palaeogeography of carthage tunisia coastal change during the first millennium bc abstract new geological data were recovered from 16 sediment sections cored in and around the cothon the harbour of ancient carthage they show a relatively thin less than 5 m post mid holocene sediment accumulation over a late pleistocene calcarenite bedrock surface analyses of core sediment samples for granulometry and microfossil remains combined with four radiocarbon dates have suggested several palaeogeographic reconstructions of the coastline of carthage and placed constraints on the nature and location of any punic port installation pre dating the visible remains of the 3rd century bc we also propose a geologically and historically plausible reconstruction of scipio s siege and capture of the city in 146 bc

characteristics of gravity waves generated by surface topography on venus comparison with the vega balloon results abstract data from the 1985 vega venus balloon mission indicate that the mountainous region known as aphrodite influences atmospheric motions at balloon float altitudes near 54 km an altitude located within the middle cloud region it is shown that stationary gravity waves generated by surface topography and doppler shifted by a wind blowing over the terrain can propagate upward to the middle cloud layers under the right circumstances waves are amplified considerably in excess of their amplification due to the decrease of density with altitude the additional amplification is due to resonance that results from variations of static stability and mean zonal wind with altitude computed atmospheric propagation characteristics combined with terrain slopes in aphrodite estimated from pioneer venus radar altimeter data can be sufficient to produce wind amplitudes at 54 km comparable to those observed by the vega 2 balloon as it overflew aphrodite the dominant waves have horizontal wavelengths of the ord

determination of venus winds by ground based radio tracking of the vega balloons a global array of 20 radio observatories was used to measure the three dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the venus atmosphere near venus midnight by the vega spacecraft on 11 and 15 june 1985 initial analysis of only radial velocities indicates that each balloon was blown westward about 11 500 kilometers 8 000 kilometers on the night side by zonal winds with a mean speed of about 70 meters per second excursions of the data from a model of constant zonal velocity were generally less than 3 meters per second however a much larger variation was evident near the end of the flight of the second balloon consistent systematic trends in the residuals for both balloons indicate the possibility of a solar fixed atmospheric feature rapid variations in balloon velocity were often detected within a single transmission 330 seconds however they may represent not only atmospheric motions but also self induced aerodynamic motions of the balloon

geoarchaeological evidence for dredging in tyre s ancient harbour levant abstract chrono stratigraphic data from tyre s ancient northern harbour delineate extensive dredging practices during the greco roman and byzantine periods radiocarbon dates from four cores consistently cluster between ca 500 b c and 1000 a d and indicate rapid rates of sedimentation in the basin namely 10 mm yr during the greco roman and byzantine periods compared to 0 5 1 mm yr for the period 6000 4000 b c absence of strata between 4000 b c and 500 b c is not consistent with a natural base level sediment sink and cannot be interpreted as a depositional hiatus in the high stand systems tract ancient dredging is further corroborated by persistent age depth inversions within the fine grained harbour facies these data support removal of middle bronze age to persian period sediment strata with deliberate overdeepening of the harbour bottom by greco roman and byzantine societies

observation and simulation of winds and hydrodynamics in st johns and nassau rivers summary water surface elevations and daily flows are measured in the st johns and nassau rivers north florida and reveal a storm event in mid may 2009 and a sea level anomaly in june and july 2009 in an effort to reproduce these events wind and tidally driven hydrodynamics are simulated from the deep ocean into the st johns and nassau rivers using a shallow water equations model calibration adjusts spatially distributed manning s roughness based on modeled observed discharge for validation the model captures the regular tidal fluctuation as well as the hydrodynamic responses of the storm event in mid may at the six water level gaging stations at the flow gaging station the model captures the ebb tendency of the tide

geoscience of ancient mediterranean harbours abstract although much has been written on the subject of ancient mediterranean harbours the relatively new area of harbour geoarchaeology remains dispersed in the geoscience and archaeological literature over a decade of research has amassed rich and varied datasets of anthropogenically forced coastal evolution with a remarkable number of between site analogies this new research field also shows the rich potential of geoscience to reconcile important archaeological questions no single publication however has yet drawn on these geological patterns to yield a detailed overview suitable for geoscientists and environmental archaeologists the aim of this review article is to 1 discuss how ancient harbours have come to be preserved in the geological record 2 expound the basic principles and palaeoenvironmental tools underpinning ancient harbour geoarchaeology 3 outline some of the most significant research advances made and 4 discuss a new chrono stratigraphic model applicable to harbour sequences

influence of venus topography on the zonal wind and uv albedo at cloud top level the role of stationary gravity waves based on the analysis of uv images at 365 nm of venus cloud top altitude 67 2 km collected with vmc venus monitoring camera on board venus express vex it is found that the zonal wind speed south of the equator from 5 s to 15 s shows a conspicuous variation from 101 to 83 m s with geographic longitude of venus correlated with the underlying relief of aphrodite terra we interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope these waves can propagate up to the cloud top level break there and transfer their momentum to the zonal flow such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the earth by lindzen 1981 but is not reproduced in the current gcm of venus atmosphere from lmd in the equatorial regions the uv albedo at 365 nm varies also with longitude we argue that this variation may be simply explained by the divergence of the horizontal wind field in the longitude region from 60 to 10 where the horizontal wind speed is increasing in magnitude stretch it triggers air upwelling which brings the uv absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude compression this picture is fully consistent with the classical view of venus meridional circulation with upwelling at equator revealed by horizontal air motions away from equator the longitude effect is only an additional but important modulation of this effect this interpretation is comforted by a recent map of cloud top h2o fedorova et al 2015 showing that near the equator the lower uv albedo longitude region is correlated with increased h2o we argue that h2o enhancement is the sign of upwelling suggesting that the uv absorber is also brought to cloud top by upwelling

variations of sulphur dioxide at the cloud top of venus s dynamic atmosphere a pulse of sulphur dioxide in venus s upper atmosphere was observed by the pioneer venus spacecraft in the 1970s and 1980s and attributed to volcanism recent sulphur dioxide measurements from venus express indicate decadal scale fluctuations in sulphur dioxide above venus s cloud tops in an atmosphere that is more dynamic than expected

superrotation of venus atmosphere analyzed with a full general circulation model 1 a general circulation model gcm has been developed for the venus atmosphere from the surface up to 100 km altitude based on the gcm developed for earth at our laboratory key features of this new gcm include topography diurnal cycle dependence of the specific heat on temperature and a consistent radiative transfer module based on net exchange rate matrices this allows a consistent computation of the temperature field in contrast to previous gcms of venus atmosphere that used simplified temperature forcing the circulation is analyzed after 350 venus days 111 earth years superrotation is obtained above roughly 40 km altitude below the zonal wind remains very small compared to observed values which is a major pending question the meridional circulation consists of equator to pole cells the dominant one being located within the cloud layers the modeled temperature structure is globally consistent with observations though discrepancies persist in the stability of the lowest layers and equator pole temperature contrast within the clouds 10 k in the model compared to the observed 40 k in agreement with observational data a convective layer is found between the base of the clouds around 47 km and the middle of the clouds 55 60 km altitude the transport of angular momentum is analyzed and comparison between the reference simulation and a simulation without diurnal cycle illustrates the role played by thermal tides in the equatorial region without diurnal cycle the gierasch rossow williams mechanism controls angular momentum transport the diurnal tides add a significant downward transport of momentum in the equatorial region causing low latitude momentum accumulation

planetary scale waves and the cyclic nature of cloud top dynamics on venus abstract pioneer venus ocpp ultraviolet images spanning eight years have been analyzed objectively to derive quantitative information on the properties of planetary scale wave modes at the venus cloud tops we infer propagation characteristics for longitudinal wavenumber 1 by fourier analyzing time series of longitudinal mean normalized image brightness the dominant equatorial mode during 1979 80 was the 4 day periodicity associated with zonal motion of the y feature the difference between this and the 4 7 day equatorial rotation period derived from the tracking of small cloud features implies that the y is a propagating wave with a prograde phase speed of about 15 ms 1 relative to the wind simultaneous time series of cloud tracked wind fluctuations also exhibit a 4 day periodicity lending support to the wave interpretation the prograde propagation and equatorial confinement of the wave and the absence of analogous meridional wind fluctuations identify it as a kelvin wave zonal winds peak near the

reconstruction of the landscape history around the remnant arch of the klidhi roman bridge thessaloniki plain north central greece abstract this paper deals with the palaeoenvironmental reconstruction of the area surrounding the remnant arch of the ancient bridge of klidhi thessaloniki plain greece 19th century travellers and 20th century historians discussed the age of the monument and concluded that it was built during late roman times 3rd cent ad and supported a branch of the via egnatia road however few studies have considered the environmental context of the construction of the bridge and until now only two hypotheses have been presented the bridge was built on or over a junction of the aliakmon and loudias rivers or on a coastal barrier within the framework of a geoarchaeological project developed in april 2008 five boreholes were drilled and the sediment cores analysed for microfauna and sedimentology seven 14 c ams dates provided a chronostratigraphic sequence and helped to define the geomorphological evolution of the area spatial interpretation of the results was possible using a landsat tm image false colour composite fcc our data indicate the gradual transition of the site from a marine to a terrestrial environment during ancient times lagoonal conditions dominated during the construction of the bridge and the presence of a palaeochannel of the aliakmon river was later revealed transition from byzantine and ottoman periods overlying sediments of a coastal barrier

the ancient harbour parasequence anthropogenic forcing of the stratigraphic highstand record abstract unique chronostratigraphic similarities are observed in recent geoscience literature on ancient mediterranean harbours from these empirical port data a clear pattern of millennial anthropogenic forcing marked by a fining up sequence can be discerned in coastal stratigraphy the stratigraphic peculiarity of this artificial or human modified parasequence leads us to define a new working model the ancient harbour parasequence

a basin to channel scale unstructured grid hurricane storm surge model applied to southern louisiana abstract southern louisiana is characterized by low lying topography and an extensive network of sounds bays marshes lakes rivers and inlets that permit widespread inundation during hurricanes a basin to channel scale implementation of the advanced circulation adcirc unstructured grid hydrodynamic model has been developed that accurately simulates hurricane storm surge tides and river flow in this complex region this is accomplished by defining a domain and computational resolution appropriate for the relevant processes specifying realistic boundary conditions and implementing accurate robust and highly parallel unstructured grid numerical algorithms the model domain incorporates the western north atlantic the gulf of mexico and the caribbean sea so that interactions between basins and the shelf are explicitly modeled and the boundary condition specification of tidal and hurricane processes can be readily defined at the deep water open boundary the unstructured grid enables highly refi

taken from the sea reclaimed by the sea the fate of the closed harbour of elaia the maritime satellite city of pergamum turkey abstract during hellenistic times when the pergamenian kingdom was prospering pergamum was operating an important harbour used by merchants and military at the city of elaia this paper focuses on the development utilisation and decay of the closed harbour of elaia which is discussed in the context of the landscape evolution of the environs of the ancient settlement based on geoarchaeological archaeological and literary evidence the construction of two harbour moles in order to provide shelter against wave action and enemies can be attributed to the early hellenistic period geoelectric measurements revealed the construction profile of the moles coring evidence indicated that together with mole construction a greater area of the formerly shallow marine and sublittoral terrain was consolidated most probably to create space for harbour installations the closed harbour basin was used intensely during hellenistic and roman times later continued siltation hindered further usage in combination with the decline of the city of elaia in late antiquity this was the reason why the harbour was abandoned scenarios for the time of the maximum transgression of the sea around 2500 bc the early hellenistic times around 300 bc and late antiquity ad 500 are presented

recent holocene paleo environmental evolution and coastline changes of kition larnaca cyprus mediterranean sea abstract sedimentological paleontological analysis and 14c dating of 17 cores obtained in the vicinity of the phoenician military harbor viii iv bc of kition bamboula cyprus provide new paleo environmental information for the reconstruction of shoreline changes for kition and larnaca bay over the last 4000 years we propose that a communication existed between the inner harbor of bamboula presently 400 m inland and the northern district of lichines which was a marine embayment our core data led us to revisit the previous hypothesis of a direct east west channel between the harbor and the open sea nicolaou k 1976 the historical topography of kition studies in mediterranean archaeology goteborg vol 153 pp 1 373 gifford j a 1978 paleogeography of archaelogical sites of the larnaca lowlands southeastern cyprus phd thesis university of minnesota pp 1 192 we propose instead that a spit of coarse material isolated the lagoon from the open sea from 2600 to 1600 years bp

the environs of elaia s ancient open harbour a reconstruction based on microfaunal evidence during hellenistic and roman times elaia the harbour city of ancient pergamum was an important place of trading and traffic intense mercantile and military activities are documented by literary sources and archaeological evidences geomagnetic and geoelectric investigations detected building structures close to the ancient coastline which are interpreted as ship sheds the aim of this study was to reconstruct the coastal evolution particularly with regard to harbour related facilities for that purpose a 10 m long sediment core was drilled in the area of the ancient open harbour immediately in front of the supposed ship sheds it was studied with the tools of micropalaeontology geophysics sedimentology and geochemistry to improve the reconstruction of the palaeoenvironmental conditions reference samples of modern environments of the area were analysed as indicated by marine ostracod and foraminifer taxa the sediment core shows from bottom to top that the initially fully marine conditions changed to a more restricted fauna indicative for a more sheltered bay with brackish waters this layer dates to hellenistic times it can however be shown that the siltation process had produced a lagoon system already several hundred years bc the elaia embayment was first used as a natural harbour it was equipped with breakwaters in the hellenistic period the progressive siltation caused the abandonment of the harbour in late roman times

cloud level winds from the venus express monitoring camera imaging abstract six years of continuous monitoring of venus by european space agency s venus express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet venus monitoring camera vmc on board the orbiter has acquired the longest and the most complete so far set of ultra violet images of venus these images enable a study the cloud level circulation by tracking motion of the cloud features the highly elliptical polar orbit of venus express provides optimal conditions for observations of the southern hemisphere at varying spatial resolution out of the 2300 orbits of venus express over which the images used in the study cover about 10 venus years out of these we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits total number of wind vectors derived in this work is 45 600 for the manual tracking and 391 600 for the digital method this allowed us to determine the mean circulation its long term and diurnal trends orbit to orbit variations and periodicities we also present the first results of tracking features in the vmc near ir images in low latitudes the mean zonal wind at cloud tops 67 2 km following rossow w b del genio a t eichler t 1990 j atmos sci 47 2053 2084 is about 90 m s with a maximum of about 100 m s at 40 50 s poleward of 50 s the average zonal wind speed decreases with latitude the corresponding atmospheric rotation period at cloud tops has a maximum of about 5 days at equator decreases to approximately 3 days in middle latitudes and stays almost constant poleward from 50 s the mean poleward meridional wind slowly increases from zero value at the equator to about 10 m s at 50 s and then decreases to zero at the pole the error of an individual measurement is 7 5 30 m s wind speeds of 70 80 m s were derived from near ir images at low latitudes the vmc observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85 m s in the beginning of the mission to 110 m s by the middle of 2012 vmc uv observations also showed significant short term variations of the mean flow the velocity difference between consecutive orbits in the region of mid latitude jet could reach 30 m s that likely indicates vacillation of the mean flow between jet like regime and quasi solid body rotation at mid latitudes fourier analysis revealed periodicities in the zonal circulation at low latitudes within the equatorial region up to 35 s the zonal wind show an oscillation with a period of 4 1 5 days 4 83 days on average that is close to the super rotation period at the equator the wave amplitude is 4 17 m s and decreases with latitude a feature of the kelvin wave the vmc observations showed a clear diurnal signature a minimum in the zonal speed was found close to the noon 11 14 h and maxima in the morning 8 9 h and in the evening 16 17 h the meridional component peaks in the early afternoon 13 15 h at around 50 s latitude the minimum of the meridional component is located at low latitudes in the morning 8 11 h the horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part i model development and validation abstract a coupled system of wind wind wave and coastal circulation models has been implemented for southern louisiana and mississippi to simulate riverine flows tides wind waves and hurricane storm surge in the region the system combines the noaa hurricane research division wind analysis system h wind and the interactive objective kinematic analysis ioka kinematic wind analyses the wave model wam offshore and steady state irregular wave stwave nearshore wind wave models and the advanced circulation adcirc basin to channel scale unstructured grid circulation model the system emphasizes a high resolution down to 50 m representation of the geometry bathymetry and topography nonlinear coupling of all processes including wind wave radiation stress induced set up and objective specification of frictional parameters based on land cover databases and commonly used parameters riverine flows and tides are validated for no storm conditions while winds wind waves hydrographs and high wa

