existence of mini break like condition during early indian monsoon onset years in the context of increasing probability of advancement in onset date of indian summer monsoon during recent years precipitation and circulation features of early monsoon onset events are investigated in detail using reanalysis data and model simulations during the onset pentad 2 days from the onset day an anomalous increase in precipitation is observed over the west coast of peninsular india and bay of bengal during early onset years compared to normal onset years the monsoon low level jet llj also becomes stronger during the onset pentad of early onset years particularly over the southern peninsular india however after a week from the onset day of early years precipitation is considerably decreased and the llj become weaker moreover convection over the eastern arabian sea and western peninsular india suppresses during that period which in turn inhibits the systematic northward propagation of monsoon rainbands this induces a mini break like condition immediately after a week from the onset day during early onset years analysis of the sea surface temperature sst shows that over the north eastern arabian sea a lower value of sst exists during early onset years compared to normal onset years which may have a triggering role in the formation of mini break like condition this aspect is examined using sensitivity simulations with the advanced research weather research and forecasting model simulations with reduced sst over the north eastern arabian sea during normal onset years exhibits considerable reduction in precipitation over the west coast of india and weakens the llj over the peninsular india whereas simulations with enhanced sst over the north eastern arabian sea during early onset years show increase in the convective activities over the eastern arabian sea and west coast of peninsular india and the existence of mini break like situation disappears from those years thus numerical simulations confirm the relation between sst over the north eastern arabian sea and the formation of mini break during early onset years

chalcophile element geochemistry and petrogenesis of high ti and low ti magmas in the permian emeishan large igneous province sw china sulfide poor mafic layered intrusions sills dykes and lava flows in the funing region sw china are part of the 260 ma emeishan large igneous province they belong to either a high ti group tio2 1 6 4 4 wt with elevated ti y ratios 351 1 018 or a low ti group tio2 1 low y pd pm ratios 0 2 7 1 and nearly constant cu pd pm ratios 1 5 3 8 the even and parallel chalcophile element patterns of the high pge low ti subgroup rocks are likely a result of olivine dominated fractionation under s undersaturated condition the low pge low ti group rocks have low mgo 4 5 8 9 wt and very poor pge pt pd 0 5 1 6 ppb ir 0 004 0 02 ppb with low cu zr ratios 0 1 0 5 high y pd pm 26 70 and variable cu pd pm ratios 2 8 14 the trough like chalcophile element patterns of the low pge low ti subgroup rocks indicate that the magmas were sulfide saturation and sulfide melts were extracted from the magmas the extracted sulfide melts might be potential ni cu sulfide ores at depth in the funing region

statistics of geomagnetic storms and ionospheric storms at low and mid latitudes in two solar cycles 1 the statistics of occurrence of the geomagnetic storms and ionospheric storms at kokubunji 35 7 n 139 5 e 26 8 n magnetic latitude in japan and boulder 40 0 n 254 7 e 47 4 n in america are presented using the dst and peak electron density nmax data in 1985 2005 covering two solar cycles 22 23 when 584 geomagnetic storms dst 50 nt occurred in addition to the known solar cycle and seasonal dependence of the storms the statistics reveal some new aspects 1 the geomagnetic storms show a preference for main phase mp onset at around ut midnight especially for major storms dst 100 nt over 100 excess mp onsets at ut midnight compared to a uniform distribution 2 the number of positive ionospheric storms at kokubunji about 250 is more than double that at boulder and 3 the occurrence of the positive storms at both stations shows a preference for the morning noon onset of the geomagnetic storms as expected from a physical mechanism of the positive storms 4 the occurrence of negative ionospheric storms at both stations follows the solar cycle phases most frequent at solar maximum better than the occurrence of positive storms which agrees with the mechanism of the negative storms

equatorial and low latitude ionosphere thermosphere system response to the space weather event of august 2005 1 the response of the equatorial and low latitude ionosphere thermosphere system to the geomagnetic storm during 23 26 august 2005 is investigated the study is carried out using the vertical total electron content vtec measured by gps receivers along the 77 78 e longitude and the o n2 ratio obtained from the global ultraviolet imager instrument on board the timed satellite the equatorial ionization anomaly eia shows a poleward latitudinal expansion on 24 august probably associated with an eastward prompt penetration electric field the equatorial and low latitudes show an increase in vtec during the main phase of the storm on 24 august the prompt penetration eastward electric field along with an increase in the o n2 ratio could be responsible for this observed positive phase the vtec variations on 24 august also reveal the signature of a large scale acoustic gravity wave traveling atmospheric disturbance propagating with a horizontal velocity of 750 m s suppression of the eia is observed during the storm recovery phase on 25 august which probably is associated with the westward disturbance dynamo electric field and the equatorward expansion of the neutral composition changes o n2 depletion

radiative dynamical consequences of dry tongues in the tropical troposphere abstract dry layers are frequently observed in atmospheric soundings from the climatologically humid western pacific warm pool region some 2400 soundings from the toga coare field program were objectively examined for humidity drops layers in which relative humidity decreases rapidly with height indicative of the bases of dry layers these occur throughout the lower and middle troposphere with frequency peaks near 550 the 0 c level 800 and 950 mb a composite constructed from these sounding data indicates the following almost all dry layers are too dry and not warm enough to be interpreted as conservative vertical displacements rather they apparently consist of filaments or tongues of low moist static energy air advected into the column often from the subtropics dry tongues are anomalously virtually warm near their bases with a slight cool layer below that is they sit atop sharp stable layers or inversions the authors hypothesize that radiation is responsible for the thermal structure o

empirical models of storm time equatorial zonal electric fields ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes we describe initially a methodology for the study of storm time dependent ionospheric electric fields we present empirical models of equatorial disturbance zonal electric fields obtained using extensive f region vertical plasma drift measurements from the jicamarca observatory and auroral electrojet indices these models determine the plasma drift perturbations due to the combined effects of short lived prompt penetration and longer lasting disturbance dynamo electric fields we show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the rice convection model for comparable changes in the polar cap potential drop we also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns when the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects the measured and modeled drift velocities are generally in good agreement however our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency and in the high latitude potential and energy deposition patterns which are not accounted for in the model these case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields

modeling of forecast sensitivity on the march of monsoon isochrones from kerala to new delhi the first 25 days abstractthis study addresses observational and modeling sensitivity on the march of the onset isochrones of the indian summer monsoon the first 25 days of the passage of the isochrones of monsoon onset is of great scientific interest surface and satellite based datasets are used for high resolution modeling of the impact of the motion of the onset isochrones from kerala to new delhi these include the asymmetries across the isochrone such as soil moisture and its temporal variability moistening of the dry soil to the immediate north of the isochrone by nonconvective anvil rains and formation of newly forming cloud elements to the immediate north of the isochrone the region immediately north of the isochrone is shown to carry a spread of buoyancy elements as these new elements grow they are continually being steered by the divergent circulations of the parent isochrone to the north and eventually to the northwest cloudsat was extremely useful for identifying the asymmetric cloud structures across t

monsoon convection in the himalayan region as seen by the trmm precipitation radar three dimensional structure of summer monsoon convection in the himalayan region and its overall variability are examined by analyzing data from the tropical rainfall measuring mission trmm precipitation radar over the june september seasons of 2002 and 2003 statistics are compiled for both convective and stratiform components of the observed radar echoes deep intense convective echoes 40 dbz echo reaching heights 10 km occur primarily just upstream south of and over the lower elevations of the himalayan barrier especially in the northwestern concave indentation of the barrier the deep intense convective echoes are vertically erect consistent with the relatively weak environmental shear they sometimes extend above 17 km indicating that exceptionally strong updraughts loft graupel to high altitudes occasionally scattered isolated deep intense convective echoes occur over the tibetan plateau wide intense convective echoes 40 dbz echo 1000 km2 in horizontal dimension also occur preferentially just upstream of and over the lower elevations of the himalayas most frequently in the northwestern indentation of the barrier the wide intense echoes have an additional tendency to occur along the central portion of the himalayas and they seldom if ever occur over the tibetan plateau the wide intense echoes exhibit three mesoscale structures amorphous areas lines parallel to the mountain barrier and arc shaped squall lines perpendicular to and propagating parallel to the steep himalayan barrier the latter are rare generally weaker than those seen in other parts of the world and occur when a midlevel jet is aligned with the himalayan escarpment deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low level moist layer of monsoon air from the arabian sea meets dry downslope flow in a manner reminiscent of severe convection leeward of the rocky mountains in the central usa as the low level layer of moist air from the sea moves over the hot arid northwestern subcontinent it is capped by an elevated layer of dry air advected off the afghan or tibetan plateau the capped low level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the himalayas broad 50 000 km2 in area stratiform echoes occur in the eastern and central portions of the himalayan region in connection with bay of bengal depressions their centroids are most frequent just upstream of the himalayas in the region of the concave indentation of the barrier at the eastern end of the range the steep topography apparently enhances the formation and longevity of the broad stratiform echoes monsoonal depressions provide a moist maritime environment for the convection evidently allowing mesoscale systems to develop larger stratiform echoes than in the western himalayan region copyright 2007 royal meteorological society

