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

hurricane formation in diabatic ekman turbulence this article investigates the emergence of hurricanes from chaotic swirling motions in a three layer model of the tropical troposphere that includes basic parametrizations of cumulus convection and air sea interaction the chaotic flow is referred to as diabatic ekman turbulence det in order to emphasize that cumulus convection and ekman pumping are critical to its behaviour the time required for hurricane formation in det is examined over a broad range of sea surface temperatures tropical latitudes and surface exchange coefficients for moist entropy and momentum the mean trends are sensible but for a given set of parameters the genesis time can vary significantly with subtle changes to the initial turbulence moreover hurricanes do not always form in the event that a tropical depression develops into a hurricane the process is highly asymmetric intensification involves a shear flow instability the production of mesovortices and contraction of the basic circulation despite the complex evolution the intensification rate is largely consistent with the expectations of a quasi linear stability analysis properties of mature hurricanes and the nature of their fluctuations are discussed in the context of the model copyright 2009 royal meteorological society

sea ice ridging in the ross sea antarctica as compared with sites in the arctic at the end of the 1980 austral winter surface roughness measurements were made by laser profilometer during a series of flights over the ross sea pack ice the total track length was 2696 km and 4365 ridges were counted the frequency distribution of individual ridge heights was found to be well described by a negative exponential distribution no clear cut regional variation was noted in ridge heights the distribution of ridge frequencies per kilometer showed a strong positive skew with a modal value of 1 88 the most frequent ridging occurred off the east coast of victoria land comparisons with similar data sets from the arctic indicate that large ridges are significantly more likely in the arctic ocean than in the ross sea utilizing a reasonable model for the geometry of ridges estimates are made of the average thickness of a hypothetical continuous layer composed only of the deformed ice from ridges the noncoastal ross sea value of 0 09 m is less than half of the lowest comparable value from the arctic 0 20 m central beaufort sea where values in excess of 1 0 m have been observed in the shear zones north of greenland

convective momentum transport associated with the madden julian oscillation based on a reanalysis dataset abstracta better understanding of multiscale interactions within the madden julian oscillation mjo including momentum exchanges is critical for improved mjo prediction skill in this study convective momentum transport cmt associated with the mjo is analyzed based on the noaa climate forecast system reanalysis cfsr a three layer vertical structure associated with the mjo as previously suggested in the mesoscale momentum tendency profile based on global cloud resolving model simulations is evident in the subgrid scale momentum tendency from the cfsr positive negative subgrid scale momentum tendency anomalies are found near the surface negative positive anomalies are found in the low to midtroposphere and positive negative anomalies in the upper troposphere are found within and to the west east of the mjo convection this tends to damp the mjo circulation in the free atmosphere while enhancing mjo winds near the surface in addition it could also reduce the mjo eastward propagation

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

on the maintenance and initiation of the intraseasonal oscillation in the ncep ncar reanalysis and in the gla and ukmo amip simulations in this study satellite derived outgoing longwave radiation olr and the reanalysis from the national centers for environmental prediction national center for atmospheric research are used as verification data in a study of intraseasonal variability in the goddard laboratory for atmospheres gla and the united kingdom meteorological office ukmo atmospheric general circulation models these models simulated the most realistic intraseasonal oscillations io of the 15 atmospheric model intercomparison project models previously analyzed during the active phase of the intraseasonal oscillation convection is observed to migrate from the indian ocean to the western central pacific ocean and into the south pacific convergence zone spcz the simulated convection particularly in the gla model is most realistic over the western central pacific ocean and the spcz in the reanalysis the baroclinic structure of the io is evident in the eddy stream function and eastward migration of the anticyclone cyclone pairs occurs in conjunction with the eastward development of convection both the gla and ukmo models exhibit a baroclinic structure on intraseasonal time scales the gla model is more realistic than the ukmo model at simulating the eastward migration of the anticyclone cyclone pairs when the convection is active over the western central pacific in the ukmo model the main heating is located off the equator which contributes to the irregular structures seen in this model on intraseasonal time scales the maintenance and initiation of the intraseasonal oscillation has also been investigated analysis of the latent heat flux indicates that evaporative wind feedback is not the dominant mechanism for promoting the eastward propagation of the intraseasonal oscillation since evaporation to the west of the convection dominants the data suggest a wave cisk conditional instability of the secondkind type mechanism although the contribution by frictional convergence is not apparent in the gla model enhanced evaporation tends to develop in place over the west pacific warm pool while in the ukmo simulation westward propagation of enhanced evaporation is evident it is suggested that lack of an interactive ocean may be associated with the models systematic failure to simulate the eastward transition of convection from the indian ocean into the western pacific ocean this hypothesis is based upon the examination of observed sea surface temperature sst and its relationship to the active phase of the intraseasonal oscillation which indicates that the io may evolve as a coupled ocean atmosphere mode the eastward propagation of convection appears to be related to the gradient of sst with above normal sst to the east of the convection maintaining the eastward evolution and decreasing sst near the western portion of the convective envelope being associated with the cessation of convection

