the algal community at an ecocline of a cold sulphidic spring sovra artesian borehole slovenia the physicochemical parameters of the sulphide spring water from a 500 m deep artesian borehole in sovra valley slovenia are stable with very little variation temperature 9 2 0 0 c ph 7 70 0 11 specific electrical conductivity 777 8 s cm and dissolved oxygen 0 19 0 11 mg l the water from the borehole is hard rich in sulphates and has a notable concentration of sulphide while it is low in chlorides communities of phototrophs were analysed at the oxygenic ecocline at the outflow from the borehole and from further downstream caloneis tenuis frustulla vulgaris gomphonema sp navicula radiosa oscillatoria sp and tribonema vulgare successfully thrive exclusively at the outflow from the borehole under sub optimum conditions for the majority of phototrophs downstream from the borehole where the hydrogen sulphide degasses autotrophic biofilms were dominated by different diatoms the bray curtis similarity index confirms the distinctive phototrophic communities along the oxygenic ecocline downstream from the sulphidic spring the sulphidic ecocline downstream from the spring is indicative of the composition of phototrophic communities as some species appear only downstream from the spring an ecocline downstream from the borehole of the sulphidic spring was reflected also in the bacterial indicator groups this study brings novel insights to the limited knowledge in the field of oxygenic phototrophy related to sulphidic springs

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

tidal variability in the lower thermosphere comparison of whole atmosphere model wam simulations with observations from timed 1 the upper atmosphere and ionosphere exhibit variability on spatial and temporal scales characteristic of tides and planetary waves originating in the lower atmosphere to study their generation vertical propagation possible nonlinear interactions and effects a new whole atmosphere model wam has been developed as part of the integrated dynamics through earth s atmosphere idea project wam is a 150 layer general circulation model based on the us national weather service s operational global forecast system gfs model extended upward to cover the atmosphere from the ground to about 600 km first simulations reveal the presence of migrating and nonmigrating tides modulated at planetary wave periods in the upper atmosphere comparisons with observations from the timed satellite in the lower thermosphere show that wam reproduces the seasonal variability of tides remarkably well including the diurnal eastward harmonic with zonal wavenumber 3 de3 recently implicated in the observed spatial morphology of the ionosphere

gypsum and dolomite biomineralization in endoevaporitic microbial niche emisal fayium egypt biogenic gypsum in the form of microbialite and potential domal stromatolite as well as endoevaporitic dolomite are deposited in a perennial saline basin characterized by microbial bloom deposition environment mode of occurrence and microscopic investigation including sem of these precipitates are discussed in conjunction with xrd xrf and ftir data combined effects of salinity gradient and the wind action on the maturity of gypsum outcrop are evident a characteristic multi color vertical gypsum profile reflects steep gradient of oxi anoxic microenvironments and encodes diverse seasonal microbial communities direct impact of microbial signature in gypsum crystal habit is conspicuous endoevaporitic authigenic dolomite is recorded in specific horizons in interstices of selenite layers

source and genesis of sulphate and phosphate sulphate minerals in a quartz sandstone cave environment gypsum caso4 2h2o alunite kal3 so4 2 oh 6 and rare phosphate sulphate sanjuanite al2 po4 so4 oh 9 h2o and rossiantonite al3 po4 so4 2 oh 2 h2o 14 have recently been identified as secondary mineral deposits in different quartz sandstone caves in the gran sabana region venezuela due to the extended time scale required for speleogenesis in the hard and barely soluble quartz sandstone lithology these caves are considered to be as old as 20 to 30 my the study of these peculiar secondary mineral deposits potentially reveals important insights for understanding the interaction between deep superficial and atmospheric processes over thousands to perhaps millions of years in this study chemical and petrographic analyses of potential host rock sources sulphur and oxygen isotope ratios and meteorological hydrological and geographical data are used to investigate the origin of sulphates and phospho sulphates the results suggest that the deposition of sulphates in these caves is not linked to the quartz sandstone host rock rather these mineral deposits originate from an external atmospheric sulphate source with potential contributions of marine non sea salt sulphates terrestrial dimethyl sulphide and microbially reduced h2s from the forests or peatbogs within the watershed air currents within the caves are the most plausible means of transport for aerosols driving the accumulation of sulphates and other secondary minerals in specific locations moreover the studied sulphate minerals often co occur with silica speleothems of biological origin although this association would suggest a possible biogenic origin for the sulphates as well direct evidence proving that microbes are involved in their formation is absent nonetheless this study demonstrates that these quartz sandstone caves accumulate and preserve allogenic sulphates playing a yet unrecognized role in the sulphur cycle of tropical environments

