convectively forced internal gravity waves results from two dimensional numerical experiments two dimensional numerical simulations were performed to investigate the nature of tropospheric internal gravity waves of the type which are observed to occur above active thermal convection over an unstable boundary layer these gravity waves are believed to be excited by a combination of pure thermal forcing and by the boundary layer eddies and cumulus clouds acting as obstacles to the flow in the presence of mean environmental wind shear large amplitude internal gravity waves were obtained in the simulations with amplitudes and horizontal scales similar to the 12 june 1984 aircraft observations over western nebraska this was a day with strong wind shear in the lowest 3 km above the ground and with scattered cumulus clouds topping the boundary layer the simulations show that there is significant difference between the early time solutions as might be predicted by linear theory and late time solutions for the boundary layer eddy structure a layer interaction occurs in which gravity waves of the stable layer are excited by the boundary layer convection there is evidence to suggest that this layer interaction occurs both with and without shear but that it is stronger in the presence of low level shear results indicate that shear or the obstacle effect is a more efficient generator of gravity waves than is the pure thermal forcing the simulations show that the gravity waves initially forced by the boundary layer eddies lead to a feedback mechanism that acts to organize the boundary layer eddies and the cumulus convection the solutions suggest that the character of fair weather convection moist or dry is a non local problem involving at times the full depth of the troposphere the clouds produced in the simulations have very little influence on the wave field or boundary layer eddy structure as they are relatively small cumuli on the other hand the clouds are strongly influenced by the interactions between the wave and eddy fields upshear growth of cumulus clouds similar to that which is frequently observed in nature is reproduced in the simulations the development of feeder feeder is used here in a dynamical sense only clouds on typically the upshear side of the cloud is found to be a result of the interaction between the gravity wave field and the dry and moist convection the relative phase velocity between the gravity waves and the cloud plays a crucial role in determining the character of the cumulus cloud growth in the present simulations these simulations suggest that the dynamics both internal and external to the boundary of a cumulus cloud is a complicated mix between wave dynamics and the usually considered convection dynamics a brief discussion of the implications of the present results to cloud boundary baroclinic instability dynamics is also presented

strain partitioning and progressive deformation history in a transpressive belt northern appalachians abstract syntectonic fibres within rocks of the gaspetrough a mid paleozoic slate belt within part of the acadian orogen of the canadian appalachians record the complex structural evolution of a transpressive belt the fibres occur around pyrite framboids and can be divided into five segments which record four distinct structural stages all four structural stages are related to a single progressive deformation since fibre segments can be traced continuously from the first segments to the last fibre growth patterns within the gaspetrough clearly indicate that folding occurred during coaxial deformation during the first three structural stages these structural stages are 1 layer parallel shortening 2 combined flattening and rigid body rotation and 3 cleavage development strain associated with vertical extension during these three stages accounts for approximately 50 shortening within the slate belt during the last structural stage deformation resulting from regional simple shear continued to affect the entire slate belt as local flattening within cleavage planes produced horizontal extension and brought about further tightening of folds strain recorded by the horizontal fibre increments produced during simple shear accounts for 25 shortening in this part of the appalachians oblique convergence during the acadian orogeny was partitioned in time between strike slip and reverse faulting convergence was accommodated by folding flattening and reverse faulting during the first part of the deformation and later on by flattening and dextral transcurrent faulting

a dual doppler radar study of longitudinal mode snowbands part i a three dimensional kinematic structure of meso γ scale convective cloud systems within a longitudinal mode snowband abstract observations of snowstorms were carried out around ishikari bay hokkaido japan from december 1991 to february 1992 on 15 january 1992 a longitudinal mode snowband was observed by a dual doppler radar system the snowband was composed of meso scale 20 km convective cloud systems the three dimensional kinematic structures and organization processes of the meso scale systems were studied in detail strong band parallel winds appeared in the upper north rear of the meso scale systems since their speed was faster than that of the cellular radar echoes the winds formed rear to front currents increasing in volume and speed the rear to front currents developed into meso scale and penetrated toward the lower front and lower south of the systems consequently the rear to front currents caused strong meso scale convergence and the enhancement of updrafts at their leading edges the transport of the band parallel momentum greatly contributed to the successive development of new convec