theoretical effects of geomagnetic activity on low latitude ionospheric electric fields 1 the influence of geomagnetic activity on middle and low latitude thermospheric winds and ionospheric electric fields is investigated using model results from the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model model runs are made for different levels of geomagnetic activity model results show that the equatorward ionospheric currents produced by disturbance winds develop positive charge accumulation at low latitudes that maximizes in the premidnight sector the local time of maximum electric potential perturbation depends significantly on universal time so that the local time of reversal of the equatorial zonal perturbation electric field varies with longitude by 2 to 3 hours depending on the intensity of geomagnetic activity the westward perturbation electric field in the postsunset period indicates that stronger geomagnetic activity will produce a lower driven height of the evening f region after geomagnetic activity ceases model results show that the zonal disturbance winds can last for many days in the postrecovery period while the meridional disturbance winds decay more rapidly the long lasting zonal winds through the pedersen currents they drive help maintain meridional disturbance potential drops that decay much more slowly than the zonal disturbance potential drops after the activity ceases

a statistical study on the characteristics of ionospheric storms in the equatorial ionization anomaly region gps tec observed over taiwan 1 positive and negative signatures of the ionospheric storms caused by the penetration electric field disturbance dynamo neutral wind neutral composition etc have been reported in this paper the ionospheric total electron content tec derived from the records of a network of ground based gps receivers in taiwan is used to statistically study the characteristics such as local time of appearance and duration of the storm signatures of various casuals in the equatorial ionization anomaly eia region during 1994 2003 a bias corrected accelerated bootstrap method and a z test are employed for the first time to detect each event and the overall storm signatures and characteristics respectively it is found that the positive signatures that appeared minutes to hours after the geomagnetic storm onset are pronounced on the storm day and the next day while the negative signatures that started hours after the geomagnetic storm onset can last for as long as the next 4 days the positive signature is statistically significant and most pronounced when the intense geomagnetic storm onset occurs during local afternoon which suggests that the signature may result from a combination of the prompt penetration electric field effect and mechanical effects of equatorward neutral wind additionally the negative signature that is statistically significant and most pronounced in the local afternoon of the storm onset day and or the next day may be produced by the disturbance dynamo or overshielding effects the long lasting negative signature occurred in local midnight noon period on days 2 4 after the storm onset may result from the neutral composition disturbances

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

the asian summer monsoon an intercomparison of cmip5 vs cmip3 simulations of the late 20th century the boreal summer asian monsoon has been evaluated in 25 coupled model intercomparison project 5 cmip5 and 22 cmip3 gcm simulations of the late twentieth century diagnostics and skill metrics have been calculated to assess the time mean climatological annual cycle interannual variability and intraseasonal variability progress has been made in modeling these aspects of the monsoon though there is no single model that best represents all of these aspects of the monsoon the cmip5 multi model mean mmm is more skillful than the cmip3 mmm for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations additionally for rainfall convection the mmm outperforms the individual models for the time mean the interannual variability of the east asian monsoon and intraseasonal variability the pattern correlation of the time pentad of monsoon peak and withdrawal is better simulated than that of monsoon onset the onset of the monsoon over india is typically too late in the models the extension of the monsoon over eastern china korea and japan is underestimated while it is overestimated over the subtropical western central pacific ocean the anti correlation between anomalies of all india rainfall and nino3 4 sea surface temperature is overly strong in cmip3 and typically too weak in cmip5 for both the enso monsoon teleconnection and the east asian zonal wind rainfall teleconnection the mmm interannual rainfall anomalies are weak compared to observations though simulation of intraseasonal variability remains problematic several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from india to the equatorial west pacific the mmm also well represents the space time evolution of intraseasonal outgoing longwave radiation anomalies caution is necessary when using gpcp and cmap rainfall to validate 1 the time mean rainfall as there are systematic differences over ocean and land between these two data sets and 2 the timing of monsoon withdrawal over india where the smooth southward progression seen in india meteorological department data is better realized in cmap data compared to gpcp data

super plasma fountain and equatorial ionization anomaly during penetration electric field 1 relative importance of diffusion electric field and neutral wind on equatorial plasma fountain and equatorial ionization anomaly eia during a strong daytime eastward prompt penetration electric field ppef event are evaluated using the sheffield university plasmasphere ionosphere model and the recorded ppef during the super geomagnetic storm of 9 november 2004 the fountain rapidly develops into a super fountain during the ppef event the super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces or stops the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss the eia crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the ppef event however the crests become stronger than normal only in the presence of an equatorward wind the results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during a daytime eastward ppef event the equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms

new aspects of thermospheric and ionospheric storms revealed by champ 1 the neutral mass density n and electron density ne at 400 km height measured by champ during nine intense geomagnetic storms bring out some new aspects of the thermospheric and ionospheric storms the thermospheric storms increase of n develop with the onset of the main phases mp of the geomagnetic storms and reach their peak phases before or by the end of the mps the ionospheric storms change of ne in general undergo an initial negative phase with the equatorial ionization anomaly eia crests shifting poleward before turning positive and the positive storms reach their peak strengths or phases centered at 25 30 magnetic latitudes in some 4 cases the positive storms develop without an initial negative phase and with the eia crests shifting equatorward in all cases the positive storms reach their peak phases before the end of the mps and turn to conventional negative storms by the end of the mps the observations agree with the different aspects of a physical mechanism of the positive storms the observations also reveal that the halloween storms of 30 october 2003 with a short mp without fluctuations produced the strongest positive ionospheric storms through impulsive response and there is strong equinoctial asymmetry in the ionosphere and thermosphere during geomagnetic storms

theoretical study of new plasma structures in the low latitude ionosphere during a major magnetic storm 1 theoretical model simulations for an intense magnetic storm show the creation of a low latitude electron density arch aligned along the geomagnetic field created by strong uplift of the f2 layer that is driven by the penetration electric field when the arch forms during the day a new f2 layer is created at the original altitude by photoionization and a density hole can be created between this new f2 layer and the arch when the arch forms during the night the f2 layer is not recreated and no hole forms in a vertical profile of electron density the daytime elevated ionospheric layer can appear distinctly from the recreated f2 layer in which case the elevated layer is called the f3 layer a latitude cut through the night side arch shows the characteristics of an equatorial electron density trough bounded to the north and south by enhanced densities associated with plasma that has diffused down along the geomagnetic field from the elevated layer it is pointed out that the signature of the night side arch has been seen in low earth orbit spacecraft data but has not been previously associated with an arch structure

neutral wind effect in producing a storm time ionospheric additional layer in the equatorial ionization anomaly region 1 a new type of the additional layer is predicted to occur in the low latitude f region ionosphere during evening hours of a major magnetic storm by using the coupled ncar thermosphere ionosphere electrodynamic general circulation model tiegcm and sheffield university plasmasphere ionosphere model supim runs during the major magnetic storm of 29 30 october 2003 we present a new type of additional layer which occurs at the equatorial ionization anomaly eia by a new physical mechanism this mechanism requires that storm time meridional neutral wind surges travel from high to low latitudes and cross into the opposite hemisphere the wind surges modify the field aligned plasma velocities in the eia regions significantly after uplift of the ionospheric layer by a penetration electric field and interact with the downward field aligned plasma velocities of the enhanced equatorial fountain the combined storm effects of the enhanced plasma fountain and the neutral wind surges result in plasma convergence in altitude and form the additional layers underneath the eia crests

nickeliferous gabbroic intrusions of the pants lake area labrador canada implications for the development of magmatic sulfides in mafic systems the pants lake intrusions are located some 80 kilometers south of the world class voisey s bay ni cu co sulfide deposit in labrador canada they are dominated by olivine gabbro with subordinate troctolite melagabbro peridotite and leucogabbro they form several sheet like bodies that were emplaced into metasedimentary gneisses that locally contain sulfides the largest of these termed the north and south intrusions have been dated by other workers at 1322 2 ma and 1337 2 ma respectively indicating that they formed in two discrete events the north intrusion is more varied petrologically and its three units show ambiguous contact relationships implying that they partly coexisted as liquids disseminated sulfide mineralization is widespread near the basal contacts of both intrusions but massive sulfide mineralization is rare in the older south intrusion sulfides are hosted by melagabbro and peridotite of cumulate origin and probably represent a gravitational accumulation in the younger north intrusion they are hosted by a complex mineralized sequence interpreted to represent two or more influxes of magma charged with sulfides and reacted country rock fragments the older south intrusion is geochemically distinct from the younger north intrusion and more closely resembles the voisey s bay intrusion mineralized rocks within both pants lake intrusions are geochemically similar to the associated unmineralized rocks and must be closer related to them the mafic rocks almost all have low ni contents and low cu zr ratios that imply extraction of metals by sulfide liquids this pervasive depletion signature coupled with consistent ni cu and ni co and clustering of sulfide metal contents suggests that sulfide liquids were developed on an intrusion wide scale probably at depth rather than by local processes sulfides at pants lake typically contain less than 2 percent ni and 2 percent cu these values agree with predictions from the low ni contents of silicate rocks and imply a low mass ratio r factor of silicate magma to sulfide liquid r 1000 the pervasive ni and cu depletion contrasts with the more localized metal depletion seen at voisey s bay this may indicate that the pants lake sulfide liquids were not as effectively upgraded by later batches of undepleted magma from the perspective of metallogenesis data from the pants lake intrusions support several key concepts proposed m models for the formation of the voisey s bay deposit suggesting that these may apply more widely as controls on the formation of magmatic sulfide deposits in broadly gabbroic magma systems

critical factors for the formation of a nickel copper deposit in an evolved magma system lessons from a comparison of the pants lake and voisey s bay sulfide occurrences in labrador canada the voisey s bay nickel copper deposit and the pants lake sulfide occurrences are the most important mineral systems discovered to date within the nain plutonic suite in northern labrador there are many intriguing similarities at both locations both are hosted by relatively small troctolite gabbro bodies that intrude the sulfide bearing paragneiss of the churchill province and these intrusions contain inclusions of the paragneiss similar chemical reactions of the gneissic inclusions with the host magmas are observed at both locations the reactions resulted in the addition of sio2 k2o na2o and sulfur to the magmas and are responsible for sulfide saturation and resultant segregation of immiscible sulfide liquids from the magmas the initial sulfide liquids in both cases were relatively poor in metals containing 2 5 wt ni and 2 wt cu the sulfides at pants lake remained poor in metals because of a lack of subsequent interaction with new chalcophile undepleted magma at voisey s bay the initial sulfides segregated in a dynamic conduit and were subsequently upgraded in metals to 6 wt ni and 3 wt cu by a new surge of undepleted magma using the same conduit these sulfides were then concentrated to form large sulfide bodies in the wider parts of the conduit and its entry to an upper chamber in response to a sudden change of liquid velocity in these environments this study confirms three of the most important factors for the formation of magmatic sulfide deposits in an evolved magma system 1 contamination of magma with sulfide bearing country rock to achieve sulfide saturation 2 a dynamic magmatic system such as a magma conduit to transport large volume of sulfide liquid and to concentrate them in limited localities and 3 upgrading of metals in the sulfide by new chalcophile undepleted magma

on the significant impact of the moderate geomagnetic disturbance of march 2008 on the equatorial ionization anomaly region over indian longitudes 1 the response of the equatorial and low latitude ionosphere plasmasphere system to the moderate geomagnetic disturbance of march 2008 is the subject of this paper this study for the first time reports large plasmaspheric electron content modulation at equatorial and low latitude regions over india during a moderate geomagnetic disturbance this paper also presents for the first time five station tomograms encompassing the entire eia region and unequivocally demonstrates the effectiveness of tomographic technique in investigating storm induced modulations of the equatorial ionization anomaly the present study has been carried out using the total electron content values derived from gps and coherent radio beacon experiment crabex data over indian longitudes ionosonde data at trivandrum 8 5 n 77 e and delhi 28 n 78 e and the geomagnetic field data from trivandrum and alibag

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

asian summer monsoon onset barrier and its formation mechanism the onset process of asian summer monsoon asm is investigated based on diagnostic analysis of observations of precipitation and synoptic circulation results show that after the asm commences over the eastern bay of bengal bob around early may the onset can propagate eastwards towards the south china sea and western pacific but is blocked on its westward propagation along the eastern coast of india this blocking termed the monsoon onset barrier mob presents a gill type circulation response to the latent heating released by bob monsoon convection this convective condensation heating generates summertime wintertime vertical easterly westerly shear to its east west and facilitates air ascent descent the convection then propagates eastward but gets trapped on its westward path to the east of the central bob the surface air temperature sat cools faster than the underlying sea surface temperature sst due to monsoon onset thus more sensible heat flux supports the onset convection to propagate eastward to the west of the central bob however the land surface sensible heating over the indian peninsula is strengthened by the enhanced anticyclone circulation and air descent induced by the bob monsoon heating the strengthened upstream warm horizontal advection then produces a warm sat center over the mob region which together with the in situ cooled sst reduces the surface sensible heating and atmospheric available potential energy to prevent the occurrence of free convection therefore it is the change in both large scale circulation and air sea interaction due to bob summer monsoon onset that contributes to the mob formation

a climatology of middle and upper atmosphere radar observations of thermospheric winds shigaraki middle and upper atmosphere mu radar observations of horizontal thermospheric winds in the magnetic meridian plane over the period september 1986 to september 1996 are reported as climatological averages in the form of time of day variations for several combinations of seasonal and solar activity conditions and are compared with winds predicted by the horizontal wind model hwm and with winds measured at saint santin and millstone hill the dominant feature of the mu wind behavior is its mean diurnal variation of northward flow by day and southward flow by night with the nighttime wind smoothly approaching and receding from a midnight maximum while the daytime wind tends to show two peaks a strong one in the early daylight hours and a weak one in the afternoon evening hwm shows the same unimodal nighttime and bimodal daytime behavior but the hwm pattern is shifted about 2 hours later in time the amplitude of the diurnal harmonic decreases from 78 m s at solar minimum to 45 m s at solar maximum while hwm shows a corresponding increase from 53 to 62 m s the diurnal amplitude is remarkably stable with season but is superposed on a steady wind of 41 m s southward in summer 15 m s northward in winter and midway between these limits at the equinoxes hwm shows a symmetric pattern of 30 m s southward in summer and 30 m s northward in winter ion drag appears to be the main regulator of wind speed and the seasonal wind patterns have a profound effect on the seasonal behavior of the ionosphere

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

redox effect on the partitioning of nickel in olivine abstract the fractionation of nickel by olivine in the lower zone of the kiglapait intrusion in company with the olivine compositions compared to estimated liquid compositions places stringent limits on the value of the olivine liquid partition coefficient for ni estimated at 4 0 0 8 at the base of the lower zone data from a strong ni mgo correlation in mauna loa picrites also require a low value of d estimated at 5 8 0 4 these values are much lower than usually considered normal for mafic magmas and the effect is ascribed to the low oxygen fugacity of the magmas estimated independently for the kiglapait case to be near the wustite magnetite buffer at this redox state a significant amount in this case about half of the ni in the melt is dissolved as ni 0 which inflates the liquid concentration without entering the olivine because the analyzed values reflect only total ni rather than the species the partition coefficient decreases with reduction as shown by recent experimental studies the mauna loa data imply a reduced condition for that magma as well knowledge of the redox regime governing the partition coefficient is vitally important in modelling fractional crystallization and in discussing early planetary history conversely knowledge of the ni fractionation in a magma series can specify the redox regime of the magma as at mauna loa

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

petrologic evolution of gneissic xenoliths in the voisey s bay intrusion labrador canada mineralogy reactions partial melting and mechanisms of mass transfer nickel copper cobalt sulfide ores in the voisey s bay intrusion are closely associated with troctolitic to gabbroic rocks that contain abundant country rock xenoliths potential sources of the xenoliths include pelitic paragneiss enderbitic orthogneiss and mafic to quartzofeldspathic gneisses that form immediate country rocks to different parts of the intrusion regardless of location all xenoliths have a similar refractory mineral assemblage composed of hercynite magnetite ca rich plagioclase and corundum the refractory mineral assemblage formed via partial melting immediately after xenoliths were engulfed by magma rapid thermal equilibration allowed the xenoliths to survive prolonged interaction with magma corundum was formed by the incongruent melting of na rich plagioclase in pelitic and quartzofeldspathic gneisses corundum and ca rich plagioclase assemblages are aluminous their origin involved either multistage melting of protoliths where the production of a granitic minimum melt was followed by the liberation of a more silica rich and al poor melt or one stage disequilibrium melting density differences between the xenoliths restite assemblages and enclosing mafic magma facilitated the separation of partial melt from restite no evidence for the melts in the form of channels or interstitial glass is observed in the restite flow of mafic magma in the conduit system is thought to have dispersed the si and alkali rich melts derived from the xenoliths the only record of the xenolith derived melts is in the form of concentric rims of plagioclase and biotite which crystallized from a hybrid melt in boundary layers around most xenoliths hercynite in the restitic assemblage was produced either by partial melting involving fe and mg bearing minerals such as garnet and pyroxene or by replacement of corundum feo and mgo that were excluded from the boundary layer diffused inward and reacted with corundum to form hercynite the thickness of the hercynite bands suggests formation times between 3 000 and 23 000 years where the insulating rims of plagioclase and biotite were not present diffusion of feo and mgo from the surrounding crystal mush continued resulting in near complete conversion of corundum to hercynite the highly refractory mineral assemblages which characterize xenoliths present in the voisey s bay intrusion provide evidence for a complex history of magma country rock interaction the transfer of xenomelts and sulfur to flowing magma may have been essential for the formation of the magmatic sulfide ores

geochronology of the voisey s bay intrusion labrador canada by precise u pb dating of coexisting baddeleyite zircon and apatite abstract the emplacement history of the voisey s bay troctolite intrusion that hosts the major ni cu co sulfide deposit of the same name has been studied using precise u pb geochronology of baddeleyite zircon and apatite the baddeleyite u pb ages of multiple drill core samples of troctolite and gabbro indicate that all of the mafic rocks studied from different components of the voisey s bay intrusion eastern deeps discovery hill zone and reid brook zone and from the adjacent red dog area were emplaced at 1332 7 1 0 ma on the basis of combined geological and geochronological evidence it is suggested that the voisey s bay ni cu co deposit was formed during the same period the zircons coexisting with the ca 1333 ma baddeleyite show a diversity of ages the zircons from normal troctolite and some of the olivine gabbro samples are coeval with the baddeleyite while zircon from the varied textured troctolite and feeder olivine gabbro are much younger at 1305 0 0 8 ma the identical ages of the younger zircon population and the voisey s bay syenite that cuts the mafic rocks indicate a link between zircon growth in the mafic rocks and contact metamorphism related to the emplacement of the syenite various mechanisms of zircon growth were probably involved including reaction of the 1333 ma baddeleyite with a silica enriched fluid with formation of a secondary polycrystalline zircon and zircon crystallization from syenite micro veins in the mafic rocks the mean 207 pb 206 pb age of 1303 5 2 6 ma of the voisey s bay apatites is similar to the age of the younger zircon population the apatite age may either be a result of resetting the u pb system in response to the syenite intrusion or may reflect the closure of the system during regional cooling and cessation of fluid circulation the presence of xenocrystic zircon in a discovery hill zone feeder olivine gabbro indicates that the voisey s bay magmas were contaminated with 1 90 ga crustal rocks

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000 the effects of the great magnetic storm of july 15 2000 on the equatorial ionosphere have been studied by ground based and satellite in situ measurements a large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo in that environment the imf bz turned southward and presumably caused penetration of e fields to low latitudes this e field initiated the onset of 250 mhz and l band scintillations at ascension island 15 w and precipitous tec decrease at fortaleza brazil 38 w bounding the narrow longitude region in the south atlantic these impulsive ionospheric effects were extremely well correlated with abrupt decreases of sym h 1 min resolution dst the dmsp in situ measurements showed the presence of severe ion density bite outs extending over 30 latitude in the south atlantic magnetic anomaly region the rocsat 1 satellite measured upward and large southward ion drifts in the same sector

variations of total electron content during geomagnetic disturbances a model observation comparison this paper studies the ionospheric response to the major geomagnetic storm of october 18 19 1995 using the ncar tie gcm simulations and the global ionospheric maps gim of total electron content tec observations from the worldwide network of global positioning system gps receivers the tie gcm results show a good agreement with the gps gim in terms of simulating storm time tec disturbances over the polar regions the model indicates that the increase of electron density in the high latitude e and lower f regions below 200 km is directly related to the magnetospheric energy input through auroral precipitation to the ionosphere while the decrease of tec is mainly due to the increase in o2 and n2 densities in the upper f region above 200 km during the recovery phase both the tie gcm and gps gim reveal a distinct hemispheric asymmetry in the tec integrated above 50 magnetic latitude with a 20 decrease in the southern summer like hemisphere and a 30 increase in the northern winter like hemisphere

regional seasonal and diurnal variations of extreme convection in the south asian region abstract temporal and spatial variations of convection in south asia are analyzed using eight years of tropical rainfall measuring mission trmm precipitation radar pr data and ncep reanalysis fields to identify the most extreme convective features three types of radar echo structures are defined deep convective cores contiguous 3d convective echo 40 dbz extending 10 km in height represent the most vertically penetrative convection wide convective cores contiguous convective 40 dbz echo over a horizontal area 1000 km2 indicate wide regions of intense multicellular convection and broad stratiform regions stratiform echo contiguous over an area 50 000 km2 mark the mesoscale convective systems that have developed the most robust stratiform regions the preferred locations of deep convective cores change markedly from india s east coast in the premonsoon to the western himalayan foothills in the monsoon they form preferentially in the evening and over land as near surface moist flow is cap

the drying tendency of shallow meridional circulations in monsoons shallow meridional overturning circulations are superimposed on the deep circulations that produce precipitation in nearly all monsoon regions and these shallow circulations transport subtropical mid tropospheric dry air into the tropical monsoon precipitation maxima here horizontal moisture advection produced by shallow meridional circulations is characterized in the monsoon regions of west africa south asia australia and southern africa during local summer horizontal flow in the upper and lower branches of the shallow meridional circulations consistently dries and moistens air respectively in the continental precipitation maxima of each region the peak drying by horizontal advection occurs at a lower altitude than peak winds in the upper branch of the shallow circulations consistent with the small scale height of water vapor advection of time mean moisture by time mean wind dominates horizontal moisture advection in south asia and west africa while most horizontal moisture advection in australia and southern africa is produced by transient eddies much of the transient eddy advection can be accurately represented as a first order horizontal diffusion with a constant globally uniform diffusivity these results suggest that horizontal moisture advection in theoretical and conceptual models of seasonal mean monsoons can be adequately represented in terms of time mean winds plus a simple horizontal moisture diffusion finally interannual variations in the summer mean regional averages of monsoon precipitation and horizontal advective drying in the lower free troposphere are shown to be negatively correlated in most regions consistent with the hypothesis that advective drying by shallow meridional circulations inhibits monsoon precipitation

the interaction of indian monsoon depressions with northwesterly midlevel dry intrusions abstractmonsoon depressions mds bring substantial monsoon rainfall to northern and central india these events usually form over the bay of bengal and travel across northern india toward pakistan using european centre for medium range weather forecasts interim reanalysis an md tracking algorithm and an objective identification method the authors find that about 40 of mds interact with northerly intrusions of dry desert air masses as the mds traverse the subcontinent md interactions with dry intrusions are often preceded by positive potential vorticity pv anomalies on the subtropical jet and low level anticyclonic anomalies over the north arabian sea dry intrusions nearly halve the precipitation rate in the southwest quadrant of mds where mds rain the most however dry intrusions increase the rainfall rate near the md center similarly ascent is reduced west of the md center and enhanced at the md center especially in the upper troposphere the reduced ascent west of md centers is likely att

low latitude ionospheric disturbances results for march 22 1979 and their general characteristics low latitude ionospheric disturbances which were characterized by severe scintillations in the c band range accompanied by complex dynamical behavior of the low latitude ionosphere were examined taking into consideration previous results from the analyses of fof2 and h f data these disturbance events are found to be characterized by a two stage process during the first stage which starts during the magnetospheric energy storage process before the onset of substorms h f begins to increase simultaneously at all observing stations due to eastward electric fields penetrating from the magnetosphere at subequatorial stations increases of fof2 follow as a signature of enhancements of the equatorial anomaly during the second stage values of h f increase again indicating a motion from north to south with no increase of fof2 in this stage dynamical effects including neutral winds become important as well as electric fields in addition it is shown from the analysis of one year s data for 1978 that the occurrence of disturbance events as presented in this paper is a general feature in the evening section under the condition of ring current developments

comprehensive imaging observations of midlatitude ionospheric disturbances during storm time substorms this paper reports comprehensive imaging observations of 630 nm airglow enhancements and related phenomena in the nighttime f region over japan we found two events during which the airglow intensity increases up to 300 r at the lower latitude side of japan associated with storm time substorms of august 26 1998 and february 18 1999 total electron content tec observations by more than 900 gps receivers over japan show a clear tec enhancement of 10 40 at latitudes below 40 which coincides with the airglow enhancements and the substorms on the other hand 2 mhz virtual heights obtained by bottomside sounding at four ionosoride stations show equatorward moving large scale structures which do not coincide with the airglow enhancements vertical ion drift data at an altitude of 800 km obtained by the defense meteorological satellite program satellites show upward ion motion in midlatitudes just after the substorm onset for the february event these observations suggest that the midlatitude airglow and tec enhancements are caused by upward electron motion fountain in the low latitudes clue to penetration of eastward electric field associated with the storm time substorms

the evolution of troctolitic and high al basaltic magmas in proterozoic anorthosite plutonic suites and implications for the voisey s bay massive ni cu sulfide deposit the voisey s bay massive ni cu sulfide deposit is contained within troctolitic plagioclase olivine intrusions of the 1 34 to 1 29 ga nain plutonic suite coastal labrador canada and represents a new setting for magmatic sulfide deposits proterozoic anorthosite plutonic suites consist of vast quantities as much as 20 000 km 2 of cumulate anorthosite leucotroctolite leuconorite intrusions of troctolite and fe enriched dioritic rocks and large granitic batholiths crystallization ages span nearly 1 200 m y within the middle proterozoic 2 12 0 92 ga many proterozoic anorthosite plutonic suites were emplaced into relatively young proterozoic crust and some were intruded along archean proterozoic boundaries e g nain labrador laramie wyoming korosten ukraine nearly all of the largest plutonic suites contain significant areas thousands of km 2 of plagioclase rich cumulate rocks that are olivine bearing olivine anorthosite leucotroctolite troctolitic rocks 20 30 modal olivine occur in proterozoic anorthosite plutonic suites principally as cumulates in layered or massive intrusions e g kiglapait hettasch jonathon nain intruded into anorthositic rocks with the notable exception of the voisey s bay deposit nearly all troctolitic rocks crystallized late in the evolution of individual plutonic suites many of the troctolitic intrusions have fine grained olivine rich marginal rocks that closely represent parental magma compositions numerous fine grained olivine normative dikes with high al basaltic compositions also occur within many plutonic suites nain harp lake laramie adirondack and share compositional characteristics with the troctolitic magmas these olivine normative high al basaltic magmas record the least evolved compositions in proterozoic anorthosite plutonic suites mg 0 43 0 64 an 45 60 have high al 2o 3 15 19 wt and feo total 9 15 wt contents and typically show the least contaminated sr and nd isotope compositions in a given plutonic suite many dikes and marginal rocks have strong positive eu anomalies a feature of the melt composition that is not related to plagioclase accumulation except at laramie the least evolved troctolitic magmas appear to have about 8 wt percent mgo and corresponding ni and s concentrations between 100 to 150 ppm and 0 02 to 0 05 wt percent respectively based on closed system fractionation in the kiglapait intrusion sulfide saturation occurs late in the crystallization history of troctolitic magmas after ni concentrations have been severely depleted by protracted olivine fractionation the optimal conditions for formation of a ni cu sulfide deposit associated with a proterozoic anorthosite plutonic suite require a relatively high mgo parental magma that has not crystallized much prior olivine and an external source of s to promote early sulfide saturation probably through desulfurization reactions as hot troctolitic magmas ascend through the crust an economically important massive ni cu sulfide deposit on the scale of voisey s bay clearly requires large volumes of magma probably involving continuous replenishment of relatively ni rich unfractionated parental magma in staging chambers or mixing between magmas in conduits during ascent a model for the formation of troctolite associated massive ni cu sulfide deposits is proposed depending on the relative degrees of sulfide saturation and fractionation of the mixed magmas mixing between troctolitic magmas in a conduit or magma chamber may either poison the system stopping sulfide segregation or enhance sulfide segregation

a theoretical study of thermospheric composition perturbations during an impulsive geomagnetic storm the compositional response of the neutral thermosphere to an impulsive geomagnetic storm has been investigated using a numerical simulation made with the national center for atmospheric research thermospheric general circulation model ncar tgcm calculated time dependent changes in neutral thermospheric composition have been studied together with detailed neutral parcel trajectories and other diagnostic information from the model to gain a greater understanding of the physical mechanisms responsible for composition variability during geomagnetic storms and in particular to investigate the causes of the positive and negative ionospheric storm effects the following principal results were obtained from this study 1 calculated perturbations in thermospheric composition following the onset of an impulsive geomagnetic storm were found to be in good qualitative agreement with the previous experimental statistical study of storm time thermospheric morphology by prolss 1981 2 during the initial onset phase of the simulated storm upward vertical winds occurred in the auroral zone and downward winds occurred in the central magnetic polar cap 3 the largest perturbations in mass mixing ratio of nitrogen n2 at f region altitudes were found to be associated with parcels of neutral gas that travelled through the cusp region and with parcels that were trapped within the auroral zone for a long time 4 storm time enhancements in n2 were found to occur in the midnight and early morning sectors both within and equatorward of the auroral zone and these were determined to be associated with the advective effects of the large antisunward polar cap neutral winds the physical size of the region of enhanced n2 values was determined to be related to the time taken for individual parcels of air to corotate out of the large day to night thermospheric wind jet and thus to the magnitudes of the antisunward polar cap winds 5 decreases in n2 were found to occur in regions of downward vertical winds and in regions into which relatively nitrogen poor air was advected by the horizontal wind 6 calculated compositional perturbations following the onset of the storm were found to propagate to mid latitudes due to the advective effects of equatorward winds leading to the mid latitude positive ionospheric storm effects this last result is in disagreement with the earlier study of rishbeth et al 1985 who found the compositional disturbance to be largely restricted to the auroral zone on a constant pressure surface however it is consistent with the more recent study undertaken by fuller rowell et al 1991 who demonstrated that composition changes were seen well beyond the auroral oval

a physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 1 a physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi instrument observations theoretical modeling and basic principles according to the mechanism an equatorward neutral wind is required to produce positive ionospheric storms the mechanical effects of the wind 1 reduce or stop the downward diffusion of plasma along the geomagnetic field lines 2 raise the ionosphere to high altitudes of reduced chemical loss and hence 3 accumulate the plasma at altitudes near and above the ionospheric peak centered at around 30 magnetic latitudes daytime eastward prompt penetration electric field ppef if it occurs also shifts the equatorial ionization anomaly crests to higher than normal latitudes up to approximately 30 latitudes the positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind the mechanism agrees with the multi instrument observations made during the supergeomagnetic storm of 7 8 november 2004 with 18 h long initial phase ip and 10 h long main phase mp the observations which are mainly in the japanese australian longitudes where the mp onset was in the morning 0600 lt 2100 ut show 1 strong positive ionospheric storms in ne nmax hmax global positioning system total electron content gps tec and 630 nm airglow intensity in both northern and southern hemispheres started at the morning 0600 lt mp onset and lasted for a day 2 repeated occurrence of strong eastward ppef events penetrated after the mp onset and superposed with westward electric field started before the mp onset and 3 storm time equatorward neutral winds inferred from 1 and 2 repeated occurrence of an unusually strong f3 layer with large density depletions around the equator was also observed during the morning noon mp