structure of the venus neutral atmosphere as observed by the radio science experiment vera on venus express 1 the european space agency venus express radio science experiment vera obtained 118 radio occultation measurements of the venusian atmosphere between july 2006 and june 2007 southern latitudes are uniformly sampled measurements in the northern hemisphere are concentrated near the pole radial profiles of neutral number density derived from the occultations cover the altitude range 40 90 km which are converted to profiles of temperature t and pressure p versus height h profiles of static stability are found to be latitude dependent and nearly adiabatic in the middle cloud region below the clouds the stability decreases at high latitudes at an altitude of 65 km the vera t p h profiles generally lie between the venus international reference atmosphere vira and vira 2 models the retrieved temperatures at any given pressure level typically are within 5 k of those derived from the pioneer venus orbiter radio occultation experiments a large equator to pole temperature contrast of 30 k is found at the 1 bar 1000 hpa level the vera observations reveal a distinct cold collar region in the southern hemisphere complementing that in the north at the latitudes of the cold collars the tropopause altitude increases relative to higher and lower latitudes by 7 km while the temperature drops roughly 60 k the observations indicate the existence of a wave number 2 structure poleward of 75 latitude at altitudes of 62 km

high latitude gravity waves at the venus cloud tops as observed by the venus monitoring camera on board venus express high resolution images of venus northern hemisphere obtained with the venus monitoring camera vmc vex allow studying small scale dynamical phenomena at the cloud tops 62 70 km altitude including features like wave trains a systematic visual search of these waves was performed more than 1500 orbits were analyzed and wave patterns were observed in more than 300 images four types of waves were identified in vmc images on the base of their morphology long medium short and irregular type waves with the aim to characterize the wave types and their possible excitation source we retrieved wave properties such as location latitude and longitude local time solar zenith angle packet length and width orientation and wavelength of each wave the long type waves appear as long and narrow straight features extending more than a few hundreds kilometers and with wavelengths between 7 and 17 km medium type waves exhibit irregular wavefronts extending more than 100 km and with wavelengths in the range 8 21 km short wave packets have a width of several tens of kilometers and extend to few hundreds kilometers and are characterized by smaller wavelengths 3 16 km irregular wave fields appear to be the result of wave interference the waves are often identified in all vmc filters and are mostly found in the cold collar region at high latitudes 60 80 n and are concentrated above ishtar terra a continental size highland that includes the highest mountain belts of the planet the high speed of the venus express spacecraft close to the pericentre does not allow to measure phase speed of waves due to the short temporal interval between image pairs the lack of information on phase velocities does not allow us to establish with absolute confidence the nature of these waves however by comparing the morphology and properties of the wave features observed in vmc images to those seen by previous observations it is reasonable to assume that the waves studied here are gravity waves

venus cloud top winds from tracking uv features in venus monitoring camera images 1 to date dynamical observations of the venus clouds have delivered mainly either only short term or long term averaged results with the venus monitoring camera vmc it finally became possible to investigate the global dynamics with a relatively high resolution in space and time on a long term basis our findings from manual cloud feature wind tracking in vmc uv image sequences so far show that the details of the mesospheric dynamics of venus appear to be highly variable although the general rotation of the atmosphere remained relatively stable since mariner 10 more than 30 years ago by now there are indications of short term variations in the general circulation pattern of the venus atmosphere at cloud top level in some cases significant variations in the zonal wind properties occur on a timescale of days in other cases we see rather stable conditions over one atmospheric revolution or longer at cloud top level it remains an interesting question whether the irregularly observed midlatitude jets are indeed variable or simply become shielded from view by higher h2so4 haze layers for varying time intervals winds at latitudes higher than 60 s are still difficult to obtain track because of low contrast and scarcity of features but increasing data is being collected over all it was possible to extend latitudinal coverage of the cloud top winds with vmc observations thermal tides seem to be present in the data but final confirmation still depends on synthesis of visible and infrared thermal imaging spectrometer and vmc observations on night and dayside although poorly resolved meridional wind speed measurements agree mainly with previous observations and with the presence of a hadley cell spanning between equatorial region and about 45 s latitude

