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

transport processes in the tropical warm pool boundary layer part ii vertical structure and variability abstract the structure of the intertropical convergence zone itcz cloud topped marine atmospheric boundary layer away from the most intense mesoscale convective systems during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare is investigated eight vertical profiles taken by the australian cessna research aircraft are analyzed representing the successive influence of a growing small cluster of precipitating cumulus upon the subcloud layer on the basis of conclusions from a spectral analysis in part i of this study results are partitioned into contributions from three distinct categories a small scale 2 km processes corresponding to meso scale motions associated mainly with the action of precipitating cumulus clouds and larger motions and c extreme processes corresponding to contributions from e

long lived mesoscale systems in a low convective inhibition environment part i upshear propagation abstractpart ii of this study of long lived convective systems in a tropical environment focuses on forward tilted downshear propagating systems that emerge spontaneously from idealized numerical simulations these systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward tilted circulation with a trailing stratiform region an overturning updraft and a mesoscale downdraft in contrast to this standard mesoscale system the downshear propagating system considered here does not feature a mesoscale downdraft and although there is a cold pool it is of secondary importance to the propagation and maintenance of the system the mesoscale downdraft is replaced by hydraulic jump like ascent beneath an elevated forward tilted overturning updraft with negligible convective available potential energy therefore the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from

a momentum budget analysis of westerly wind events associated with the madden julian oscillation during dynamo abstractthe dynamics of the madden julian oscillation dynamo field campaign was conducted over the indian ocean io from october 2011 to february 2012 to investigate the initiation of the madden julian oscillation mjo three mjos accompanying westerly wind events wwes occurred in late october late november and late december 2011 momentum budget analysis is conducted to understand the contributions of the dynamical processes involved in the wind evolution associated with the mjo over the io during dynamo using european centre for medium range weather forecasts analysis this analysis shows that westerly acceleration at lower levels associated with the mjo active phase generally appears to be maintained by the pressure gradient force pgf which could be partly canceled by meridional advection of the zonal wind westerly acceleration in the midtroposphere tends to be mostly attributable to vertical advection the results herein imply that there is no simple linear dynamic model that can capture t

a multiscale model for tropical intraseasonal oscillations the tropical intraseasonal 40 to 50 day oscillation tio is the dominant component of variability in the tropical atmosphere with remarkable planetary scale circulation generated as envelopes of complex multiscale processes a new multiscale model is developed here that clearly demonstrates the fashion in which planetary scale circulations sharing many features in common with the observational record for the tio are generated on intraseasonal time scales through the upscale transfer of kinetic and thermal energy generated by wave trains of organized synoptic scale circulations having features in common with observed superclusters the appeal of the multiscale models developed below is their firm mathematical underpinnings simplicity and analytic tractability while remaining self consistent with key features of the observational record the results below demonstrate in a transparent fashion the central role of organized vertically tilted synoptic scale circulations in generating a planetary circulation resembling the tio

a new multiscale model for the madden julian oscillation abstract a multiscale model of the mjo is developed here that accounts in a simplified fashion for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic scale circulations in a moving convective envelope as well as direct mean heating on planetary scales this model involves idealized thermally driven congestus synoptic scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope the model self consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the mjo including the vertical structure in both the westerly onset region and the strong westerly wind burst region as well as the horizontal quadrupole planetary vortex structure the westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transpor

simulations of the west african monsoon with a superparameterized climate model part ii african easterly waves abstractthe relationship between african easterly waves and convection is examined in two coupled general circulation models the community climate system model ccsm and the superparameterized ccsm sp ccsm in the ccsm the easterly waves are much weaker than observed in the sp ccsm a two dimensional cloud resolving model replaces the conventional cloud parameterizations of ccsm results show that this allows for the simulation of easterly waves with realistic horizontal and vertical structures although the model exaggerates the intensity of easterly wave activity over west africa the simulated waves of sp ccsm are generated in east africa and propagate westward at similar although slightly slower phase speeds to observations the vertical structure of the waves resembles the first baroclinic mode the coupling of the waves with convection is realistic evidence is provided herein that the diabatic heating associated with deep convection provides energy to the waves simulated in sp ccsm in co

calculating surface water pco2 from foraminiferal organic δ13c abstract the 13c of organic matter bound within the crystal lattice of foraminiferal calcite tests may provide a potential tracer of the isotopic composition of the surface water primary photosynthate using 13c of the organic matter extracted from the crystal lattice and the calcite test it is theoretically possible to estimate the paleo surface water pco2 we have tailored this technique initially for the subpolar planktonic foraminifera species globigerina bulloides initial surface water pco2 estimates from deep sea core bofs 5k 50 41 3 n 21 51 9 w water depth 3547 m indicate that the northeast atlantic ocean may have been a greater sink for co2 during the last glacial than during the holocene greatly reduced benthic foraminifera abundances especially phytodetritus feeders in bofs 5k during the last glacial indicates low surface productivity this rules out a productivity driven co2 sink the enhanced glacial co2 sink must therefore have results from a southwards shift of the centre of deep water formation

shear parallel moist convection over the tropical ocean a case study from 18 february 1993 toga coare abstract this paper describes a newly observed form of shear parallel rainbands that were observed on 18 february 1993 in tropical ocean global atmosphere coupled ocean atmosphere response experiment using the ncar eldora airborne doppler radar interesting features of these rainbands included their rapidly changing and highly cellular nature their complicated and layered kinematic structure and the effects of the rainbands on the tropical environment in their lower levels the rainbands consisted of east west elongated clusters of small convective cells aligned with the z 0 5 km shear vector strong low level convergence inflow from the north and enhanced westerly winds extended from the surface up to 5 km much of this air was vented out of the storm at midlevels exiting to the north in the 0 c stable layer at z 5 7 km this midlevel outflow fed an area of widespread stratiform precipitation lying to the north of the rainband the cold pool outflow emanating from this area of precipitation t

an ensemble of convective systems on 11 february 1993 during toga coare morphology rainfall characteristics and anvil cloud interactions abstract an active day during the coupled ocean atmosphere response experiment coare intensive observation period iop is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the intensive flux array ifa within westerly wind burst conditions the detailed genesis morphology and interactions between these cloud systems are documented from a radar and satellite perspective one of these systems was a large and complex elliptical cluster among the largest observed during the tropical ocean global atmosphere coare multiple parallel deep convective lines spaced 20 30 km apart and embedded within this system were initially oriented from north northwest to south southeast oblique to the storm motion furthermore the lines underwent counterclockwise realignment as the system moved eastward the influence of strong lower tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic

western pacific warm pool region sensitivity to convective triggering byboundary layer thermals in the nogaps atmospheric gcm the sensitivity of the atmospheric general circulation model of the navy operational global atmospheric prediction system to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated the study focuses on the western pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987 88 a parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer surface based deep convection is allowed only for boundary layer regimes associated with the presence of thermals the regime classification is expressed in terms of a richardson number that reflects the relative significance of buoyancy and shear in the boundary layer by constraining deep convection to conditions consistent with the occurrence of thermals high buoyancy to shear ratios there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical pacific and along the itcz this decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the pacific warm pool improvements in the simulated distribution of precipitation precipitable water and low level winds in the tropical pacific are demonstrated over the western pacific the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed low level winds thus play the major role in regulating the ability of thermals to initiate deep convection the lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard

the oceanic mesoscale convective system and associated mesovortex observed 12 december 1992 during toga coare this study documents the precipitation and kinematic structure of a mature mature to decaying westward propagating near equatorial oceanic mesoscale convective system mcs observed by airborne doppler radars during toga coare the tropical ocean global atmosphere coupled ocean atmosphere response experiment this system occurred on 12 december 1992 during the convectively active phase of an intraseasonal oscillation and was followed at its dissipating stage by a redevelopment of convection that led to the mcs observed on 13 december 1992 these two successive mcss were associated with a two day atmospheric disturbance radar deduced airflows at two time periods reveal many similarities with other tropical oceanic cloud clusters in particular a marked rear inflow jet associated with a midlevel cyclonic mesovortex was observed within the rear of the stratiform region the mesovortex was better defined both in size and depth during the mature to decaying stage and was located more inside the system within a region of convergence due to the westward propagation of the rear inflow countergradient transports of momentum normal to the mean orientation of the system at midlevels and downgradient transports at lower and higher levels helped to intensify this rear inflow these transports were mostly accomplished by eddy structures cyclonic vorticity was concentrated at the rear of the mcs and peaked at the centre of the observed closed wind circulation as previously observed stretching of the pre existing vertical vorticity was the dominant dynamical mechanism which helped to amplify the mesovortex at mid to upper levels while tilting of the horizontal vorticity into the vertical was a lesser mechanism and had an opposite effect in most respects advective processes were negatively correlated with the stretching and tilting mechanisms but not sufficiently to be balanced the resulting tendency was an increase of cyclonic vorticity at low to mid levels and a net decrease above

impact of explicit atmosphere ocean coupling on mjo like coherent structures in idealized aquaplanet simulations this paper discusses the impact of the atmosphere ocean coupling on the large scale organization of tropical convection simulated by an idealized global model applying the cloud resolving convection parameterization crcp superparameterization because the organization resembles the madden julian oscillation mjo the results contribute to the debate concerning the role of atmosphere ocean coupling in tropical intraseasonal oscillations the modeling setup is an aquaplanet with globally uniform mean sea surface temperature sst of 30 c tropics everywhere in radiative convective quasi equilibrium the simulations apply an interactive radiation transfer model and a slab ocean model with a fixed oceanic mixed layer depth results from several 80and 100 day long simulations are discussed where the only difference between the simulations is the prescribed oceanic mixed layer depth which varied from 5 to 45 m a simulation with a very deep oceanic mixed layer is also performed to represent constant sst conditions the simulations demonstrate that the interactive sst impedes the development of large scale organization and has insignificant impact on the dynamics of mature mjo like systems the impediment is the result of a negative feedback between the large scale organization of convection and sst the convection sst feedback in this feedback sst increases in regions of already suppressed convection and decreases in regions with enhanced convection thus hindering the large scale organization once developed however the mjo like systems are equally strong in interactive and constant sst simulations and compare favorably with the observed mjo the above impacts of the atmosphere ocean coupling contradict the majority of previous studies using traditional general circulation models where typically an enhancement of the intraseasonal signal occurs compared to prescribed sst simulations an explanation of this discrepancy is suggested

the dynamic and thermodynamic structure of the monsoon over southern india new observations from the incompass iop some of the highest summer monsoon rainfall in south asia falls on the windward slopes of the western ghats mountains on india s west coast and offshore over the eastern arabian sea understanding of the processes determining the spatial distribution and temporal variability of this region remains incomplete in this paper new interaction of convective organization and monsoon precipitation atmosphere surface and sea incompass aircraft and ground based measurements of the summer monsoon over the western ghats and upstream of them are presented and placed within the context of remote sensing observations and reanalysis the transition from widespread rainfall over the eastern arabian sea to rainfall over the western ghats is documented in high spatial and temporal resolution heavy rainfall offshore during the campaign was associated primarily with mid tropospheric humidity secondarily with sea surface temperature and only weakly with orographic blocking a mid tropospheric dry intrusion suppressed deep convection offshore in the latter half of the campaign allowing the build up of low level humidity in the onshore flow and enhancing rainfall over the mountains rainfall on the lee side of the western ghats occurred during the latter half of the campaign in association with enhanced mesoscale easterly upslope flow diurnal cycles in rainfall offshore maximum in the morning and on the mountains maximum in the afternoon were observed considerable zonal and temporal variability was seen in the offshore boundary layer suggesting the presence of convective downdrafts and cold pools persistent drying of the subcloud mixed layer several hundred kilometres off the coast was observed suggesting strong mixing between the boundary layer and the free troposphere these observations provide quantitative targets to test models and suggest hypotheses on the physical mechanisms determining the distribution and variability in rainfall in the western ghats region

the precipitating cloud population of the madden julian oscillation over the indian and west pacific oceans 1 the variability of the precipitating cloud population of the madden julian oscillation mjo is represented by statistics of echo features seen by the tropical rainfall measuring mission s precipitation radar over the central indian and west pacific oceans echo features include isolated shallow echoes deep convective cores wide convective cores and broad stratiform regions isolated shallow echoes are ever present but most numerous during suppressed mjo phases broad stratiform regions dominate variability in areal coverage and maximize during active phases deep convective and wide convective cores are more common and variable in number than broad stratiform regions the magnitude of variability is similar in both regions in the central indian ocean active mjo phases have synchronous maximization of deep convective entities in the west pacific broad stratiform regions maximize prior to wide convective cores reanalysis indicates that isolated shallow echoes are most numerous in dry mid tropospheric conditions and strong low level 1000 750 hpa shear mid tropospheric moisture increases before deeper convective features increase in number maximizes as deep convective features maximize and decreases as wide convective cores and broad stratiform regions decline in population active stage deep and wide convective cores occur preferentially with moist mid tropospheric conditions and strong low level shear acute shear may favor downdraft momentum transport and consequently more robust gust front convective triggering broad stratiform regions maximize with a moist mid troposphere strong low level shear and moderate upper level 750 500 hpa shear that is not so strong that the stratiform region disconnects from its convective moisture source

the vertical structure of toga coare convection part i radar echo distributions radar data collected by the 5 cm mit radar which was deployed aboard the r v vickers during the intensive observing period of the tropical ocean global atmosphere coupled ocean atmosphere response experiment are partitioned into convective and stratiform cartesian grid columns the vertical structure of convective echo is examined through the use of two variables echo top height and the height of the 30 dbz reflectivity contour the first of these variables has traditionally been used to describe the vertical structure characteristics of convection and the second has recently been linked to internal microphysical properties and lightning histograms of the relative frequency of convective only echo top heights and 30 dbz contour heights were constructed for the three cruises of the vickers with each cruise experiencing different phases of the intraseasonal oscillation iso cruise 1 which was dominated by the convectively inactive phase of the iso was characterized by the highest frequency of shallow convection based on echo top heights whereas cruise 2 which was dominated by a particularly well defined passage of the convective phase of the iso exhibited the tallest echo top heights cruise 3 convection was influenced by moderate westerly surface winds characteristic of postwesterly wind burst conditions and convection was of intermediate height when viewed as a function of internal vertical structure i e 30 db z contour height the frequency distributions vary less from cruise to cruise with cruises 1 and 2 having nearly identical distributions of convective 30 dbz contour heights furthermore when the contribution to convective rainfall is examined as a function of 30 dbz contour height it is seen that relatively more rain fell from vertically intense convection i e convection with tall 30 dbz contours during cruises 1 and 3 than during cruise 2 instantaneous correlations between rainfall rate and radar echo height were highly scattered about a mean value of about 0 55 whereas rainfall rate and 30 dbz contour height correlations peaked at about 0 8 and exhibited much less scatter

diurnally modulated cumulus moistening in the preonset stage of the madden julian oscillation during dynamo abstractatmospheric soundings radar and air sea flux measurements collected during dynamics of the madden julian oscillation dynamo are employed to study mjo convective onset i e the transition from shallow to deep convection in the tropical indian ocean the findings indicate that moistening of the low midtroposphere during the preonset stage of the mjo is achieved by simultaneous changes in the convective cloud population and large scale circulation namely cumuliform clouds deepen and grow in areal coverage as the drying by large scale subsidence and horizontal westerly advection wane the reduction of large scale subsidence is tied to the reduction of column radiative cooling during the preonset stage which ultimately links back to the evolving cloud population while net column moistening in the preonset stage is tied to large scale circulation changes a new finding of this study is the high degree to which the locally driven diurnal cycle invigorates convective clouds and cumulus moiste

the oceanic mesoscale convective system observed with airborne doppler radars on 9 february 1993 during toga coare structure evolution and budgets data collected on 9 february 1993 during the tropical ocean and global atmosphere programme coupled ocean atmosphere response experiment toga coare with the doppler radars on board the two national oceanic and atmospheric administration wp 3d and the national center for atmospheric research electra aircraft are analysed to study the structure and evolution of an equatorial oceanic mesoscale convective system mcs observations lasted more than five hours a period during which the cloud cluster characteristics changed from convective to stratiform this mesoscale system was approximately aligned along the tropospheric wind shear but it was nearly perpendicular to the low level shear series of three dimensional fields of reflectivity air velocity components retrieved pressure and temperature perturbations show similarities with previously observed convective systems over the tropical oceans in particular although the cloud top reached 18 km altitude relatively weak vertical motions and temperature perturbations resulted from a moderate convective instability in the low levels a cold front to rear flow intensified and deepened as the overall structure evolved from convective to stratiform the vertical profiles of mean horizontal divergence evolved from low level convergence in the cross line direction for the earliest analyses to mid level convergence from all directions during the later stratiform phase vertical momentum fluxes were important and led to an increase in the cross line wind shear and a decrease in the along line one analysis of radiosounding data from the nearest stations of the toga coare array shows that the period during which airborne doppler observations were conducted was characterized by relatively strong large scale ascent and apparent sources of heat moisture and momentum these diagnosed values and the mean radarderived ones agree fairly well this shows that the early convective and late stratiform phases of the mcs are equally important for the apparent sources of heat and momentum

water s two height scales the moist adiabat and the radiative troposphere summary the temperature structure of the tropical troposphere resembles a moist adiabat with a lapse rate transition toward dry adiabatic where water becomes scarce at an altitude hma n 8 km 350 hpa infrared emission by water vapour cools a deeper layer extending up to hd 14 km 160 ma five consequences of these unequal heights are reviewed 1 upper tropospheric relative humidity is often low highly variable and bimodal due to the rapidity of drying by radiative subsidence 2 large scale divergent circulations e g equatorial u wind exhibit a two celled vertical structure with an elevated convergence layer near 8 10 km in the rising branch 3 the dominant deep convective heating process changes from latent heating at low levels to eddy heat flux convergence in the upper troposphere this requires a substantial updraught environment temperature difference which leads to large entrainment near hma yielding stratiform anvil clouds which also contribute radiative heating 4 the rising branches of deep hd vertical circulations export more heat than they import as moisture so that large scale tropical dynamics can be characterized by a gross moist stability 5 divergent motions with a vertical wavelength 8 km corresponding to kelvin or gravity wave speeds of 15 m s are excited by simple e g uniform heating profiles extending through the lapse rate change near hma

the madden julian oscillation recorded in early observations from the tropical rainfall measuring mission trmm a satellite data analysis is performed to explore the madden julian oscillation mjo focusing on the potential roles of the equatorial rossby er and kelvin waves measurements from the tropical rainfall measuring mission trmm precipitation radar pr and visible infrared scanner virs are analyzed in the frequency wavenumber domain to identify and ultimately filter primary low frequency modes in the tropics the space time spectrum of deep storm fraction estimated by pr and virs exhibits notable kelvin wave signals at wavenumbers 5 8 a distinct mjo peak at wavenumbers 1 7 and periods of about 40 days and a signal corresponding to the er wave these modes are separately filtered to study the individual modes and possible relationship among them in the time longitude space in 10 cases analyzed here an mjo event is often collocated with a group of consecutive kelvin waves as well as an intruding er wave accompanied with the occasional onset of a stationary convective phase the spatial and temporal relationship between the mjo and kelvin wave is clearly visible in a lag composite diagram while the ubiquity of the er wave leads to a less pronounced relation between the mjo and er wave a case study based on the geostationary meteorological satellite gms imagery together with associated dynamic field captures the substructure of the planetary scale waves a cross correlation analysis confirms the mjo related cycle that involves surface and atmospheric parameters such as sea surface temperature water vapor low clouds shallow convection and near surface wind as proposed in past studies the findings suggest the possibility that a sequence of convective events coupled with the linear waves may play a critical role in mjo propagation an intraseasonal radiative hydrological cycle inherent in the local thermodynamic conditions could be also a potential factor responsible for the mjo by loosely modulating the envelope of the entire propagation system

convective organization in evolving large scale forcing represented by a highly truncated numerical archetype abstractconsidered as a prognostic generalization of mass flux based convection parameterization the highly truncated nonhydrostatic anelastic model with segmentally constant approximation nam sca is tested with time evolving large scale forcing the 20 day gate phase iii period is taken as a major data source the main advantage of the nam sca parameterization is consistency with subgrid scale dynamics as represented by the nonhydrostatic anelastic formulation the approach explicitly generates important dynamical structures of convection e g mesoscale circulations cold pools spontaneously without further tuning or treatment as additional subcomponents as with other convection parameterizations the numerical simulation of the precipitation rate the apparent heat source and the apparent moisture sink is straightforward and reasonably insensitive to the numerical procedures however convective momentum transport by organized convection turns out to be difficult even with nam sca especially fo

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

westerly wind bursts and their relationship with intraseasonal variations and enso part ii energetics over the western and central pacific abstract the mechanism of synoptic scale eddy development in the generation of westerly wind bursts wwbs over the western central pacific and their relationship with the el nino southern oscillation enso and the madden julian oscillation mjo were examined in the wwb occurrences barotropic structures of equatorial eddy westerlies with cyclonic disturbances were found from the surface to the upper troposphere the dominant contributions to substantial eddy kinetic energy eke were the barotropic energy conversion kmke in the lower and middle tropospheres and the conversion from eddy available potential energy peke in the upper troposphere low frequency environmental westerlies centered near the equator preceded strong zonal convergence and meridional shear resulting in the substantial kmke the activation of synoptic convection also contributed to an increase in eke through peke these energies were redistributed to the lower equatorial troposphere through energy flux convergence gke the

momentum transport processes in the stratiform regions of mesoscale convective systems over the western pacific warm pool summary momentum transport by the stratiform components of mesoscale convective systems mcss during the tropical ocean global atmosphere coupled ocean atmosphere response experiment in december 1992 is investigated using a cloud resolving model the mesoscale momentum transport by the stratiform regions of mcss is examined in two distinct large scale flow regimes associated with the intraseasonal oscillation over the western pacific warm pool model simulations for 14 december 1992 characterize the westerly onset period which has relatively weak low level westerlies with easterlies above simulations for 23 24 december represent the strong westerly regime when westerlies extend from the upper troposphere to the surface with a jet 2 3 km above the surface in the westerly onset simulation the extensive stratiform region of a mcs contained a broad region of descent that transported easterly momentum associated with the mid level easterly jet downward thus the stratiform regions acted as a negative feedback to decrease the large scale mean westerly momentum developing at low levels in the strong westerly regime the mesoscale downward air motion in the stratiform regions of large mcss transported westerly momentum downward and thus acted as a positive feedback strengthening the already strong westerly momentum at low levels momentum fluxes by the mesoscale stratiform region downdraughts are shown to have a systematic and measurable impact on the large scale momentum budget

