dynamical aspects of twin tropical cyclones associated with the madden julian oscillation abstract a nonlinear shallow water model on the sphere is used to study barotropic aspects of the formation of twin tropical disturbances by madden julian oscillation mjo convection in the model the effect of mjo convection upon the lower tropospheric tropical circulation was simulated by an eastward moving meridionally elongated mass sink straddling the equator the intensity and propagation speed of the mass sink were chosen to simulate observations that mjo convection intensifies while nearly stationary in the eastern equatorial indian ocean weakens while moving eastward over the maritime continent again intensifies once it reaches the west pacific ocean and finally becomes stationary and dies off near the date line this mass sink produced twin cyclones in the two regions where it was stationary namely where it was initially turned on and where it was turned off in addition the mass sink produced two zonally elongated cyclonic potential vorticity anomalies straddling the equator in the reg

an analysis of moisture fluxes into the gulf of california this study examines the nature of episodes of enhanced warm season moisture flux into the gulf of california both spatial structure and primary time scales of the fluxes are examined using the 40 yr ecmwf re analysis data for the period 1980 2001 the analysis approach consists of a compositing technique that is keyed on the low level moisture fluxes into the gulf of california the results show that the fluxes have a rich spectrum of temporal variability with periods of enhanced transport over the gulf linked to african easterly waves on subweekly 3 8 day time scales the madden julian oscillation mjo at intraseasonal time scales 20 90 day and intermediate 10 15 day time scale disturbances that appear to originate primarily in the caribbean sea western atlantic ocean in the case of the mjo enhanced low level westerlies and large scale rising motion provide an environment that favors large scale cyclonic development near the west coast of central america that over the course of about 2 weeks expands northward along the coast eventually reaching the mouth of the gulf of california where it acts to enhance the southerly moisture flux in that region on a larger scale the development includes a northward shift in the eastern pacific itcz enhanced precipitation over much of mexico and the southwestern united states and enhanced southerly southeasterly fluxes from the gulf of mexico into mexico and the southwestern and central united states in the case of the easterly waves the systems that reach mexico appear to redevelop reorganize on the pacific coast and then move rapidly to the northwest to contribute to the moisture flux into the gulf of california the most intense fluxes into the gulf on these time scales appear to be synchronized with a midlatitude short wave trough over the u s west coast and enhanced low level southerly fluxes over the u s great plains the intermediate 10 15 day time scale systems have zonal wavelengths roughly twice that of the easterly waves and their initiation appears to be linked to an extratropical u s east coast ridge and associated northeasterly winds that extend well into the caribbean sea during their development phase the short 3 8 day and to a lesser extent the intermediate 10 15 day time scale fluxes tend to be enhanced when the convectively active phase of the mjo is situated over the americas

three different downstream fates of the boreal summer mjos on their passages over the maritime continent the boreal summer mjos exhibit three distinctive downstream evolutions on their passages over the maritime continent mc i smoothly transitioning from indian ocean io to western pacific type i ii rapidly decayed over the mc type ii and iii significantly intensified over the mc type iii during the life cycles of type i and iii mjos basin wide overturning circulations connect the convective dipoles between western and eastern north pacific for type ii mjo regional overturning circulations connect the convective dipoles between the io and western north pacific wnp for type i and iii mjos the associated convection over eastern io is able to generate strong kevin wave responses and significant positive sst anomalies over the mc and western pacific on the other hand for type ii mjo in the io a persistent convection lingers around the wnp it intensifies westerly monsoon flows thus preventing the generation of coherent positive sst anomalies ahead of the io mjo convection it also blocks the formation of a robust kelvin wave response over the mc and western pacific by delaying the northeastward migrations of the dry phase the convection of type i and iii mjos at eastern io is able to generate positive boundary layer moisture anomalies along with positive column integrated moisture tendencies over the mc and western pacific thus allowing them to propagate eastward smoothly on the other hand the type ii mjo convection in eastern io is associated with a very dry troposphere and negative column integrated moisture tendency over western pacific which result in the rapid decay of convection over the mc these results emphasize the important roles of robust kelvin wave responses and positive sst anomalies on the eastward propagation of boreal summer mjos over the mc through moistening the troposphere ahead of the convection

the madden julian oscillation barotropic dynamics and north pacific tropical cyclone formation part i observations low level barotropic dynamics may help to explain the modulation of eastern and western north pacific tropical cyclones by the madden julian oscillation mjo during northern hemisphere summer the mjo is characterized by alternating periods of westerly and easterly 850 mb zonal wind anomalies across the tropical pacific ocean when mjo 850 mb wind anomalies are westerly small scale slow moving eddies grow through barotropic eddy kinetic energy eke conversion from the mean flow these growing eddies together with strong surface convergence 850 mb cyclonic shear and high mean sea surface temperatures create a favorable environment for tropical cyclone formation periods of strong mjo easterlies over the pacific are characterized by lesser eke and negligible eddy growth by barotropic conversion the term 2 x is a leading contributor to low level barotropic eke conversion during mjo westerly 2 u9 u periods across the pacific indicating the importance of zonal variations in the westerly jet for producing concentrations of eddy energy this mechanism can be described as wave accumulation associated with variations of the low level zonal flow the conversion term 2 y contributes a smaller portion of the total conversion u9y9 u over the eastern pacific but is of comparable importance to 2 x during westerly mjo events in the 2 u9 u western pacific

northward propagation of the subseasonal variability over the eastern pacific warm pool 1 previous studies suggest that easterly vertical shear of summer mean flow could be a key factor in the northward propagation of the subseasonal variability ssv over the asian monsoon region e g jiang et al 2004 analysis indicates that this same mechanism may also be dictating propagation features over the eastern pacific epac consistent with the presence of local easterly vertical wind shear northward propagation of the ssv is also evident over the epac with a phase speed of about 0 6 deg day 1 moreover similar to its counterpart in the indian ocean the northward propagating ssv over this region is also characterized by positive anomalies of equivalent barotropic vorticity and lower tropospheric specific humidity and planetary boundary layer pbl convergence to the north of the convection center thus the present study provides another independent example of the essential role that easterly vertical wind shear may be playing in regulating the meridional migration of the ssv

clustering of synoptic activity by indian summer monsoon intraseasonal oscillations 1 active and break phases of the indian summer monsoon are characterized by enhancement and decrease of precipitation over the monsoon trough region using genesis data of monsoon low pressure systems lps and circulation data for the period 1954 to 1993 it is shown that the frequency of occurrence of lps is nearly 3 5 times higher in the active phase of monsoon as compared to the break phase in addition the tracks of these synoptic systems are also strongly spatially clustered along the monsoon trough during the active phase of the monsoon the enhanced decreased frequency of occurrence of lps during active break phases is due to modulation of meridional shear of zonal winds and cyclonic vorticity along the monsoon trough by the intraseasonal oscillations iso

observations of tropical precipitating clouds ranging from shallow to deep convective systems 1 regional and temporal variability in a broad spectrum of tropical precipitation systems is investigated in conjunction with the large scale environment the analysis utilizes four storm categories shallow cumulus congestus deep stratiform and deep convective determined from tropical rainfall measuring mission trmm measurements deep stratiform and deep convective systems are found to be clearly correlated with large scale circulation deduced from a reanalysis data set and are modulated by a distinct seasonal cycle over land the shallow category is practically the only component of tropical oceanic rainfall for cold sea surfaces while it gives way to deeper systems as sst exceeds 28 29 c the cloud horizontal scale of organized rainfall systems tends to be increasingly extensive relative to the raining portion as the system becomes larger the present results are discussed in light of existing relevant studies

representation of boreal winter mjo and its teleconnection in a dynamical ensemble seasonal prediction system abstractthis study examines the representation of the madden julian oscillation mjo and its teleconnection in boreal winter in the global seasonal forecast system version 5 glosea5 using 20 y

seasonal variations of tropical intraseasonal oscillations a 20 25 day oscillation in the western pacific abstract spectral analysis within a movable time window is used to investigate the frequency and intensity of tropical oscillations with intraseasonal time scales surface and rawinsonde time series from several locations in the western pacific and indian oceans are used evidence is provided that the madden julian oscillation mjo in the indian ocean region shows a seasonal variation in its preferred period from 50 days during northern hemisphere winter to about 35 days during summer though this evidence is weak and stretches the limits of our ability to define a precise period for the oscillation in the western tropical pacific during the september december season a pronounced spectral peak with a central frequency between 20 and 25 days is observed this spectral peak appears to reveal an oscillation that is distinct from the mjo but may also result from coupling between the large scale motion and latent heat release on much smaller scales a relationship between the oscillation and the occurrence