an analysis of the environmental moisture impacts of western north pacific tropical cyclones abstractthe present study examines the environmental moisture anomalies present during western north pacific tropical cyclone tc passage using storm relative composites composited precipitable water anomalies reveal asymmetric anomalies with dry anomalies to the northwest and southwest of the tc and moist anomalies to the east of the tc precipitable water anomalies filtered in space and time suggest that the moisture anomalies in the northwest southwest and east regions nwr swr and er respectively are partially due to the tc while the anomalies in the swr are also forced by a convectively suppressed madden julian oscillation mjo and equatorial rossby wave erw composited vertically integrated moisture budgets and backward parcel trajectories reveal that the moisture anomalies in the nwr swr and er are primarily due to the convergence of climatological mean moisture by the anomalous meridional wind this convergence is induced by the secondary circulation of the tc in the nwr and er and b

a 15 year climatology of north atlantic tropical cyclones part i size parameters abstract the extended best track ebt dataset combines the information contained in the tropical cyclone best track dataset with measurements of tropical cyclone size parameters these parameters include the radii of the eye reye maximum winds rmw gale force winds or size 17 5 m s 1 r17 damaging force winds 25 7 m s 1 r26 hurricane force winds 32 9 m s 1 r33 and the outermost closed isobar roci the latest update of this dataset to be used in this study for a size parameter climatology contains the size parameters for north atlantic tropical cyclones from 1988 to 2002 such a climatology has not yet been established in this basin most of the results of this north atlantic study agree with documented tropical cyclone theory and results from similar studies of northwest pacific tropical cyclones this provides confidence that the observations of the size parameters in the dataset are reliable furthermore data west and east of 55 w the boundary beyond which no aircraft observati

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

the temporal autocorrelation structure of sea surface winds abstractthe temporal autocorrelation structures of sea surface vector winds and wind speeds are considered analyses of scatterometer and reanalysis wind data demonstrate that the autocorrelation functions acf of surface zonal wind meridional wind and wind speed generally drop off more rapidly in the midlatitudes than in the low latitudes furthermore the meridional wind component and wind speed generally decorrelate more rapidly than the zonal wind component the anisotropy in vector wind decorrelation scales is demonstrated to be most pronounced in the storm tracks and near the equator and to be a feature of winds throughout the depth of the troposphere the extratropical anisotropy is interpreted in terms of an idealized kinematic eddy model as resulting from differences in the structure of wind anomalies in the directions along and across eddy paths the tropical anisotropy is interpreted in terms of the kinematics of large scale equatorial waves and small scale convection modeling the vector w

