observations of variability on synoptic timescales in the east pacific itcz abstract data obtained in the eastern pacific intertropical convergence zone itcz during the tropical eastern pacific process study tepps show a 3 6 day variability the noaa ship ronald h brown collected surface meteorological observations c band doppler radar volumes atmospheric soundings and rainfall data while on station at 7 8 n 125 w from 8 23 august 1997 the 3 6 day variability was a prominent timescale in the meridional wind and humidity data the maxima of the surface to 700 mb meridional wind anomalies were 5 12 m s 1 maxima of the moisture anomalies at the same levels were 1 3 g kg 1 in phase with the low level southerlies while upper level moisture lagged the southerlies by less than a day the radar indicated a close connection between precipitation in the vicinity of the ship and the meridional wind with the precipitation occurring when the surface southerlies were strongest the meridional and zonal wind components had a maximum of 850 450 mb wind shear during the southerly e

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

tracking and mean structure of easterly waves over the intra americas sea abstract easterly waves ews are prominent features of the intertropical convergence zone itcz found in both the atlantic and pacific during the northern hemisphere summer and fall where they commonly serve as precursors to hurricanes over both basins a large proportion of atlantic ews are known to form over africa but the origin of ews over the caribbean and east pacific in particular has not been established in detail in this study reanalyses are used to examine the coherence of the large scale wave signatures and to obtain track statistics and energy conversion terms for ews across this region regression analysis demonstrates that some ew kinematic structures readily propagate between the atlantic and east pacific with the highest correlations observed across costa rica and panama track statistics are consistent with this analysis and suggest that some individual waves are maintained as they pass from the atlantic into the east pacific whereas others are generated locally in the caribbean a

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

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

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

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

an observational study of easterly waves over the eastern pacific in the northern summer using fgge data abstract fgge revel iii b data provided by the european centre for medium range weather forecasts and the outgoing longwave radiation data measured by satellites are used to investigate observationally relationships between deep cloud activity and large scale meteorological fields during the northern hemisphere summer may september of 1979 over the eastern pacific aside from the summer monsoon area over southern and eastern asia the eastern pacific is the area where strong deep convection frequently develops in the northern summer this is also one of the tropical ocean areas that have been least explored meteorologically a power spectral analysis using the maximum entropy method is made for the meridional wind component at 850 mb at various grid points in the analysis domain for each mouth from may through september the waves with a period of 4 6 days are not only stronger in july and august than those of other months but active in the regions of 100 130 w in the eastern pacific and 130 160 e i

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

a vortex based perspective of eastern pacific tropical cyclone formation tropical cyclone formation over the eastern pacific during 2005 and 2006 was examined using primarily global operational analyses from the national centers for environmental prediction this paper represents a vortex view of genesis adding to previous work on tropical cyclone formation associated with tropical waves between 1 july and 30 september during 2005 and 2006 vortices at 900 hpa were tracked and vortex following diagnostic quantities were computed vortices were more abundant during periods of an enhanced hadley circulation with monsoon westerlies around 10 n in the lower troposphere this zonally confined hadley circulation was significantly stronger during the genesis of developing vortices developing vortices were stronger at the outset with a deeper potential vorticity maximum compared to nondeveloping vortices this implies that developing disturbances were selected early on by favorable synoptic scale features the characteristic time mean reversal of the meridional gradient of absolute vorticity in the lower troposphere was found to nearly vanish when the aggregate contribution of strong vortices was removed from the time mean vorticity this finding implies that it is difficult to unambiguously attribute development to a preexisting enhancement of vorticity on the synoptic scale the time mean enhancement of cyclonic vorticity primarily results from the accumulated effect of vortices it is suggested that horizontal deformation in the background state helps distinguish developing vortices from nondevelopers and also biases the latitude of development poleward of the climatological itcz axis

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

modeling tropical precipitation in a single column abstract a modified formulation of the traditional single column model for representing a limited area near the equator is proposed this formulation can also be considered a two column model in the limit as the area represented by one of the columns becomes very large compared to the other only a single column is explicitly modeled but its free tropospheric temperature rather than its mean vertical velocity is prescribed this allows the precipitation and vertical velocity to be true prognostic variables as in prior analytical theories of tropical precipitation two models developed by other authors are modified according to the proposed formulation the first is the intermediate atmospheric model of j d neelin and n zeng but with the horizontal connections between columns broken rendering it a set of disconnected column models the second is the column model of n o renno k a emanuel and p h stone in the first model the set of disconnected column models is run with a fixed temperature

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

mjo and tropical cyclogenesis in the gulf of mexico and eastern pacific case study and idealized numerical modeling the role of the madden julian oscillation mjo in modulating the frequency and location of tropical cyclogenesis over the eastern pacific and the gulf of mexico during august september 1998 is examined during the nonconvective phase of the mjo convection and low level cyclonic vorticity occurred primarily in conjunction with the intertropical convergence zone itcz during the convective phase convection low level cyclonic vorticity and convergence expanded into the northeastern pacific and the gulf of mexico this was accompanied by enhanced eddy kinetic energy and barotropic energy conversions as compared to the nonconvective phase consistent with previous research during the nonconvective phase of the mjo vertical shear was relatively weaker but tropical cyclones tended to form mainly within the itcz on the contrary during the convective phase vertical wind shear exceeded 10 m s 1 over much of this region and tropical cyclone development occurred north of the itcz near the mexican pacific coast and the gulf of mexico idealized numerical experiments are conducted using a barotropic model with time invariant basic states representative of the nonconvective and convective phases of the mjo the simulations indicate that the propagation paths as well as the amplification of the eddies differ substantially between the two phases during the nonconvective phase the waves tend to propagate westward into the eastern pacific during the convective phase stronger southerlies steer the waves into the gulf of mexico the mjo related modulation of tropical cyclogenesis in the eastern pacific and gulf of mexico thus appears to involve anomalous convergence cyclonic vorticity vertical wind shear and differing tracks of easterly waves

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

secondary magnetizations cast doubt on exceptional palaeointensity values from the lousetown creek lavas of nevada usa summary renewed palaeomagnetic investigation of pliocene lavas of the lousetown creek formation of nevada usa has given reason to question the conclusions of earlier palaeofield direction and palaeofield intensity studies of these lavas contrary to the suggestion of heinrichs 1967 the lavas do not record a complete transition of the geomagnetic field from reversed to normal polarity rather it is found that lavas recording an intermediate direction for the palaeomagnetic field overlie lavas recording a normal polarity direction the presence of large secondary magnetizations of random direction is widespread they might account for the unusually high transitional palaeointensity obtained for one of the lavas by shaw 1977

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

temperature moisture dependence of the deep convective transition as a constraint on entrainment in climate models abstractproperties of the transition to strong deep convection as previously observed in satellite precipitation statistics are analyzed using parcel stability computations and a convective plume velocity equation a set of alternative entrainment assumptions yields very different characteristics of the deep convection onset boundary here measured by conditional instability and plume vertical velocity in a bulk temperature water vapor thermodynamic plane in observations the threshold value of column water vapor above which there is a rapid increase in precipitation referred to as the critical value increases with temperature but not as quickly as column saturation and this can be matched only for cases with sufficiently strong entrainment this corroborates the earlier hypothesis that entraining plumes can explain this feature seen in observations and it places bounds on the lower tropospheric entrainment examination of a simple interactive entrainment scheme in which a minimum turbulent entrai

a review of the palynostratigraphy of gondwana sediments from the godavari graben india global comparison and correlation of the permian triassic palynoflora abstract the continental sequences of gondwana deposits from the chintalapudi sub basin of the godavari graben south india have been palynologically investigated to explore the permian triassic palynoflora total 11 distinct palynoassemblages belonging to the asselian sakmarian i ii artinskian iii iv guadalupian v vi lopingian vii viii ix induan x and olenekian xi age have been documented the palynological studies support the existence of the two coal bearing horizons in the chintalapudi sub basin one in the karharbari and barakar formations sakmarian artinskian while other in the raniganj formation guadalupian lopingian the lack of the upper barakar and barren measures roadian palynoflora indicates apparent discordance in stratigraphic sequence in this sub basin presently studied the permian triassic palynofloral transition has been found akin to the palynoflora of the salt range madagascar antarctica australia and south africa the palynofloral correlation supports the presence of guttulapollenites palaeophytogeographic province in the gondwana during the guadalupian lopingian the guttulapollenites palaeophytogeographic province co exists with the glossopteris megafloral province and extends from the salt range in the north to amery basin in the south mid zambesi luangwa basin in the west to satpura wardha godavari basin in the east

on the convective coupling and moisture organization of east pacific easterly waves abstractprocesses associated with the local amplification of easterly waves ews in the east pacific warm pool are explored developing ews favor convection in the southwest and northeast quadrants of the disturbance in nascent ews convection favors the southwest quadrant as the ew life cycle progresses convection in the northeast quadrant becomes increasingly prominent and southwest quadrant convection wanes the ew moisture budget reveals that anomalous meridional winds acting on the mean meridional moisture gradient of the itcz produce moisture anomalies supportive of convection in the southwest quadrant early in the ew life cycle as ews mature moisture anomalies on the poleward side of the ew begin to grow and are supported by the advection of anomalous moisture by the mean zonal wind in the southwest and northeast portions of the wave where convection anomalies are favored lower tropospheric vorticity is generated locally through vertical stretching that supports a horizontal tilt of the wav

planetary and synoptic scale influences on eastern pacific tropical cyclogenesis abstract the structure and evolution of lowpass filtered background flow and synoptic scale easterly waves were examined during the 1991 eastern pacific hurricane season active and inactive cyclogenesis periods conformed well to the sign of the near equatorial lowpass filtered 850 mb zonal wind anomaly consistent with the recent results of maloney and hartmann this behavior emphasizes the importance of westerly wind bursts associated with the madden julian oscillation mjo in creating an environment favorable for eastern pacific tropical cyclogenesis synoptic scale easterly waves reached the western caribbean and eastern pacific regularly from upstream usually from africa the amplitude of waves leaving africa had little correlation with the likelihood of a wave producing an eastern pacific storm rather easterly waves intensified and tropical depressions formed during the convectively active phase of the mjo in the western caribbean and eastern pacific wave growth measured by strengthening o

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

convection and easterly wave structures observed in the eastern pacific warm pool during epic 2001 abstract during september october 2001 the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 intertropical convergence zone itcz field campaign focused on studies of deep convection in the warm pool region of the eastern pacific this study combines c band doppler radar sounding and surface heat flux data collected aboard the r v ronald h brown during epic to describe the kinematic and thermodynamic states of the itcz environment together with tendencies in convective structure lightning rainfall and surface heat fluxes as a function of 3 5 day easterly wave phase three easterly waves were observed at the location of the r v brown during epic 2001 wind and thermodynamic data reveal that the wave trough axes exhibited positively correlated u and winds a slight westward phase tilt with height and relatively strong weak northeasterly tropospheric shear following the trough ridge axis temperature and humidity perturbations exhibited mid to

a simple model of climatological rainfall and vertical motion patterns over the tropical oceans abstract a simple model is developed that predicts climatological rainfall vertical motion and diabatic heating profiles over the tropical oceans given the sea surface temperature sst using statistical relationships deduced from the 40 yr ecmwf re analysis era 40 the model allows for two modes of variability in the vertical motion profiles a shallow mode responsible for all boundary layer convergence between 850 hpa and the surface and a deep mode with no boundary layer convergence the model is based on the argument expressed in the authors companion paper that boundary layer convergence can be usefully viewed as a forcing on deep convection not just a result thereof the shallow mode is either specified from satellite observations or modeled using a simple mixed layer model that has sst as well as 850 hpa geopotential height winds and temperature as boundary conditions the deep mode amplitude is empirically shown to be proportional to a simple measure of conditional instability in conve

projection of tropical cyclones on wavenumber frequency filtered equatorial waves theimpactoflocalizedconvectionassociatedwithtropicalcyclones tcs onactivityascribedtoequatorial waves is estimated an algorithm is used to remove outgoing longwave radiation olr signal in the vicinity of observed tropical cyclones and equatorial wave modes are extracted using the standard wavenumber frequency decomposition method the results suggest that climatological activity of convection coupled equatorial waves is overestimated where tc tracks are densest the greatest impact is found for equatorial rossby er and tropical depression td type waves followed by the madden julian oscillation mjo the basins most affected are the eastern and western north pacific ocean where on average tcs may contribute up to 10 15 of the climatological wave amplitude variance in these modes in contrast kelvin waves are least impacted by the projection of tcs the results are likely relevant for studies on the climatology of equatorial waves in observations and global climate model simulations and for those examining individual cases of tc genesis modulated by equatorial wave activity