implications of the vega balloon results for venus atmospheric dynamics both vega balloons encountered vertical winds with typical velocities of 1 to 2 meters per second these values are consistent with those estimated from mixing length theory of thermal convection however small scale temperature fluctuations for each balloon were sometimes larger than predicted the approximate 6 5 kelvin difference in temperature consistently seen between vega 1 and vega 2 is probably due to synoptic or planetary scale nonaxisymmetric disturbances that propagate westward with respect to the planet there is also evidence from doppler data for the existence of solar fixed nonaxisymmetric motions that may be thermal tides surface topography may influence atmospheric motions experienced by the vega 2 balloon

morphology and dynamics of the upper cloud layer of venus esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life venus is completely covered by a thick cloud layer with the cloud tops in fast retrograde rotation global and small scale properties of these clouds and their temporal and latitudinal variations are investigated and the wind velocities are derived the southern polar region is highly variable and can change dramatically on time scales as short as one day perhaps arising from the injection of so2 into the mesosphere venus is completely covered by a thick cloud layer of which the upper part is composed of sulphuric acid and some unknown aerosols1 the cloud tops are in fast retrograde rotation super rotation but the factors responsible for this super rotation are unknown2 here we report observations of venus with the venus monitoring camera3 on board the venus express spacecraft we investigate both global and small scale properties of the clouds their temporal and latitudinal variations and derive wind velocities the southern polar region is highly variable and can change dramatically on timescales as short as one day perhaps arising from the injection of so2 into the mesosphere the convective cells in the vicinity of the subsolar point are much smaller than previously inferred4 5 6 which we interpret as indicating that they are confined to the upper cloud layer contrary to previous conclusions7 8 but consistent with more recent study9

bathymetrically controlled velocity shear front at a tidal river confluence nonbuoyant front formation at the confluence of nanjemoy creek and the main potomac river md channel is examined terra satellite aster imagery reveals a sediment color front emerging from nanjemoy creek when the potomac is near maximum ebb nearly contemporaneous aster and landsat etm imagery are used to extract surface velocities which suggest a velocity shear front is collocated with the color front in situ velocities measured by riverray traverses near the nanjemoy creek mouth confirm the shear front s presence a finite element simulation using adcirc replicates the observed velocity shear front and is applied to decipher its physics three results emerge 1 the velocity shear front forms confined to a shoal downstream of the creek river confluence for most of the tidal cycle 2 a simulation with a flat bottom in nanjemoy creek and potomac river i e no bathymetry variation indicates the velocity shear front never forms hence the front cannot exist without the bathymetry and 3 an additional simulation with a blocked off creek entrance demonstrates that while the magnitude of the velocity shear is largely unchanged without the creek shear front formation is delayed in time without the creek there is no advection of the m6 tidal constituent generated by nonlinear interaction of the flow with bottom friction onto the shoals only a locally generated contribution a tidal phase difference between nanjemoy and potomac causes the ebbing nanjemoy creek waters to intrude into the potomac as far south as its deep channel and draw from a similar location in the potomac during nanjemoy flood

cloud tracked winds from pioneer venus ocpp images abstract analysis of ultraviolet image sequences obtained from the pioneer venus orbiter cloud photopolarimeter and covering five 80 day periods from 1979 1985 provides the first climatological description of the cloud top circulation on venus the average zonal winds can be characterized as a 5 day retrograde rotation of the whole cloud level atmosphere with weak jets at middle to high latitudes both the midlatitude and equatorial zonal winds vary by about 5 8 m s 1 over time spans of 1 6 years the average meridional circulation is poleward in both hemispheres up to at least 60 latitude consistent with the presence of a thermally direct hadley circulation associated with the clouds the strength of the hadley circulation also varies with time four wave modes are clearly identified a diurnal solar tide a semi diurnal solar tide a 4 day equatorial wave and a 5 day midlatitude wave the semidiurnal tide appears to have an amplitude of about 5 m s 1 and to be approximately constant with time