a method for estimating momentum fluxes of deep precipitating convection using profiling doppler radar 1 this paper outlines a novel approach for obtaining estimates of momentum fluxes for deep precipitating convection this method relies on data collected by vertically incident profiling doppler radars but may be applied to aircraft or space based radar systems this work represents a significant step forward toward the evaluation of convective momentum transports across regional scales using data from operational satellite systems e g the tropical rainfall measuring mission trmm instrument the new method is demonstrated as convective momentum flux terms and are estimated for deep convection occurring during the third convection and atmospheric moisture experiment camex 3 which was conducted during august and september 1998 these terms contain the most information on the momentum transported in the updrafts and downdrafts of cumulus convection key to the method is that the tilt and orientation of the convective drafts relative to earth s surface are quantified from radar information into perturbation horizontal wind components once an accurate storm motion estimate is provided for perturbation vertical velocities the evaluation of drop size diameters from radar reflectivities and the subsequent evaluation of terminal velocities of hydrometeors and draft motions are necessary information toward applying this technique doppler velocity measurements from the upward looking rd 69 disdromet disdrometer joss waldvogel disdrometer calibrated 915 mhz profiler are used to test the procedures for estimating w the method is tested against numerically simulated convection using the university of wisconsin nonhydrostatic modeling system uw nms mesoscale and cloud resolving model the radar estimated momentum fluxes are found to match in sign and relative magnitude through the depth of the convective clouds studied compared to those obtained from model simulation

observations of longitudinal rolls in a near neutral atmosphere abstract aircraft and satellite data an used to study the structure of longitudinal roll vortices in a nearly neutral zi l 1 2 where zi is the inversion height and l is the monin obukhov length boundary layer over the ice covered bering sea during february steam fog formed over cracks and leads in the ice was used as a tracer to delineate the various scales of roll motion seen in satellite images the satellite information combined with aircraft data collected by the noaa p 3 indicated the presence of a hierarchy of roll vortex motions it is suggested that interactions of the various scales of motion resulted in certain scales dominating in one area and other scales dominating in another two kilometer wavelength variations an attributed to the inflection point instability mechanism while 12 15 km variations seen to have been reinforced by the upstream topography on the chukotka peninsula organization of the fog banks on scales of 30 km was also present and may be attributable to resonant subharm

analysis of folding by superposition of strain patterns abstract two methods have been developed in this paper to model the strain state and the layer geometry of folds these methods analyse the superposition of strain patterns due to layer shortening tangential longitudinal strain flexural flow and fold flattening the first method multiplies the deformation gradients of these strain patterns to model the successive superposition of mechanisms the second method is more general and is based on the transformation of points from the initial configuration to deformed points according to the geometrical properties of the folding mechanisms involved this method simulates the simultaneous and successive superposition of strain patterns both methods generate graphic outputs that describe the strain variation through the folded layer another application of these methods is to attempt to find theoretical folds that fit natural or experimental folds and to perform a geometric and kinematical analysis of these folds knowledge of the shape of the folded layer and the cleavage pattern is the most common basic information available in natural folds that can be used to perform the analysis additional strain data from the folded rocks are valuable for improving knowledge of the kinematical mechanisms involved in the folding

a single doppler radar study of horizontal roll convection in a lake effect snow storm abstract the boundary layer structure and circulation over lake michigan were probed with a doppler radar and an aircraft during a lake effect snow storm on 9 december 1978 evidence is presented that observed wind parallel echo bands and satellite cloud bands resulted from horizontal roll convection in the boundary layer the organization of precipitation within the roll field is discussed and the roll geometry is compared with cases of dry horizontal roll convection reported in the literature