the mineralogy of the voisey s bay ni cu co deposit northern labrador canada influence of oxidation state on textures and mineral compositions the voisey s bay ni cu deposit is one of the most significant discoveries made in canada in the last 30 yr known reserves plus indicated and inferred resources amount to 136 7 106 metric tons t grading 1 59 wt percent ni and 0 85 wt percent cu the deposit can be described in terms of four geologic settings the eastern deeps consisting of massive and disseminated sulfide along the line of intersection of a feeder sheet with the base of a troctolite intrusion the ovoid a 600 m long by 350 m wide 350 by 110 m deep lens of massive sulfide underlain by a feeder sheet the discovery hill zone which comprises a series of swellings containing disseminated and massive sulfides in the troctolite feeder and the reid brook zone which is where the feeder sheet opens out into a deeper level intrusion the principal sulfide minerals are hexagonal pyrrhotite troilite pentlandite chalcopyrite cubanite and magnetite troilite is restricted to the reid brook discovery hill and ovoid zones where it occurs as exsolution lamellae in hexagonal pyrrhotite the texture of pentlandite varies with the presence of troilite in coexisting pyrrhotite where troilite is present pentlandite occurs as equant masses up to several centimeters across where troilite is absent it occurs around pyrrhotite grain margins and as lamellae in a pyrrhotite host the ni content of hexagonal pyrrhotite averages 0 28 wt percent 14 analyses in troilite bearing zones and 0 51 wt percent 8 analyses in troilite absent zones cubanite is restricted to troilite bearing zones the presence of troilite indicates a metal rich high temperature hexagonal monosulfide solid solution from which pentlandite will exsolve at a higher temperature than from a more sulfur rich monosulfide solid solution thus developing as larger masses cubanite can exist with metal rich pyrrhotite but not with sulfur rich pyrrhotite metal rich pyrrhotite indicates an original metal rich sulfide melt which in turn indicates a low oxygen fugacity in the silicate magma with which the sulfides equilibrated this is thought to be due to the presence of graphite in the region where the magma extracted sulfide from surrounding gneisses

tropical inversions near the 0 c level abstract soundings taken from the tropical western pacific warm pool region during toga coare reveal the common occurrence of temperature and moisture perturbations near the 0 c level the perturbations frequently are characterized by shallow layers of increased stability or occasionally temperature inversions and reversals or inflections in the vertical profile of specific humidity similar temperature and moisture inversions have been observed elsewhere in the tropics and midlatitudes but have not received much attention isothermal layers are known to exist just below the melting level in stratiform rain regions however not all stable layers observed over the warm pool are confined to precipitation systems the perturbation in the specific humidity profile accounts for the often observed double peak structure in the apparent moisture sink q2 in tie tropics stratification of the data based on relative humidity criteria indicates that the stable layers near the 0 c level generally fall into two main

platinum group element geochemistry of intraplate basalts from the aleppo plateau nw syria early middle miocene intraplate basalts from the aleppo plateau nw syria have been analysed for their platinum group elements pges they contain extremely low pge abundances comparable with most alkali basalts such as those from hawaii and mid ocean ridge basalts the low abundances together with high pd ir pt ir ni ir cu pd y pt and cu zr are consistent with sulphide fractionation which likely occurred during partial melting and melt extraction within the mantle some of the basalts are too depleted in pges to be explained solely by partial melting of a primitive mantle like source such ultra low pge abundances however are possible if the source contains some mafic lithologies many of the basalts also exhibit suprachondritic pd pt ratios of up to an order of magnitude higher than primitive mantle and chondrite an increase too high to be attributable to fractionation of spinel and silicate minerals alone the elevated pd pt associated with a decrease in pt but not ir and ru are also inconsistent with removal of pt bearing pge minerals or alloys which should have concurrently lowered pt ir and ru in contrast melting of a metasomatized source comprising sulphides whose pt and to a lesser extent rh were selectively mobilized through interaction with silicate melts may provide an explanation

effects of prolonged southward interplanetary magnetic field on low latitude ionospheric electron density the present work describes the low latitude ionospheric variability during an unusually prolonged 33 h geomagnetically disturbed condition that prevailed during 15 16 july 2012 the low latitude electron density in summer hemisphere investigated using ground and satellite based observations responded to this by generating strong negative ionospheric storm on 16 july the maximum electron density on 16 july over indian low latitudes was reduced by more than 50 compared to that on a geomagnetically quiet day 14 july 2012 in contrast to the extreme reduction in total electron content tec in the northern hemisphere tec from a winter hemispheric station revealed substantial 23 total electron content unit 1 tecu 1016 el m 2 enhancements on the same day this contrasting hemispherical response in tec is suggested to be due to the combined effects of strong interhemispheric and solar driven day night winds further very weak equatorial electrojet eej strength on 16 july indicated that the westward electric field perturbations in the low latitude ionosphere were possibly due to the disturbance dynamo effect associated with meridional circulation from polar to equatorial latitudes interestingly despite reduction in the integrated eej strength on 15 july the low latitude electron density showed substantial enhancement highlighting the significant effect of the positive ionospheric storm on the low latitude ionosphere the roles of electrodynamical neutral dynamical and compositional disturbances are discussed in view of these observations to understand low latitude ionospheric response when geomagnetic disturbance persists for longer duration

equatorial density depletions observed at 840 km during the great magnetic storm of march 1989 early on march 14 1989 a thermal plasma probe on the defense meteorological satellite program dmsp f9 spacecraft detected extensive and dramatic decreases in the ion density at 840 km near 2130 lt during two consecutive transequatorial passes over south america the order of magnitude decreases in the ion density extended more than 4000 km along the satellite track the depletions were accompanied by upward and westward plasma drifts both in excess of 100 m s their onsets and terminations were marked by extremely sharp density gradients dmsp f9 observed no similar depletions over the atlantic during preceding orbits a partial depletion was detected over the eastern pacific during the following orbit the dmsp f9 ground track passed slightly west of a brazilian total electron content tec station and two brazilian ionosondes during the first depletion encounter the tec fell far below normal during the night of march 13 14 the ionosonde measurements indicate that in the hour after sunset before dmsp passed through the depletions the f2 layer rose rapidly and disappeared but at the time of the first depletion encounter hmf2 was decreasing over one of the stations the dmsp f8 satellite which orbits in the dawn dusk meridian made related measurements on march 13 and 14 crossing the equator at dust on march 13 at the same longitude where dmsp f9 encountered the first depletion dmsp f8 detected upward and westward drifts but it measured extremely large rather then depleted ion densities during two dawn passes over the eastern pacific on march 14 dmsp f8 observed depletions somewhat similar to those detected by dmsp f9 large westward drifts accompanied the depletions detected by dmsp f8 it is quite probable that the morningside depletions detected on march 14 are remnants of those detected earlier by dmsp f9 in the evening sector we develop a phenomenological model reconciling dmsp f8 f9 and ground based measurements our calculations show that rapid upward drifts sustained for several hours can produce depletions in the equatorial ion density with sharp gradients at their high latitude boundaries consistent with the data we discuss possible contributing mechanisms for generating these upward drifts these include direct penetration of the magnetospheric electric field to low latitudes the electric fields generated by the disturbance dynamo and the effects of conductivity gradients near the dusk terminator and the south atlantic anomaly

multi element variations in olivine as geochemical signatures of ni cu sulfide mineralization in mafic magma systems examples from voisey s bay and pants lake intrusions labrador canada olivine from the olivine gabbro to troctolite intrusions at voisey s bay and at pants lake labrador was analyzed for multiple elements ca sc mg si ti v cr mn fe co ni cu zn sr y and zr with secondary ion mass spectrometry sims both intrusions have similar lithologies and petrographic characteristics and are approximately coeval 1 34 and 1 32 ga respectively members of the mesoproterozoic nain plutonic suite the voisey s bay intrusion hosts a producing economic ni cu sulfide deposit whereas the pants lake intrusion displays evidence of ni cu sulfide mineralization but to date a viable ore deposit has not been discovered olivine from both barren and mineralized lithologies was analyzed to assess the potential of the olivine composition for providing a record of silicate melt evolution and sulfide saturation related to formation of a massive sulfide deposit two detailed transects were sampled using five diamond drill holes that laterally approach the basal massive sulfide in the eastern deeps portion of the voisey s bay intrusion from the barren central part olivine displays distinct trace element distributions that vary coherently with host lithology and proximity to sulfide mineralization in particular olivine shows an increase in fe fo80 to fo60 mn 2500 to 5000 ppm and zn 280 to 700 ppm generally coupled with a decrease in ni 1600 to 900 ppm co 270 to 190 ppm and cr 110 to 45 ppm from barren troctolite normal troctolite nt and weakly mineralized troctolite variable textured troctolite vtt towards the heavily mineralized brecciated basal succession basal breccia sequence bbs the enrichment in fe mn zn is most pronounced in samples that laterally approach but do not directly intersect the massive sulfide deposit at the base of the intrusion particularly in samples from the lower variable textured troctolite and the basal breccia olivine from gabbro lithologies within the basal gabbro bg and upper gabbro ug of the pants lake intrusion is fairly homogeneous fo60 4300 ppm mn 460 ppm zn 340 ppm ni 50 ppm cr with a more evolved composition 2100 ppm ca 20 ppm sc 300 ppm ti 4 ppm y than the average olivine of the voisey s bay intrusion 570 ppm ca 6 ppm sc 65 ppm ti 0 3 ppm y pants lake olivine also commonly lacks the mutually mn zn rich signature of olivine from the basal breccia at voisey s bay that is characteristic of contamination of the parent magma by country rock gneiss and there reflects a close proximity to massive sulfides in conjunction with petrographic observation and the stratigraphic context a multiple element v cr mn fe co ni zn regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the eastern deeps part of the voisey s bay intrusion over a distance exceeding 150 m the compositional variations in olivine from the economic voisey s bay intrusion bimodal and primitive and the mainly barren pants lake intrusion homogeneous and evolved provide potential as a regional scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

ionospheric storm of early november 1993 in the indian equatorial region an investigation is made of the response of equatorial ionosphere in the indian 75 e sector to the major magnetic storm of november 3 1993 using data from the ionosonde and magnetometer networks spanning the region 0 3 34 5 n dip some outstanding and new aspects of the storm time ionospheric behaviour are revealed an anomalous and striking positive gradient in 0f2 from the magnetic equator to 34 5 dip developed under counter electrojet cej condition in the morning on november 4 corresponding to the early stage of the storm main phase this storm effect is attributed to plasma transport by a poleward surge in transequatorial winds due to large scale atmospheric gravity waves agws launched by auroral heating remarkable wave like variations in hpf2 and 0f2 immediately followed at locations away from dip equator till local sunset with concomitant disruptions in the development of the equatorial ionization anomaly eia rapid variations in meridional neutral winds due to large scale agws are assessed as the cause of the oscillations in hpf2 and the associated cyclic sequence of development and inhibition of eia as the outcome of the combined effects of plasma transport due to meridional winds and the plasma fountain driven by e b drift just after the onset of the storm recovery phase at 1800 lt a sudden and anomalous drop 54 57 in 0f2 prevailed throughout the anomaly region over the interval 1915 2330 lt with an apparent time delay in occurrence toward the magnetic equator this premidnight collapse of equatorial f region is interpreted in terms of horizontal transport of plasma across the equator toward the opposite hemisphere by an equatorward surge in meridional winds the case study showed that besides disturbances in the zonal electric field due to prompt penetration and ionospheric disturbance dynamo effects perturbations in neutral meridional winds played a prominent role in the ionospheric storm of november 4 1993 in the indian equatorial region

the interaction of moist convection and mid level dry air in the advance of the onset of the indian monsoon the advance of the onset of the indian monsoon is here explained in terms of a balance between the low level monsoon flow and an over running intrusion of mid tropospheric dry air the monsoon advances over a period of about 6 weeks from the south of the country to the northwest given that the low level monsoon winds are westerly or southwesterly and the midlevel winds northwesterly the monsoon onset propagates upwind relative to midlevel flow and perpendicular to the low level flow and is not directly caused by moisture flux toward the northwest lacking a conceptual model for the advance means that it has been hard to understand and correct known biases in weather and climate prediction models the mid level northwesterlies form a wedge of dry air that is deep in the far northwest of india and over runs the monsoon flow the dry layer is moistened from below by shallow cumulus and congestus clouds so that the profile becomes much closer to moist adiabatic and the dry layer is much shallower in the vertical toward the southeast of india the profiles associated with this dry air show how the most favourable environment for deep convection occurs in the south and onset occurs here first as the onset advances across india the advection of moisture from the arabian sea becomes stronger and the mid level dry air is increasingly moistened from below this increased moistening makes the wedge of dry air shallower throughout its horizontal extent and forces the northern limit of moist convection to move toward the northwest wetting of the land surface by rainfall will further reinforce the north westward progression by sustaining the supply of boundary layer moisture and shallow cumulus the local advance of the monsoon onset is coincident with weakening of the mid level northwesterlies and therefore weakened mid level dry advection

low latitude ionospheric disturbance electric field effects during the recovery phase of the 19 21 october 1998 magnetic storm 1 low latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity these perturbations can last for several hours after geomagnetic quieting we use incoherent scatter radar measurements from jicamarca and arecibo during 19 21 october 1998 to study for the first time the low latitude disturbance electric fields during the recovery phase of a large magnetic storm on 19 october the jicamarca data showed initially large and short lived time scale of about 10 20 min upward and westward drift perturbations in the early afternoon sector due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure following the decrease of auroral activity very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over jicamarca but surprisingly only small and sporadic perturbation drifts were present over arecibo the latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds the disturbance dynamo drifts also indicate significantly different local storm time and possibly latitudinal dependences for their vertical perpendicular and zonal drift components suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector in the next day during moderately disturbed conditions the daytime perturbation drifts were small but following transient increases in geomagnetic activity large upward perpendicular drifts were observed near dusk over jicamarca and arecibo where simultaneous westward perturbation drifts were also seen these perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator the measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models later at night under moderately disturbed conditions relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars our results illustrate the large variability of the low latitude perturbation electric fields relative to their climatological values after large storms probably due to the importance of additional disturbance processes they also indicate that a much deeper understanding of solar wind magnetospheric ionospheric processes is required for accurate predictions of these electric fields

high resolution simulation of the south asian monsoon using a variable resolution global climate model this study examines the feasibility of using a variable resolution global general circulation model gcm with telescopic zooming and enhanced resolution 35 km over south asia to better understand regional aspects of the south asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation for this purpose two sets of ten member realizations are produced with and without zooming using the lmdz laboratoire meteorologie dynamique and z stands for zoom gcm the simulations without zoom correspond to a uniform 1 1 grid with the same total number of grid points as in the zoom version so the grid of the zoomed simulations is finer inside the region of interest but coarser outside the use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields it is found that the monsoon simulation with high resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the western ghats the northeastern mountain slopes and northern bay of bengal bob a realistic monsoon trough mt is also noticed in the zoomed simulation together with remarkable improvements in representing the associated precipitation and circulation features as well as the large scale organization of meso scale convective systems over the mt region additionally a more reasonable simulation of the monsoon synoptic disturbances lows and disturbances along the mt is noted in the high resolution zoomed simulation on the other hand the no zoom version has limitations in capturing the depressions and their movement so that the mt zone is relatively dry in this case overall the results from this work demonstrate the usefulness of the high resolution variable resolution lmdz model in realistically capturing the interactions among the monsoon large scale dynamics the synoptic systems and the meso scale convective systems which are essential elements of the south asian monsoon system

response of the equatorial and low latitude ionosphere in the indian sector to the geomagnetic storms of january 2005 1 the equatorial and low latitude ionospheric response to three moderate geomagnetic storms 17 18 and 22 january during the period from 16 to 23 january 2005 is investigated in the context of development inhibition of the equatorial ionization anomaly eia and the subsequent occurrence nonoccurrence of equatorial spread f esf irregularities on these days the study is carried out using the total electron content tec measured with the gps receivers along the 80 e longitude sector and the f layer bottom height obtained from the ionosonde located over the dip equatorial location of trivandrum 8 5 n 77 e dip latitude 0 5 n in india it is observed that for the storms on days 17 and 22 the development of the anomaly was inhibited probably due to the westward disturbance dynamo electric fields subsequently the post sunset enhancement in the vertical drift of the equatorial f region was also inhibited significantly compared to the quiet day pattern and as anticipated no esf was observed on these days a large vertical drift of the equatorial f region followed by nearly simultaneous onset of weak esf was observed on day 18 the late development of the eia on this day could be due to the eastward prompt penetration electric field associated with the southward turning of the interplanetary magnetic field also strong and distinct f3 layer appeared for a short time in the morning reappeared later in the noon time and then quickly ascended to the topside ionosphere during the main phase of the storm on day 18

impact of mjo on the intraseasonal variation of summer monsoon rainfall over india the summer monsoon rainfall over india exhibits strong intraseasonal variability earlier studies have identified madden julian oscillation mjo as one of the most influencing factors of the intraseasonal variability of the monsoon rainfall in this study using india meteorological department imd high resolution daily gridded rainfall data and wheeler hendon mjo indices the intra seasonal variation of daily rainfall distribution over india associated with various phases of eastward propagating mjo life cycle was examined to understand the mechanism linking the mjo to the intraseasonal variability during mjo phases of 1 and 2 formation of mjo associated positive convective anomaly over the equatorial indian ocean activated the oceanic tropical convergence zone otcz and the resultant changes in the monsoon circulation caused break monsoon type rainfall distribution associated with this negative convective anomalies over monsoon trough zone region extended eastwards to date line indicating weaker than normal northern hemisphere inter tropical convergence zone itcz the positive convective anomalies over otcz and negative convective anomalies over itcz formed a dipole like pattern subsequently as the mjo propagated eastwards to west equatorial pacific through the maritime continent a gradual northward shift of the otcz was observed and negative convective anomalies started appearing over equatorial indian ocean during phase 4 while the eastwards propagating mjo linked positive convective anomalies activated the eastern part of the itcz the northward propagating otcz merged with monsoon trough western part of the itcz and induced positive convective anomalies over the region during phases 5 and 6 the dipole pattern in convective anomalies was reversed compared to that during phases 1 and 2 this resulted active monsoon type rainfall distribution over india during the subsequent phases 7 and 8 the convective and lower tropospheric anomaly patterns were very similar to that during phase 1 and 2 except for above normal convective anomalies over equatorial indian ocean a general decrease in the rainfall was also observed over most parts of the country the associated dry conditions extended up to northwest pacific thus the impact of the mjo on the monsoon was not limited to the indian region the impact was rather felt over larger spatial scale extending up to pacific this study also revealed that the onset of break and active events over india and the duration of these events are strongly related to the phase and strength of the mjo the break events were relatively better associated with the strong mjo phases than the active events about 83 of the break events were found to be set in during the phases 7 8 1 and 2 of mjo with maximum during phase 1 40 on the other hand about 70 of the active events were set in during the mjo phases of 3 to 6 with maximum during phase 4 21 the results of this study indicate an opportunity for using the real time information and skillful prediction of mjo phases for the prediction of break and active conditions which are very crucial for agriculture decisions

analysis of the african easterly jet using aircraft observations from the jet2000 experiment analyses of the african easterly jet aej are presented which are based on meridional transects of high resolution dropsonde observations made during jet2000 an aircraft campaign conducted in the last week of august 2000 the observations have confirmed that the aej is closely defined by geostrophic balance the baroclinicity between the extreme northern and southern profiles accurately determines the altitude of the jet core while the location and morphology of the jet core correspond to a locally defined geostrophic wind measure the potential vorticity pv structure has also been found to accord with theoretical expectations with distinctive positive and negative pv anomalies equatorward and poleward of the jet core respectively the thermodynamic structure of the aej environment can be categorized into coherent layers the monsoon layer is a humid zone connected to the land surface extending northwards into the sahel and increasing in depth towards the south this layer is affected by the land surface on diurnal time scales through the growing convective mixed layer and through shallow cumulus clouds above the monsoon layer is the saharan air layer sal which can be identified as a layer of low static stability and low pv the sal is deep where it merges with the saharan boundary layer in the north and becomes thinner toward the south it has been shown that the boundaries of the sal can be approximated to good accuracy as adiabatic surfaces meaning that the sal comprises air which is adiabatically connected to the land surface via the saharan boundary layer the upper region of the sal is identified as a layer of high relative humidity where altocumulus and stratocumulus layers are observed finally the troposphere above the sal is again almost pseudoadiabatic with small baroclinicity which determines the closure of the aej core aloft through inspection of thermodynamic tracers evidence of convective and lateral transport and exchange between these layers is also presented copyright 2005 royal meteorological society

modelling the moistening of the free troposphere during the northwestward progression of indian monsoon onset understanding and prediction of the indian monsoon onset is of paramount importance for agricultural planning that affects food production and the gross domestic product of the country a recent observational study suggests that the progression of the indian monsoon onset in a northwestward direction which is perpendicular to the mean flow is reinforced by the moistening of the free troposphere by pre monsoon showers and wetting of the land surface as the onset progresses the mid tropospheric dry layer is thought to be constantly moistened from below by detrainment from shallow cumulus and congestus clouds from the southeast the dry layer becomes much shallower towards southeast india making the profile closer to moist adiabatic providing favourable conditions for deep cumulus convection increased moistening of the free troposphere thereby pushes the northern limit of moist convection to move northwestwards here we examine the representation of this process in hindcast simulations from the fully coupled atmosphere ocean seasonal forecast system of the uk met office glosea5 the model effectively captures the mid level dry air intrusion from the northwest which suppresses convection over the northwestern parts of india we also show that detrainment from shallow convection measured by moisture tendencies around the freezing level acts to saturate the free troposphere ahead of the monsoon onset eroding the dry layer from the southeast this work suggests that initialized coupled models are capable of simulating dynamic and thermodynamic processes inherent in monsoon progression during the onset

dynamical response of the south asian monsoon trough to latent heating from stratiform and convective precipitation simulation experiments using a simplified atmospheric gcm and supplementary diagnostic analyses of observations are performed to understand how the south asian monsoon trough mt responds dynamically to latent heating from mesoscale convective systems mcss observations reveal that the mt during active monsoons is characterized by a deep cyclonic vorticity extending from the surface to 350 hpa and organized mcss covering over 3500 4000 km along the indo gangetic plains the mcss during active monsoons are composed of a relatively higher abundance of stratiform type precipitation mostly nimbostratus as compared to the convective type the results suggest that a stratiform type heating profile is very effective in promotingupward development of continental scale cyclonic circulation well above the midtroposphere over the mt region the vertical development involves a dynamical uplift of the layer of cyclonic circulation and is induced by midlevel 600 500 hpa convergence and vorticity stretching above 500 hpa by varying the population of stratiform and convective rain types in the simulation the horizontal scale of midlevel vorticity response is shown to increase significantly with stratiform population in contrast the midlevel response is more localized when the mcs is dominated by deep convective clouds for large stratiform populations the midlevel responseis found to extend far westward up to the northernflanks of the africanitcz indicativeof rossby wave dispersion of pv anomalies that are generated near the level of maximum heating gradient from the present findings one can conclude that the vertical deepening of mt during active monsoons is not merely a localized phenomenon instead it represents a large scale dynamical response to organized mcss that exert pivotal influence on the upward development of cyclonic circulation well above the midtroposphere

air sea interaction and formation of the asian summer monsoon onset vortex over the bay of bengal in spring over the southern bay of bengal bob a vortex commonly develops followed by the asian summer monsoon onset an analysis of relevant data and a case study reveals that the bob monsoon onset vortex is formed as a consequence of air sea interaction over bob which is modulated by tibetan plateau forcing and the land sea thermal contrast over the south asian area during the spring season tibetan plateau forcing in spring generates a prevailing cold northwesterly over india in the lower troposphere strong surface sensible heating is then released forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern bob this southwesterly induces a local offshore current and upwelling resulting in cold sea surface temperatures ssts the southwesterly together with the near equatorial westerly also results in a surface anticyclone with descending air over most of bob and a cyclone with ascending air over the southern part of bob in the eastern part of central bob where sky is clear surface wind is weak and ocean mixed layer is shallow intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer resulting in the development of a unique bob warm pool in spring near the surface water vapor is transferred from northern bob and other regions to southeastern bob where surface sensible heating is relatively high the atmospheric available potential energy is generated and converted to kinetic energy thereby resulting in vortex formation the vortex then intensifies and moves northward where sst is higher and surface sensible heating is stronger meanwhile the zonal mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex and the vortex turns eastward eventually southwesterly sweeps over eastern bob and merges with the subtropical westerly leading to the onset of the asian summer monsoon