madden julian oscillation analog and intraseasonal variability in a multicloud model above the equator the madden julian oscillation mjo is the dominant component of tropical intraseasonal variability and a theory explaining its structure and successful numerical simulation remains a major challenge a successful model for the mjo should have a propagation speed of 4 7 m s predicted by theory a wavenumber 2 or 3 structure for the planetary scale low frequency envelope with distinct active and inactive phases of deep convection an intermittent turbulent chaotic multiscale structure within the planetary envelope involving embedded westward and eastward propagating deep convection events and qualitative features of the low frequency envelope from the observational record regarding e g its zonal flow structure and heating here such an mjo analog is produced by using the recent multicloud model of khouider and majda in an appropriate intraseasonal parameter regime for flows above the equator so that rotation is ignored key features of the multicloud model are i systematic low level moisture convergence with retained conservation of vertically integrated moist static energy and ii the use of three cumulus cloud types congestus stratiform and deep convective together with their differing vertical heating structures besides all of the above structure in the mjo analog waves there are accurate predictions of the phase speed from linear theory and transitions from weak regular mjo analog waves to strong multiscale mjo analog waves as climatological parameters vary with all of this structure in a simplified context these models should be useful for mjo predictability studies in a fashion akin to the lorenz 96 model for the midlatitude atmosphere

a simple multicloud parameterization for convectively coupled tropical waves part i linear analysis abstract recent observational analysis reveals the central role of three multicloud types congestus stratiform and deep convective cumulus clouds in the dynamics of large scale convectively coupled kelvin waves westward propagating two day waves and the madden julian oscillation a systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds a systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation a nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere in particular a dry troposphere

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

a reexamination of the jordan mean tropical sounding based on awareness of the saharan air layer results from 2002 abstract the jordan mean tropical sounding has provided a benchmark for representing the climatology of the tropical north atlantic and caribbean sea since 1958 however recent studies of the saharan air layer sal have suggested that the tropical atmosphere in these oceanic regions may contain two distinct soundings sal and non sal with differing thermodynamic and kinematic structures and that a single mean sounding like jordan s does not effectively represent these differences this work addresses this possibility by examining over 750 rawinsondes from the tropical north atlantic ocean and caribbean sea during the 2002 hurricane season it was found that a two peak bimodal moisture distribution dry sal and moist non sal exists in this region and that the jordan sounding does not represent either distribution particularly well additionally sal soundings exhibited higher values of geopotential height unique temperature profiles and stronger winds with an enhanced easterly component compared to

momentum and mass transport by convective bands comparisons of highly idealized dynamical models to observations the importance of the vertical transport of horizontal momentum by convective clouds has been documented in studies of momentum budgets e g shapiro and stevens 1980 sui and yanai 1986 furthermore it is obvious that the boundary layer wind itself and hence surface heat moisture and momentum transports is affected by deep convection most of the airsea transfer in tropics is concentrated in regions with deep convection

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

convective momentum transport in a simple multicloud model for organized convection abstractconvective momentum transport cmt is the process of vertical transport of horizontal momentum by convection onto the environmental flow the significance of cmt from mesoscale to synoptic and planetary scale organized cumulus convection has been established by various theoretical and observational studies a new strategy mimicking the effect of unresolved mesoscale circulation based on the weak temperature gradient wtg approximation with a gaussian profile to redistribute the heating due to parameterized cumulus convection at the subgrid scale is adopted here to construct a cmt parameterization for general circulation models gcms two main regimes of cmt are considered an upscale squall line regime and a downscale non squall line regime an exponential probability distribution is used to select which of these two effects is active conditional on the state of the large scale shear the shear itself is used as a measure of the persistence of mesoscale organized circulation due to the presen

collective effects of organized convection and their approximation in general circulation models abstract the collective effects of organized convection the environment were estimated using a two dimensional two way nested cloud resolving numerical model with a large outer domain 4500 km as initial conditions the authors used an idealized environment of the onset stage of the december 1992 westerly wind burst that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment two key aspects relating to convective parameterization were examined first the transports sources and sinks of heat moisture and momentum were derived using the model produced dataset in particular the total momentum flux compares well with moncrieff s dynamical theory second the bulk energetics of the cloud system were examined using the model produced dataset the authors found that the shear generation of kinetic energy is comparable to the buoyancy generation and dominates the sum of the buoyancy and water loading generation this means that in addition to the thermodynam

realistic initiation and dynamics of the madden julian oscillation in a coarse resolution aquaplanet gcm 1 the main mechanisms for the initiation and propagation of the madden julian oscillation mjo are still widely debated the capacity of operational global climate models gcms to correctly simulate the mjo is hindered by the inadequacy of the underlying cumulus parameterizations here we show that a coarse resolution gcm coupled to a simple multicloud model parameterization mimicking the observed dynamics and physical structure of organized tropical convection simulates the mjo in an idealized setting of an aquaplanet without ocean dynamics we impose a fixed nonhomogeneous sea surface temperature replicating the indian ocean western pacific warm pool this results in a succession of mjos with realistic phase speed amplitude and physical structure each mjo event is initiated at a somewhat random location over the warm pool and dies sometimes near the eastern boundary of the warm pool and sometimes at a random location way beyond the warm pool also occasionally the mjo events stall at the center of maximum heating this is reminiscent of the fact that in nature some mjos stall over the maritime continent while others reach the central pacific ocean and beyond the initiation mechanism in the model is believed to be a combination of persistent intermittent convective events interacting with observed large scale flow patterns and internal tropical dynamics the large scale flow patterns are associated with planetary scale dry kelvin waves that are triggered by preceding mjo events and circle the globe while congestus cloud decks on the flanks of the warm pool are believed to force rossby gyres which then funnel moisture toward the equatorial region

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

relating relative hydraulic and electrical conductivity in the unsaturated zone numerical modeling was used to generate pore scale structures with different structural properties they were partially saturated according to wetting and drainage regimes using morphological operations for a range of saturations the hydraulic and electrical conductivities of the resulting partially saturated grain packs were numerically computed to produce relative hydraulic conductivity versus saturation and relative electrical conductivity versus saturation curves the relative hydraulic conductivities were then compared to the relative electrical conductivities for the same saturations and it was found that relative hydraulic conductivity could be expressed as relative electrical conductivity to a power law exponent this exponent was not correlated to porosity specific surface area or tortuosity it did change according to whether the soil was wetting or draining however a value of 2 1 reproduced relative hydraulic conductivity from relative electrical conductivity with little added error the effects of surface conduction on the observed power law relationship due to either low fluid electrical conductivity or increased clay content were analyzed the relationship was found to hold for fluid conductivities typical of groundwater and for clay content of less than 5 if the clays were layered perpendicular to electrical flow the relationship breaks down for electrical flow parallel to clay layers which makes the choice of electrode arrangement important in cases where clay may be present this relationship can be used with secondary pressure or saturation data to characterize a soil s hydraulic conductivity curve

chronosequence development and soil variability from a variety of sub alpine post glacial landforms and deposits in the southeastern san juan mountains of colorado abstract surficial processes acting on post glacial alpine and sub alpine landscapes vary at small temporal and spatial scales and are thus often difficult to conceptualize in the context of large scale landscape evolution models soils developing in this setting can thus provide valuable information about landform genesis sedimentology and age relatively few post glacial chronosequences have been examined in these settings however particularly for the variety of landforms and parent materials that exist within alpine and sub alpine environments here we examine a chronosequence of relatively young post glacial landforms with varying parent materials and climate histories we dug and described 39 soil pits in the upper conejos river valley of colorado on a variety of deposits and landforms including alluvial fans terraces colluvium glacial till and terminal moraines and compared soil properties with radiocarbon ages from the area our results suggest that some typical chronosequence soil properties e g ph structure color do not correlate with time over short time scales however extractable iron ratios feo fed show a relatively strong correlation with age across late pleistocene and holocene time scales and maximum profile clay content shows a weak but statistically significant relationship with age both of these trends are stronger when examined across a single parent material differences in initial parent material texture and dust inputs seem to be the most significant complicating factors over post glacial time scales soil property development through time is most inconsistent in cumulic alluvial fan soils this observation may indicate that alluvial fans are more responsive to sub basin scale processes as opposed to fluvial terraces that are more likely respond to processes active across the entire basin these differences would explain why stratigraphically similar alluvial fans are mantled by soils with varying development nonetheless horizonation clay content and extractable iron ratios provide a useful tool for correlating young deposits assigning ages and interpreting the geomorphic history of complex post glacial environments

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

synoptic scale dual structure of precipitable water along the eastern pacific itcz abstractusing 10 yr high resolution satellite and reanalysis data the synoptic scale dual structure of precipitable water pw in which the southern and northern bands straddled at the itcz produce zonally propagating meridional dipoles is observed over the eastern pacific ep during boreal summer and fall composites indicate that the pw dipole concurrent with the dipole like filtered divergence has a shift to the west of the anomalously cyclonic circulation the vertical structure of filtered meridional wind is characterized by a wavenumber 1 baroclinic mode and the vertical motion has two peaks situated at 850 and 300 hpa respectively to the east of the pw dipole the shallow convection is embedded within the deep convection forming a multilevel structure of meridional wind on the itcz equatorward side to the west of the pw dipole the deep convection tends to be suppressed because of the invasion of midlevel dry air advected by northerly flows the generation and propagation of the dual pw

stochastic models for convective momentum transport the improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long range ensemble forecasting of weather and short term climate change observations theory and detailed smaller scale numerical simulations suggest that convective momentum transport cmt from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models here a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of cmt on the large scales due to organized unresolved convection from squall lines properties of the stochastic model for cmt are developed below in a test column model environment for the large scale variables the effects of cmt from the stochastic model on a large scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem here the upscale transports from stochastic effects are significant and even generate a large scale mean flow which can interact with the convectively coupled wave

simulation of monsoon intraseasonal oscillations in a coarse resolution aquaplanet gcm the skill of the global climate models gcms to realistically simulate the monsoon intraseasonal oscillations misos is related to the sensitivity of their convective parameterization schemes here we show that by coupling a simple multicloud parameterization to a coarse resolution aquaplanet gcm realistic misos can be simulated we conduct three different simulations with a fixed nonhomogeneous sea surface temperature mimicking the indian ocean western pacific warm pool wp centered at the three latitudes 5 n 10 n and 15 n respectively to replicate the seasonal migration of the tropical convergence zone tcz this results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer succession of eastward propagating madden julian oscillation mjo disturbances with phase speed amplitude and structure similar to summer mjos are simulated when the wp is at 5 n when the wp is located over 10 n northward and eastward propagating misos are simulated this case captures the meridional seesaw of convection between continental and oceanic tcz observed during boreal summer over south asia westward propagating rossby wave like disturbances are simulated when the wp is over 15 n congruous with the synoptic disturbances seen over the monsoon trough the initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the wp associated with internal dynamics

multiscale waves in an mjo background and convective momentum transport feedback abstractthe authors use linear analysis for a simple model to study the evolution of convectively coupled waves ccws in a background shear and background moisture mimicking the observed structure of the madden julian oscillation mjo this is motivated by the observation in an idealized setting of intraseasonal two way interactions between ccws and a background wind it is found here that profiles with a bottom heavy moisture content are more favorable to the development of mesoscale squall line like waves whereas synoptic scale ccws are typically more sensitive to the shear strength the mjo envelope is thus divided into three regions in terms of the types of ccws that are favored an onset region in front that is favorable to kelvin waves a mature or active region in the middle in which squall lines are prominent and the stratiform and decay phase region in the back that is favorable to westward inertia gravity wig waves a plausible convective momentum transport cmt feedback is then provide

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

improved extraction of hydrologic information from geophysical data through coupled hydrogeophysical inversion 1 there is increasing interest in the use of multiple measurement types including indirect geophysical methods to constrain hydrologic interpretations to date most examples integrating geophysical measurements in hydrology have followed a three step uncoupled inverse approach this approach begins with independent geophysical inversion to infer the spatial and or temporal distribution of a geophysical property e g electrical conductivity the geophysical property is then converted to a hydrologic property e g water content through a petrophysical relation the inferred hydrologic property is then used either independently or together with direct hydrologic observations to constrain a hydrologic inversion we present an alternative approach coupled inversion which relies on direct coupling of hydrologic models and geophysical models during inversion we compare the abilities of coupled and uncoupled inversion using a synthetic example where surface based electrical conductivity surveys are used to monitor one dimensional infiltration and redistribution through this illustrative example we show that the coupled approach can provide significant reductions in uncertainty for hydrologic properties and associated predictions if the underlying model is a faithful representation of the hydrologic processes however if the hydrologic model exhibits structural errors the coupled inversion may not improve the hydrologic interpretation despite this limitation our results support the use of coupled hydrogeophysical inversion both for the direct benefits of reduced errors during inversion and because of the secondary benefits that accrue because of the extensive communication and sharing of data necessary to produce a coupled model which will likely lead to more thoughtful use of geophysical data in hydrologic studies

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

organized convection parameterization for the itcz abstractmesoscale convective systems mcss are of fundamental importance in the dynamics of the atmospheric circulation and the climate system they are often observed to develop over significant terrain in ambient shear flows in midlatitudes and embedded within the madden julian oscillation mjo and convectively coupled equatorial wave ccew envelopes as well as in the intertropical convergence zone itcz yet general circulation models gcms fail to resolve these systems and their underlying convective parameterizations are not directed to represent organized circulations shear parallel mcss which are common in the itcz have a three dimensional structure and as such present a serious modeling challenge here a previously developed multicloud model mcm is modified to parameterize mcss one of the main modifications is the parameterization of stratiform condensation to capture extended stratiform outflows which characterize mcss resulting from strong upper level jets linear analysis show

structures and dynamics of quasi 2d mesoscale convective systems abstract recently three distinct archetypes for midlatitude linear mesoscale convective systems mcss have been identified this article focuses on the fundamentals of two of these archetypes convective lines with trailing stratiform ts precipitation and convective lines with leading stratiform ls precipitation both the ts and ls modes typically exhibit quasi 2d reflectivity patterns and quasi 2d environmental storm relative wind fields ongoing work has revealed that there are three common flow structures for these quasi 2d mcss front fed ts systems which are sustained by front to rear storm relative inflow as well as front fed ls and rear fed ls systems which are sustained by rear to front storm relative inflow this paper summarizes the observed structures of the front fed ts front fed ls and rear fed ls modes and then outlines an idealized numerical experiment in which these modes were simulated the authors analyze the basic simulated kinematic and microphysical structures and provid

multicloud models for organized tropical convection enhanced congestus heating abstract despite the recent advances in supercomputing the current general circulation models gcms poorly represent the large scale variability associated with tropical convection multicloud model convective parameterizations based on three cloud types congestus deep and stratiform introduced recently by the authors have been revealed to be very useful in representing key features of organized convection and convectively coupled waves here a new systematic version of the multicloud models is developed with separate upper and lower troposphere basis functions for the congestus and stratiform clouds it naturally leads to a new convective closure for the multicloud models enhancing the congestus heating in order to better pinpoint the congestus preconditioning and moistening mechanisms the models are studied here for flows above the equator without rotation effects first the new model results consist of the usual synoptic scale convectively coupled moist gravity wave packets moving at 15 20 m

coupling of convective momentum transport with convective heating in global climate simulations abstract the effects of convective momentum transport cmt on global climate simulations are examined in this study comparison between two sets of 20 yr 1979 98 integration using the ncar community climate model version 3 ccm3 illustrates that the inclusion of cmt in the convection scheme systematically modifies the climate mean state over the equatorial region the convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection this reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the hadley circulation the major heating peak during the boreal winter is moved to south of the equator at about 10 s which is closer to the heat budget residuals of the ecmwf reanalysis data the responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone

the mjo and convectively coupled waves in a coarse resolution gcm with a simple multicloud parameterization abstract the adequate representation of the dominant intraseasonal and synoptic scale variability in the tropics characterized by the madden julian oscillation mjo and convectively coupled waves is still problematic in current operational general circulation models gcms here results are presented using the next generation ncar gcm the high order methods modeling environment homme as a dry dynamical core at a coarse resolution of about 167 km coupled to a simple multicloud parameterization the coupling is performed through a judicious choice of heating vertical profiles for the three cloud types congestus deep and stratiform that characterize organized tropical convection important control parameters that affect the types of waves that emerge are the background vertical gradient of the moisture and the stratiform fraction in the multicloud parameterization which set the strength of large scale moisture convergence and unsaturated downdrafts in the wake of deep convection respectively three

the mjo in a coarse resolution gcm with a stochastic multicloud parameterization abstractthe representation of the madden julian oscillation mjo is still a challenge for numerical weather prediction and general circulation models gcms because of the inadequate treatment of convection and the associated interactions across scales by the underlying cumulus parameterizations one new promising direction is the use of the stochastic multicloud model smcm that has been designed specifically to capture the missing variability due to unresolved processes of convection and their impact on the large scale flow the smcm specifically models the area fractions of the three cloud types congestus deep and stratiform that characterize organized convective systems on all scales the smcm captures the stochastic behavior of these three cloud types via a judiciously constructed markov birth death process using a particle interacting lattice model the smcm has been successfully applied for convectively coupled waves in a simplified primitive equation model and validated against radar data of

characterization of momentum transport associated with organized moist convection and gravity waves abstract tropical convection is inherently multiscalar involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters in addition to being a crucial component of the atmospheric water cycle and the global heat budget tropical convection induces vertical fluxes of horizontal momentum there are two main contributions to the momentum transport the first resides entirely in the troposphere and is due to ascent descent and organized circulations associated with precipitating convective systems the second resides in the troposphere stratosphere and farther aloft and is caused by vertically propagating gravity waves both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models yet in existing parameterizations these two processes are treated independently this paper examines the relationship between the convective momentum transport and