numerical simulations of radiative cooling beneath the anvils of supercell thunderstorms abstract numerical simulations of supercell thunderstorms that include parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps to investigate the effects of anvil shadows on the near storm environment if the simulated storm is nearly stationary the maximum low level air temperature deficits within the shadows are about 2 k which is roughly half the cooling found in some previous observations it is shown that the extinction of downwelling shortwave radiation by the anvil cloud creates a differential in the flux of downwelling shortwave radiation between the sun and the shade that is at least an order of magnitude greater than the differential of any other term in either the surface radiation or the surface energy budgets the loss of strong solar heating of the model surface within the shaded regions leads to a reduction of surface temperatures and stabilization of the model surface layer beneath the anvil the reduction in vertical mixing

polarimetric and dual doppler radar observations of the lipscomb county texas supercell thunderstorm on 23 may 2002 abstract polarimetric and dual doppler observations of a supercell observed by the national center for atmospheric research ncar s band polarimetric spol radar two doppler on wheels dow radars and the greek xpol radar on 23 may 2002 during the international h2o project ihop are presented the polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase the hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm the dual doppler radar observations began around the time that the polarimetric radar observations concluded and they covered the end of the mature phase and much of the dissipation phase of the storm the dual doppler wind syntheses are used to evaluate the importance of the forward flank outflow in augmenting the horizontal vorticity field near the storm above 400 m in this case having a relatively weak low level mesocyclone the pa

rear flank outflow dynamics and thermodynamics in the 10 june 2010 last chance colorado supercell abstracton 10 june 2010 the second verification of the origins of tornadoes experiment vortex2 armada observed a supercell thunderstorm near last chance colorado tempest unmanned aircraft system uas data collected in the rear flank outflow revealed what appeared to be an elevated outflow head turbulent wake and a cold rear flank internal surge rfis surface thermodynamic and kinematic data collected by the sticknet and mobile mesonet indicated that the outflow wake may have extended to or very near the surface perhaps modifying or outright replacing the leading edge of the outflow at times single doppler data collected by the noaa x pol mobile polarimetric doppler radar noxp were supportive of the possibility of a downdraft in the outflow wake associated with low level divergence a conceptual model of the hypothesized rear flank outflow structure in the nontornadic phase of the last chance supercell is presented the observed turbulent wake is consistent with mixing associated with the rel

analysis of a nontornadic storm during vortex 95 abstract analysis of a supercell storm that did not produce a tornado near hays kansas is presented a well defined midlevel mesocyclone was apparent throughout most of the storm s life cycle numerous shallow circulations were observed along the rear flank gust front during the data collection period six of these circulations strengthened into intense low level mesocyclones each of these mesocyclones failed to produce a tornado the strongest low level mesocyclone referred to as vortex 4 underwent a life cycle that was consistent with other tornadic mesocyclones documented in the literature these results illustrate that the presence of a long lived mesocyclone at low levels is not sufficient for tornadogenesis to occur the kinematic structure of the low level mesocyclone that did not produce a tornado is compared with a tornadic mesocyclone from another storm in order to understand the characteristic differences between these circulations the results lead to the conclusion that the presence of

the cause of internal outflow surges in a high resolution simulation of the 8 may 2003 oklahoma city tornadic supercell abstracta high resolution simulation of the 8 may 2003 oklahoma tornadic supercell is analyzed to determine the origin of internal outflow surges within the low level cold pool the analyzed simulation has 50 m horizontal grid spacing and is quadruply nested within larger lower resolution domains that were initialized via three dimensional variational data assimilation 3dvar of radar and other observations the high resolution simulation produces two tornadoes that track in close proximity to the observed tornado on 8 may 2003 the authors previous study determined that an internal outflow surge instigated tornadogenesis for the first tornado in this simulation but the cause of this internal outflow surge was unclear in this study the vertical momentum equation is analyzed along backward trajectories that are initialized within the tornado triggering internal outflow surge the analysis reveals that the internal outflow surge is forced by the dynamic part of the vertical pressure gradient further ex

vortex2 observations of a low level mesocyclone with multiple internal rear flank downdraft momentum surges in the 18 may 2010 dumas texas supercell abstractobservations collected in the second verification of the origins of rotation in tornadoes experiment during a 15 min period of a supercell occurring on 18 may 2010 near dumas texas are presented the primary data collection platforms include two ka band mobile doppler radars which collected a near surface short baseline dual doppler dataset within the rear flank outflow of the dumas supercell an x band phased array mobile doppler radar which collected volumetric single doppler data with high temporal resolution and in situ thermodynamic and wind observations of a six probe mobile mesonet rapid evolution of the dumas supercell was observed including the development and decay of a low level mesocyclone and four internal rear flank downdraft rfd momentum surges intensification and upward growth of the low level mesocyclone were observed during periods when the midlevel mesocyclone was minimally displaced from the low level circulation suggesting an upward directed perturbation pressure g

polarimetric radar metrics related to tornado life cycles and intensity in supercell storms abstractpolarimetric radar signatures have been related to the typical evolution of supercell storms including through tornado life cycles now that polarimetric radar observations are available for a large sample of supercell storms time series of new radar metrics can be derived these metrics can be compared with phases of known tornado life cycles in an effort to develop new methods of anticipating tornadoes and to increase understanding of storm scale structural and microphysical changes through supercell and tornado life cycles in this paper radar metrics including measures of differential reflectivity zdr columns zdr arcs polarimetrically inferred hailfall regions and mean value of copolar correlation coefficient hv in the echo appendage are compared to the tornado life cycle and to storm maximum tornado intensity in a sample of 35 tornadic supercells it is shown that these radar metrics may change repeatedly and thus can be used to distinguish tornadic and nontornadic periods in single su

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part ii intensification of low level rotation abstractthe dynamical processes responsible for the intensification of low level rotation prior to tornadogenesis are investigated in the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the circulation of material circuits that converge upon the low level mesocyclone is principally acquired along the southern periphery of the forward flank precipitation region which is a corridor characterized by a horizontal buoyancy gradient thus much of the circulation appears to have been baroclinically generated the descending reflectivity core drc documented in part i of this paper has an important modulating influence on the circulation of the material circuits a circuit that converges upon the low level mesocyclone center prior to the drc s arrival at low levels approximately the arrival of the 55 dbz reflectivity isosurface in this case loses some of its previously acquired circulation during the final f

near ground pressure and wind measurements in tornadoes since the spring of 2002 tornadoes were sampled on nine occasions using hardened in situ tornado pressure recorder probes video probes and mobile mesonet instrumentation this study describes pressure and in some cases velocity data obtained from these intercepts in seven of these events the intercepted tornadoes were within the radar indicated or visually identified location of the supercell low level mesocyclone in the remaining two cases the intercepted tornadoes occurred outside of this region and were located along either the rear flank downdraft gust front or an internal rear flank downdraft surge boundary the pressure traces sometimes augmented with videography suggest that vortex structures ranged from single cell to two cell quite similar to the swirl ratio dependent continuum of vortex structures shown in laboratory and numerical simulations although near ground tornado observations are quite rare the number of contemporary tornado measurements now available permits a comparative range of observed pressure deficits for a wide variety of tornado sizes and intensities to be presented

rapid scan polarimetric doppler radar observations of tornadogenesis and tornado dissipation in a tornadic supercell the el reno oklahoma storm of 24 may 2011 abstracton 24 may 2011 a mobile rapid scan x band polarimetric doppler radar raxpol collected data on a supercell as it produced two tornadoes near el reno oklahoma the first tornado rated an ef 3 was documented from intensification to decay and the genesis and intensification of a second tornado that was rated an ef 5 was subsequently also documented the objective of this study is to examine the spatiotemporal evolution of the rotation associated with the tornadoes i as the first tornado weakened to subtornadic intensity and ii as the second tornado formed and intensified it is found that weakening did not occur monotonically the transition from tornadic to subtornadic intensity over the depth of the radar volume 4 km occurred in less than 30 s but this behavior is contingent upon the threshold for doppler shear used to define the tornado similarly the onset of a tornadic strength doppler velocity couplet occurred within a 30 s period over all elevations additionally the evolutio

river floodplain aggradation history and cultural activities geoarchaeological investigation at the yuezhuang site lower yellow river china abstract archaeobotanical research at the yuezhuang and xihe sites of the houli culture in the lower yellow river has found abundant carbonised plant remains including rice millet weed seeds and many other plants 7800 7000 cal bp although studies of the diverse economic practices of the houli people have begun issues such as ecological diversity and relationships between site formation processes with environmental changes are still poorly understood applying soil micromorphology and related methods such as particle size distribution and loss on ignition at yuezhuang this paper presents results of the geoarchaeological investigation and the implications for the reconstruction of site formation processes in relation to river alluvial history a long alluvial sequence is reconstructed consisting of frequent alternations of short periods surface stabilities and succeeding alluviations human occupations corresponded to those short term surface stabilities and are evidenced by the presence of anthropogenic inclusions in thin sections including burned bone fragments and pottery sherds the significances of this study to an ecological approach focusing on environmental changes and cultural adaption are discussed

vortex lines within low level mesocyclones obtained from pseudo dual doppler radar observations abstract vortex lines passing through the low level mesocyclone regions of six supercell thunderstorms three nontornadic three tornadic are computed from pseudo dual doppler airborne radar observations obtained during the verification of the origins of rotation in tornadoes experiment vortex in every case at least some of the vortex lines emanating from the low level mesocyclones form arches that is they extend vertically from the cyclonic vorticity maximum then turn horizontally usually toward the south or southwest and descend into a broad region of anticyclonic vertical vorticity this region of anticyclonic vorticity is the same one that has been observed almost invariably to accompany the cyclonic vorticity maximum associated with the low level mesocyclone the vorticity couplet straddles the hook echo of the supercell thunderstorm the arching of the vortex lines and the orientation of the vorticity vector along the vortex line arches compared to the orientation of the ambient barotrop

finescale single and dual doppler analysis of tornado intensification maintenance and dissipation in the orleans nebraska supercell abstract finescale single and dual doppler observations are used to diagnose the three dimensional structure of the wind field surrounding a tornado that occurred near the town of orleans nebraska on 22 may 2004 the evolution of the vorticity and divergence fields and other structures near the tornado are documented in the lowest kilometer changes in tornado intensity are compared to the position of the tornado relative to primary and secondary gust fronts circulation on scales of a few kilometers surrounding the tornado remains relatively constant during the analysis period which spans the intensifying and mature periods of the tornado s life cycle stretching of vertical vorticity and tilting of horizontal vorticity are diagnosed but the latter is near or below the threshold of detectability in this analysis during the observation period in the analyzed domain low level circulation within 500 m of the tornado increased several minutes before vortex relative and ground relative near surface wind

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

impacts of lapse rates on low level rotation in idealized storms abstractadiabatic lapse rates appear to be a common feature in the lower troposphere on tornado days this article reviews physical reasons why lapse rates may influence surface vortex intensification and reports on numerical simulations designed to study the key processes in the idealized numerical model an initial mesocyclone like vortex and nonvarying convection like heat source are used in different environmental stability profiles the scales of interest in these simulations typify those of a parent supercell and the developing circulations constitute direct responses to the imposed heating downward parcel displacements are needed for surface vortex development in environments with no preexisting surface vorticity in the simulations under neutral stratification there is strong heating induced subsidence anchored near the storm edge whereas under stable stratification there are instead gravity waves that propagate away to the far field in addition under weak or neutral low level stratification

the bowdle south dakota cyclic tornadic supercell of 22 may 2010 surface analysis of rear flank downdraft evolution and multiple internal surges abstractmobile mesonet sampling in the hook echo rear flank downdraft rfd region of a tornadic supercell near bowdle south dakota provided the opportunity to examine rfd thermodynamic and kinematic attributes and evolution focused analysis of the fifth low level mesocyclone cycle that produced two significant tornadoes including a violent tornado revealed four rfd internal surge rfdis events rfdiss appeared to influence tornado development intensity and demise by altering the thermodynamic and kinematic character of the rfd region bounding the pretornadic and tornadic circulations significant tornadoes developed and matured when the rfd modulated by internal surges was kinematically strong only weakly negatively buoyant and very potentially buoyant in contrast the demise of the bowdle tornado was concurrent with a much cooler rfdis that replaced more buoyant and far more potentially buoyant rfd air near the tornado this surge also likely contributed to a displacement of the tornado from

single and dual doppler analysis of a tornadic vortex and surrounding storm scale flow in the crowell texas supercell of 30 april 2000 abstract fine resolution single and dual doppler data were collected in the tornadic region of a supercell storm intercepted by two doppler on wheels radars on 30 april 2000 near crowell texas eleven dual doppler analyses characterize the 2d and 3d near surface wind fields associated with a tornado during a 13 min period an interesting evolution of the low level rotation is observed initially concentric tornado 500 m wide and tornado cyclone 2 km wide radar velocity couplets make a transition into a solitary intermediate sized 750 m wide circulation that widens and makes a further transition into a two celled multiple vortex structure with an asymmetric distribution of vertical vorticity the asymmetry and eventual disruption of the multiple vortex structure may have been partially controlled by locally strong outflow winds that affect the convergence fields in its vicinity a smaller 500 m wide tornado embedded in a broad area of rotation is subsequently observed the dual doppler wi

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

forcing mechanisms for an internal rear flank downdraft momentum surge in the 18 may 2010 dumas texas supercell abstractthe forcing and origins of an internal rear flank downdraft rfd momentum surge observed by the second verification of the origin of rotation in tornadoes experiment vortex2 within a supercell occurring near dumas texas on 18 may 2010 is assessed through ensemble kalman filter enkf storm scale analyses enkf analyses are produced every 2 min from mobile doppler velocity data collected by the doppler on wheels and shared mobile atmospheric research and teaching radars as well as radial velocity and reflectivity data from the kama amarillo texas wsr 88d enkf analyses are found to reproduce the structure and evolution of an internal rfd momentum surge observed in independent mobile doppler radar observations pressure retrievals of enkf analyses reveal that the low level rfd outflow structure is primarily determined through nonlinear dynamic perturbation pressure gradient forcing horizontal acceleration into a trough of low perturbation pressure between the low level mesocyclone and mesoa

palaeochannels on the north china plain palaeoriver geomorphology abstract variations in the geomorphology of the north china plain are related to differences between river deposits the river deposits from different periods form the various geomorphological features different combinations of palaeochannels form different geomorphological regions different kinds of palaeochannels form different kinds of micro geomorphology during the early glaciation of the late pleistocene the river deposits formed piedmont plains and floodplains by the early holocene the rivers had cut the piedmonts into dissected valleys and deposited alluvial fans at the front edge of the piedmonts to form alluvial plains below by the middle holocene lake sediments covered the alluvial plains and filled in the dissected valleys of the piedmont plains by the late holocene rivers dissected the piedmonts again to form dissected valleys and deposited alluvial fans in the lower reaches to form alluvial plains and deltas at the river mouths

high temporal resolution polarimetric x band doppler radar observations of the 20 may 2013 moore oklahoma tornado abstract on 20 may 2013 the cities of newcastle oklahoma city and moore oklahoma were impacted by a long track violent tornado that was rated as an ef5 on the enhanced fujita scale by the national weather service despite a relatively sustained long track damage surveys revealed a number of small scale damage indicators that hinted at storm scale processes that occurred over short time periods the university of oklahoma ou advanced radar research center s px 1000 transportable polarimetric x band weather radar was operating in a single elevation ppi scanning strategy at the ou westheimer airport throughout the duration of the tornado collecting high spatial and temporal resolution polarimetric data every 20 s at ranges as close as 10 km and heights below 500 m agl this dataset contains the only known polarimetric radar observations of the moore tornado at such high temporal resolution providing the opportunity to analyze and study finescale phenomena occurring on rapid time scales analysis

the 8 june 1995 mclean texas storm part ii cyclic tornado formation maintenance and dissipation abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected a unique dataset with the electra doppler radar eldora the eldora observations document the sequential life cycles of storm scale circulations associated with three large tornadoes in a supercell thunderstorm near mclean texas a qualitative description of the evolution of the storm was provided in part i of this paper during the first stage of development of each storm scale circulation interaction of the updraft with the environmental low level horizontal vorticity produced a vorticity column that increased in intensity with height as the vortex matured vorticity increased greatly at low levels i e below 2 km agl and exceeded that aloft each tornadic vortex was located near the rear side of the updraft where the surrounding low level horizontal vorticity was modified locally most likely by weak baroclinity within the storm tilting of low level horizo

palaeochannels on the north china plain stage division and palaeoenvironments abstract the late pleistocene and holocene palaeochannels in the north china plain were divided into six stages on the basis of seven indicators basal erosion surface and channel lag deposits macropalaeontology organic matter content ground water quality heavy minerals grain size and sedimentary structures they were called the stages i vi palaeochannels from oldest to youngest on the basis of the percentage area and thickness of fluvial sand bodies of the total area and thickness of sediments of the same period there were three palaeochannel development stages or periods of fluvial activity and two palaeoswamp development stages or periods of fluvial inactivity on the north china plain during the late pleistocene and the holocene

environmental changes around the jurassic cretaceous transition new nannofossil chemostratigraphic and stable isotope data from the lokut section transdanubian range hungary abstract new biostratigraphical chemical and stable isotope c o data are presented from the lokut section transdanubian range hungary representing a ca 13 m thick continuous succession of lower tithonian lower berriasian pelagic limestones the study is conducted to verify timing of nannofossil events and major palaeoenvironmental changes at the jurassic cretaceous transition including lithogenic input palaeoredox and palaeoproductivity variations nannofossil zones from njt 16b to nkt have been identified in the lokut section and correlated with magnetostratigraphy covering an interval from polarity zone m21r to m18r the nannofossil zone njt 16b spans the interval from the upper part of m21r to lowermost part of m19n2n but its lower limit is poorly defined due to large diachronism in first occurrence fo of nannoconus infans in various tethyan sections fos of n kamptneri minor and n steinmannii minor are situated in the topmost part of the m19n2n and lowermost part of m19n1r magnetozones respectively they are located ca 2 2 5 m above the j k boundary defined as intermedia alpina subzonal boundary which falls within the lower half of magnetozone m19n2n the position of first occurrences of these taxa is similar to that from the puerto escano section southern spain and slightly lower than in italian sections southern alps concentrations of chemical element proxies of terrigenous transport al k rb th decrease towards the top of the lokut section which suggests a decrease in input of terrigenous material and increasing carbonate productivity during the early tithonian and the berriasian slight oxygen depletion at the sea bottom decrease of th u ratio and large increase in concentrations of productive elements p ba ni cu is observed upsection nutrients supply via upwelling seems to be the most likely explanation increase in phosphorus accumulation rate and a microfacies change from saccocoma to calpionellid dominated took place in the polarity chron m19r which apparently coincided with the worldwide nannofossil calcification event related to a bloom of strongly calcified calcareous nannoplankton taxa deposition in the lokut area was probably affected by long term climatic trends aridization and warming decreasing 13c values of bulk carbonates throughout the tithonian and the berriasian are interpreted as a result of a global trend of accelerated carbonate productivity supported by local factors such as increased upwelling intensity and a possible change in the composition of carbonate mud

aerial damage survey of the 2013 el reno tornado combined with mobile radar data abstracta detailed damage survey of the el reno oklahoma tornado of 31 may 2013 combined with rapid scanning data recorded from two mobile radars is presented one of the radars was equipped with polarimetric capability the relationship between several suction vortices visually identified in pictures with the high resolution doppler velocity data and swath marks in fields is discussed the suction vortices were associated with small shear features in doppler velocity and a partial ringlike feature of high spectral width for the first time a suction vortex that created a swath mark in a field was visually identified in photographs and high definition video while the rotational couplet was tracked by radar a dual doppler wind synthesis of the tornadic circulation at low levels near the location of several storm chaser fatalities resolved ground relative wind speeds in excess of 90 m s 1 greater than the minimum speed for ef5 damage the vertical vorticity analysis revealed a rapid transition from a s

a comparison of near surface buoyancy and baroclinity across three vortex2 supercell intercepts abstractobservations obtained during the second verification of the origin of rotation in tornadoes experiment vortex2 are analyzed for three supercell intercepts these intercepts used a fleet of deployable sticknet probes complemented by mobile radars and a mobile mesonet to map state quantities over the expanse of target storms two of the deployments occurred for different stages of a supercell storm near and east of dumas texas on 18 may 2010 a comparison of the thermodynamic and kinematic characteristics of the storm provides a possible explanation for why one phase was weakly tornadic and the other nontornadic the weakly tornadic phase features a stronger horizontal virtual temperature gradient antiparallel to the forward flank reflectivity gradient and perpendicular to the near surface flow direction suggesting that air parcels could acquire more significant baroclinic vorticity as they approach the low level mesocyclone the strongly tornadic 10 may 2010 case near seminole oklahoma fea

tornadogenesis in a high resolution simulation of the 8 may 2003 oklahoma city supercell abstracta 50 m grid spacing advanced regional prediction system arps simulation of the 8 may 2003 oklahoma city tornadic supercell is examined a 40 min forecast run on the 50 m grid produces two f3 intensity tornadoes that track within 10 km of the location of the observed long track f4 intensity tornado the development of both simulated tornadoes is analyzed to determine the processes responsible for tornadogenesis trajectory based analyses of vorticity components and their time evolution reveal that tilting of low level frictionally generated horizontal vorticity plays a dominant role in the development of vertical vorticity near the ground this result represents the first time that such a mechanism has been shown to be important for generating near surface vertical vorticity leading to tornadogenesis a sensitivity simulation run with surface drag turned off was found to be considerably different from the simulation with drag included a tornado still developed in the no drag simulation but it was

compiling the map of shallow buried palaeochannels on the north china plain abstract the 4 methods used in compiling the shallow buried palaeochannel maps are as follows geohydrologic electrical resistivity areo electro magnetism and drilling methods on the north china plain the drilling method was used mainly accompanied by the geohydrologic and the electrical resistivity methods before compiling the map detailed studies of typical palaeochannels were undertaken of palaeochannel sediments their ages and relation to the storage of shallow groundwater quantity and quality this provides the theoretical foundation for compiling the map of a large area and for dividing the palaeochannels then data from drilling samples were collected and each drilling hole divided into zones 1 and 2 and marked on the base map the boundaries of zones 1 and 2 were drawn on the base map from the map of the shallow buried palaeochannels we can conclude that the shallow buried palaeochannel zones and shallow groundwater zones are identical with the sand bodies of stage i iii and iv palaeochannels

paleochannel controlled earth fissures in daming north china plain and their implication for underground paleogeomorphology abstract earth fissures are a geologic phenomenon that mainly affects the medium with shallow surface soil and mainly developed in the quaternary sediment cover in the yellow river qinghe river zhanghe river shallow buried paleochannel band hqz qh2 ii band on the north china plain 93 earth fissures are developed among them 29 fissures are evolved in the daming zone in the upper reaches of the paleochannel band thus the zone belongs to a densely grouped fissure area this study through a series of field trenching and surveying revealed that these earth fissures have unique plane distribution rules and profile structure features of short length several meters to several hundred meters shallow depth smaller than 10 m and good correspondence to daming paleochannels these basic characteristics reveal that unlike other tectonic earth fissures daming earth fissures are a new and unknown type of fissures i e paleochannel controlled earth fissures theoretical analysis of their features showed that they were formed due to the actions of gravity primary joint factors and groundwater pumping activities and controlled by ancient river factors including paleochannels sediments and groundwater among them the process of mode i can be summed up as self gravity action tensile cracks surface water scouring earth fissures the process of mode ii is primary join surface water infiltration piping cave in earth fissures the process of mode iii is groundwater extraction aquifer compression inhomogeneous ground subsidence earth fissures these formation mechanisms of paleochannel induced earth fissures can be used to predict the fine distribution of shallow buried paleochannels and the overall migration process of the rivers thus this kind of earth fissures is of great significance for understanding the underground paleogeomorphology buried paleochannel of the north china plain and other alluvial plains of the world

processes preventing the development of a significant tornado in a colorado supercell on 26 may 2010 abstracta supercell produced a nearly tornadic vortex during an intercept by the second verification of the origins of rotation in tornadoes experiment on 26 may 2010 using observations from two m

documenting a rare tornado merger observed in the 24 may 2011 el reno piedmont oklahoma supercell abstractunique observations of the interaction and likely merger of two cyclonic tornadoes are documented one of the tornadoes involved in the interaction was the enhanced fujita scale ef5 el reno piedmont oklahoma tornado from 24 may 2011 and the other was a previously undocumented tornado data from three s band radars twin lakes oklahoma ktlx norman oklahoma koun and the multifunction phased array radar mpar are used to detail the formation of the second tornado which occurred to the northwest of the original tornado in an area of strong radial convergence radar data and isosurfaces of azimuthal shear provide evidence that both tornadoes formed within an elongated area of mesocyclone scale cyclonic rotation the path taken by the primary tornado and the formation location of the second tornado are different from previous observations of simultaneous cyclonic tornadoes which have been most often observed in the cyclic tornadogenesis process the merger of the two tornadoes occurred d

doppler radar observations of anticyclonic tornadoes in cyclonically rotating right moving supercells abstractsupercells dominated by mesocyclones which tend to propagate to the right of the tropospheric pressure weighted mean wind on rare occasions produce anticyclonic tornadoes at the trailing end of the rear flank gust front more frequently mesoanticyclones are found at this location most of which do not spawn any tornadoes in this paper four cases are discussed in which the formation of anticyclonic tornadoes was documented in the plains by mobile or fixed site doppler radars these brief case studies include the analysis of doppler radar data for tornadoes at the following dates and locations 1 24 april 2006 near el reno oklahoma 2 23 may 2008 near ellis kansas 3 18 march 2012 near willow oklahoma and 4 31 may 2013 near el reno oklahoma three of these tornadoes were also documented photographically in all of these cases a strong mesocyclone i e vortex signature characterized by azimuthal shear in excess of 5 10 3 s 1 or a 20 m s 1 change in doppler velocity over 5 km

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

no evidence for fungal infection of upper jurassic horseshoe crabs a comment on blazejowski et al 2019 abstract blazejowski et al 2019 intended to provide evidence for fungal infection of upper jurassic horseshoe crabs from poland based on the presence of boring traces preserved on their carapaces and assigned to the ichnogenus mycelites however the borings are in fact burrows which can be assigned to the ichnogenus arachnostega thus their hypothesis about the fungal infection is rejected on the basis of erroneous identification of the ichnofossils preserved there is also no compelling evidence for environmental deterioration causing the infection rather the bottom waters were oxygenated and thus hospitable for benthic organisms

a finescale radar examination of the tornadic debris signature and weak echo reflectivity band associated with a large violent tornado abstracthigh resolution data of the tornadic debris signature tds and weak echo reflectivity band wrb associated with a large violent tornado on 24 may 2011 in central oklahoma are examined using a rapid scan x band polarimetric mobile doppler radar various characteristics of these features and their evolution are examined over time intervals of 20 s or less the formation of the tds debris fallout and inhomogeneities in the tds structure are analyzed from volumetric and single elevation observations constant radius vertical cross sections of doppler velocity reflectivity and copolar cross correlation coefficient are compared at various times during the tornado s life cycle from them it is found that the weak echo column wec is considerably narrower than the tds and the wec is confined to the strong gradient of doppler velocities in the tornado s core the tds of the mature tornado extends radially outward bound approximately by the 40 m s 1 radial isodop rapid scan near surface data w

the structure and evolution of a numerically simulated high precipitation supercell thunderstorm the structure and evolution of a high precipitation hp supercell thunderstorm is investigated using a threedimensional nonhydrostatic cloud scale numerical model tass the model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 november 1988 raleigh tornadic thunderstorm tass produces a long lived convective system that compares favorably with the observed raleigh tornadic thunderstorm the simulated storm evolves from a multicell type storm to a multiple updraft supercell storm the storm complex resembles a hybrid multicell supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic hp supercells that are characterized by shallow mesocyclones the origin of rotation in this type of storm is often in the lowest levels interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure an intense low level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity the stretching of this preexisting vertical vorticity in the storm s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft s development interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows overall the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms however classic supercell signatures are seen early in the simulation associated with other updrafts e g formation of vortex couplet due to tilting of ambient horizontal vorticity storm splitting etc and are deemed important in the storm s supercell stage rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone pulsating downdrafts periodically invigorate the storm and the gust front never occludes thus allowing the main updraft to persist for a prolonged period of time the storm s intensity is also maintained by frequent updraft mergers

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

sensitivity of real data simulations of the 3 may 1999 oklahoma city tornadic supercell and associated tornadoes to multimoment microphysics part i storm and tornado scale numerical forecasts abstractnumerical predictions of the 3 may 1999 oklahoma city oklahoma tornadic supercell are performed within a real data framework utilizing telescoping nested grids of 3 km 1 km and 250 m horizontal spacing radar reflectivity and radial velocity from the oklahoma city wsr 88d are assimilated using a cloud analysis procedure coupled with a cycled 3dvar system to analyze storms on the 1 km grid for subsequent forecast periods single double and triple moment configurations of a multimoment bulk microphysics scheme are used in several experiments on the 1 km and 250 m grids to assess the impact of varying the complexity of the microphysics scheme on the storm structure behavior and tornadic activity on the 250 m grid this appears to be the first study of its type to investigate single versus multimoment microphysics within a real data context it is found that the triple moment scheme overall performs the best producing the smallest track errors for the mesocyclone on the 1 km grid and str

dynamical influences of anvil shading on simulated supercell thunderstorms abstractnumerical simulations of supercell thunderstorms including parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps model to investigate how low level air temperature deficits within anvil shadows affect the simulated storms the maximum temperature deficits within the modeled cloud shadows are 1 5 2 0 k which is only about half that previously observed within the shadows the loss of strong solar heating cools and stabilizes the near surface layer which suppresses vertical mixing and modifies the near surface vertical wind shear in a case of a stationary storm the enhanced easterly shear present beneath the anvil leads to a thinning of the outflow layer and corresponding acceleration of the rear flank gust front far ahead of the overlying updraft weakening the low level mesocyclone it is further shown that the direct absorption and emission of radiation by clouds does not significantly affect the simulated supercells varying th

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

the role of surface drag in mesocyclone intensification leading to tornadogenesis within an idealized supercell simulation abstractthe idealized supercell simulations from our previous study are further analyzed to clarify the physical mechanisms leading to differences in mesocyclone intensification between an experiment with surface friction applied to the full wind fwfric and an experiment with friction applied to the environmental wind only envfric the low level mesocyclone intensifies rapidly during the 3 minutes preceding tornadogenesis in fwfric while the intensification during the same period is much weaker in envfric which fails to produce a tornado to quantify the mechanisms responsible for this discrepancy in mesocyclone evolution material circuits enclosing the low level mesocyclone are initialized and traced back in time and circulation budgets for these circuits are analyzed the results show that in fwfric surface drag directly generates a substantial proportion of the final circulation around the mesocyclone especially below 1 km agl in envfric circulation budgets indicate the mesocyclone circulat

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

a numerical study of the 6 may 2012 tsukuba city supercell tornado part ii mechanisms of tornadogenesis abstractin part i the vorticity sources of midlevel and low level mesocyclones in the 6 may 2012 tsukuba city japan tornadic supercell were investigated by using high resolution simulation results with a 50 m horizontal grid spacing in part ii the analyses are extended to the mechanisms of tornadogenesis the tornado was generated at the leading edge of a rear flank downdraft rfd outflow surge backward trajectory and vortex line analyses revealed that the rfd outflow surge was a triggering factor for tornadogenesis and that horizontal vorticity around the strong rfd outflow region was ingested into the tornado to identify the vorticity source of the tornado the evolution of circulation along a material circuit surrounding the tornado was investigated owing to baroclinity at the tip of a hook shaped distribution of hydrometeors hereafter hook echo the circulation increased rapidly from a negative value when the core of the hydrometeors was descending about 10 min prior to tornadogenesis ana

surface analysis near and within the tipton kansas tornado on 29 may 2008 abstract data collected by a mesonet within the near tornado environment and in the tipton tornado on 29 may 2008 provided a rare opportunity to analyze rear flank downdraft rfd outflow properties closely bounding a tornado and to characterize parcel thermodynamics being ingested into a tornado from the rear flank downdraft parcels moving into the tornado on its right flank had very small negative buoyancy and considerable potential buoyancy measurements within and very near the tornado showed similar buoyancy characteristics to the storm inflow analyzed surface divergence and videographic evidence indicated that the rfd outflow just to the right and wrapping in front of the tornado was supported by parcels moving out of a narrow downdraft bordering the right flank of the tornado surface flow field analysis showed that parcels moved out of the downdraft associated divergence region and into the right side of as well as in front of the tornado an internal rfd surge boundary was positioned roughly

dual doppler and single doppler analysis of a tornadic storm undergoing mergers and repeated tornadogenesis abstract dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field in and near a tornado occurring near kiefer oklahoma on 26 may 1997 analyses of the dual doppler vector wind fields document in detail for the first time several structures associated with the tornado a proximate updraft region a rear flank downdraft wrapping around the tornado a double gust front structure occluding near the tornado and a region of enhanced vorticity separated from the tornado that may have been associated with cyclic tornadogenesis the analyses are compared to conceptual and computer models of tornadic storms a subsequent tornadogenesis was observed with radar every 18 s providing a finescale temporal view of the genesis process the genesis process was complex and the evolution of tornado intensity parameters was not monotonic in time low level rotation contracted and intensified then broadened then contracted and intensified a se

an investigation of the goshen county wyoming tornadic supercell of 5 june 2009 using enkf assimilation of mobile mesonet and radar observations collected during vortex2 part ii mesocyclone scale processes affecting tornado formation maintenance and decay abstractstorm scale and mesocyclone scale processes occurring contemporaneously with a tornado in the goshen county wyoming supercell observed on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 are examined using ensemble analyses produced by assimilating mobile radar and in situ observations into a high resolution convection resolving model this paper focuses on understanding the evolution of the vertical structure of the storm the outflow buoyancy and processes affecting the vertical vorticity and circulation within the mesocyclone that correspond to changes in observed tornado intensity tornadogenesis occurs when the low level mesocyclone is least negatively buoyant relative to the environment possesses its largest circulation and is collocated with the largest azimuthally averaged convergence during the analysis period the average buoyancy circulation and convergence within the near surface mesocyclone on spatial scales resolved by the

the genesis of mesovortices within a real data simulation of a bow echo system abstractthe genesis of two mesovortices mvs within a real data convection resolving simulation of the 8 may 2009 central u s bow echo system is studied both mvs form near the bow apex but differ distinctively in intensity lifetime and damage potential the stronger and longer lived mesovortex mva stays near the bow apex where the system scale rear inflow jet rij is present the descending rij produces strong downdrafts and surface convergence which in turn induce strong vertical stretching and intensification of mva into an intense mesovortex in contrast the weaker and shorter lived mesovortex mvb gradually moves away from the bow apex accompanied by localized convective scale downdrafts lagrangian circulation and vorticity budget analyses reveal that the vertical vorticity of mvs in general originate from the tilting of near surface horizontal vorticity which is mainly created via surface friction the circulation of the material circuit that ends up to be a horizontal circuit at the fo

observations of the surface boundary structure within the 23 may 2007 perryton texas supercell abstractin situ data collected within a weakly tornadic high precipitation supercell occurring on 23 may 2007 near perryton texas are presented data were collected using a recently developed fleet of 22 durable rapidly deployable probes dubbed sticknet as well as four mobile mesonet probes kinematic and thermodynamic observations of boundaries within the supercell are described in tandem with an analysis of data from the shared mobile atmospheric research and teaching radar observations within the rear flank downdraft of the storm exhibit large deficits of both virtual potential temperature and equivalent potential temperature with a secondary rear flank downdraft gust front trailing the mesocyclone a primarily thermodynamic boundary resided across the forward flank reflectivity gradient of the supercell this boundary is characterized by small deficits in virtual potential temperature coupled with positive perturbations of equivalent potential temperature the opposing thermodynamic perturbatio

variations in supercell morphology part i observations of the role of upper level storm relative flow abstract it is hypothesized that the precipitation intensity beneath a supercell updraft is strongly influenced by the amount of hydrometeors that are reingested into the updraft after being transported away in the divergent upper level flow of the anvil this paper presents the results of a climatological analysis of soundings associated with three types of isolated supercells having distinctive precipitation distributions the so called classic low precipitation lp and high precipitation hp storms it is shown that storm relative flow at 9 10 km above the ground is strongest in the environments of lp storms and relatively weak in the environments of hp storms with classic storms occurring in environments with intermediate magnitudes of upper storm relative flow it is plausible that comparatively strong flow in the anvil bearing levels of lp storms transports hydrometeors far enough from the updraft that they are relatively unlikely to be reingested into the updraft leading to greatly diminishe

environment deterioration and related fungal infection of upper jurassic horseshoe crabs with remarks on their exceptional preservation abstract approximately 10 of late jurassic tithonian horseshoe crabs collected from the kcynia formation in the owadow brzezinki quarry central poland display microborings covering the entire carapace of specimens detailed examination of the surrounding sediment indicates the occurrence of short term fluctuations in the oxygenation level of bottom waters and their salinities the identified palynomorph assemblage from the sediment suggests pathogenic algal blooms as the probable cause for mass mortality anoxic conditions resulting from algal blooms in restricted environments facilitated fungal infection evidenced by the damage microborings caused by the hyphae on the surface of the exoskeletons associated biochemical factors contributed to the excellent preservation of diversified fauna with soft tissues

reply to the comment on no evidence for fungal infection of upper jurassic horseshoe crabs a comment on blazejowski et al 2019 by zaton 2020 palaeo3 xxx xxx abstract in the comment on our paper this issue zaton 2020 questions the conclusions reported in blazejowski et al 2019 we present further arguments defending our theses late jurassic horseshoe crabs preserved in sediments of the kcynia formation owadow brzezinki quarry lived in a restricted lagoon repeatedly subjected to dysoxia anoxia which promoted their excellent state of preservation the palaeobiological interpretation of the traces visible on horseshoe crab exoskeletons is consistent with the occurrence of temporal oxygen deficiency

on the mechanisms of rain formation in an idealized supercell storm abstractdeep convective storms produce raindrops through three mechanisms condensation and coalescence growth of cloud liquid droplets i e warm processes melting of ice hydrometeors and shedding from wet hailstones to investigate the relative importance of these mechanisms and their contributions to exotic drop size distributions dsds observed near the surface in supercell storms an idealized simulation of a supercell is performed using a modified version of the morrison two moment microphysics scheme the modified scheme includes separate categories for warm shed and melted rain rain originating from melting ice dominates the rain mass at low levels especially along the right forward flank precipitation shield whereas shed rain drops dominate a region within the left forward flank warm rain is only dominant in the upshear portion of the rear flank of the storm at low levels though it dominates the total rain mass within the main updraft aloft the warm rain mass at low levels is associat

a method to control the environmental wind profile in idealized simulations of deep convection with surface friction abstractin idealized horizontally homogeneous cloud model simulations of convective storms the action of surface friction can substantially modify the near ground environmental wind profile over

surface in situ observations within the outflow of forward flank downdrafts of supercell thunderstorms abstract in the long standing conceptual model of a supercell thunderstorm the forward flank downdraft ffd and its associated negative buoyancy originate from precipitation loading and the latent chilling of air due to the melting and evaporation of precipitation the horizontal buoyancy gradient within the outflow of the ffd has been identified as an important source of low level streamwise vorticity in three dimensional numerical simulations of supercells these simulations have demonstrated that the formation of low level mesocyclones is critically dependent on the baroclinic generation of horizontal vorticity within the ffd outflow despite the implied dynamical importance of the ffd outflow in the evolution of supercell thunderstorms only a very limited number of thermodynamic observations have been obtained within ffd outflow the range of thermodynamic conditions within ffd outflow is not well known nor is it known whether any systematic relationship exists between the thermodynamic character