planetary scale wave observations over a low latitude e region using simultaneous observations of vhf radar and ionosonde over sanya 18 34 n 109 62 e 1 the planetary scale oscillations of the field aligned irregularities fai and the sporadic e es layers in the low latitude e region were studied in terms of the observations from 8 june to 22 august 2009 using coherent backscatter radar and a digital ionosonde installed at sanya 18 34 n 109 62 e hainan island china quasi 2 day waves were observed both in the meridional wind and in daytime backscatter echo occurrence simultaneous observations on sporadic e layers in daytime showed a planetary scale wave signature in the low latitude region for the first time close correlation between echo occurrence and the mean critical frequency foes was found when the quasi 2 day planetary wave qtpw existed these results suggest that the es plays an important role in determining the long term variability of the low latitude e region fai to test the nonlinear interactions between tides and qtpw the hourly meridional and zonal winds are analyzed the subsidiary waves with anticipated frequencies and their height evolutions provide evidence of tide qtpw interactions bispectral analysis on the winds further validates the strong nonlinear interactions between tides and the qtpw in the meridional wind our results suggest that the mechanism proposed by pancheva et al 2003 is a reasonable explanation for the planetary scale variability of the low latitude e region fai and es the different responses of the es layers and the e region fais on the qtpw between day and night can be attributed to diurnal variations in ion densities in the region between 100 and 160 km

planetary and tidal wave type oscillations in the ionospheric sporadic e layers over tehran region 1 it is believed that in the lower ionosphere particularly in the ionospheric sporadic e es layers 90 130 km the planetary and tidal wave type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere in the present work the presence of wave type oscillations including planetary and tidal waves in the ionospheric sporadic e layers over tehran region is examined data measured by a digital ionosonde at the ionospheric station of the institute of geophysics university of tehran from july 2006 to june 2007 are used to investigate seasonal variations of planetary and tidal waves activities for the purpose of accurate comparison between different seasons wavelet transform is applied to time series of foes and h es namely the critical frequency and virtual height of es layers respectively the results show that the sporadic e layers over tehran region are strongly under the influence of upward propagation of waves from below more specifically among diverse range of periodicities in the sporadic e layers we found that diurnal 24 hours and semidiurnal 12 hours oscillations in all seasons for both parameters moreover terdiurnal 8 hours tide like variation is observed during spring and summer for foes parameter and summer and winter for h es furthermore the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons and their activities decrease during the late spring and summer in addition periods of about 2 4 6 10 14 and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere moreover planetary waves have their maximum activities during equinox

a multiscale model for tropical intraseasonal oscillations the tropical intraseasonal 40 to 50 day oscillation tio is the dominant component of variability in the tropical atmosphere with remarkable planetary scale circulation generated as envelopes of complex multiscale processes a new multiscale model is developed here that clearly demonstrates the fashion in which planetary scale circulations sharing many features in common with the observational record for the tio are generated on intraseasonal time scales through the upscale transfer of kinetic and thermal energy generated by wave trains of organized synoptic scale circulations having features in common with observed superclusters the appeal of the multiscale models developed below is their firm mathematical underpinnings simplicity and analytic tractability while remaining self consistent with key features of the observational record the results below demonstrate in a transparent fashion the central role of organized vertically tilted synoptic scale circulations in generating a planetary circulation resembling the tio

a new multiscale model for the madden julian oscillation abstract a multiscale model of the mjo is developed here that accounts in a simplified fashion for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic scale circulations in a moving convective envelope as well as direct mean heating on planetary scales this model involves idealized thermally driven congestus synoptic scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope the model self consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the mjo including the vertical structure in both the westerly onset region and the strong westerly wind burst region as well as the horizontal quadrupole planetary vortex structure the westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transpor

upscale impact of mesoscale disturbances of tropical convection on 2 day waves abstractwestward propagating 2 day waves with embedded mesoscale disturbances contribute a large portion of synoptic variability of tropical convection over the western pacific it is of crucial im

planetary waves and variability of the semidiurnal tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter 1 the main features of the planetary waves and the variability of the semidiurnal tide with planetary wave periods observed by meteor radar over esrange 68 n 21 e have been investigated the interval of 39 months covering continuous measurements from october 1999 to december 2002 has been examined the planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere 80 100 km over esrange are 5 8 to 10 16 and 23 day waves the quasi 2 day wave is excluded in this study they are strongly amplified in the winter some differences between high and middle latitude planetary waves notwithstanding the 5 10 and 16 day waves are most probably related to the well known normal mode there are some reasons to believe that the vertically upward propagating 23 day wave could be generated by solar forcing the variability of the semidiurnal tide with periods of planetary waves has been thoroughly studied as well it is found that in the winter when the planetary waves are significantly amplified a very strong periodic variability of the semidiurnal tide is observed as well this result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between tides and planetary waves two winter periods have been examined 1999 2000 and 2001 2002 in order to find strong evidence supporting this suggestion the validity of the frequency phase and vertical wavenumber wavelength relationship between the prime the planetary wave and semidiurnal tide and secondary waves has been established the novel aspect of this work is that we show for the first time that the calculated vertical structures vertical wavelengths of the sum and difference secondary waves which have very close periods are actually very different

cryoturbation versus tectonic deformation along the southern edge of the tunka basin baikal rift system siberia new insights from an integrated morphotectonic and stratigraphic study the tunka basin is a broad emerging basin situated between the baikal lake to the east and the the hovsgol lake to the west the basin is bounded to the north and to the south by the tunka and the khamar daban mountain ranges respectively the tunka normal fault located at the southern foothills of the tunka mountain range is the main structure that controlled the development of the tunka basin during the neogene paleoearthquake surface ruptures attest of its present activity and show that its western and eastern terminations are undergoing a tectonic inversion characterized by left lateral reverse deformations the southern edge of the tunka basin is classically interpreted as being tectonically controlled in this paper we present the results of a geomorphological and stratigraphic analysis within its southwestern and southeastern parts suggesting that there is no active fault affecting the foothills of the khamar daban mountain range the different features observed in the quaternary deposits are interpreted to be the result of periglacial processes induced by alternating episodes of permafrost aggradation and degradation during the holocene our study concludes that the khamar daban range and the tunka basin are uplifting together and that the tunka and mondy faults are the two main triggers of regional earthquakes

planetary scale variability in the low latitude e region field aligned irregularities first results from gadanki observations 1 in this paper we present for the first time planetary scale wave signatures in the low latitude e region field aligned irregularities fai observed during june 2004 to may 2005 using the gadanki mesosphere stratosphere troposphere radar we have observed a clear signature of 5 8 day variability in echo occurrence in snr and also in doppler velocity observed above 100 km concurrent temperature observations made using the sounding of the atmosphere using broadband emission radiometry saber on board the thermosphere ionosphere mesosphere energetic and dynamics timed satellite have also clearly shown the presence of 5 8 day variability similar to that of fai the temperature variations have been characterized with zonal wave numbers of 3 and 4 and vertical wavelength of 15 20 km these waves are found to have increasing amplitude with increasing height and phase progressing downward suggesting that they were of lower atmospheric origin it is emphasized that the planetary scale characteristics of neutral atmosphere in the fai observations are important in understanding the vertical coupling of the low latitude ionosphere atmosphere system these observations and the pertinent issues are discussed in the light of current understanding of the planetary scale role on the fai variability

contemporary sand wedge development in seasonally frozen ground and paleoenvironmental implications abstract contemporary sand wedges and sand veins are active in seasonally frozen ground within the extensive discontinuous permafrost zone in northwest territories canada the region has a subarctic continental climate with 291 mm a 1 precipitation 4 1 c mean annual air temperature warm summers july mean 17 0 c and cold winters january mean 26 6 c five years of continuous observations indicate that interannual variation of the ground thermal regime is dominantly controlled by winter air temperature and snow cover conditions at sandy sites thin snow cover and high thermal conductivity promote rapid freezing high rates of ground cooling and low near surface ground temperatures 15 to 25 c resulting in thermal contraction cracking to depths of 1 2 m cracking potentials are high in sandy soils when air temperatures are