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

large scale organization of tropical convection in two dimensional explicit numerical simulations the large scale organization of tropical deep convection is investigated in idealized two dimensional cloud resolving simulations a 20 000 km periodic computational domain allows interactions among moist convection mesoscale organization and surface exchange on a wide range of scales a uniform 10 m s 1 easterly wind and a uniform sea surface temperature of 30 c are assumed a prescribed temperature tendency mimicking the mean radiative cooling of the tropical troposphere is used in this pilot study the large scale organization of convection resembles the observed tropical atmosphere as well as results from some previous numerical studies using parametrized convection the simulation highlights mesoscale convective systems with horizontal scales of several hundred kilometres moving east to west with speeds similar to the mean flow and an envelope of convection with a horizontal extent of a few thousand kilometres and propagating west to east the propagation speed of the large scale envelope compares well with the phase velocitites of convectively coupled kelvin waves observed in the equatorial waveguide convective momentum transport and the impact of convective systems on temperature and moisture near the surface are key processes responsible for the large scale organization of convection these results are discussed in the context of recent observations and numerical studies of convection organization in the tropics

heightened hurricane surge risk in northwest florida revealed from climatological hydrodynamic modeling and paleorecord reconstruction historical tropical cyclone tc and storm surge records are often too limited to quantify the risk to local populations paleohurricane sediment records uncover long term tc activity but interpreting these records can be difficult and can introduce significant uncertainties here we compare and combine climatological hydrodynamic modeling including a method to account for storm size uncertainty historical observations and paleohurricane records to investigate local surge risk using apalachee bay in northwest florida as an example the modeling reveals relatively high risk with 100 year 500 year and worst case surges estimated to be about 6 3 m 8 3 m and 11 3 m respectively at bald point a paleorecord site and about 7 4 m 9 7 m and 13 3 m respectively at st marks the head of the bay supporting the inference from paleorecords that apalachee bay has frequently suffered severe inundation for thousands of years both the synthetic database and paleorecords contain a much higher frequency of extreme events than the historical record the mean return period of surges greater than 5 m is about 40 years based on synthetic modeling and paleoreconstruction whereas it is about 400 years based on historical storm analysis apalachee bay surge risk is determined by storms of broad characteristics varies spatially over the area and is affected by coastally trapped kelvin waves all of which are important features to consider when accessing the risk and interpreting paleohurricane records in particular neglecting size uncertainty may induce great underestimation in surge risk as the size distribution is positively skewed while the most extreme surges were generated by the uppermost storm intensities medium intensity storms categories 1 3 can produce large to extreme surges due to their larger inner core sizes for apalachee bay the storms that induced localized barrier breaching and limited sediment transport overwash regime surge between 3 and 5 m are most likely to be category 2 or 3 storms and the storms that inundated the entire barrier and deposited significantly more coarse materials inundation regime surge 5 m are most likely to be category 3 or 4 storms

organization of tropical convection in low vertical wind shears the role of water vapor abstract a modeling study is conducted to gain insight into the factors that control the intensity and organization of tropical convection and in particular to examine if organization occurs in the absence of factors such as vertical wind shear or underlying sea surface temperature sst gradient the control experiment integrates a cloud resolving model for 15 days using a 3d domain exceeding 1000 km in length with no imposed winds and horizontally uniform sst and forcing for convection after 2 days of random activity the convection organizes into clusters with dimensions of approximately 200 km convective systems propagate through the clusters at speeds of 2 3 m s 1 while the clusters themselves propagate at minimal speeds of around 0 5 m s 1 examining the thermodynamic structure of the model domain it is found that the convective free bands separating the clusters are very dry throughout the troposphere and due to virtual temperature effects are correspondingly warmer in the lower tropospher

numerical study of coastal hydrodynamics using a coupled model for hudhud cyclone in the bay of bengal abstract the past decade has witnessed an increased intensity of cyclones in the bay of bengal region with higher winds spread over a larger area the associated risk and coastal vulnerability have increased with wider destructive potential from high waves storm surges and associated coastal inundation the very severe cyclones that made landfall over the bay of bengal in the past decade had strong winds in their outer cores unlike those cyclones that made landfall in previous years the original parametric wind formulation performs well for more compact cyclones but at a radial distance far away from the cyclone centre the winds are under estimated hence there is a need to revisit and modify this formula for practical applications and this study attempts to provide a better representation of the overall radial distance in the wind field envelope the study postulates a 3 5 power law fitted to the original wind formulae which provides a reasonably good estimate for the surface wind field the recent very severe cyclones that developed over the bay of bengal provided an excellent test bed to verify this hypothesis which is supported by validation from six in situ buoys the modified wind formula used with a coupled hydrodynamic model adcirc swan simulated the storm surge and wave characteristics associated with a recent very severe cyclonic storm hudhud that made landfall in andhra located on the east coast of india in 2014 the study also investigated the dependence of coastal geomorphic features and beach slope on the variability of wave induced setup computed significant wave height and storm surge show an excellent match with wave rider buoy and tide gauge observations

self stratification of tropical cyclone outflow part i implications for storm structure extant theoretical work on the steady state structure and intensity of idealized axisymmetric tropical cyclones relies on the assumption that isentropic surfaces in the storm outflow match those of the unperturbed environment at large distances from the storm s core these isentropic surfaces generally lie just above the tropopause wheretheverticaltemperaturestructureisapproximatelyisothermal soithas beenassumedthat the absolute temperature of the outflow is nearly constant here it is shown that this assumption is not justified at least when applied to storms simulated by a convection resolving axisymmetric numerical model in whichmuchofthe outflowoccursbelowtheambienttropopauseanddevelopsits ownstratification unrelated to that of the unperturbed environment the authors propose that this stratification is set in the storm s core by the requirement that the richardson number remain near its critical value for the onset of small scale turbulence this ansatz is tested by calculating the richardson number in numerically simulated storms and then showing that the assumption of constant richardson number determines the variation of the outflow temperature with angular momentum or entropy and thereby sets the low level radial structure of the storm outside its radius of maximum surface winds part ii will show that allowing the outflow temperature to vary also allows one to discard an empirical factor that was introduced in previous work on the intensification of tropical cyclones

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

a class of nonhydrostatic global models abstract a cartesian small to mesoscale nonhydrostatic model is extended to a rotating mountainous sphere thereby dispensing with the traditional geophysical simplifications of hydrostaticity gentle terrain slopes and weak rotation the authors discuss the algorithmic design relative efficiency and accuracy of several different variants hydrostatic nonhydrostatic implicit explicit elastic anelastic etc of the global model and prepare the ground for a future global cloud model a research tool to study effects of small and mesoscale phenomena on global flows and vice versa there are two primary threads to the discussion a presenting a novel semi implicit anelastic global dynamics model as it naturally emerges from a small scale dynamics model and b demonstrating that nonhydrostatic anelastic global models derived from small scale codes adequately capture a broad range of planetary flows while requiring relatively minor overhead due to the nonhydrostatic formulation of the governing

a model for the complete radial structure of the tropical cyclone wind field part ii wind field variability abstractpart i of this work developed a simple physical model for the complete radial structure of the low level azimuthal wind field in a tropical cyclone that compared well with observations however wind field variability in the model is tied principally to its external parameters given by the maximum wind speed and the radius of maximum wind the latter of which lacks a credible independent physical model for its variability here the authors explore the modes of variability that arise from the alternative specification of the model which takes the outer radius in lieu of the radius of maximum wind nondimensionalization of the model reveals two theoretical modes of structural variability in absolute angular momentum that are shown to closely match observations these two modes correspond to three modes of wind field variability associated with variations in intensity outer storm size and latitude these wind field modes are demonstrated to mirror the dominant modes of variability found in nature

a statistical analysis of the effects of vertical wind shear on tropical cyclone intensity change over the western north pacific abstractthe effect of vertical wind shear vws between different pressure levels on tc intensity change is statistically analyzed based on the best track data of tropical cyclones tcs in the western north pacific wnp from the joint typhoon warning center jtwc and the ecmwf interim reanalysis era interim data during 1981 2013 results show that the commonly used vws measure between 200 and 850 hpa is less representative of the attenuating deep layer shear effect than that between 300 and 1000 hpa moreover the authors find that the low level shear between 850 or 700 and 1000 hpa is more negatively correlated with tc intensity change than any deep layer shear during the active typhoon season whereas deep layer shear turns out to be more influential than low level shear during the remaining less active seasons further analysis covering all seasons exhibits that a tc has a better chance to intensify than to decay when the deep layer shear is lower than 7 9 m s 1 and the low level shear is below