a simple multicloud parameterization for convectively coupled tropical waves part ii nonlinear simulations observations in the tropics point to the important role of three cloud types congestus stratiform and deep convective clouds besides ubiquitous shallow boundary layer clouds for both the climatology and large scale organized anomalies such as convectively coupled kelvin waves two day waves and the madden julian oscillation recently the authors have developed a systematic model convective parameterization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with lower troposphere heating and cooling corresponding respectively to congestus and stratiform clouds the model includes both a systematic moisture equation 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 and also a nonlinear switch that favors either deep or congestus convection depending on whether the lower middle troposphere is moist or dry here these model convective parameterizations are applied to a 40 000 km periodic equatorial ring without rotation with a background sea surface temperature sst gradient and realistic radiative cooling mimicking a tropical warm pool both the emerging walker cell climatology and the convectively coupled wave fluctuations are analyzed here while various parameters in the model are varied the model exhibits weak congestus moisture coupled waves outside the warm pool in a turbulent bath that intermittently amplify in the warm pool generating convectively coupled moist gravity wave trains propagating at speeds ranging from 15 to 20 m s 1 over the warm pool while retaining a classical walker cell in the mean climatology the envelope of the deep convective events in these convectively coupled wave trains often exhibits large scale organization with a slower propagation speed of 3 5 m s 1 over the warm pool and adjacent region occasional much rarer intermittent deep convection also occurs outside the warm pool the realistic parameter regimes in the multicloud model are identified as those with linearized growth rates for large scale instabilities roughly in the range of 0 5 k day 1

lack of westerly wind bursts in unmaterialized el nino years abstractthe lack of westerly wind bursts wwbs when atmospheric intraseasonal variability isv events occur from boreal spring to autumn is investigated by comparing two types of el nino years with unmaterialized el nino uen years although high ocean heat content buildup and several isv events propagating eastward are observed in all three types of years few wwbs accompany these in the uen years the eddy kinetic energy budget analysis based on isv shows that mean westerly winds in the lower troposphere facilitate the development of eddy disturbances including wwbs through convergence and meridional shear of zonal winds in the uen years these westerly winds are retracted westward and do not reach the equatorial central pacific mainly due to interannual components in addition positive sea surface temperature anomalies in the western pacific which are conducive to active convection spread widely in a meridional direction centered on 15 n both westward retracted mean westerlies and off equator

the vertical structure of toga coare convection part ii modulating influences and implications for diabatic heating abstract the temporal variability of western pacific warm pool convection especially its vertical structure is examined in this study distributions of convective echo top heights and 30 dbz contour heights have been produced from shipboard radar data collected during tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare elevation and suppression of convective heights was primarily influenced by the phase of the intraseasonal oscillation iso with heights being suppressed during convectively inactive and westerly wind burst wwb phases of the iso echo top heights were greatest during the convective phases and post wwb phases of the iso however at least some very deep convection was always present within the area observed by radar indicating that local conditions were favorable for deep convection even when the large scale environment was not capable of supporting widespread deep convection in addition to the iso echo top and 30 dbz contour heights were als

surface fluxes and ocean coupling in the tropical intraseasonal oscillation abstract sensitivity of tropical intraseasonal variability to mixed layer depth is examined in the modified national center for atmospheric research community atmosphere model 2 0 1 cam with relaxed arakawa schubert convection coupled to a slab ocean model som whose mixed layer depth is fixed and geographically uniform but varies from one experiment to the next intraseasonal west pacific precipitation variations during boreal winter are enhanced relative to a fixed sst infinite mixed layer depth simulation for mixed layer depths from 5 to 50 m with a maximum at 20 m interestingly near the observed value in the regions where the madden julian oscillation mjo is active but are strongly diminished in the 2 m depth simulation this nonmonotonicity of intraseasonal precipitation variance with respect to mixed layer depth was predicted by sobel and gildor using a highly idealized model further experiments with the same idealized model help to interpret results derived from the modified ncar c

subseasonal atmospheric variability and el nino waveguide warming observed effects of the madden julian oscillation and westerly wind events abstractwesterly wind events wwes have previously been shown to initiate equatorial pacific waveguide warming the relationship between wwes and madden julian oscillation mjo activity as well as the role of mjo events in initiating waveguide warming is reconsidered here over the 1986 2010 period wwes are identified in observations of near surface zonal winds using an objective scheme mjo events are defined using a widely used index and 64 are identified that occur when the el nino southern oscillation enso is in its neutral state of these mjo events 43 have one or more embedded wwes and 21 do not the evolution of sea surface temperature anomaly over the equatorial pacific waveguide following the westerly surface wind phase of the mjo over the western equatorial pacific is examined waveguide warming is found for the mjo with wwe events in similar magnitudes as following the wwes not embedded in an mjo there is very little statistically significant waveguide warming following mjo events that

the role of surface friction in tropical intraseasonal oscillation abstract the role of surface friction in the tropical intraseasonal oscillation or the madden julian oscillation mjo is investigated by comparing two 4 yr integrations with the goddard atmospheric general circulation model one with the original model design with one added feature to enhance the intensity of the mjo and the other is identical but with surface friction in the tropics replaced by its zonal mean value this comparison indicates that in the second experiment the mjo not only still exists but also exists with similar intensity the oft cited frictional wave cisk fwc interpretation for the origin of the mjo which emphasizes the role of frictionally induced convergence in the surface layer is reassessed in light of these experiments the possibility of the mjo in the second experiment being forced by the middle latitudes is excluded by a third experiment these experiments do not support one of the central ideas in fwc that surface friction plays an instability enhancing role

a numerical investigation of boundary layer quasi equilibrium despite the large energy input from surface evaporation the moist static energy mse of the tropical boundary layer remains relatively constant on large spatial and temporal scales due to lifting of vapor by cloudy updrafts and the addition of dry air from the layers above arakawa and schubert 1974 suggested that drying is due mainly to clear air turbulent entrainment between cloudy updrafts while raymond 1995 described drying due mainly to convective downdrafts we used cloud resolving numerical simulations to investigate the transport of mse into the boundary layer and found turbulent entrainment between clouds to be the dominant process

detecting major terrain parameters relating to mass movements occurrence using gis remote sensing and statistical correlations case study lebanon abstract among the various natural hazards mass movements mm are probably the most damaging to the natural and human environment in mediterranean countries including lebanon which represents a good case study this research deals with how to use geographic information systems gis for establishing the relationships between mm occurrence and different factor terrain parameters over a representative region of lebanon parameters expressed by 1 ancillary data like lithology proximity to fault zone soil type land cover use distance to drainage line and rainfall quantity and 2 derived data like slope gradient and slope aspect were correlated with mm using gis approaches the mm were first detected through visual interpretation of two stereo pairs of spot 4 images anaglyph at 10 m resolution this study indicates depending on bivariate remote sensing and gis statistical correlations kendall tau b correlation that the lithology is the most influencing factor on mm occurrence it also shows that statistical correlations to mass movements exist best between factors at the following decreasing order of importance lithology proximity to fault line lithology soil type and lithology distance to drainage line at 1 level of significance and soil land cover use slope aspect land cover use and soil slope gradient at 5 level of significance these correlations were verified and checked through field observations and explained using univariate statistical correlations therefore they could be extrapolated to other mediterranean countries having similar geoenvironmental conditions

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

squall lines and convectively coupled gravity waves in the tropics why do most cloud systems propagate westward abstractthe coupling between tropical convection and zonally propagating gravity waves is assessed through fourier analysis of high resolution 3 hourly 0 5 satellite rainfall data results show the familiar enhancement in power along the dispersion curves of equatorially trapped inertia gravity waves with implied equivalent depths in the range 15 40 m i e pure gravity wave speeds in the range 12 20 m s 1 here such wave signals are seen to extend all the way down to zonal wavelengths of around 500 km and periods of around 8 h suggesting that convection wave coupling may be important even in the context of mesoscale squall lines this idea is supported by an objective wave tracking algorithm which shows that many previously studied squall lines in addition to 2 day waves can be classified as convectively coupled inertia gravity waves with the dispersion properties of shallow water gravity waves most of these disturbances propagate westward at speeds faster than the background flow to under

convective characteristics of the madden julian oscillation over the central indian ocean observed by shipborne radar during dynamo abstractthis study investigates the convective population and environmental conditions during three mjo events over the central indian ocean in late 2011 using measurements collected from the research vessel r v roger revelle deployed in dynamics of the mjo dynamo radar based rainfall estimates from the revelle c band radar are first placed in the context of larger scale tropical rainfall measuring mission trmm rainfall data to demonstrate that the reduced revelle radar range captured the mjo convective evolution time series analysis and mjo phase based composites of revelle measurements both support the recharge discharge mjo theory time series of echo top heights indicate that convective deepening during the mjo onset occurs over a 12 16 day period composite statistics show evident recharging discharging features in convection and the environment population of shallow isolated convective cells sst cape and the lower tropospheric moisture increase recharge substantially approximately tw

tropical pacific sea surface temperature anomalies el nino and equatorial westerly wind events abstract the authors examine global statistical relationships between westerly wind events wwes and sea surface temperature anomaly ssta variability using a compositing technique for the period 1986 98 the authors describe the extent to which equatorial wwes are associated with central and eastern equatorial pacific waveguide warming and with local ssta changes under the wwe their goal is to quantify the extent to which equatorial wwes are fundamental to the onset and maintenance of warm el nino southern oscillation conditions in order to understand the effect of wwes on ssta evolution they begin by examining how ssta changes in the absence of equatorial wwes they find that ssta tends toward mean climate values in the absence of equatorial wwes whether the eastern equatorial pacific has close to normal ssta or warmer than normal ssta the two equatorial wwe types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling the equatorial wwe type t

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

modulation of equatorial subseasonal convective episodes by tropical extratropical interaction in the indian and pacific ocean regions composite relationships among outgoing longwave radiation sea level pressure surface winds and upper tropospheric circulation are examined for northern winter during subseasonal episodes of eastward progression of convection from the indian ocean to the western pacific this evolution often culminates with westerly wind burst events and strong air sea interaction associated with regional scale convective blowups in the western equatorial pacific we first document some of these interactions in the composites for two timescales the submonthly 6 30 days and that of the madden julian oscillation mjo timescale 30 70 days we then analyze the december 1992 period during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare to illustrate how these composite relationships are manifested in a case study convection in the indian ocean for the composites is shown to be associated with a northern hemisphere wave train at 200 mbar arcing through the midlatitudes that can contribute to convective blowups farther east on the submonthly 6 30 days timescale in the intertropical convergence zone itcz in the eastern pacific the eastern asian trough that is part of this wave train is associated with pressure surges from the northern hemisphere and subsequent convection over southeast asia as the mjo convective envelope moves east to australasia midlatitude wave trains in either hemisphere include upper level troughs east of asia and australia and pressure surges from either hemisphere that contribute to pressure rises over the indonesian region and a subsequent shift of the convective envelope to the western pacific the vertical wind structure for the december 1992 case study is consistent with the composite surface and upper level winds and also shows strong vertical wind shear in the boundary layer a sharply defined westerly maximum near 700 mbar and an intensification of the upper level easterlies near 100 mbar very deep westerlies to 200 mbar are confined to shorter timescales the case study illustrates the various time and space scale interactions noted in the composites reciprocal interactions between the tropics and the midlatitudes on the submonthly and mjo timescales in both the composites and the case study involve pressure surges and wave interaction that influence subsequent convection as the convective envelope migrates eastward from the tropical indian to pacific ocean region

the madden julian oscillation observed during the toga coare iop global view abstract during the toga coare intensive observing period november 1992 february 1993 two pronounced madden julian oscillation mjo events associated with super cloud clusters and westerly wind bursts were observed this paper presents a global view of the mjos including the origin of the super clusters in the indian ocean their migration into the maritime continent and the toga coare large scale soundings array lsa in the western equatorial pacific and their rapid decay over cold water of the eastern pacific the structure and evolution of the mjo are examined with emphasis on the coupling between large scale motion and convection because of differences in propagation speeds the positions of maximum zonal wind perturbations relative to deep convection undergo systematic changes during the travel of the mjo however the centers of deep convection always coincide with those of large scale ascent the super cloud cluster accompanies a wide area of warm air in the upper troposphere over the warm

relationship between convection over central america and the intensity of the jet stream bearing on the 1999 december european storms during 26 28 december 1999 two very powerful and devastating extratropical cyclones hit western europe these two storms were associated with an upper level zonal jet remarkable in its intensity and its large extension over the atlantic ocean in this study we focus on the relationship between the exceptional features of this jet stream and some heavy precipitation that occurred over central america during mid december a rossby wave train excited by strong convective activity over this area is likely to play a key role in this teleconnection to assess this tropical extratropical interaction several numerical experiments have been performed with the french global model arpege firstly the effects of convection have been neutralized within a domain localized over central america then to combine the model with observations a new strategy has been devised within a selected window the parametrized latent heat release has been deduced from tropical rainfall measuring mission trmm precipitation data translated in terms of a potential vorticity hereafter pv source and incorporated into the model using pv inversion these simulations show in particular that the convective activity over central america triggers a wave train that moves poleward and eastward with the group velocity finally to strengthen the north atlantic jet stream leading to windstorms lothar and martin copyright 2011 royal meteorological society

effects of ice microphysics on tropical radiative convective oceanic quasi equilibrium states abstract the effects of ice microphysics on the mean state of tropical atmosphere and ocean are quantified using a coupled cloud ocean model the cloud resolving model crm treats explicitly the cloud scale dynamics instead of using parameterization as is necessary in a general circulation model gcm the ocean model is a one dimensional 1d mixed layer model with a nonlocal k profile parameterization to represent the vertical mixing in the oceanic surface boundary layer two sets of 40 day simulations attain radiative convective oceanic quasi equilibrium states one is a coupled simulation the other has a fixed sea surface temperature sst each set consists of two simulations with a larger and smaller ice fall speed respectively the two coupled simulations t0c and m2c yield dramatically different radiative convective oceanic quasi equilibrium states demonstrating the profound impact of ice microphysics on the water vapor cloud and radiation fields the mean sst and mixed layer depth in m2c i

mjo like coherent structures sensitivity simulations using the cloud resolving convection parameterization crcp abstract interaction between equatorially trapped disturbances and tropical convection is investigated using a nonhydrostatic global model that applies the cloud resolving convection parameterization crcp the crcp represents subgrid scales of the global model by embedding a 2d cloud resolving model in each column of the global model the modeling setup is a constant sst aquaplanet with the size and rotation of earth in radiative convective quasi equilibrium the global atmosphere is assumed to be initially at rest no large scale organization of convection is present outside the equatorial waveguide inside the waveguide on the other hand the model simulates spontaneous formation of coherent structures with deep convection on the leading edge and strong surface westerly winds to the west the westerly wind bursts these coherent structures resemble the madden julian oscillation mjo observed in the terrestrial tropics and are present in simulations applying prescribed and interactive radiation an

intraseasonal perturbations in sea surface temperatures of the equatorial eastern pacific and their association with the madden julian oscillation abstract a particular pattern of intraseasonal perturbations in sea surface temperature sst is observed in the eastern pacific ocean following events of strong surface winds associated with the madden julian oscillation mjo this intraseasonal sst pattern straddles at the equator with its longitudinal scales of 2 5 103 km and meridional scales of about 500 km the amplitude of the perturbations is 0 5 c or greater positive and negative perturbations sometimes follow one another they show tendencies of both eastward and westward movement such equatorially elongated perturbations in sst in the eastern pacific are hypothesized to be caused by intraseasonal oceanic kelvin waves forced by the mjo over the western central pacific as the kelvin waves propagate eastward changes in the vertical temperature gradient in the upper ocean due to the fluctuations in the depth of the thermocline modify the thermal effect of the equatorial upwelling as a result mixed layer and surface temperatures may fluctua

a mesovortex within a near equatorial mesoscale convective system during toga coare abstract airborne doppler radar observations are used to investigate the internal structure of a midlevel mesovortex that developed within the rear part of the stratiform precipitation region of a mature to decaying mesoscale convective system this system composed of several convective elements occurred on 13 december 1992 on the eastern side of the intensive flux array of the tropical ocean global atmosphere coupled ocean atmosphere response experiment near the equator 2 s the mesovortex contained several features that were previously observed in other tropical and midlatitude systems radar observations show that the closed wind circulation at midlevels had a horizontal dimension of 150 km and was coincident with a marked rear inflow at the central rear of the stratiform region where a notch pattern clearly identified the rear dry air intrusion it was associated with positive vertical vorticity anticyclonic for the southern hemisphere and could be classified as a cooling induced vortex maxi

evolution of the population of precipitating convective systems over the equatorial indian ocean in active phases of the madden julian oscillation three dimensional radar reflectivity fields from a dual wavelength doppler polarimetric radar s polka deployed in the equatorialindian ocean are used to evaluate the composition of the populationof convective cloud elements during active phases of the mjo rainfall in active periods was intermittent occurring in 11 episodesofabout 2 4days separated byseveralnonrainydays dataforthese 2 dayperiodswerecomposited relative to the time of maximum rainfall analysis of the s polka data shows the makeup of the convective population during the rainfall episodes four types of echo structures were analyzed statistically for the 11 rainfallepisodes shallowconvectiveechoes sce deepconvectivecores dcc wideconvectiveechocores wcc and broad stratiform bsr echo regions sce and dcc events were most frequent before the maximum rainfall with the peak frequency of sce leading that of dccs wccs were most frequent during therainfallmaximum and bsr regionswere most frequentinthe later part oftherainfallepisode composited ecmwf interim re analysis era interim data and 3 hourly atmospheric soundings indicate that the 2 4 day episodes were related to the passage of equatorial waves in the early part of a rainfall episode the wave passageconditionswereunstable favoringdeeppenetratingconvectiveelements whileinthelaterperiod the wave divergence profile was commensurate with convective systems in late anvil producing stages these results support the stretched building block notion of the life cycle of tropical convection and confirm satellitebased interpretations of sce dcc wcc and bsr statistics in the composition of the convective population

scale interactions involved in the initiation structure and evolution of the 15 december 1992 mcs observed during toga coare part i synoptic scale processes this paper the first of a series examines the synoptic scale mechanisms involved in the initiation structure and evolution of a mesoscale convective system observed during toga coare this study relies upon the use of the japanese geosynchronous meteorological satellite 4 imagery and ecmwf model outputs from which diagnostic parameters are derived and interpreted this mesoscale convective system consists initially of two groups of convective entities that progressively move toward each other and merge it is shown that the synoptic scale flow creates a favorable environment for the formation of this large convective system through the production of convective available potential energy cape by horizontal advection and the enhancement of low level convergence in the region where the convective system formed moreover the general evolution of the system is found to be governed by the synoptic scale circulation and more precisely by the temporal evolution of cape and low level convergence the mechanisms leading to the initiation and general evolution of the system are examined the easterly equatorial jet at 500 hpa triggered positive potential vorticity areas that propagated westward and generated an anticyclonic circulation this anticyclonic circulation was enhanced during the development phase of the convective system through vortex stretching and tilting which accelerated the low level westerlies corresponding to the southern branch of this circulation and enhanced the low level convergence associated with the studied convective system in a companion paper the mesoscale and convective scale processes involved in the internal organization of this mesoscale convective system are examined using the airborne doppler radar dataset collected within the system from 1700 to 2100 utc the downscale interactions i e from synoptic scale to mesoscale and convective scale are scrutinized using both the synoptic scale context described in this paper and the mesoscale and convective scale characteristics derived from the airborne radar observations

convection over the pacific warm pool in relation to the atmospheric kelvin rossby wave abstract deep convection over the western tropical pacific warm pool is analyzed in terms of its relation to the atmospheric kelvin rossby wave which dominates the large scale flow during the austral summer the study uses doppler radar data collected by aircraft and ship radars during different time periods in the tropical ocean global atmosphere coupled ocean atmosphere response experiment to characterize the mesoscale circulations of organized convective cloud systems occurring throughout the season the study focuses on convection in two contrasting phases of the wave the westerly onset region just west of the point within the wave where low level easterlies change to westerlies and the strong westerly region or westerly wind burst lying between the large scale counterrotating gyres of the kelvin rossby wave in the westerly onset region the zonal wind component had midlevel easterlies overlying low level westerlies in the strong westerly region a deep layer of westerlies extended from 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

self aggregation and large scale control of tropical deep convection a modeling study abstract the pennsylvania state university national center for atmospheric research mesoscale model version 5 mm5 is used to investigate whether superclusters represent a mode of self aggregation of tropical deep convection that occurs spontaneously under horizontally uniform boundary conditions and large scale forcings the nonhydrostatic version of mm5 is run with prescribed domain averaged vertical velocity and periodic boundary conditions in both east west and north south directions domain averaged horizontal winds are relaxed to a specified reference wind profile two vertical profiles of mean ascent are used one has an elevated maximum at the upper troposphere and near zero vertical velocity in the lower troposphere the other peaks at the midtroposphere representing the vertical velocity distribution of convective towers only simulations with the same initial conditions but two different forcings show significant differences in convective organization the run with elevated forcing develops l

breakdown and reformation of the intertropical convergence zone in a moist atmosphere abstract the effects of moisture on the intertropical convergence zone itcz over the eastern pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model the quasi equilibrium tropical circulation model qtcm1 on an aquaplanet the dry simulation shows results consistent with those of simple dynamic models except that a slightly stronger heating rate is needed owing to different model designs in the moist simulations the most important result is the formation of a tail southwest of a vortex during and after the itcz breakdown this tail may extend zonally more than 60 longitude and last for more than two weeks in an idealized simulation in the eastern north pacific this phenomenon is often observed in cases that involve easterly waves in a sense the formation of the tail suggests a possible mechanism that forms an itcz efficiently this study shows that the surface convergent flow induced by a disturbance initializes a positive wind evapor

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

estimates of large scale divergence in the lower troposphere over the western equatorial pacific a network of 915 mhz wind profilers measured half hourly lower tropospheric winds over the western equatorial pacific with vertical resolutions as high as 100 m during november 1992 through february 1993 the intensive observing period iop of the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare these wind data are used in conjunction with collocated surface wind measurements to examine the near surface divergent flow over the western pacific warm pool during austral summer as well as the synoptic scale variability of divergence in both time and space the synoptic scale wind field estimated from profiler data exhibits stronger near surf ace divergence than sonde based estimates from the same time period temporal variations of the lower tropospheric divergence profiles are described by three vertical structure functions derived from varimax rotated eigenvector analysis one vertical mode appears to be associated with deep convection one with near surface processes and one with shallower convection these structure functions vary zonally across the coare region with the convective modes having convergence maxima at lower elevations to the west of the intensive flux array ifa than over and east of it

the march 1997 westerly wind event and the onset of the 1997 98 el nino understanding the role of the atmospheric response in a previous study the effect of the march 1997 westerly wind event wwe on the evolution of the tropical pacific ocean was studied using an ocean general circulation model gcm the response was characterized by i a cooling of the far western pacific 0 88c ii a rapid eastward displacement of the warm pool 2000 km in a month and iii a weak warming of the central eastern pacific along the path of the oceanic kelvin wave excited by the wwe 0 58c in this study the atmospheric response to these aspects of the sea surface temperature sst response are investigated using an atmospheric gcm forced with the sst anomalies from the ocean only experiments the results have demonstrated that the three aspects of the sst anomaly field generated by the wwe

assessing the relationship between mjo and equatorial pacific wwbs in observations and cmip5 models abstractthis study evaluates the relationship between the madden julian oscillation mjo and the occurrence of equatorial pacific westerly wind bursts wwbs during the convective mjo phase anom

modelling the links between vegetation and landforms vegetation is the most important intermediate through which climate and land use modify geomorphological processes and landforms in this paper we explore three types of model which attempt to simulate the links to uncultivated vegetation all sharing a common basis in hydrology the first simulates the relationship between climate vegetation and erosion rates for a fixed topography and soil cover the second group of models takes into account longer term interactions with soil properties which are thought to be important on the times scales of current concern with global change an expanded illustration of this interaction is the relationship between wash erosion processes vegetation cover and the evolution of microtopography the third group of models looks at geological time spans for which consistent differences in vegetation and landform between climatic areas create responses in the pattern of erosion rates jointly to a combination of past and present climates

identifying the skeleton of the madden julian oscillation in observational data the madden julian oscillation mjo skeleton model offers a theoretical prediction of the mjo s structure here a method is described for identifying this structure in observational data the method utilizes projections onto equatorial wave structures and a main question is can this method isolate the mjo without using temporal filtering or empirical orthogonal functions for the data projection a wide range of data is incorporated multiple variables wind geopotential height water vapor and as a proxy for convective activity outgoing longwave radiation multiple pressure levels 850 and 200hpa and multiple latitudes both equatorial and off equatorial such a data variety is combined using a systematic method and it allows for a distinction between the kelvin and rossby components of the mjo s structure results are illustrated for some well known cases and statistical measures are presented to quantify the variability of the mjo skeleton signal mjos x t and its amplitude mjosa t the robustness of the methods is demonstrated through a suite of sensitivity studies including tests with two projection methods when the projection is based on the skeleton model s energy as opposed to the standard l 2 energy water vapor is seen to be of primary importance finally a simple interpretation is given for the mjo skeleton structure it is related to the wave responseto amovingheatsource from eitherperspective themethods hereidentifysignalsthatproject onto coupled convection circulation patterns and the results suggest that a large portion of the mjo s structure is consistent with such a coupled pattern

gravity waves in shear and implications for organized convection abstract it is known that gravity waves in the troposphere which are often excited by preexisting convection can favor or suppress the formation of new convection here it is shown that in the presence of wind shear or barotropic wind the gravity waves can create a more favorable environment on one side of preexisting convection than the other side both the nonlinear and linear analytic models developed here show that the greatest difference in favorability between the two sides is created by jet shears and little or no difference in favorability is created by wind profiles with shear at low levels and no shear in the upper troposphere a nonzero barotropic wind or equivalently a propagating heat source is shown to also affect the favorability on each side of the preexisting convection it is shown that these main features are captured by linear theory and advection by the background wind is the main physical mechanism at work these processes should play an important role in the organization of

assessing soil erosion in mediterranean karst landscapes of lebanon using remote sensing and gis abstract maps showing the potential for soil erosion at 1 100 000 scale are produced in a study area within lebanon that can be used for evaluating erosion of mediterranean karstic terrain with two different sets of impact factors built into an erosion model the first set of factors is soil erodibility morphology land cover use and rainfall erosivity the second is obtained by the first adding a fifth factor rock infiltration high infiltration can reflect high recharge therefore decreasing the potential of surface runoff and hence the quantity of transported materials infiltration is derived as a function of lithology lineament density karstification and drainage density all of which can be easily extracted from satellite imagery the influence of these factors is assessed by a weight rate approach sharing similarities between quantitative and qualitative methods and depending on pair wise comparison matrix the main outcome was the production of factorial maps and erosion susceptibility maps scale 1 100 000 spatial and attribute comparison of erosion maps indicates that the model that includes a measure of rock infiltration better represents erosion potential field investigation of rills and gullies shows 87 5 precision of the model with rock infiltration this is 17 5 greater than the precision of the model without rock infiltration these results indicate the necessity and importance of integrating information on infiltration of rock outcrops to assess soil erosion in mediterranean karst landscapes

alternative methods for specification of observed forcing in single column models and cloud system models we discuss alternative methods for prescribing advective tendencies in single column models scms and cloud system models these include revealed forcing in which the total advective tendency is prescribed from observations horizontal advective forcing in which the horizontal advective tendencies are prescribed together with the observed vertical motion which is combined with the predicted sounding to determine the tendencies due to vertical advection and relaxation forcing in which the horizontal advective tendencies are computed by relaxing the sounding toward the observed upstream sounding with a relaxation timescale determined by the time required for the wind to carry parcels across the grid column when relaxation forcing is used the horizontal advective tendencies can be diagnosed from the model output and compared with the corresponding observed tendencies we present scm results to illustrate these three forcing methods based on data from several field experiments in both the tropics and the midlatitudes each method is shown to have its strengths and weaknesses overall the results presented here do not show unambiguous differences between revealed forcing and horizontal advective forcing the two methods appear to be generally comparable revealed forcing may therefore be preferred for its simplicity relaxation forcing guarantees realistic soundings of the state variables but can produce large errors in parameterized processes which are driven by rates e g fluxes rather than states in particular relaxation forcing gives large errors in the precipitation rate in this model we demonstrate that relaxation forcing leads to unrealistically high low precipitation in versions of the model which tend to produce unrealistically dry humid soundings the observed horizontal advective tendencies in the tropics are so weak especially for temperature that small absolute errors in the diabatic tendencies diagnosed with relaxation forcing can lead to large relative errors in the diagnosed horizontal advective tendencies

fine structure of cloud patterns within the intraseasonal oscillation during toga coare abstract the relationship of satellite derived cloud motions to actual convective systems within a convectively active phase of the intraseasonal oscillation is examined by using both cloud scale properties produced by a cloud resolving model and field observations to clarify what is going on at shorter time and space scales each convective system has a life cycle of up to 1 2 days described in terms of active convection the system consists of successive precipitation cells generated ahead of the gust front described in terms of its cloud shield the system is more continuous when easterly winds prevail above 2 km both precipitating clouds and upper tropospheric anvil clouds move westward with about the same phase speed 10 m s 1 however during the westerly wind period precipitating clouds move eastward with a phase speed of 10 m s 1 which is better represented by the radar observations and surface precipitation the westward movement of cloud patterns viewed from the satellite images is mos

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

kinematic and thermodynamic characteristics of the flow over the western pacific warm pool during toga coare abstract rawinsonde and satellite infrared radiation ir data from the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare are used to investigate mean and transient behavior and horizontal variability of the atmosphere over the western pacific warm pool infrared data for the 4 mo intensive observing period iop and vertical motion fields indicate that the intensity of convection height of maximum upward motion and sst all increased from west 140 e to east across the coare domain iop mean ir data show a double itcz intertropical convergence zone structure north and south of the intensive flux array ifa centered at 2 s 156 e although marked variability in the patterns occurred on a month to month basis three prominent westerly wind bursts occurred over the ifa during the 4 mo iop in association with the intraseasonal oscillations isos strong upward motion usually occurred 1 3 weeks prior to the peak low level westerlies subsidence dominated when

westward generation of eastward moving tropical convective bands in toga coare mechanisms responsible for westward generation of eastward moving tropical convective bands in the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare are investigated using a two dimensional numerical cloud model sequential generation of new convective bands to the west of an old eastward moving convective band is successfully simulated in an environment of a convectively active day during toga coare characterized by west winds at low levels and strong easterlies aloft it is concluded that the westward generation of new convective bands is explained by a gravity wave mechanism two westward propagating modes excited below the convective cells moving westward relative to the convective bands appear to play an important role a slow propagating mode 15 ms 21 excited by a shallow convective band is ducted in the troposphere under an unstable layer of small richardson number containing its critical level a fast propagating mode 25 m s21 excited by a deep convective band is ducted in the troposphere under the remaining region of the convective cell containing its critical level these two modes propagate horizontally to the west and promote the growth of shallow convection into long lived convective bands a dry model with thermal forcing representing the convective cell showed that preferential excitation of westward propagating waves below the convective cell is due to westward motion and ascension of the convective cell a comparative simulation without the critical level confirms the proposed gravity wave mechanism

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

a joint satellite and global cloud resolving model analysis of a madden julian oscillation event model diagnosis 1 in this study a methodology to diagnose a global cloud resolving model gcrm is explored on the basis of a joint analysis with satellite measurements the madden julian oscillation experiment carried out with the nonhydrostatic icosahedral atmospheric model nicam is used as the test bed the nicam output is compared with tropical rainfall measuring mission trmm and cloudsat measurements in terms of composite analysis contoured frequency by altitude diagrams cfads and the joint histogram of cloud top and precipitation top heights it is found in the composite diagram that the gcrm reproduces a slow eastward migration of a convective envelope well comparable to the satellite measurement the gcrm cfad qualitatively reproduces trmm and cloudsat cfads except that the gcrm tends to overly produce snow in deep convection the joint histograms reveal that while the overproduction of snow is evident nicam simulated snow is incapable of producing 94 ghz radar echoes higher than 5 dbz this deficiency can be mitigated by a modification to microphysical parameterization in the way that a proportion of small particles is enhanced in the snow mass spectrum

two day disturbances in the equatorial western pacific from november 1992 to february 1993 westward propagating disturbances with scales of 1000 1500 km frequented the equatorial western pacific they propagated at about 16 m s 1 and their passage was accompanied by a two day oscillation in high cloudiness their convection was most intense when the lower troposphere was cool and the level of free convection was relatively low the disturbances propagated westward at about 18 m s 1 faster than the lower tropospheric flow this rapid propagation may have been the result of a coupling between the disturbance s convection and the 20 m s 1 vertical mode the signal of this mode was apparent in vertical profiles of temperature and wind and the most intense convection began when the mode dynamically cooled the lower troposphere lowering the level of free convection

effect of stratiform heating on the planetary scale organization of tropical convection abstractit is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front to rear tilt in the heating profile precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems the wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer leading to further lifting here aquaplanet simulations with a warm pool like surface forcing based on a coarse resolution gcm of approximately 170 km grid mesh coupled with a stochastic multicloud parameterization are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales when the model paramet

clouds associated with the madden julian oscillation a new perspective from cloudsat abstractthe evolution of total cloud cover and cloud types is composited across the madden julian oscillation mjo using cloudsat data for june 2006 may 2010 two approaches are used to define mjo phases 1 the local phase is determined at each longitude and time from filtered outgoing longwave radiation and 2 the global phase is defined using a popular real time multivariate mjo rmm index which assigns the tropics to an mjo phase each day in terms of local phase cloudsat results show a familiar evolution of cloud type predominance in the growing stages shallow clouds coexist with deep intense but narrow convective systems widespread cloud coverage and rainfall appear during the active phases becoming more anvil dominated with time and finally suppressed conditions return results are compared to the convectively coupled kelvin wave which has a similar life cycle to the mjo convection in the mjo tends to be modulated more by moisture variations compared to the kelvin wave in terms of globa

a mechanism of tropical convection inferred from observed variability in the moist static energy budget temporal variability in the moist static energy mse budget is studied with measurements from a combination of different satellites including the tropical rainfall measuring mission trmm and a train platforms a composite time series before and after the development of moist convection is obtained from the observations to delineate the evolution of mse and moisture convergences and in their combination gross moist stability gms a new algorithm is then applied to estimate large scale vertical motion from energy budget constraints through vertical mode decomposition into first and second baroclinic modes and a background shallow mode the findings are indicative of a possible mechanism of tropical convection a gradual destabilization is brought about by the mse convergence intrinsic to the positive second baroclinic mode congestus mode thatincreasingly counteracts a weak mse divergence inthe backgroundstate gms isdriven to nearly zero as the first baroclinic mode begins to intensify accelerating the growth of vigorous large scale updrafts and deep convection as the convective burst peaks the positive second modeswitches tothe negative mode stratiform mode and introduces an abrupt rise in mse divergence that likely discourages further maintenance of deep convection the first mode quickly dissipates and gms increases away from zero eventuallyreturningtothebackgroundshallow modestate anotablecaveattothisscenarioisthatgmsserves as a more reliable metric when defined with a radiative heating rate included to offset mse convergence

upscale impact of mesoscale convective systems and its parameterization in an idealized gcm for an mjo analog above the equator abstractthe madden julian oscillation mjo typically contains several superclusters and numerous embedded mesoscale convective systems mcss it is hypothesized here that the poorly simulated mjo

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

a multiscale model for the intraseasonal impact of the diurnal cycle over the maritime continent on the madden julian oscillation abstractthe eastward propagating madden julian oscillation mjo typically exhibits complex behavior during its passage over the maritime continent sometimes slowly propagating eastward and other times stalling and even terminating there with large amounts of rainfall this is a huge challenge for present day numerical models to simulate one possible reason is the inadequate treatment of the diurnal cycle and its scale interaction with the mjo here these two components are incorporated into a simple self consistent multiscale model that includes one model for the intraseasonal impact of the diurnal cycle and another one for the planetary intraseasonal circulation the latter model is forced self consistently by eddy flux divergences of momentum and temperature from a model for the diurnal cycle with two baroclinic modes which capture the intraseasonal impact of the diurnal cycle the mjo is modeled as the planetary scale circulation response to a moving heat source on the synoptic and planetary scales

structural evolution of the madden julian oscillation from cosmic radio occultation data 1 the atmospheric temperature and specific humidity profiles derived from 4 years of constellation observing system for meteorology ionosphere and climate cosmic radio occultation ro measurements during the boreal winter november thru april in 2006 2010 were employed to study the large scale vertical structure of the madden julian oscillation mjo in a composited mjo cycle both ro temperature and moisture anomalies propagate eastward along with the enhanced mjo convection over the indo pacific region in the same region the ro temperature anomaly is positively correlated with the convection tropical rainfall measuring mission trmm rainfall anomaly in the middle and upper troposphere 800 hpa 200 hpa and negatively correlated in the lower troposphere and at the tropopause a positive ro moisture anomaly has a westward tilt below 300 hpa and is well associated with the convection anomaly ro bending angle and refractivity anomalies show vertical structure similar to that of temperature mjo anomaly above 300 hpa and to that of the moisture anomaly below that these salient mjo features agree well with those revealed by global reanalysis data and meteorological satellite observations such as the atmospheric infrared sounder airs even though ro anomalies exhibit sharper structure at the tropopause region due to the higher vertical resolution of the ro investigation of the cold point tropopause anomaly indicates that the enhanced convection is preceded by cooling of the tropopause and followed by lowering of the tropopause height the mjo moisture structures during two boreal winters november 2007 april 2008 la nina and november 2009 april 2010 el nino are individually presented to demonstrate the el nino southern oscillation enso effect on the mjo structure