a theoretical and numerical study of density currents in nonconstant shear flows the previous idealized two fluid model of a density current in constant shear is extended to the case where the inflow shear is confined to the low levels the analytical solution is determined by the conservation of mass momentum vorticity and energy it is found that a low level shear acts in a similar manner to a uniform vertical shear in controlling the depth of a steady state density current when the shear enhances the low level flow against the density current propagation the current is deeper than half of the domain depth time dependent numerical experiments are conducted for a variety of parameter settings including various depths and strengths of the shear layer the numerical results agree closely with the theoretical analyses numerical experiments are also performed for a case where the initial depth of the density current is set to be comparable to the low level shear which is much shallower than that given by the steady state solution the circulation at the density current head remains shallow and is nonsteady in this case whereas the time averaged flow still exhibits a deep jump updraft pattern that is close to the theoretical solution suggesting the applicability of the theoretical results to even more transient flows the simulated flow features are discussed in terms of balanced and unbalanced dynamics and in the context of forcing and uplifting at the frontal zone in long lived convective systems here the term balance refers to a flow configuration that satisfies the steady state solution of the idealized theoretical model

delta progradation and neoglaciation laguna paron cordillera blanca peru the history of holocene glaciation serves as an important record of glacier mass balance and therefore of climatic change the moraine record of holocene glaciation in the tropical andes however is fragmentary and poorly dated in contrast increases in the rate of accumulation of inorganic sediment in glacier fed lakes have been linked to periods of neoglaciation in many mountain regions the interpretation of such a record of neoglaciation from sediment cores in glacier fed lakes in the tropical andes can provide the continuity and chronologic control that is lacking in the existing moraine record unusual exposures of glacial lacustrine sediment in the cordillera blanca peru provide a rare opportunity to assess the link between climatic change glaciation and lacustrine sedimentation intentional lowering of water levels in laguna paron 9 s 77 44 w 4200 m a s l in 1985 resulted in the incision and exposure of at least 20 m of deltaic deposits at the eastern end of the lake three deltaic units can be identified horizontal topset beds steeply dipping and deformed foreset beds and horizontally laminated fine grained sediment six radiocarbon ages ranging from 1800 210 to 465 95 14c yr bp on wood indicate that the average rate of delta progradation in the late holocene has been approximately 290 m per 1000 yr the lake formed during deglaciation at least 10 000 yr ago and if such a rate of progradation of the delta had prevailed over the entire holocene then the delta would be at least three times as extensive as it is today thus the rate of delta progradation has varied significantly over the holocene we suggest that the rate of delta progradation was at least three times greater when glaciers were in advanced positions these positions are clearly delimited by neoglacial moraines which are within 1 2 km of the exposures studied and within 1 km of modern ice limits the most recent increase in the rate of delta progradation is evidenced by an increase in sedimentation rate ca 575 90 14c yr bp coincident with the onset of the little ice age copyright 2005 john wiley sons ltd

a seasonal climatology of rossby wave breaking in the 320 2000 k layer abstract differential advection in rossby waves can lead to potential vorticity pv p contours on isentropic surfaces folding over in latitude py 0 in a process called rossby wave breaking rwb exploring the properties of rwb may shed light on underlying dynamics and enable quantification of irreversible transport a seasonal climatology of py and rwb statistics is presented for the 320 850 k layer using ncep reanalysis data during 1979 2005 and for the 320 2000 k layer using the met office ukmo data during 1991 2003 a primary goal is to depict the spatial extent and seasonality of rwb maxima this analysis shows seven distinct rwb regimes poleward and equatorward of the subtropical westerly jets poleward and equatorward of the stratospheric polar night jets flanking the equator in the stratosphere and mesosphere equatorward of subtropical monsoon anticyclones and the summertime polar stratosphere a striking pv gradient maximum exists at the equator throughout the layer 360 2000 k flanke

quasi biennial and semi annual oscillations in equatorial wind fields constructed by data assimilation since october 1991 the u k meteorological office has used the technique of data assimilation to produce global meteorological analyses of the troposphere and stratosphere these analyses are constructed from conventional meteorological measurements in the troposphere and lower stratosphere and temperature soundings from noaa polar orbiting satellites the analyses show very clear quasi biennial and semi annual oscillations in equatorial winds the quasi biennial oscillation has its maximum amplitude of about 20 ms 1 near 30 hpa and exhibits descending easterly and westerly shear zones analysed winds compare well with radiosonde observations in the lower stratosphere the semi annual oscillation has its peak amplitude of about 30 ms 1 near the stratopause winds near the equatorial stratopause show strong longitudinal variations on a planetary scale during both the westerly and easterly phases of the semi annual oscillation

on the formation of ozone laminae at the edge of the arctic polar vortex ozone vertical profiles commonly display thin layered structures or laminae in the lower stratosphere of the extratropics predominantly during winter and spring the mechanism for their formation is still uncertain in this study high resolution isentropic transport of a passive tracer on synoptic time scales is performed with an off line transport model which is forced by winds derived from global meteorological analyses or forecasts the study focuses on a meteorological situation which occurred in late january 1992 on isentropic surfaces the tracer distribution initialized as the analysed potential vorticity is eroded into filamentary structures in the mid latitude surf zone repeated poleward intrusions of mid latitude air are shown to lead to the formation of convoluted filamentary structures at high latitudes by performing isentropic advection on many closely spaced independent levels the vertical structure of these tracer filaments can be studied they are shown to be part of tracer sheets which are vertically tilted in the shear zone in the vicinity of the polar jet thin laminar structures in the tracer vertical profiles appear as the result of isentropic wrapping and vertical shearing of such tracer sheets a comparison is made with ozone laminae found in balloon borne soundings during the european arctic stratospheric ozone experiment

the two day wave in eos mls temperature and wind measurements during 2004 2005 winter 1 two day wave observations during january march 2005 are reported using the recently launched microwave limb sounder mls aboard nasa s earth observing system aura mission wave induced disturbances in temperature water vapor carbon monoxide and mls line of sight wind appear in early january peak near the end of january and persist until late february temperature and wind amplitudes as large as 9 k and 50 m s are observed near 90 km the wave disturbance is initially confined in the mid to low summer latitudes where the climatological summer easterly jet exhibits strong shear the wave then develops features akin to the third rossby gravity global normal mode with a weak temperature disturbance in the winter hemisphere anti symmetric about the equator and wind disturbance over the equator strong wind perturbation episode around 17 23 january 2005 in the mid latitude southern hemisphere coincides with a particularly intense solar proton event

eliassen palm fluxes of the 2 day wave abstract high resolution doppler imager hrdi winds and temperatures are used to diagnose a 2 day wave event detected in the southern hemisphere during january 1994 a novel aspect of this study is the focus upon the wave fluxes throughout the 65 100 km range and their relationship to the background state a wave packet composed of zonal wavenumbers 2 3 and 4 propagates westward with a phase speed near 60 m s 1 the periods associated with zonal wavenumbers 2 3 and 4 are 3 5 2 1 and 1 7 days respectively the morphology of the 2 day temperature and wind fields is consistent with that of a developing baroclinic wave the divergence of the eliassen palm flux of zonal wavenumbers 2 4 is dominated by the vertical convergence of meridional heat flux the wave driving or eliassen palm flux divergence per unit mass is predominantly westward with magnitudes on the order of 5 m s 1 day 1 a steady state quasigeostrophic model of the mean meridionai circulation is used to estimate the mean wind respon

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

two day wave observations of uars microwave limb sounder mesospheric water vapor and temperature 1 a two day wave disturbance is observed in the mesospheric temperature and water vapor on the basis of new version data from the upper atmosphere research satellite microwave limb sounder using two data segments during the austral summers january february of 1992 and 1993 and the asynoptic mapping method a strong wave signal is identified as having zonal wave number 3 and a westward period of about 2 1 days the wave amplitudes are located near the core of the summer easterly jet with strongest wave amplitudes as large as 11 k and 0 35 part per million by volume near the mesopause the temperature and water vapor wave strengths are highly correlated in time but their peaks are almost longitudinally out of phase poleward heat flux associated with upward wave energy propagation in the southern hemisphere points to baroclinic instability as the cause for the wave appearance a growing wave signature in water vapor is observed in regions of strong meridional gradient of water vapor near the mesopause wave breaking is suggested as moist polar air is displaced into the much drier subtropics and wave amplitude decays

paleoseismicity and neotectonics of the cordillera blanca fault zone northern peruvian andes the cordillera bianca fault zone is a major west dipping normal fault that bounds the west side of a 120 to 170 km wide zone of active extension along the crest of the northern peruvian andes the fault is approximately 210 km long and exhibits continuous geomorphic evidence of repeated late pleistocene and holocene displacements but has not been the source of historical or teleseismically recorded earthquakes trenching and mapping of fault scarps provide new information on earthquake recurrence slip rate timing of the most recent events and andean neotectonics at quebrada queroccocha 55 km from the south end of the zone an 11 000 to 14 000 year old moraine is displaced 12 15 m and younger valley fill lacustrine and fluvial deposits are displaced 7 5 8 m scarp profiles tectonic terraces and trench exposures indicate five to seven scarp forming earthquakes of 2 3 m per event during the past 11 000 14 000 years at this location considering uncertainties in the number of events and in the age of the displaced moraine the average recurrence interval is estimated to be 2440 1060 years detrital charcoal from colluviums that predate and postdate the most recent event yielded ages of 2480 65 and 750 80 14c years b p respectively and stratigraphic relationships suggest that the event may be closer to the older date the late quaternary slip rate at quebrada queroccocha is 0 86 1 36 mm yr and appears to be representative of much of the fault zone at pachma bajo located 30 km from the north end of the zone on a separate segment displacement during each of the past two events was 2 to 3 m the morphology of scarps in alluvial fan and debris flow deposits indicates recurrence intervals of about 1000 3000 years relationships between pre inca walls and faulted deposits suggest that 1500 2000 years have elapsed since the most recent event fault behavior parameters particularly displacement per event and fault segment length show that the cordillera bianca fault zone is similar to seismogenic normal faults that nucleate m 7 7 earthquakes at depths of approximately 15 km the quebrada queroccocha slip rate and analysis of other normal faults in the region suggest cumulative late quaternary extensional strain rates of about 1 4 mm yr across the complete zone of andean crestal extension

the tropical stratopause in the ukmo stratospheric analyses evidence for a 2 day wave and inertial circulations summary large scale atmospheric motions near the low latitude stratopause in the uk meteorological office stratospheric analyses during the northern hemisphere winter are investigated focusing in particular on the 2 day wave and inertial eddies the 2 day wave is a westward propagating planetary wave which appears recurrently in the summer subtropical upper stratosphere and mesosphere space time spectral analysis of the assimilated fields of temperature and winds and high resolution transport of water vapour reveal large amplitude breaking planetary waves in the summer subtropics principally a 2 day wave 3 and a wave 1 of a period near 7 days a region of anomalous zonal mean meridional gradient of potential vorticity also exists pointing to a barotropic instability mechanism for the origin of the 2 day wave by contrast the winter subtropics are characterized by mixing on less than planetary scales during the period considered occurring during the easterly phase of the stratospheric semi annual oscillation water vapour is mixed turbulently into gyres and drawn in narrow filaments out of the southern hemisphere the potential vorticity field displays vertically layered zonally asymmetric variations the behaviour of the model assimilated fields is supported by along track water vapour distribution observed by the microwave limb sounder aboard the upper atmosphere research satellite shows evidences for intermittent filamentary mixing in the northern subtropics and a 2 day wave signature in the summer subtropics based on these results a possible mechanism connecting the initiation of the austral 2 day wave events to strong planetary wave activity in the winter is proposed the winter planetary waves provide the background conditions for development of inertial instabilities at low latitudes of the winter hemisphere which in turn create conditions favourable for barotropic instability of the summer subtropical easterly jet

recent evolution and degradation of the bent jatunraju glacier cordillera blanca peru abstract this article brings new insight into the recent evolution and degradation of the bent jatunraju glacier in the northern part of the cordillera blanca peru analysis of topographical maps aerial photos and satellite images covering a period of 66 years and a field survey performed in june 2013 and may 2014 helped to describe the geomorphological setting and ongoing processes recent evolution and degradation processes are also deduced from surface movements historical geodetic measurements 1967 1968 1977 1984 and current landsat images 2001 2013 were used to estimate surface velocities and changes in surface velocities over time our investigation showed that the most significant changes happened at an altitude of between 4300 and 4450 m asl a significant decrease in surface velocities and increase in debris thickness indicate that this part of jatunraju turned from a debris covered glacier into an ice cored rock glacier during the analyzed period particular parts of the article describe the cycle of formation and extinction of supraglacial lakes and the melting of buried debris covered ice a scenario of future evolution is outlined and discussed as well we assume that ice degradation within the debris covered glacier will continue and that the altitude of its presence will increase hand in hand with the changing environment

numerical simulation of a midlatitude squall line in two dimensions abstract a two dimensional anelastic cloud model was used in attempts to numerically replicate the observed structure of a midlatitude squall line initial conditions were adapted from observations of the 22 may 1976 oklahoma line model simulations were made with and without considering the ice phase of water these model storms have within the constraints of the model s geometry replicated the basic multicellular character and general line normal airflow typical of these lines in addition the structure and intensity of the subcloud cold air pool and the propagation speeds developed by the storms appear to be reasonable further it was found that the initial conditions chosen resulted in model storms which were not only long lasting but also essentially repetitive indicating that a state of quasi equilibrium had been attained the storms did not decay because the environmental conditions ahead of the storms were favorable and essentially unchanged during the course of the simulations the inclusio

observed temperature two day wave and its relatives near the stratopause the two day wave is observed in the upper atmosphere research satellitemicrowave limb sounder temperature data around 40 58 km between december 1991 and september 1994 the two day wave temperature signature is most significant after each solstice when the derived easterly winds near the stratopause extend across the equator to at least 208 latitude in the winter hemisphere and the zonal mean winds near the equator are inertially unstable with observed inertial instability disturbances the observed two day wave consists of a 2 0 day period zonal wavenumber 3 and a 1 8 day period zonal wavenumber 4 component named 3 2 0 and 4 1 8 respectively the 3 2 0 component is dominant during two of the three available austral summers but its amplitude is much weaker than the 4 1 8 component during the two observed boreal summers during the austral summers correspondence between amplification of the two day wave temperature signatures regions of reversed potential vorticity gradient due to meridional curvature of the zonal mean flow and the critical lines for the 3 2 0 and 4 1 8 modes suggest barotropic instability as a source of both wave components momentum redistribution by observed inertial instability appears to barotropically destabilize the equatorward flank of the easterly jet where the wave components subsequently grow during the boreal summers the 4 1 8 component appears to be excited by instability that is associated with vertical shear and curvature of the flow seated above the observational domain the boreal 3 2 0 mode appears unrelated to the zonal flow instability within the observational domain and may reflect a normal mode like response during these periods

intraseasonal and interannual variability of the quasi 2 day wave in the northern hemisphere summer mesosphere this study uses global synoptic meteorological fields from a high altitude data assimilation system to investigate the quasi 2 day wave q2dw and migrating diurnal tide during the northern hemisphere nh summers of 2007 2009 by applying a two dimensional fast fourier transform to meridional wind and temperature fields we identify q2dw source regions and diagnose propagation of q2dw activity into the upper mesosphere and lower thermosphere we find that the q2dw in nh summer is composed primarily of westward propagating zonal wave number 3 and wave number 4 components that originate within baroclinically unstable regions along the equatorward flank of the summer midlatitude easterly jet the amplitude of the wave number 3 q2dw tends to peak in july while the amplitude of the wave number 4 q2dw tends to peak in late june and again in early august the seasonal mean q2dw amplitudes are largest in 2009 when the amplitude of the migrating diurnal tide in the upper mesosphere near 30 n was relatively weak however there is no evidence of rapid amplification of the q2dw via nonlinear interaction with the diurnal tide instead variations of q2dw amplitudes during nh summer appear to be linked to variations in the strength and location of the mesospheric easterly jet from one summer to the next with a stronger jet producing larger q2dw amplitudes linear instability model calculations based on the assimilated wind fields indicate that the fastest growing modes are zonal wave numbers 3 and 4 with periods near 2 days that originate in the vicinity of the easterly jet

the maintenance of the zonal mean state of the upper atmosphere as represented in a three dimensional general circulation model extending to 100 km abstract a primitive equation general circulation model has been developed to simulate the atmosphere from the surface to 100 km the model was based on the semispectral technique and has 15 zonal wavenumbers and 40 grid points between poles the simulation was for fixed january conditions was nondiurnal had land sea contrast with specified sea surface temperatures but omitted both orography and the hydrologic cycle for convenience and brevity only the zonal mean state of the model is presented in this paper the overall simulation revealed several interesting and novel features of the atmosphere the mean meridional wind exhibited a distinctly layered structure which was confined to the tropics throughout the stratosphere and mesosphere this was attributed to inertial instability in the winter hemisphere resulting from the intense mesospheric jet the actual mesosphere also may experience such an instability to a much lesser extent some observational evidence exists to support layering in the synopt

recession of yanamarey glacier in cordillera blanca peru during the 20th century for yanamarey glacier in cordillera blanca peru mostly situated between about 5000 and 4600 m maps of the surface topography at a scale of 1 5000 obtained by terrestrial triangulation for 1973 1982 and 1988 and by aerial photogrammetry for 1948 and 1962 are compared with the glacier boundaries from a 1939 map and an undated maximum extent inferred from moraine morphology the glacier length decreased from the maximum 2800 m to 1600 m in 1948 and to 1250 m in 1988 with an accompanying decrease in area from 17 10 5 to 10 10 5 and thence to 8 10 5 m 2 the shrinkage of ice volume was 35 10 6 m 3 from the maximum to 1948 and 29 10 6 m 3 from 1948 to 1988 compared to a total remaining icevolume of about 25 10 6 m 3 in 1988 this quantitative assessment of mass loss rates creates the observational basis for sensitivity studies of the climatic forcing

extensional basin evolution in the cordillera blanca peru stratigraphic and isotopic records of detachment faulting and orogenic collapse in the andean hinterland 1 sedimentologic provenance oxygen isotope and 40ar 39ar results provide insights into late cenozoic evolution of an extensional hinterland basin in the peruvian andes the 5 6 5 km cordillera blanca composes the glaciated footwall of a low angle normal fault parallel to active contractional structures in the andean fold thrust belt the 200 km long wsw dipping 19 36 cordillera blanca detachment fault accommodated 12 15 km of dip slip displacement inducing subsidence of the hanging wall supradetachment basin which is filled by 1300 m of conglomerate sandstone siltstone and limited carbonate of the upper miocene pliocene lloclla formation lithofacies associations are attributed to lacustrine fan delta to proximal stream dominated alluvial fan sedimentation provenance data record footwall unroofing of jurassic through miocene volcanic and sedimentary rocks during nw directed axial dispersal of sediment provenance data record the appearance of footwall derived granite clasts from the upper miocene cordillera blanca batholith and a change to transverse wsw directed transport variations in the character and preservation of basin fill suggest along strike propagation of the fault through time initial extension and subsidence is constrained to the latest miocene by an 40ar 39ar biotite age of 5 4 0 1 ma for a basal tuff in the lloclla formation estimation of paleolake water composition shows very negative 18o vsmow values 13 6 to 18 2 indicating that high elevations comparable to modern were already attained in the cordillera blanca during earliest normal faulting and basin evolution these results lend support to models suggesting that substantial shortening crustal thickening and surface uplift were necessary precursor conditions for the generation of the cordillera blanca detachment fault

inertial instability and rossby wave breaking in a numerical model abstract a mechanistic model of the middle atmosphere is used to study the interaction between rossby waves forced at the extratropical tropopause and inertial instability in the equatorial lower mesosphere the impact of cross equatorial shear strength and rossby wave forcing amplitude is explored model results support the hypothesis based on satellite temperature observations that rossby waves organize regions of equatorial inertial instability into coherent large scale circulations horizontal convergence and divergence maxima are found stacked over the boundaries of regions of anomalous potential vorticity pv this supports observational diagnoses and theoretical expectations that parcel inertial accelerations arise in regions of anomalous pv with divergence and convergence occurring at the boundaries although cross equatorial shear determines the initial volume of inertially unstable air rossby waves arriving from the winter hemisphere deform pv contours such that zonally confined regions of

properties of the quasi 16 day wave derived from eos mls observations 1 this paper describes the use of eos microwave limb sounder mls data to observe the field of traveling planetary waves with quasi 16 day periods this study utilizes mls v2 2 temperature and geopotential data between 1 january 2005 and 31 december 2008 in the range 316 hpa to 0 001 hpa approximately 8 to 97 km to examine these waves analysis demonstrates that the quasi 16 day wavefield is made up of a number of components with westward and eastward propagating s 1 and s 2 waves generally dominant in the northern hemisphere the westward and eastward propagating s 1 waves have similar magnitudes and are larger than the other modes while in the southern hemisphere the eastward propagating s 1 and s 2 waves are larger than the westward propagating wave modes all of the modes examined display strong seasonal patterns in the temperature amplitude significant variability in the wave activity from year to year and the presence of strong pulse like patterns in the activity all of the modes also display large median temperature amplitudes poleward of 40 degrees in both hemispheres our analysis also demonstrates that the variability in winter from year to year is larger in the northern hemisphere than the southern hemisphere detailed study also suggests that the exclusion of waves from regions of negative refractive index squared likely forms much of the seasonal pattern observed thus regions of strong westward wind speeds effectively exclude vertically propagating waves as expected from theory the reflection and absorption of waves associated with critical lines is also likely to explain the frequent occurrence of standing wave patterns in the eos mls temperature observations this study highlights the potential of mls observations for observing waves from the upper troposphere to the lower mesosphere

the 2 day wave during the boreal summer of 1994 1 the 2 day wave during the boreal summer of 1994 was observed using stratospheric analyses from the british met office and at mesospheric heights using medium frequency mf radars and the microwave limb sounder mls and high resolution doppler imager hrdi satellite instruments most of the evidence from our study points to a high latitude source for the boreal 2 day wave event we observed we found little evidence for a connection between the 2 day wave event in the mesosphere and activity at lower altitudes instead we contend that the 2 day wave observed at upper mesospheric heights was excited in situ this event was predominantly zonal wave number 2 was highly localized in time and the disturbance propagated equatorially from high northern latitudes at stratopause and lower mesospheric heights the largest 2 day wave amplitudes were seen at high southern hemisphere latitudes i e in the winter hemisphere however the austral winter 2 day wave was trapped and did not penetrate to upper mesospheric heights

convection initiation by density currents role of convergence shear and dynamical organization abstract steady state analytic models establish two key points concerning the impact of vertical shear on density currents and the implication for convection initiation first shear decreases the horizontal convergence and therefore the mean ascent associated with downshear propagating currents second shear has a basic effect on the dynamical organization if the downshear current travels at the speed of the ambient flow at a critical steering level an overturning circulation provides deep lifting although mean ascent is increased by shear in the case of upshear propagating currents the lifting is comparatively shallow because jumplike ascent occurs rather than deep overturning the convection initiation mechanism involving the downshear current is therefore very different from the upshear case these basic principles are borne out in two dimensional numerical simulations density currents generated by a stationary cold source imposed on an initially horizontally homogeneous sheared and neutra

multicell squall line structure as a manifestation of vertically trapped gravity waves abstract two dimensional and three dimensional simulations of a midlatitude squall line with a high resolution non hydrostatic model suggest that the multicellular structure of the storm may be associated with gravity waves generated by convection time lapse display of model output demonstrates that the commonly described cut off process is actually a gravity wave phenomenon the convective cells arise as gravity waves which are forced by continuous strong low level convergence at the storm s gust front the waves propagate to both sides of the gust front the stronger westward front to rear mode dominates at the mature stage of the squall line continuous low level updraft is generated at the nose of the cold pool which propagates at the speed of a density current updraft cells periodically break away from this persistent low level gust front updraft and move at phase speeds of their associated gravity waves not at the surrounding airflow speeds as implied by the traditional multicell model lin

multiscale convective wave disturbances in the tropics insights from a two dimensional cloud resolving model abstract multiscale convective wave disturbances with structures broadly resembling observed tropical waves are found to emerge spontaneously in a nonrotating two dimensional cloud model forced by uniform cooling to articulate the dynamics of these waves model outputs are objectively analyzed in a discrete truncated space consisting of three cloud types shallow convective deep convective and stratiform and three dynamical vertical wavelength bands model experiments confirm that diabatic processes in deep convective and stratiform regions are essential to the formation of multiscale convective wave patterns specifically upper level heating together with low level cooling serves to preferentially excite discrete horizontally propagating wave packets with roughly a full wavelength structure in troposphere and dry phase speeds cn in the range 16 18 m s 1 these wave packets enhance the triggering of new deep convective cloud systems via low level destabilization the new convection in turn caus

the sensitivity of two dimensional simulations of tropical squall lines to environmental profiles abstract two dimensional experiments are carried out to determine the effect of various wind and thermodynamic structure on squall line characteristics two ideas concerning the effect of shear are found useful in explaining many of the outcomes of the numerical experiments first in two dimensions shear in the absence of vorticity sources and sinks is detrimental to convection kuo asai second there is a specific value of low level slim interacting with a cold pool which produces deep uplift and hence strong forcing of convection rotunno et al results suggest that moist midlevel air tends to be favorable for squall lines increasing the total buoyancy or altering the distribution of buoyancy with height such that it is increased at low levels produces stronger systems with updrafts more tilted from the vertical the formula by von karm n for the speed of a gravity current gives qualitative agreement with the speed of most of the simulated systems however at least two additional factors need

the timing of the last deglaciation in cordillera oriental northern peru based on glacial geology and lake sedimentology the degree of soil development on moraines and radiocarbon ages indicate that the cordillera oriental a part of the eastern andes in northern peru 7 30 7 55 s 77 20 77 35 w was last glaciated during the last glacial maximum marine isotope stage 2 this glaciation was the most extensive late quaternary glaciation in the area radiocarbondated sedimentological changes in six sediment cores from three lakes and one bog reveal that the last deglaciation is marked by a two stepped transition from rhythmically laminated inorganic sediment to massive organic rich sediment the first step of this transition commenced before 12 1 0 2 ka 1 and probably by ca 13 5 ka glaciers covered less than 50 of their last glacial maximum area by 12 1 0 6 ka and cirques west of the main divide were probably ice free by this time a return to rhythmically laminated inorganic sediment in the lakes and the bog occurred between 12 1 0 6 and 10 3 0 4 ka this may reflect an episode of increased stream discharge and glacier expansion during which glaciers reoccupied cirques above 3 800 m this glacier expansion adds to widespread evidence of a late glacial readvance in the tropical andes all cirques have been ice free since between 10 3 0 4 and 9 7 0 5 ka

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

observations of the 2 day wave in nmc stratospheric analyses abstract observational characteristics of the 2 day wave a westward propagating zonal wave 3 oscillation in the summer subtropical upper stratosphere and mesosphere are studied based on five years of national meteorological center nmc operational stratospheric analyses these data show episodic occurrence of the 2 day wave in the upper stratosphere in january centered near 20 s and july august centered near 20 n these episodes are strongly correlated with observed reversals of the zonal mean potential vorticity gradient near the core of the summer easterly jet consistent with previous suggestions that the 2 day wave is generated by an in situ instability of this jet on the other hand the horizontal and vertical structure of the waves is very similar to that calculated by salby for a global normal mode rossby wave the combination of normal mode structure and instability signature suggests that the 2 day wave is a near resonant mode forced by dynamical instability

multiscale phenomena in the tropical atmosphere over the western pacific abstract multiscale variabilities in the atmosphere over the tropical western pacific during the 1979 northern hemisphere winter are studied with an aim at identifying possible interactions between phenomena of different spatial and temporal scales based on the convection index information derived from satellite measurements two intra seasonal oscillations isos are identified within the equatorial belt between 0 and 10 s in the analyzed period the two isos accompanied by both rotational and divergent circulations propagate eastward from the indian ocean to the western pacific over the warm pool in the western pacific the isos develop into quasi stationary systems with an enhanced rotational circulation characterized by a strong westerly jet in the lower troposphere the isos appear to interact with a number of regional and synoptic scale phenomena in the maritime continent and western pacific region for example the onset of the monsoon coincides with the arrival of the first iso at northern a

vertically stacked temperature disturbances near the equatorial stratopause as seen in cryogenic limb array etalon spectrometer data temperature data derived from the cryogenic limb array etalon spectrometer claes on board the upper atmosphere research satellite uars are used to investigate planetary scale temperature disturbances near the equatorial stratopause for january 1992 to may 1993 the disturbances are characterized by vertically stacked temperature extrema of alternating sign with a vertical scale of about 10 km and have a localized and stationary nature in the longitudinal direction with persistence of about 1 week these are nearly identical to so called pancake structures first identified by hitchman et al 1987 using data from the limb infrared monitor of the stratosphere lims their analysis suggested that pancake structures are consistent with those predicted by inertial instability theory and that their appearance is synchronized with strong planetary waves in the winter midlatitude though the lims observations were made only during the northern winter using the claes data for about 14 months this study shows that pancake structures occur not only during the northern winter but also during the southern winter in addition it is found that an equatorial pancake structure has its counterpart with reversed phase in the winter midlatitude suggesting clear evidence for inertial instability further analyses on the basis of ertel s potential vorticity show that inertially unstable regions intrude locally far into the winter hemisphere around pancake structures that appear when planetary wave breaking is going on this implies a mechanism of localized inertial instability and resulting pancake structures caused by midlatitude planetary waves in the winter hemisphere as some numerical studies have inferred

global climatology of inertial instability and rossby wave breaking in the stratosphere 1 climatologies using united kingdom met office assimilated analyses from november 1991 through march 2004 are used to juxtapose the evolution of inertial instability and rossby wave breaking in longitude latitude altitude and time the results for the upper and middle stratosphere indicate deep poleward and eastward channels of higher inertial instability frequency extending from the central equatorial pacific in both winter hemispheres these corridors of enhanced inertial instability frequency are generally found just poleward of regions of frequent rossby wave breaking a result confirmed with a case study drawn from the period of the climatology both of these patterns are evident from the stratopause downward into the middle stratosphere with the frequency of events diminishing with decreasing altitude analysis of interannual variability of rossby wave breaking and inertial instability in the middle stratosphere channels confirms a correlation between them as well as a possible quasi biennial oscillation signal in the early years of the climatology in the lower stratosphere a channel of enhanced inertial instability frequency exists near east asia in northern hemisphere winter again just poleward of a rossby wave breaking maximum these results generally agree closely in space and time with and significantly extend the relatively few previously published climatologies and case studies of episodes of rossby wave triggered inertial instability for the stratosphere

a study of the response of deep tropical clouds to mesoscale processes three dimensional numerical experiments abstract a three dimensional numerical cloud ensemble model has been developed to investigate the collective feedback effects of cloud systems on the large scale environment an observed large scale lifting is imposed continuously in the model small amplitude random perturbations in the form of temperature fluctuations are also continuously fed into the model at low levels to simulate random thermals over the tropical ocean the model allows several clouds of various sizes to develop simultaneously inside the domain an integration of the model is made for six hours of simulated time in order to allow large numbers of convective clouds to develop following each simulation the collective feedbacks of cloud systems on the large scale temperature moisture and horizontal momentum fields are computed horizontal and time averages of various relevant variables are also computed to elucidate the statistical properties of the clouds the model was applied to a case of a well defined itcz rainband over the eas

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

wintertime temperature maximum at the subtropical stratopause in a t213l256 gcm 1 a wintertime temperature maximum can be observed at the subtropical stratopause but does not appear in the radiative equilibrium temperature distribution this structure was well simulated using a high resolution general circulation model and examined in detail the stratopause temperature is latitudinally maximized in the winter subtropics because of a strong downwelling of the meridional circulation from summer tropics to winter subtropics passing above the stratopause its strong meridional flow consists of two parts a strong poleward flow in the winter subtropics with nearly vertically aligned contours of absolute angular momentum m and a strong cross equatorial flow toward winter hemisphere above the tropical stratopause with nearly horizontally aligned m contours the strong poleward flow in the winter subtropics is driven by a large eliassen palm e p flux convergence in a small absolute vorticity region the large e p flux convergence is due to extratropical planetary waves and asymmetric inertial instability on the other hand the strong cross equatorial flow is induced along the m contour to satisfy mass continuity with the strong poleward flow in the winter subtropics and exists in the easterly phase of s sao with a small latitudinal gradient of m the easterly of s sao during its mature phase acts as a corridor for cross equatorial meridional circulation while cross equatorial meridional circulation contributes to driving the easterly of s sao in its development phase

barotropic stability of realistic stratospheric jets abstract the stability of realistic jets is examined in a linearized barotropic model on a sphere approximately non dispersive modes associated with a region of negative basic state absolute vorticity gradient on the poleward side of the jet are examined in detail as in previous studies broader jets and those which peak at higher latitudes produce poleward modes that are less dispersive jet profiles derived from observational data at 10 5 and 2 mb for three southern hemisphere winter months are used in the model and the results are compared with quasi nondispersive features qndf which have been observed in satellite data in the southern hemisphere winter stratosphere characteristics of the barotropically unstable modes compare remarkably well with those of the observed modes the barotropic model results for a month in which these features are not observed indicate the presence of equatorward modes at wavenumbers 3 and 4 which grow considerably faster than the quasi nondispersive poleward modes

horizontal wind disturbances induced by inertial instability in the equatorial middle atmosphere as seen in rocketsonde observations 1 rocketsonde observations at kwajalein 8 7 n 167 7 e were used for investigation of horizontal wind disturbances induced by inertial instability two characteristic cases were found in the 1978 1979 northern winter during which the limb infrared monitor of the stratosphere lims made observations in both the cases the eastward component and the northward component of horizontal winds are negatively correlated in the vertical direction near the stratopause level which is thought to be due to inertial instability the wind disturbances have a wavelength of about 10 km and their maximum amplitudes are estimated as over 10 ms 1 examinations of the lims temperatures support a possibility that the wind disturbances are induced by inertial instability it was revealed that temperature disturbances characteristic of inertial instability called pancake structures appear in the same height and time as the wind disturbances do the relationship between the rocketsonde wind disturbances and the lims pancake structures is 90 out of phase as expected by the theory of inertial instability in addition it was confirmed that the two inertial instability events follow enhancements of the midlatitude planetary wave this is consistent with a mechanism of the inertially unstable disturbances in the equatorial region inferred in some observational and numerical studies analyses of rocketsonde data were extended to the entire observation period at kwajalein which suggests that the occurrence of inertially unstable disturbances is biased toward the winter season however at some other stations in the tropics wind disturbances which may be induced by inertial instability do not appear so frequently as they do at kwajalein this seasonality and regionality of inertially unstable disturbances would be due to the seasonality and regionality of planetary wave breakings at midlatitude

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

the temporal behavior of numerically simulated multicell type storms part i modes of behavior abstract the temporal behavior of mature multicellular model storms created in an experiment that varied the vertical wind shear layer depth is examined herein these storms form new cells at low levels on the storm s forward side in or near the forced lifting zone at the edge of the evaporationally chilled subcloud cold air pool each moves upward and rearward within the storm as it intensifies matures and decays and becomes replaced by a new cell development as a result the storms oscillate in time with respect to updraft intensity and the generation of condensation and surface rainfall a few model storms oscillate in a simply periodic fashion during maturity generating a series of nearly identical cells separated by a nearly constant period other storms are still periodic but in a more complex fashion manifesting repeat cycles consisting of two or more cells several simulations appear quite aperiodic spectral analyses of temporal statistics reveal the existence of a fundamental period of o

a seasonal climatology of effective diffusivity in the stratosphere a 7 year 1992 1998 seasonal climatology of effective horizontal diffusivity is presented for the stratosphere 350 1900 k as in previous studies the diagnosis is based on the equivalent length of a test tracer advected on isentropic surfaces in this case using the van leer flux limiting scheme driven by the united kingdom meteorological office assimilated winds although the magnitude of equivalent length is resolution dependent its structure is shown to be reasonably robust for quantifying the inhomogeneous mixing in the stratosphere the van leer calculation agrees well with a more expensive spectral transform calculation at a comparable resolution suggesting that the diagnostic is not sensitive to the advection scheme or subgrid representation of the models a first attempt is also made at estimating the implicit numerical diffusion of the van leer scheme which is necessary to convert equivalent length to effective diffusivity compared with the spectral calculations with a constant diffusion coefficient the van leer results show notably greater diffusivity within the winter polar vortices despite the comparable equivalent lengths suggesting that the scheme may be overdiffusing in the vicinities of mobile tracer extrema the climatology of equivalent length is then presented and the seasonal evolution is discussed in detail for the lower middle and upper stratosphere the major mixing barriers winter and summer polar vortices and tropical eddy transport barrier are easily identified as well as the strong mixing regions surf zones generally equivalent length tends to be small in regions of strong zonal wind and large in regions of weak wind large values of equivalent length are observed in the summer lower stratosphere and in the middle stratosphere during the breakup of the polar vortices interhemispheric asymmetry is observed both after the winter polar vortex breakup where in the middle stratosphere the southern hemisphere shows much larger equivalent lengths and in the summer tropical region where larger equivalent lengths are observed in the northern hemisphere likely related to the monsoon circulation a monthly averaged equivalent length climatology is presented and implications for two dimensional stratospheric chemistry transport modeling are discussed

nonlinear zonal propagation of organized convection in the tropics abstracta wide range of the observed variability in the itcz is frequently explained in terms of equatorially trapped modes arising from matsuno s linear shallow water model here a series of zona

evolution of the zonal mean state in the equatorial middle atmosphere during october 1978 may 1979 abstract the evolution of the zonal mean state in the equatorial middle atmosphere is investigated with the use of daily mapped temperatures derived from the limb infrared monitor of the stratosphere lims experiment these quasi global high vertical resolution data cover the pressure range 100 05 mb and the period 25 october 1978 28 may 1979 the equatorial semiannual oscillation sao in zonal mean temperature derived zonal wind and meridional shear of the zonal wind is described in detail rocket profiles are used to validate features seen in lims data these include ranges in temperature and zonal wind of 20 k and 100 m s 1 and cross equatorial shears of at 3 day 1 consistent with the theory that the wave mean flow interaction is essential to the sao flow acclerations over the equator exhibit strong week to week variations while easterly accelerations are moderate and occur in deep cool layers westerly accelerations are generally stronger and occur in shallow warm layers which descend with time

genesis and evolution of hierarchical cloud clusters in a two dimensional cumulus resolving model abstract a two dimensional cloud ensemble model is integrated over a basin scale domain with prescribed sea surface temperature sst to study the formation and evolution of cloud clusters over a large scale warm pool neither a basic zonal flow is prescribed nor is a single perturbation initially given the results show that deep convective clouds appear in hierarchical clustered patterns and are limited to the area of warm sst above 28 c the most fundamental cloud cluster in the model has a horizontal scale of a few hundred kilometers in which new cumulus clouds are generated at the leading edge of a propagating surface cold air pool the gust front it may last for days and propagate for a long distance if the background flow is broad and persistent as is the case in the low level convergence zone of the sst induced background flow the largest hierarchical propagating cloud systems in the model have horizontal scales up to 3000 km and consist of up to four cloud clusters that are generally of gust

the quasi two day wave event of january 1984 and its impact on the mean mesospheric circulation abstract studies of the quasi two day wave show that it is a summertime phenomenon in the summer of 1983 84 at adelaide 35 s 138 e the main phase of the wave appeared as a pulse in mid january which lasted about seven cycles 14 days coincident with the onset of the pulse a temporary but substantial change occured in the prevailing circulation throughout a deep layer of the upper mesosphere a perturbation of more than 10 m s 1 occurred in the northward flow whereas the change in the zonal flow about 30 m s 1 westward actually caused a reversal of the prevailing eastward simulation above 84 km it is suggested that these changes in the prevailing circulation were a response to the wave pulse a simple calculation is performed to estimate the anticipated response to the observed wave event under plausible assumptions about the magnitude of mean and eddy dissipation processes predicted circulation changes agree reasonably well with those observed it is concluded that such events have a substan

glacial landform assemblages and pedestal moraines in the cordillera blanca peru abstract the article provides a contribution to the glacial geomorphology of tropical high altitude mountains it focuses on the diversity of glacial landforms in the cordillera blanca peru the landforms are classified as individual landform types as well as in their hypsometric sequence their spatial arrangement is depicted in vertical series and summarised in a glacial morphological altitudinal belt model the glacial landforms are analysed in a genetic succession from the moraine delimited glacier forefields to the excessive pedestal moraines and taking account of the topographical conditions in the verticality the pleistocene glacial relief formation is considered as one of the dominating factors in the development of the moraine types the sediments are on the one hand in situ deposition forms and on the other depositions dislocated by mass movements and represent paraglacial landforms using the example of the paron valley in the artesonraju huandoy massif and neighbouring valleys the article provides a typology of the range of glacial and paraglacial landforms based on a holistic glacial landsystem approach with special reference to pedestal moraines

tropical intraseasonal oscillation super cloud clusters and cumulus convection schemes abstract a new framework for interpreting the origin of the tropical intraseasonal oscillation tiso which avoids the speed and scale selection problems in the previous theories is proposed in this study in this interpretation tiso is viewed as an oscillation driven by an eastward moving convective region this convective region consists of one or more super cloud clusters originating in the indian ocean and terminating in mid pacific and is then followed by another convective region arising in the indian ocean in a period of 40 50 days additionally a formal analogy is pointed out between super cloud clusters and the middle latitude baroclinic wave packets this study includes a simulation of tiso in a 2d model to support our interpretation experiments were conducted with four different convection schemes the authors advocate that the successful simulation of tiso depends on the successful simulation of super cloud clusters which in turn depends on the successful simulation of the life cycle of

a numerical simulation of the two day wave near the stratopause abstract the middle atmosphere version of the national center for atmospheric research community climate model 2 maccm2 mechanistic model is used to simulate several aspects of the observed two day wave near the stratopause and its possible connection with inertial instability model experiments show that for a prescribed initial wind condition with strong horizontal wind variation in the tropics inertial instability can trigger the two day wave an increase in horizontal wind curvature fostered by inertial instability circulation barotropically destabilizes the easterly jet in low summer latitudes and allows first the growth of the wavenumber 4 and then the wavenumber 3 component of the two day wave near the stratopause the two day wave eliassen palm flux is directed equatorward away from the wave s critical line source and westerly momentum is transported into the easterly jet core by the wave while much of the wavenumber 4 energy is confined near the stratopause the wavenumber 3 energy can prop

early local last glacial maximum in the tropical andes the local last glacial maximum in the tropical andes was earlier and less extensive than previously thought based on 106 cosmogenic ages from beryllium 10 dating from moraines in peru and bolivia glaciers reached their greatest extent in the last glacial cycle 34 000 years before the present and were retreating by 21 000 years before the present implying that tropical controls on ice volumes were asynchronous with those in the northern hemisphere our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle

observation of the two day wave near the southern summer stratopause temperature and h2o measurements from the upper atmospheric research satellite microwave limb sounder uars mls data sets during southern hemisphere summer of 1991 92 are analyzed using the asynoptic mapping method results show a prominent wavenumber 3 two day wave confined to latitudes between 60 s and 4 n and to altitudes above 2 hpa the temperature wave amplitude increases upward to the upper limit of the observations and maximizes at 2 0 k near 0 465 hpa the h2o wave amplitude reaches a maximum of 0 25 ppmv near 1 hpa evidence suggestive of wave breaking and meridional mixing associated with the interaction between this wave and a lower frequency wavenumber 1 is shown

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

multiscale variability of deep convection in relation to large scale circulation in toga coare deep convection over the indo pacific oceanic warm pool in the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare occurred in cloud clusters which grouped together in regions favoring their occurrence these large groups of cloud clusters produced large scale regions of satellite observed cold cloud top temperature this paper investigates the manner in which the cloud clusters were organized on time and space scales ranging from the seasonal mean pattern over the whole warm pool region to the scale of individual cloud clusters and their relationship to the large scale circulation and sea surface temperature sst the dominant convective variability was associated with the intraseasonal oscillation iso a large eastward propagating ensemble of cloud clusters marked the iso s progress the meridional structure of the iso was strongly affected by the seasonal cycle with a southward shift from the northern hemisphere in october november to the southern hemisphere in january february the sst had an intraseasonal signal in lagged quadrature with the cold cloudiness and rainfall in coare the sst increased decreased during the convectively suppressed active phases of the iso enhanced low level westerly winds occurred toward the later stages of the enhanced convection periods of the iso though not always centered at the equator the strongest westerlies tended to be located between two synoptic scale cyclonic gyres which were often not symmetric about the equator in the low level wind field this asymmetry in the anomalous equatorial low level westerlies may have different implications for the oceanic response in the coupled atmosphere ocean system than those centered on the equator the cyclonic gyres contained highly concentrated deep convection and in four cases the gyres developed into tropical cyclones within the envelope marking the convectively active phase of the iso cloud clusters were frequently concentrated into westward propagating disturbances with a local periodicity of similar to 2 days these 2 day disturbances have been identified in earlier spectral studies and appear to be related to westward propagating inertio gravity waves in coare they typically contained numerous cloud clusters which underwent a distinct diurnal cycle most of the cloud clusters embedded in the 2 day disturbances moved westward though some were stationary and a few moved eastward a cloud duster tracking program identified groups of clusters lime dusters that exhibited continuity in time and space in the most convectively active period of the iso the tracking program identified almost the entire iso cloud ensemble as a long lasting trackable superconvective system this observation indicates the lack of a distinct scale separation between convection and large scale disturbances during the most intense convective periods in coare

the state of stress in an overriding plate situated above a flat slab the andes of central peru in the andes of central peru that are situated above a flat dipping slab analysis of both structural data collected in the field and available focal mechanisms show that the quaternary and recent state of stress is characterized by n s trending extension in the western cordillera and along the pacific coast whereas e w trending compression prevails in the sub andean lowlands and at the contact between the nazca and south american plates the eastern cordillera deformations suggest an intermediate state of stress i e strike slip faulting characterized by e w trending compression and n s trending extension thus major fault zones striking nw se i e parallel to the central peruvian andes are normal with a sinistral component in the western cordillera e g cordillera bianca and reverse sinistral in the eastern cordillera e g cordillera de huaytapallana this state of stress displays similarities with that of southern peru and may be also interpreted as an effect of compensated high topography in this model the vertical stress zz increases with the topography and hmax is considered as fairly constant trending e w roughly parallel to the convergence on both edges of the andes tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then hmax is 2 allowing hmin striking n s to be 3 along the pacific coast tectonics is not compressional as expected and a nearly neutral state of stress may be due to a topographical effect related to the nearby deep peru chile trench however a conspicuous difference occurs in the andes of central peru in respect to the southern peru andes compressional strike slip tectonics is observed in the eastern cordillera indeed the mean elevation of the eastern cordillera is 3 7 km whereas that of the western cordillera is 4 2 km allowing an intermediate state of stress to occur therefore in central peru a lower mean andean topography and a stronger coupling consequence of the flat subduction seems to explain that compressional tectonics is distributed in a more widespread area than in southern peru superficial deformations related to the subduction of the aseismic nazca ridge are restricted to the coastal domain opposite to this ridge they support the fact that submarine topography of large extension may subduct without producing compressional deformation in the overriding plate which can be reminiscent of a collisional setting

mixing zone in the tropical stratosphere above 10 mb observations of trace constituents obtained from the upper atmosphere research satellite in late winter 1991 92 reveal a zone of quasi horizontal stirring in the tropical stratosphere above 10 mb equatorward of the subtropical jet this mixing region was separated from the midlatitude surf zone by a strong gradient of potential vorticity and tracer along the jet axis the jet and accompanying gradients are climatological features mixing equatorward of the jet evidently depends on the phase of the quasi biennial oscillation

observations of cloud cluster hierarchies over the tropical western pacific infrared radiance measurements at cloud top by the japanese geostationary meteorological satellite gms were used to study the structure and propagation of tropical convective systems over the equatorial western pacific results indicate that tropical convection in this region possesses three fundamental periodicities 1 day 2 3 days and 10 15 days cloud clusters within these convective systems interact to produce a hierarchy of collective motions covering all of these three basic time scales the 10 to 15 day time scale is closely related to the intraseasonal or 30 60 day oscillations that propagate from the indian ocean to the western pacific along the equator all year round large convective complexes known as supercloud clusters scc are found to organize in the 10 to 15 day time scale especially over the open warm water of the western central pacific 160 e to 180 the sccs generally propagate eastward although occasionally they can also propagate westward the zonal propagation can occur either continuously or intermittently in both cases the scc is found to be made up of several well organized cloud clusters which are generated at 2 to 3 day intervals and propagate in the opposite direction to the scc the diurnal variation is most pronounced over the maritime continent although significant amplitudes are also found over the open ocean the amplitude of the diurnal cycle is strongly modulated by the 2 to 3 day and 10 to 15 day oscillations advanced spectral analysis methods applied to convective indices derived from the radiance data confirm this hierarchical structure in cloud clusters in the tropical western pacific in addition to the embedding of well organized clusters within a scc in the spatial domain there is also a similar embedding by successive longer scales in the time domain interactions between the major frequency groups appear also to give rise to intermediate frequency variations a discussion of the present results in the context of equatorial wave dynamics of the moist tropical atmosphere is also presented