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

north south variations of tropical storm genesis locations in the western hemisphere in the western hemisphere tropical storms or hurricanes form in the north atlantic and eastern north pacific previous studies have focused on storm variability in the frequency duration and intensity in each basin here we find that the tropical storm genesis location in one ocean basin ties to the other one on both interannual and multidecadal timescales a northward southward shift of the tropical storm genesis location is associated with a southward northward variation in the other ocean basin the change of cross central america wind in the upper troposphere which induces an out of phase relation of vertical wind shear bridges storm activity in the two ocean basins sea surface temperatures in both the tropical pacific and north atlantic can induce the zonal wind change across central america it implies that hurricane outlooks can be improved by considering the two ocean basins together and thus helping reduce the damage caused by hurricane landfall

impact of the madden julian oscillation on the summer west african monsoon in amip simulations at intraseasonal timescales convection over west africa is modulated by the madden julian oscillation mjo in this work we investigate the simulation of such relationship by 11 state of the art atmospheric general circulation models runs with prescribed observed sea surface temperatures in general the atmospheric model intercomparison project simulations show good skill in capturing the main characteristics of the summer mjo as well as its influence on convection and rainfall over west africa most models simulate an eastward spatiotemporal propagation of enhanced and suppressed convection similar to the observed mjo although their signal over west africa is weaker in some models in addition the ensemble average of models composites gives a better performance in reproducing the main features and timing of the mjo and its impact over west africa the influence on rainfall is well captured in both sahel and guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as in the observations furthermore the results show that a strong active convection phase is clearly associated with a stronger african easterly jet aej but the weak convective phase is associated with a much weaker aej our analysis of the equatorial waves suggests that the main impact over west africa is established by the propagation of low frequency waves within the mjo and rossby spectral peaks results from the simulations confirm that it may be possible to predict anomalous convection over west africa with a time lead of 15 20 day

a signal processing algorithm for the extraction of thin freshwater ice thickness from short pulse radar data a radar data processing algorithm is presented which can estimate freshwater ice thicknesses both greater than and less than the normal minimum resolvable thickness the basis for the algorithm is a model of the geophysical system and the resulting phase signature of the transfer function the algorithm attempts to isolate this signature and estimate the relevant parameters in principle the method can be used to detect layering in other dielectric media the algorithm was based on a simple model for scattering from a thin ice layer and refined using radar returns taken over a range of thin ice thicknesses in a laboratory environment the method was also applied to data obtained with two different radar frequencies and over a wide range of thickness and surface roughness the results were compared to thickness estimates from classical deconvolution methods

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

mid wisconsin sediment record from baldwin lake reveals hemispheric climate dynamics southern ca usa abstract recently acquired cores from baldwin lake southern california document the first regional terrestrial based evidence for glacial period millennial to orbital scale climate variability eight ams 14c dates on a 14 m core from the lake s present day depocenter provide initial age control over the interval from 20 000 to 48 000 years before present bp a linear age model extends the record to a minimum age of 65 000 years bp a combination of lithologic description and one cm contiguous sedimentological analyses indicates significant changes in the dominant type of depositional environment over the length of the record at millennial to orbital time scales as a first order interpretation the dominant sedimentary environments alternate between permanent and ephemeral lake systems orbital scale forcing includes long term winter summer insolation variability and its modulation of winter storm tracks and the north american monsoon respectively millennial scale variability is attributed to extra tropical ocean atmosphere dynamics akin to historical interdecadal pacific climate variability in addition there is notable correspondence to the independently dated greenland ice core record gisp 2 at millennial to orbital time scales suggesting that baldwin lake contains in addition to its local regional record a hemispheric record of climate change similar to owens pyramid and summer lake of central and northwestern north america an initial comparison to gisp2 18o ice indicates that north atlantic interstadials correlate to permanent lake environments in coastal southwestern north america these results present a notable conflict with the proposed super enso phenomenon in the western tropical pacific these results also highlight the necessity for acquiring additional high resolution glacial period records for resolving questions of spatial temporal phasing of late quaternary climates

dynamics of a simulated north american monsoon gulf surge event abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well documented but their detailed dynamical evolution is still unclear in this study a convection permitting simulation is performed over the core monsoon region for the 12 14 july 2004 gulf surge event and the dynamics of the simulated surge are examined initially convection associated with the tropical easterly wave precursor to tropical cyclone blas creates a disturbance in the southern goc on early 12 july this disturbance is a precursor to the gulf surge on 13 july and is a kelvin shock internal bore under the influence of rotation that diss

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

effect of dry large scale vertical motions on initial mjo convective onset anomalies of eastward propagating large scale vertical motion with 30 day variability at addu city maldives move into the indian ocean from the west and are implicated in madden julian oscillation mjo convective onset using ground based radar and large scale forcing data derived from a sounding array typical profiles of environmental heating moisture sink vertical motion moisture advection and eulerian moisture tendency are computed for periods prior to those during which deep convection is prevalent and those during which moderately deep cumulonimbi do not form into deep clouds convection with 3 7 km tops is ubiquitous but present in greater numbers when tropospheric moistening occurs below 600 hpa vertical eddy convergence of moisture in shallow to moderately deep clouds is likely responsible for moistening during a 3 7 day long transition period between suppressed and active mjo conditions although moistening via evaporation of cloud condensate detrained into the environment of such clouds may also be important reduction in large scale subsidence associated with a vertical velocity structure that travels with a dry eastward propagating zonal wavenumbers 1 1 5 structure in zonal wind drives a steepening of the lapse rate below 700 hpa which supports an increase in moderately deep moist convection as the moderately deep cumulonimbi moisten the lower troposphere more deep convection develops which itself moistens the upper troposphere reduction in large scale subsidence associated with the eastward propagating feature reinforces the upper tropospheric moistening helping to then rapidly make the environment conducive to formation of large stratiform precipitation regions whose heating is critical for mjo maintenance

energetics of east pacific easterly waves during intraseasonal events abstractthe background atmospheric state of the east pacific warm pool in which easterly waves develop varies dramatically on intraseasonal time scales east pacific intraseasonal variability is well known to modulate local convective and circulation patterns westerly easterly intraseasonal phases are associated with westerly easterly low level wind and positive negative convective anomalies this study investigates the perturbation available potential energy pape and perturbation kinetic energy pke budgets of easterly waves composited during westerly easterly and neutral intraseasonal phases respectively the mechanisms magnitudes locations and vertical structures of easterly waves are shown to strongly vary as a function of intraseasonal phase easterly waves draw energy from low level barotropic conversion regardless of phase although the location and magnitude of the conversion varies strongly during neutral and westerly intraseasonal phases the generation of pape associated with

rossby waves in zonally opposing mean flow behavior in northwest pacific summer monsoon abstract the interactions between monsoon circulations and tropical disturbances in the northwest pacific where the low level mean flow is westerly in the west and easterly in the east are studied with a barotropic model the authors model results suggest that the scale contraction by the confluent background flow the nonlinear dynamics the effect and the large scale convergence are important for the energy and enstrophy accumulation near the region where the zonal flow reverses the energy enstrophy accumulation can be maintained with a continuous rossby wave emanation upstream the largest accumulation occurs when the emanating zonal wavelength is around 2000 km longer rossby waves experience less scale contraction and nonlinear effects while shorter rossby waves cannot hold a coherent structure against dispersive effects the nonlinear energy enstrophy accumulation mechanism is significantly different from previous linear energy accumulation theories in the linear theories this is primarily a

effects of monsoon trough intraseasonal oscillation on tropical cyclogenesis over the western north pacific abstractthe effects of intraseasonal oscillation iso of the western north pacific wnp monsoon trough on tropical cyclone tc formation were investigated using the advanced research weather research and forecasting arw model a weak vortex was specified initially and inserted into the background fields containing climatological mean anomalies associated with active and inactive phases of monsoon trough isos the diagnosis of simulations showed that monsoon trough iso can modulate tc development through both dynamic and thermodynamic processes the dynamic impact is attributed to the lower midtropospheric large scale vorticity associated with monsoon trough iso interactions between cyclonic vorticity in the lower middle troposphere during the active iso phase and a vortex lead to the generation of vortex scale outflow at the midlevel which promotes the upward penetration of friction induced ascending motion and thus upward moisture transport in addition the low level convergence associated with ac

the influence of the mjo on upstream precursors to african easterly waves abstractthe madden julian oscillation mjo produces alternating periods of increased and reduced precipitation and african easterly wave aew activity in west africa this study documents the influence of the mjo on the west african monsoon system during boreal summer using reanalysis and brightness temperature fields mjo related west african convective anomalies are likely induced by equatorial kelvin and rossby waves generated in the indian ocean and west pacific by the mjo which is consistent with previous studies the initial modulation of tropical african convection occurs upstream of west africa near the entrance of the african easterly jet aej previous studies have hypothesized that an area to the east of lake chad is an initiation region for aews called the trigger region in this study this area exhibits significant intraseasonal convection and wave activity anomalies prior to the wet and dry mjo phases in the west african monsoon region in the trigger region cold tropospheric tempera

diagnosis of the mjo modulation of tropical cyclogenesis using an empirical index the modulation of tropical cyclone activity by the madden julian oscillation mjo is explored using an empirical genesis potential gp index composite anomalies of the genesis index associated with the different mjo phases are consistent with the composite anomalies in tc genesis frequency that occur in the same phases indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes of the four environmental variables that enter the genesis potential index the midlevel relative humidity makes the largest contribution to the mjo composite gp anomalies the second largest contribution comes from the low level absolute vorticity and only very minor contributions come from the vertical wind shear and potential intensity when basin integrated mjo composite anomalies of the gp index are regressed against basin integrated composite anomalies of tc genesis frequency the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities the gp index captures the mjo modulation of tc genesis to a lesser degree than the climatological annual cycle of genesis to which it was originally tuned this may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances not well captured in the gp index computed from weekly data to the intraseasonal tc genesis frequency fluctuations

mjo initiation in the real time multivariate mjo index abstractmadden julian oscillation mjo initiation in the real time multivariate mjo rmm index is explored through an analysis of observed case studies and composite events specific examples illustrate that both the dates of mjo initiation and the existence of the mjo itself can vary substantially among several well known mjo indices depending on whether the focus is on convection or circulation composites of primary mjo initiation events in which the rmm index rapidly increases in amplitude from a non mjo state to an mjo state are presented and are supplemented by two case studies from the 1985 86 winter season results illustrate that for primary mjo initiation events in the indian ocean rmm phase 1 slowly eastward propagating 850 hpa 200 hpa easterly westerly anomalies over the indian ocean precede the amplification of the rmm index by at least 10 days while suppressed convection over the western pacific ocean precedes the amplification by 5 days these local eastern hemispheric prede

influence of the madden julian oscillation and caribbean low level jet on east pacific easterly wave dynamics abstractthe east pacific warm pool exhibits basic state variability associated with the madden julian oscillation mjo and caribbean low level jet cllj which affects the development of easterly waves ews this study compares and contrasts composite changes in the background environment eddy kinetic energy eke budgets and ew tracks during mjo and cllj events while previous studies have shown that the mjo influences jet activity in the east pacific the influence of the mjo and cllj on the east pacific and ews is not synonymous the cllj is a stronger modulator of the itcz than the mjo while the mjo has a more expansive influence on the northeastern portion of the basin anomalous low level westerly mjo and cllj periods are associated with favorable conditions for ew development paralleling the central american coast contrary to previous findings about the relationship of the cllj to ews easterly mjo and cllj periods support enhanced itcz ew development although the cllj is a greater modulato

global association of the madden julian oscillation with monsoon lows and depressions previous research has revealed that monsoon lows and depressions are modulated on intraseasonal time scales in a few regions including india australia and the east pacific this study examines whether such modulation occurs on a global scale and in particular how the madden julian oscillation mjo is associated with changes in synoptic scale vortices across all monsoon regions the spatial climatology of monsoon disturbances is largely insensitive to mjo amplitude however monsoon disturbance frequency mdf varies substantially with mjo phase with regional perturbations of 25 to 90 percent of the seasonal mean value across the tropics in off equatorial locations mdf maxima occur in locations where the mjo enhances low level cyclonic vorticity typically near the western edge of mid level moisture perturbations in contrast equatorial mdf perturbations are in phase with mjo moisture and rainfall anomalies with maxima in regions with strong low level zonal wind convergence

fluid flow along a strike slip fault at the toe of the oregon accretionary prism implications for the geometry of frontal accretion sediment offscraping and accretion takes place predominantly by landward vergent thrusting along most of the oregon accretionary prism north of latitude 44 50 n this indicates very low basal shear stress probably due to near lithostatic fluid pressure on the decollement horizon recent multichannel seismic and sidescan sonar studies have demonstrated the existence of an oblique basement involved left lateral strike slip fault termed the wecoma fault it cuts abyssal plain sediments and oceanic basement of the subducting plate where the wecoma fault intersects the wedge thrust front at 45 09 n accretion to the wedge occurs through an anomalous seaward vergent thrust linear fault parallel erosional gullies which trend obliquely across the slope on the seaward flank of the frontal anticline in the accretionary wedge are interpreted as marking the surface traces of splays of the wecoma fault data collected during six alvin dives on and around these gullies demonstrate that fluid expulsion from the deforming sediments is preferentially concentrated along the fault traces evidence includes the presence of chemosynthetic biological communities pervasive veining and fracturing of the rock and extensive carbonate cementation all forming preferentially within the gullies this strike slip fault apparently acts as a high angle fluid escape conduit channeling fluids from deep within the wedge to the surface we propose that this fluid conduit causes the local inversion of thrusting to seaward vergence by allowing the escape of highly overpressured fluids from the incipient decollement horizon the consequent increase in basal effective normal stress favors the development of a seaward vergent thrust the discovery of this strike slip fault acting as an efficient fluid conduit to the surface of the wedge emphasizes the generally unappreciated importance of strike slip and normal faults in dewatering accretionary prisms such dewatering features may significantly influence the development of large scale structures and they have broad applicability to other tectonic settings including collision zones and continental fold and thrust belts

tropical cyclogenesis associated with kelvin waves and the madden julian oscillation abstractthe madden julian oscillation mjo influences tropical cyclone formation around the globe convectively coupled kelvin waves are often embedded within the mjo but their role in tropical cyclogenesis remains uncertain this case study identifies the influences of the mjo and a series of kelvin waves on the formation of two tropical cyclones typhoons rammasun and chataan developed in the western north pacific on 28 june 2002 two weeks earlier conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection the easterlies gave way to equatorial westerlies as the convective envelope of the madden julian oscillation moved into the region a series of three kelvin waves modulated the development of the westerlies cyclonic potential vorticity pv developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward rammasun and chataan emerged from the apparent breakdown of this strip the

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

systematic variation of summertime tropical cyclone activity in the western north pacific in relation to the madden julian oscillation abstract the variability of observed tropical cyclone tc activity i e genesis track and landfall in the western north pacific wnp is examined in relation to the various categories of the madden julian oscillation mjo during summer june september for the period 1979 2004 the mjo categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data the number of tcs increases when the mjo related convection center is located in the wnp the axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large scale environments associated with both the eastward and northward propagation of the mjo and the intraseasonal variability of the wnp subtropical high furthermore the authors show that the density of tc tracks in each mjo category depends on the systematic shift in the main genesis regions at first order also the shift is affected by the prevailing large scale steering flows in each mjo category when th

north central pacific tropical cyclones impacts of el nino southern oscillation and the madden julian oscillation abstractboth el nino southern oscillation enso and the madden julian oscillation mjo have been documented in previous research to impact tropical cyclone tc activity around the globe this study examines the relationship of each mode individually along with a combined index on tropical cyclone activity in the north central pacific approximately twice as many tropical cyclones form in the north central pacific in el nino years compared with la nina years these differences are attributed to a variety of factors including warmer sea surface temperatures lower sea level pressures increased midlevel moisture and anomalous midlevel ascent in el nino years when the convectively enhanced phase of the mjo is located over the eastern and central tropical pacific the north central pacific tends to have more tropical cyclone activity likely because of reduced vertical wind shear lower sea level pressures and increased vertical motion the convectively enhanced phase of the mjo is also responsible for

remote influences on the indian monsoon low level jet intraseasonal variations a strong low level jet llj also known as the findlater jet develops over the arabian sea during the indian summer monsoon this jet is an essential source of moisture for monsoonal rainfall over the densely populated indian subcontinent and is a key contributor to the indian ocean oceanic productivity by sustaining the western arabian sea upwelling systems the llj intensity fluctuates intraseasonally within the 20 to 90 day band in relation with the northward propagating active and break phases of the indian summer monsoon our observational analyses reveal that these large scale regional convective perturbations only explain about half of the intraseasonal llj variance the other half being unrelated to large scale convective perturbations over the indian ocean we show that convective fluctuations in two regions outside the indian ocean can remotely force a llj intensification four days later enhanced atmospheric deep convection over the northwestern tropical pacific yields westerly wind anomalies that propagate westward to the arabian sea as baroclinic atmospheric rossby waves suppressed convection over the eastern pacific north american monsoon region yields westerly wind anomalies that propagate eastward to the indian ocean as dry baroclinic equatorial kelvin waves those largely independent remote influences jointly explain 40 of the intraseasonal llj variance that is not related to convective perturbations over the indian ocean i e 20 of the total with the northwestern pacific contributing twice as much as the eastern pacific taking into account these two remote influences should thus enhance the ability to predict the llj

mjo related sst variations over the tropical eastern pacific during northern hemisphere summer abstract the madden julian oscillation mjo significantly modulates eastern tropical pacific sea surface temperatures ssts during northern hemisphere summer typical sst variations during an mjo life cycle are 0 4 0 5 c considerably higher variations occur with the strongest events 1 2 c the magnitudes of these variations are comparable to those associated with west pacific mjo variability during nh winter sst anomalies to the north of 4 n where the strongest modulation of east pacific convection by the mjo occurs are 180 out of phase with equatorial anomalies these sst variations are responsible for variations in surface saturation equivalent potential temperatures of greater than 3 c the highest ssts lead maximum convection by about 10 days and ssts begin to cool with the onset of enhanced convection off equatorial sst anomalies are most likely due to variations in surface latent heat flux although shortwave flux anomalies are important in the heart of the mjo convective region decrea

the amplification of east pacific madden julian oscillation convection and wind anomalies during june november abstract madden julian oscillation mjo wind and convection anomalies are locally amplified over the northeast pacific warm pool during june november composite analysis using ncep reanalysis data indicates that perturbation available potential energy pape production through the positive correlation of intraseasonal temperature and convective diabatic heating anomalies supports the local intensification of mjo related east pacific warm pool wind anomalies pape production is maximum during periods of strong mjo convection and low level westerly wind perturbations pape is converted to perturbation kinetic energy through positive correlations between intraseasonal temperature and vertical velocity microwave sounding unit msu temperature and noaa outgoing longwave radiation data support the energy budget results derived from ncep reanalysis the amplified east pacific circulation enhances surface convergence and latent heat flux anomalies during mjo convective periods the surface convergence anomalie

roles of the synoptic scale wave train the intraseasonal oscillation and high frequency eddies in the genesis of typhoon manyi 2001 abstractexperiments using the weather research and forecasting wrf model were conducted to investigate the effects of multiscale motions on the genesis of typhoon manyi 2001 in the western north pacific the precursor signal associated with this typhoon genesis was identified as a northwest southeast oriented synoptic scale wave train swt the model successfully simulated the genesis of the typhoon in the wake of the swt further experiments were conducted to isolate the effects of the swt the intraseasonal oscillation iso and high frequency shorter than 3 days eddies in the typhoon formation removing the swt in the initial and boundary conditions eliminates the typhoon genesis this points out the importance of the swt in the typhoon genesis it was noted that the swt strengthened the wake cyclone through southeastward energy dispersion the strengthening wake cyclone triggered multiple episodes of strong sustained convective updrafts leading to aggregation of vertical vorticity and formatio

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

on the formation of amex tropical cyclones irma and jason abstract the amex observational dataset with its high temporal and spatial resolution has been used to study the formation and structure of tropical cyclones irma and jason these systems developed and evolved entirely within the experiment s special observing network the study is mostly based upon six hourly numerical analyses of the mass and wind fields on 11 vertical levels over a 1 25 lat long grid the systems are traced from prior to the formation of a resolvable closed surface circulation to when they were operationally classified as tropical cyclones the discussion focuses on the synoptic to cyclone scale changes during formation time sections of various kinematic variables together with an index of deep convection obtained from digital satellite cloud imagery are used to trace the development both systems developed during active phases of the monsoon and initially were of maximum intensity in the middle troposphere low level spinup occurred in three stages the first stage was associate

external influences on hurricane intensity part i outflow layer eddy angular momentum fluxes abstract outflow layer winds were objectively analyzed every 12 h for 6 days during the life cycle of hurricane elena 1985 a high correlation was found between angular momentum fluxes by azimuthal eddies at large radii and central pressure changes in the storm 27 33 h later momentum flux by eddies exceeded that by the azimuthal mean outside the 800 km radius while vortex spinup by the eddies reached instantaneous magnitudes as large as 25 m s 1 day outflow maxima and minima repeatedly appeared more than 1000 km from the hurricane center and tracked inward with time the results provide evidence of significant environmental control on the behavior of the storm after reaching hurricane strength elena experienced a major secondary intensification associated with a large inward cyclonic eddy momentum flux produced by the passage of a middle latitude trough north of the hurricane an outflow maximum appeared radially inside of the eddy momentum source consistent with balanced vortex theory and tracke

causes of intraseasonal diabatic heating variability over and near the tibetan plateau in boreal summer the structure and evolution features of the first two leading modes of the intraseasonal diabatic heating variability over the tibetan plateau tp during northern summer are investigated using reanalysis and observational data both of the leading modes present a dominant 10 30 day intraseasonal oscillation iso the first mode is characterized by a perturbation center over the southern tp stp which remains quasi stationary and is closely related to the low latitude iso the associated low latitude iso is originated from the tropical western pacific wp and propagates westward northwestward toward northwestern india along the mean monsoon trough the westward propagation near the south china sea is mainly attributed to anomalous meridional vorticity advection and the advection of the planetary vorticity by iso flow the stationary feature of the perturbation over the stp is ascribed to the topographical features around the stp the intraseasonal heating variability over the stp is attributed to the alternation of anticyclonic and cyclonic flow associated with the westward propagating iso perturbation originated from the tropical wp the second leading mode is characterized by an east west asymmetric structure over the tp the intraseasonal diabatic heating anomaly propagates clockwise from the northwestern to eastern tp while a heating anomaly with an opposite sign propagates from the southeastern to western tp the mid latitude rossby wave trains play an essential role in forming the dipole structure the wave trains propagate southeastward before reaching the tp and then eastward as they cross the tp the source of anomalous water vapor over the tp is originated from lower latitudes the upper and lower level wave trains are well coupled over the tp exhibiting a baroclinic structure

