inertial instability and mesoscale convective systems part ii symmetric cisk in a baroclinic flow abstract numerous budget studies of organized persistent systems of convective clouds outside the tropics suggest that circulations of mesoscale proportions are important in supplying moisture to the convective clouds though the dynamical nature of mesoscale flows remains poorly defined in part i emanuel 1979 hereafter referred to as part i it is demonstrated that circulations resulting from symmetric instability of shear flows in rotating fluids have a fundamentally mesoscale character in that both ambient rotation and ageostrophic advection are necessary for instability the results of part i are here extended to include the effects of latent heat release in a conditionally unstable atmosphere using the formalism of the cisk approach it is found that the presence of shear parallel to the wave fronts introduces new wave cisk modes which are not strongly dependent on the specified vertical structure of the cumulus heating the new baroclinic modes are of mesoscale dimensions have growth rates pro

a wave cisk model of squall lines abstract the wave cisk model of raymond incorporating lag effects in the updraft and downdraft is implemented as an initial value problem in physical space examples of both midlatitude and tropical squall lines are successfully simulated diagnosis of the model shows that condensational heating in the updraft is the primary driving mechanism of a mature squall line with evaporative cooling and convective momentum transfer playing subsidiary roles however an instability involving the displacement of boundary layer air by downdrafts apparently plays an important role in squall line initiation a weakness of the model is its inability to predict the direction of squall line propagation relative to the low level wind shear this is traced to the insensitivity of the convective parameterization to midlevel entrainment however unlike strict two dimensional squall lint models the parameterization allows cross stream mass transfer to occur in the context of overall slab symmetry such transfer is dynamical

an early holocene greenland whale from melville bugt greenland abstract radiocarbon age determination of a greenland whale balaena mysticetus vertebra from melville bugt in northwestern greenland yields an age of 9259 8989 cal yr bp the margin of the greenland ice sheet in melville bugt was situated behind its ad 1950 2000 position in the early holocene at a similar position to that being reached following rapid retreat in recent years such an early deglaciation of areas close to the greenland ice sheet is unusual this probably reflects the unique glaciological setting resulting from the narrow fringe of ice free islands and peninsulas and offshore waters with deep areas that characterize this part of greenland the timing of greenland ice sheet retreat to its present margin varies significantly around greenland

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

odessa tsunami of 27 june 2014 observations and numerical modelling on 27 june a 1 2 m high wave struck the beaches of odessa the third largest ukrainian city and the neighbouring port town illichevsk northwestern black sea throughout the day prominent seiche oscillations were observed in several other ports of the black sea tsunamigenic synoptic conditions were found over the black sea stretching from romania in the west to the crimean peninsula in the east intense air pressure disturbances and convective thunderstorm clouds were associated with these conditions right at the time of the event a 1 5 hpa air pressure jump was recorded at odessa and a few hours earlier in romania we have utilized a barotropic ocean numerical model to test two hypotheses 1 a tsunami like wave was generated by an air pressure disturbance propagating directly over odessa experiment 1 2 a tsunami like wave was generated by an air pressure disturbance propagating offshore approximately 200 km to the south of odessa and along the shelf break experiment 2 both experiments decisively confirm the meteorological origin of the tsunami like waves on the coast of odessa and imply that intensified long ocean waves in this region were generated via the proudman resonance mechanism while propagating over the northwestern black sea shelf the odessa tsunami of 27 june 2014 was identified as a beach meteotsunami similar to events regularly observed on the beaches of florida usa but different from the harbour meteotsunamis which occurred 1 3 days earlier in ciutadella baleares spain mazara del vallo sicily italy and vela luka croatia in the mediterranean sea despite that they were associated with the same atmospheric system moving over the mediterranean black sea region on 23 27 june 2014

palaeoecological studies of holocene lake sediments from west greenland abstract colonisation by plants and animals and subsequent biotic development in west greenland was studied by analyses of macrofossils in four holocene lake sequences one of the lake basins located near the outer coast was deglaciated shortly after the transition from the last glacial stage to the holocene and a basal date of 12 100 11 300 cal years bp was obtained two of the lake basins located near the margin of the greenland ice sheet were deglaciated several millennia later the oldest sediments contain low diversity floras and faunas some of the first immigrants were chironomidae and daphnia pulex soon followed by other insects crustaceans and other invertebrates water mosses ranunculus confervoides hippuris vulgaris and potamogeton filiformis were among the first plants that colonised the lakes the earliest holocene terrestrial flora in west greenland was probably entirely herbaceous with salix herbacea and empetrum nigrum being some of the first woody plants to arrive a number of invertebrates are new to the fossil fauna of greenland and the ostracod ilyocypris bradyi that was found in one sequence from 7000 to 6500 cal years bp has not been recorded from greenland before

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

numerical simulations of an observed gravity current and gravity waves in an environment characterized by complex stratification and shear abstract numerical simulations of a gravity current in an environment characterized by complex stratification and vertical wind shear have been performed using a nonhydrostatic two dimensional dry primitive equation model data from one of the most complete documentations to date of gravity waves associated with a gravity current presented in an earlier study are used both to prescribe the gravity current s environment and for validation of the simulated gravity current and its associated gravity waves these comparisons indicate that the gravity current observed by a doppler wind profiler and sodars was well simulated in terms of depth density contrast and propagation speed and that the model produced a variety of gravity waves similar in many ways to these observed because uncertainties remained concerning the gravity wave generation mechanisms derived from the observations e g wavelengths were not observed the validated simulations are used to test these tentative hypotheses the simulatio

on the reconstruction of the transfer function for atmospherically generated seiches a method recently proposed to separate source and topographic effects in observed tsunami spectra is revised and applied to atmospherically generated seiches the method is used to investigate the origin of abnormal seiche events rissaga waves recorded in the region of ciutadella balearic islands the reconstructed open sea source spectra and the observed atmospheric pressure spectra are combined to estimate the transfer function between the atmosphere and the sea surface this function is used to predict sea level spectra for given locations near to the coast theoretically computed spectra for two rissaga events are in good agreement with observations

fresh evidence relating the great adriatic surge of 21 june 1978 to mesoscale atmospheric forcing 1 on the morning of 21 june 1978 exceptional sea level oscillations with a trough to crest height of 6 m and a period of 10 20 min were observed in vela luka bay slightly less pronounced variability was observed in a wider middle and south adriatic east coastal area and with some delay along the west coast in this paper one of the original hypotheses put forward to interpret the event relating it to a mesoscale air pressure disturbance is reconsidered by using all the available data as well as state of the art meteorological and oceanographic models a fresh look at the meteorological data confirms that the atmospheric disturbance propagated at about 22 m s in a northeastward direction additionally the data suggest that it had the shape of the boxcar function characterized by an air pressure offset of 3 mbar and duration of 10 min the meteorological model employed weather research and forecasting wrf advanced research wrf proves unable to reproduce the mesoscale disturbance coinciding with the surge but it shows that the background atmospheric conditions were favorable for the development of such disturbances the oceanographic model advanced circulation model for shelves coasts and estuaries two dimensional depth integrated forced by the described air pressure disturbance successfully reproduces sea level variability in vela luka bay reaching a few meters and thus surpassing the inverted barometer response by two orders of magnitude the enhancement appears to be due to a four phase process the model also suggests that the scattering due to the variable bathymetry and the reflection from the east adriatic coast resulted in waves that returned towards the west coast and generated considerable sea level activity there

possible atmospheric origin of the 7 may 2007 western black sea shelf tsunami event 1 the paper examines the possibility that tsunami event recorded in the western black sea on 7 may 2007 was triggered by a traveling atmospheric disturbance as meteotsunamis are favored by specific synoptic conditions we inspected available ground and sounding observations european centre for medium range weather forecasts reanalysis fields and satellite based products and compared them to the documented mediterranean meteotsunamis we found an atmospheric disturbance traveling toward 30 nne with amplitude of 2 3 hpa and propagation speed of about 16 m s passing through few tens of kilometers wide pathway over the region affected by the tsunami this disturbance occurred in the lower troposphere but it was capped by instable convective cell that preserved gravity disturbance s coherence over a region at least 150 km long an ocean modeling study showed that such a disturbance is capable of generating large tsunami waves and strong currents over the shallow regions following the observations over the region where maximum sea level oscillations have been documented therefore this event has a potential to be classified as a meteotsunami the first of such kind in the black sea

the mad sea phenomenon in the strait of sicily sea level observations at cape bon tunisia and mazara del vallo sicily show that large coherent oscillations exist across the strait of sicily with significant energy bands centered at periods of 35 3 41 6 50 6 75 8 and 134 5 min whose possible structure is confirmed by a numerical approximation to the gravitational barotropic normal modes with realistic topography it is observed that these oscillations are related to the passage of synoptic weather systems over the region an investigation on the configuration phase velocity and direction of approach of atmospheric disturbances over the region suggests that the oscillations in the strait of sicily could be forced by instabilities that develop in large scale low pressure fronts that propagate as pressure gravity waves with an approximate phase speed between 24 and 30 m s21

are meteotsunamis an underrated hazard meteotsunamis are generated by meteorological events particularly moving pressure disturbances due to squalls thunderstorms frontal passages and atmospheric gravity waves relatively small initial sea level perturbations of the order of a few centimetres can increase significantly through multi resonant phenomena to create destructive events through the superposition of different factors the global occurrence of meteotsunamis and the different resonance phenomena leading to amplification of meteotsunamis are reviewed results from idealized numerical modelling and field measurements from southwest australia are presented to highlight the relative importance of the different processes it is shown that the main influence that leads to amplification of the initial disturbance is due to wave shoaling and topographic resonance although meteotsunamis are not catastrophic to the extent of major seismically induced basin scale events the temporal and spatial occurrence of meteotsunamis are higher than those of seismic tsunamis as the atmospheric disturbances responsible for the generation of meteotsunamis are more common high energy events occur only for very specific combinations of resonant effects the rareness of such combinations is perhaps the main reason why destructive meteotsunamis are exceptional and observed only at a limited number of sites globally

multicell squall line structure as a manifestation of vertically trapped gravity waves abstract two dimensional and three dimensional simulations of a midlatitude squall line with a high resolution non hydrostatic model suggest that the multicellular structure of the storm may be associated with gravity waves generated by convection time lapse display of model output demonstrates that the commonly described cut off process is actually a gravity wave phenomenon the convective cells arise as gravity waves which are forced by continuous strong low level convergence at the storm s gust front the waves propagate to both sides of the gust front the stronger westward front to rear mode dominates at the mature stage of the squall line continuous low level updraft is generated at the nose of the cold pool which propagates at the speed of a density current updraft cells periodically break away from this persistent low level gust front updraft and move at phase speeds of their associated gravity waves not at the surrounding airflow speeds as implied by the traditional multicell model lin

convective destabilization by a tropopause fold diagnosed using potential vorticity inversion there is observational evidence to suggest that at the time tropopause folds in extra tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection here we consider the dynamical reasons for such a linkage using so called potential vorticity pv attribution concepts in particular pv inversion is used to find the wind shear attributable to the tropopause fold itself then this shear is used to quantify the tendency to generate regions of potential instability for an observed case of a modest tropopause fold it is found that the pv anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability indeed at some locations it overcame a tendency to stabilize by the atmosphere without the fold on the other hand only a fraction of the region with increased potential instability experienced sufficient large scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized the importance of tropopause folds or indeed of tropopause depressions in general in the context of convection is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally this may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately currently numerical weather prediction models often do not handle these small scales very accurately

atmospheric gravity waves and the rissaga phenomenon the atmospheric forcing of large sea level oscillations up to 1 5 m amplitude with about a 10 min period in some bays and inlets of the balearic islands is described using simultaneous measurements of pressure and sea level elevation in the port of ciutadella at the end of a large and narrow inlet during 5 7 july 1989 the influence of atmospheric pressure oscillations on these large sea level variations locally known as rissaga is investigated coherence and cross correlation functions reveal that the large oscillations in the inlet are associated with and probably forced by a 10 min gravity wave in the atmosphere the effect of longer period waves on the inlet is seen in the well known inverted barometric effect forcing small oscillations in the water level of just some centimetres these latter waves have a period of around 50 min and an unusually large amplitude of some 3 mb the phase spectrum between sea level and pressure suggests that the inlet may behave as a damped harmonic oscillator which during rissaga is externally forced by the atmospheric pressure oscillations