are multiple tropical cyclone events similar among basins abstractthe present study intercompares multiple tropical cyclone event mtce characteristics among each global tropical cyclone tc basin using best track data specific focus is placed on examining the number of mtces and tcs during mtces the zonal distance between tcs during mtces and the spatiotemporal separation between genesis events during mtces the results suggest that the ratio of mtces relative to single tcs is substantially higher in the eastern north pacific enp western north pacific wnp and south indian ocean si basins compared to the north atlantic na and south pacific sp the prolific nature of enp wnp and si mtce activity results in approximately half of tcs occurring during mtces during new tc genesis the majority of preexisting tcs are generally located westward at a consistent zonal distance from new tc genesis for mtces within each basin with median values between 1620 and 1961 km tc induced rossby wave dispersion may set this zonal length scale as implied by it

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

tropical intraseasonal variability in version 3 of the gfdl atmosphere model abstracttropical intraseasonal variability is examined in version 3 of the geophysical fluid dynamics laboratory atmosphere model am3 in contrast to its predecessor am2 am3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds the am3 cumulus parameterization is a mass flux based scheme but also unlike that in am2 incorporates subgrid scale vertical velocities these play a key role in cumulus microphysical processes the am3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds which strongly influence large scale moisture and radiation fields the authors examine four am3 simulations using a control model and three versions with different modifications to the deep convection scheme in the control am3 using a convective closure based on cape relaxation both mjo and kelvin waves are weak relative to those in observations by modifying the convective closure and trigger assumptions to inhibit deep c

analysis of convectively coupled kelvin waves in the indian ocean mjo abstract the active convective phase of the madden julian oscillation hereafter active mjo comprises enhanced moist deep convection on its own temporal and spatial scales as well as increased variance in convection associated with higher frequency modes synoptic scale cloud superclusters apparently associated with convectively coupled kelvin waves occur within the active convective envelopes of most mjo events these convectively coupled kelvin waves also occur during the suppressed convective phase of the mjo hereafter suppressed mjo this observational study presents an analysis of outgoing longwave radiation and reanalysis data to determine how these waves behave differently as they propagate through the active and suppressed mjo time indices of the mjo and kelvin waves are derived for over the equatorial indian ocean dates of local extrema in these indices are used to composite data to discern how the waves and associated circulations behave on average then further composites are made based o

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

on large scale circulations in convecting atmospheres the dominant thinking about the interaction between large scale atmospheric circulations and moist convection holds that convection acts as a heat source for the large scale circulations while the latter supply water vapour to the convection we show that this idea has led to fundamental misconceptions about this interaction and offer an alternative paradigm based on the idea that convection is nearly in statistical equilibrium with its environment according to the alternative paradigm the vertical temperature profile itself rather than the heating is controlled by the convection which ties the temperature directly to the subcloud layer entropy the understanding of large scale circulations in convecting atmospheres can therefore be regarded as a problem of understanding the distribution in space and time of the subcloud layer entropy we show that the subcloud layer entropy is controlled by the sea surface temperature the surface wind speed and the large scale vertical velocity in the convecting layer and demonstrate how the recognition of this control leads to a simple physically consistent view of large scale flows ranging from the hadley and walker circulations to the 30 50 day oscillation in particular we argue that the direct effect of convection on large scale circulations is to reduce by roughly an order of magnitude the effective static stability felt by such circulations and to damp all of them

vertical mode and cloud decomposition of large scale convectively coupled gravity waves in a two dimensional cloud resolving model this paper describes an analysis of large scale o 1000 km convectively coupled gravity waves simulated using a two dimensional cloud resolving model the waves develop spontaneously under uniform radiative cooling and approximately zero mean flow conditions with wavenumber 2 of the domain appearing most prominently and right moving components dominating over left moving components for random reasons the analysis discretizes the model output in two ways first a vertical mode transform projects profiles of winds temperature and heating onto the vertical modes of the model s base state atmosphere second a cloud partitioning algorithm sorts sufficiently cloudy grid columns into three categories shallow convective deep convective and stratiform anvil results show that much of the tilted structures of the waves can be captured by just two main vertical spectral bands each consisting of a pair of vertical modes the slow modes have propagation speeds of 16 and 18 m s 1 and roughly a full wavelength vertical structure through the troposphere while the fast modes have speeds of 35 and 45 m s 1 and roughly a half wavelength structure deep convection anomalies in the waves are more or less in phase with the low level cold temperature anomalies of the slow modes and in quadrature with those of the fast modes owing to the characteristic life cycle of deep convective cloud systems shallow convective heating peaks 2 h prior to maximum deep convective heating while stratiform heating peaks 3 h after the onset of deep convection in the waves is preceded by a gradual deepening of shallow convection lasting a period of many hours results of this study are in broad agreement with simple two mode models of unstable large scale wave growth under the name stratiform instability differences here are that 1 the key dynamical modes have speeds in the range 16 18 m s 1 rather than 23 25 m s 1 owing to a shallower depth of imposed radiative cooling and 2 deep convective heating as well as stratiform heating is essential for the generation and maintenance of the slow modes

on the size distribution of atlantic tropical cyclones 1 the size of a tropical cyclone is known to vary considerably across storms though little is understood about the environmental and internal factors that modulate it making use of newly available extended tropical cyclone records that include information about storm structure we examine the size distribution of atlantic tropical cyclones using as a metric the radius of vanishing storm winds normalized by the theoretical upper bound given by the ratio of the potential intensity to the coriolis parameter we find that the distribution of this normalized outer radius is closely log normal

a quikscat climatology of tropical cyclone size 1 quikscat data of near surface wind vectors for the years 1999 2008 are used to create a climatology of tropical cyclone tc size defined as the radius of vanishing winds the azimuthally averaged radius of 12 ms 1 wind r12 is calculated for a subset of tcs n 2154 whose centers of circulation were clearly identifiable via subjective analysis of the quikscat analyzed wind field the outer radius r0 is determined from r12 using an outer wind structure model that assumes no deep convection beyond r12 the global median values of r12 and r0 are 197 km and 423 km respectively with statistically significant variation across ocean basins the global distribution of r12 is found to be approximately log normal the distribution of r0 is quantitatively much closer to log normal and the improvement in fit between r12 and r0 is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 and f moreover the normalization employed by dean et al 2009 is found to weaken rather than improve the log normal fit finally within a given storm both r12 and r0 tend to expand very slowly with time early in the storm lifecycle and then becomes quasi constant though significant variance exists across storms

observed tropical cyclone size revisited abstractthis work revisits the statistics of observed tropical cyclone outer size in the context of recent advances in our theoretical understanding of the storm wind field the authors create a new dataset of the radius of 12 m s 1 winds based on a recently updated version of the quikscat ocean wind vector database and apply an improved analytical outer wind model to estimate the outer radius of vanishing wind the dataset is then applied to analyze the statistical distributions of the two size metrics as well as their dependence on environmental parameters with a specific focus on testing recently identified parameters possessing credible theoretical relationships with tropical cyclone size the ratio of the potential intensity to the coriolis parameter is found to perform poorly in explaining variation of size with the possible exception of its upper bound the latter of which is in line with existing theory the rotating radiative convective equilibrium scaling of khairoutdinov and emanuel is also f

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

the present day simulation and twenty first century projection of the climatology of extratropical transition in the north atlantic abstractthis study explores the simulations and twenty first century projections of extratropical transition et of tropical cyclones tcs in the north atlantic with a newly developed global climate model the forecast oriented low ocean resolution flor version of the geophysical fluid dynamics laboratory gfdl coupled model version 2 5 cm2 5 flor exhibits good skill in simulating present day et properties e g cyclone phase space parameters a version of flor in which sea surface temperature sst biases are artificially corrected through flux adjustment flor fa shows much improved simulation of et activity e g annual et number this result is largely attributable to better simulation of basinwide tc activity which is strongly dependent on larger scale climate simulation flor fa is also used to explore changes of et activity in the twenty first century under the representative concentration pathway rcp 4 5 scenario a contrasting pattern is found in which regional tc density increas

hierarchical tropical cloud systems in an analog shallow water model abstract recent observations have revealed an hierarchy of cloud clusters and superclusters within the madden julian oscillation of the equatorial troposphere the authors here report on the results of simulations with a model based on a simple nonlinear analog of the shallow water equations the model consists of a troposphere represented by single values of vertical velocity and temperature and in which the horizontal motions are assumed always to represent the first baroclinic mode the troposphere overlies a subcloud layer of fixed depth in which the evolution of moist entropy is predicted the model is driven by specified values of radiative cooling and sea surface temperature and a newtonian relaxation of the surface wind toward a specified value the system is horizontally homogeneous except for an anisotropy owing to the equatorial effect an eastward propagating low wavenumber disturbance containing an hierarchy of superclusters and cloud clusters is spontaneously generated from a random initi

cloud resolving modeling of tropical circulations driven by large scale sst gradients this paper considers interactions between the moist atmospheric convection and the large scale flow driven by the large scale gradient of sea surface temperature a two dimensional computational framework is used with the horizontal domain size of 4000 km in which both the convective dynamics and the large scale flow are resolved rotational effects are not considered simulations are performed using either a prescribed temperature tendency mimicking the effects of radiative processes or a fully interactive radiation transfer model the simulations are performed for a period of 60 days with quasi equilibrium conditions attained after about a month the time mean large scale flow in the simulations features an ascending branch occupied by moist convection over a warm ocean and a cloud free descending branch over a cold ocean the time mean flow for the prescribed radiation case features a complex vertical structure characterized by two somewhat decoupled circulations in the lower and upper troposphere this is in stark contrast with the predominant first baroclinic mode structure typical of the observed large scale tropical circulations which is characterized by a single cell an idealized dry model featuring prescribed convective heat source suggests that the complex vertical structure is directly related to the deviation of the model temperature profile from the climatology quasi two day oscillations are a major transient feature of the simulations the oscillations are associated with radiation of gravity waves from the convective branch into the descending branch inclusion of the interactive radiation results in a significant modification of the large scale flow and has a dramatic impact on the strength and horizontal extent of convection water vapor and cloud condensate strongly interact with radiative processes to induce these paramount effects on the tropical large scale circulations

upscale impact of mesoscale disturbances of tropical convection on convectively coupled kelvin waves abstracttropical convection associated with convectively coupled kelvin waves cckws is typically organized by an eastward moving synoptic scale convective envelope with numerous embedded westward moving mesoscale disturbances such a multiscale structure of tropical convection is a challenge for present day cloud resolving simulations and its representation in global climate models it is of central importance to assess the upscale impact of mesoscale disturbances on cckws as mesoscale disturbances propagate at various tilt angles and speeds besides it is still poorly understood whether the front to rear tilted vertical structure of cckws can be induced by the upscale impact of mesoscale disturbances in the presence of upright mean heating here a simple multiscale model is used to capture this multiscale structure where mesoscale fluctuations are directly driven by mesoscale heating and synoptic scale circulation is forced by mean heating and eddy transfer of momentum and temperature the results s

upscale impact of mesoscale disturbances of tropical convection on synoptic scale equatorial waves in two dimensional flows abstractsuperclusters on the synoptic scale containing mesoscale systems are frequently organized by convectively coupled equatorial waves ccews present day global models struggle to simulate multiscale tropical convection and the upscale effects of mesoscale systems are not well understood a simple two dimensional multiscale model with prescribed two scale heating and eddy transfer of momentum and temperature drives the synoptic scale circulation successfully reproduces key features of flow fields with a front to rear tilt and compares well with results from a cloud resolving model crm in the scenario with an elevated upright mean heating the tilted vertical structure of synoptic scale circulation is still induced by the upscale impact of mesoscale disturbances in a faster propagation scenario the upscale impact becomes less important as a result of competing effects of eddy transfer of momentum and temperature while the synoptic scale circulation response to mean heating dominates in agre

on the spacing and draft distributions for pressure ridge keels the negative exponential distribution is reconsidered as a description of pressure ridge spacings and drafts it is found to give an excellent fit for drafts but not for spacings the spacing distribution is found to be fitted much better by a three parameter lognormal distribution of which the third parameter the threshold is dependent on the beam width of the instrument used to collect the ice bottom profile

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

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

eastward propagating 2 to 15 day equatorial convection and its relation to the tropical intraseasonal oscillation anomalies of outgoing longwave radiation olr in 1980 1989 were examined in a narrow latitude band about the equator to elucidate the propagation and interaction of tropical intraseasonal oscillations tios and synoptic scale convective activity hovmoller diagrams of olr data reconstructed from two frequency bands corresponding to periods of 30 60 days and 2 15 days respectively revealed a clear distinction between the phase speed of eastward moving tios 3 7 m s 1 and that of eastward synoptic scale convection 10 13 m s 1 coherent propagation of tios from the indian to the western pacific oceans was often observed with temporary diminution of amplitude over the maritime continent propagation of high frequency anomalies was generally confined to an individual basin dominance of eastward propagating synoptic scale convection in the equatorial zone contrasts sharply with the westward propagation of off equatorial convergence zones interaction between the tio and high frequency activity resolved by daily olr was visible as a modest enhancement of eastward synoptic scale events and of high frequency activity in general during the convectively active phase of the tio

a model for convectively coupled tropical waves nonlinearity rotation and comparison with observations abstract recent observational analysis of both individual realizations and statistical ensembles identifies moist convectively coupled kelvin waves in the tropics with supercluster envelopes of convection this observational analysis elucidates several key features of these waves including their propagation speed of roughly 15 m s 1 and many aspects of their dynamical structure this structure includes anomalously cold temperatures in the lower troposphere and warm temperatures in the upper troposphere below 250 hpa within and sometimes leading the heating region and strong updrafts in the wave and an upward and westward tilting structure with height below roughly 250 hpa other key features in the wave are that anomalous increases in convective available potential energy cape and surface precipitation lead the wave while the trailing part of the supercluster is dominated by stratiform precipitation the main result in this paper is the development of a simple model convective parameterization with n

a reassessment of the integrated impact of tropical cyclones on surface chlorophyll in the western subtropical north atlantic the impact of tropical cyclones on surface chlorophyll concentration is assessed in the western subtropical north atlantic ocean during 1998 2011 previous studies in this area focused on individual cyclones and gave mixed results regarding the importance of tropical cyclone induced mixing for changes in surface chlorophyll using a more integrated and comprehensive approach that includes quantification of cyclone induced changes in mixed layer depth here it is shown that accumulated cyclone energy explains 22 of the interannual variability in seasonally averaged june november chlorophyll concentration in the western subtropical north atlantic after removing the influence of the north atlantic oscillation nao the variance explained by tropical cyclones is thus about 70 of that explained by the nao which has well known impacts in this region it is therefore likely that tropical cyclones contribute significantly to interannual variations of primary productivity in the western subtropical north atlantic during the hurricane season

global composites of surface wind speeds in tropical cyclones based on a 12 year scatterometer database a 12 year global database of rain corrected satellite scatterometer surface winds for tropical cyclones tcs is used to produce composites of tc surface wind speed distributions relative to vertical wind shear and storm motion directions in each tc prone basin and various tc intensity stages these composites corroborate ideas presented in earlier studies where maxima are located right of motion in the earth relative framework the entire tc surface wind asymmetry is down motion left for all basins and for lower strength tcs after removing the motion vector relative to the shear direction the motion removed composites indicate that the surface wind asymmetry is located down shear left for the outer region of all tcs but for the inner core region it varies from left of shear to down shear right for different basin and tc intensity groups quantification of the surface wind asymmetric structure in further stratifications is a necessary next step for this scatterometer data set