modulation of eastern north pacific hurricanes by the madden julian oscillation abstract hurricane and tropical storm statistics verify the modulation of eastern pacific tropical systems by the madden julian oscillation mjo as hypothesized by maloney and hartmann over twice as many named tropical systems hurricanes and tropical storms accompany equatorial 850 mb westerly anomalies than accompany equatorial easterly anomalies and the systems that do exist are stronger hurricanes are over four times more numerous during westerly phases of the mjo than during easterly phases the current study constructs a composite life cycle of the mjo during may november 1979 95 using an index based on the 850 mb equatorial zonal wind equatorial kelvin waves propagating eastward from convective regions of the western pacific ocean alter dynamical conditions over the eastern pacific ocean westerly easterly equatorial 850 mb wind anomalies are accompanied by enhanced suppressed convection over the eastern pacific hurricane region convection locally amplifies the wind anomalies over the ea

intraseasonal variability associated with wet monsoons in southeast arizona the intraseasonal evolution of the north american monsoon in southeast arizona during the 1980 93 period is investigated using a neural network based nonlinear classification technique known as the self organizing map som the goal of the som algorithm is to discover meaningful low dimensional structures hidden in the high dimensional observations various daily lagged atmospheric fields 850 hpa meridional winds 700 hpa specific humidity 500 hpa geopotential heights and 850 500 hpa thickness for the summer season june july august september of the 1980 93 period are used in the nonlinear classification of monsoon modes special emphasis is given to the wettest monsoon modes the neural network classification successfully captures the multidimensional interaction of the atmospheric variables during the monsoon evolution and shows monsoon bursts and breaks in a given year spectral analysis of daily summer rainfall in the study area reveals a significant peak in the 12 18 day band a secondary and significant peak is also found near 40 days thus monsoon bursts and breaks seem to be modulated by low frequency variability the som nonlinear classification shows that the mature phase of the monsoon is associated with two distinct intraseasonal 10 days wet monsoon modes the signature of the wettest monsoon mode is a zonal three cell anomalous midtropospheric height pattern over the north pacific north american sector suggesting a largescale dynamical mechanism possibly linked to sea surface temperature sst anomalies in the north pacific this zonal mode which is most frequent in july and august is characterized by an enhanced and northeastwarddisplaced monsoon ridge large amounts of midtropospheric moisture over the study area and an out of phase relationship between precipitation in the southwest united states and precipitation in the great plains the zonal mode has been recognized in longer datasets and it is the most typical mode that characterizes the mature phase of the monsoon in the southwest united states in contrast the second wettest intraseasonal monsoon mode does not show a monsoon ridge but a meridional three cell anomalous midtropospheric height pattern along the west coast of north america weak height anomalies over the rest of north america and large amounts of moisture over the study area importantly this meridional mode which is most frequent in august and september does not show out of phase links to great plains precipitation the meridional wet mode also shows an anomalous low level cyclonic circulation off the west coast of central south mexico suggesting that convective activity off the southern mexican coast possibly associated with the intertropical convergence zone may cross over the isthmus of tehuantepec toward the gulf of mexico and the southern united states this would explain the weak link between precipitation in the southwest and precipitation in the great plains during august and september of the 1980 93 period at more regional scales the zonal wet mode is also characterized by a latitudinal gradient of sst anomalies between baja california and southern mexico and reversed low level flow over the gulf of california looking at extreme wet monsoons outside of the study period e g 1955 1959 1999 it is shown that the positive sst anomaly pattern along the pacific coast of baja california which characterized wet events during 1980 93 can be completely reversed during other extreme wet events these contrasting results suggest that interaction between local and remote forcing mechanisms over the study area are complex during extreme events and needs further investigation

the itcz in the central and eastern pacific on synoptic time scales the itcz in the central and eastern pacific on synoptic time scales is highly dynamic the active season extends roughly from may through october during the active season the itcz continuously breaks down and re forms and produces a series of tropical disturbances the life span of the itcz varies from several days to 3 weeks sixty five cases of itcz breakdown have been visually identified over five active seasons 1999 2003 in three independent datasets itcz breakdown can be triggered by two mechanisms 1 interaction with westward propagating disturbances wpds and 2 the vortex rollup vr mechanism results show that the frequency of occurrence of itcz breakdown from these two mechanisms is the same the vr mechanism may have been neglected because the produced disturbances are rather weak and they may dissipate quickly the itcz shows a strong tendency to re form within 1 2 days in the same location the itcz may break down via the vr mechanism without any other support and thus it may continuously generate numerous tropical disturbances throughout the season there are two main differences between the two mechanisms 1 the wpds induced itcz breakdown tends to create one or two vortices that may be of tropical depression strength the vr induced itcz breakdown generates several nearly equal sized weak disturbances 2 the wpds tend to disturb the itcz in the eastern pacific only disturbances generally move along the mexican coast after shedding off from the itcz and do not further disturb the itcz in the central pacific therefore the vr mechanism is observed more clearly and is the dominating mechanism for itcz breakdown in the central pacific

the influence of the madden julian oscillation on tropical cyclone activity in the fiji region abstract this study examines the modulation of tropical cyclone tc activity by the madden julian oscillation mjo in the fiji samoa and tonga regions fst region using joint typhoon warning center best track cyclone data and the mjo index developed by wheeler and hendon results suggest strong mjo tc relationships in the fst region the tc genesis patterns are significantly altered over the fst region with approximately 5 times more cyclones forming in the active phase than in the inactive phase of the mjo this modulation is further strengthened during el nino periods the large scale environmental conditions i e low level relative vorticity upper level divergence and vertical wind shear associated with tc genesis show a distinct patterns of variability for the active and inactive mjo phases the mjo also has a significant effect on hurricane category and combined gale and storm category cyclones in the fst region the occurrences of both these cyclone categories are increased in the active

a statistical analysis of relationships between western north pacific tropical cyclones and extratropical circulation patterns accompanying the madden julian oscillation abstractrelationships between the madden julian oscillation mjo and the extratropical circulation have been studied extensively and applied in operational settings to improve subseasonal predicti

interactions between typhoon megi 2010 and a low frequency monsoon gyre abstractthe arw model is used to investigate the sharp northward turn of super typhoon megi 2010 after it moved westward and crossed the philippines the ncep analyzed fields during this period are separated into a slowly varying background flow component a 10 60 day low frequency component representing the monsoon gyre and a 10 day high pass filtered component representing megi and other synoptic scale motion it appears that the low frequency 10 60 day monsoon gyre interacted with megi and affected its track to investigate the effect of the low frequency mode on megi numerical experiments were designed in the control experiment the total fields of the analysis are retained in the initial and boundary conditions and the model is able to simulate megi s sharp northward turn in the second experiment the 10 60 day monsoon gyre mode is removed from the initial and lateral boundary fields and megi moves westward and slightly northwestward without turning north tracks of the relative positions b

on relationships between nonrecurving western north pacific tropical cyclones the madden julian oscillation and the east asian subtropical jet abstracta 200 hpa zonal momentum budget is performed to examine the role that western north pacific tropical cyclones tcs play in helping to organize intraseasonal extratropical circulation anoma

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

latent heating characteristics of the mjo computed from trmm observations the tropical rainfall measurement mission s trmm spectral latent heating algorithm shows the contributions of different forms of convection to the latent heating profiles of the madden julian oscillation over the central indian and west pacific oceans in both oceanic regions storms containing broad stratiform regions produce increased upper level heating during active madden julian oscillation mjo phases the largest differences between the central indian and west pacific ocean heating are associated with heating produced by convective elements examination of the most extreme forms of convection shows that mesoscale organized convection often produces at least as much latent heat as young vigorous deep convection heating from nonextreme often midlevel topped convection is an important component of the mjo heating in both regions in all stages of the mjo over the central indian ocean the heating profile changes from having a maximum at 2 km due to nonextreme convection to a profile during the active stage that has two maxima one at 3 km due to nonextreme convection and 6 km owing to numerous mature mesoscale storms with broad stratiform precipitation components over the west pacific the maxima at 3 and 6 km are present in all mjo stages but the magnitude of the 6 km maximum sharply increases in the active mjo stage due to an increase in the number of storms with broad stratiform precipitation areas

seasonal modulation of tropical intraseasonal oscillations on tropical cyclone geneses in the western north pacific the seasonal modulationof tropicalintraseasonal oscillation tiso on tropicalcyclone tc geneses over the western north pacific ocean wnp is investigated in three periods of the wnp tc season may june mj july september jas and october december ond the modulation of the tiso tc geneses over the wnp is strong in mj while it appears weaker in jas and ond in mj tiso propagates northward via two routes the west route through the south china sea and the east route through the wnp monsoon trough region which are two clustering locations of tc geneses tiso can synchronously influence most tc geneses overthese two regions in jas however the modulation is out of phase betweenthe monsoontrough region and the east asian summer monsoon region as well as the wnp subtropical high region as a result of further northward propagation of tiso and scattered tc geneses the tiso tc genesis modulation in each individual region is comparable to that in mj although the modulation over the entire wnp in jas appears weaker in ond tiso has a stronger influence on tc geneses west than east of 1508e because tiso decays and its convection center located at the equator is out of the tc genesis region when propagating eastward into east of 1508e midlevel relative humidity is the primary contribution to the modulations of tiso on the genesis environment while vorticity could contribute to the modulation over the subtropics in jas

potential vorticity modeling of the itcz and the hadley circulation abstract a simple zonally symmetric balanced model of the hadley circulation is presented the model is based on potential vorticity arguments and consists of a predictive equation for the potential pseudodensity and an invertibility principle to diagnose the associated balanced wind and mass fields when the theory is formulated in the potential latitude coordinate the meridional advection is implicit in the coordinate transformation which makes the prediction equation for potential pseudodensity analytically solvable for convective heating patterns that simulate the itcz the model produces upper and lower tropospheric potential vorticity anomalies of opposite sign the associated winds are easterly at low levels and westerly aloft except between the equator and the itcz where there are low level westerlies and upper level easterlies since the potential vorticity anomalies develop within a background state that has potential vorticity increasing to the north reversed poleward gradients of potenti

variation of tropical cyclone activity in the south indian ocean el nino southern oscillation and madden julian oscillation effects 1 the present study examines variation of tropical cyclone tc activity in the south indian ocean sio during tc seasons december march for the period 1979 2004 the impact of the el nino southern oscillation and the madden julian oscillation mjo on the variation is revealed through a composite analysis during el nino periods tc genesis was shifted westward enhancing the formation west of 75 e and reducing it east of 75 e these changes in the genesis correspond to a westward shift of convection it may be explained by a remote effect on the sio that is the increase in sea surface temperature in the central eastern pacific alters the walker circulation and forms an anomalous anticyclonic circulation in the east sio during el nino the spatial difference in tc passages between el nino and la nina shows a significant decrease to the southeast of madagascar but a moderate increase in the central midlatitude sio indicating that tcs move farther east during el nino this change is possibly due to the anomalous southwesterlies east of madagascar variation of tc activity also depends on various mjo phases frequent tc passages for phases 2 4 strong convective activity straddles along the equatorial indian ocean versus infrequent tc passages for other phases tc tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4 this is possibly caused by the increased steering northerlies which are a part of the anticyclonic rossby wave of gill type in response to the suppressed mjo related convection in the maritime continent

attributing tropical cyclogenesis to equatorial waves in the western north pacific abstract tropical cyclogenesis is attributed to an equatorial wave when the filtered rainfall anomaly exceeds a threshold value at the genesis location it is argued that 0 mm day 1 simply requiring a positive anomaly is too small a threshold because unrelated noise can produce a positive anomaly a threshold of 6 mm day 1 is too large because two thirds of storms would have no precursor disturbance between these extremes consistent results are found for a range of thresholds from 2 to 4 mm day 1 roughly twice as many tropical cyclones are attributed to tropical depression td type disturbances as to equatorial rossby waves mixed rossby gravity waves or kelvin waves the influence of the madden julian oscillation mjo is even smaller the use of variables such as vorticity and vertical wind shear in other studies gives a larger contribution for the mjo it is suggested that its direct influence on the rainfall in forming tropical cyclones is less than for other variables the impacts of tropical

observations of eastward propagation of atmospheric intraseasonal oscillations from the pacific to the atlantic received 19 april 2010 revised 20 september 2010 accepted 29 september 2010 published 19 january 2011 1 significant 40 60 day intraseasonal variability in surface winds sea level and thermocline depth were observed in the tropical atlantic during the atlantic nino year of 2002 satellite derived quikscat winds and noaa outgoing longwave radiation olr measurements for the period of 2000 2006 together with reanalysis of winds from a longer record are analyzed to understand the sources of this 40 60 day wind variability and the global propagation of the madden julian oscillation mjo surface signatures the results demonstrate that the mjo propagated eastward from the indo pacific ocean to the atlantic during winter and spring of 2002 causing 40 60 day wind variations in the equatorial atlantic the isthmus of panama appears to be a dominant pathway for these surface wind anomalies to propagate into the atlantic where they can produce important climate impacts this result is consistent with previous work that has demonstrated a strong mjo influence on the north american monsoon nam region and complements other work demonstrating the propagation of intraseasonal wind anomalies and accompanying sea level pressure signals associated with dry equatorial kelvin waves that reach the caribbean through the panama gap the mjo is also shown to have a large influence on the subtropical atlantic ocean seasonality of the mjo impact on atlantic surface winds is investigated using data from an extended record and the most direct influence is found to be during boreal winter and spring with a delayed influence during summer and fall

the central american midsummer drought regional aspects and large scale forcing abstract the midsummer drought msd is a diminution in rainfall experienced during the middle of the rainy season in southern mexico and central america as well as in the adjacent caribbean gulf of mexico and eastern pacific seas the aim of this paper is to describe the regional characteristics of the msd and to propose some possible forcing mechanisms satellite and in situ data are used to form a composite of the evolution of a typical msd which highlights its coincidence with a low level anticyclone centered over the gulf of mexico and associated easterly flow across central america the diurnal cycle of precipitation over the region is reduced in amplitude during midsummer the msd is also coincident with heavy precipitation over the sierra madre occidental part of the north american monsoon reanalysis data are used to show that the divergence of the anomalous low level flow during the msd is the main factor governing the variations in precipitation a linear baroclinic model is used to show

on wind convection and sst variations in the northeastern tropical pacific associated with the madden julian oscillation abstract lagged maximum covariance analysis lmca is used to examine the intraseasonal variability of zonal wind sea surface temperature sst and outgoing longwave radiation olr in the northeastern tropical pacific ocean during northern hemisphere summertime the analysis shows a strong temporal asymmetry in that wind and convection anomalies lead to sst anomalies but sst anomalies are not followed by comparably strong wind and convection anomalies this suggests that sst anomalies associated with the mjo in the northeastern tropical pacific are largely subject to atmospheric variability

on the westward turning of hurricane sandy 2012 effect of atmospheric intraseasonal oscillations abstracthurricane sandy 2012 experienced an unusual westward turning and made landfall in new jersey after its northward movement over the atlantic ocean the landfall caused severe casualties an