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

meteorological tsunami of 19 march 2017 in the persian gulf observations and analyses on 19 march 2017 destructive tsunami like waves impacted the northeast shore of the persian gulf pg the maximum surveyed runup of about 3 m was observed at dayyer in southern iran where damaging waves inundated the land for a distance of 1 km and resulted in the deaths of five people because the pg has always been considered safe from extreme oceanic waves the event was totally unexpected in this study we examined sea level data from 12 stations across the pg and a variety of meteorological information including satellite imagery high altitude isohypse maps and high resolution air pressure records from 47 instruments along the pg our results show that the event was very local with recorded maximum trough to crest wave heights of 197 cm at dayyer and 234 cm at asaluyeh near field cities in iran located 80 km apart the dominant wave periods were in the range of 15 20 min at all distant tide gauges the observed wave heights were 35 cm no earthquakes or landslides were evident at the time of the event on the other hand atmospheric processes during 18 22 march were very active and 10 distinctive tsunamigenic air pressure disturbances were observed propagating over the pg suggesting that the event of 19 march 2017 was a meteorological tsunami atmospheric conditions over the pg were highly favourable for the generation of meteotsunamis and very similar to those that caused a chain of strong meteotsunamis in the mediterranean and black sea regions during 23 27 june 2014 based on the 500 hpa wind we evaluated that the disturbances had propagation speeds of 21 38 m s with the disturbance at dayyer having a speed of 26 m s toward 77 true the froude number fr estimated as the ratio of the air disturbance speed to the long wave speed on 19 march 2017 in the dayyer asaluyeh region was close to resonance fr 0 9 to 1 1 which is highly favourable for meteotsunami generation our findings indicate that the dayyer asaluyeh area is a hot spot that is highly vulnerable to extreme weather induced tsunami like waves

pressure forced seiches of large amplitude in inlets of the balearic islands 2 observational study in part 1 of this study gomis et al 1993 proposed a possible mechanism for the generation of large amplitude seiches observed in inlets of the balearic islands in part 2 we revise the proposed mechanism in light of recent observations these consist of simultaneous records of sea level bottom pressure measured at three locations inside and outside ciutadella inlet and atmospheric pressure measured at four sites inland nearby first results that support the existence of offshore surface waves of atmospheric origin are shown next a detailed analysis of atmospheric data reveals the passage of non dispersive waves with a predominant direction and phase speed that seem to be about the same during seiche events finally coherence phase difference and admittance functions estimated for different pairs of instruments are compared with the theoretical results all observations indicate that large amplitude seiches observed in ciutadella are likely the result of a resonant coupling between offshore surface waves generated by atmospheric disturbances and the fundamental mode of that inlet as suggested in part 1 however the analytical model used in part 1 is clearly too simple to explain the observed characteristics of the offshore surface waves

numerical simulations of a gravity wave event over ccope part iii the role of a mountain plains solenoid in the generation of the second wave episode abstract mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11 12 july 1981 during the cooperative convective precipitation experiment the dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain plains solenoid mps as this updraft impinged upon a stratified shear layer above the deep well mixed boundary layer that developed due to strong sensible heating over the absaroka mountains the gravity wave was created this wave rapidly weakened as it propagated eastward however explosive convection developed directly over the remnant gravity wave as an eastward propagating density current produced by a rainband generated within the mps leeside convergence zone merged with a westward propagating density current in eastern montana the greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the move

source of the 2007 ist meteotsunami adriatic sea 1 siroka bay on the island of ist in the northern adriatic was struck by a severe inundation around 1530 utc on 22 august 2007 the maximum wave height reached 4 m and substantial material damage was induced this paper investigates the generating force of the inundation data analysis indicates that the inundation was provoked through a double resonance mechanism with initiation by a pronounced atmospheric disturbance that generated open ocean waves through the proudman resonance the waves were then further amplified inside the affected bay the air pressure disturbance which propagated at a speed of about 21 24 m s 1 over the northern adriatic shelf was investigated through both data analysis and atmospheric numerical modeling apparently the air pressure disturbance was a surface manifestation of a ducted gravity wave which propagated through the atmosphere from the apennines to the eastern adriatic coast over the northern adriatic according to the model simulation the wave was trapped in a stable layer adjacent to the ground which was capped by a dynamically unstable layer with wind speeds of about 22 m s 1 this made the unstable layer also a critical layer for gravity waves propagating with the same speed and allowed for their ducting in the layer below

post glacial relative sea level history of northwestern spitsbergen svalbard the late weichselian and holocene raised beach sequences on northwestern spitsbergen provide a detailed record of sea level oscillations during the last deglacial hemicycle initial emergence commenced at 13 ka coincident with local deglaciation and until 10 5 ka was characterized by a relative slow rate of emergence 1 5 to 5 m ka interrupted by minor stillstands or transgressions associated with possible glacier re advances the orientation of paleo spits and the paucity of whale remains at the late weichselian marinelimit indicate that the prevailing westerly fetch was dampened by a semi permanent sea ice cover allowing long shore drift to predominate a period of accelerated emergence 15 to 30 m ka between 10 5 and 9 ka is correlative with rapid deglaciation of fiords the middle and late holocene is characterized by two brief transgressions one between 6 5 and 5 0 ka that did not exceed 7 m asl and a present probable slow rise in sea level that commenced 2 to 1 ka the strandline tilts in northwestern spitsbergen and the pattern and rate of emergence on svalbard indicate that the maximum glacier loads during the late weichselian were centered on nordaustlandet and on the central and eastern part of the archipelago northwestern and southwestern spitsbergen were marginal to glacial loading and were deglaciated early 13 ka which is presently incompatible with maximum ice sheet extent and the timing and position of deglacial margins recently reconstructed for the barents sea and svalbard mountain ranges and large fiords probably confined major outlet glaciers to the central part of the archipelago preventing inundation of much of western spitsbergen by an inferred large ice sheet based in eastern svalbard and the barents sea

consistent vertical and horizontal resolution abstract simple physical relations namely the rossby ratio between vertical and horizontal scales in quasi geostrophic flow and the dispersion relation for internal gravity waves are used to estimate the vertical resolution consistent with a given horizontal resolution using these relations we find that virtually all large scale models and observing systems have inadequate vertical resolutions in models the excess horizontal resolution can lead to increased model noise rather than improved accuracy in observing systems the finer horizontal scales can be severely misrepresented

wave cisk in a baroclinic basic state abstract prefrontal squall lines are mesoscale convective systems that often cannot be linked to any preexisting organizing mechanism this suggests the possibility that they are manifestations of a mesoscale instability involving the interaction between convective and larger scales to investigate this hypothesis a wave cisk model is developed for two dimensional disturbances in a baroclinic basic state with constant vertical wind shear the governing equations are the linearized boussinesq equations for an inviscid and hydrostatic fluid on an f plane the model domain is infinite in the horizontal and consists of two layers in the vertical representing the troposphere and the stratosphere the model stratosphere has a larger static stability and no wind shear the convective heating is confined to the troposphere normal mode solutions are assumed and the convective heating is parameterized in the standard simple fashion its vertical structure is specified and it is set proportional to the low level

the deglaciation and neoglaciation of upernavik isstrom greenland abstract we constrain the history of the greenland ice sheet margin during the holocene at upernavik isstrom a major ice stream in northwestern greenland radiocarbon dated sediment sequences from proglacial threshold lakes adjacent to the present ice margin constrain deglaciation of the sites to older than 9 6 0 1 ka this age of deglaciation is confirmed with 10 be ages of 9 9 0 1 ka from an island adjacent to the historical ice position the lake sediment sequences also constrain the ice margin to have been less extensive than it is today for the remainder of the holocene until 1100 to 700 yr ago when it advanced into two lake catchments the ice margin retreated back out of these lake catchments in the last decade the early holocene deglaciation in melville bugt one of few locations around greenland where a vast stretch of the current ice margin is marine based preceded deglaciation in most other parts of greenland earlier deglaciation in this ice sheet sector may have been caused by additional ablation mechanisms that apply to marine based ice margins furthermore despite ice sheet models depicting this sector of greenland as relatively stable throughout the holocene our data indicate a 20 km advance retreat cycle within the last millennium

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

response of a stably stratified flow to cooling abstract the spreading of the low level cold pool produced by evaporation of precipitation is generally acknowledged to be an important mechanism for the regeneration of moist convection we show that cooling a stably stratified nocturnal boundary layer produces very different results from the corresponding daytime case in which the boundary layer is neutral in particular dynamic behavior is sometimes closer to that of a gravity wave than to a density current the gravity wave speed defines a minimum propagation speed for a self regenerating convective system

gravity wave observations using an array of microbarographs in the alearic islands time series of surface pressure from an array of microbarographs in the balearic islands western mediterranean are used to obtain wavelength phase speed and direction of propagation of gravity waves on the balearic islands these pressure waves are commonly found during the summer and they force the large seal level oscillations observed in the inlet of ciutadella a phenomenon locally known as rissaga four events are described here each of which has a duration of between 30 and 48 hours radiosonde data from palma de mallorca are used to relate the waves to the vertical structure of the atmosphere the various source mechanisms of these waves and also the possibility of the existence of a duct layer trapping the wave energy near the surface are discussed the waves are found to have no significant variation of phase speed with frequency and so they are basically non dispersive this is an indicator pointing either to a local generation of gravity waves by wind shear instability or to the existence of neutral trapped waves in the lower troposphere

atmospheric origin of the devastating coupled air sea event in the east adriatic enhanced sea level oscillations with devastating effects occurred on 26 27 june 2003 in the east adriatic the phenomenon was recognized as a resonantly coupled air sea interaction where the sea wave is forced by the propagating atmospheric pressure disturbance this study examines the dynamics and predictability of the atmospheric component of the coupled system first the initiation amplification and maintenance of the system are examined the source of the perturbation is traced back to the alpine region where the potentially unstable air in the westerly current lifts over the alps resulting in convection and wave development the wave and convective activity apparently couple in a wave cisk manner and propagate southeastward down the eastern adriatic coast due to the potentially unstable air above the adriatic the system additionally amplifies along its track the dissipation of the system occurs after the landfall second the performance of the numerical model at the resolution that is similar to operational nwp model resolution is examined this severe event is highly susceptible to the details of the model configuration presumably due to the sensitivity in coupling of the wave and mcs thus although the model is able to reproduce and forecast this kind of event at a fairly coarse resolution the details of the spatial structure as well as the time of onset are questionable in this case the greatest sensitivity is primarily in the treatment of moist and convective processes

resonant coupling of a traveling air pressure disturbance with the east adriatic coastal waters 1 exceptional sea level oscillations and strong current reversals observed in the east adriatic on 27 june 2003 are analyzed using available meteorological and tide gauge measurements and numerical model results it is shown that the variability in the atmosphere sea system was characterized by high frequencies 0 01 0 1 min 1 and sea level and current amplitudes surpassing 1 m and 1 m s 1 respectively the event was related to the occurrence of a gravity disturbance in the atmosphere above the adriatic the disturbance traveled toward the east southeast at a speed of 22 m s 1 and was resonantly coupled with a wave in the sea 50 m deep the resulting forced wave was further amplified when entering funnel shaped bays opened to it there are indications that the forcing disturbance and its counterpart in the sea excited normal modes of the bays and harbors in the area moreover nonlinear steepening of the forced wave seemingly occurred resulting in the formation of high frequency wave trains this process along with the generation of coastal seiches could explain the observed and modeled differences between the spectra of coastal variability and the spectrum of forcing wave

a deliberate tracer experiment in santa monica basin the mixing of heat and chemical constituents across density strata in the ocean plays a major role in ocean circulation and in the response of the climate to thermal and chemical perturbations we are developing a tracer technique which in conjunction with fluid dynamical measurements promises to improve our understanding and our estimates of such diapycnal mixing in a prototype tracer experiment in santa monica basin 50km west of los angeles two tracers sulphur hexafluoride sf6 and per fluorodecalin pfd have been injected on an isopycnal surface near the centre of the basin after 50 days the tracers had mixed along the isopycnal surface to nearly every part of the basin although relatively little had penetrated to the basin walls the diapycnal spreading of the tracer distributions during this first stage of the experiment yielded an apparent eddy diffusivity of 0 33 0 08 cm2s 1 at the ambient density gradient of 4 0 0 5 10 9g cm 4

amino acid ratios in reworked marine bivalve shells constrain greenland ice sheet history during the holocene reconstructions of ice sheet fluctuations during the holocene which encompassed cooler and warmer conditions than those that are captured in the historic record help to elucidate ice margin sensitivity to climate change we used amino acid geochronology to constrain the history of the western greenland ice sheet margin during intervals of relative warmth in the middle holocene we measured the extent of amino acid racemization in 251 ice sheet reworked marine bivalve shells from three locations spanning western greenland a significant relationship between shell age and the ratio of aspartic acid asp isomers asp d l was revealed using bayesian model fitting on 20 radiocarbon dated shell fragments the range of asp inferred bivalve ages at each site corresponds well with independent records of early holocene ice retreat and late holocene ice advance furthermore the frequency of asp inferred bivalve ages from the three widely separated locations is nearly identical with most ages between 5 and 3 ka coinciding with optimum oceanic conditions because ice margin changes in western greenland are tightly linked with oceanographic conditions the distribution of reworked bivalve ages provides important information about relative ice margin position during smaller than present ice sheet configurations this approach adds a new chronometer to our toolkit for constraining smaller than present ice sheet configurations and may have wide applicability around greenland

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

a general circulation model study of a tropopause folding event at middle latitudes the uk universities global atmospheric modelling programme general circulation model ugcm has been run at high horizontal resolution to investigate a tropopause folding event at middle latitudes geopotential height potential vorticity and specific humidity distributions were diagnosed from the model and showed a realistic representation of the synoptic development of the cut off low associated with the tropopause fold the model also successfully portrayed the frontogenesis associated with tropopause folding and represented both the upper level frontal region and the corresponding jet streaks as they progressed through the region of the developing trough a series of vertical cross sections at the ends of the jet streaks demonstrated that a fold could be captured by the ugcm using potential vorticity and specific humidity although more small scale features were evident in the specific humidity contours than in the corresponding potential vorticity fields the corresponding baroclinic zone was also resolved although both the slope and thickness were rather larger than sometimes observed both the spatial and temporal extent of the fold compared well with observations in addition the model simulated the ageostrophic winds in the entrance exit and middle streak regions a direct circulation was obtained at the entrance and an indirect circulation at the exit region of the jet streak in good agreement with theory and with observational data a combination of confluence cold advection and curvature was responsible for the forcing of the ageostrophic motion at the jet entrance whereas the forcing at the jet exit was attributed mainly to diffluence and curvature q vectors were employed to investigate the vertical motion in the vicinity of the fold and showed the precise positions of descent corresponding to the fold along the entire length of the jet streak finally a tropopause fold around a jet that was not subject to the development of strong baroclinic instabilities was reproduced by the model it was smaller in size than the fold of the cyclonic trough a q vector analysis confirmed the position of the small fold along the jet and revealed large scale ascending motion that may have been responsible for the small size of fold the possibility of using the model to yield a realistic estimate of the transfer of air from the stratosphere to the troposphere in a tropopause folding event at mid latitudes is discussed

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

wave cisk and mesoscale convective systems abstract the basic assumptions of conventional wave cisk theory are examined against observations of mesoscale organized convective systems the quasi equilibrium assumption is disputed and a nonequilibrium model of clouds actively responding to mesoscale low level mass fluxes in a preexisting conditionally unstable atmosphere is formulated the growth rates of the most unstable mode exhibit evident scale selection over a broad range of mesoscale wavelengths reasonable response to variations of external parameters strong dependence on the gross features of cloud heating especially on the elevation of maximum heating upper tropospheric heating lower tropospheric cooling and cooling just above the tropopause insensitivity to local variations of cloud heating i e to a redistribution of cloud heating within a relatively thin layer the structures of the resulting propagating growing waves are comparable with observations of midlatitude mesoscale convective systems some insights pertaining to the i

numerical simulation and analysis of a prefrontal squall line part ii propagation of the squall line as an internal gravity wave abstract a numerical study of the squall line that occurred on 17 18 june 1978 was described in part i of this paper the squall line was collocated with a surface front during its initial development at 0000 utc 18 june 1978 but then propagated faster than the front resulting in a separation of approximately 200 km by 0300 utc and 300 400 km by 0600 utc in this paper part ii the movement of the squall line in the model is shown to be due to the propagation of a deep tropospheric internal gravity wave in a wave cisk like conditional instability of the second kind process the thermal and dynamic perturbations associated with the hypothesized wave are shown to be consistent with internal gravity wave theory and the characteristics of the wave are compared to similar results from other wave cisk studies the current literature favors the mechanism of gust front convergence to explain squall line propagation although there are other modeling studies that show specific instances of squall line pro

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

barotropic waves generated by storms moving rapidly over shallow water 1 in the falls of both 1999 and 2000 waves with characteristics similar to tsunami hit the southeast coast of newfoundland canada the waves were large enough to cause local flooding damage to docks and other destruction there is however no evidence of seismic events underwater landslides or slumping events on either occasion other explanations such as storm surge also appear unlikely and local weather conditions at the coast were not exceptional at the time on both occasions tropical storms moved rapidly across the grand banks of newfoundland from southwest to northeast with a translation speed of 30 m s 1 a significant nonisostatic response to atmospheric pressure forcing can be expected over the shallow water of the banks since the translation speed of the storms is comparable to the local shallow water gravity wave speed we speculate that the atmospheric pressure forcing associated with the storms generated a barotropic wake and we use a numerical model to argue that as the storm moved back over the deep ocean the wake was refracted and or reflected by the variable bathymetry at the edge of the banks and that it was the refraction of the wake toward the coast that led to the unusual sea level events in southeastern newfoundland the numerical model results are in general agreement with the eye witness reports the model computed wave activity hits the southeast coast of newfoundland at about the right time and in the right areas for both events although for the 1999 event the model response is weaker than is observed at port rexton in trinity bay the reason for the poorer model performance in the 1999 case is not known although we do find that the model results are sensitive to uncertainty in the exact track taken by the storm across the banks the model results demonstrate that the period and wavelength of the gravity waves comprising the wake are in general proportional to the length scale of the pressure forcing an exception being the model response in conception bay newfoundland where a resonant seiche response is found to dominate index terms 4504 oceanography physical air sea interactions 0312 4564 oceanography physical tsunamis and storm surges 4219 oceanography general continental shelf processes 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 4255 oceanography general numerical modeling keywords tsunami barotropic tropical storm modeling air sea

pressure forced seiches of large amplitude in inlets of the balearic islands large amplitude harbor seiches usually occur in summer in the balearic islands a significant correlation between sea level oscillations and atmospheric pressure disturbances has been found though a proved physical mechanism to account for this atmosphere ocean interaction is still missing using a flat bottom shallow water model we show that a direct coupling between atmospheric pressure and the free mode of an inlet is unlikely but that an oceanic wave of atmospheric origin can act as an intermediate mechanism and adequately force the inlet by resonance the phase relationship derived from this mechanism is in good agreement with observations provided the whole spectrum of oceanic waves is in opposite phase to the generating atmospheric disturbance we also show that the very large oscillations observed at ciutadella an elongated shallow inlet in the west coast of menorca balearic islands can be explained in terms of the particular shape of this inlet

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

impact of geomorphological changes to harbor resonance during meteotsunamis the vela luka bay test case in engineering studies harbor resonance including quality and amplification factors is typically computed for swell and waves with periods shorter than 10 min however in various locations around the world such as vela luka bay in croatia meteotsunami waves of periods greater than 10 min can excite the bay or harbor natural modes and produce substantial structural damages in this theoretical study the impact of some geomorphological changes of vela luka bay i e deepening of the bay dredging the harbor adding a pier or a marina to the amplification of the meteotsunami waves are presented for a set of 6401 idealized pressure wave field forcing used to derive robust statistics the most substantial increase in maximum elevation is found when the vela luka harbor is dredged to a 5 m depth which is in contradiction with the calculation of the quality factor showing a decrease of the harbor natural resonance it has been shown that the forcing energy content at different frequency bands should also be taken into account when estimating the quality and amplification factors as their typical definitions derived from the peak frequency of the sea level spectrum fail to represent the harbor response during meteotsunami events new definitions of these factors are proposed in this study and are shown to be in good agreement with the results of the statistical analysis of the vela luka bay maximum elevation results in addition the presented methodology can easily be applicable to any other location in the world where meteotsunamis occur