first measurements of tidal modes in the lower thermosphere by the eiscat svalbard radar first measurements by the eiscat svalbard radar of ion velocities in the lower thermosphere show the presence of strong tidal or quasi tidal modes with periods of 24 12 and 8 hours the diurnal mode shows no variation of phase with height above 100 km in contrast the semidiurnal and terdiurnal modes show a steady variation of phase with height corresponding to vertical wavelengths of about 40 km and 30 km respectively in addition there is evidence at 93 km the lowest height measured of a planetary wave with a period of 2 3 days

collapse of permafrost mounds along a subarctic river over the last 100 years northern quebec widespread permafrost decay is currently occurring in the northern hemisphere in subarctic quebec most permafrost mounds are located in peatlands in the form of palsas and peat plateaus the formation and degradation of these periglacial landforms are influenced by several regional and local factors including air temperature depth of snow cover and peat insulation mineral palsas are another type of permafrost landforms found along river shores in subarctic canada due to their peculiar position near or in the river floodplain the dynamics of these palsas are influenced by water level fluctuations this study examines palsa dynamics along a subarctic river the boniface river in northern quebec mapping of palsas and thermokarst ponds over a 44 year period i e from 1957 from aerial photographs to 2001 from field surveys was used to evaluate changes in the distribution and area covered by permafrost landforms also the decay of 14 palsas was assessed using the mortality dates of black spruce trees as determined by tree ring analysis between 1957 and 2001 the area occupied by palsas decreased by 23 whereas 76 of the present day thermokarst area formed since 1957 no new palsas developed during this period for the 14 palsas studied degradation began at the end of the 19th century and accelerated during the 20th century palsa degradation was closely related to distance from the river channel palsas located in the river floodplain were the most affected by thawing and showed a 48 reduction in area degradation was less severe for palsas located 1 to 15 m from the river margin which experienced a 19 reduction in area the spatiotemporal distribution of palsas suggests that changes in water level are among the most important factors influencing the dynamics of riparian palsas particularly for those palsas directly in contact with the river water

an explanation for the seasonal dependence of midlatitude sporadic e layers 1 the midlatitude sporadic e layers form when metallic ions of meteoric origin in the lower thermosphere are converged vertically in a wind shear the occurrence and strength of sporadic e follow a pronounced seasonal dependence marked by a conspicuous summer maximum although this is known since the early years of ionosonde studies its cause has remained a mystery as it cannot be accounted for by the windshear theory of e s formation we show here that the marked seasonal dependence of sporadic e correlates well with the annual variation of sporadic meteor deposition in the upper atmosphere the later has been established recently from long term measurements using meteor radar interferometers in the northern and southern hemispheres knowing that the occurrence and strength of sporadic e layers depends directly on the metal ion content which apparently is determined primarily by the meteoric deposition the present study offers a cause and effect explanation for the long going mystery of sporadic e layer seasonal dependence

evidence for planetary wave effects on midlatitude backscatter and sporadic e layer occurrence in this paper a large database of midlatitude e region coherent backscatter obtained with a 50 mhz doppler system is used to investigate the long term variability in echo occurrence the backscatter is found to be dominated by pronounced quasi periodic variations with periods in the range from about 2 to 9 days that persist for time intervals from about 10 to maybe more than 20 days and have no relation to geomagnetic activity the most commonly observed periods appear in two preferential bands that is the 2 to 3 day and the 4 to 6 day band using concurrent ionosonde data we find the variations in backscatter to be exactly in phase with similar periodicities in the occurrence of relatively strong sporadic e layers the present findings support the possibility that planetary waves are responsible for the observed long term periodicities which indicates also a close relation between planetary waves and the well known but not well understood seasonal es dependence we suggest the planetary wave option constitutes a new component into the research of midlatitude sporadic e layer formation and occurrence that needs to be considered and closely investigated

evidence of a role for modulated atmospheric tides in the dependence of sporadic e layers on planetary waves 1 a large amplitude 7 day period westward propagating s 1 planetary wave pw of global response has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere mlt during the second half of august and well into september 1993 following recent suggestions that pw might play a role in the formation of midlatitude sporadic e layers es haldoupis and pancheva 2002 found a strong 7 day periodicity present in all stations concurrently with the 7 day planetary wave reported elsewhere by analyzing sporadic e critical frequency foes time series from eight midlatitude ionosonde stations covering a longitudinal zone from about 58 e to 157 w this study provided the first direct proof in favor of a pw role on es formation in the present paper we further investigate this role by considering the same pw event and correlating the 7 day periodicity in foes directly with concurrent variations in the mesospheric neutral wind measured with atmospheric radars in saskatoon canada and in sheffield united kingdom although our analysis cannot exclude a direct pw role on es formation it shows clearly that es is affected indirectly by the pw through the action of the diurnal and semidiurnal tides which are strongly modulated by the same pw apparently through a nonlinear interaction process at altitudes below 100 km this 7 day pw modulation was found to be clearly present simultaneously in the amplitude of the zonal 12 hour tidal wind the meridional 24 hour tidal wind and in both the 12 hour and 24 hour periodicities which existed in the foes time series the results here provide a new physical explanation for the observed relation between sporadic e layers and planetary waves

vertical coupling from the lower atmosphere to the ionosphere observations inferred from indian mst radar gps radiosonde ionosonde magnetometer olr noaa and saber timed instrument over gadanki

climatology of the migrating terdiurnal tide tw3 in saber timed temperatures 1 the present paper is focused on the global spatial altitude and latitude structure and seasonal and interannual temporal variability of the migrating terdiurnal tide tw3 seen in 8 years 2002 2009 of observations of the kinetic temperature measured by the saber instrument on the timed satellite the tides migrating and nonmigrating and the planetary waves zonally traveling and stationary are simultaneously extracted from the satellite data it is found that the saber tw3 tide is dominated by different hough modes below and above 80 to 90 km height in the mesosphere it reflects mainly the evanescent feature of the first symmetric mode and in the lower thermosphere propagating modes with shorter vertical wavelengths dominate its structure the seasonal behavior of the terdiurnal tide at low latitudes is dominated by an annual variation with local summer amplification while that at midlatitudes is a combination of semiannual variation with maxima in equinoxes and an annual variability with winter enhancement the hough modes of the solar heating from waccm heating to a large extent determine the predominantly antisymmetric features of the saber tw3 tide during the solstice but are not able to explain well the predominant symmetric features in the equinoxes the tw3 tide reveals some interannual variability with a period of quasi 2 years which indicates an enhancement during the eastward phase of the stratospheric qbo

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

quasi periodic radar echoes from midlatitude sporadic e and role of the 5 day planetary wave using measurements of magnetic aspect sensitive radar echoes from midlatitude sporadic e collected over a two month period from tanegashima japan we show that while their occurrence duration from night to night did not exhibit any systematic variation that of the so called quasi periodic qp echoes varied sinusoidally with a period of 5 days we have interpreted this behavior in terms of effects produced by a planetary wave and identified its presence through neutral wind measurements made with a partial reflection drift radar located nearby at yamagawa we propose that the occurrence of qp echoes is affected both by a contribution of the wind to the dynamo electric field and by the direction of the neutral wind we argue that because the wind vector of the planetary wave is elliptically polarized at midlatitudes a preferred wind direction conducive to the generation of qp echoes occurs once every 5 days on the other hand this wave is linearly polarized and directed zonally over the geographic equator the fact that qp echoes are most fully developed at midlatitudes and less so at lower latitudes suggests that zonal flow is not particularly favorable for qp echo production

the 8 hour tide in the arctic mesosphere and lower thermosphere an all sky vhf meteor radar at esrange 68 n 21 e near kiruna in northern sweden has been used to investigate the 8 hour tide in the arctic mesosphere and lower thermosphere we present a climatology of the 8 hour tide over the period october 1999 to april 2001 the tide appears to be a persistent feature of the arctic atmosphere although a large day to day variability of the tidal amplitude is observed at times the 8 hour tide reaches amplitudes over 30 m s 1 the amplitude of the tide increases with height across the observed height range of 80 100 km monthly mean tidal amplitudes range from 2 m s 1 to values as large as 10 m s 1 a clear seasonal behavior is apparent with maximum amplitudes observed in the autumn vertical wavelengths are shortest in winter and spring 25 35 km and longest in summer and autumn 50 90 km at least on some occasions the vertical wave number relationships between the 8 12 and 24 hour tides suggest that the 8 hour tide is being generated by nonlinear interaction between the 12 and 24 hour tides