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

an analysis of tidal and planetary waves in the neutral winds and temperature observed at low latitude e region heights we present an extensive analysis of tidal and planetary waves in the altitude range of 94 to 144 km for the january 20 30 1993 period using the temperature and winds measured by the arecibo incoherent scatter radar isr this is the first time that simultaneous observational results for the 6 8 12 24 hour tides and a quasi 2 day planetary wave at e region heights have been reported at tropical latitudes in order to derive the major oscillations from the mainly daytime data we fill in the nighttime periods with assumed data values and large error bars when valid measurements are not obtainable and then fit the data using the measured and assumed errors as weight simulated results show that such a method is demonstratively better than leaving the nighttime as a gap the salient features of the tidal analysis results include the following 1 despite their large day to day variabilities in amplitude the 6 8 hour oscillations are shown to be upward propagating tides 2 the vertical wavelength of the semidiurnal tide in the zonal wind lengthens from 25 to 110 km for the altitude range from 94 to 135 km while the vertical wavelength of the meridional wind remains constant the semidiurnal component of the meridional wind experiences little dissipation above 106 km which is indicative of the turbopause height 3 the diurnal tide which has often been assumed to be negligible in earlier observations can be quite substantial above 110 km 4 a 2 day planetary wave dominates the diurnal and semidiurnal tides in the meridional wind between 97 and 108 km continuous isr operation during the january 20 30 1993 campaign also provides an opportunity to examine the tidal variability both in phase and amplitude

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

benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems siliciclastic evaporitic salty and evaporitic carbonatic abstract peritidal sedimentary systems are widely colonized by benthic cyanobacteria that form biofilms and microbial mats the bacterial communities interfere with physical and chemical sedimentary dynamics which is documented by the formation of microbially induced sedimentary structures miss the structures form a new fifth category in the existing classification of primary sedimentary structures siliciclastic depositional systems are dominated by physical dynamics by biostabilization cyanobacteria shelter their substrata against erosion during periods of intensive hydraulic reworking or they permit flexible deformation of sandy sediments during low hydrodynamic disturbance the bacteria enhance deposition of sediments by baffling trapping and binding such biotic physical interference is recorded by miss such as erosional remnants and pockets or planar stromatolites chemical depositional systems include i evaporitic salty environments characterized by evaporation and dissolution and ii evaporitic carbonatic environments that include evaporation dissolution and in situ lithification of organic matter here cyanobacterial mats experience periodical desiccation or evaporation of crystals and mat related structures such as petees and polygonal patterns of cracks are formed cyanobacteria and heterotrophic bacteria provide a chemical microenvironment that supports in situ lithification of organic matter in thin sections carbonate precipitates as ooids or lines of decaying filaments are visible miss occur in modern and ancient depositional systems they record i biological abilities of benthic cyanobacteria to cope with sedimentary dynamics and ii paleoclimate and paleoenvironmental conditions during earth history similar structures are also expected in extraterrestrial paleo environments

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

mineralogical footprints of microbial life earth s geosphere is intimately tied to its biosphere a major link between the two lies in the microbial realm microorganisms grow in and upon rocks and minerals often relying on their substratum for critical compounds needed in order to produce cellular energy the presence of a metabolizing cell on a mineral substrate has a significant effect on the mineral texture and on the geochemistry of the surrounding microenvironment in nature microorganisms exist in microbial commu nities as mats or biofilms growing upon a solid substrate as such they cover a vast surface area both within and below the surface of earth s land and sea the following review will provide a glimpse into the latest findings in the field of geomicrobiology and is intended to convey a sense of the profound influence microorganisms can have upon the geological environment they inhabit

sources of nonmigrating tides in the tropical middle atmosphere 1 temperature measurements from the cryogenic infrared spectrometers and telescopes for the atmosphere crista experiment taken during the u s space shuttle mission sts 66 in november 1994 provide a variety of zonally symmetric and asymmetric tidal signatures in the altitude range from 40 90 km the most prominent zonally asymmetric tidal pattern is identified to be the westward propagating nonmigrating diurnal tide of zonal wavenumber 2 s 2 this mode has an amplitude of approximately half the amplitude of the migrating s 1 component of the diurnal tide the observational findings are compared to model results from the global scale wave model gswm and from the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm gswm and time gcm account for different tidal sources and therefore allow an analysis of the tidal forcing responsible for the observed signatures the gswm tidal forcing in the model version used is based upon latent heat release associated with tropical deep convection while nonmigrating tides in the time gcm are predominantly forced by nonlinear interactions between the migrating diurnal tide and stationary planetary waves it is shown that the latter mechanism forces a large part of the s 2 mode while the stationary zonally uniform s 0 diurnal nonmigrating tide is mainly driven by latent heat release this result suggests that dynamical models for the mesosphere lower thermosphere mlt region need to account for the tropospheric latent heat source and stationary planetary wave activity in order to predict realistic longitudinal diurnal tidal variability

lithifying microbial mats in lagoa vermelha brazil modern precambrian relics abstract bacterial populations microbial and mineral forming processes and their products were analyzed in lagoa vermelha brazil the microbial mat and underlying sediment were studied as a unique system to define the boundary conditions responsible for high mg calcite and dolomite formation in the uppermost layers of the microbial mat oxygenic photosynthesis and aerobic respiration resulted in calcite precipitation whereas in the underlying anoxic layers of the mat sulfide oxidation and sulfate reduction induced formation of a range of carbonate minerals with increasing mg concentrations the chemical mineralogical and biological conditions presently found in lagoa vermelha may have been more common in the precambrian the microorganisms performing the metabolic processes related to carbonate mineral formation within lagoa vermelha s hypersaline microbial mat may have already been present in the precambrian thus microbial carbonate as a biomineral could be a record of metabolism throughout geological time

global ionospheric response to nonmigrating de3 and de2 tides forced from below 1 in this paper we present the global spatial structure and seasonal variability of the cosmic electron density response to the forced from below de3 and de2 tides during the period january 2008 to march 2009 the cosmic electron density at fixed altitudes and saber temperatures were utilized in order to define the ionospheric de3 and de2 tidal response to the de3 and de2 temperature tides coming from below the tidal waves from both data sets have been extracted by the same data analysis method the latitude structure of the ionospheric response for heights up to 450 500 km is distributed on both sides of the dip equator at about 30 modified dip latitude above 500 km the response is approximately confined over the equator two altitude regions of enhanced ionospheric response are found an upper level response above 300 km and a bottom level one below 250 km the two regions are separated by a narrow altitude zone with no tidal response the different phase structure of the ionospheric response in both altitude regions suggests that 1 the upper level response is mainly due to the de3 de2 modulated vertical plasma drift and 2 the bottom level response is complex and in all likelihood is caused by more than one mechanism

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

satellite observations of thermospheric tides results from the wind imaging interferometer on uars thermospheric winds measured by the wind imaging interferometer windii on the upper atmosphere research satellite are analyzed for migrating solar tides the data cover a 2 year period commencing february 1992 and are obtained from the atomic oxygen o 1s 557 7 nm emission which provides observations of the 90 to 200 km altitude range during daytime and the 90 to 110 km range at night the subtropical lower thermosphere is dominated by the diurnal propagating tide which exhibits a vertical wavelength of approximately 22 km grows in amplitude up to 95 km and decays rapidly above where molecular diffusion greatly reduces the vertical shears although the phase remains fairly uniform throughout the year a pronounced semiannual oscillation is observed in the diurnal tide amplitude at both 20 n and 20 s the meridional and zonal wind components attain their maximum values at equinox of approximately 70 and 40 m s respectively while the solstitial minima are nearly a factor of 2 smaller at 35 n the diurnal tide semiannual amplitude oscillation is still present in the lower thermosphere but above 100 km it is replaced by an annual cycle with a maximum in july and august this contrasts with 35 s where the july august peak is absent and the semiannual oscillation extends to 110 km at midlatitudes the zonal and meridional winds are of similar magnitude and no significant hemispheric asymmetries in amplitudes are observed in the lower thermosphere the semidiurnal tide amplitude exhibits an annual oscillation with maximum values of 30 to 40 m s occurring in june july near 100 km at 35 n 35 s and the equator a bimodal structure in the seasonal variation of the semidiurnal phase is observed this feature is characterized by rapid equinoctial transitions and is particularly well defined at the equator examination of the equatorial middle thermosphere indicates that the semidiurnal tide attains its maximum amplitude at 140 km and exhibits a vertical wavelength of approximately 60 km these findings indicate the predominance of the antisymmetric 2 3 hough mode in the tropics

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 1 middle valley juan de fuca ridge samples from the ocean drilling program leg 169 in middle valley ne pacific ocean were analyzed to study maturation by accelerated diagenesis and catagenesis of the sedimentary organic matter to hydrothermal petroleum some data from site 858 in middle valley leg 139 are also discussed for completeness sediments at sites 858 and 1036 in middle valley were altered either by the full variety of high temperature fluids which generated hydrothermal petroleum or by accelerated thermal diagenesis of the immature organic matter in situ without specific migration of those petroleum bitumen products the hydrothermal petroleums from the deeper sediments have migrated and accumulated in discrete intervals at shallower depths within a contemporary temperature window of 60 135 c at both of these sites maturation for the n alkanes proceeded from high cpi values immature to 1 0 mature i e strong even c number preference due to their low toc contents these sediments did not generate high amounts of hydrocarbons from the kerogen and thus revealed this unique even c number preference furthermore the significant content of terrestrial organic matter yielded petroleums low in gas and volatiles biomarkers were converted from the biological natural product precursors to the geological derivatives with maturities reflecting the thermal stress high temperature alteration also yielded polynuclear aromatic hydrocarbons

nonlinear interactions in the upper atmosphere the s 1 and s 3 nonmigrating semidiurnal tides 1 a semidiurnal oscillation with zonal wave number s 1 has been observed over the south pole and longitudinal variations of the semidiurnal tide at northern midlatitudes have been ascribed to the presence of nonmigrating tides a three dimensional nonlinear spectral model is used herein to study nonlinear wave wave interaction as a possible mechanism for the generation of nonmigrating tides in the mesosphere and lower thermosphere in particular the s 1 and s 3 nonmigrating semidiurnal tides are studied as a by product of the nonlinear interaction between the semidiurnal s 2 migrating tide and a stationary s 1 planetary wave in the lower and middle atmosphere this process is found to yield significant amplitudes 10 30 m s 1 of the nonmigrating semidiurnal components with s 1 and s 3 in the upper atmosphere comparisons with monthly nonmigrating tidal amplitudes and phases at 95 km derived from high resolution doppler imager and wind imaging interferometer wind measurements from uars show good agreement with the model simulations the effect of the dissipating nonmigrating tides on the zonal mean circulation is found to reinforce that of the migrating component contributing 10 20 m s 1 to the zonal wind field and 5 10 m s 1 to the mean meridional wind field several other wave components are generated through nonlinear interactions including 6 hour tides with zonal wave numbers s 0 1 4 and a semidiurnal oscillation with s 6 these wave components have amplitudes in the range 6 30 m s 1 in the 110 150 km height regime the combination of all nonmigrating tides together with the migrating component suggests significant longitudinal variations in the semidiurnal tide in the e region which may be important for studies of the quiet time generation of ionospheric electric fields by the dynamo mechanism

momentum budget of the migrating diurnal tide in the whole atmosphere community climate model at vernal equinox 1 the momentum budget of the migrating diurnal tide dw1 at the vernal equinox is studied using the whole atmosphere community climate model version 4 waccm4 classical tidal theory provides an appropriate first order prediction of the dw1 structure while gravity wave gw forcing and advection are the two most dominant terms in the momentum equation that account for the discrepancies between classical tidal theory and the calculation based on the full primitive equations it differs from the conclusion by mclandress 2002a that the parameterized gw effect is substantially weaker than advection terms based on the canadian middle atmosphere model cmam in the region where dw1 maintains a large amplitude gw forcing in the wave breaking region always damps dw1 and advances its phase the linear advection largely determined by the latitudinal shear of the zonal mean zonal wind makes a dominant contribution to the phase change of dw1 in the zonal wind compared to the gw forcing and nonlinear advection however nonlinear advection is more important than gw forcing and linear advection in modulating the amplitude and phase of dw1 in the meridional wind the dw1 amplitudes in temperature and winds are smaller than the timed observations suggesting that gw forcing is overestimated in the waccm4 and results in a large damping of dw1

incoherent scatter radar study of the terdiurnal tide in the e and f region heights at arecibo 1 we report the analysis of the terdiurnal tide in the meridional wind from 90 to 350 km at a low latitude station our data is based on nine days of consecutive observation made by the arecibo incoherent scatter radar during january 14 23 2010 the terdiurnal tide is observed to be prominent at e region heights in the first four days jan 14 18 and at the f region heights in the last five days jan 18 23 the terdiurnal tide is among the two strongest tidal components in both regions the vertical wavelength of the terdiurnal tide is about 100 km and 950 km for the altitude range of 128 to 142 km and 180 to 320 km respectively the f region terdiurnal tide amplitude is found to be well correlated with the background meridional wind in the lower f region our analysis does not reveal any evidence that non linear interaction between diurnal and semidiurnal tides is important for the f region terdiurnal tide

atmospheric tides in the low latitude e and f regions and their responses to a sudden stratospheric warming event in january 2010 an extensive analysis of atmospheric tides in the low latitude thermosphere and their responses to a major sudden stratospheric warming ssw event 18 23 january 2010 is presented the analysis is based on observational data from the arecibo dual beam incoherent scatter radar important findings of the present study are as follows 1 the diurnal tide with an evanescent phase structure dominates the f region meridional wind field the diurnal tide has a peak amplitude of 45 m s occurring at about 245 km and it is very stable throughout the nine consecutive days observation below 114 km the vertical structures of the diurnal tide in the meridional and zonal components are consistent which resemble the classical solar s 1 s 1 tidal mode 2 the f region semidiurnal tide is much weaker and has larger day to day variability than the diurnal tide in the e region the semidiurnal amplitudes in the meridional and zonal components grow continuously in the altitude ranges from 106 to 121 km and from 100 to 115 km respectively the vertical wavelength of the zonal component is estimated to be 45 km above 100 km which is close to the solar s 2 s 4 and s 2 s 5 tidal modes 3 the semidiurnal and terdiurnal tides respond strongly to the ssw while the impact that the ssw has on the diurnal tide in the meridional wind is limited during the ssw event the amplitudes of the semidiurnal and terdiurnal tides are enhanced in the f region but reduced in the upper e region