multiscale variability of the flow during the north american monsoon experiment abstract the 2004 north american monsoon experiment name provided an unprecedented observing network for studying the structure and evolution of the north american monsoon this paper focuses on multiscale characteristics of the flow during name from the large scale to the mesoscale using atmospheric sounding data from the enhanced observing network the onset of the 2004 summer monsoon over the name region accompanied the typical northward shift of the upper level anticyclone or monsoon high over northern mexico into the southwestern united states but in 2004 this shift occurred slightly later than normal and the monsoon high did not extend as far north as usual consequently precipitation over the southwestern united states was slightly below normal although increased troughiness over the great plains contributed to increased rainfall over eastern new mexico and western texas the first major pulse of moisture into the southwest occurred around 13 july in association with a strong gulf of californi

how systematic is organized tropical convection within the mjo 1 recent theories of the dynamics of the madden julian oscillation mjo have been building on its multiscale structure while it is observed that much of the convection within the mjo envelope is related to higher frequency equatorial waves it is not known to what extent this organization is systematic from one mjo event to another for instance it is of interest to know whether mjo favors waves of particular types and propagation direction and how this variability changes seasonally this work presents a wavenumber frequency spectral analysis of the mjo convective envelope which indicates that there is no strong preferred scale of high frequency organization that is ubiquitous to the mjo this null finding supports the use of convective parametrizations in modeling the mjo since while moist convection is likely critical to its initiation and maintenance the particular details of that organization may not be critical for its prediction and simulation

madden julian oscillation in a climate model with a well resolved stratosphere 1 this work evaluates how well a coupled ocean atmospheric climate model with a well resolved stratosphere captures the observed madden julian oscillation mjo signal in the upper troposphere and lower stratosphere the model is the centro euro mediterraneo per i cambiamenti climatici cmcc coupled modeling system cmcc cms with 95 atmospheric levels cmcc cms produces mjo composites of precipitation that are very similar to those of the observations and the era 40 reanalysis product furthermore model precipitation is found to propagate eastward near the observed speed there is also strong agreement in the tropics and subtropics in the temperature and flows at 100 and 200 hpa upon comparing the composites based on the full 340 years of model output and those for the past 20 years of the model output with those of the era 40 reanalysis at the 100 hpa level the temperature anomalies in the model output and reanalysis propagate eastward at about 7 m s 1 at the equator 25 n and 65 n longitude and height cross sections at 25 n suggest vertically propagating rossby waves up to near the 10 hpa level in both the model and observations latitude and height cross sections of temperature and zonal and meridional winds indicate strong vertical propagation in the tropics in both the model and reanalysis overall the cmcc cms model shows mjo characteristics in the tropical and subtropical troposphere and lower stratosphere that are in very good agreement with observed analyses

the madden julian oscillation barotropic dynamics and north pacific tropical cyclone formation part ii stochastic barotropic modeling abstract a stochastic barotropic model linearized about the 850 mb flow is used to investigate the relationship between wind variations associated with the madden julian oscillation mjo and eddy kinetic energy variations in the tropics such a model is successful in predicting the observed location of eddy kinetic energy maxima during the westerly phase of the mjo and the suppression of eddy activity during the easterly phase of the mjo the concentration of eddy energy during the westerly phase results from the strong east west and north south gradients of the large scale wind fields the model shows that barotropic wave propagation and wave mean flow interaction tend to concentrate small scale rossby wave energy in regions of convergence which may be an important mechanism for organizing convection into tropical cyclones the structure and barotropic energetics of the wave activity are similar to those observed but the modeled eddies are smaller in scale and do not move westward as do the observed e

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

an analysis of tropical cyclone formations in the south china sea during the late season abstractthis study examines tropical cyclone tc formations in the south china sea scs associated with the strong northeasterly monsoon during the late season results show that the percentage of all vortices that develop to tc intensity is lower in the late season when compared to that associated with the mei yu front in may and june but the average formation time for the late season cases is significantly shorter than that for the mei yu frontal cases composite analyses show that the formation cases in the late season have larger low level vorticity and upper level divergence as well as higher 700 hpa relative humidity when compared to the nonformation cases another major difference between the formation and the nonformation cases is the low level northeasterlies to the north or upstream of the incipient disturbance which weakens right before the pre tc disturbance reaching 25 kt 13 m s 1 the weakening of the northeasterlies may be important to tc formation because it decreases the vertical

westerly wind events and precipitation in the eastern indian ocean as predictors for el nino climatology and case study for the 2002 2003 el nino 1 this study expands on recent work linking intraseasonal to seasonal variability in observed precipitation and wind from september to march in the eastern indian ocean with the initiation of el nino events during the last 25 years first westerly wind burst wwb events are defined as days when westerly wind speeds averaged over 5 15 s and 70 100 e were greater than 1 5 standard deviations from the mean the number of wwb days from september to march was high before the onset of the 1982 1983 1991 1992 1997 1998 and 2002 2003 el nino events but not the 1986 1987 el nino this study suggests that for the 1979 2002 period variations in precipitation in the eastern indian ocean is a more robust predictor of el nino onset than analyzed winds on the basis of the work of curtis et al 2002 a real time precipitation based el nino onset index is presented which during the austral summer of 2001 2002 successfully predicted the 2002 2003 el nino the index focuses on the magnitude of 30 60 day oscillations and mean conditions in the precipitation field case studies of high resolution satellite based data sets of precipitation wind and sea surface temperature sst for the 2001 2002 season are examined to better understand how events in the indian ocean are linked to pacific ocean wind disturbances and sst changes twice during this season maxima in precipitation and zonal winds propagated eastward the first near the equator and the second to the south for the southern case warm waters preceded heavy precipitation in the eastern indian ocean which preceded strong westerly winds a cooling of the sea surface followed the wind rain system this sequence of events moved through the ocean passage between indonesia and australia suggesting a coupling of convection wind and sea surface temperatures on the timescale of days these case studies provide a basis for how the east indian ocean variations are linked to subsequent events in the pacific ocean including the initiation of el nino events

genesis of twin tropical cyclones as revealed by a global mesoscale model the role of mixed rossby gravity waves 1 in this study it is proposed that twin tropical cyclones tcs kesiny and 01a in may 2002 formed in association with the scale interactions of three gyres that appeared as a convectively coupled mixed rossby gravity ccmrg wave during an active phase of the madden julian oscillation mjo this is shown by analyzing observational data including ncep reanalysis data and meteosat 7 ir satellite imagery and performing numerical simulations using a global mesoscale model a 10 day control run is initialized at 0000 utc 1 may 2002 with grid scale condensation but no sub grid cumulus parameterizations the ccmrg wave was identified as encompassing two developing and one non developing gyres the first two of which intensified and evolved into the twin tcs the control run is able to reproduce the evolution of the ccmrg wave and thus the formation of the twin tcs about two and five days in advance as well as their subsequent intensity evolution and movement within an 8 10 day period five additional 10 day sensitivity experiments with different model configurations are conducted to help understand the interaction of the three gyres leading to the formation of the tcs these experiments suggest the improved lead time in the control run may be attributed to the realistic simulation of the ccmrg wave with the following processes 1 wave deepening intensification associated with a reduction in wavelength and or the intensification of individual gyres 2 poleward movement of gyres that may be associated with boundary layer processes 3 realistic simulation of moist processes at regional scales in association with each of the gyres and 4 the vertical phasing of low and mid level cyclonic circulations associated with a specific gyre

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

contributions of tropical waves to tropical cyclone genesis over the western north pacific the present study investigates the relationship between the tropical waves and the tropical cyclone tc genesis over the western north pacific wnp for the period 1979 2011 five wave types are considered in this study it is shown that the tc genesis is strongly related to enhanced low level vorticity and convection of tropical waves and significant difference are detected in the tc modulation by dynamic and thermodynamic components of the waves more tcs tend to form in regions of waves with overlapping cyclonic vorticity and active convection about 83 2 of tcs form within active phase of tropical waves mainly in a single wave and two coexisting waves each wave type related genesis accounts for about 30 of all tc geneses except for the kelvin waves that account for only 25 2 of tc geneses the number of each wave type related tc genesis consistently varies seasonally with peak in the tc season july november which is attributed to a combined effect of active wave probability and intensity change the interannual variation in the tc genesis is well reproduced by the tropical wave related tc genesis especially in the region east of 150 e an eastward extension of the enhanced monsoon trough coincides with increased tropical wave activity by accelerated wave mean flow interaction

potential vorticity easterly waves and eastern pacific tropical cyclogenesis abstract a significant sign reversal in the meridional potential vorticity gradient was found during the summer of 1991 on the 310 k isentropic surface near 700 mb over the caribbean sea the charney stern necessary condition for instability of the mean flow is met in this region it is speculated that the sign reversal permits either invigoration of african waves or actual generation of easterly waves in the caribbean during the same season a correlation existed between the strength of the negative potential vorticity gradient in the caribbean and subsequent cyclogenesis in the eastern pacific the meridional pv gradient convective heating measured by outgoing longwave radiation data and eastern pacific cyclogenesis all varied on the timescale of the madden julian oscillation mjo it is hypothesized that upstream wave growth in the dynamically unstable region provides the connection between the mjo or any other convective forcing and the associated enhanced downstream tropical cyclogenesis

the effect of the mjo on the north american monsoon abstract the effect of the madden julian oscillation mjo in the eastern pacific on the north american monsoon is documented using ncep ncar reanalysis and daily mean precipitation data from 1958 to 2003 it is found that positive zonal wind anomalies in the eastern tropical pacific lead to above normal precipitation in northwest mexico and arizona from several days to over a week later this connection between the tropical pacific and monsoon precipitation appears to be limited to regions influenced by moisture surges from the gulf of california as a similar connection does not exist for new mexico precipitation the evidence suggests that the mjo might affect monsoon precipitation by modulating the strength of low level easterly waves off the coast of mexico which in turn triggers the development of a gulf surge

air sea interaction over the eastern pacific warm pool gap winds thermocline dome and atmospheric convection high resolution satellite observations are used to investigate air sea interaction over the eastern pacific warm pool in winter strong wind jets develop over the gulfs of tehuantepec papagayo and panama accelerated by the pressure gradients between the atlantic and pacific across narrow passes of central american cordillera patches of cold sea surface temperatures ssts and high chlorophyll develop under these wind jets as a result of increased turbulent heat flux from the ocean and enhanced mixing across the base of the ocean mixed layer despite a large decrease in sst exceeding 38c in seasonal means the cold patches associated with the tehuantepec and papagayo jets do not have an obvious effect on local atmospheric convection in winter since the intertropical convergence zone itcz is located farther south the cold patch of the panama jet to the south on the other hand cuts through the winter itcz and breaks it into two parts a pronounced thermocline dome develops west of the gulf of papagayo with the 208c isotherm only 30 m deep throughout the year in summer when the panama jet disappears and the other two wind jets weaken sst is 0 58c lower over this costa rica dome than the background this cold spot reduces local precipitation by half punching a hole of 500 km in diameter in the summer itcz the dome underlies a patch of open ocean high chlorophyll this thermocline dome is an ocean dynamic response to the positive wind curls south of the papagayo jet which is optimally oriented to excite ocean rossby waves that remotely affect the ocean to the west the meridionally oriented tehuantepec and panama jets by contrast only influence the local thermocline depth with few remote effects on sst and the atmosphere the orographical triggered air sea interaction described here is a good benchmark for testing high resolution climate models now under development

an anomalous genesis potential index for mjo modulation of tropical cyclones abstractmodulation of tropical cyclone tc genesis by the madden julian oscillation mjo has been quantitatively diagnosed by using a climatological genesis potential index gpi analysis of tc genesis during november april of 1979 2014 indicates the most effective factors controlling intraseasonal tc genesis are 850 hpa relative vorticity weighted by the coriolis parameter f r850 and 500 hpa vertical motion 500 the total vertical wind shear and maximum potential intensity are unimportant and the role of 600 hpa relative humidity is greatly represented by 500 the mjo modulates tc genesis primarily through changing low level vorticity induced by its rossby wave gyres and meridional shears of equatorial zonal winds a new intraseasonal gpi isgpi is proposed to quantify the mjo s modulation of tc genesis the isgpi significantly improves representation of intraseasonal variation of tc genesis in the tropics and in each subregion of the southern indian ocean australian monsoon and south pacific i

asymmetric modulation of western north pacific cyclogenesis by the madden julian oscillation under enso conditions abstractthe present study investigates the modulation by the madden julian oscillation mjo and the impact of the el nino southern oscillation enso on tropical cyclone tc genesis in the western north pacific wnp during the period 1975 2010 results reveal a stronger modulation of cyclogenesis by the mjo during el nino years while the modulations in neutral and la nina years are comparable to each other the asymmetric background modification by enso is found to greatly affect the extent of mjo modulation under different enso conditions first mjo activity is intensified and extends farther eastward during el nino years instead of being confined west of 150 e as in neutral and la nina periods thus the influence of mjo is stronger and more zonally widespread in el nino years causing significant differences in cyclogenesis parameters in most parts of the wnp in el nino years cyclogenesis is further enhanced in the active phase due to synchronization of mjo signals with favorable background enso

large scale environmental parameters associated with tropical cyclone formations in the western north pacific abstract the local environmental conditions associated with 405 tropical cyclone tc formations in the western north pacific during 1990 2001 are examined in this study six large scale parameters are obtained and computed from the ncep reanalyses with 2 5 latitude resolution these include the sea surface temperature 200 850 hpa vertical and meridional zonal shear 500 700 hpa average relative humidity convective available potential energy and 200 hpa divergence it is found that these parameters show quite consistent values in almost all the cases examined and near gaussian distributions are found for them the mean values of these distributions are 28 9 c 3 2 m s 1 2 3 m s 1 61 8 1184 1 j kg 1 and 5 2 10 6 s 1 for the above six domain averaged parameters respectively based on these distributions of values a formation potential area is defined as a location that possesses these environmental parameters all within the thresholds one standard deviation from the mean value found above

influence of the madden julian oscillation and intraseasonal waves on surface wind and convection of the tropical atlantic ocean abstractatmospheric intraseasonal variability in the tropical atlantic is analyzed using satellite winds outgoing longwave radiation olr and reanalysis products during 2000 08 the analyses focus on assessing the effects of dominant intraseasonal atmospheric convective processes the madden julian oscillation mjo and rossby waves on surface wind and convection of the tropical atlantic ocean and african monsoon area the results show that contribution from each process varies in different regions in general the mjo events dominate the westward propagating rossby waves in affecting strong convection in the african monsoon region the rossby waves however have larger contributions to convection in the western atlantic ocean both the westward and eastward propagating signals contribute approximately equally in the central atlantic basin the effects of intraseasonal signals have evident seasonality both convection amplitude and the number of strong convective events associated with the mjo are l

what percentage of western north pacific tropical cyclones form within the monsoon trough abstractit is frequently stated that 70 80 of western north pacific tropical cyclones form within the monsoon trough but without an objective definition of the term several definitions are tested here when the monsoon trough mt is defined as the contiguous region where long term 1988 2010 mean july november 850 hpa relative vorticity is positive 73 of all july november tropical cyclones form within the mt this percentage varies interannually however from as low as 50 to nearly 100 the percentage correlates with the nino 3 4 index with more storms forming within the mt during warm periods when the mt is defined instead using long term monthly mean 850 more than 80 of tropical cyclones form within the mt in all months except july and august when more than 30 of storms form poleward of the mt it is hypothesized that the known peak in the frequency of upper tropospheric midlatitude wave breaking in july and august is responsible it is argued that any long term mean provides a suita

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a