitation over the central and eastern united states are shown to be strongly linked to variations in the moisture entering the continent from the gulf of mexico within a longitudinally confined channel referred to here as the texas corridor or tc these variations reflect the development of low level southerly wind maxima or jets on a number of different timescales in association with distinct subcontinental and larger scale phenomena on the diurnal timescale the tc moisture flux variations are tied to the development of the great plains low level jet the composite nighttime anomalies are characterized by a strong southerly moisture flux covering northeast mexico and the southern great plains and enhanced boundary layer convergence and precipitation over much of the upper great plains the strongest jets tend to be associated with an anomalous surface low over the great plains reflecting a predilection for periods when midlatitude

statistical analysis and updated climatology of explosive cyclones abstract a statistical analysis of 12 and 24 hour deepening rates for all surface lows analyzed on at least two successive nmc 12 hourly front half hemispheric surface charts was performed for one year of data both 12 and 24 hour deepening distributions showed statistically significant at the 5 level departures from normality with the largest deviations occurring along the tail of the distribution associated with most rapid deepening the sum of two normal curves of different means and standard deviations was successfully fitted to the deepening distributions suggesting that most cases of explosive cyclogenesis are the result of some additional physical mechanism distinct from ordinary baroclinic instability the climatology of explosive cyclones sanders and gyakum was updated to include the 1979 82 cold seasons and compared to the previous three year sample in addition a climatology of formation positions maximum deepening positions and dissipation positions for all cyclones in a one year d

the march 1993 superstorm cyclogenesis incipient phase synoptic and convective scale flow interaction and model performance abstract the incipient stages of the 12 14 march 1993 superstorm ss93 cyclogenesis over the gulf of mexico are examined noteworthy aspects of ss93 include 1 it is the deepest extratropical cyclone ever observed over the gulf of mexico during the 1957 96 period and 2 existing operational prediction models performed poorly in simulating the incipient cyclogenesis over the northwestern gulf of mexico a dynamic tropopause dt analysis shows that ss93 is triggered by a potent potential vorticity pv anomaly as it crosses extreme northern mexico and approaches the gulf of mexico the low level environment over the western gulf of mexico is warmed moistened and destabilized by a persistent southerly flow ahead of the approaching pv anomaly ascent and a lowering of the dt associated with a lowering of the potential temperature ahead of the pv anomaly contributes to further destabilization that is realized in the form of a massive convective outbreak an examination of the national centers for envi

ionospheric zonal velocities at conjugate points over brazil during the copex campaign experimental observations and theoretical validations 1 we analyze in detail the zonal velocities of large scale ionospheric plasma depletions over two conjugate stations inferred from oi 630 nm airglow all sky images obtained during the conjugate point equatorial experiment copex campaign carried out in brazil between october and november 2002 the conjugate stations were boa vista bv geogr 2 8n 60 7w dip angle 22 0 n and campo grande cg geogr 20 5s 54 7w dip angle 22 32 s over campo grande the zonal velocities were measured also by a system of spaced gps scintillation receivers the airglow zonal velocities at the conjugate sites were seen to agree very closely except for a slightly increased velocity over cg which we attribute to the presence of the geomagnetic anomaly the results show a high degree of alignment of the bubbles along the geomagnetic field lines during the bubble development phase and as the bubbles travel eastward thereby suggesting that the neutral zonal wind effect in the zonal plasma motion is an integrated effect along the flux tube the zonal velocities obtained from the gps technique were always larger than those calculated by the airglow technique which permitted observation of zonal plasma velocity shear between the altitudes of the airglow emitting layer and of the gps scintillation theoretical ambient plasma zonal velocities calculated using the formulations by haerendel et al 1992 and eccles 1998 are compared with the experimental results our results also reveal some degree of dependence of the zonal velocities on the solar flux f10 7 and magnetic kp indices during the copex period

abnormal evening vertical plasma drift and effects on esf and eia over brazil south atlantic sector during the 30 october 2003 superstorm 1 equatorial f region vertical plasma drifts spread f and anomaly responses in the south american longitude sector during the superstorm of 30 october 2003 are analyzed using data from an array of instruments consisting of digisondes a vhf radar gps tec and scintillation receivers in brazil and a digisonde and a magnetometer in jicamarca peru prompt penetrating eastward electric field of abnormally large intensity drove the f layer plasma up at a velocity 1200 ms 1 during post dusk hours in the eastern sector over brazil the equatorial anomaly was intensified and expanded poleward while the development of spread f plasma bubble irregularities and gps signal scintillations were weaker than their quiet time intensity significantly weaker f region response over jicamarca presented a striking difference in the intensity of prompt penetration electric field between peru and eastern longitudes of brazil the enhanced post dusk sector vertical drift over brazil is attributed to electro dynamics effects arising energetic particle precipitation in the south atlantic magnetic anomaly sama these extraordinary results and their longitudinal differences are presented and discussed in this paper

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

equatorial density depletions observed at 840 km during the great magnetic storm of march 1989 early on march 14 1989 a thermal plasma probe on the defense meteorological satellite program dmsp f9 spacecraft detected extensive and dramatic decreases in the ion density at 840 km near 2130 lt during two consecutive transequatorial passes over south america the order of magnitude decreases in the ion density extended more than 4000 km along the satellite track the depletions were accompanied by upward and westward plasma drifts both in excess of 100 m s their onsets and terminations were marked by extremely sharp density gradients dmsp f9 observed no similar depletions over the atlantic during preceding orbits a partial depletion was detected over the eastern pacific during the following orbit the dmsp f9 ground track passed slightly west of a brazilian total electron content tec station and two brazilian ionosondes during the first depletion encounter the tec fell far below normal during the night of march 13 14 the ionosonde measurements indicate that in the hour after sunset before dmsp passed through the depletions the f2 layer rose rapidly and disappeared but at the time of the first depletion encounter hmf2 was decreasing over one of the stations the dmsp f8 satellite which orbits in the dawn dusk meridian made related measurements on march 13 and 14 crossing the equator at dust on march 13 at the same longitude where dmsp f9 encountered the first depletion dmsp f8 detected upward and westward drifts but it measured extremely large rather then depleted ion densities during two dawn passes over the eastern pacific on march 14 dmsp f8 observed depletions somewhat similar to those detected by dmsp f9 large westward drifts accompanied the depletions detected by dmsp f8 it is quite probable that the morningside depletions detected on march 14 are remnants of those detected earlier by dmsp f9 in the evening sector we develop a phenomenological model reconciling dmsp f8 f9 and ground based measurements our calculations show that rapid upward drifts sustained for several hours can produce depletions in the equatorial ion density with sharp gradients at their high latitude boundaries consistent with the data we discuss possible contributing mechanisms for generating these upward drifts these include direct penetration of the magnetospheric electric field to low latitudes the electric fields generated by the disturbance dynamo and the effects of conductivity gradients near the dusk terminator and the south atlantic anomaly

the structure and evolution of a continental winter cyclone part ii frontal forcing of an extreme snow event abstract the production of a narrow heavy occasionally convective snowband that fell within a modest surface cyclone on 19 january 1995 is examined using gridded model output from a successful numerical simulation performed using the university of wisconsin nonhydrostatic modeling system it is found that the snowband was produced by a thermally direct vertical circulation forced by significant lower tropospheric warm frontogenesis in the presence of across front effective static stability differences as measured in terms of the equivalent potential vorticity pve the sometimes convective nature of the snowband resulted from the development of freely convective motions forced by frontal lifting of the environmental stratification model trajectories demonstrate that a stream of warm moist air ascended through the trowal portion of the warm occluded structure that developed during the cyclone life cycle the lifting of air in the trowal was in this case forced by lower tropospheric frontogenesis occ

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

equatorial ionospheric responses to high intensity long duration auroral electrojet activity hildcaa 1 the knowledge of the coupling processes between the magnetosphere and the equatorial ionosphere is of basic importance to the understanding of the near earth space weather this study focuses on observational results of such coupling processes based on data collected during the phenomenon defined as high intensity long duration continuous ae activity hildcaa which occurs outside the main phase of geomagnetic storms the fact that the responses of the equatorial low latitude ionosphere to hildcaa events have not been specifically focused so far is one of the motivations for this study ionosonde data on hmf2 h f and fof2 from three locations in brazil magnetic equatorial station sao luis sl subequatorial station fortaleza fz and low latitude station cachoeira paulista cp are analyzed together with ace satellite data on solar wind and interplanetary magnetic and electric fields during three hildcaa events that occurred in the years 2000 and 2001 the results did not indicate any presence of penetrating electric field disturbance during these events however they provided clear evidence of disturbance dynamo electric field and disturbance thermospheric winds through f layer height changes that were similar but generally less intense than those observed during a typical storm event the fof2 presented no particular disturbances that can be clearly attributed to the hildcaa event previous extensive studies carried out by the authors on ionospheric storm effects for these same three stations clearly illustrate the much more intense f layer storm disturbances compared with hildcaa events disturbances

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

f region east west drifts at jicamarca f region east west drifts have been measured at jicamarca for almost 10 years using incoherent scatter the drifts are westward during the day and eastward at night the daytime drift velocities are about 50 m s and change very little with season or solar cycle the evening reversal occurs at about 1600 local time throughout the solar cycle the maximum nighttime eastward drifts are about 105 and 130 m s during solar minimum and maximum respectively the daytime and nighttime drifts show very litle variation with magnetic activity these jicamarca incoherent scatter results especially the reversal times differ appreciably from results obtained using other techniques but there appear to be fairly simple explanations for the apparent disagreements

characteristics of the equatorial plasma drifts as obtained by using canadian doppler ionosonde over southern tip of india we present here characteristics of the doppler drift measurements over tirunelveli 8 73 n 77 70 e dip 0 5 n an equatorial site over southern india using doppler interferometry technique of canadian ionosonde three dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic e w and n s directions after having compared with lowell s digisonde drifts at trivandrum we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012 the observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons the comparison of doppler vertical drifts with the drifts obtained from a virtual height and b fejer drift model suggests that doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods further it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread f in the ionograms and gps l band scintillations the zonal drifts on the other hand showed westward during daytime with mean drifts of 150 200 m s and correlated well with equatorial electrojet strength indicating the role of e region dynamo during daytime while they are eastward during nighttime with mean drifts of 100 m s resembling f region dynamo process also zonal drifts showed large westward prior to the spread f onset during autumn equinox than vernal equinox suggesting strong zonal shears which might cause equinoctial asymmetry in spread f

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

shear in the zonal drifts of 3 m irregularities inside spread f plumes observed over sanya incoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma with westward drifts below the equatorial f region peak and eastward drifts above we report here observations of a clear shear structure in the zonal drifts of 3 m irregularities inside spread f sf backscatter plumes measured with a 47 5 mhz coherent scatter radar operated at a low latitude site sanya 18 4 n 109 6 e dip latitude 12 8 n the radar interferometry analysis on the zonal drifts of the 3 m irregularities yields results consistent with that estimated from the irregularity echo doppler velocity measurements with multiple beams it is shown that the sf 3 m irregularities move westward at the lowest altitudes while at higher altitudes in the same sf plume structure the 3 m irregularities drift eastward one interesting point is that the vertical shear of zonal drifts was centered at 300 km altitude over sanya which maps to an apex altitude of 650 km at magnetic equator and is thus apparently higher than the apex altitudes 250 450 km where the zonal velocity shear has usually been observed analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of f region 3 m irregularities measured over sanya cannot be totally ruled out

magnetospheric disturbance induced equatorial plasma bubble development and dynamics a case study in brazilian sector 1 equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 august 1998 are investigated using the data collected by a multistation and multi instrument diagnostic network operated at equatorial and low latitude sites in brazil and auroral electrojet activity au al imf and dst indices a magnetospheric disturbance onset in the morning of 26 august 1998 was initiated by a solar wind shock and associated imf bz polarity reversals and ssc that were soon followed by a succession of substorm like auroral electrojet ae intensifications and dst development an imf bz southward turning and associated ae intensifications in the brazilian dusk sector produced intense prompt penetration eastward electric field that caused large f region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles the latter event lasting the entire night as observed by digital ionosondes at sao luis 2 33 s 315 8 e dip angle 5 and fortaleza 3 9 s 321 55 w dip angle 9 and an all sky imager two scanning photometers and a digisonde at the low latitude site cachoeira paulista 22 6 s 315 e dip angle 28 a notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours the results show for the first time a relationship between the zonal drift velocities of optically observed large scale bubbles tens to hundreds of kilometers and that of the smaller scale kilometer sizes structures as observed by a digital ionosonde the results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours as an important finding the results further show that significant contribution to the westward plasma bubble irregularity drift normally attributed to disturbance dynamo effect could arise from prompt penetration disturbance zonal electric field in the course of a disturbance sequence lasting several hours such effect is attributed to hall electric field arising from the primary disturbance zonal electric field under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation in the brazilian longitude sector in agreement with recent evidences abdu et al 1998b

mid latitude ionospheric irregularities persisting into late morning during the magnetic storm on 19 march 2001 1 post sunrise intense ionospheric irregularities at low to mid latitudes are reported for the first time a method based on spaced receiver technique is proposed to estimate the apparent drift velocity of the irregularities by using the correlation of the slant total electron content tec from 3 gps receivers the irregularities were detected at 23 45 n by the gps earth observation network geonet of japan from 0455 lt to 1051 lt on 21 march 2001 during the recovery phase of the magnetic storm at the corresponding time spread f was observed with 3 ionosondes located meridionally at okinawa 127 8 e 26 3 n 20 7 n magnetic latitude kokubunji 139 5 e 35 7 n 30 0 n magnetic latitude and wakkanai 141 7 e 45 4 n 40 5 n magnetic latitude while an intense negative ionospheric storm was processing and propagating from mid to lower latitudes the irregularities were seen as plasma bubbles by the defense meteorological satellite program dmsp in situ measurements westward drift with the speed of 100 m s was estimated by spaced receivers from geonet and confirmed by dmsp during the evolution of the irregularities the plasma bubbles at mid latitude sustained 1 5 hour after sunrise and at the lower latitudes they survived more than 4 hours after sunrise the observations suggested that the irregularities were generated by an eastward electric field associated with the disturbance dynamo and the long time existence of the irregularities after sunrise seemed to be related to the daytime intense negative ionospheric storm on 21 march

classifying dynamical forcing mechanisms using a climatology of extratropical cyclones summary a climatology of almost 700 extratropical cyclones is compiled by applying an automated feature tracking algorithm to a database of objectively identified cyclonic features cyclones are classified according to the relative contributions to the midlevel vertical motion of the forcing from upper and lower levels averaged over the cyclone intensification period average u lratio and also by the horizontal separation between their upper level trough and low level cyclone tilt the frequency distribution of the average u lratio of the cyclones contains two significant peaks and a long tail at high u lratio although discrete categories of cyclones have not been identified the cyclones comprising the peaks and tail have characteristics that have been shown to be consistent with the type a b and c cyclones of the threefold classification scheme using the thresholds in average u lratio determined from the frequency distribution type a b and c cyclones account for 30 38 and 32 of the total number of cyclones respectively cyclones with small average u l ratio are more likely to be developing cyclones attain a relative vorticity 1 2 10 4 s 1 whereas cyclones with large average u lratio are more likely to be non developing cyclones 60 of type a cyclones develop whereas 31 of type c cyclones develop type a cyclogenesis dominates in the development region east of the rockies and over the gulf stream type b cyclogenesis dominates in the region off the east coast of the usa and type c cyclogenesis is more common over the oceans in regions of weaker low level baroclinicity

equatorial disturbance dynamo electric field longitudinal structure and spread f a case study from guar eits campaigns digisondes ionosondes an hf doppler radar and magnetometers were operated in brazil and india during the september october 1994 guara eits campaigns analysis of the data for the two disturbed intervals 2 4 october and 25 27 september provided evidence of a longitudinal structure in the disturbance dynamo dd electric field at low latitudes the dd electric field which is westward in the evening inhibited the developments of the equatorial prereversal electric field and postsunset esf whereas the simultaneous eastward field in the predawn sector did not lead to esf contrary to what is normally expected this nondevelopment of esf is suggested as evidence of the stabilizing effect of transequatorial neutral winds associated with stormtime circulation the campaign observations clearly demonstrate that the dd electric fields could often mask the low latitude ionospheric responses to prompt penetration electric fields in the course of sustained substorm activity

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

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

effects of solar and geomagnetic activities on the zonal drift of equatorial plasma bubbles equatorial plasma bubbles are mostly generated in the postsunset sector and then move in the zonal direction plasma bubbles can last for several hours and move over hundreds of kilometers even more than 1000 km in this study we use measurements of ion density by the communication navigation outage forecasting system satellite to determine the orbit averaged drift velocity of plasma bubbles the objective of the study is to identify the dependence of the bubble drift on the solar radio flux and geomagnetic activities in total 5463 drift velocities are derived over may 2008 to april 2014 and a statistical analysis is performed the average pattern of the bubble drift is in good agreement with the zonal drift of the equatorial f region plasma the zonal drift velocity of plasma bubbles increases with the solar radio flux however the increase shows different features at different local times geomagnetic activities cause a decrease of the eastward drift velocity of plasma bubbles equivalent to the occurrence of a westward drift through disturbance dynamo process in particular the decrease of the eastward drift velocity appears to become accelerated when the dst index is smaller than 60 nt or kp is larger than 4

optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble 1 optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the haleakala volcano hawaii geographic 20 71 n 203 83 e geomagnetic 21 31 n 271 45 e typically only the western wall of depletions at tropical latitudes are susceptible to secondary structuring this event occurs during a minor geomagnetic storm when the plasma bubble is observed to be drifting to the west rather than with the typical eastward drift velocity the data are interpreted in terms of the generalized e b instability with an anomalous wind directed westward and toward the equator this wind drives the eastern wall of the depletion region unstable the anomalous wind is associated with an equatorward propagating neutral wind surge caused by an ongoing geomagnetic storm the observations of the growth of these instabilities in the local tropical ionosphere are in stark contrast to the typical development of secondary instabilities on equatorial plasma bubbles which grow near the equatorial plane on the western wall of the primary depletion and map along the magnetic field lines to off equatorial latitudes

explosive cyclone development in the southern hemisphere and a comparison with northern hemisphere events abstract a compilation of southern hemisphere sh explosively developing cyclones or bombs has been assembled based on the national centers for environmental prediction department of energy reanalysis 2 data over the 21 yr period from 1979 to 1999 the identification of these features was undertaken with an objective automated cyclone finding and tracking scheme the procedure allows for the confounding influence of spatial variations of climatological mean pressure on the pressure deepening of explosive cyclones a perspective of particular importance in the sh on average 26 explosive cyclones occur per year in the sh they are more prevalent in winter although their seasonality is more modest than that seen in the northern hemisphere nh the distribution of sh explosive cyclones has a close association with that of strong baroclinicity although the relationship is not one to one it is found that many of these cyclones occurring south of 50 s show equatorward movement in contrast with the pol