features caused by ground ice growth and decay in late pleistocene fluvial deposits paris basin france last glacial fluvial sequences in the paris basin show laminated lacustrine deposits osl and radiocarbon dated to between 24 6 and 16 6 ka in one site and overlying alluvial sandy gravel a thermokarst origin of the lakes is supported by abundant traces of ground ice particularly ice wedge pseudomorphs beneath the lacustrine layers and synsedimentary deformation caused by thaw settlement the features include brittle deformation normal and reverse faults resulting from ground subsidence owing to ice melting and ductile deformations caused by slumping of the sediments heaved by the growth of ice cored mounds these correspond to lithalsas or lithalsa plateaus and or to open system pingos at least two generations of thermokarst are recorded and may reflect the millennial climate variability typical of the last glacial the structures studied in quarries are associated with an undulating topography visible in 5 m dems and a spotted pattern in aerial photographs the search for similar patterns in the paris basin indicates that many other potential thermokarst sites exist in the last glacial terrace fy of rivers located north of 48 n when they cross the lower cretaceous sands and marls in some sites the presence of organic poor fine grained deposits presumably of lacustrine origin was confirmed by borehole data the site distribution coincides broadly with that already known for ice wedge pseudomorphs this study provides new evidence of permafrost induced ground deformations in france and strongly suggests that thermokarst played a significant and probably largely underestimated role in the genesis of late pleistocene landscapes

new multiscale models and self similarity in tropical convection abstract one of the unexplained striking features of tropical convection is the observed statistical self similarity in clusters superclusters and intraseasonal oscillations through complex multiscale processes ranging from the mesoscales to the equatorial synoptic scales to the intraseasonal planetary scales here new multispatial scale multitime scale simplified asymptotic models are derived systematically from the equatorial primitive equations on the range of scales from mesoscale to equatorial synoptic to planetary intraseasonal which provide a useful analytic framework for addressing these issues new mesoscale equatorial synoptic dynamical mesd models and balanced mesd bmesd models are developed for the multitime multispace interaction from mesoscales to equatorial synoptic scales new multitime versions of the intraseasonal planetary equatorial synoptic dynamics ipesd models are developed for multiple spatiotemporal interactions on equatorial synoptic scales and planetary scales the m

mean winds and tides in the arctic mesosphere and lower thermosphere 1 a new meteor radar has been deployed at esrange 68 n 21 e near kiruna in sweden the radar has been used to measure winds and tides in the arctic mesosphere lower thermosphere region over the interval august 1999 to july 2000 conspicuous features of the measured mean winds include a strong shear of up to 5 m s 1 km 1 in the summer zonal flow resulting in eastward flows of in excess of 30 m s 1 at the upper heights observed 97 km an equatorward meridional flow is observed in summer and winter which reaches maximum values of 13 m s 1 in a summer jet poleward flow in comparison is weak and only occurs at the equinoxes the monthly mean and seasonal mean behaviors of the amplitudes and phases of the 12 and 24 hour tides are examined and compared to the global scale wave model 98 the observations are generally very close to the model predictions for the 24 hour tide and for the 12 hour tide in winter in other seasons particularly summer the observed 12 hour tidal amplitudes are significantly larger than those predicted in spring and summer the wavelength of the 12 hour tide is significantly larger than that predicted

measurements and modelling of intermediate descending and sporadic layers in the lower ionosphere results and implications for global scale ionospheric thermospheric studies we demonstrate that conventional ionosondes can provide long term observations of intermediate descending and transitional layers in the 100 200 km altitude region of the ionosphere using 15 consecutive days of observations at townsville australia during the sundial campaign of september 1989 we tracked the birth of the layers at altitudes above 150 km and their systematic downward motion to the 110 km region at rates between 4 and 5 km hr the observations are compared with ncar tigcm simulations and the results show i that the layering process is identifiable with meridional wind shear node convergence of ions ii that zonal wind controls of the layers are insignificant under the prevailing conditions and iii that electric fields play an important role in the effectiveness of the ion convergence and downward transport processes at altitudes above 125 km the measurement and modelling comparisons are the first of a kind providing insight into the relative roles of winds and electric fields and opening possibilities for determining the global characteristics of the layers and their cause effect roles in the dynamics of the lower ionospheric thermospheric domain

drivers of holocene palsa distribution in north america abstract palsas and peat plateaus are climatically sensitive landforms in permafrost peatlands climate envelope models have previously related palsa peat plateau distributions in europe to modern climate but similar bioclimatic modelling has not been attempted for north america recent climate change has rendered many palsas peat plateaus in this region and their valuable carbon stores vulnerable we fitted a binary logistic regression model to predict palsa peat plateau presence for north america by relating the distribution of 352 extant landforms to gridded modern climate data our model accurately classified 85 3 of grid cells that contain observed palsas peat plateaus and 77 1 of grid cells without observed palsas peat plateaus the model indicates that modern north american palsas peat plateaus are supported by cold dry climates with large seasonal temperature ranges and mild growing seasons we used palaeoclimate simulations from a general circulation model to simulate holocene distributions of palsas peat plateaus at 500 year intervals we constrained these outputs with timings of peat initiation deglaciation and postglacial drainage across the continent our palaeoclimate simulations indicate that this climate envelope remained stationary in western north america throughout the holocene but further east it migrated northwards during 11 5 6 0 ka bp however palsa extents in eastern north america were restricted from following this moving climate envelope by late deglaciation drainage and peat initiation we validated our holocene simulations against available palaeoecological records and whilst they agree that permafrost peatlands aggraded earliest in western north america our simulations contest previous suggestions that late permafrost aggradation in central canada was climatically driven

the impact of climate change on an emerging coastline affected by discontinuous permafrost manitounuk strait northern quebec a comparative analysis of air photos and a field survey show that permafrost affected sectors of the coastline along manitounuk strait receded at an increasing rate between 1950 and 1995 these sectors are in bays where post glacial tyrrell sea clays outcrop during the same period sand beaches at the mouths of streams and rock and till shorelines on headlands prograded at the pace of isostatic uplift permafrost that had aggraded and formed lithalsas and plateaus during the 19th century i e during the little ice age had expanded over the tidal marsh and had locally provoked accelerated coastal emergence as frost heaving added to post glacial isostatic uplift climate warming during the 20th century particularly during the summer months generated a chain of impacts involving forest growth snow cover ground warming and permafrost degradation waves and tidal currents are mainly responsible for the evacuation and transport of thermokarst produced silts and clays from the shore into the marine basin

terdiurnal migrating tide signature in ionospheric total electron content we report the latitudinal seasonal and solar cycle variations of terdiurnal migrating tide i e terdiurnal westward wave number 3 tw3 signature in ionospheric total electron content tec our investigations are based on the jpl global ionospheric maps gims during 1999 2011 the absolute amplitude of tw3 exhibits maximum values in the magnetic equatorial region which reaches about 8 tecu under high solar activity and 1 5 tecu under low solar activity the relative amplitude of zonal mean tec in equatorial region however shows persistent patterns from 1999 to 2011 with little solar activity dependence the relative amplitude of tw3 has a peak of similar to 10 in the magnetic equatorial region and a second one of similar to 7 at magnetic middle latitudes 30 degrees 50 degrees at high latitudes in local winter seasons the maximum relative amplitude occurs which varies between 8 and 15 with slightly larger amplitudes in the northern hemisphere the global structure of tw3 signature in tec should shed some light on the coupling between the ionosphere thermosphere and the lower atmosphere

a 6 5 day westward propagating planetary wave origin and characteristics a large 10 30 m s 1 6 7 day period westward propagating planetary wave was seen in both ground radar and satellite data within the 80 100 km height regime during august and september 1993 previous analyses of these data argue that it was most likely a manifestation of the 1 2 rossby planetary wave commonly referred to as the 5 day wave perhaps shifted to longer periods by interaction with the mean zonal winds in this study the global scale wave model gswm hagan et al 1993 is used to analyze the characteristics of this westward propagating wave we propose that the observed wave is not a doppler shifted 5 day wave but rather an unstable mode drawing energy from unstable regions in the upper mesosphere whose realization is global in scale the concept of atmospheric instability is used to determine a likely source region and the model is used determine the characteristic period growth rate and perturbation fields of the instability driven wave

coordinated investigation of summer time mid latitude descending e layer es perturbations using na lidar ionosonde and meteor wind radar observations over logan utah 41 7 n 111 8 w 1 it is well known that there is a strong correlation between the formation of a descending sporadic e layer es and the occurrence of large upper atmospheric zonal wind shears most likely driven by solar thermal tides and or gravity waves we present new results of es perturbation events captured between 13 and 17 july 2011 ut days 194 198 as part of a coordinated campaign using a wind temperature na lidar at utah state university 41 7on 111 8 w and a canadian advanced digital ionosonde cadi scientific instrumentation ltd saskatoon saskatchewan canada and skiymet meteor wind radar both located at nearby bear lake observatory 41 9 n 111 4 w during this period the cadi detected strong descending es on 2 days 195 and 197 when large modulations of the top side mesospheric na layer occurred in synchronism with strong oscillations in the ionosonde e region echoes a weakening in the descending e layer echoes was observed on the other 2 days 196 and 198 coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for es formation and its downward propagation further investigation indicates that the weakening tidal amplitudes and the occurrence of the es events were also influenced by a strong quasi two day period modulation suggesting significant quasi two day wave qtdw interactions with the tides indeed a nonlinear wave wave interaction induced 16 hour period child wave was also detected with amplitude comparable to that of the prevailing tides these interaction processes and their associated effects are consistent with earlier thermosphere ionosphere mesosphere electrodynamics general circulation model studies of nonlinear interactions between the migrating tidal waves and the qtdw and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the es

segregated ice structures in various heaved permafrost landforms through ct scan the growth of segregated ice lenses in frost susceptible sediments in the discontinuous permafrost zone is the dominant mechanism for the formation of permafrost mounds such as palsas lithalsas and permafrost plateaus thawing of these mounds creates thermokarst lakes which are particularly abundant in nunavik east of the hudson bay area the inception of the permafrost in mounds and their growth are regulated by climate conditions by local quaternary geology and by environmental factors such as topography vegetation snow cover and surface humidity variable sizes and morphology of the permafrost mounds can be attributed to local factors that affect the ice segregation process particularly the supply of water needed for ice lens growth and grain size composition of the soil into which aggradation takes place computer image analysis of ct scans on high quality cores obtained from permafrost mounds and plateaus of various shapes reveal that the ice layer sequences and permafrost internal structure vary with landform types a relationship therefore exists between different morphological type within a family of landforms and their microscale internal structure copyright 2007 john wiley sons ltd

the terdiurnal tide in the mesosphere and lower thermosphere over london canada 43 n 81 w radars have been used successfully for many years to measure atmospheric diurnal and semidiurnal tides but studies of the atmospheric terdiurnal tide have only rarely been reported to date in the literature in this paper we investigate the amplitude phase and vertical wavelength for the terdiurnal tide using the university of western ontario uwo 2 mhz radar near london canada emphasis is placed on short term monthly seasonal and annual variations of the terdiurnal tide the results of the present study bring out certain new aspects of the terdiurnal tide at midlatitudes in the northern hemisphere we show that terdiurnal tides have significant amplitudes in the mesosphere and lower thermosphere indeed the terdiurnal amplitudes are often comparable to the diurnal ones we also draw attention to the annual variability and especially highlight the occurrence of the terdiurnal tide in non winter months for example the occurrence of the terdiurnal tide in spring months is not uncommon thus it seems that the 8 hour component observed over london canada cannot be explained by the terdiurnal tide being due to solar heating alone particular cases of the terdiurnal tide are examined and the observed amplitude and phase profiles of the terdiurnal tide at certain times of the year are discussed in terms of nonlinear interaction between the diurnal and semidiurnal tides we suspect that this effect may also explain the fact that diurnal and semidiurnal tides at our station often seem suppressed relative to other sites thayaparan et al 1995a on the basis of our previous and present observations it is also possible that large terdiurnal amplitudes observed at certain times of the year may be partly explained in terms of tidal gravity wave interactions however this possibility needs to be further investigated in the future

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

itcz breakdown and its upscale impact on the planetary scale circulation over the eastern pacific abstractthe eastern pacific ep intertropical convergence zone itcz is sometimes observed to break down into several vortices on the synoptic time scale it is still a challenge for present day numerical models to simulate the itcz breakdown in the baroclinic modes also the upscale impact of the associated mesoscale fluctuations on the planetary scale circulation is not well understood here a simplified multiscale model for the modulation of the itcz is used to study these issues a prescribed two scale heating drives the planetary scale circulation through both planetary scale mean heating and eddy flux divergence of zonal momentum where the latter represents the upscale impact of mesoscale disturbances in an idealized scenario where the heating only varies on the mesoscale key features of the itcz breakdown in the baroclinic modes are captured the eddy flux divergence of zonal momentum is characterized by midlevel low level eastward westward momentum forcing at subtropical latitudes of th

lithalsa distribution morphology and landscape associations in the great slave lowland northwest territories canada abstract lithalsas are permafrost mounds formed by ice segregation in mineral rich soil that occur within the zone of discontinuous permafrost nearly 1800 lithalsas were mapped using archival aerial photographs within the great slave lowland northwest territories canada these are up to 8 m high and several hundred meters in length and width one lithalsa examined by electrical resistivity and boreholes rises 4 to 6 m above an adjacent peatland shows clear evidence of ice segregation at depth and ground heave of between 2 5 and 4 0 m and is estimated to have formed within the past 700 years regionally lithalsas are typically located adjacent to ponds and streams with mature forms vegetated by deciduous birch forest or mixed birch and spruce forest with a herb shrub understory and include circular crescentic and linear forms they are abundant within the lowland region which contains widespread glaciolacustrine lacustrine and alluvial fine grained sediments the lithalsas are most common within the first few tens of meters above the present level of great slave lake indicating that many are late holocene and some less than 1000 years in age a comparison with lithalsas in contemporary environments reveals that comparatively warm but extensive discontinuous permafrost fine grained sediments alluvial lacustrine marine or glaciomarine and available groundwater supply provide the climatic and hydro geological parameters for the development of lithalsas in permafrost terrain the identification of lithalsas in this region is important given their sensitivity to climate change and potential hazards to northern infrastructure upon thawing

terdiurnal tidelike variability in sporadic e layers 1 time series analysis was performed on a large database of ionosonde recordings taken over 12 years for the 6 month period from the beginning of may to the end of october when sporadic e layer occurrence is frequent the results show that in addition to the well known 24 and 12 hour tidal variations there is also a weaker but regular 8 hour periodicity in midlatitude sporadic e layers es statistically this terdiurnal periodicity is significant and occurs in both the sporadic e layer critical frequency foes and the layer virtual height h es becoming strongest around summer solstice and later in october after a minimum in september at times a weak 6 hour periodicity can also be present in es but its effects are much less significant than those of the 8 hour oscillation the 8 hour periodicity in es is attributed to the terdiurnal tide presumably acting through its vertical wind shear forcing of the metallic ions in the lower thermosphere the relation to the terdiurnal tide was inferred from simultaneous ionosonde recordings from three widely spaced stations in the same midlatitude zone showing the 8 hour oscillation to be present simultaneously in all ionosonde stations and have phases which are consistent with a westward propagating terdiurnal wave of zonal wave number 3 the present study establishes the regular occurrence of a terdiurnal tidelike oscillation in es which needs to be incorporated into the physics and modeling of sporadic e layer formation and dynamics

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

the remnants of younger dryas lithalsas on the hautes fagnes plateau in belgium and elsewhere in the world this paper summarizes all the available information about the viviers of the hautes fagnes i e closed and ramparted depressions which are numerous above 500 m a s l on the highest belgian plateau these features and cross sections in the ramparts are described the ramparts are the result of both mass wasting on the slopes of the mounds and toppling of inside material 14c dating of a peat layer preserved under a rampart allerod volcanic ashes and palynological studies have proved that the viviers formed their origin during the younger dryas in the first place the depressions were interpreted as excavations by prehistoric men from 1956 on they were interpreted as pingo remnants the pingo hypothesis is now abandoned the viviers are remnants of mineral palsas lithalsas features which nowadays exist in hudsony canada present day lithalsas are solely known in subarctic quebec and in lapland they form in the discontinuous permafrost zone close to the tree line i e in zones where mean annual temperature mat ranges from 4 to 6 c and where the average temperature of the warmest month is between 9 and 11 5 c such climatic conditions are rarely encountered nowadays in periglacial regions remnants of lithalsas are very infrequent too they appear like ramparted depressions forming clusters such traces dating from the younger dryas have been described only at elevation above 500 m a s l on the belgian hautes fagnes plateau around 250 m a s l in wales and at sea level in ireland in these few places according to r isarin s palaeoclimatic results climatic conditions during the younger dryas were similar to present day conditions in subarctic quebec where lithalsas are numerous

the character of polar tidal signatures in the extended canadian middle atmosphere model the characteristics of the diurnal semidiurnal and terdiurnal tides zonal wave numbers 5 to 5 in temperature and zonal wind in the polar mesosphere and lower thermosphere region as simulated by the extended canadian middle atmosphere model are examined the most significant diurnal semidiurnal and terdiurnal tides in the polar regions are ds0 dw1 and de1 sw3 sw2 sw1 ss0 se1 and se2 and tw3 ts0 and tw1 respectively and their latitudinal structures seasonal variations and hemispheric asymmetries noted of these components ds0 tw1 ts0 and tw3 exhibit a seasonally symmetric variation with both hemispheres strengthening simultaneously on the other hand dw1 strengthens asymmetrically so that when one hemisphere is strong the other is weak the remainder show no seasonal tendency but vacillate on shorter than seasonal time scales in a symmetric or antisymmetric manner at different times of the year global scale correlations of the amplitudes of the migrating tides dw1 sw2 and the stationary planetary wave 1 and the assumed child nonmigrating tides are also examined the results indicate that the correlations are highly time scale dependent and the significant correlations seen with the original time series are mainly due to longer term variations 18 days there are no consistent global correlations associated with the short term variations 18 days among these waves

mesospheric planetary wave signatures in the equatorial electrojet 1 using five years 1994 1998 of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere mlt region and geomagnetic field measurements in the indian geomagnetic dip equatorial region an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet eej the winds are measured using medium frequency mf radar 1 98 mhz located at tirunelveli the eej strength is determined by measuring the geomagnetic field strength at both the geomagnetic dip and off dip equatorial stations trivandrum and alibag india by noting the simultaneous time evolution of spectral signal morlet wavelet analysis in both the eej strength and mesospheric winds at 88 km it is found that mesospheric planetary waves with periodicities of 2 25 days often do propagate up to the ionospheric dynamo region and have their influences on eej strength sometimes only one of the parameters shows strong spectral signal in this periodicity range it is also observed that often the diurnal oscillation in eej strength and mesospheric winds exhibits coherent variations in amplitude when the signature of mesospheric planetary scale oscillations is found in the eej strength also it is found that variations in high energy solar radiations f10 7 is used as a proxy can influence the eej strength at planetary timescales this leads to an interesting question what actually causes the vertical coupling between ionosphere and atmosphere through upward propagating planetary waves to be operative only during some and not all of the episodes

a statistical analysis of sporadic e layer occurrence in the midlatitude china region a statistical analysis of sporadic e layer recorded from september 2011 to september 2015 at four chinese ionospheric sounding stations of mohe 122 37 e 53 50 n beijing 116 25 e 40 25 n wuhan 114 61 e 30 53 n and hainan 109 13 e 19 52 n are presented to investigate the characteristics of sporadic e layer at the middle latitudes over china the occurrence of the sporadic e layer in mid latitude china region shows strong dependence on local time and season consistent with previous studies the occurrence of the mid latitude sporadic e layer is prominent at local daytime in summer season the results also reveal that the post sunset sporadic e layer is statistically pronounced in mid latitude china region possibly related to the nighttime mid latitude e region irregularities the mid latitude sporadic e layer is modulated by atmospheric tidal waves and planetary waves at different latitudes the occurrence of the mid latitude sporadic e layer also tends to increase with the level of geomagnetic activity on basis of both the statistical analysis and case study

tropical cyclogenesis within an equatorial rossby wave packet a packet of equatorial rossby er waves that lasted 2 5 months is identified in the lower troposphere of the northwest pacific waves within the packet had a period of 22 days a wavelength of 3600 km a westward phase speed of 1 9 m s 1 and a near zero group speed the wave properties followed the er wave dispersion relation with an equivalent depth near 25 m the packet was associated with the development of at least 8 of the 13 tropical cyclones that formed during the period a composite was constructed around the genesis locations tropical cyclones formed east of the center of the composite er wave low in a region of strong convection and a separate 850 hpa vorticity maximum the background flow during the life of the packet was characterized by 850 hpa zonal wind convergence and easterly vertical wind shear wave amplitude peaked at the west end of the convergent region suggesting that wave accumulation played a significant role in the growth of the packet the presence of easterly vertical wind shear provided an environment that trapped energy in the lower troposphere each of these processes increases wave amplitude and thus the likelihood of tropical cyclone formation within the waves the initial low pressure region within the wave packet met lander s definition of a monsoon gyre it developed to the west of persistent localized convection that followed the penetration of an uppertropospheric trough into the subtropics it is argued that the monsoon gyre represented the initial er wave low within the packet

planetary waves and midlatitude sporadic e layers strong experimental evidence for a close relationship 1 a large amplitude 7 day period westward propagating s 1 planetary wave has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere mlt during the second half of august and well into september 1993 following recent suggestions that planetary waves might play a role in the formation of midlatitude sporadic e layers es we have obtained and analyzed for the period from august 1 to september 30 1993 the sporadic e critical frequency foes time series from eight midlatitude ionosonde stations covering a large longitudinal zone from 58 e to 157 w the analysis revealed that all eight station foes data showed a strong 7 day periodicity occurring concurrently with the 7 day planetary wave reported elsewhere using independent methods for the analysis of the foes time series we computed identical estimates for the propagation direction zonal wave number and phase velocity of the 7 day wave which are in agreement with those reported from radar and satellite neutral wind mlt measurements the present findings provide the first direct evidence proving that planetary waves play an important role in the physics of midlatitude sporadic e region layers in addition our results include an important implication that the es parameters measured routinely and rather reliably with a dense global network of digital ionosondes as well as the enormous ionogram databases existing in world data centers may be used as an alternative means of studying large scale neutral atmospheric dynamics in the mlt region

modeling and analysis of the structure and generation of the terdiurnal tide the terdiurnal or 8 h tide has been seen in a number of midlatitude radar measurements and has recently been mapped globally at 95 km a series of calculations and model simulations are used to examine the processes responsible for generating this tide and for its strong hemispheric asymmetry the model tidal structure deviates significantly from the structure of a single hough mode in contrast to the diurnal tide the dominant cause of the hemispheric asymmetry is the sensitivity of the propagation to the background state particularly the static stability several conceptual views of the tide are explored to give a heuristic view of this asymmetry this analysis predicts that particular modes are prohibited from propagating in large regions of the summer mesosphere the tide occurs naturally in a three dimensional nonlinear model extending from the tropopause to the lower thermosphere the model tide shows a number of features in common with observations including amplitude maxima in midlatitudes a wintertime peak and zonal winds larger than meridional winds the tidal amplitude in the model is weaker than observed at 95 km several interactive model integrations are performed to determine the forcing mechanism for the tide these calculations indicate that the direct solar forcing of the terdiurnal tide is the dominant mechanism occurring in the model at middle and high latitudes nonlinear interactions contribute to the low latitude tide

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

moist multi scale models for the hurricane embryo determining the finite amplitude preconditioned states in the hurricane embryo which lead to tropical cyclogenesis is a central issue in contemporary meteorology in the embryo there is competition between different preconditioning mechanisms involving hydrodynamics and moist thermodynamics which can lead to cyclogenesis here systematic asymptotic methods from applied mathematics are utilized to develop new simplified moist multi scale models starting from the moist anelastic equations three interesting multi scale models emerge in the analysis the balanced mesoscale vortex bmv dynamics and the microscale balanced hot tower bht dynamics involve simplified balanced equations without gravity waves for vertical vorticity amplification due to moist heat sources and incorporate nonlinear advective fluxes across scales the bmv model is the central one for tropical cyclogenesis in the embryo the moist mesoscale wave mmw dynamics involves simplified equations for mesoscale moisture fluctuations as well as linear hydrostatic waves driven by heat sources from moisture and eddy flux divergences a simplified cloud physics model for deep convection is introduced here and used to study moist axisymmetric plumes in the bht model a simple application in periodic geometry involving the effects of mesoscale vertical shear and moist microscale hot towers on vortex amplification is developed here to illustrate features of the coupled multi scale models these results illustrate the use of these models in isolating key mechanisms in the embryo in a simplified content

glacial lake mcconnell paleogeography age duration and associated river deltas mackenzie river basin western canada abstract glacial lake mcconnell lasted from 11 8 to 8 3 ka bp while occupying parts of the great bear great slave and athabasca lake basin the retreating laurentide ice front formed the eastern margin whereas low rolling hills formed the north west and south shorelines three major deltas were deposited at the mouths of the laird peace and athabasca rivers the total extent of all phases of the lake was 240 000 km 2 while the largest extent was 210 000 km 2 at 10 5 ka bp downwarping of the basin by glacial ice was the main cause of the lake whereas sediment blockage between jean marie river and fort simpson was secondary initially glacial lake mcconnell occupied the northwestern corner smith arm of the great bear lake basin and discharged through the hare indian river outlet by 11 5 ka bp the enlarged water body flowed out the great bear river but only for a short period of time the mackenzie river formed the third outlet near jean marie river at 11 ka bp and flow in the great bear river ceased until 9 ka bp at 9 9 ka bp glacial lake mcconnell was impacted by a major flood from glacial lake agassiz with a peak discharge of 2 7 10 6 m 3 sec flood water discharged from glacial lake mcconnell peaking at 0 35 0 57 10 6 m 3 sec and receding flow continued for 30 months the massive influx of floodwater into glacial lake mcconnell caused an abrupt increase of discharge which enlarged the outlet channel to between 6 and 13 km wide between fort simpson and jean marie river at 8 3 ka bp isostatic rebound ended the 3500 year old extensive lake by dividing it into the great slave lake and lake athabasca

seasonal variations of the terdiurnal tide in the mesosphere and lower thermosphere a model study observations of the terdiurnal 8 hour tidal wind oscillations in the mesosphere and lower thermosphere mlt reveal strong seasonal and latitudinal variations the tidal amplitudes reach a maximum of about 15 20 m s 1 at midlatitudes in winter the vertical phase progression corresponds to very long vertical wavelengths during summer the amplitudes are typically weaker and the phases are less regular first simulations of the terdiurnal tide with the spectral mesosphere lower thermosphere model are presented the model explicitly accounts for the solar thermal excitation in the middle and upper atmosphere and reproduces the salient features of the terdiurnal wind oscillations well the preferential solar excitation of antisymmetric terdiurnal modes capable of propagating into the mlt combined with an asymmetric atmospheric response appears to be primarily responsible for the observed seasonal variations nonlinear interactions of the diurnal and semidiurnal tides are demonstrated to make a noticeable in situ contribution to the excitation of the terdiurnal tide at 95 100 km especially during equinox

gravity wave tidal interactions in the mesosphere and lower thermosphere over rothera antarctica 68 s 68 w 1 a simple technique for measuring gravity wave activity has been used to investigate gravity wave tidal interactions in the polar mesosphere and lower thermosphere mlt the technique uses the radial velocities of individual meteors recorded by meteor radar to derive a statistical measure variance of the activity of the high frequency gravity wave field this technique can measure gravity waves with horizontal wavelengths of up to about 400 km and periods up to approximately 3 hours interactions between the observed gravity wave field and the background wind are investigated using data collected between february 2005 and december 2008 by a meteor radar based at rothera antarctica 68 s 68 w the results reveal the presence of significant modulations of the observed gravity wave field at tidal periods of 12 and 24 hours correlations between the hourly zonal winds and the gravity wave field measured by the meteor radar reveal an in phase relationship between the hourly zonal winds and gravity wave variance in winter and an anti phase relationship in summer this is consistent with the theory of filtering by tidal winds acting on a zonally asymmetric gravity wave field in which westward waves dominate in winter and eastward waves dominate in summer the limitations of the technique and the effect this has on the interpretation of these results are also considered the effects of the diurnal cycles in meteor count rates the uncertainty in recorded radial velocities and the uncertainty in the measured heights of meteors are considered

internal structure and the thermal and hydrological regime of a typical lithalsa significance for permafrost growth and decay this study presents new knowledge about the ice segregation and frost heave processes taking place in a typical lithalsa a tomodensitometric scanner was used to produce high resolution computer images of ice lenses soil layers faults sedimentary structures and gas bubbles scan image analysis allowed the interpretation of the ice lenses and soil cryostructures resulting from permafrost aggradation it also provided an accurate estimation of volumetric contents of ice and gas present in the permafrost isotopic analyses on the various phases of the permafrost i e ice gas and soil provided supplementary information 18 o deuterium and tritium analyses were undertaken on ground ice and on surface water monitoring of the thermal regime of the lithalsa provided clues relative to gradients that drive groundwater movements and ice lens growth compilation and interpretation of the data in a three dimensional and temporal context suggest that the lithalsa under study grew under climate conditions slightly colder than those of the 20th century however post aggradational water penetrated into the permafrost of the lithalsa ground temperatures increased since 2000 most likely because of underground warming owing to groundwater flow around the permafrost body as a result the mound has started to settle down and an incipient thermokarst pond became conspicuous in 2003

the potential lateral growth of lithalsas the lithalsas in the hudson bay region of northern quebec canada are the closest modern analogs of ancient features that collapsed to form conspicuous circular depressions viviers common in the hautes fagnes a region in belgium observations made in both regions are complementary and suggest that these mounds formed by frost heaving displacing soil not only upward as previously assumed but also laterally this lateral displacement is consistent with diverse observations and inferences which include 1 the simple rounded outline either circular or oval typical of both active and relic lithalsas 2 evidence of local lateral extension inferred from exposures of the relic forms 3 the relative inefficiency of solifluction in accumulating surface material to form the peripheral ramparts of remnant lithalsas due to the very gentle slopes of the mounds and 4 the dip of ice lenses within a lithalsa in the hudson bay region perhaps indicating that the freezing front dipped outward along its periphery the growth of segregation ice is the primary driver for the vertical growth and lateral enlargement of a lithalsa

development and decay of a lithalsa in northern quebec a geomorphological history the complete life cycle of a permafrost mound is reconstructed from its growth until its degradation the study site is a lithalsa which is the subject of a long term monitoring that includes geocryological observations measurements of permafrost properties on cores ground temperature measurements and observations of landform changes the landform likely grew as a palsa under cold climatic conditions in the past the peat cover was subsequently eroded early stages of degradation are witnessed since 2003 as a new thermokarst pond is starting to form though mound collapse settlement of the structure has been observed and a rim ridge has begun to form ultimately the lithalsa shall disappear and be replaced by a circular thermokarst pond surrounded by a rampart similar to many other ones in the study area the monitoring of the thermal regime of the lithalsa illustrates the pattern of internal warming and points to the causes of its degradation

the dynamic ionosphere over arecibo a theoretical investigation numerical simulations of the f region ionosphere over arecibo puerto rico are presented we deduce from these simulations that the dynamic behavior of the arecibo ionosphere particularly the so called midnight collapse phenomenon is strongly influenced by the upward propagating semidiurnal tidal component of the neutral meridional wind excited below thermospheric levels presence of a terdiurnal component in the wind field improves the agreement with experiment and could result from nonlinear interactive coupling between the neutral wind and ion drag the steep underside density gradients occurring in conjunction with the collapse are due to vertical shear in the meridional wind field associated with the propagating semidiurnal tide these gradients are capable of triggering the gradient drift instability thus accounting for plasma irregularity formation and observations of vhf scintillations associated with the collapse phenomenon

