numerical diagnosis of a small quasi tropical cyclone over the western mediterranean dynamical vs boundary factors a small quasi tropical cyclone occurred on 12 september 1996 over the western mediterranean intense convective activity over the region during this period also produced a tornado outbreak in the balearic islands and torrential precipitation over eastern mainland spain mesoscale model runs properly simulate the cyclone formation and show convection and heavy precipitation following the cyclone trajectory during its eastward progression a sensitivity study examining the upper level dynamic forcing latent and sensible heat fluxes from the sea and orography is conducted a potential vorticity pv inversion technique is used to reduce the amplitude of the upper level trough in the model initial conditions the results show that neither the orography nor the sensible heat flux from the sea play a significant role during this particular cyclone development conversely both the latent heat flux and the upper level trough are shown to be crucial for low level cyclogenesis features common to hurricane like polar lows are found for the cyclone and an analysis of the precise role of the upper level structures and the convective development is conducted a factor separation technique is used to determine the individual effects of the aforementioned factors as well as their interaction at the first stage of the cyclogenesis the upper level pv anomaly enhanced the low level circulation of the synoptic scale low and enhanced the latent heat flux from the sea during its mature stage the circulation associated with the small scale cyclone enhanced the latent heat flux from the sea thereby helping to maintain the development of deep convection and inducing further cyclone deepening by diabatic heating this scenario has many similarities with the air sea interaction instability mechanism thus the joint action of the upper level anomaly as a spin up agent and the latent heat flux as a sustainer of convection emerges as the primary factor for the genesis and evolution of the small quasi tropical cyclone copyright 2003 royal meteorological society

pressure transients within mcs mesohighs and wake lows by animating enhanced coarse surface pressure observations of 12 1985 preliminary regional experiment for storm scale operational research meteorology pre storm mesoscale convective systems mcss the authors exposed 92 transitory highs and lows living within virtually all of the systems mesohighs and wake lows a quasi lagrangian feature following not material following analysis of the pressure fields produced five primary results first these transients with magnitudes of a few millibars horizontal dimensions of order 100 km and average lifetimes of about 2 h collectively composed spatial and temporal envelopes that contributed at least part of the total pressure field within mesohighs and wake lows transients did not apparently favor formation or dissipation in any location of the envelopes second as the mcss matured the difference between each complex s transitory highs mean pressure and transitory lows mean pressure increased in 78 of the conclusive cases apparently one frequent role of mcss is locally to magnify storm scale pressure gradients third transient paths reflect the frequent symmetric to asymmetric metamorphoses of the mcss fourth the temporal fluctuations of the numbers and apparent sizes of transients within a composite mcs partially support theories of mcs upscale evolution finally the composite s transient numbers and apparent sizes varied almost identically with time in a pattern that closely resembles the fluctuation of stratiform and convective volumetric rain rates of mcss

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part i model description and verification abstract the pennsylvania state university ncar mesoscale model originally developed by anthes and warner is modified to simulate the meso scale structure and evolution of convectively driven weather systems the modifications include i two way interactive nested grid procedures ii the fritsch chappell convective parameterization scheme and iii the blackadar boundary layer package an 18 h simulation of the johnstown flood of july 1977 is conducted compared to the documentation of hoxit et al and bosart and sanders the simulation reproduced many of the different aspect of the mesoscale convective complex and squall line that were responsible for the heavy rain over western pennsylvania in particular the model predicts the size propagation rate and orientation of the mesoscale convective components that were observed in the mid atlantic states the simulated evolution of the planetary boundary layer cool outflow boundaries and surface pressure perturbations such as meso scale lows h

structure of a midlatitude squall line formed in strong unidirectional shear abstract data from five doppler radars the surface mesonet aircraft and rawinsondes from the cooperative convective precipitation experiment ccope are used to document the structure and evolution of a squall line with unusually persistent cells and an anvil that spreads downwind in strong upper level westerlies the environmental sounding showed linear shear of 4 m s 1 km 1 through the troposphere a convective available potential energy of 600 m2 s 2 and a convective richardson number of 10 based on the wind in the lowest 6 km the orientation of the squall line comprised of high reflectivity centers spaced 20 40 km apart changed with time initially the squall line axis was normal to the environmental shear but with time it became parallel to the shear vector as the northeastern portion of the subcloud cold dome merged with cold air generated by individual storms that had formed ahead of the line the intensity of the cells within the squads line diminished as its axis became more parallel

a cloud base quasi balance constraint for parameterized convection application to the kain fritsch cumulus scheme abstract a quasi balance with respect to parcel buoyancy at cloud base between destabilizing processes and convection is imposed as a constraint on convective cloud base mass flux in a modified version of the kain fritsch cumulus parameterization supporting evidence is presented for this treatment showing a cloud base quasi balance cbq on a time scale of approximately 1 3 h in explicit simulations of deep convection over the u s great plains and over the tropical pacific ocean with the naval research laboratory s coupled ocean atmosphere mesoscale prediction system coamps 1 with the exception of the smaller of two convective events in the great plains simulation a cbq is still observed upon restriction of the data analysis to instances where the available buoyant energy abe exceeds a threshold value of 1000 j kg 1 this observation is consistent with the view that feedbacks between convection and cloud base parcel buoyancy can control the rate of convection on shorter time scales than those asso

confirmation of elevated methane emissions in utah s uintah basin with ground based observations and a high resolution transport model large ch4 leak rates have been observed in the uintah basin of eastern utah an area with over 10 000 active and producing natural gas and oil wells in this paper we model ch4 concentrations at four sites in the uintah basin and compare the simulated results to in situ observations at these sites during two spring time periods in 2015 and 2016 these sites include a baseline location fruitland two sites near oil wells roosevelt and castlepeak and a site near natural gas wells horsepool to interpret these measurements and relate observed ch4 variations to emissions we carried out atmospheric simulations using the stochastic time inverted lagrangian transport model driven by meteorological fields simulated by the weather research and forecasting and high resolution rapid refresh models these simulations were combined with two different emission inventories 1 aircraft derived basin wide emissions allocated spatially using oil and gas well locations from the national oceanic and atmospheric administration noaa and 2 a bottom up inventory for the entire u s from the environmental protection agency epa at both horsepool and castlepeak the diurnal cycle of modeled ch4 concentrations was captured using noaa emission estimates but was underestimated using the epa inventory these findings corroborate emission estimates from the noaa inventory based on daytime mass balance estimates and provide additional support for a suggested leak rate from the uintah basin that is higher than most other regions with natural gas and oil development

early growth of mesoscale convective complexes a meso β scale cycle of convective precipitation abstract the evolution of precipitation fields associated with several mesoscale convective complexes mccs has been inferred from radar reflectivity data in almost all cases examined including those described in the literature the system s convective ensemble undergoes a marked modulation in intensity on a meso time scale during the early growth stage of its meso scale life cycle this scale convective cycle is most evident in time series of volumetric precipitation rate due to convective echo and is characterized by a temporal maximum followed by a minimum 0 5 1 h later superimposed on an otherwise several hour monotonically increasing trend while the latter is due to a concurrent several hour increase in the areal extent of convective echo the scale perturbation is dominated by a modulation in intensity of the existing convective entities that the system constitutes at that stage of growth the scale cycle also marks the onset of a sustained increased growth rate of the mcc s s

composite life cycle of maritime tropical mesoscale convective systems in scatterometer and microwave satellite observations this study examines scatterometer observed surface wind divergence and vorticity along with precipitable water pw across the life cycle of tropical maritime mesoscale convective systems mcss as resolved in 0 5 data simple composites were constructed around first appearances of cold 210 k cloud tops in infrared ir data at 3 hourly resolution many thousands of such events from the tropical indopacific in 2000 were used composites of subpopulations were also constructed by subdividing the dataset according to ir event size and duration as well as by prevailing values of pw and vorticity at a 5 scale the composite mcs life cycle here spans about a day and covers a few hundred kilometers with a remarkable sameness across subpopulations surface wind convergence and pw buildup lead cold cloud appearance by many hours afterward there are many hours of divergence indicative of downdrafts contrary to motivating hypotheses the strength of this divergence relative to convergence is scarcely different in humid and dry subpopulation composites normalized time series of composite vorticity show an evolution that seems consistent with vortex stretching by this convergence divergence cycle with peak vorticity near the end of the period of convergence 3 h prior to cold cloud appearance in rotating conditions the common 1 day mcs life cycle is superposed on large scale mean vorticity and convergence approximately in proportion which appear to be well scale separated covering the whole of the 48 h and 5 10 averages and are as strong as or stronger than the mcs signature

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

three dimensional kinematic and microphysical evolution of florida cumulonimbus part i spatial distribution of updrafts downdrafts and precipitation abstract this paper is the first in a three part study that examines the kinematic and microphysical evolution of florida cumulonimbus and focuses on the convective to stratiform transition of the storm this first paper lays the groundwork for the subsequent papers by defining the problem under study delineating the setting for the storm and describing the spatial distribution of updrafts downdrafts and precipitation high resolution radar data of a typical line of storms associated with the florida sea breeze is the centerpiece of this study the high resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall line studies radar reflectivity filled in between cells at upper levels as the storm evolved reflectivity values were only weakly associated with updraft and downdraft magnitude the updrafts and downdrafts in the storm tended to be irregular in their three dimensional shape and less than 5 km in horizontal extent at any giv

ocean wave scattering by natural sea ice transects 1 ocean waves propagate in continuous sea ice as flexural gravity waves so named because their dispersion is influenced by bending of the ice plate and by buoyancy such waves are scattered by topographic heterogeneity in the ice e g features like pressure ridges yet current models fail to account for the complexity that is symptomatic of sea ice here a two dimensional wave scattering model is described that allows real data from natural sea ice to be assimilated rather than synthetic ice terrain on the basis of linear wave theory and the elastic thin plate equation the model assumes an unbroken compliant sea ice cover with no free edges and uses green s functions to obtain an integral equation that is solved numerically while scattering in physical stretches of sea ice can vary greatly all transects behave as low pass filters and can display resonances that relate to how features are separated or to transect length the latter being an undesirable trait of the model in the paper an association is made between the statistical properties of the sea ice terrain and the nature of the scattering that results not unexpectedly sea ice with greater relative draft variation is more reflective it is proposed that this observation can be used to identify the draft variation for an unknown transect if its scattering response is known finally the progression of median energy density for ensembles of similarly sampled transects is examined at wave periods of less than 10 s and is found to decay exponentially with distance traveled in accord with the few observations available

interactions between a developing mesoscale convective system and its environment part i observational analysis this paper is the first in a two part series in which the interactions between a growing mesoscale convective system mcs and its surrounding environment are investigated the system studied here developed in northeastern colorado on 19 july 1993 and propagated into kansas as a long lived nocturnal mcs high resolution dual doppler and surface mesonet data collected from this system are discussed in part i while the results of a numerical simulation are discussed in part ii the observations show that organized mesoscale surface pressure and flow features appeared very early in the lifetime of this system long before the development of any trailing stratiform precipitation most of the stratiform anvil advected ahead of the convective line in the strong upper tropospheric westerlies in accordance with this most of the mid and upper tropospheric storm relative flow behind the line remained westerly or rear to front despite the westerlies the strongest flow perturbations with respect to the ambient winds developed to the rear of the line the structure of these perturbations was similar to the upper tropospheric front to rear and midtropospheric rear to front flows typically found in more mature leading line trailing stratiform systems the presence of these perturbations on the upwind side of the convective line indicates that gravity wave propagation was primarily responsible for their development

a convective cell in a hurricane rainband abstract on 10 october 1983 the two noaa wp 3d aircraft completed a mission designed to provide airborne doppler radar data for a convective cell embedded in a weak rainband on the trailing side of hurricane raymond comparisons of the wind field produced from the pseudo dual doppler radar technique with in situ wind measurements suggest that the larger convective scale feature may be resolved if the sampling time is kept to a minimum the convective cell was found to move downband faster than any environmental winds but slightly slower than the winds found in the reflectivity core that delineates the cell in the core of the cell the tangential wind is increased and the radial inflow turns to outflow with respect to the circulation center the flow field demonstrates that the downband stratiform portion of a rainband is not from cells currently active since the updraft detrains upwind relative to the cell but rather it is due to the fallout from ice particles placed into the upper troposphere by clouds t

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

a numerical study of the genesis of extratropical convective mesovortices part i evolution and dynamics abstract the purpose of this study is to understand the genesis of extratropical convective mesovortices and the large scale environmental features that influence the vortex formation a hypothesis is proposed that mesovortices form in the stratiform rain regions of mesoscale convective systems mcss due to the reduction of static stability that reduces the effective local rossby radius in such regions a conceptual model of the mesoscale convective cyclogenesis is introduced which describes the three stages of the mesovortex formation a modified version of the pennsylvania state university national center for atmospheric research three dimensional hydrostatic mesoscale model is used to simulate mesovortex genesis in analytically generated pre mcs large scale environments the model simultaneously incorporates parameterized convection and a grid resolvable convective scheme containing the effects of hydrostatic water loading condensation evaporation freezing melting and sublimation a control si

upscale evolution of mcss doppler radar analysis and analytical investigation abstract the development of two small mesoscale convective systems mcss in northeastern colorado is investigated via dual doppler radar analysis the first system developed from several initially isolated cumulonimbi which gradually coalesced into a minimal mcs with relatively little stratiform precipitation the second system developed more rapidly along an axis of convection and generated a more extensive and persistent stratiform echo and mcs cloud shield in both systems the volumetric precipitation rate exhibited an early meso scale convective cycle a maximum and subsequent minimum followed by reintensification into a modest mature stage this sequence is similar to that noted previously in the developing stage of larger mcss by mcanelly and cotton they speculated that the early meso convective cycle is a characteristic feature of development in many mcss that is dynamically linked to a rather abrupt transition toward mature stage structure this study presents kinematic evidence in suppo

kinematic and precipitation structure of the 10 11 june 1985 squall line abstract high frequency 90 min rawinsonde data from a special mesoscale network 26 sites have been combined with wind profiler dense automated surface network data 80 stations spaced 50 km apart and a series of high resolution dual doppler radar analyses in a common framework attached to a moving squall line system to form a comprehensive dataset describing the mature phase of the 10 11 june 1985 squall line observed during pre storm the dual doppler radar analyses covered a 200 300 km2 area from the leading edge of the convective line to the back edge of the trailing stratiform precipitation region thus providing high resolution wind information over a very broad portion of the storm system the comprehensive analysis is used to resolve several aspects of the trailing stratiform region that had remained unclear from previous studies first a difference in the horizontal scale was found between the mesoscale updraft which at upper levels was on the scale of the trailing stratiform cloud a

heat and moisture budgets of an intense midlatitude squall line abstract rawinsonde data from ok pre storm are used to calculate the heat and moisture budgets during the late mature through dissipating stages of an intense squall line system with a trailing stratiform region budgets have been computed at three separate times using composited data from approximately 30 rawinsondes over three hour intervals data spacing is marginally adequate to resolve features within the broad 200 km stratiform region but not the narrow 40 km leading convective line low level radar data and surface accumulated rainfall are used to partition the system into convective line and stratiform regions and to cheek the accuracy of the heat and moisture budgets the squall line had a pronounced descending rear inflow jet that extended toward the front of the system with time and strong front to rear flow above and beneath this jet the diagnosed vertical motion showed deep ascent in the leading convective line and upper level ascent above lower level descent in the trailing stratif

a numerical simulation of the 7 may 1985 mesoscale convective system abstract on 7 may 1985 a mesoscale convective system mcs developed within a moderately forced large scale environment for upward motion and moved into the observing network of the oklahoma kansas preliminary regional experiment for storm pre storm the initial region of convective development occurred out side the pre storm network in a data sparse area simulations using the pennsylvania state university national center for atmospheric research psu ncar mesoscale model are produced using initial conditions from two different initialization techniques static initialization and improved dynamic initialization to evaluate the ability of the mesoscale model to reproduce the complex evolution and structure of this mcs the results indicate that even when including the special pre storm data in the model initialization process the numerical simulation that uses the initial condition from the static initialization fails to simulate the observed evolution of the 7 may 1985 mcs this is attributed to bo

observations and analyses of an intense waves in ice event in the sea of okhotsk 1 ice draft ice velocity ice concentration and current profile data gathered at an array of eight continental shelf monitoring sites east of sakhalin island were analyzed in conjunction with regional meteorological data to document and explain intense wave occurrences several hundred kilometers inside the sea of okhotsk ice pack the studied event was associated with the 19 21 march 1998 passage of an intense cyclone which produced waves with amplitudes in excess of 1 m at the most offshore monitoring location the relatively monochromatic character of the waves allowed extraction of wave intensity time series from ice draft time series data spatial and temporal variations in these data were used to establish directions and speeds of wave energy propagation for comparisons with an earlier interpretation liu and mollo christensen 1988 of an antarctic intense waves in ice event it was concluded that although both events are compatible with a two stage process in which initially slowly advancing wave activity increases subsequent ice cover wave transmissivity the first stage of the sea of okhotsk event was not explicable in terms of the static stress induced changes in the waves in ice dispersion relationship proposed by liu and mollo christensen an alternative explanation is offered that eschews the linkage between wave group velocities and the observed slow rates of wave energy propagation and attributes the subsequent transition to more normal wave propagation behavior to ice pack divergence

mesoscale convective systems in weakly forced large scale environments part iii numerical simulations and implications for operational forecasting abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of mesoscale convective systems developed within a weakly forced large scale environment two of these systems had a large component of motion against the midtropospheric flow and propagated in a direction nearly opposite to that of the travelling upper level disturbances this evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper level disturbances it presents a tremendous challenge for three dimensional numerical models since the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional upper air network and may not be well approximated in the model parameterization schemes mesoscale model simulations are conducted to evaluate the ability of the model to reproduce this complex event and to examine the model sensitivities to differences in the convective trigger function and model i

ocean wave sea ice interactions in the south eastern coastal zone of sakhalin island abstract a long duration set of wave observations is reported conducted in the coastal region of south eastern sakhalin island in the sea of okhotsk using bottom mounted pressure sensors during both ice free conditions and while sea ice was present although one instrument was not able to be recovered the two remaining high precision instruments device located close to the shoreline and situated 7 5 km seaward in the south easterly direction provided time series sampled at 1 s allowing wave periods from 2 s to 20 min to be detected and spectrally analysed the time series reveal intriguing significant differences between open water periods and times when sea ice covered the surface e g preferential resonant frequencies appear in seastate energy density spectra during episodes of sizeable swell when sea ice is present but not when it is absent and what is believed to be a trapped edge wave of approximately 11 min period in open water increases in period to 11 8 min when the sea ice is there although no technical mathematical theory is advanced the authors speculate on potential explanations for these anomalies and invite readers to provide alternative hypotheses

quantifying atmospheric methane emissions from oil and natural gas production in the bakken shale region of north dakota we present in situ airborne measurements of methane ch4 and ethane c2h6 taken aboard a noaa dhc 6 twin otter research aircraft in may 2014 over the williston basin in northwestern north dakota a region of rapidly growing oil and natural gas production the williston basin is best known for the bakken shale formation from which a significant increase in oil and gas extraction has occurred since 2009 we derive a ch4 emission rate from this region using airborne data by calculating the ch4 enhancement flux through the planetary boundary layer downwind of the region we calculate ch4 emissions of 36 13 27 13 27 12 27 12 and 25 10 103 kg h from five transects on 3 days in may 2014 downwind of the bakken shale region of north dakota the average emission 28 5 103 kg h extrapolates to 0 25 0 05 tg yr which is significantly lower than a previous estimate of ch4 emissions from northwestern north dakota and southeastern saskatchewan using satellite remote sensing data we attribute the majority of ch4 emissions in the region to oil and gas operations in the bakken based on the similarity between atmospheric c2h6 to ch4 enhancement ratios and the composition of raw natural gas withdrawn from the region

evolution of quasi two dimensional squall lines part i kinematic and reflectivity structure abstract doppler radar observations that establish common patterns in the evolution of the reflectivity and flow structures of squall lines are described a number of squall lines have been analyzed with unprecedented time resolution in order to identity these patterns all of the squall lines appeared to be approximately two dimensional and featured a solid leading edge at some time during their life cycle instead of being composed of discrete cells separated by echo free regions a large variety of intensities and evolution lime scales was observed it is shown that squall lines of this type evolve through identifiable stages of reflectivity structure this evolution appears to be strongly related to changes that occur in the kinematic structure as a typical system evolves a rearward sloping zone of horizontal vorticity predominantly associated with vertical shear develops on the scale of the system presumably driven by the horizontal buoyancy gradients across the system the vorticity that is gen

quantifying atmospheric methane emissions from the haynesville fayetteville and northeastern marcellus shale gas production regions we present measurements of methane ch4 taken aboard a noaa wp 3d research aircraft in 2013 over the haynesville shale region in eastern texas northwestern louisiana the fayetteville shale region in arkansas and the northeastern pennsylvania portion of the marcellus shale region which accounted for the majority of marcellus shale gas production that year we calculate emission rates from the horizontal ch4 flux in the planetary boundary layer downwind of each region after subtracting the ch4 flux entering the region upwind we find 1 day ch4 emissions of 8 0 2 7 107 g h from the haynesville region 3 9 1 8 107 g h from the fayetteville region and 1 5 0 6 107 g h from the marcellus region in northeastern pennsylvania finally we compare the ch4 emissions to the total volume of natural gas extracted from each region to derive a loss rate from production operations of 1 0 2 1 from the haynesville region 1 0 2 8 from the fayetteville region and 0 18 0 41 from the marcellus region in northeastern pennsylvania the climate impact of ch4 loss from shale gas production depends upon the total leakage from all production regions the regions investigated in this work represented over half of the u s shale gas production in 2013 and we find generally lower loss rates than those reported in earlier studies of regions that made smaller contributions to total production hence the national average ch4 loss rate from shale gas production may be lower than values extrapolated from the earlier studies

multiscale convective overturning in mesoscale convective systems reconciling observations simulations and theory abstract an analysis of how parameterized convection interacts with hydrostatic explicitly resolved precipitation processes to represent multiscale convective overturning in a mesoscale resolution numerical simulation is presented critically important ingredients of the successful simulation are identified and the degree to which simulations are consistent with observations and theoretical considerations is examined of particular concern is how convective parameterization routines reconcile the deep moist absolutely unstable structures that form in mesoscale convective systems it is found that these structures arise primarily from resolvable scale vertical motion and that the model responds to these structures not only by maintaining parameterized convection but also by developing a hydrostatic manifestation of convective overturning on its smallest resolvable horizontal scales the strongest and most distinctive mesoscale perturbations develop in regions where the mesoscale contribution to convectiv

approximations to wave scattering by an ice sheet of variable thickness over undulating bed topography an investigation is carried out into the effect on wave propagation of an ice sheet of varying thickness floating on water of varying depth in three dimensions by deriving a variational principle equivalent to the governing equations of linear theory and invoking the mild slope approximation in respect of the ice thickness and water depth variations a simplified form of the problem is obtained from which the vertical coordinate is absent two situations are considered the scattering of flexural gravity waves by variations in the thickness of an infinite ice sheet and by depth variations and the scattering of free surface gravity waves by an ice sheet of finite extent and varying thickness again incorporating arbitrary topography numerical methods are devised for the two dimensional versions of these problems and a selection of results is presented the variational approach that is developed can be used to implement more sophisticated approximations and is capable of producing the solution of full linear problems by taking a large enough basis in the rayleigh ritz method it is also applicable to other situations that involve wave scattering by a floating elastic sheet

the oklahoma kansas mesoscale convective system of 10 11 june 1985 precipitation structure and single doppler radar analysis abstract the 10 11 june mesoscale convective system observed in kansas during pre storm is studied using a variety of observations including conventional radar satellite and single doppler radar this storm at maturity consisted of a strong line of convection trailed by a broad region of stratiform rain the pre storm doppler radar observations show that the general airflow pattern is similar to that seen in previously analyzed cases however since the doppler observations were quite extensive in time and space they permit several details of the airflow to be revealed for the first time a rear inflow jet front to rear flow aloft and a mesoscale updraft and downdraft were all present the mesoscale downdraft commenced at the top of the slanted rear inflow jet sublimation and evaporation of hydrometeors in this flow apparently generated the necessary cooling to drive the mesoscale downdraft circulation the intensity and slope of the rear inflow jet varied with location in the storm which apparen

ice coupled wave propagation across an abrupt change in ice rigidity density or thickness the model of fox and squire 1990 1991 1994 which discusses the oblique propagation of surface gravity waves from the open sea into an ice sheet of constant thickness and properties is augmented to include propagation across an abrupt transition of properties within a continuous ice sheet or across two dissimilar ice sheets that abut one another but are free to move independently rigidity thickness and or density may change across the transition allowing for example the modeling of ice coupled waves into across and out of refrozen leads and polynyas across cracks and through coherent pressure ridges reflection and transmission behavior is reported for various changes in properties under both types of transition conditions

the influence of convectively generated thermal forcing on the mesoscale circulation around squall lines abstract the dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2d squall lines are examined using a series of numerical simulations the features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a dry simulation with no microphysical parameterization the thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation the mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines it includes an ascending front to rear flow a midlevel rear inflow a mesoscale up and downdraft an upper level rear to front flow ahead of the thermal forcing and an upper level cold anomaly to the rear of the thermal forcing it is also shown t

roll circulations in the convective region of a simulated squall line abstract in high resolution numerical simulations using horizontal grid spacing less than 1 km the convective region of squall lines will sometimes overturn as quasi horizontal convective rolls the authors study one case in detail using output from a simulation with 125 m grid spacing the rolls have an average spacing of 3 km and are aligned parallel to the vertical wind shear individual convective cells often have long lived undiluted cores that entrain primarily on the sides of the rolls i e between the roll updraft and downdraft the following set of conditions is proposed for obtaining roll overturning the formation of a moist absolutely unstable layer maul vertical shear of the horizontal wind within the maul an environment without large amplitude perturbations and quasi horizontal flow over the squall line s surface based cold pool further insight is gained through a series of more idealized simulations wherein a specified maul is perturbed by analytic potential temperature pertur

the triple point on 24 may 2002 during ihop part ii ground radar and in situ boundary layer analysis of cumulus development and convection initiation abstract cumulus formation and convection initiation are examined near a cold front dryline triple point intersection on 24 may 2002 during the international h2o project ihop a new lagrangian objective analysis technique assimilates in situ measurements using time dependent doppler derived 3d wind fields providing output 3d fields of water vapor mixing ratio virtual potential temperature and lifted condensation level lcl and water saturated i e cloud volumes on a subdomain of the radar analysis grid the radar and lagrangian analyses reveal the presence of along wind i e longitudinal and cross wind i e transverse roll circulations in the boundary layer bl a remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft vertical vorticity and reflectivity cores for periods of up to 30 min or more while moving approximately with the local bl wind satellite cloud images and single camera ground photogrammetry imply tha

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 underside of arctic sea ice imaged by sidescan sonar despite extensive submarine operations in the arctic little is yet known about the three dimensional morphology of the ice underside several studies have been done using upward looking sonar1 7 which yields a linear profile of ice draft from which the distributions of features such as pressure ridges and leads may be derived such a profile gives no information about the spatial morphology or appearance of the ice bottom surface in contrast the upper ice surface has been well documented from airborne and satellite borne sensors such as synthetic aperture radar passive microwave infrared and visual imaging here i report the first extensive set of imagery of the underside of sea ice in the arctic ocean sidescan sonar images show a distinct difference between the appearance of first year ice and of multi year ice first year ice has a smooth bottom except for a network of cracks while multi year ice is covered with an array of blisters or bulges the clear discrimination between ice types enables sidescan sonar to be used as a means of validating airborne passive microwave data

the impact of spatial variations of low level stability on the life cycle of a simulated supercell storm abstract this study reports on the dynamical evolution of simulated long lived right moving supercell storms in a high cape strongly sheared mesoscale environment which initiate in a weakly capped region and subsequently move into a cold boundary layer bl and inversion region before dissipating the storm simulations realistically approximate the main morphological features and evolution of the 22 may 1981 binger oklahoma supercell storm by employing time varying inflow lateral boundary conditions for the storm relative moving grid which in turn are prescribed from a parent fixed steady state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day a series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability the

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

mesoscale circulation growth under conditions of weak inertial instability abstract the hypothesis that inertial instability plays a role in the upscale development of mesoscale convective systems mcss is explored by sampling environments that supported the growth of mcss in the preliminary regional experiment for storm stormscale operational and research meteorology pre storm network with high quality special soundings secondary circulations that occurred in the presence of inertial instabilities were analyzed and documented using rawinsonde data with high spatial and temporal resolution from the pre storm field program additional examples of mcs environments were examined using data from the mesoscale analysis and prediction system results show strong divergence and cross stream accelerations occurred at upper tropospheric levels where inertial instabilities were present these accelerations were not uniform over the domain but were focused in the regions of instability also the analyses of these data showed that regions of inertial instability may be more commonpla

simulation of a progressive derecho using composite initial conditions abstract this study focuses on the progressive derecho a widespread convectively induced windstorm produced by a mesoscale convective system that often occurs within a relatively benign synoptic scale environment sounding data from 12 progressive derechos which occurred in weakly forced large scale environments are composited in order to examine important large scale features in the preconvective environment this analysis captures many features that are common in warm season derecho environments such as an upper level wind maximum a relatively dry midtroposphere and low level warm advection initial and boundary conditions for the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 are created using this analysis a three dimensional horizontally nonhomogeneous explicitly resolved simulation of a progressive derecho is produced and compared to previous more idealized simulations of similar convective systems that have been used to expla

gravity waves compensating subsidence and detrainment around cumulus clouds abstract gravity waves play an important role in the redistribution of heat and moisture in a deep convecting cloud field we explore this role in a two dimensional numerical experiment on a simple moist convecting system consisting of an isolated long lasting nonprecipitating cloud in a calm atmosphere with no surface forcing the cloud develops a horizontally averaged density variation with height which is neutrally buoyant with respect to a moist adiabatic the buoyancy difference between the cloud and the undisturbed sounding produces circulations that can be understood as spreading gravity waves which adjust the environmental buoyancy to be equal to the cloud buoyancy by compensating subsidence unlike the circulations inside clouds this adjustment takes place without turbulent mixing hence the buoyancy adjustment time t1 during which the environment comes into rough buoyant equilibrium with the clouds is much shorter than the mixing time t2 which it takes a tracer initially concentrated at s

interactions between a developing mesoscale convective system and its environment part ii numerical simulation the 19 july 1993 mesoscale convective system mcs discussed in part i was simulated using the regional atmospheric modeling system rams the model was initialized with variable physiographic and atmospheric data with the goal of reproducing the convective system and its four dimensional environment four telescopically nested moving grids allowed for horizontal grid spacings down to 1 67 km on the cloud resolving grid comparisons with the analysis show that the propagation evolution and structure of this mcs were well simulated the simulation is used to further investigate the interactions between this mcs and its surrounding environment in part i the doppler derived winds indicated that upshear westward propagating gravity waves left uppertropospheric front to rear and midtropospheric rear to front flow perturbations in their wake a similar flow structure developed in the simulated mcs and unlike the doppler results the low frequency waves that produced it were resolved in the data in the simulation much of the convectively generated temperature and momentum perturbations propagated westward with the waves leaving a warm wake in the clear air trailing the system although the gravity waves traveled rearward the perturbation flow in their wake was not strong enough to reverse the upper tropospheric storm relative winds thus most of the anvil condensate advected ahead of the convective line as the mcs encountered the low level jet the midtropospheric upward mass flux increased but gravity wave motions became less detectable the upper tropospheric anvil pushed westward into the strong flow as the system expanded into a characteristically oval shape temperature and momentum perturbations propagated rearward along with the anvil in a disturbance that resembled an advective outflow unlike the gravity waves this disturbance became almost stationary with respect to the ground and it retained its continuity through the rest of the simulation vertical cross sections indicate that a large slab of convectively processed air had detrained into the upper troposphere prior to this event much of the warm temperature anomalies generated within the convective towers either remained in the updrafts or propagated outward with the gravity waves early on individual updrafts were relatively erect and although condensate did detrain eastward in the forward anvil the temperature anomalies did not propagate with it in contrast convective updrafts associated with the expanding oval anvil disturbance were more continuous and they tilted strongly westward with height

spurious convective organization in simulated squall lines owing to moist absolutely unstable layers abstract a spurious updraft pattern has been documented in some numerical simulations of squall lines the pattern is notable because of a regular repeating pattern of updrafts and downdrafts that are three six grid lengths wide this study examines the environmental and numerical conditions that lead to this problem the spurious pattern is found only in simulations of upshear tilted convective systems furthermore the pattern coincides with deep 2 3 km and wide 5 20 km moist absolutely unstable layers mauls saturated layers of air that are statically unstable in this physical environment small scale perturbations grow rapidly the necessarily imperfect numerical schemes of the model introduce spurious small scale perturbations into the mauls and these perturbations amplify owing to the unstable stratification some techniques are investigated that diffuse the perturbations or minimize their introduction in the statically unstable flow

a composite model of mesoscale convective complexes abstract a composite analysis technique is used to investigate the evolution of mesoscale features of mesoscale convective complexes mccs the early stage of the mcc lifecycle is characterized by convergence vertical motion and heating being centered in the lower troposphere as the mcc matures the level of peak upward motion and heating shifts to the upper troposphere the system achieves and maintains its maximum divergence upward motion and anticyclonic vorticity in the upper troposphere during the latter half of the life cycle this is in contrast to gate tropical clusters where the maximum divergence upward motion and anticyclonic vorticity occurred at the mature stage of the cluster and then weakened this difference might be explained by an mcc being an inertially stable form of mesoscale convective system whose radius exceeds the rossby radius of deformation the mcc is shown to be an efficient rain producer exhibiting a precipitation efficiency exceeding 100 at the mature stage due to th

mesoscale organization of springtime rainstorms in oklahoma abstract radar reflectivity and raingage data obtained during six springtimes indicate the types of mesoscale organization that occur in association with major rain events in oklahoma at least 25 mm of rain in 24 h over an area exceeding 12 500 km2 in these storms the primary rain area is found to be a contiguous region of precipitation 10s to 100s of km in scale that consists partly of deep convection and partly of stratiform rain the patterns of rain formed by the convective and stratiform areas comprise a continuous spectrum of mesoscale structures about two thirds of the cases examined exhibited variations on the type of organization in which convective cells arranged in a moving line are followed by a region of stratiform rain storm organization was graded according to the degree to which it matched an idealized model of this leading line trailing stratiform structure the precipitation pattern was further graded according to whether its structure was relatively symmetric with respect to an a

methane emissions from the marcellus shale in southwestern pennsylvania and northern west virginia based on airborne measurements natural gas production in the u s has increased rapidly over the past decade along with concerns about methane ch4 leakage total fugitive emissions and climate impacts quantification of ch4 emissions from oil and natural gas o ng operations is important for establishing scientifically sound cost effective policies for mitigating greenhouse gases we use aircraft measurements and a mass balance approach for three flight experiments in august and september 2015 to estimate ch4 emissions from o ng operations in the southwestern marcellus shale region we estimate the mean 1 ch4 emission rate as 36 7 1 9 kg ch4 s 1 or 1 16 0 06 tg ch4 yr 1 with 59 coming from o ng operations we estimate the mean 1 ch4 leak rate from o ng operations as 3 9 0 4 with a lower limit of 1 5 and an upper limit of 6 3 this leak rate is broadly consistent with the results from several recent top down studies but higher than the results from a few other observational studies as well as in the u s environmental protection agency ch4 emission inventory however a substantial source of ch4 was found to contain little ethane c2h6 possibly due to coalbed ch4 emitted either directly from coalmines or from wells drilled through coalbed layers although recent regulations requiring capture of gas from the completion venting step of the hydraulic fracturing appear to have reduced losses our study suggests that for a 20 year time scale energy derived from the combustion of natural gas extracted from this region will require further controls before it can exert a net climate benefit compared to coal

scattering of ice coupled waves by variable sea ice terrain the reflection and transmission of ice coupled waves under a sea ice sheet is re examined in this work recent theory can account for inhomogeneities in ice sheets such as the sails of pressure ridges and cracks or leads but has only examined small numbers of features here the scattering coefficients can be obtained for an ice sheet containing a region of arbitrarily varying thickness that more closely approximates a real ice sheet and consequently models wave scattering more effectively we explore the consequences of inverting ridge keels placing the mass above the ice sheet as a technique by which the keel can be partially accounted for it is found that the ridge sails themselves can reasonably be neglected upward looking submarine sonar data are used to demonstrate the use of the model noting that there are choices as to how to interpret such data the model is tested to establish its sensitivity to these choices

a comparative evaluation of impact of domain size and parameterization scheme on simulation of tropical cyclones in the bay of bengal 1 a large number of processes and factors control the quality of simulations with a numerical weather prediction model and especially with mesoscale models identification and optimization of these processes are critical for improving forecast skill the importance of cumulus parameterization schemes in simulation of tropical cyclones was recognized early and a large number of studies have addressed this issue however certain other aspects have received relatively less attention in particular unlike simulation with a global circulation model a mesoscale simulation is characterized by a limited domain and hence inhomogeneous lateral boundary conditions that strongly affect the quality of the simulation in this work we investigate the relative impact of size of the model domain and the cumulus parameterization scheme on simulation of 10 cyclones over the bay of bengal during the period 1999 2009 for five domains with different spatial extents simulations were carried out for three different cumulus parameterization schemes anthes kuo grell and kain fritsch2 for each of the 10 events using the mesoscale model mm5 our results show that the size of the domain also plays an equally critical role as the parameterization scheme in simulation of maximum intensity track and spatial structure of the cyclones the impact of domain size is not linear while each domain chosen is large enough neither the largest nor the smallest domain provides the best simulation however there is consistency in the sense that a single domain emerges as best for intensity and track among the five considered while the specific conclusions may depend on the ocean basin the methodology is generic and can be applied to any ocean basin of cyclogenesis

cloud to ground lightning activity in the 10 11 june 1985 mesoscale convective system observed during the oklahoma kansas pre storm project abstract as part of the field program for the oklahoma kansas pre storm project conducted in may june 1985 a network of electromagnetic direction finders was deployed to locate and detect the polarity of cloud to ground cg lighting flashes associated with mesoscale convective systems mcss we present an analysis of such data for the 10 11 june mcs this storm consisted of a line of convective cells trailed by an 80 km wide stratiform precipitation region data from the lightning strike locating network along with both conventional and doppler radar data are analyzed over a significant portion of the storm s lifetime to examine the relationship between the storm precipitation structure and the position and polarity of the lighting activity the majority of the negative cg activity is located in the convective precipitation region the frequency of negative cg activity is highest around the period of most intense convective rainfall positive cg activity is mainly confined to the trailing stratiform

numerical simulation of an intense squall line during 10 11 june 1985 pre storm part i model verification abstract a 24 h nested grid simulation of an intense squall line during the 1985 pre storm experiment is presented using an improved version of the pennsylvania state university national center for atmospheric research three dimensional mesoscale model although the model is initialized at 1200 utc 10 june 1985 with conventional meteorological observations it reproduces remarkably well many observed meso scale features that are analyzed from the high resolution network data these include 1 the generation of two areas of deep convection at the model initial time 2 the timing of the initiation of the squall line along a surface front 9 h into the model integration 3 the development of several convective bands at 2100 utc 4 the rapid intensification and rapid dissipation processes of the squall line as it entered and moved out of the network respectively 5 the generation of a presquall mesolow a squall induced mesohigh and a wake low as well as corresponding multiple surface convergence diverg

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

energy transport in the marginal ice zone a novel approach to modeling ocean wave scattering in the marginal ice zone that uses the coherent potential approximation to compute the energy transport velocity is reported the necessary theory is developed by considering sea ice floes to be thin elastic beams governed by the euler bernoulli equation with the open water surrounding each floe subject to the same equation with its material coefficients set to be very small quantities this mathematical stratagem facilitates the solution of the problem and yields interesting results about the speed at which wave energy propagates through a marginal ice zone the dispersion relation for a random mixture of ice floes and water and the mean free path or attenuation coefficient results from the model are compared with data reported by wadhams et al 1988

ice motions forced by boundary layer turbulence the motions of ice on frozen oceans in the frequency band from 0 05 to 10 0 s 1 have typically been associated with surface gravity waves which were generated by distant storms in the open ocean and which then propagate into the ice evidence relating these motions to local wind forcing has been less direct data on ice motions have been obtained with tilt meters on a land locked frozen lake and the motions are shown to be directly related to forcing by the local wind the variance of ice surface tilt increased by more than 3 orders of magnitude when the mean wind speed increased by a factor of less than 2 even when the wind speed remained below the minimum phase speed for freely propagating waves a model is presented in which ice motions result from an interaction between turbulent eddies in the atmosphere and the ice surface model predictions are shown to be consistent with the lake observations