propagation and the vertical structure of the madden julian oscillation abstract the madden julian oscillation mjo dominates tropical variability on time scales of 30 70 days during the boreal winter spring it is manifested as an eastward propagating disturbance with a strong convective signature over the eastern hemisphere the space time structure of the mjo is described using the national centers for environmental prediction national center for atmospheric research reanalysis advanced very high resolution radiometer outgoing longwave radiation observed sea surface temperature and the climate prediction center merged analysis of precipitation empirical orthogonal function analysis is used to identify the convective signature of the mjo and regression is used to identify key relationships with the convection compared to analyzing successive years of data the selection of years of strong mjo activity results in a more robust lead lag structure and an increase in explained variance the mjo exhibits a rich vertical structure with low level moisture convergence bein

barrier effect on mjo propagation by the maritime continent in the mjo task force gewex atmospheric system study models abstractthe simulated madden julian oscillation mjo events in 27 general circulation models gcms are identified using an mjo tracking method the results suggest that the occurrence frequencies

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

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

prominent magsat anomalies over india abstract the present study confirms the well known pogo and magsat anomalies showing a broad magnetic high on the indian shield and a broad low over the himalayas a characteristic difference in magnetic signatures over the peshawar himalaya a broad high the punjab himalaya a broad low and the kumaun himalaya north of sarda depression a sharp and deeper low indicates the existence of different blocks in the himalayas the short wavelength low over the rifted region of the narmada son lineament can be interpreted as a reflection of an ancient suture zone interestingly the surface bouguer gravity picture shows an inverse correlation with magsat anomalies over peninsular india and a positive correlation over the himalayan region quantitative model estimates from the observed satellite magnetic and surface gravity data have revealed compositional changes in the peninsular india and thickening of magnetic crust in the himalayas

role of the boundary layer moisture asymmetry in causing the eastward propagation of the madden julian oscillation the moisture budget associated with the eastward propagating madden julian oscillation mjo was diagnosed using 1979 2001 40 yr ecmwf re analysis era 40 data a marked zonal asymmetry of the moisture relative to the mjo convection appears in the planetary boundary layer pbl below 700 hpa creatingapotentiallymoreunstablestratificationtotheeastofthemjoconvectionandfavoringtheeastward propagation of mjo the pbl integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low level moistening ahead of the convection a further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the mjo ascending flow associated with pbl convergence the cause of the zonally asymmetric pbl convergence is further examined it is found that heating induced free atmospheric wave dynamics account for 75 90 of the total pbl convergence while the warm sst anomaly induced by air sea interaction contributes 10 25 of the total pbl convergence the horizontal moisture advection also plays a role in contributing to the pbl moistening ahead of the mjo convection the leadingterm in the moistureadvectionis the advectionacross the backgroundmoisture gradient by the mjo flow in the western indian ocean maritime continent and western pacific the meridional moisture advection by the mjo northerly flow dominates while in the eastern indian ocean the zonal moisture advection is greater the contribution of the moisture advection by synoptic eddies is in generalsmall ithas a negativeeffect overthetropicalindianoceanand westernpacificandbecomespositive in the maritime continent region

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

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

interpretation of resistivity measurements over 2d structures1 resistivity measurements were carried out in a survey area in the south of germany this area is characterized by complicated subsurface geology schlumberger full arrays and their respective half arrays were recorded simultaneously the results obtained by the one dimensional 1d interpretation of the full array measurements were incorrect because of a resistivity discontinuity this discontinuity under a relatively thick overburden could only be located by the half array soundings its exact location and the resistivity distribution in the subsurface were ascertained by comparing the sounding curves with 2d model curves which are calculated by a finite difference method

role of horizontal advection of seasonal mean moisture in the madden julian oscillation a theoretical model analysis abstractthe impact of horizontal advection of seasonal mean moisture smm on madden julian oscillation mjo dynamics is investigated here using a theoretical model that includes moisture advection processes the zonal advection of smm with an eastward gradient is found to produce planetary scale instability and promote slow eastward propagation corresponding to an intraseasonal periodicity this is because the smm advection by an anomalous easterly of the kelvin waves generates a moisture source to the east of precipitation which favors eastward propagation and unstable growth on the other hand the advection of smm with a westward gradient results in a westward propagating unstable mode for a realistic smm distribution the simulated eastward propagation is enhanced over the indo pacific warm pool while the westward propagation prevails over the central eastern pacific in contrast to the zonal advection of smm the meridional advection of smm only affects short waves and leaves planetary waves nea

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

evolution of the madden julian oscillation in two types of el nino abstractevolution characteristics of the madden julian oscillation mjo during the eastern pacific ep and central pacific cp types of el nino have been investigated mjo activities are strengthened over the western pacific during the predeveloping and developing phases of ep el nino but suppressed during the mature and decaying phases in contrast mjo activities do not show a clear relationship with cp el nino before their occurrence over the western pacific but they increase over the central pacific during the mature and decaying phases of cp el nino lag correlation analyses further confirm that mjo activities over the western pacific in boreal spring and early summer are closely related to ep el nino up to 2 11 months later but not for cp el nino ep el nino tends to weaken the mjo and lead to a much shorter range of its eastward propagation anomalous descending motions over the maritime continent and western pacific related to el nino can suppress convection and moisture flux convergence the

mjo propagation across the maritime continent in the ecmwf ensemble prediction system abstractthe characteristics of the mjo propagation across the maritime continent are investigated using a 20 yr reforecast dataset from the ecmwf ensemble prediction system analysis of the mjo events initialized over the indian ocean phase 2 shows that the initial mjo amplitude and prediction skill relationship is not linear particularly when the predictions start in moderate between strong and weak mjo amplitude category to examine the key factors that determine the prediction skill reforecasts in the moderate category are grouped into high and low skill events and the differences in their ocean atmospheric conditions as well as the physical processes during reforecast period are examined the initial distribution of olr anomalies in high skill events shows a clear dipole pattern of convection with an enhanced convective anomalies over the indian ocean and strongly suppressed convective anomalies in the western pacific ocean this dipole mode may support the mjo propagation across the maritime

distinctive roles of air sea coupling on different mjo events a new perspective revealed from the dynamo cindy field campaign abstractprevious observational analysis and modeling studies indicate that air sea coupling plays an essential role in improving mjo simulations and extending mjo forecasting skills however whether the sst feedback plays an indispensable role for the existence of the mjo remains controversial and the precise physical processes through which the sst feedback may lead to better mjo simulations and forecasts remain elusive the dynamo cooperative indian ocean experiment on intraseasonal variability in the year 2011 cindy field campaign recently completed over the indian ocean reveals a new perspective and provides better data to improve understanding of the mjo it is found that among the five mjo events that occurred during the dynamo cindy field campaign only two mjo events the november and march ones have robust sst anomalies associated with them for the other three mjo events the october december and january ones no coherent sst anomalies are observed this observational scenario suggests th

a unified moisture mode framework for seasonality of the madden julian oscillation abstractthe madden julian oscillation mjo exhibits pronounced seasonality while it is largely characterized by equatorially eastward propagation during the boreal winter mjo convection undergoes marked poleward movement over the asian monsoon region during summer producing a significant modulation of monsoon rainfall in classical mjo theories that seek to interpret the distinct seasonality in mjo propagation features the role of equatorial wave dynamics has been emphasized for its eastward propagation whereas coupling between mjo convection and the mean monsoon flow is considered essential for its northward propagation in this study a unified physical framework based on the moisture mode theory is offered to explain the seasonality in mjo propagation moistening and drying caused by horizontal advection of the lower tropospheric mean moisture by mjo winds which was recently found to be critical for the eastward propagation of the winter mjo is also shown to play a dominant role in operating t

interaction between the mjo and high frequency waves over the maritime continent in boreal winter abstractthe two way interaction between madden julian oscillation mjo and higher frequency waves hfw over the maritime continent mc during boreal winter of 1984 2005 is investigated it is no

circulation factors determining the propagation speed of the madden julian oscillation abstractthe eastward propagating madden julian oscillation mjo events exhibit various speeds ranging from 1 to 9 m s 1 but what controls the propagation speed remains elusive this study attempt

prediction of the madden julian oscillation a review abstractthere has been an accelerating interest in forecasting the weather and climate within the subseasonal time range the madden julian oscillation mjo an organized envelope of tropical conv

propagating versus nonpropagating madden julian oscillation events abstractbasinwide convective anomalies over the indian ocean io associated with the madden julian oscillation mjo sometimes propagate eastward and reach the west pacific wp but sometimes do not long term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating mjo events io convection onset events associated with the mjo are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern maritime continent and wp the io convection anomaly preferentially makes eastward propagation and reaches the wp when the dry anomaly is stronger analysis of the column integrated moist static energy mse budget shows that horizontal advection moistens the atmosphere to the east of the positive mse anomaly associated with the active convection over the io and is of sufficient magnitude to explain the eastward propagation of the positive mse anomaly interpretation is complicated however by lack of closure in

the onset of convection in the madden julian oscillation abstract an observational study of the onset of convection in the madden julian oscillation mjo was performed composites of radiosonde data from the comprehensive aerological reference data set were constructed for an ensemble of tropical stations located in the indian ocean maritime continent and western pacific ocean the composites suggest that for the off equatorial stations used in this study the mjo period may be set by the buildup and discharge of the low level moist static energy this result supports the discharge recharge hypothesis of blade and hartmann mjo events appear to begin when the off equatorial atmosphere has been destabilized through a combination of low level moist static energy buildup and concurrent drying of the middle troposphere by subsidence in the wake of the previous cycle of mjo convection the low level moist static energy buildup is controlled by a corresponding increase in low level moisture the increase in low level moisture is not caused by the 1000 mb convergen

a frictional skeleton model for the madden julian oscillation abstractthe madden julian oscillation mjo is a multiscale system a skeleton model developed by majda and stechmann can capture some of planetary scale aspects of observed features such as slow eastward propagation nondispersive behavior and quadrupole vortex structure however the majda stechmann model cannot explain the source of instability and the preferred planetary scale of the mjo since the mjo major convection region is leaded by its planetary boundary layer pbl moisture convergence here a frictional skeleton model is built by implementing a slab pbl into the neutral skeleton model as a skeleton model allowing the scale interaction this model is only valid for large scale waves this study shows that the pbl frictional convergence provides a strong instability source for the long eastward modes although it also destabilizes very short westward modes for the long waves wavenumber less than 5 the pbl ekman pumping moistens the low troposphere to the east of the mjo convective envel

mjo propagation shaped by zonal asymmetric structures results from 24 gcm simulations abstracteastward propagation is an essential characteristic of the madden julian oscillation mjo yet simulation of mjo propagation in general circulation models gcms remains a major challenge and understanding the causes of propagation remains controversial the present study explores why the gcms have diverse performances in mjo simulation by diagnosis of 24 gcm simulations an intrinsic linkage is found between mjo propagation and the zonal structural asymmetry with respect to the mjo convective center the observed and realistically simulated mjo eastward propagations are characterized by stronger kelvin easterly waves than rossby westerly waves in the lower troposphere which is opposite to the gill pattern where rossby westerly waves are 2 times stronger than kelvin easterly waves the gcms simulating stronger rossby westerly waves tend to show a stationary mjo mjo propagation performances are robustly correlated with the quality of simulated zonal asymmetries in the 850 hpa equatorial zonal w

effect of vertical moist static energy advection on mjo eastward propagation sensitivity to analysis domain previous studies have shown great uncertainty in assessing the effect of vertical moist static energy mse advection term to the zonal asymmetry of mse tendency this study addresses this issue by qualitatively assess the fractional contribution of the vertical mse advection to the zonal asymmetric pattern of the mse tendency field and how its contribution depends on the choice of the analysis domain based on both observational and numerical simulation results it is shown that the vertical mse advection indeed plays a critical role in generating the zonal asymmetry of mse tendency accounting for 60 of the total mse tendency field in observation and even more in aqua planet simulations it is indicated that the underestimated contribution from vertical mse advection by some previous studies is attributed to the unphysical selection of analysis domain for the zonal asymmetric mse tendency pattern

a case study of the impact of boreal summer intraseasonal oscillations on yangtze rainfall the impact on yangtze rainfall of the boreal summer intraseasonal oscillations bsisos over the entire asian summer monsoon region during summer 1996 was investigated using the aphrodite gridded rainfall and the ncep doe reanalysis ii products wavelet analyses suggest that the isos of yangtze rainfall were regulated mainly by both 30 60 and 10 25 day oscillations respectively linked to bsiso1 and bsiso2 activity phase locking of the wet phases of these two isos resulted in a prolonged wet episode from late june to mid july the circulation evolution of the bsiso1 mode showed that active convection accompanied by strong convergence of anomalous zonal winds first developed over the equatorial indian ocean with suppressed convection over the south china sea scs philippine sea and with active convection over the yangtze basin the triple convection anomaly that aligned meridionally in the east asian sector arose from a local meridional vertical cell associated with a rossby wave like coupled circulation convection system the opposite flow patterns occurred during the dry phase of yangtze rainfall the composite bsiso2 cases demonstrated a weak convective anomaly initially appeared around the maritime continent with a huge anomalous anticyclone accompanied by suppressed convection over the scs philippine sea the low level convergence of the anomalous southwesterlies on the northwestern side of the anticyclone and the consequent ascent led to positive rainfall anomalies over the yangtze basin when the entire scs was dominated by an anomalous cyclone resulting from interaction with upstream systems convection over the yangtze basin was suppressed

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

moisture asymmetry and mjo eastward propagation in an aquaplanet general circulation model abstractthe role of zonal moisture asymmetry in the eastward propagation of the madden julian oscillation mjo is investigated through a set of aquaplanet atmospheric general circulation model agcm experiments with a zonally symmetric sea surface temperature distribution in the control experiment the model produces eastward propagating mjo like perturbations with a dominant period of 30 90 days the model mjo exhibits a clear zonal asymmetry in the lower tropospheric specific humidity field with a positive negative anomaly appearing to the east west of the mjo convection a diagnosis of the lower tropospheric moisture budget indicates that the asymmetry primarily arises from vertical moisture advection associated with boundary layer convergence while horizontal moisture advection has the opposite effect in a sensitivity experiment the lower tropospheric specific humidity field is relaxed toward a zonal mean basic state derived from the control simulation in this case the model s mean state r

a coupled moisture dynamics model of the madden julian oscillation convection interaction with first and second baroclinic modes and planetary boundary layer a theoretical model with a single prognostic variable column integrated moist static energy mse was constructed to understand the dynamics of mjo eastward propagation and planetary scale selection a key process in the model is the interaction of mse dependent convection with free atmospheric first second baroclinic modes and planetary boundary layer under a realistic parameter regime the model reproduces the most unstable mode at zonal wavenumber 1 with a slow eastward phase speed of about 5 ms 1 the slow eastward phase speed in the model arises from the competition of eastward moving mse tendencies caused by horizontal mse advection vertical mse advection and boundary layer moistening with westward moving tendencies contributed by surface latent heat flux and atmospheric longwave radiative heating the planetary scale selection is primarily attributed to the phase lag of longwave radiative heating associated with upper level stratiform clouds that occur in the rear of mjo deep convection

regional simulation of the october and november mjo events observed during the cindy dynamo field campaign at gray zone resolution abstractthis study investigates the october and november mjo events observed during the cooperative indian ocean experiment on intraseasonal variability in the year 2011 cindy dynamics of the mjo dynamo field campaign through cloud permitting numerical simulations the simulations are compared to multiple observational datasets the control simulation at 9 km horizontal grid spacing captures the slow eastward progression of both the october and november mjo events in surface precipitation outgoing longwave radiation zonal wind humidity and large scale vertical motion the vertical motion shows weak ascent in the leading edge of the mjo envelope followed by deep ascent during the peak precipitation stage and trailed by a broad second baroclinic mode structure with ascent in the upper troposphere and descent in the lower troposphere both the simulation and the observations also show slow northward propagation components and tropical cyclone like vortices after the passage of the mjo active phase

why rainfall response to el nino over maritime continent is weaker and non uniform in boreal winter than in boreal summer why rainfall response to el nino is uniform and stronger over the maritime continent mc during el nino developing summer and fall but is weaker and non uniform during el nino mature winter is investigated through the diagnosis of anomalous large scale circulation patterns and a local moisture budget analysis it is found that when anomalous walker cells across the equatorial pacific and indian ocean are strengthened toward el nino mature winter a low level ascending motion anomaly starts to develop over western mc in northern fall due to topographic lifting near sumatra and anomalous wind convergence near west kalimantan easterly anomalies as a part of an anomalous anticyclone in south china sea scs that is developed during el nino and a part of the south easterly from java sea associated with anomalous walker circulation bump into the mountain ridge of sumatra and induce ascending motion anomalies near sumatra meanwhile the anomalous north easterly in the southern flank of the anomalous anticyclone over scs and south easterly over java sea converge into west kalimantan leading to ascending motion there the anomalous ascending motion tend to advect mean moisture upward to moisten lower troposphere in situ this low level moistening eventually sets up a convectively unstable stratification and induces a positive precipitation anomaly in the western mc how the mechanism discussed here is relevant to previous hypotheses and how processes during el nino might differ during la nina are discussed

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

the zonal dipole pattern of tropical cyclone genesis in the indian ocean influenced by the tropical indo pacific ocean sea surface temperature anomalies abstractfrom a basinwide perspective the dominant mode of indian ocean tropical cyclone genesis tcg in september november son shows an equatorially symmetric east west zonal dipole pattern wh

oceanic impetus for convective onset of the madden julian oscillation in the western indian ocean abstracta theory for intraseasonal atmosphere ocean atmosphere feedback is supported whereby oceanic equatorial rossby waves are partly forced in the eastern indian ocean by the madden julian oscillation mjo reemerge in the western indian ocean 70 days later and force large scale convergence in the atmospheric boundary layer that precedes mjo deep convection downwelling equatorial rossby waves permit high sea surface temperature sst and enhance meridional and zonal sst gradients that generate convergent circulations in the atmospheric boundary layer the magnitude of the sst and sst gradient increases are 0 25 c and 1 5 c mm 1 1 megameter is equal to 1000 km respectively the atmospheric circulations driven by the sst gradient are estimated to be responsible for up to 45 of the intraseasonal boundary layer convergence observed in the western indian ocean the sst induced boundary layer convergence maximizes 3 4 days prior to the convective maximum and is hypothesized to serve as a trigger for

impact of rossby and kelvin wave components on mjo eastward propagation abstractthere are contrasting views concerning the impact of rossby wave component of mjo flow on its eastward propagation one view called drag effect argues that because rossby waves propagat

mjo initiation processes over the tropical indian ocean during dynamo cindy2011 abstracta multination joint field campaign called the dynamics of mjo cooperative indian ocean experiment on intraseasonal variability in year 2011 dynamo cindy2011 took place in the equatorial indian ocean io in late 2011 during the campaign period two strong mjo events occurred from the middle of october to the middle of december referred to as mjo i and mjo ii respectively both the events were initiated over the western equatorial indian ocean wio around 50 60 e using multiple observational data products era interim the ecmwf final analysis and nasa merra the authors unveil specific processes that triggered the mjo convection in the wio it is found that 10 days prior to mjo i initiation a marked large scale ascending motion anomaly appeared in the lower troposphere over the wio the cause of this intraseasonal vertical motion anomaly was attributed to anomalous warm advection by a cyclonic gyre anomaly over the northern io the mjo ii initiation was preceded by a low level specifi

idealized modeling of the atmospheric boundary layer response to sst forcing in the western indian ocean abstractthe atmospheric response to sea surface temperature sst variations forced by oceanic downwelling equatorial rossby waves is investigated using an idealized convection resolving model dow

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

role of scale interactions in the abrupt change of tropical cyclone in autumn over the western north pacific tropical cyclone tc activity in autumn september november over the western north pacific experienced an abrupt change in 1998 which can be detected by the bayesian change point analysis during the decade before the regime shift 1988 1997 the occurrence frequency of tc genesis increased significantly over the tropical western pacific where the seasonal cyclonic flow intraseasonal oscillation iso and synoptic scale eddy sse were all strengthened compared to those observed in the decade after 1998 1998 2007 the tc trajectories also exhibited spatial differences during the active decade the tcs had a higher probability to move westward into the philippine sea and the south china sea and recurved northeastward toward the east of japan meanwhile the northwestward propagating tcs approaching taiwan and southeastern coast of china were reduced to understand the role of mean flow iso sse interaction in the decadal changes of sse and associated tc activity we diagnosed a newly proposed sse kinetic energy ke equation that separates the contributions of seasonal mean circulation and iso to the sse the results show that during the active tc decade the sse obtained higher ke from both mean flow and iso through eddy barotropic energy conversion when the enhanced sse momentum flux interacted with the strengthened monsoon trough and vigorous iso cyclonic anomaly over the western tropical pacific the increased sse ke contributed positively to the increased tc genesis over the main genesis region 7 5 20 n 130 170 e it also benefited the growth of tcs over the philippine sea and the south china sea during the active decade the decadal change in tc frequency over the extratropics was related to the eddy baroclinic energy conversion instead of the barotropic conversion associated with scale interaction during the active tc decade sse gained more less ke from the sse available potential energy over the east of japan the east china sea favoring disfavoring the succeeding development of tcs in this region

the influence of sea surface temperature on the tropical intraseasonal oscillation a numerical study abstract the development and movement of the tropical intraseasonal system tis exhibit remarkable annual variations it was hypothesized that spatial and temporal variation in sea surface temperature sst is one of the primary climatic factors that are responsible for the annual variation of tiss this paper examines possible influences of sst on the tis through numerical experiments with a 2 5 layer atmospheric model on an equatorial plane in which sst affects atmospheric heating via control of the horizontal distribution of moist static energy and the degree of convective instability the gradient of the antisymmetric with respect to the equator component of sst causes a southward propagation of the model tis toward northern australia in boreal winter and a northward propagation over the indian and western pacific oceans in boreal summer the phase speed of the meridional propagation increases with the magnitude of antisymmetric sst gradients the poleward propagation of the equatorial disturba