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

quasi 16 day oscillation in the mesosphere and lower thermosphere a quasi 16 day wave in the mesosphere and lower thermosphere is investigated through analyses of radar data during january february 1979 and through numerical simulations for various background wind conditions previous workers have examined about 19 days of tropospheric and stratospheric data during january 10 28 1979 and present conflicting evidence as to whether a large westward propagating wavenumber 1 oscillation observed during this period can be identified in terms of the second symmetric rossby normal mode of zonal wavenumber 1 commonly referred to as the 16 day wave in the present work we have applied spectral analysis techniques to meridional and zonal winds near 95 km altitude obtained from radar measurements over obninsk russia 54 n 38 e and saskatoon canada 52 n 107 w these data reveal oscillations of the order of 10 m s 1 with a period near 16 days as well as waves with periods near 5 and 10 days these periodicities all correspond to expected resonant frequencies of atmospheric disturbances associated with westward propagating free rossby modes of zonal wavenumber 1 numerical simulations are performed which demonstrate that the 95 km measurements of the 16 day wave are consistent with upward extension of the oscillation determined from the tropospheric and stratospheric data noteworthy features of the model in terms of its applicability in the mesosphere lower thermosphere regime are explicit inclusion of eddy and molecular diffusion of heat and momentum and realistic distributions of mean winds especially between 80 and 100 km the latter include a westerly wind regime above the summer easterly mesospheric jet thus providing a ducting channel enabling interhemispheric penetration of the winter planetary wave disturbance this serves to explain the appearance of a quasi 16 day wave recently reported in the high latitude summer mesopause williams and avery 1992 however the efficiency of this interhemispheric coupling may be reduced by gravity wave stress no significant penetration of the 16 day oscillation above about 100 km is predicted by the model reported signatures of a 16 day periodicity in ionospheric data therefore require modulation of tidal or gravity wave accessibility to the thermosphere or perhaps in situ excitation

cryostratigraphical studies of ground ice formation and distribution in a high arctic polar desert landscape resolute bay nunavut ground ice distribution and abundance have wide ranging effects on periglacial environments and possible impacts on climate change scenarios in contrast very few studies measure ground ice in th

oceanic cyclogenesis as induced by a mesoscale convective system moving offshore part ii genesis and thermodynamic transformation abstract the genesis of intense cyclonic vorticity in the boundary layer and the transformation of a low level cold pool to a warm core anomaly associated with the long lived mesoscale convective systems mcss which produced the july 1977 johnstown flash flood and later developed into a tropical storm are examined using a 90 h real data simulation of the evolution from a continental mcs vortex to an oceanic cyclone storm system it is shown that the midlevel vortex trough at the end of the continental mcs s life cycle is characterized by a warm anomaly above and a cold anomaly below the mesovortex as it drifts toward the warm gulf stream water plays an important role in initiating and organizing a new mcs and a cyclonic shear vorticity band at the southern periphery of the previously dissipated mcs it is found from the vorticity budget that the vorticity band is amplified through stretching of absolute vorticity as it is wrapped around in a slantwise manner toward the cyclone center then the as

evidence for nonlinear coupling of planetary waves and tides in the antarctic mesopause analyses of hourly mean meridional and zonal winds near 95 km observed with the meteor radar system at molodezhnaya station 68 s 45 e during 1990 reveal the presence of long period 2 18 day waves with dominant periods corresponding to those of rossby normal modes modified by mean zonal winds time varying analyses indicate that although significant contributions at planetary wave periods persist with nearly constant periods for intervals of days to weeks temporal variability of these periods is observed over longer intervals tidal motions which mainly consist of the semidiurnal and the diurnal periods demonstrate considerable modulation of their amplitudes that vary with time the observed tidal amplitude modulations are investigated through bispectral analyses the results of these analyses suggest nonlinear interactions of quadratic form between oscillations with periods in the range of 2 to 19 days and the diurnal and semidiurnal tides at various intervals during 1990

terdiurnal tide in the extended canadian middle atmospheric model cmam 1 we use the extended canadian middle atmosphere model cmam a general circulation model gcm to investigate the nature of the terdiurnal tide temperature and horizontal winds from a model run are analyzed to delineate the character of this tide for zonal wave numbers s 5 to 5 descriptions of the annual mean amplitudes seasonal variations and total tide superposed from the migrating and 10 nonmigrating components are provided the amplitudes and vertical wavelengths of the various components and the total terdiurnal tide are found to depend strongly on season latitude and altitude the migrating terdiurnal component maximizes at mid and high latitudes with significant amplitudes annual mean amplitude in wind temperature 10 m s k in the upper mesosphere and lower thermosphere mlt region between 80 and 100 km maximum amplitudes occur in winter in both hemispheres whereas above 100 km maximum amplitudes occur during solstices for the zonal wind field the nonmigrating terdiurnal components te5 te3 te4 tw4 and tw5 tend to peak at 50 n s with amplitudes between 2 and 8 m s the other nonmigrating components maximize in the polar regions with amplitudes of 2 10 m s possible generation mechanisms solar heating and nonlinear interactions for the migrating terdiurnal tide in the mlt region are also examined correlation analysis indicates that nonlinear interactions between the migrating diurnal and semidiurnal tides are unlikely to be the source of the migrating terdiurnal tide

seasonal variations of mlt tides revealed by a meteor radar chain based on hough mode decomposition seasonal variations of different tides in the mesosphere and lower thermosphere are investigated from wind observations of a meteor radar chain on the basis of hough mode decomposition first the observed winds are decomposed into different diurnal semidiurnal and terdiurnal tidal components different seasonal patterns are revealed for each component pronounced semiannual oscillation sao is presented in the diurnal component while latitude dependent seasonal variation is found in the semidiurnal and terdiurnal components at the low midlatitude stations the semiannual annual oscillation is relatively stronger then hough mode decomposition is utilized to extract the dominant tidal modes of each decomposed component it is found that each component is dominated by one of its symmetric tidal modes with strong seasonal dependency apparent sao is observed in the dominant 1 1 mode 2 4 mode is strong in the autumn and winter months after the september equinox based on the extracted results we further map the three dimensional distribution latitude altitude season of each tidal component the mapped results are finally compared with the corresponding values observed by the thermosphere ionosphere mesosphere energetics and dynamics doppler interferometer tidi and modeled from the global scale wave model gswm each mapped tidal component agrees well with corresponding tidi observation in the seasonal variation meanwhile coincidences are found in the seasonal dependency of the diurnal component between the mapped values and the modeled results from gswm while difference between them exists in that of the semidiurnal one

coordinated observations of 8 and 6 hr tides in the mesosphere and lower thermosphere by three meteor radars near 60 s latitude

large scale waves in the upper mesosphere at antarctic high latitudes upper mesosphere combined optical measurements of wind and temperature fields at amundsen scott station south pole and wind radar measurements at scott base 78 s 167 e show the presence of large scale waves in this region of the atmosphere at amundsen scott the largest amplitude wave observed with sub diurnal periodicity appears with a frequency near 2 4 day 10 1 hour period with a westward phase progression of wavenumber one the presence of a wave with this periodicity is confirmed by the observations at scott base the combination of the experimentally found period phase progression associated small temperature oscillations and theoretical considerations lead to the interpretation of this wave as a lamb wave the present combination of spatially resolved optical measurements and radar measurements illustrates the value of multiple station and multiple technique observations in elucidating the upper mesosphere dynamical state as well as the properties of the waves propagating through the medium where the observations are being made

tropical cyclone formation in a sheared environment a case study abstract the development of hurricane danny 1997 from depression to hurricane was examined using cloud to ground lightning data reconnaissance aircraft data and satellite imagery vertical wind shear between 850 and 200 hpa of 5 11 m s 1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development early in the period the storm intensified steadily in the presence of this downshear convection during the last and most intense outbreak a second vortex appeared to develop within the convection evidence is presented that the new downshear vortex became the dominant vortex and absorbed the original based on these events it is hypothesized that the presence of moderate vertical wind shear accelerated the early development process equivalent potential temperature fields within 500 m of the surface were examined only well after the period of vortex interaction did the characteristic mature tropical cyclone radial profile of eq

an upper e region quarterdiurnal tide at arecibo studies of the time height trajectories of ionosphere e region layers at arecibo have revealed not only the usual diurnal sporadic e and semidiurnal intermediate layer structures but also that on occasion extra layers form and descend through the e region in particular during january 1981 four layers per day were observed to descend through the upper e region this four per day layer system was remarkably coherent over the 3 days of observation and suggests the existence of a 6 hour period or quarterdiurnal tidal wind system in the upper e region numerical simulations of ion trajectories in a realistic model atmosphere with diurnal semidiurnal and quarterdiurnal tidal wind systems of appropriate amplitude and phase structures confirm that the presence of a quarterdiurnal tide is sufficient to explain the observations