extensional fault bend folding and synrift deposition an example from the central sumatra basin indonesia we describe an analytical method for interpreting the geometry and structural history of asymmetric half grabens in rift basins with extensional fault bend fold theory using seismic reflection profiles from the central sumatra basin and balanced forward models we show how local variations in tectonic subsidence relative to deposition rates yield distinctive patterns of folded synrift strata and unconformities that record basin history if the deposition rate exceeds the local subsidence rate folded growth strata form upwardly narrowing kink bands that have been described previously as growth triangles in contrast if the deposition rate is less than or equals the local subsidence rate growth strata are folded and truncated at the surface on half graben margins subsequent increases in deposition rate relative to subsidence rate form angular unconformities near the half graben margins these unconformities develop without the necessity of erosion and are folded by continuing fault slip strata above and below the unconformities are concordant in the deeper parts of the half grabens thus angular unconformities on half graben margins are helpful for defining sequence boundaries that may reflect changes in deposition and tectonic subsidence rates in addition fault bend fold interpretations yield fault geometry and measures of horizontal extension both of which control three dimensional half graben geometry copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 4 1995 revised manuscript received june 4 1996 final acceptance october 23 1996 2texaco exploration and production technology dept 3901 briarpark houston texas 77042 3pt caltex pacific indonesia rumbai pekanbaru 28271 indonesia we thank hongbin xiao and john suppe for helpful insights into their extensional fault bend fold theory which provided the foundation for this work exceptional reviews by m scott wilkerson and walter f dula jr improved the manuscript in addition discussions with karsani aulia richard e bischke peter a brennan chris d connors paul w genovese tom l heidrick and elizabeth a lorenzetti provided insights into our structural interpretations and presentation of the theory seismic reflection data were provided by pt caltex pacific indonesia

thermodynamic variability within the convective boundary layer due to horizontal convective rolls abstract data from the convection and precipitation electrification cape experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer cbl potential temperature variations were only about 0 5 k while variations in water vapor mixing ratio values of 1 5 2 5 g kg 1 were observed throughout the cbl using radar aircraft and sounding data it is shown that horizontal convective rolls are the likely cause of these variabilities the enhanced moisture occurred within the roll updraft regions thus rolls were transporting moist air from the surface upward the observed cloud base heights obtained from cloud photogrammetry were produced from the highest moisture values within the roll updraft regions since the roll ascending branches contained moisture values that were most representative of the observed cloud base heights it is likely that measurements from within the roll updrafts would prov

observations of the sea breeze front during cape part i single doppler satellite and cloud photogrammetry analysis abstract an analysis of two sea breeze events on 6 august an onshore flow event and 12 august an offshore flow event 1991 is presented using single doppler observations satellite images and cloud pictures collected during the convection and precipitation electrification cape experiment documentation of the alongfrontal variability at the leading edge of the sea breeze circulation is presented for the first time the horizontal structure of the front was strongly modulated by the near perpendicular intersections of horizontal convective rolls developing in the ambient air out ahead of the sea breeze on 12 august these intersection points also appeared to be preferred locations for cloud development along the front horizontal convective rolls were also documented on 6 august however their orientation was nearly parallel to the sea breeze front as a result extended sections of these rolls appeared to have merged with the front as it propagated inland rather than having distinct intersection po

estimating the detachment depth in cross sections involving detachment folds this paper evaluates four different methods that have been proposed for the estimation of the detachment depth beneath detachment folds guidelines are presented in order to use the most suitable method in a particular region deformed by detachment folds these guidelines are constructed considering the assumptions of each method the influence of different parameters on the estimation of the detachment depth folding mechanisms cross sectional area variations position and orientation of the regional datum number of stratigraphic horizons bed length and thickness dip and position of the bounding lines initial thickness of the ductile unit single anticlines or fold trains and the available data ductile unit thickness regional datum detachment depth moreover a new simple method based on two previous methods is presented the advantages of this new method are that the calculations are extremely simple and it uses information from more than one stratigraphic horizon therefore it does not depend strongly on the accuracy of the data at one level the precision of the proposed methods is tested by their application to a number of natural and experimental single anticlines and fold trains it appears that better predictions are obtained when analysing a complete detachment fold train than when dealing with a single detachment anticline the reason might be that ductile material flow beneath the folds along the cross sectional plane is taken into account when dealing with a long enough cross section we also suggest some hypotheses concerning what the shape and dimensions of the detachment folds indicate about the detachment depth in those cases where insufficient data are available to apply the methods proposed

strain paths of three small folds from the appalachian valley and ridge maryland structural analysis indicates that for a given set of conditions subtle differences in layer configuration and rheology can result in major differences in fold kinematics we studied three hand sample scale folds from the maryland valley and ridge province in an effort to understand the accommodation of folding on meso and microscopic scales and to constrain the deformation histories of the folds sampled two single layer folds and one multilayer fold were taken from two nearby outcrops of the wills mountain anticline and are therefore interpreted to have developed under virtually identical pressure and temperature conditions although all three folds are dominated by carbonate material structural fabrics are unique for each fold indicating rheological contributions to and local structural control of fabric development both single layer folds have asymmetric vein distributions that are consistent with strain directions expected from asymmetric flexural flow slickenlines on one sample and cleavage in an adjacent layer in the other sample support this interpretation the first of these folds appears to have undergone late stage hinge tightening as evidenced by the development of crosscutting bed normal stylolites in contrast veins stylolites and the intracrystalline deformation in the multilayer fold are suggestive of symmetric tangential longitudinal strain followed by heterogeneous sub horizontal flattening the three folds are interpreted to be buckle folds with differing mechanisms accommodating strain within the competent layers

u pb geochronology of detrital zircons from a continental margin assemblage in the northern coast mountains southeastern alaska metamorphic rocks within and west of the northern coast mountains in southeastern alaska consist of an upper proterozoic to upper paleozoic continental margin assemblage that we interpret to belong to the yukon tanana terrane u pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of 495 ma 750 ma 1 05 1 40 ga 1 75 2 00 ga 2 3 ga 2 5 2 7 ga and 3 0 ga multigrain fractions from two samples yield upper intercepts between 2 0 and 2 3 ga but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of 2 3 ga grains zircons in these rocks generally overlap in age with i detrital zircons in metasedimentary rocks of the yukon tanana terrane in eastern alaska and yukon ii detrital zircons in strata of the cordilleran miogeocline and iii plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata in addition the p

episodic folding inferred from syntectonic carbonate sedimentation the santaren anticline bahamas foreland abstract sedimentation coeval with growth of the santaren anticline provides an excellent opportunity to study the relationships between sedimentation and anticline uplift through time the santaren anticline is a kilometre scale nw se trending fold offshore of cuba in the bahamas foreland of the cuban fold and thrust belt the growth strata associated with this anticline consist of a thick package of carbonate sediments that were deposited without major interruptions from neogene and perhaps before to present day the excellent seismic resolution and age control of a number of seismic horizons within the growth strata allowed us to define 25 growth beds each of them representing between 0 1 and 3 2 ma an analysis of the thickness of these beds allowed us to determine accurate quantitative values of cumulative decompacted thickness and crestal structural relief at the time of their deposition in addition for the same periods sedimentation and fold uplift rates were calculated moreover some information on relationships between sedimentation and fold uplift rates was inferred from the growth stratal geometry growth beds that overlap the fold crest and thin over it indicate that sedimentation rates outpaced fold growth rates during their deposition some overlapping beds have constant thickness indicating that no fold uplift occurred during their sedimentation the rest of the growth beds exhibit onlap offlap geometries that do not indicate a unique sedimentation fold uplift rate relationship only in those cases in which the geometry of the underlying bed at the end of its deposition is known is it possible to infer a specific sedimentation fold uplift rate relationship as a result of this analysis we have been able to 1 illustrate that the geometry of the growth strata associated with the santaren anticline results from competition between sedimentation and tectonic fold uplift 2 document the episodic and non steady nature of fold growth and 3 show that short term rates at the scale of hundreds of thousands years provide much insight into the interplay between sedimentation and tectonic fold uplift that control the growth stratal patterns

strain fabric associated with the meade thrust sheet implications for cross section balancing abstract emplacement of the meade thrust sheet southeastern idaho u s a was accompanied by the development of a strain fabric and significant footwall deformation characteristics of the strain fabric are based on strain estimates using pressure solution cleavage and deformed fossils within the jurassic twin creek formation the strain fabric formed during early layer parallel shortening at the thrust front and accommodates from 10 to 35 shortening within the incipient thrust sheet footwall strata were later folded above a detachment at the base of the twin creek formation and the early strain fabric was passively rotated the structural development of this area consisting of 1 strain fabric development 2 folding of the footwall and 3 the truncation of footwall structures by imbricates of the meade thrust are placed in a relative time frame to aid in section reconstruction the passive reorientation of the strain fabric and the truncation and incorporation of footwall structures into the thrust sheet are used as kinematic and geometric constraints for cross section balancing we present a sequential retrodeformation of the meade thrust sheet in which strain is removed from the cross section at the appropriate geometric stages in the deformation these sections illustrate some methods by which strain data can be incorporated into cross sections and also indicate the difficulty involved in balancing cross sections of internally deformed thrust sheets interpretation of these sections suggests that a significant amount of footwall deformation accompanied the emplacement of the meade thrust sheet and that footwall deformation is strongly controlled by the local stratigraphic package the sections also illustrate that the earliest deformation within a thrust sheet may be unrelated to motion on the underlying incipient thrust and that the trace of a thrust fault which cuts previously deformed strata will not restore to a typical ramp and flat geometry

synchronous extension and contraction in frontal thrust sheets of the spanish pyrenees the ainsa marine foreland basin of the southern pyrenees contains eocene deltaic and turbidite sequences that were deformed synchronously by both thrusting and extensional faulting during sedimentation two basin scale extensional truncation surfaces developed within a prograding imbricate thrust wedge in the footwall of the cotiella thrust sheet detailed mapping and analysis have shown that these features are major extensional detachment faults that produced complex sedimentological and stratal relations

predicting strain using forward modelling of restored cross sections application to rollover anticlines over listric normal faults a strategy to predict strain across geological structures based on previous techniques is modified and evaluated and a practical application is shown the technique which employs cross section restoration combined with kinematic forward modelling consists of restoring a section placing circular strain markers on different domains of the restoration and forward modelling the restored section with strain markers until the present day stage is reached the restoration algorithm employed must be also used to forward model the structure the ellipses in the forward modelled section allow determining the strain state of the structure and may indirectly predict orientation and distribution of minor structures such as small scale fractures the forward model may be frozen at different time steps different growth stages allowing prediction of both spatial and temporal variation of strain the method is evaluated through its application to two stages of a clay experiment that includes strain markers and its geometry and deformation history are well documented providing a strong control on the results to demonstrate the method s potential it is successfully applied to a depth converted seismic profile in the central sumatra basin indonesia this allowed us to gain insight into the deformation undergone by rollover anticlines over listric normal faults

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

shear instability wave along a snowband instability structure evolution and energetics derived from dual doppler radar data abstract this article presents a detailed analysis of a meso scale 17 km wavelength shear instability wave along a snowband using a series of dual doppler radar data the wave developed along a low level shear line that formed under the strain wind field caused by an adjacent mesoscale vortex the horizontal wind shear across the line was largest at lower levels and the eddy component horizontal winds and the retrieved pressure anomaly showed a bottom intensified structure as well the resultant vertical pressure gradient force was found to be responsible for the enhancement of alternating updrafts and downdrafts that were subsequently related to the formation of the reflectivity core gap structure of the wave eddy kinetic energy eke budgets of the evolving disturbance were investigated using time series of retrieved kinematic and thermodynamic data the wave grew at an approximately constant growth rate for about 40 min from its onset the eke in this quasi linear growth period was primarily gen

the estimation of diffuse strains in the toe of the western nankai accretionary prism a kinematic solution arcward changes in the vertical spacing of seismically defined stratigraphic reflectors and sediment porosities determined from drill cores and seismic interval velocities suggest a compact kinematic solution for estimating diffuse deformation within accretionary prism toes the method involves the solution of the lagrangian form of the conservation of mass equation for the two dimensional finite deformation gradient field within discrete deforming domains we apply this technique to the unfaulted protothrust zone ptz along a western transect across the nankai accretionary prism in the vicinity of deep sea drilling project sites 582 and 583 the results yield horizontal shortening estimates of about 1 7 km or about 20 this shortening appears to be accommodated through different strain responses depending on the consolidation state of the sediments at the time of accretion shallow sediments respond to horizontal shortening dominantly by expelling pore fluids producing volume strains up to 30 while deeper sediments accommodate horizontal shortening dominantly through vertical extension reaching 70 in the footwall of the frontal thrust horizontal shear strains within the ptz are not well resolved by this solution due to uncertainties in the porosity distribution but they generally appear to be quite small

the relationship between radar reflectivities and clouds associated with horizontal roll convection on 8 august 1982 abstract horizontal convective rolls hcrs and cloudstreets that occurred in northeastern colorado are studied using doppler radar data cloud photography and vertical soundings examination of the environment in which the hcrs form indicates a boundary layer wind speed that is much lower than those measured in previous studies evidence shows that the hcrs form in a well defined boundary layer yet the cloudstreets that develop seem to exist within a stable layer above a relationship between the radar reflectivity echoes and the cloudstreets is firmly established the echoes are aligned directly under the cloudstreets the echoes at lower levels are shown to be caused by convergence of particulate matter into updraft portions of the hcr circulation yet evidence indicates the cloud level echoes are due to backscatter from refractive index inhomogeneities at the surfaces of rising thermals examination of the echoes show that the strongest and tallest echoes are associated with cloud formation and tha

large eddy simulation of turbulent flow in a marine convective boundary layer with snow abstract a large eddy simulation les model with ice phase included has been used to study the marine convective boundary layer filled with snow extensions to moeng s les model include the diagnosis of cloud ice mixing ratio snow precipitation and the parameterization of detailed microphysical processes model simulations are compared with cold air outbreak field observations over lake michigan as well as with the liquid phase les results for the same atmospheric conditions the buoyancy flux and vertical velocity variance profiles generated by the ice phase les are found to be more consistent with the observations than those generated by the liquid phase les results the incorporation of the ice phase into the les model has also improved the agreement of vertical velocity skewness sw between observations and les model results it has also been found that the presence of precipitation and the associated microphysical processes has a significant effect on the structure of the convective boundary

kinematic structural restorations and discrete fracture modeling of a thrust trap a case study from the tarija basin argentina the integration between kinematic structural restorations and discrete fracture simulation is applied to a thrusted and fractured fault block in the tarija basin northern argentina the emphasis is on the influence of the factor time on the deformation history and fracture growth the structural evolution of the gas bearing santa rosa reservoir forms the basis for understanding the development of the 3d fracture system as simulated with 3d kinematic restorations during the restoration the cumulative dilatational strain was calculated and mapped and compared to traditional curvature analyses the strain maps are subsequently used to simulate geologically realistic discrete fracture networks that form the basis for further exploration and development of the field

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc