sensitivity of the initiation of an isolated thunderstorm over the beijing metropolitan region to urbanization terrain morphology and cold outflows to gain insight into the processes leading to the convective initiation ci of an isolated thunderstorm near the central urban area cua of the beijing metropolitan region bmr on 9 august 2011 a series of numerical sensitivity experiments by removing or modifying the cua terrain morphology and convectively generated cold outflows is performed results show that the cua accounts for the formation of cloud condensation near the top of the mixed layer at the ci site as a result of the growing boundary layer depth through its urban heat island effects and urban induced convergence between a warm and moist southerly flow and an easterly flow on the downstream side the northerly approaching cold outflows from the mesoscale convective system mcs facilitate the generation of northerly flows through a northwestward concaved valley such that the enhanced low level convergence with the southerly and easterly flows near the cua could determine the timing of the outbreak of shallow clouds near the mixed layer top into an intense thunderstorm when the concaved valley on the northwest of the cua is eliminated little northerly flows ahead of the cold outflow boundaries into the ci site would be present the results obtained herein appear to have significant implications to understanding and forecasting the development of afternoon thunderstorms in the bmr under weak gradient environments

thunderstorm genesis zones in the colorado rocky mountains as determined by traceback of geosynchronous satellite images abstract mountain thunderstorms often originate in preferred regions of the topography as shown qualitatively by pilot reports and more quantitatively by meteorological radar satellite and lightning detector studies to further investigate the phenomenon of mountain thunderstorm initiation we used time sequences of goes imagery to locate storms and to trace them back to their points of origin using three summers of data from days which started out clear we backtracked over 600 storms in the mountains of colorado and northern new mexico we plotted the origin points on a terrain map and drew contours of initiation frequency to identify regions with a high likelihood of producing thunderstorms we found that initiation sites tended to cluster into identifiable geographical locations or genesis zones consistent with findings based on the other data sources when cloud propagation effects were taken into account the locations of these genesis zones were also consistent with the locations of clusteri

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part i model description and verification abstract the pennsylvania state university ncar mesoscale model originally developed by anthes and warner is modified to simulate the meso scale structure and evolution of convectively driven weather systems the modifications include i two way interactive nested grid procedures ii the fritsch chappell convective parameterization scheme and iii the blackadar boundary layer package an 18 h simulation of the johnstown flood of july 1977 is conducted compared to the documentation of hoxit et al and bosart and sanders the simulation reproduced many of the different aspect of the mesoscale convective complex and squall line that were responsible for the heavy rain over western pennsylvania in particular the model predicts the size propagation rate and orientation of the mesoscale convective components that were observed in the mid atlantic states the simulated evolution of the planetary boundary layer cool outflow boundaries and surface pressure perturbations such as meso scale lows h

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

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

processes driving deep convection over complex terrain a multi scale analysis of observations from cops iop 9c the convective and orographically induced precipitation study cops analyses the processes driving deep convection over complex terrain convection initiation ci is mainly not only expressed by a single process but by a variety of them which interact on different scales in time and space and finally can lead to deep convection a study of such a case over inhomogeneous terrain is presented in this article data from the cops network of stations are taken to identify the time and location of ci in many cases this is not the same location as the first convective clouds showers or even thunderstorms it is shown that the interaction of the ci processes on multiple scales locally leads to either deep convection and severe storms or calm weather the boundary conditions between the different outcomes are narrow during iop 9c 20 july 2007 a mesoscale convective system mcs embedded in a surface low over eastern france propagated north eastward and a gust front of the mcs reached the cops area during the passage of the gust front through the rhine valley convective activity was significantly reduced the gust front reached the slope of the black forest and the warm and humid air above the mountain range prior to the gust front was lifted up to 2000 m within a short time period within the air prior to the gust front aloft from the surface ci started along a north south oriented line above the crest due to insolation ahead of the gust front a convergence line developed the interaction of local scale orographic winds the regional scale gust front the mesoscale convergence line and the synoptic scale cold front led to a squall line finally individual severe convective cells formed along the outer section of the synoptic scale cold front copyright 2011 royal meteorological society

orogenic convection in subtropical south america as seen by the trmm satellite abstractextreme orogenic convective storms in southeastern south america are divided into three categories storms with deep convective cores storms with wide convective cores and storms containing broad stratiform regions data from the tropical rainfall measuring mission satellite s precipitation radar show that storms with wide convective cores are the most frequent tending to originate near the sierra de cordoba range downslope flow at upper levels caps a nocturnally enhanced low level jet thus preventing convection from breaking out until the jet hits a steep slope of terrain such as the sierra de cordoba mountains or andean foothills so that the moist low level air is lifted enough to release the instability and overcome the cap this capping and triggering is similar to the way intense convection is released near the northwestern himalayas however the intense storms with wide convective cores over southeastern south america are unlike their himalayan counterparts in that they exhibit leadi

a simulation of the development of successive cells along a cold outflow boundary abstract a three dimensional numerical simulation is presented in which five new cells clouds develop in succession over a 4 h period the cells that develop have common characteristics including a lifetime of 40 min they form at 30 min intervals in a convergent region along the cold outflow boundary that is established by previous cells the propagation of the cloud system is several meters per second faster than individual cell movement due to the discrete development of new cells on the right flank of previous ones analysis of the simulation indicates that the most pronounced changes near the surface are due to downdraft development in contrast there is only a weak signature of new updraft development near the surface in the convergence field each new updraft develops along the cold outflow boundary which moves slowly away from the previous cell the air participating in the generation of a new cell appears to have originated 1 1 5 km below cloud base 2 6 km as the cell grows and rain begins

the initiation and organization of convective cells atop a cold air outflow boundary abstract on 13 july 1986 a cold air outflow from thunderstorms over illinois and missouri propagated through the mist microburst and severe thunderstorm network over northern alabama the study of this outflow is important since the gust front was solely responsible for the initiation of numerous convective cells previous studies have documented the initiation of convection due to colliding gust fronts in addition there was a pronounced mesoscale organization of the cells atop the outflow boundary this was most likely due to a combination of kelvin helmholtz k h and internal gravity ig wave activity in contrast to previous cases the k h wave crests were oriented nearly perpendicular to the gust front within the analysis area the resulting intersections between the circulations associated with the k h waves and the gust front produced favorable locations for the initiation of convection subsequently the convective cells remained along the updraft side of the k h wave circulations as they pro

a high resolution modeling study of the 24 may 2002 dryline case during ihop part i numerical simulation and general evolution of the dryline and convection abstract results from a high resolution numerical simulation of the 24 may 2002 dryline convective initiation ci case are presented the simulation uses a 400 km 700 km domain with a 1 km horizontal resolution grid nested inside a 3 km domain and starts from an assimilated initial condition at 1800 utc routine as well as special upper air and surface observations collected during the international h2o project ihop 2002 are assimilated into the initial condition the initiation of convective storms at around 2015 utc along a section of the dryline south of the texas panhandle is correctly predicted as is the noninitiation of convection at a cold front dryline intersection triple point located farther north the timing and location of predicted ci are accurate to within 20 min and 25 km respectively the general evolution of the predicted convective line up to 6 h of model time also verifies well mesoscale convergence associated with the confluent flow around the dryline is shown to produce an u

numerical study of an observed orogenic mesoscale convective system part 2 analysis of governing dynamics abstract a detailed analysis of the dynamics and thermodynamics responsible for the structure growth and propagation of an orogenic mesoscale convective system simulated in two dimensions is made the process of scale interaction is addressed through fourier analysis and reynolds averaging analysis of representative predicted variables diabatic forcing and momentum acceleration terms additional dynamical analysis is accomplished through sensitivity experiments in which coriolis diabatic heating and ambient airflow are varied the general conclusion is that the simulated orogenic development is a geostrophic adjustment process to convective heating which is itself modulated and maintained by orographically induced flow systems the heating scales range over a nearly continuous spectrum ranging from 10 250 km the heating occurs in response to primary advective gravity modes the larger scale gravity wave disturbances modulate the smaller scales by organizing mean upward vertical motion patterns the la

plinian pumice fall deposit of the campanian ignimbrite eruption phlegraean fields italy abstract a plinian pumice fall deposit associated with the campanian ignimbrite eruption 36 ka phlegraean fields caldera italy occurs at the base of the distal grey ignimbrite in 15 localities spread over an area exceeding 1500 km2 between benevento and the sorrentina peninsula in the thickest stratigraphic section at voscone 130 cm 45 km east of the phlegraean caldera centre pozzuoli the deposit consists of two units the lower fall unit lfu is well sorted exhibits reverse size grading and is composed of equidimensional light grey pumice clasts with very subordinate accidental lithics the upper fall unit ufu is from well to poorly sorted crudely stratified richer in lithics and composed of both equidimensional and prolate pumice clasts the two fall units show slightly different dispersal axis n90 for the lfu and n95 for the ufu volumes calculated with the method of pyle 1989 are about 8 km3 for the lfu and 7 km3 for the ufu the maximum height of the eruptive columns are estimated using the model of the maximum lithic clasts dispersal at 44 km for the lfu and 40 km for the ufu classifying both fall units as ultraplinian in character reverse size grading within the lfu suggests an increase of the height of the column and magma discharge rate with time moderate sorting and crude stratification of the ufu are consistent with short period oscillation of the column possibly associated with repeated partial column collapses sharp increases in lithic content at the transition to ufu and within the ufu suggest that changes in the eruptive behaviour was produced by a dramatic increase in conduit vent erosion the phase of column instability preceded the emplacement of widely dispersed pyroclastic flow the ultraplinian nature of the fall fits well with the wide dispersal of the campanian ignimbrite with an estimated aspect ratio of 3 4 10 4 lari

the kinematics of orographic airflow during sierra storms abstract two case studies of the kinematics of the airflow over the sierra barrier are presented the observations consisted of rawinsondes and single doppler rhi and velocity azimuth display vad analysis of ppi scans the rhi scans were made orthogonal to the nearly two dimensional sierra barrier the cloud in the first case study contained a strong stable layer at 0 c while the second storm was highly unstable the radar bright band and soundings near the radar indicated that an 250 m thick 0 c isothermal layer was present in response to the diabatic process of melting when the bright band was impinging upon the barrier the associated 0 c isothermal layer was inferred to expand until it finally reached the ground at that point it was 1 km in depth direct thermodynamic soundings am presented for a similar situation which agrees with the modified soundings inferred for this study the resulting effects on the airflow and precipitation are discussed the unstable case contained a line of deep conve

initiation of convection over the black forest mountains during cops iop15a doppler on wheels radar observations made during the convective and orographically induced precipitation study cops on 12 august 2007 showed that precipitating clouds only developed between the north south orientated murg and nagold valleys of the northern black forest the clouds produced moderate precipitation the weather research and forecasting wrf model run at 700 m horizontal resolution in the inner domain was able to simulate the location of the precipitation insight is therefore gained into the physical mechanisms responsible for the initiation and development of the convection convergence lines resulting from thermally driven flows constrained the initial location of the convection within warm and moist cores produced by heating on elevated surfaces the heaviest precipitation was later produced by secondary convection which was initiated within the cores at the boundary between cold pool outflows and thermal flows copyright 2011 royal meteorological society

clinopyroxene liquid trace element partitioning in natural trachyte trachyphonolite systems insights from campi flegrei southern italy trace element partition coefficients between clinopyroxenes and associated glassy matrix cpx l d have been determined for 13 ree hfse4 5 u th sr pb sc and v from combined la icp ms emp analyses in selected trachytes and trachyphonolites from campi flegrei composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites pointing to an overall attainment of the equilibrium conditions in trachytes conversely phases show some compositional heterogeneity due to the presence of clinopyroxene xenocrysts that requested a more careful petrographic and geochemical inspection of the samples to assess the equilibrium clinopyroxene composition in the trachyte clinopyroxenes ree are compatible from nd to lu cpx l d up to 2 9 like y ti sc and v the cpx l d for eu is lower than those of the adjacent ree highlighting eu2 contribution high d values are also shown by u th pb zr hf nb and ta relatively to basaltic and andesitic systems whereas the d sr is roughly similar to that found for less evolved magmas trachyphonolites are characterized by an overall decrease of the cpx l d for highly charged cations with the exception of v and by a slight increase of d sr ree are still compatible from nd to lu cpx l d up to 2 1 like ti y sc and v this variation is also predicted for ree and y by models based on the elastic strain theory being consistent with the slightly lower polymerization degree estimated for the trachyphonolites however the observed cpx l d ree y are matched by the modelled ones only considering very low t 825 c which are believed unlikely this mismatch cannot be attributed to effects induced by the water rich composition of the trachyte trachyphonolite suite since they would lower the observed cpx l d ree y moreover the anomalous inflections of measured cpx l d for hree suggests some crystal chemical control such as the entrance of these elements in a site distinct from m2 it is concluded that the large cpx l d determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the z3 activities related to the composition of melt and or solid all these considerations strongly highlight the importance of a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental studies

summary of convective storm initiation and evolution during ihop observational and modeling perspective abstract the data rich international h2o project ihop 2002 experiment is used to study convective storm initiation and subsequent evolution for all days of the experiment initiation episodes were almost evenly divided between those triggered along surface based convergence lines and elevated initiation episodes that showed no associated surface convergence the elevated episodes occurred mostly at night and the surface based episodes occurred during the afternoon and evening surface based initiations were mostly associated with synoptic fronts and gust fronts and less so with drylines and bores elevated initiations were frequently associated with observable convergent or confluent features in the rapid update cycle ruc wind analysis fields between 900 and 600 hpa the ruc10 3 h forecast of the precipitation initiation episodes were correct 44 of the time allowing a tolerance of 250 km in space and for the forecast being early by one period however the accuracy was closely tied to the scale of

daytime boundary layer evolution over mountainous terrain part 1 observations of the dry circulations abstract this paper presents the boundary layer structure which accompanies the development of daytime local wind systems in a broad mountain valley as revealed by cross sections of potential temperature it describes how this structure leads to the occurrence of a region of convergence to the downwind side of mountains previous studies based primarily on one dimensional sounding of potential temperature and horizontal winds have shown that profiles of static stability and the presence of winds aloft have an important effect on the manner in which daytime thermally forced wind systems develop in the present study two dimensional cross sections obtained from aircraft data vertical soundings and surface mesonet data show several relevant features in mid to late morning near the surface for example upslope winds form in a shallow mixed layer at the underside of the nocturnal inversion layer cold pool at elevations above the top of this cold pool convectively mixed surface winds exist the spat

convective initiation near the andes in subtropical south america abstractsatellite radar and radiometer data indicate that subtropical south america has some of the deepest and most extreme convective storms on earth this study uses the full 15 yr trmm precipitation radar dataset in conjunction with high resolution simulations from the weather research and forecasting model to better understand the physical factors that control the climatology of high impact weather in subtropical south america the occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening south american low level jet sallj in the la plata basin the orography of the andes is critical and model sensitivity calculations removing and or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems mcss reduced andes experiments show more widespread convective initiation weaker average storm intensity and more rapid propagation

numerical simulation of the mesa β scale structure and evolution of the 1977 johnstown flood part iii internal gravity waves and the squall line abstract the interaction between internal gravity waves and a squall line that developed early in the evolution of the 1977 johnston flood event is studied based on available surface observations and a three dimensional model simulation of the flood related mesoscale convective systems mcss several experimental simulators are carried out to investigate the mechanisms whereby gravity waves form and obtain energy both observations and model simulators of the wave convection interaction fit certain theories of gravity wave propagation following the formation of the squall line subsequent deep convection typically initiates behind a pressure trough associated with the lint and ahead of or along the axis of the trailing ridge the zero contours of vertical motion correspond closely to the axis of the surface pressure trough positive potential temperature perturbations correspond with descending motion occurring ahead of the trough while negative perturbations occur with increasing ascending motion towar

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes over contiguous north china the diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes at the 925 hpa and 500 hpa levels over contiguous north china have been studied using a climatology based on radar reflectivity mosaics soundings and reanalysis data from 15 may to 15 september in 2008 2011 in the wind regimes at the 925 hpa level the frequency of occurrence of convection is highest for south southwesterly flows followed by that for south southeasterly flows the low level southerly warm and moist flow over the foothills and plains favors initiation and intensification of convection resulting from topographic forcing among the wind regimes at the 500 hpa level the frequency of occurrence of convection shows a pronounced maximum for west southwesterly flows and most of these storms initiate and develop over the foothills and plains convection in the wind regime shows the morphology and slowly east southeastward moving characteristics of well organized longer lived systems with environmental conditions conducive to vertical wind shear and instability at the 500 hpa level the high frequency of occurrence of convection for west southwesterly flows is followed by that for west northwesterly flows under west northwesterly flows convective storms initiated over mountains located to the northwest in the early afternoon move rapidly to the plains in the southeast of the study region these storms show the primary formation characteristics of shorter lived convection and intensify noticeably as they move from the mountains to the foothills and plains

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

quantifying volcanic ash dispersal and impact of the campanian ignimbrite super eruption 1 we apply a novel computational approach to assess for the first time volcanic ash dispersal during the campanian ignimbrite italy super eruption providing insights into eruption dynamics and the impact of this gigantic event the method uses a 3d time dependent computational ash dispersion model a set of wind fields and more than 100 thickness measurements of the ci tephra deposit results reveal that the ci eruption dispersed 250 300 km 3 of ash over 3 7 million km 2 the injection of such a large quantity of ash and volatiles into the atmosphere would have caused a volcanic winter during the heinrich event 4 the coldest and driest climatic episode of the last glacial period fluorine bearing leachate from the volcanic ash and acid rain would have further affected food sources and severely impacted late middle early upper paleolithic groups in southern and eastern europe citation costa a a folch g macedonio b giaccio r isaia and v c smith 2012 quantifying volcanic ash dispersal and impact of the campanian ignimbrite super eruption geophys res lett 39 l10310 doi 10 1029 2012gl051605

the ground layer of the campanian ignimbrite an example of deposition from a dilute pyroclastic density current a thin fines poor and lithic and crystal rich layer locally present from proximal to distal areas at the base of the pyroclastic density current deposits of the campanian ignimbrite eruption 39 ka sourced from campi flegrei italy is interpreted as a ground layer gl it has an average lithic and crystal content of 57 and 25 wt respectively the gl rests on a paleosol or an early fall deposit and is capped by a stratified ash deposit it is bounded by erosion surfaces and its thickness does not change systematically from the source the occurrences of gl in places separated from the source by a stretch of sea and the angular to sub angular shape of the lithic clasts are consistent with deposition from a dilute current the presence of the gl up to 971 m above sea level and beyond 1400 1500 m high mountain ridges allows estimation of the thickness of the pdc as having been at least 1 5 km to investigate the parameters influencing the transport and emplacement mechanisms that produced the gl we use field and sedimentological data grain size and componentry from samples collected between 30 and 70 km from the source the progressive decrease in maximum lithic clast and median grain size with distance from the vent and increasing altitude corresponds to lateral and vertical grading of lithic clasts within the current the coarser clasts moved toward the basal part of the current settling in more proximal areas and at low altitude farther from the vent 45 50 km the lower part of the pyroclastic current impacted against the reliefs surrounding the campanian plain causing the emplacement of coarser and more poorly sorted deposits on slopes oriented toward the source

progressive assembly of a massive layer of ignimbrite with a normal to reverse compositional zoning the zaragoza ignimbrite of central mexico the zaragoza ignimbrite and two enclosing rhyodacite pumice fall layers were emplaced during the 15 km3 dre 0 1 ma zaragoza eruption from los humeros volcanic centre 180 km east of mexico city the ignimbrite comprises several massive flow units the largest of which locally exceeds 20 m in thickness and is regionally traceable it comprises massive lapilli ash with vertical elutriation pipes and has a fine grained inverse graded base and a pumice concentration zone at the top it also exhibits an unusual gradational double vertical compositional zonation that is widely traceable a basal rhyodacitic 67 6 69 wt sio2 zone grades up via a mixed zone into a central andesitic 58 62 wt sio2 zone which in turn grades up into an upper rhyodacitic 67 6 69 wt sio2 zone zoning is also defined by vertical variations in lithic clast populations we infer that pyroclastic fountaining fed initially rhyodacite pumice clasts to a sustained granular fluid based pyroclastic density current the composition of the pumice clasts supplied to the current then gradually changed first to andesite and then back to rhyodacite inverse grading at the base of the massive layer may reflect initial waxing flow competence the pumice concentration at the top of the massive layer is entirely rhyodacitic and was probably deposited during waning stages of the current when the supply of andesitic pumice clasts had ceased the return to rhyodacitic composition may have been the result of eruption conduit modification during collapse of los potreros caldera marked in the ignimbrite by a widespread influx of hydrothermally altered lithic blocks and or a decrease in draw up depth from a compositionally stratified magma chamber as the eruptive mass flux waned the massive layer of ignimbrite thins locally to less than 2 m yet it still shows the double zonation correlation of the zoning suggests that the thin massive layer is stratigraphically condensed and aggraded relatively slowly during the same time interval as did the much thicker 50 m massive layer

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

an observational and modeling study of the processes leading to deep moist convection in complex terrain abstracta case study of orographic convection initiation ci that occurred along the eastern slopes of the vosges mountains in france on 6 august 2007 during the convective and orographically induced precipitation study cops is presented global positioning system gps receivers and two doppler on wheels dow mobile radars sampled the preconvective and storm environments and were respectively used to retrieve three dimensional tomographic water vapor and wind fields these retrieved data were supplemented with temperature moisture and winds from radiosondes from a site in the eastern rhine valley high resolution numerical simulations with the weather research and forecasting wrf model were used to further investigate the physical processes leading to convective precipitation this unique time varying combination of derived water vapor and winds from observations illustrated an increase in low level moisture and convergence between upslope easterlies and downslope westerlies along the eastern slo

effects of the quasi biennial oscillation on low latitude transport in the stratosphere derived from trajectory calculations 1 the quasi biennial oscillation qbo of stratospheric zonal winds induces a secondary meridional circulation smc consisting of qbo variations in meridional and vertical winds in this work we investigate how these instantaneous meridional circulation anomalies add over time to variations of stratospheric transport to that end we compute backward parcel trajectories on the basis of the output of a chemistry climate model ccm at the equator the trajectories show the strongest vertical parcel displacement over a seasonal timescale when the qbo progresses toward easterly phase in the middle stratosphere during the solstitial seasons a large number of parcels come from the summer hemisphere causing in addition a qbo variation in the spread of the total ascent among equatorial parcels a qbo effect on meridional transport is diagnosed from pv gradients during summer in the easterly phase of the qbo which suggests a variation of the tropical subtropical barrier strength analyses of the parcel trajectories and ccm trace gas distributions confirm this finding we suggest that this variation is due to the combined effects of qbo and annual variation in meridional advection and in wave induced eddy transport

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

convective initiation at the dryline a modeling study abstract a nonhydrostatic three dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the processes responsible for the formation of drylines and the subsequent initiation of deep moist dryline convection a range of cumuliform cloud types are explicitly simulated along drylines on 15 16 and 26 may 1991 in accordance with observations in the simulations narrow convergence bands along the dryline provide the lift to initiate deep moist convection the thermally direct secondary convective boundary layer cbl circulations along the dryline are frontogenetic and solenoidally forced maximum updrafts reach 5 m s 1 and the bands are 3 9 km wide and 10 100 km or more in length the updrafts penetrate and are decelerated by the overlying stable air above the cbl reaching depths of about 2000 m in the cases studied moisture convergence along the mesoscale updraft bands destabilizes the local sounding to deep convection while simultaneously

the generation of a mesoscale convective system from mountain convection a mesoscale convective system mcs that formed just to the east of denver is investigated with a nonhydrostatic numerical model to determine which processes were important in its initiation the mcs developed from outflow from previous convective activity in the rocky mountains to the west model results indicate that this outflow was necessary for the development of the mcs even though a convergence line was already present in the area where the mcs developed a simulation with a 3 km grid spacing more fully resolves the convective activity in the mountains but the development of the mcs can be simulated with a 6 67 km grid cloud effects on solar radiation and ice sedimentation both influence the strength of the outflow from the mountain convection but only the ice sedimentation makes a significant impact on the development of the mcs after its initiation the frequent convective activity in the rocky mountains during the warm season provides outflow that would make mcs generation favorable in this region thus there is a close connection between mountain convective activity and mcs generation the implications of such a connection are discussed and possible directions of future research are indicated

numerical study of an observed orogenic mesoscale convective system part 1 simulated genesis and comparison with observations abstract the interaction of topographically induced thermally and mechanically driven diurnal flow regimes in the lee of the rockies is shown to lead to the growth of a mesoscale convective system mcs an organic mcs observed during the 1977 combined south park area cumulus experiment and high plains experiment is numerically simulated with a two dimensional nonhydrostatic cloud model covering spatial scales of 1000 km in this numerical investigation meso meso and meso scales of motion are represented simultaneously as a result interesting features of cloud mesoscale interaction are predicted that cannot be represented in cloud parameterization frameworks based on the results of this simulation a six stage conceptual model of orogenic development is given

daytime boundary layer evolution over mountainous terrain part ii numerical studies of upslope flow duration abstract numerical simulators of upslope flow forming on the lee side of a heated mountain ridge showed this flow to be a transient phenomenon in agreement with observations the simulations performed with a two dimensional dry version of the cloud model of tripoli and cotton included a nocturnal inversion layer cold pool and ridgetop winds cross sections of potential temperature and vertical profiles of potential temperature and horizontal winds reproduced observations well runs with and without the inversion layer showed that this layer was important in the formation of upslope winds near the ground when ridgetop level winds were present the runs without an inversion layer never developed upslope flow on the lee slopes runs in which the upper level winds were varied showed that the duration of the upslope flow on the lee slope bore an inverse relationship to upper level wind speed runs with stronger winds had shorter lived upslope flow a set of observations from south park colorado supporte

a chemostratigraphic study of the campanian ignimbrite eruption campi flegrei italy insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework abstract petrochemical analyses of juvenile samples from twenty stratigraphic sections of the campanian ignimbrite medial deposits located from 30 to 79 km from the vent are presented here sampling has accurately followed a well defined stratigraphic framework and the new component facies scheme the campanian ignimbrite succession is formed by a basal plinian pumice fall deposit overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion the deposit is broadly zoned from more evolved trachyte at its base to less evolved trachyte at its top and is similarly less evolved with increasing distance from the area of emission irregular chemical trends are locally observed and interpreted to represent only a limited patchy record of the entire vertical geochemical trend the petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography the results of this study were used to propose a unified volcanological petrological model for the campanian ignimbrite eruption taking into account the emplacement of both the proximal i e the breccia museo formation and medial deposits

the campanian ignimbrite y5 tephra layer a regional stratigraphic marker for isotope stage 3 deposits in the lower danube region romania a number of volcanic ash layers embedded in pleistocene loess and fluvial deposits of the lower jiu and olt valleys in south western romania have been analyzed for glass chemical compositions and general chronological relations the wds epma chemical analyses document remarkably similar major and minor element compositions at the four investigated sites and total alkali silica diagrams ascribe these volcanic ashes a phonolite to trachyte affinity a comparison with the quaternary carpathian volcanism chemical data refutes this volcanic field as the primary source even though earlier works have tentatively taken some of these volcanic ashes as evidence of volcanic activity in this particular field instead the chemical data suggest an origin in the campi flegrei volcanic province in italy and a comparison with chemical data from proximal and distal outcrops of the campanian ignimbrite y5 tephra confirm that the ash layers presented here are distal occurrences of this widespread tephra layer the campanian ignimbrite y5 tephra is the product of one of the largest late quaternary explosive events in the mediterranean and is consistently dated elsewhere to about 39 40 ka it is one of the most important chronologic stratigraphic markers of western eurasia that provide an independent basis for establishing age depth relationships for the embedding deposits optical luminescence age estimates obtained at two of the investigated sites further confirm that these volcanic ash occurrences represent a regionally synchronous depositional event around 40 ka these results highlight the important role that the campanian ignimbrite y5 tephra could play as marker horizon at sub continental scale providing that more potential tephra locations such as these from the pleistocene sedimentary deposits in the lower danube region are chemically and chronologically constrained

a two dimensional numerical investigation of the interaction between sea breezes and deep convection over the florida peninsula abstract deep convection initiated by sea breezes over the florida peninsula is simulated using a two dimensional nonhydrostatic model reasonable agreement is obtained between model results and observations for the three types of undisturbed days classified by blanchard and lopez the convergence of the east and west coast sea breezes is the primary control on the timing and location of rapid convective development and this is mainly determined by the low level winds the simulated convection is spatially concentrated and does not produce an extensive stratiform region sensitivity tests are performed for a variety of wind and thermodynamic profiles and for different soil moisture contents during the early stages of these simulations small convective cells develop in between the sea breeze fronts as the outer cells at the sea breeze fronts deepen these smaller cells are suppressed typically during the midafternoon a new cell explosively develops in between the sea breeze fronts and the outer cells

the breccia museo formation campi flegrei southern italy geochronology chemostratigraphy and relationship with the campanian ignimbrite eruption the breccia museo is one of the most debated volcanic formations of the campi flegrei volcanic district the deposit made up of six distinctive stratigraphic units has been interpreted by some as the proximal facies of the major caldera forming campanian ignimbrite eruption and by others as the product of several more recent independent and localized events new geochemical and chemostratigraphical data and ar ar age determinations for several units of the breccia museo deposits 39 ka correlate well with the campanian ignimbrite forming eruption the chemical zoning of the breccia museo deposits is interpreted here to be a consequence of a three stage event that tapped a vertically zoned trachytic magma chamber

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen