lithospheric flexure and the origin of the dichotomy boundary on mars the crustal dichotomy between the ancient highlands of the southern hemisphere and the young appearing northern lowlands is a defining feature of mars in the eastern hemisphere the dichotomy boundary is marked by a prominent scarp and extensional and compressional tectonic features topographic data across the boundary returned from the mars global surveyor indicate lithospheric flexure of the southern highlands the topography of the boundary can be fit by a universal lithospheric deflection profile that corresponds to an elastic thickness of 31 36 km flexure of the southern highlands may be due to late noachian early hesperian vertical loading of the northern lowlands fracturing and normal faulting along the boundary may be in response to bending stresses while thrust faulting may result from a combination of stresses due to flexure erosion and global contraction

geochemistry and fluid characteristics of the dalli porphyry cu au deposit central iran abstract the miocene dalli porphyry cu au deposit in the central part of urumieh dokhtar magmatic arc is the first reported au rich porphyry cu deposit in the zagros orogenic belt the cu au mineralization is mainly hosted in diorite and quartz diorite intrusions presenting as numerous veinlets in the altered wall rocks with potassic phyllic and propylitic alteration developed based on the mineral assemblages and crosscutting relations of veinlets hydrothermal mineralization alteration occurred in at least three stages characterized by veinlets of 1 qtz kfs mag ccp 2 qtz py ccp bn cv cc and 3 qtz chl bt the ore bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas including lree fractionated pattern strong enrichment in lile cs rb ba pb and u and depletion of hfse with marked negative ti and nb anomalies the adakite like ore hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of y and eu eu with increasing sio2 content respectively moreover they exhibit a significant increasing trend of sr y with decreasing of y which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma a relatively flat hree pattern with low dyn ybn and nb ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust based on the phase assemblages confirmed by detailed laser raman spectroscopy analyses and proportion of solid liquid and gaseous components five types of fluid inclusions were recognized which are categorized as 1 liquid rich two phase liquidh2o vaporh2o iia 2 vapor rich two phase vaporh2o co2 liquidh2o iib 3 high saline simple fluids iiia liquidh2o vaporh2o hl 4 high saline opaque mineral bearing fluids iiib liquidh2o vaporh2o hl hem ccp py and 5 multi phase type iiiab liquidh2o vaporh2o hl anh hem mag ccp in early stage veins the homogenization temperature of multiphase inclusions as high as 620 c with corresponding salinities of up to 75 wt nacl equivalent represent the initial ore forming fluids from early to late stage veins the gradual decrease of homogenization temperature of saline inclusions iiiab iiia and iiib from 620 to 340 c corresponding salinities of 75 35 wt nacl equivalent may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater the common association of hematite and anhydrite daughter phases with the most primitive inclusions iiiab in early stage veins and the lack of co2 bearing inclusions in the middle to late stage veins reveal co2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization second generation of veins it seems that magnetite crystallization and co2 escape have a decisive role in oversaturation of s2 and subsequent rapid and large scale precipitation of sulfides in second generation of veins at the dalli deposit

decadal time scale variability recorded in the quelccaya summit ice core delta o 18 isotopic ratio series and its relation with the sea surface temperature the spectral characteristics of the delta sup 18 o isotopic ratio time series of the quelccaya ice cap summit core are investigated with the multi taper method mtm the singular spectrum analysis ssa and the wavelet transform wt techniques for the 500 y long 1485 1984 period the most significant at the 99 8 level cycle according to the mtm f test has a period centered at 14 4 y while the largest variance explaining oscillation according to the ssa technique has a period centered at 12 9 y the stability over time of these periods is investigated by performing evolutive mtm and ssa on the 500 y long delta sup 18 o series with a 100 y wide moving window it is shown that the cycles with largest amplitude and that the oscillations with largest extracting variance have corresponding periods aggregated around 13 5 y that are very stable over the period between 1485 and 1984 the wt of the same isotopic time series reveals the existence of a main oscillation around 12 y which are also very stable in time the relation between the isotopic data at quelccaya and the annual sea surface temperature sst field anomalies is then evaluated for the overlapping 1919 1984 period significant global correlation and significant coherency at 12 1 y are found between the isotopic series and the annual global sea surface temperature gsst series moreover the correlation between the low over 8 y frequency component of the isotopic time series and the annual sst field point out significant values in the tropical north atlantic this region is characterized by a main sst variability at 12 8 y

impact of tropical heat sources on the south american tropospheric upper circulation and subsidence the nonlinear adjustment of the wind and mass fields to idealized tropical heat sources is studied with a simple nonlinear primitive equation model with emphasis on the upper level circulation over south america and neighboring oceanic regions during the austral summer numerical experiments are performed with 1 an idealized symmetrical heat source in the amazon region 2 the asymmetry induced in source 1 by the sacz 3 the effect of the atlantic itcz off the amazon mouth 4 the african heat source 5 the west pacific source and 6 the central pacific source during the warm phase of enso the linear response is obtained through the reduction of the heat source by a factor of 10 and subsequent multiplication of the results by the same factor two basic questions are discussed 1 are localized heat sources important for the development of the observed cyclonic flow in the midequatorial atlantic and 2 where is the compensating subsidence associated with the amazon heat source located the nonlinearity helps organizing a weak cyclonic curvature in the midequatorial atlantic with the inclusion of source 2 the basic state generated by the west pacific source and primarily by the central pacific source has a large impact on the cyclonic curvature on the equatorial atlantic the compensating subsidence associated with the amazon source is concentrated on the southwest side of the source the sacz extension helps to enhance the subsidence over the northern argentina and the atlantic itcz enhances the subsidence over northeast brazil and central equatorial atlantic nonlinearity weakens the subsidence at the 500 hpa level inducing a more barotropic structure in the dynamical response to the heating

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

recent changes in the precipitation driving processes over the southern tropical andes western amazon analyzing december february djf precipitation in the southern tropical andes sta 12 circ hbox s 20 circ hbox s 3000 m a s l allows revisiting regional atmospheric circulation features accounting for its interannual variability over the past 35 years 1982 2018 in a region where in situ rainfall stations are sparse the chirps precipitation product is used to identify the first mode of interannual djf precipitation variability pc1 andes a network of 98 rain gauge stations further allows verifying that pc1 andes properly represents the spatio temporal rainfall distribution over the region in particular a significant increase in djf precipitation over the period of study is evident in both in situ data and pc1 andes using the era interim data set we found that aside from the well known relationship between precipitation and upper level easterlies over the sta pc1 andes is also associated with upward motion over the western amazon wa a link that has not been reported before the ascent over the wa is a component of the meridional circulation between the tropical north atlantic and western tropical south america wtsa 80 circ hbox w 60 circ hbox w 35 circ hbox s 10 circ hbox n indeed the precipitation increase over the last 2 decades is concomitant with the strengthening of this meridional circulation an intensified upward motion over the wa has moistened the mid troposphere over wtsa and as a consequence a decreased atmospheric stability between the mid and the upper troposphere is observed over this region including the sta we further show that over the last 15 years or so the year to year variability of sta precipitation periodicity 8 years has been significantly associated with upward motion over the wa while upper level easterlies are no longer significantly correlated with precipitation these observations suggests that the sta have experienced a transition from a dry to a wet state in association with a change in the dominant mode of atmospheric circulation in the former dominant state zonal advection of momentum and moisture from the central amazon associated with upper level easterlies is necessary to develop convection over the sta since the beginning of the 21st century djf precipitation over the sta seems to respond directly and primarily to upward motion over the wa beyond improving our understanding of the factors influencing sta precipitation nowadays these results point to the need of exploring their possible implications for the long term evolution of precipitation in a context of global warming

the long lived and recent seismicity at the lunar orientale basin evidence from morphology and formation ages of boulder avalanches tectonics and seismic ground motion

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

evidence of nonlinear dynamics in the eastward shift of the nao 1 hilmer and jung 2000 have identified an eastward shift in the sea level pressure slp pattern associated with interannual variability of the north atlantic oscillation nao that took place around 1980 we investigate the nature of the eastward shift using a primitive equation dry atmospheric model driven by diabatic forcing diagnosed from observations the model results reveal the nonlinear dependence of the spatial pattern of the nao on the nao index the pattern being shifted to the east west for high low nao index general agreement is found between the model and observations we suggest that the eastward shift noted by hilmer and jung 2000 is a consequence of the trend towards higher nao index during the last several decades of the 20th century

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

multidecadal variations in the relationship between the nao and winter precipitation in the hindu kush karakoram abstractwinter precipitation over the hindu kush karakoram hkk range in the western himalayas is generated by westerly perturbations whose dynamics is affected by the north atlantic oscillation nao larger precipitation is typically recorded during the positive nao phase in this work the relationship between the nao and winter precipitation in the hkk is explored further using an ensemble of precipitation datasets and the 40 yr ecmwf re analysis era 40 and twentieth century reanalysis 20cr data the mechanisms underlying this relationship are discussed with a focus on the secular variations that occurred in the last century the nao exerts its control on hkk precipitation by altering the intensity of westerly winds in the region of the middle east jet stream mejs results indicate that evaporation from the persian gulf the northern arabian sea and the red sea plays an important role during positive nao phases westerlies are strengthened and enhanced evaporation occurs from these basins o

the sparta fault southern greece from segmentation and tectonic geomorphology to seismic hazard mapping and time dependent probabilities the sparta fault system is a major structure approximately 64 km long that bounds the eastern flank of the taygetos mountain front 2407 m and shapes the present day sparta basin it was activated in 464 b c devastating the city of sparta this fault is examined and described in terms of its geometry segmentation drainage pattern and post glacial throw emphasising how these parameters vary along strike qualitative analysis of long profile catchments shows a significant difference in longitudinal convexity between the central and both the south and north parts of the fault system leading to the conclusion of varying uplift rate along strike catchments are sensitive in differential uplift as it is observed by the calculated differences of the steepness index ksn between the outer ksn 83 and central parts 121 ksn 138 of the sparta fault along strike the fault system based on fault throw rates and the bedrock geology a seismic hazard map has been constructed that extracts a locality specific long term earthquake recurrence record based on this map the town of sparta would experience a destructive event similar to that in 464 b c approximately every 1792 458 years since no other major earthquake m 7 0 has been generated by this system since 464 b c a future event could be imminent as a result not only time independent but also time dependent probabilities which incorporate the concept of the seismic cycle have been calculated for the town of sparta showing a considerably higher time dependent probability of 3 0 1 5 over the next 30 years compared to the time independent probability of 1 66 half of the hanging wall area of the sparta fault can experience intensities ix but belongs to the lowest category of seismic risk of the national seismic building code on view of these relatively high calculated probabilities a reassessment of the building code might be necessary

spatial pattern and zonal shift of the north atlantic oscillation part ii numerical experiments abstract in this part the spatial evolution of an initial dipole anomaly in a prescribed jet is at first investigated by numerically solving linear and nonlinear models without forcing in order to examine how the spatial pattern of a dipole anomaly depends on the meridional distribution of a specified jet it is shown that in a linear experiment an initial symmetric dipole anomaly in the meridional direction can evolve into a northeast southwest ne sw or northwest southeast nw se tilted dipole structure if the core of this jet is in higher latitudes the north or in lower latitudes the south this is in agreement with the result predicted by the linear rossby wave theory in slowly varying media the conclusion also holds for the nonlinear and unforced experiment north atlantic oscillation nao events are then reproduced in a fully nonlinear barotropic model with a wavemaker that mimics the atlantic storm track eddy activity in the absence of topography the spatial tilting of the eddy driven nao

carbonate xenoliths hosted by the mesoproterozoic siddanpalli kimberlite cluster eastern dharwar craton implications for the geodynamic evolution of southern india and its diamond and uranium metallogenesis a number of limestone and metasomatised carbonate xenoliths occur in the 1 090 ma siddanpalli kimberlite cluster raichur kimberlite field eastern dharwar craton southern india these xenoliths are inferred to have been derived from the carbonate horizons of the kurnool palnad and bhima proterozoic basins and provide evidence for a connection between these basins in the geological past a revised mesoproterozoic age is proposed for the bhima and kurnool palnad basins based on this kimberlite association and is in agreement with similar proposals made recently for the chattisgarh and upper vindhyan sediments in central india the observed bhima kurnool interbasinal uplift may have been caused by 1 extension or plume related mafic alkaline magmatism that included the emplacement of the southern indian kimberlites at 1 1 ga 2 mantle plume related doming of the peninsular india during the cretaceous or 3 quaternary differential uplift in this region it is not possible with the currently available geological information to constrain the exact timing of this uplift the deep erosion of primary diamond sources in the raichur kimberlite field in the upper reaches of the krishna river caused by this uplift could be the elusive source of the alluvial diamonds of the krishna valley mesoproterozoic sedimentary basins can host world class unconformity type uranium deposits in light of its inferred mesoproterozoic age a more detailed stratigraphic and metallogenic analysis of the kurnool basin is suggested for uranium exploration

role of climate changes for wind gap formation in a young actively growing mountain range wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift the role of climate changes in their formation has never been explored here we use a coupled tectonics landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation in models with a constant precipitation rate rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late if at all if precipitation varies wind gaps form mostly 100 200 ka after a transition to drier conditions because of sediment aggradation upstream of the range our results suggest that the pliocene quaternary aridification of central asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern tibet this article is protected by copyright all rights reserved

crustal structure of the arabian plate new constraints from the analysis of teleseismic receiver functions an edited version of this paper was published by elsevier science copyright 2005 elsevier science see also http dx doi org 10 1016 j epsl 2004 12 020 http atlas geo cornell edu saudiarabia publications al damegh 202005 htm

an outline of early proterozoic crustal evolution in the sao francisco craton brazil a review abstract the early proterozoic evolution of the sao francisco craton sfc occurred between 1 8 2 5 ga and includes the transamazonian cycle 1 9 2 2 ga one of the main periods of crustal growth affecting the south american continent this synthesis of the available data is largely concerned with the early proterozoic terranes of the sfc and presents a modeled crustal evolution integrated with that of the west congo craton interpretation of radiometric ages geochemical and structural data metamorphism p t conditions and lithostratigraphical correlations leads to the characterization of three early proterozoic belts in the sfc named the correntina guanambi itabuna and mineiro belts these belts are here described following a geographic scenario as given by their representatives medium to high grade sequences low grade supracrustal sequences and intrusive igneous rocks the anatomy and regional structures of these belts indicate that they developed along the margin of a large archean protocontinent although characteristic older mantled gneiss domes are also found within the itabuna and mineiro belts available isotopic evidence suggests an episodic growth of the continental crust during the late archean 2 6 3 2 ga with the formation of microcontinents that gradually coalesced around 2 6 ga ago after the archean proterozoic transition the tectonic evolution of the proterozoic mobile belts evolved by mantle accretion differentiation and crustal reworking the main early proterozoic magmatic arc of the sfc is represented by the itabuna mobile belt whereas the minciro belt is chiefly ensialic the nature of the salvador correntina belt is still poorly constrained by geochronological and geochemical data by the end of the transamazonian cycle around 1 8 1 9 ga ago the sfc was fully cratonized

validation of a method for determining the depth of glacial melt ponds using satellite imagery in situ measurements of water depth and optical properties of a melt pond in east greenland were collected to verify a previously developed algorithm for determining supraglacial water depths using satellite imagery that algorithm made five simplifying assumptions which we have tested using the in situ data and laboratory analysis of water samples we conclude that three assumptions were justified one was not and the remaining one substrate homogeneity requires further study but probably has a minor effect on the retrieved water depths and volumes measured water depths of 0 2 3 0m agree well with those derived from a satellite image using the algorithm numerically modeled depths also agree well with those from the satellite image this new analysis demonstrates the validity of our algorithm as a means for determining meltwater volumes in supraglacial ponds and lakes

on the source of midlatitude low frequency variability part i a statistical approach to persistence abstract the forcing of low frequency variability by synoptic transient traveling perturbations is investigated within a quasi geostrophic channel forced by a localized baroclinic jet spontaneously generated baroclinic perturbations grow and decay along a storm track at the end of the track a maximum of low frequency variability is obtained in agreement with atmospheric observations the structure of low frequency variability is studied with a combination of statistical methods using a multivariate red noise model as a random reference we show that the anomalies are preferentially linked with local stationary structures or long wave vacillations according to their location and their sign a systematic study of persistence is conducted with a criterion based on rms of the streamfunction variations the interesting quantity is the probability of persistence which shows a very inhomogeneous distribution in phase space and several separated maxima the composites based on these maxima exhibit the charact

paragenesis and fluid evolution of the halasu iii porphyry cu deposit east junggar nw china implications for the paleozoic multiphase superimposing mineralization in the central asian orogenic belt abstract the halasu iii deposit an important cu deposit in the southernmost part of the halasu porphyry cu belt is situated in the east junggar block in nw china copper and mo sulfide mineralization commonly occurs as disseminations or veinlets and is mainly associated with devonian granodiorite porphyry our detailed field geological investigation identified late stage high grade cu sulfide bearing veining superimposed on the earlier porphyry cu mo mineralization four hydrothermal alteration and mineralization stages were identified namely the early epidote alteration stage i porphyry style alterations stage ii comprising ii a potassic ii b propylitic and ii c phyllic alteration sub stages late veining stage iii and supergene processes stage iv in the northern and southern mineralization zones at halasu iii multiphase granodiorite and alkali granite dykes intruded the beitashan formation volcanic rocks generating the early epidote alteration potassic alteration stage ii a occurred in and around the nnw treading granodiorite dykes while the propylitic alteration stage ii b occurred in the intrusions or volcanic wall rocks around the potassic zone these early alteration assemblages were overprinted by the subsequent structurally controlled phyllic alteration stage ii c confined within the granodiorite porphyry late veins stage iii include sulfide bearing stage iii a and sulfide barren stage iii b ones supergene process stage iv represented by hematite and jarosite replacing primary sulfides extends tens of meters down depth and is commonly fracture controlled three fluid inclusion fi types were recognized namely type a single phase b liquid vapor two phase and c liquid vapor solid three phase for type b fis those of potassic alteration homogenized at 183 347 c with corresponding salinities of 6 2 17 8 wt nacl equiv the propylitic and phyllic fis homogenized at 172 425 c and 231 352 c respectively with the corresponding salinities of 0 9 14 0 wt nacl equiv and 0 4 10 5 wt nacl equiv the sulfide bearing vein fis homogenized at 243 410 c stage iii a 1 260 362 c stage iii a 2 and 117 235 c stage iii a 3 along with the corresponding salinities of 1 9 9 2 wt nacl equiv 1 1 6 7 wt nacl equiv and 6 5 17 1 wt nacl equiv respectively the sulfide barren vein fis yielded homogenization temperatures of 260 380 c stage iii b 1 and 114 297 c stage iii b 2 with corresponding salinities of 1 7 9 8 wt nacl equiv and 0 2 13 6 wt nacl equiv respectively we suggest that hydrothermal veins at halasu iii may have undergone complex and superimposing alteration due to the episodic reopening of the preexisting veins with stage iii a 3 veining overprinting the phyllic alteration and stage iii a 2 veining stage iii b 2 veining superimposed on the potassic alteration as well as on stages iii a 1 and iii b 1 veining paragenetic sequence and fluid evolution at halasu iii indicate that these complex hydrothermal alteration stages were formed in accordance with the regional tectonic evolution these various alteration and mineralization stages at halasu iii deposit reveal a prolonged history of magmatic and hydrothermal processes extending episodically from the middle devonian to middle permian wherein early mineralization was overprinted by late hydrothermal events such superimposed mineralization may occur commonly in the paleozoic central asia orogenic belt

robustness of low frequency circulation patterns derived from eof and rotated eof analyses abstract the robustness of low frequency circulation patterns defined by unrotated and rotated empirical orthogonal functions e0fs are compared based on the northern hemisphere 10 day low pass filtered wintertime 500 hpa height field the pacific north american pattern and the north atlantic oscillation are the most prominent modes of low frequency variability in the data the reproducibility of the spatial patterns derived from eof and rotated eof analysis is assessed by repeating the analysis on 50 subsets of the data each comprised of the maps belonging to 22 randomly selected winters from the 44 winters in the total record the results indicate that rotated spatial patterns are less sensitive to sampling fluctuations than their unrotated counterparts

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

a possible mechanism for the eastward shift of interannual nao action centers in last three decades 1 a weakly nonlinear north atlantic oscillation nao model proposed recently by luo et al 2006 is used to examine the dynamical processes that dominate the eastward shift of the nao action centers of interannual variability it is shown that in a weak mean westerly flow the nao pattern can exhibit a westward shift due to the eddy forcing from high frequency transient eddies such an eddy induced westward shift can become rather pronounced if the transient eddies are rather strong however if the mean westerly flow is enhanced considerably the nao pattern undergoes an eastward shift because the mean flow induced eastward shift exceeds the westward shift this result suggests that the eastward shift of the nao centers of action of interannual variability during the period after 1980 is probably due to an increase in the strength of the zonal mean westerly winds in the north atlantic region

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

the north atlantic oscillation and the north atlantic jet variability precursors to nao regimes and transitions abstractin this paper precursors to the north atlantic oscillation nao and its transitions are investigated to understand the dynamical cause of the interdecadal nao variability from dominant negative nao events during 1950 77 p1 to dominant positive nao events during 1978 2010 p2 it is found that the phase of the nao event depends strongly on the latitudinal position of the north atlantic jet naj prior to the nao onset the nao nao events occur frequently when the naj core prior to the nao onset is displaced southward northward as the situation within p1 p2 thus the northward southward shift of the naj from its mean position is a precursor to the nao nao event this finding is further supported by results obtained from a weakly nonlinear model furthermore the model results show that when the atlantic mean zonal wind exceeds a critical strength under which the dipole anomaly prior to the nao onset is stationary in situ nao nao events which are events not preceded b

an ocean model s response to north atlantic oscillation like wind forcing the response of the atlantic ocean to north atlantic oscillation nao like wind forcing was investigated using an ocean only general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the interannual to multi decadal frequency response of the ocean to a winter wind anomaly pattern overall the strength of the sst response increased slightly with longer forcing periods in the subpolar gyre however the model showed a broad response maximum in the decadal band 12 16 years

a pioneer of precambrian geology boris choubert s fit of the continents across the atlantic 1935 and his insights into the proterozoic tectonic structure of the west african craton and adjacent areas abstract plate tectonics revolutionized the earth sciences during the 1960s and led to a fundamentally new view of tectonic processes inside mountain belts application of the new theory to pre permian and especially precambrian orogenic belts developed somewhat reluctantly during the 1970s and 1980s the present article presents and discusses the ideas of boris choubert 1906 1983 a french colonial geologist of russian origin which he first developed in 1935 he tried to test wegener s theory of continental displacement a forerunner of plate tectonics by applying it to paleozoic and precambrian orogenic belts around the atlantic a topic altogether neglected by wegener to achieve this he produced a fit of the continents across the atlantic which is almost identical to the famous 1965 fit of bullard et al starting from this paleozoic continental configuration he presented an inter continental synthesis of precambrian geology and discussed problems from a wide array of topics ranging from regional tectonics of the west african craton questionable precambrian fossils tillites and cap carbonates to the supposed origin of detrital diamonds in gabon and brazil he also provided probably the first precambrian plate reconstruction avant la lettre after his 1935 paper choubert worked for decades in africa and south america and had opportunity to test and refine his synthesis his example is a call addressed to present day geologists working on precambrian geology in africa and other regions to consult the old colonial literature which contains a wealth of factual information and theoretical inspiration which is still of interest today

monsoons as eddy mediated regime transitions of the tropical overturning circulation monsoons are generally viewed as planetary scale sea breeze circulations caused by contrasts in the thermal properties between oceans and land surfaces that lead to thermal contrasts upon radiative heating1 2 but the radiative heating evolves gradually with the seasons whereas the onset of monsoon precipitation and the associated circulation changes such as reversal of surface winds occur rapidly3 4 here we use reanalysis data to show that the onset of the asian monsoon marks a transition between two circulation regimes that are distinct in the degree to which eddy momentum fluxes control the strength of the tropical overturning circulation rapid transitions of the circulation between the two regimes can occur as a result of feedbacks between large scale extratropical eddies and the tropical circulation5 using simulations with an aquaplanet general circulation model we demonstrate that rapid eddy mediated monsoon transitions occur even in the absence of surface inhomogeneities provided the planet surface has sufficiently low thermal inertia on the basis of these results we propose a view of monsoons in which feedbacks between large scale extratropical eddies and the tropical circulation are essential for the development of monsoons whereas surface inhomogeneities such as land sea contrasts are not

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

continental lithospheric evolution constraints from the geochemistry of felsic volcanic rocks in the dharwar craton india abstract felsic magmatism associated with ocean ocean and ocean continent subduction processes provide important evidence for distinct episodes of crust generation and continental lithospheric evolution rhyolites constitute an integral component of the tholeiitic to calc alkaline basalt andesite dacite rhyolite badr association and contribute to crustal growth processes at convergent plate margins the evolution of the dharwar craton of southern peninsular india during meso to neoarchean times was marked by extensive development of greenstone belts these granite greenstone terranes have distinct volcano sedimentary associations consistent with their geodynamic setting the present study deals with geochemistry of rhyolites from the chitradurga shimoga greenstone belts of western wdc and the gadwal kadiri greenstone belts of eastern edc sectors of dharwar craton to compare and evaluate their petrogenesis and geodynamic setting and their control on the continental lithospheric evolution of the dharwar craton at a similar range of sio2 al2o3 fe2o3 the rhyolites of wdc are more potassic whereas the edc rhyolites are more sodic and less magnesian with slight increase in tio2 minor increase in mgo content of wdc rhyolites reflects their ferromagnesian trace elements which are comparatively lower in the rhyolites of edc the relative enrichment in lile k rb and depletion in hfse nb ta zr hf marked by negative nb ta zr hf and ti anomalies endorse the convergent margin processes for the generation of rhyolites of both the sectors of dharwar craton the high silica potassic rhyolites of shimoga and chitradurga greenstone belts of wdc showing prominent negative eu and ti anomalies flat hree patterns correspond to type 3 rhyolites and clearly point towards their generation and emplacement in an active continental margin environment the geochemical characteristics of gadwal and kadiri rhyolites from eastern dharwar craton marked by aluminous compositions with low and fractionated hree patterns and minor negative eu anomalies are in conformity with type 1 rhyolites and suggest that they were erupted in an intraoceanic island arc system the overall geochemical systematics of the rhyolites from both the sectors of dharwar craton suggest a change in the geodynamic conditions from intraoceanic island arc of eastern dharwar craton and an active continental margin of western dharwar marked by ocean ocean subduction and migration of oceanic arc towards a continent followed by arc continent collision that contributed for the evolution of continental lithosphere in the dharwar craton

dynamics of eddy driven low frequency dipole modes part iii meridional displacement of westerly jet anomalies during two phases of nao abstract in this paper the north south variability of westerly jet anomalies during the two phases of the north atlantic oscillation nao is examined in a theoretical model it is found that the north south variability of the zonal mean westerly anomaly results from the interaction between the eddy driven anomalous stationary waves with a dipole meridional structure nao anomalies and topographically induced climatological stationary waves with a monopole structure which is dependent upon the phase of the nao the westerly jet anomaly tends to shift northward during the positive nao phase but southward during the negative phase synoptic scale eddies tend to maintain westerly jet anomalies through the excitation of nao anomalies but the climatological stationary wave and its position relative to the eddy driven anomalous stationary wave appear to dominate the north south shift of westerly jet anomalies on the other hand it is shown that when the climatological stationary wave ridge is located downs

22 year survey of tropical convection penetrating into the lower stratosphere 1 a 22 year survey of tropical convection penetrating into the stratosphere has been conducted using special subsets of the international satellite cloud climatology project cloud data set in addition to refined information about the geographic distribution of penetrating convective systems these results show that penetrating convection occurs predominantly in the larger organized mesoscale convective systems whereas smaller unorganized convective systems rarely penetrate durations of penetrating events are longest for the largest systems hurricanes and typhoons generally exceeding one day

relationship between upper tropospheric humidity and deep convection satellite measurements of upper tropospheric humidity uth are used together with global cloud imagery to study the relationship between deep convection and moisture in the upper troposphere throughout the tropics regions of cold cloud coincide with regions of enhanced uth in time mean distributions in daily synoptic maps and even on the short scales that characterize individual convective systems cold cloud fraction and uth have very similar instantaneous structure the horizontal correlation scales are narrow for both cloud fraction and uth at 315 hpa and 215 hpa the correlation scale of uth expands at 146 hpa signaling an increased role of horizontal transport ventilation of the upper troposphere by convection is also evidenced by thermal structure inside regions of deep convection the vertical separation of surfaces is expanded stability being weakened by convective mixing inside a deep layer centered near 200 hpa supported by a cloud detrainment convection humidifies the upper troposphere elevating mixing ratio surfaces over their surroundings the reverse is observed at subtropical latitudes where air is anomalously dry jointly these features characterize vertical transport by the hadley and walker circulations

what controls the transition from shallow to deep convection abstract in this study a 2d cloud system resolving model csrm is used to assess the control mechanism for the transition from shallow to deep convection in the diurnal cycle over land by comparing with a 3d csrm under conditions taken from the large scale biosphere atmosphere field study in the amazon the authors show that the 2d csrm reproduces the main features evident in previous 3d simulations reasonably well to extract the essence of the transition from shallow to deep convection the observed case is idealized to isolate two control parameters the free troposphere stability and the relative humidity the emergence of a distinct transition between shallow and deep convection shows that the convective transition is an intrinsic property of the system a transition time is defined to evaluate the key mechanism of the transition the authors show that the transition coincides with the time when the lapse rate of the virtual potential temperature of the clouds becomes larger than that of the env

the crustal structure of the central mozambique continental margin wide angle seismic gravity and magnetic study in the mozambique channel eastern africa abstract the continental margin of mozambique formed during the initial dispersal of gondwana about 180 ma due to the lack of deep seismic and dense potential field data many details of the timing and geometry of the early breakup in this region remained unknown to date to close this gap a research project mobamasis mozambique basin marine seismic survey with the french research vessel r v marion dufresne ii was conducted in 2007 this paper presents the results of p wave magnetic and 2d gravity modelling along two parallel seismic refraction profiles between 37 and 41 e crossing the mozambique rifted margin the crust shows the characteristics of normal to slightly thickened oceanic crust a lower crustal high velocity body with p wave velocities of 7 0 7 5 km s is observed along both profiles its origin is discussed in the context of upper mantle convection and thermal properties the existing magnetic anomaly identifications have been extended to older ages we postulate that the oldest oceanic crust near the central mozambique continental margin has been formed around m41n 166 ma closer to the coast a pronounced negative magnetic anomaly exists that we interpret to coincide with the continent ocean transition this implies that the position of the continent ocean transition is located significantly closer to the shoreline than proposed before

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

weather regime transitions and the interannual variability of the north atlantic oscillation part ii dynamical processes inthisstudy attentionisfocused on identifyingthedynamicalprocessesthatcontributetothenegativenorth atlantic oscillation nao 2 to positive nao nao 1 and nao 1 to nao 2 transitions that occur during 1978 90 p1 and 1991 2008 p2 by constructing atlantic ridge ar and scandinavian blocking sbl indices thecompositeanalysis demonstratesthatinastrongerar sbl winter nao 2 nao 1 eventcanmore easily transition into an nao 1 nao 2 event composites of 300 hpa geopotential height anomalies for the nao 2 tonao 1 andnao 1 tonao 2 transitioneventsduringp1andp2arecalculated itisshownforp2 p1 that the nao 1 to sbl to nao 2 nao 2 to ar to nao 1 transition results from the retrograde drift of an enhanced high latitude large scale positive negative anomaly over northern europe during the decay of the previous nao 1 nao 2 event this finding cannot be detected for nao events without transition moreover itisfoundthattheamplificationofretrogradingwavenumber1ismoreimportantforthenao 2 to nao 1 transitionduringp1 but themarkedreintensificationandretrogrademovementofbothwavenumbers1 and 2 after the nao 1 event decays is crucial for the nao 1 to nao 2 transition during p2 it is further shown that destructive constructive interference between wavenumbers 1 and 2 over the north atlantic during p1 p2 is responsible for the subsequent weak nao 1 strong nao 2 anomaly associated with the nao 2 to nao 1 nao 1 to nao 2 transition also the weakening strengthening of the vertically integrated zonal wind upstream atlantic storm track is found to play an important role in the nao regime transition

em modeling of the central northern portion of ponta grossa arch parana basin brazil abstract broadband remote referenced magnetotelluric data were collected at 16 sites along a sw ne profile across one of the main tectonic features of parana basin the ponta grossa arch this major structure was uplifted before the voluminous flood basalt event occurred during the early cretaceous here we present a 2d model for the crustal structure of parana basin traversing the ponta grossa arch the geoelectrical strike is controlled by nw structures that cut through the crust as indicated by groom bailey decomposition several smooth 2d inversions were used as a starting point to a 2d forward modeling exercise where a priori shallow information was used as constraints that modeling strategy allowed the interpretation of two important regional features a crustal scale sub vertical shear zone 200 m in a resistive 1000 m crust and a 30 m lower crustal conductor confined within 25 40 km we have interpreted the enhanced conductivity in these two features as caused by fluids originated in mantle derived material crustal scale shear zones are considered elsewhere to be important conduits for the connection of upper and lower crustal fluids in the studied area the interpreted shear zone can be associated to main lava conduits at the time of the basalt flows the lower crustal conductor is associated to the hydrated material that intruded in the base of the crust during the mesozoic crustal underplating

the origin of diamonds in western minas gerais brazil important diamond mineralized alluvium colluvium occurs in western minas gerais wmg in the brasilia orogenic belt 700 450 my diamonds are geographically related to glacial and periglacial sediments upper proterozoic and permo carboniferous wadi and debris flow conglomerates lower cretaceous and upper cretaceous and ultramafic alkaline rocks intrusive and extrusive including kimberlites leucitites kamafugites carbonatites etc of cretaceous age petrological data indicate that the rocks originally petrographically classified as kimberlites present mineralogical chemical and isotopical differences with group i and ii kimberlites and more closely resemble kamafugites the brasilia orogenic belt presents features of a wilson cycle implying that wmg does not fulfil the geotectonic and geothermometric requisites to host primary diamond sources an analysis of field relations and sedimentology in wmg shows that the majority of the diamonds have been transported by glacial events from the sao francisco craton further east

linear response of a stratified tropical atmosphere to convective forcing abstract the three dimensional response of the tropical atmosphere to an isolated heat source is investigated using a primitive equation model linearized about a resting basic state on an equatorial plane the model equations are solved by applying vertical and horizontal normal mode transforms the thermal forcing was chosen to simulate the convection which occurs over tropical south america during the southern hemisphere summer the vertical dependence of the forcing is such that the heating is zero at the top and bottom boundaries with a variable level of maximum beating the model results with steady forcing are compared with the average circulation over tropical south america for a 19 day period in the southern hemisphere summer of 1979 and it is shown that the model reproduces many aspects of the observed circulation the partition of the energy of the steady state response between the vertical modes is calculated and it is shown that the internal mode with an equivalent depth of 208 m is domina

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

wind forced interannual variability of the atlantic meridional overturning circulation at 26 5 n the observed atlantic meridional overturning circulation amoc at 26 5 n shows interannual variability consisting of an increase from early 2004 to late 2005 and a following downtrend which reaches a minimum in the winter of 2009 2010 these interannual amoc fluctuations are dominated by changes in the upper mid ocean geostrophic flow except during the winter of 2009 2010 when the anomalous wind driven ekman transport also has a significant contribution the physical mechanisms for the interannual changes of the amoc are proposed and evaluated in a two layer model while the ekman transport is linked to the north atlantic oscillation nao the anomalous geostrophic transport involves the oceanic adjustment to surface wind forcing in particular the intensification and weakening of the southward interior geostrophic flow is modulated by the internal rossby wave adjustment to the surface wind forcing the gulf stream on the other hand is controlled by both topographic waves along the us coast and westward propagating planetary waves our study suggests that a large part of the observed amoc interannual variability at 26 5 n can be explained by wind driven dynamics

steady incision of grand canyon at the million year timeframe a case for mantle driven differential uplift abstract the grand canyon region provides an excellent laboratory to examine the interplay between river incision magmatism and the geomorphic and tectonic processes that shape landscapes here we apply u series ar ar and cosmogenic burial dating of river terraces to examine spatial variations in incision rates along the 445 km length of the colorado river through grand canyon we also analyze strath terrace sequences that extend to heights of several hundred meters above the river and integrate these with speleothem constrained maximum incision rates in several reaches to examine any temporal incision variations at the million year time frame this new high resolution geochronology shows temporally steady long term incision in any given reach of grand canyon but significant variations along its length from 160 m ma in the east to 101 m ma in the west spatial and temporal patterns of incision and the long timescale of steady incision rule out models where geomorphic controls such as climate oscillations bedrock strength sediment load effects or isostatic response to differential denudation are the first order drivers of canyon incision the incision pattern is best explained by a model of neogene and ongoing epeirogenic uplift due to an eastward propagating zone of increased upper mantle buoyancy that we infer from propagation of neogene basaltic volcanism and a strong lateral gradient in modern upper mantle seismic structure

the continuum of northern hemisphere teleconnection patterns and a description of the nao shift with the use of self organizing maps abstract in this study the method of self organizing maps soms is used with ncep ncar reanalysis data to advance the continuum perspective of northern hemisphere teleconnection patterns and to shed light on the secular eastward shift of the north atlantic oscillation nao that began in the late 1970s a 20 pattern som analysis of daily wintertime northern hemisphere sea level pressure reveals a continuum of patterns that correspond closely with well known teleconnection patterns this analysis also reveals that interdecadal variability of the hemispheric sea level pressure field may be understood in terms of changes in the frequency distribution within the continuum of sea level pressure patterns described by the som based on the continuum perspective illustrated with the som the above secular shift of the nao may be understood as a change in dominance from westward displaced negative nao like patterns to eastward displaced positive nao like patterns though westward and eastward displaced nao

horizontal energy propagation in a barotropic atmosphere with meridional and zonal structure abstract to investigate how the propagation of energy away from steady sources may be influenced by the horizontal structure of the time averaged flow in the troposphere solutions to a barotropic model are displayed and interpreted the model is steady and linearized about a basic state which varies in latitude and longitude emphasis is placed on cases where the longitudinal variations are gradual many of the results can be analyzed by locally applying tools developed for zonally symmetric basic states e g ray tracing and refractive indices simple background flows are constructed which have longitudinally confined critical lines reflective surfaces wave guides and regions conducive to propagation an example is given in which longitudinal derivatives of the basic state are significant the theory of ray tracing in a two dimensional wind must be employed as an interpretive tool in this case it is concluded that zonal variations tend to enhance poleward equatorward propagation in large scale tr

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

spatial pattern and zonal shift of the north atlantic oscillation part i a dynamical interpretation abstract this paper presents a possible dynamical explanation for why the north atlantic oscillation nao pattern exhibits an eastward shift from the period 1958 77 p1 to the period 1978 97 p2 or 1998 2007 p3 first the empirical orthogonal function analysis of winter mean geopotential heights during p1 p2 and p3 reveals that the nao dipole anomaly exhibits a northwest southeast nw se tilting during p1 but a northeast southwest ne sw tilting during p2 and p3 the nao pattern especially its northern center undergoes a more pronounced eastward shift from p1 to p2 the composite calculation of nao events during p1 and p2 also indicates that the negative positive nao phase dipole anomaly can indeed exhibit such a nw se ne sw tilting second a linear rossby wave formula derived in a slowly varying basic flow with a meridional shear is used to qualitatively show that the zonal phase speed of the nao dipole anomaly is larger smaller in higher latitudes and smaller larger in lower latitud

simulations of the summer circulation over the south american region with an eta coordinate model abstract a multilevel limited area primitive equations model in eta coordinate is used to simulate the effects of the amazonian latent heat source and the andean topography on the summer december january february circulation over the south american region the observed circulation features such as the bolivian high and the trough near the coast of northeast brazil in the upper troposphere the elongated south atlantic convergence zone sacz oriented northwest to southeast from the southern amazon region into the atlantic ocean and the subtropical anticyclones in the south pacific and south atlantic oceans in the lower levels are well simulated although heating alone produces the sacz the mountain and the basic flow put it in the observed position it is found that regular daily pulses of heating are necessary for the maintenance of the sacz the position and intensity of the sacz change rather substantially from the no mountain case to the mountain case thus showing the importance of the effect

observational evaluation of a convective quasi equilibrium view of monsoons abstract idealized dynamical theories that employ a convective quasi equilibrium qe treatment for the diabatic effects of moist convection have been used to explain the location intensity and intraseasonal evolution of monsoons this paper examines whether observations of the earth s regional monsoons are consistent with the assumption of qe it is shown here that in local summer climatologies based on reanalysis data maxima of free tropospheric temperature are indeed nearly collocated with maxima of subcloud equivalent potential temperature eb in all monsoon regions except the north and south american monsoons free tropospheric temperatures over north africa also exhibit a strong remote influence from the south asian monsoon consistent with idealized dynamical theories peak precipitation falls slightly equatorward of the maxima in eb and free tropospheric temperature in regions where qe seems to hold vertical structures of temperature and wind reveal two types of monsoon circulations one

relationship between amazon and high andes rainfall 1 a regional climate model is used to study the connections between amazon and high andes rainfall the modeling effort focuses on understanding the rainfall response during the last glacial maximum lgm 21 000 years ago as paleoproxy evidence generally suggests that the high andes were wet during this period while conditions over the amazon were drier although there is more uncertainty about the latter analysis of the yearlong present day and full lgm integrations reveals that the delayed onset of amazon convection in the lgm during austral spring is associated with an enhancement of rainfall over the high andes in the absence of convection over the amazon in the austral spring zonal geopotential height gradients over the amazon strengthen resulting in anomalous easterly flow between the amazon and the high andes instead of the low level flow paralleling the andes e g northwesterly the flow impinges more directly onto the eastern slopes of the andes during the lgm where it rises and transports moisture from the amazon up into the mountains enhancing convection over the andes this circulation mechanism explains how the moisture and rainfall over the high andes of peru and bolivia can increase such as the case for the lgm despite large scale drying over south america present day observations are then explored for 1984 2002 and 2003 to identify whether mechanisms identified in the paleoclimate modeling are observable in the present day climate comparison of these particular springs reveals a response analogous to the lgm model response suggesting that this mechanism that connects tropical atlantic sea surface temperatures amazon convection and high andes rainfall is operating in the present climate

are the north atlantic oscillation and the northern annular mode distinguishable this study addresses the question of whether persistent events of the north atlantic oscillation nao and the northern annular mode nam teleconnection patterns are distinguishable from each other standard daily index time series are used to specify the amplitude of the nao and nam patterns the above question is examined with composites of sea level pressure and 300 and 40 hpa streamfunction along with tests of field significance a null hypothesis is specified that the nao and nam persistent events are indistinguishable this null hypothesis is evaluated by calculating the difference between time averaged nao and nam composites it is found that the null hypothesis cannot be rejected even at the 80 confidence level the wave breaking characteristics during the nam life cycle are also examined both the positive and negative nam phases yield the same wave breaking properties as those for the nao the results suggest that not only are the nao and nam persistent events indistinguishable but that the nao nam events are neither confined to the north atlantic nor are they annular

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

modelling landscape evolution in the waipaoa catchment new zealand a phenomenalogical approach landscape evolution models require detailed strength measurements which are difficult to obtain for large areas we offer an alternative phenomenalogical approach to modelling landscape evolution one that requires few input parameters the phenomena are hills channels floodplains knickpoints and coastal floodplain the model is demonstrated on the highly erodible waipaoa catchment in new zealand a digital elevation model is simulated every thousand years from 63000 bp through to present day there is good agreement between predicted and observed terrace heights and also good agreement between predicted and observed knickpoint locations suggesting the phenomenalogical approach is indeed representing the main drivers of landscape evolution in the waipaoa catchment

interdecadal variations in northern hemisphere winter storm track intensity abstract in this paper the interannual variations in the northern hemisphere winter storm tracks have been examined based on 51 winters december january february of ncep ncar reanalysis data the leading empirical orthogonal function eof corresponds to the simultaneous strengthening weakening of both the pacific and atlantic storm tracks interannual and month to month variations in the pacific and atlantic storm tracks are found to be significantly correlated the principal component associated with the leading hemispheric eof exhibits pronounced interdecadal variability there appears to be a transition during the early 1970s from a weak storm track state prior to 1972 73 to a strong storm track state subsequently decadal mean storm track intensity during the 1990s is about 30 stronger than that during the late 1960s and early 1970s the relationship between variations in storm track intensity and low frequency seasonal mean flow anomalies has also been examined it is shown that storm track va

the diamonds of south australia abstract diamonds in south australia occur in kimberlites at eurelia orroroo and in placer deposits which include the springfield basin and the historic echunga goldfield to identify the kimberlitic and mantle sources of the placer diamonds and to determine any possible connections between the placer diamonds and the diamonds from the eurelia kimberlites we examined the physical and compositional characteristics and the mineral inclusion content of 122 diamonds from the springfield basin and 43 diamonds from kimberlites at eurelia additional morphological data for three echunga diamonds are also given most of the diamonds from the springfield basin are similar to the diamonds from eurelia with respect to their crystal shapes surface textures and colors the diamond populations from both areas are characterized by a high abundance of low nitrogen

formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on titan and mars abstract in many terrestrial channels the gravel bed is only transported during rare floods threshold channels and rates of erosion are very slow in this paper we explore how coarse debris delivered to channels on mars and titan from erosion may inhibit further erosion once a coarse gravel channel bed develops portions of the equatorial region of titan are fluvially eroded into banded crenulated terrain some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment no mechanism that can chemically or physically break down ice likely the most important component of titans crust has been unambiguously identified this paper examines a scenario in which fluvial erosion on titan has largely involved erosion into an impact generated megaregolith that contains a modest component of gravel sized debris as the megaregolith is eroded coarse gravel gradually accumulates as a lag pavement on channel beds limiting further erosion and creating a dissected but largely inactive or senescent landscape similar development of gravel pavements occur in ancient mountain belts on earth and partially explain the persistence of appreciable relief after hundreds of millions of years likewise coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on mars particularly if weathering were largely due to physical rather than chemical weathering processes in a relatively cold and or arid environment

moisture sources to the 2010 2012 anomalous wet season in northern south america during 2010 2012 northern south america experienced one of the strongest wet seasons during the recent decades with socio economic implications of wide proportions this period was characterized by two stronger than average la nina events one occurred in 2010 2011 and another less intense event in 2011 2012 this study focused on identifying the main moisture sources besides the eastern pacific for the anomalous wet season occurred in this region during 2010 2012 and their association with the la nina events observed in the equatorial pacific the results discussed here suggest that the main moisture sources to this anomalous wet season were the pacific ocean via the westerly flow of the choco jet and the caribbean sea via the weakening of the caribbean low level jet and the development of southward anomalies toward northern south america such changes appear to be associated not only to el nino southern oscillation enso driven sea surface temperature anomalies in the eastern pacific caribbean sea and north atlantic but also to enso independent variability in the atlantic ocean the latter is related to an enhanced atlantic meridional mode

dynamics of the extratropical response to a tropical atlantic sst anomaly abstract previous atmospheric general circulation model agcm experiments revealed that atmospheric responses to a tropical atlantic sea surface temperature anomaly ssta were asymmetric with respect to the sign of the ssta a positive ssta produced a south north dipole in geopotential heights much like the north atlantic oscillation nao while a negative ssta yielded an eastward propagating wave train with the northern lobe of the nao absent here these height responses are decomposed into components that are symmetric or antisymmetric with respect to the sign of the ssta the symmetric or notionally linear component is a nearly south north dipole projecting on the nao while the antisymmetric or notionally nonlinear component is a different dipole experiments with a diagnostic linear baroclinic model lbm suggest that both components are maintained primarily by transient eddy forcing dynamical mechanisms for the formation of the two components are explored using the lbm and a nonlinear baro

stratigraphic relations kimberlite emplacement and lithospheric thermal evolution quirico basin minas gerais state brazil abstract the quirico basin covers an area of 10 000 km 2 and is situated to the west of the conventionally defined southwestern margin of the archean sao francisco craton in minas gerais state brazil the sedimentary infill of the quirico basin consists of lightly metamorphosed shallow marine clastic bedrock sediments of the bambui group 650 15 ma unconformably overlain by early cretaceous terrigenous lacustrine quirico formation alluvial fan abaete formation and fluvial aeolian tres barras formation deposits of the areado group rare kimberlites and ubiquitous kamafugites of the alto paranaiba igneous province apip erupted through the recently deposited sediments of the quirico basin in the time period 95 61 ma the 120 m thick mata da corda group overlies the late cretaceous areado group over an area of 8000 km 2 and is composed largely of extrusive kamafugite and related volcanosedimentary material unusually large diamonds with proximal surface features and population characteristics are well known to occur in rivers and streams that drain the stratigraphic succession in the quirico basin prompting the search for their presumably local primary source s and a possibly associated archean basement or cratonic root conceptual exploration models for this setting may in part be based on the diamondiferous 120 ma canastra and 95 ma tres ranchos kimberlites but require reconciliation with the observed abundance of 85 61 ma old diamond free kamafugites field relations and carefully controlled stratigraphic samples show that a distinctive mantle derived indicator mineral suite occurs in the maxixe member a volcaniclastic breccia unit that occurs at the base of the mata da corda group a detailed thermobarometric comparison of mantle derived xenocrystic clinopyroxene compositions from this member with clinopyroxene populations derived from kimberlites and kamafugites situated in the quirico basin shows a distinct and abrupt change in geothermal conditions at the onset of kamafugite magmatism kimberlites entrained fragments of garnet peridotite along a cool craton like geotherm which intersected the diamond stability field in the temperature range 880 1000 c clinopyroxene xenocrysts in early stage kamafugites maxixe member record heating by 240 c placing much of the deep lithosphere inside the graphite stability field clinopyroxenes contained in samples from common apip kamafugites indicate the loss of the entire garnet facies lithospheric section estimated at 75 km thick at the time this critical event fundamentally changed the lithospheric architecture and geothermal regime of the quirico basin from cratonic and diamond friendly to noncratonic and diamond unfriendly over a short time interval the lithospheric evolution constrained here by judicious investigation of geological relationships during diamond exploration by canabrava diamond confirms the potential of the quirico basin to host diamondiferous kimberlites that have tapped cool cratonic lithosphere at times prior to eruption of mata da corda kamafugites

eddy mediated regime transitions in the seasonal cycle of a hadley circulation and implications for monsoon dynamics in a simulation of seasonal cycles with an idealized general circulation model without a hydrologic cycle and with zonally symmetric boundary conditions the hadley cells undergo transitions between two regimes distinguishable according to whether large scale eddy momentum fluxes strongly or weakly influence the strength of a cell the center of the summer and equinox hadley cell lies in a latitude zone of upper level westerlies and significant eddy momentum flux divergence the influence of eddy momentum fluxes on the strength of the cell is strong the center of the cross equatorial winter hadley cell lies in a latitude zone of upper level easterlies and is shielded from the energy containing midlatitude eddies the influence of eddy momentum fluxes on the strength of the cell is weak mediated by feedbacks between eddy fluxes mean zonal winds at upper levels and the mean meridional circulation the dominant balance in the zonal momentum equation at the center of a hadley cell shifts at the transitions between the regimes from eddies dominating the momentum flux divergence in the summer and equinox cell to the mean meridional circulation dominating in the winter cell at the transitions a feedback involving changes in the strength of the lower level temperature advection and in the latitude of the boundary between the winter and summer cell is responsible for changes in the strength of the cross equatorial winter cell the transitions resemble the onset and end of monsoons for example in the shift in the dominant zonal momentum balance rapid shifts in the latitudes of maximum meridional mass flux and of maximum convergence at lower levels rapid changes in strength of the upward mass flux and changes in direction and strength of the zonal wind at upper and lower levels in the monsoonal regime the maximum upward mass flux occurs in an off equatorial convergence zone located where the balance of the meridional geopotential gradient in the planetary boundary layer shifts from nonlinear frictional to geostrophic similar dynamic mechanisms as at the regime transitions in the simulation mechanisms that can act irrespective of land sea contrasts and other inhomogeneities in lower boundary conditions may be implicated in large scale monsoon dynamics in earth s atmosphere

influence of the madden julian oscillation on upper tropospheric humidity 1 variations of upper tropospheric humidity uth and cold cloud in the tropics reveal coherent changes that propagate eastward from the indian ocean into the pacific the coherence of uth is high at periods of 30 90 days along the equator near the tropical tropopause uth coherence is large over the equator in the indian ocean and over the subtropics in the central pacific a composite life cycle shows that enhanced uth in the subtropics coincides with two anticyclonic gyres they straddle anomalous cold cloud over the equator as it propagates eastward the enhancement of uth is consistent with anomalously cold temperature which mirrors the anticyclonic gyres those temperature anomalies cancel the height anomaly of the gyres overhead the complex of anomalous uth cold cloud and anticyclonic motion marches eastward across the western pacific until reaching the dateline anomalous convection over the equator then collapses along with the subtropical gyres and enhanced uth accompanying it index terms 3374 meteorology and atmospheric dynamics tropical meteorology 3399 meteorology and atmospheric dynamics general or miscellaneous 3319 meteorology and atmospheric dynamics general circulation 3314 meteorology and atmospheric dynamics convective processes keywords madden julian oscillation upper tropospheric humidity tropical convection

zonal asymmetry of the annular mode and its downstream subtropical jet an idealized model study abstractthis study investigates linkages between the zonal asymmetry of the annular mode am zonal pattern and the subtropical jet stj over its downstream regions of the storm track by using an idealized model observational analyses show that the am zonal patterns are more zonally asymmetric during days when the stj downstream of the storm track is unusually strong and vice versa in the idealized model the stj downstream of the storm track is varied by introducing an additional zonally localized tropical heating the model s am variability exhibits a nearly zonally uniform structure when there is no or only weak tropical heating however the signatures of the am are locally strengthened in the heating sector thus the am zonal pattern is zonally asymmetric when the tropical heating is large enough to create a strong stj the model results also show that the percentage of the variance explained by the am the persistence of the am index and the intensity of eddy feedback are also increased when t

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

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

the 30 60 day convection seesaw between the tropical indian and western pacific oceans abstract the tropical indian and western pacific oceans are two prominent action centers for tropical 30 60 day convective variability when convection is enhanced over the equatorial indian ocean the tropical western pacific often experiences an abnormal dry condition phase i whereas the development of the convection over the tropical western pacific tends to be accompanied by suppressed convection in the equatorial indian ocean phase ii this convection seesaw is a fundamental characteristic of the tropical 30 60 day oscillation the seesaw is intimately associated with the activity of propagating low frequency convective systems lfcss its formation process is season dependent typical boreal summer seesaw results from a time lagged development of two systems a western system that originates in the equatorial indian ocean and moves eastward and or northward and an eastern system that develops in the western pacific monsoon region and moves westward and or northward the boreal winter seesaw o

transient eddy forcing of the rotational flow during northern winter abstract the total direct transient eddy forcing of the vorticity balance in the upper troposphere during northern winter is examined using 11 years of 2 to 8 day bandpassed global analyses most examinations of the importance of high frequency eddy vorticity fluxes to the maintenance of either the climatological standing waves or low frequency anomalous flows have focused on only the horizontal blow or the rotational component of the horizontal transient flow the latter simplification has been shown to be questionable for planetary scales the vorticity flux by the transient divergent flow produces a forcing of the mean streamfunction that is of comparable magnitude with the equivalent rotational term however the streamfunction forcing by the sum of the transient vertical advection and twisting terms largely balances the fearing by the vorticity flux convergence associated with the divergent flow the result is that the convergence of the eddy vorticity flux by the total transient flow is not a good a

the positive north atlantic oscillation with downstream blocking and middle east snowstorms impacts of the north atlantic jet abstracta recent study revealed that cold winter outbreaks over the middle east and southeastern europe are caused mainly by the northeast southwest ne sw tilting of european blocking eb associated with the positive phase north atlantic oscillation nao here the north atlantic conditions are examined that determine the eb tilting direction defined as being perpendicular to the dipole anomaly orientation using daily reanalysis data the nao events are classified into strong sjn and weak wjn north atlantic jet types a composite analysis shows that the eb is generally stronger and located more westward and southward during sjn events than during wjn events during sjn events the nao and eb dipoles exhibit ne sw tilting which leads to strong cold advection and large negative temperature anomalies over the middle east and southeastern europe in contrast northwest southeast nw se tilting without strong negative temperature anomalies over the middle east is seen during wjn events a nonline

moisture variability over the south american altiplano during the south american low level jet experiment salljex observing season 1 during the austral summer precipitation over the high altitude plateau of the south american altiplano exhibits a marked intraseasonal variability which has been associated with alternating moist and dry conditions observed at surface stations near the altiplano western cordillera in this study the characteristics of humid wet and dry dry episodes observed at a station on the western rim of the altiplano during the summer of 2002 2003 are examined using observational data from the south american low level jet experiment salljex and satellite based estimates of precipitable water pw from global positioning system moderate resolution imaging spectrometer and passive microwave radiometer instruments we find that on wet days mean moist conditions pw greater than 10 mm prevail across the entire plateau this moisture is apparently brought to the altiplano by sustained westward advection of air at similar altitude above the continental basin and propagates across the altiplano to moisten the atmosphere over the pacific ocean a considerable distance 1000 km west of the plateau in contrast during dry events significant drying of the boundary layer is observed mainly along the western mountain range and over the southern altiplano there is no evidence of strong midlevel advection of dry air across the northern altiplano and moisture remains constant and high over the northern basin and along the altiplano eastern ridge consequently precipitation and convective cloudiness show the strongest relation to moisture along the western cordillera of the altiplano significant diurnal variability of moisture is found to occur most strongly on the outer slopes of the altiplano there is little indication that daytime upslope flow on the eastern slope of the altiplano plays a major role in the transport of moisture to the altiplano during wet episodes

the shift of convection from the indian ocean to the western pacific ocean during a 30 60 day oscillation abstract a strong 30 60 day oscillation during november december 1981 is studied using analyzed winds from the national meteorological center outgoing longwave radiation and satellite low level moisture data the outgoing longwave radiation and 150 mb velocity potential for five adjacent events are also examined consistent features include the slow 5 m s 1 propagation of convective energy over the indian ocean western pacific ocean and the fast 15 m s 1 propagation of 150 mb tropical velocity potential in regions remote from the oceanic warm pool the individual events have characteristics of the seasonal and anomalous base state within which they are embedded for the november december 1981 event we concentrate on the details of the shift of convection from the eastern indian ocean to the western pacific ocean an intense cold surge and accompanying convective increase near 110 e precede the shift cast by about 12 days the regional 150 mb circulation responds to the enhanced convection with an i

diamonds in brazil and a proposed model for the origin and distribution of diamonds in the coromandel region minas gerais brazil the geology of diamonds in brazil is briefly summarized in relation to the known primary source localities and secondary host rocks emphasis is placed on the geotectonic control of mineralized primary diamond source rocks and it is shown that the distribution and occurrences in brazil of diamond bearing versus nondiamond bearing kimberlites and or lamproites are compatible with the geotectonic constraints observed worldwide in brazil the distribution of the majority of the diamonds can be correlated with three principal glaciations the first in the lower proterozoic is designated the jequitai glaciation the second probably in the cambrian is represented by the santa fe tillites and the third in the carboniferous is represented by the itarare subgroup these glaciations with the capacity to transport kimberlitic minerals and diamonds intact for extreme distances are considered the principal sources of diamonds in for example the coromandel region of western minas gerais cretaceous kimberlites and lamproites of unknown age in brazil were intruded along major arcs and lineaments along basin borders and on the amazonico craton upper cretaceous kimberlites in the alto paranaiba are noneconomic in respect to diamonds to date the only known economically viable primary diamond sources are cretaceous kimberlites in the guapore shield within a substratum that has remained tectonically and thermally stable for more than 1 500 ma it is postulated that a precambrian diamondiferous kimberlite event occurred in brazil which intruded principally into the sao francisco craton it is proposed that these are the primary diamond source s for the large diamonds 100 kt that are found in the alluvial deposits of the coromandel region of minas gerais

origin of the polygons and the thickness of vastitas borealis formation in western utopia planitia on mars 1 many middle scale about 100m cracking space polygons are located between the area of the giant polygons and the thumbprint terrains in western utopia planitia most of the patterns are located on vastitas borealis formation the polygonal patterns have frequently been associated with collapsed features such as a covered trough like features the width of the underground crack is approximately 400 500 m the thickness of the surface materials 6 12 m where polygonal patterns occur was calculated based on the space of cracking relationship polygonal networks with strongly oriented features and parallel to the contour line are likely caused by structural geological origin as well as bending forces from the center of the basin

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations