longitudinal variations in the f region ionosphere and the topside ionosphere plasmasphere observations and model simulations 1 constellation observing system for meteorology ionosphere and climate cosmic observations of the total electron content tec above and below 800 km are used to study the local time and seasonal variation of longitude structures in both the f region ionosphere as well as the topside ionosphere and plasmasphere the cosmic observations reveal the presence of distinct longitude variations in the topside ionosphere plasmasphere tec and these further exhibit a seasonal and local time dependence the predominant feature observed at all local times in the topside ionosphere plasmasphere tec is a substantial maximum minimum during northern hemisphere winter summer around 300 360 geographic longitude around equinox at a fixed local time a wave 4 variation in longitude prevails in the daytime f region tec as well as the topside ionosphere plasmasphere tec the wave 4 variation in longitude persists into the nighttime in the f region however the nighttime topside ionosphere plasmasphere tec exhibits two maxima in longitude the cosmic observations clearly reveal the presence of substantial longitude variations in the f region and topside ionosphere plasmasphere and to elucidate the source of the longitude variations results are presented based on the coupling between the global ionosphere plasmasphere model and the thermosphere ionosphere electrodynamics general circulation model the model simulations demonstrate that the orientation of the geomagnetic field plays a fundamental role in generating significant longitude variations in the topside ionosphere plasmasphere but does not considerably influence longitude variations in the f region ionosphere the model results further confirm that nonmigrating tides are the primary mechanism for generating longitude variations in the f region ionosphere the coupled model additionally demonstrates that nonmigrating tides are also of considerable importance for the generation of longitude variations in the topside ionosphere plasmasphere tec

the influence of nonmigrating tides on the longitudinal variation of the equatorial electrojet 1 the climatological model of the equatorial electrojet eejm 1 derived from orsted champ and sac c satellite measurements provides the opportunity to investigate the longitudinal variation of the current strength in detail special emphasis is put in this study on the effect of nonmigrating tides we have found that the influence of the diurnal eastward propagating mode with wavenumber 3 de3 is particularly strong in polar orbiting satellite observations the de3 tidal signal appears as a four peaked longitudinal structure we have put special emphasis in our analysis to isolate the de3 contribution from other sources contributing to the wavenumber 4 structure in satellite data the amplitude of the de3 signature in the eej not only peaks during equinox seasons but is also strong around the june solstice when looking at the modulation of the eej intensity the de3 accounts for about 25 during the months of april through september it is thus the dominant cause for longitudinal variations during december solstice months the influence of de3 is negligible a secondary three peaked longitudinal pattern emerges during solstice seasons when the de3 influence is removed from the data available it is however not clear whether this pattern is related to any tidal drivers

tidal variability in the ionospheric dynamo region 1 the seasonal and interannual variability of migrating sun synchronous and nonmigrating solar atmospheric tides at altitudes between 100 and 116 km are investigated using temperature measurements made with the saber instrument on the timed spacecraft during 2002 2006 quasi biennial variations of order 10 15 in migrating diurnal and semidiurnal tidal amplitudes are found presumably due to modulation by the quasi biennial oscillation qbo as the tides propagate from their troposphere and stratospheric sources to the lower thermosphere a number of nonmigrating tidal components are found that have the potential to produce significant longitudinal variability of the total tidal fields the most prominent of these i e those that appear at amplitudes of order 5 10 k in a 5 year mean climatology include the zonally symmetric s 0 diurnal tide d0 the eastward propagating diurnal and semidiurnal tides with zonal wave numbers s 2 de2 and se2 and s 3 de3 and se3 and the following westward propagating waves diurnal s 2 dw2 semidiurnal s 1 sw1 s 3 sw3 and s 4 sw4 and terdiurnal s 5 tw5 these waves can be plausibly accounted for by nonlinear interaction between migrating tidal components and stationary planetary waves with s 1 or s 2 or by longitudinal variations of tropospheric thermal forcing additional waves that occur during some years or undergo phase cancellation within construction of a 5 year climatology include dw5 se1 se4 sw6 te1 tw1 and tw7 it is anticipated that the winds that accompany all of these waves in the 100 170 km region will impose longitudinal variability in the electric fields produced through the ionospheric dynamo mechanism thereby modulating vertical motion of the equatorial ionosphere and the concomitant plasma densities in addition to the wave 4 modulation of the equatorial ionosphere that has recently been discovered and replicated in modeling studies the waves revealed here will generate wave 1 sw1 sw3 d0 dw2 wave 2 sw4 tw1 wave 3 de2 se1 wave 4 de3 se2 dw5 sw6 te1 tw7 wave 5 se3 and wave 6 se4 components of this ionospheric variability depending on year and time of year however the absolute and relative efficiencies with which these waves produce electric fields remains to be determined

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

mean zonal acceleration and heating of the 70 to 100 km region the dynamical interactions which occur in the atmospheric region around the mesopause 90 km determine the boundary characteristics for the thermospheric region above a significant data base of radar wind measurements exists which characterizes the global circulation at altitudes between 70 and 110 km in the present work using an empirical model of eulerian mean meridional motions based on monthly climatological winds from these radar data the net vertical motions in this atmospheric regime are derived from the continuity equation assuming empirical prescriptions of the mean density and temperature fields mean heat flux divergences and momentum flux divergences are estimated which exhibit very specific characteristics in the height versus latitude domain for winter summer and equinox conditions in both hemispheres a numerical circulation model including gravity wave mean flow and tide mean flow interactions is utilized to examine possible origins of these heat and acceleration sources at low latitudes 30 it is evident that atmospheric tides represent the primary wave source contribution to zonal mean acceleration and heating of this region of the atmosphere similarly at middle and high latitudes 30 below about 90 km dissipation of vertically propagating gravity waves appears to provide the dominant momentum source for the mean zonal circulation however above approximately 90 km and between about 40 and 70 latitude very significant regions of mean heating and acceleration exist which are not accounted for by the effects of vertically propagating gravity waves and tides the possible origins of these effects are examined we suggest that the two most likely candidates to explain these observed features are 1 obliquely propagating gravity waves and or 2 planetary scale waves

comparative study of short term diurnal tidal variability examination of the simultaneous temperature measurement from the sounding of the atmosphere using broadband emission radiometry saber instrument on board the thermosphere ionosphere mesosphere energetics and dynamics timed satellite not only confirms the existence of the inversion layer but also reveals the global nature of the inversion suggesting the presence of a transient planetary wave in the mesosphere the large tidal variability therefore is probably a consequence of the interaction between the transient planetary wave and tides this possibility is investigated by using the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm and by comparing model results with the lidar saber and timed doppler interferometer tidi measurements with a large transient planetary wave specified at the model lower boundary the model is able to produce strong diurnal tidal variability comparable to that from the lidar observation and the modeled temperature inversion is similar to that from the saber measurement the model results suggest that the planetary tidal wave interaction excites nonmigrating tides and modulates the gravity modes and or the rotational modes of the diurnal migrating tide among the nonmigrating tides the diurnal zonally symmetric s 0 component is the strongest and its interaction with the planetary wave leads to a strong diurnal eastward wave number 1 component

connections between deep tropical clouds and the earth s ionosphere 1 we report on a series of simulations with the national center for atmospheric research ncar thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm which were designed to replicate and facilitate the interpretation of the longitudinal structure discovered in image satellite airglow observations of the equatorial ionization anomaly eia at the far ultraviolet fuv 135 6 nm wavelength during march april 2002 equinox our time gcm results indicate that the four peaked longitudinal variation in the eia observed by image fuv near 20 00 local solar time can be explained by the effects of an eastward propagating zonal wavenumber 3 diurnal tide de3 that is excited by latent heat release associated with raindrop formation in the tropical troposphere

troposphere thermosphere tidal coupling as measured by the saber instrument on timed during july september 2002 1 coupling between the troposphere and lower thermosphere due to upward propagating tides is investigated using temperatures measured from the saber instrument on the timed satellite the data analyzed here are confined to 20 120 km altitude and 40 latitude during 20 july to 20 september 2002 apart from the migrating sun synchronous tidal components the predominant feature seen from the satellite frame during this period is a wave 4 structure in longitude with extrema of up to 40 50 k at 110 km amplitudes and longitudes of maxima of this structure evolve as the satellite precesses in local time and as the wave s responsible for this structure vary with time the primary wave responsible for the wave 4 pattern is the eastward propagating diurnal tide with zonal wave number s 3 de3 its average amplitude distribution over the interval is quasi symmetric about the equator similar to that of a kelvin wave with maximum of about 20 k at 5 s and 110 km de3 is primarily excited by latent heating due to deep tropical convection in the troposphere it is demonstrated that existence of de3 is intimately connected with the predominant wave 4 longitude distribution of topography and land sea difference at low latitudes and an analogy is drawn with the strong presence of de1 in mars atmosphere the predominant wave 2 topography on mars and the wave 2 patterns that dominate density measurements from the mars global surveyor mgs spacecraft near 130 km additional diurnal semidiurnal and terdiurnal nonmigrating tides are also revealed in the present study these tidal components are most likely excited by nonlinear interactions between their migrating counterparts and the stationary planetary wave with s 1 known to exist in the southern hemisphere during this period just prior to the austral midwinter stratospheric warming of 2002

monthly tidal temperatures 20 120 km from timed saber 1 the saber instrument on the timed satellite provides unprecedented geographical coverage for the determination and study of atmospheric tides however the slow local time precession rate of timed can cause longer term temperature variations to alias into the tidal signals a new method of analyzing satellite data for tides has been developed to circumvent this difficulty but at the expense of temporal resolution of the tidal fields i e 120 day mean tidal structures are obtained in this work we apply this method to saber temperature data to derive a series of 120 day mean tidal structures extending between 20 and 120 km altitude 50 s 50 n latitude and centered on each month from september 2003 to september 2004 in addition to the migrating sun synchronous diurnal and semidiurnal tides a number of nonmigrating tides are revealed in the saber measurements some of these waves are thought to originate via nonlinear coupling between the migrating tides and the stationary planetary wave with zonal wave number s 1 other nonmigrating tidal components appear to be forced by latent heating due to deep tropical convection of the latter the eastward propagating diurnal tide with s 3 is dominant and is as large as the migrating diurnal tide during some months of particular interest is the wave 4 structure with respect to longitude that characterizes both the diurnal and semidiurnal total tidal fields this feature is a result of the predominant wave 4 topography land sea longitude dependence at the surface which is reflected in the diurnal and semidiurnal components of the latent heating rates due to deep tropical convection the ability of the global scale wave model gswm to approximate the observed tidal fields including the wave 4 total tidal structures is also assessed

comparison of champ and time gcm nonmigrating tidal signals in the thermospheric zonal wind 1 four years 2002 2005 of continuous accelerometer measurements taken onboard the champ satellite orbit altitude 400 km offer a unique opportunity to investigate the thermospheric zonal wind on a global scale recently we were able to relate the longitudinal wave 4 structure in the zonal wind at equatorial latitudes to the influence of nonmigrating tides and in particular to the eastward propagating diurnal tide with zonal wave number 3 de3 the de3 tide is primarily excited by latent heat release in the tropical troposphere in deep convective clouds in order to investigate the mechanisms that couple the tidal signals to the upper thermosphere we undertook a comparison with the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm developed at the national center for atmospheric research ncar we ran the model for a day in march june september and december and applied the same processing steps to the model output as was done for the champ tidal analysis the main results of the comparison can be summarized as follows 1 time gcm simulations do not correctly reproduce the observed intra annual variations of de3 and the eastward propagating diurnal tide with zonal wave number 2 de2 2 simulations of de3 for june are more successful both time gcm and champ show an increase in de3 amplitudes with decreasing solar flux level 3 the amplitudes of the simulated westward propagating diurnal tide with zonal wave number 2 dw2 and the standing diurnal tide d0 increase with increasing solar flux in june the predicted dependence of dw2 and do on solar flux is also observed by champ

climatology of upward propagating diurnal and semidiurnal tides in the thermosphere 1 a major challenge in delineating and understanding the space weather of the ionosphere thermosphere system is the lack of global tidal observations in the 120 400 km thermospheric gap between satellite remote sensing and in situ tidal diagnostics this paper aims to close this gap by presenting an observation based climatological tidal model of the thermosphere ctmt of self consistent upward propagating migrating and nonmigrating diurnal and semidiurnal tides from 80 400 km and pole to pole for moderate f10 7 110 sfu solar flux conditions ctmt includes the 6 8 most important diurnal semidiurnal tidal components for temperature density and zonal meridional and vertical winds and is based on hough mode extension fits to 2002 2008 mean timed satellite tidal diagnostics in the mesosphere lower thermosphere mlt validation with independent 2002 2008 champ tidal diagnostics f10 7 105 sfu around 400 km proves that the approach captures nonmigrating tides well indicating that these waves propagate directly upward without significant tidal forcing occurring in the thermosphere notable exceptions are the dw2 and d0 components that are most likely generated in situ by nonlinear interaction forcing in the upper thermosphere ctmt is suitable for driving upper atmosphere models that require self consistent tidal fields in the mlt region as a lower boundary condition it does not include migrating tides due to in situ euv absorption in the upper thermosphere but allows us to quantitatively assess thermospheric variability due to tides from the lower atmosphere this is done by discussing longitude latitude maps of reconstructed diurnal and semidiurnal tidal variations as function of altitude and local time

the evolution of crustal deformation in an oceanic extensional environment abstract fault statistics collected along the slow spreading reykjanes ridge are used to investigate its complex tectonic evolution the reykjanes ridge is oriented oblique to the spreading direction and is located close to the iceland hotspot a wide distribution in fault strike and fault throw occurs across the axis of the reykjanes ridge with a sharp change in mean strike and mean throw occurring at the edge of the axial zone within the axial zone there is no significant change in the distribution of faults with increasing distance from iceland proximity to the hotspot does not influence the detailed tectonics near the axis we infer that the fault development within the axial zone is controlled by the plate tectonic generated regional stress field outside the axial zone the faults strike oblique to the spreading normal direction this change in fault strike coupled with the lack of any evidence for strike slip movement suggests that these faults develop as a passive response to the thermal evolution of the lithosphere our results indicate that at a slow spreading ridge the crust is deformed by two stress fields one responsible for the fault formation within the axial zone the other for the faults which bound the axial zone

impacts of vertically propagating tides on the mean state of the ionosphere thermosphere system the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model tie gcm is utilized to understand the role that upward propagating tides play in determining the zonal mean state of the ionosphere thermosphere system a sensitivity assessment of the tie gcm shows that tie gcm solutions greatly depend on the lower boundary conditions we also establish the veracity of our tie gcm solutions within and above the dynamo region to isolate the mean effects of tidal dissipation differences between tie gcm simulations with and without lower boundary tidal forcing as specified by the climatological tidal model of the thermosphere are investigated dissipation of the dw1 diurnal westward propagating tide with zonal wave number 1 diurnal eastward propagating tide with zonal wave number 3 and sw2 semidiurnal tide with zonal wave number 2 explains most of 10 30 m s 1 seasonal and latitudinal variability in zonal winds within the dynamo region with sw2 playing a greater role than ascribed in previous studies tidal dissipation at low latitudes causes a 9 decrease 30 increase in o o2 number densities near the f2 layer peak leading to at least a 9 decrease in peak electron density nmf2 throughout the year f2 layer peak height hmf2 differences of 4 to 2 km at low latitudes are explained by variations in the field aligned plasma motion driven by meridional wind differences induced by tidal dissipation compositional effects are mainly driven by dw1 and sw2 which differs from previous interpretations of tidal driven composition changes by dw1 tidal mixing exclusively we suggest that tides may produce a net transport of constituents in the thermosphere similar to the way that e g gravity waves can drive net transport of sodium in the mesosphere

longitudinal structure of the equatorial anomaly in the nighttime ionosphere observed by image fuv 1 the far ultraviolet imager fuv on board the image satellite provides an instantaneous global view of the oi 135 6 nm nightglow with 2 min time resolution because the oi 135 6 nm emission from the nighttime ionosphere is determined by the line of sight integrated plasma density the nightglow images are useful for studying the nighttime low latitude ionosphere globally with the image fuv 135 6 nm observations from march to june 2002 we have examined the global characteristics of the nighttime equatorial anomaly ea by constructing a constant local time map lt map in which pixels within an assigned local time range are extracted from the image fuv nightglow images obtained over an observation period of 3 days or more and are put together to compose a global distribution map of emission intensities at that local time these lt maps show that the development of the ea has a significant longitudinal structure in which peaks and dips of the crest emission intensity and the crest latitude have about 90 longitudinal separation in the longitude range from 0 to 250 although there is not enough data over the american sector this result suggests that the ea longitudinal structure has a prominent zonal component of the wave number 4 the observed longitudinal structure of the nighttime ea could not be fully explained by factors such as the empirical electric field and neutral wind models the geomagnetic declination angle or the displacement of the geomagnetic equator from the geographic equator to explain the observed longitudinal structure of the ea in particular the wave number 4 feature we may need to consider other forcing for example nonmigrating tide originated from the lower atmosphere

intra annual variability of the low latitude ionosphere due to nonmigrating tides 1 in situ plasma density measurements from the champ satellite between about 350 420 km altitude are used to delineate intra annual variations in the longitudinal structure of the f region ionosphere it is shown that the longitude structures during mid day local times are dominated by the space based longitudinal wavenumbers ks 2 4 and 3 in january july and december respectively these conform to the same dominating ks values characterizing solar thermal tide zonal winds in the dynamo region namely the westward propagating semidiurnal tide with planetary fixed zonal wavenumber s 4 sw4 and the eastward propagating diurnal tides with s 3 de3 and s 2 de2 respectively de3 is the dominating tide during the other months the results presented indicate that nonmigrating tides other than de3 may significantly impact the longitudinal structure of the low latitude ionosphere during certain months

nonmigrating diurnal tides in the thermosphere 1 horizontal wind measurements from the hrdi and windii instruments on the upper atmosphere research satellite are analyzed to reveal the most prominent nonmigrating diurnal tidal components at 95 km the eastward propagating diurnal tide with zonal wave number s 3 de3 the standing s 0 diurnal oscillation d0 and the westward propagating diurnal tide with s 2 dw2 the strongest de3 occurs primarily during northern hemisphere summer fall with maximum eastward winds near the equator of order 15 ms 1 and is a vertical extension of the s 3 kelvin wave the first antisymmetric mode of de3 dominates during october april with maximum meridional winds near the equator of order 8 ms 1 d0 exists during nearly all months and is nonsymmetric about the equator with maximum northward wind amplitudes in the southern hemisphere of order 7 10 ms 1 dw2 closely resembles the first symmetric propagating mode from classical tidal theory with maximum northward wind amplitudes of order 10 12 ms 1 during september through february the combination of de3 d0 and dw2 with dw1 gives rise to significant longitude variations in the diurnal tide between 40 latitude forcing in the global scale wave model gswm is calibrated according to the above observations thus enabling global estimates of nonmigrating tidal temperatures and other fields for instance it is estimated that the temperature and eastward wind perturbations associated with de3 may be as large as 20k and 35 ms 1 at 145 km and 115 km respectively over the equatorial region during july

effect of atmospheric tides on the morphology of the quiet time postsunset equatorial ionospheric anomaly longitudinal wave number four pattern in the magnetic latitude and concentration of the f region peak ion density when measured at a fixed local time in a new comparison of two data sets with observations made by the ogo 4 satellite this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross equator winds during other periods it is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere a longitudinal modulation of the dayside equatorial fountainisthemostlikelydrivingmechanism throughcomparisonwithgwsm 02model it isshownthatthepredictedmodulationofthedaysidethermosphericwindsandtemperaturesat e region altitudes created by non migrating diurnal tides can explain the modulation in the dayside equatorial fountain this result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the f region ionosphere it may also provide a possible further means of testing our understanding of atmospheric tides on a global scale

effects of vertically propagating thermal tides on the mean structure and dynamics of mars lower thermosphere 1 a general circulation model of mars atmosphere is used to elucidate the effects of vertically propagating thermal tides excited near the surface on the zonal mean density temperature and wind structure of mars atmosphere between 90 and 160 km the effects are substantial and amount to order 10 40 10 50 k and 50 160 m s 1 respectively at these altitudes under low dust conditions dust visible optical depth 0 3 these induced changes in the zonal mean structure are dominated by the non migrating tides of particular note are the mean density perturbations which represent an important consideration for modeling of the aerobraking region 100 170 km

tropospheric tidal effects on the middle and upper atmosphere 1 numerical experiments that explore the effects of tides of tropospheric origin on the upper and middle atmosphere reveal strong signatures of an eastward propagating zonal wave number 3 diurnal tide de3 which peaks near 110 km and penetrates into the upper thermosphere we demonstrate that nonmigrating tidal dissipation dominated by de3 effects in the upper mesosphere and lower thermosphere mlt strongly accelerates the zonal mean wind field affecting both the altitude and magnitude of the low latitude jets we also quantify for the first time a stationary planetary wave 4 oscillation spw4 in the mlt which is excited by nonlinear interaction between the de3 and the migrating diurnal tide dw1 our results suggest that the spw4 modulates the de3 mlt response and may impact the e region dynamo as well as ionospheric and thermospheric signatures at much higher altitudes