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general

a study of tidal and planetary wave periodicities present in midlatitude sporadic e layers the diurnal and semidiurnal atmospheric tides are known to be of fundamental importance in the formation of midlatitude sporadic e layers acting through their vertical windshear forcing of the long living metallic ions in the lower thermosphere also recent studies suggested that planetary waves play a role on sporadic e generation as well a fact that went unnoticed in the long going research of sporadic layers in this paper a methodology is employed to investigate the tidal and planetary wave periodicities imprinted onto sporadic e critical frequencies foes in this approach standard analysis techniques used in neutral atmospheric dynamics are applied on foes time series obtained during summertime when sporadic e occurrence is nearly continuous it is shown that besides the dominant and known 24 hour and 12 hour tidal periodicities in foes there is often a weaker terdiurnal 8 hour oscillation present as well in addition there are planetary wave periodicites in foes with periods near the normal rossby modes that is 2 5 10 and 16 days it is also found that the tidal oscillations in foes undergo a strong amplitude modulation with periods comparable to the dominant planetary wave periodicities present in the data our results are in line with recent findings based on a single event study which suggested that sporadic e layers are affected indirectly by planetary waves through their nonlinear interaction and modulation of the atmospheric tides at lower altitudes the close relationship between neutral wave dynamics and midlatitude sporadic e periodicities suggests that the ionosonde data can be used as an alternative means of studying tidal and planetary wave characteristics and their climatology in the lower thermosphere

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

tropical cyclogenesis and vertical shear in a moist boussinesq model tropical cyclogenesis is studied in the context of idealized three dimensional boussinesq dynamics with perhaps the simplest possible model for bulk cloud physics with low altitude input of water vapour on realistic length and time scales numerical simulations capture the formation of vortical hot towers from measurements of water vapour vertical velocity vertical vorticity and rain it is demonstrated that the structure strength and lifetime of the hot towers are similar to results from models including more detailed cloud microphysics the effects of low altitude vertical shear are investigated by varying the initial zonal velocity profile in the presence of weak low level vertical shear the hot towers retain the low altitude monopole cyclonic structure characteristic of the zero shear case starting from zero velocity some initial velocity profiles with small vertical shear can have the effect of increasing cyclonic predominance of individual hot towers in a statistical sense as measured by the skewness of vertical vorticity convergence of horizontal winds in the atmospheric boundary layer is mimicked by increasing the frequency of the moisture forcing in a horizontal subdomain when the moisture forcing is turned off and again for zero shear or weak low level shear merger of cyclonic activity results in the formation of a larger scale cyclonic vortex an effect of the shear is to limit the vertical extent of the resulting emergent moist vortex for stronger low altitude vertical shear the individual hot towers have a low altitude vorticity dipole rather than a cyclonic monopole the dipoles are not conducive to the formation of larger scale vortices and thus sufficiently strong low level shear prevents the vortical hot tower route to cyclogenesis the results indicate that the simplest condensation and evaporation schemes are useful for exploratory numerical simulations aimed at better understanding of competing effects such as low level moisture and vertical shear

internal structure and conditions of permafrost mounds at umiujaq in nunavik canada inferred from field investigation and electrical resistivity tomography a systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at umiujaq in nunavik canada to assess their internal structure and conditions prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo section of apparent electrical resistivity the geocryologic model was developed from the synthesis of previous field investigations including shallow and deep sampling temperature and electrical resistivity logging and cone penetration tests performed in the permafrost mounds values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion the constrained resistivity model clearly show the presence of ice rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 m while t

on the occurrence and variability of the terdiurnal tide in the equatorial mesosphere and lower thermosphere and a comparison with the kyushu gcm 1 we studied the occurrence characteristics and variability of the terdiurnal tide 8 hour period in the equatorial mesosphere and lower thermosphere mlt using a meteor radar at koto tabang 0 2 s 100 3 e and mf radars at tirunelveli 8 7 n 77 8 e and pameungpeuk 7 4 s 107 4 e these locations one being located right over the equator and the other two at conjugate points around the equator within 10 form a unique experimental setup to study equatorial mlt dynamics the terdiurnal tide exists as a distinct wave signature at all three locations while the daily amplitudes can be as large as 15 m s 1 the monthly mean amplitudes lie between 1 and 10 m s 1 the amplitude of the terdiurnal tide at pameungpeuk is generally smaller than that observed at tirunelveli and koto tabang the seasonal variation in amplitude shows both annual and semiannual oscillations of 1 m s 1 at all three locations the present observations combined with previous reports indicate that the timing of the primary maximum of the terdiurnal tide amplitude shifts from autumn to late spring and early summer as one moves from high latitudes to the equator all with respect to the northern hemisphere the amplitudes and seasonal variation in the present observations show good comparison with that simulated by the general circulation model gcm developed by kyushu university japan this study supports the occurrence of nonlinear interaction between diurnal and semidiurnal tides and shows that gravity waves play an important role in the generation of the terdiurnal tide

multiscale models for cumulus cloud dynamics cumuluscloudsinvolveprocessesonavastrangeofscales includingclouddroplets turbulentmixing and updrafts and downdrafts and it is often difficult to determine how processes on different scales interact with each other in this article several multiscale asymptotic models are derived for cumulus cloud dynamics in order to i provide a systematic scale analysis on each scale and ii clarify the nature of interactions between different scales in terms of scale analysis it is shown that shallow cumulus updrafts can be described by balanceddynamicswithabalancebetweensourcetermsandascent descent thisis acloud scale versionofsocalled weak temperature gradient models in terms of multiscale interactions a model is derived that connects these balanced updrafts to the fluctuations within the balanced updraft envelope these fluctuations describe parcels and updraft pulses and this model encompasses some of the multiscale aspects of entrainment in addition to this shallow cumulus model to provide a broad picture of general cumulus dynamics multiscale models are also derived for other scales these include models for parcels and subparcel turbulent mixing and models for deep cumulus broadly speaking the differences between the shallow and deep cases convey the notion that shallow cumulus dynamics are parcel dominated whereas deep cumulus dynamics are updraft dominated this is largely due to the difference in the apparent magnitude of the background temperature stratification in addition to their use in guiding theory the multiscale models also provide a framework for multiscale numerical simulations

structure of the terdiurnal tide at 95 km satellite wind observations from the high resolution doppler interferometer hrdi instrument on the upper atmosphere research satellite uars are used to describe the latitudinal structure and seasonal variation of the terdiurnal 8 hour atmospheric tide at 95 km the amplitude of the annual average tide is 5 m s meridional and 15 m s zonal within the range observed 60 s to 60 n the maximum amplitudes are found during fall and winter at midlatitudes only weak temporal correlations with the diurnal and semidiurnal tides are seen on the monthly time scales resolved

the role of tropical waves in tropical cyclogenesis abstract this paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth s major tropical cyclone basins twenty nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis five wave types are examined in this study including mixed rossby gravity waves tropical depression type or easterly waves equatorial rossby waves kelvin waves and the madden julian oscillation the latter is not one of the classical tropical wave types but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the kelvin band in each basin the structure o