an observational study of a coastal barrier jet induced by a landfalling typhoon abstractin this study the structure and evolution of a coastal barrier jet cbj along the east coast of taiwan is documented using operational doppler radars the formation of the cbj was control

kinematic characteristics of a mei yu front detected by the quikscat oceanic winds abstract based on conventional surface observations and nasa quick scatterometer quikscat data a heavy rainfall event that occurred in the taiwan mei yu season was chosen to further study the kinematic characteristics of the accompanying surface front with the help of the quikscat oceanic surface winds it was found that the location and propagation of a mei yu front over the ocean to the east of taiwan during 10 12 june 2000 are better represented by the frontal wind shift line which was located approximately on the leading edge of the baroclinic zone the mesoscale system with cyclonic circulation embedded within the frontal zone was clearly shown in the wind field and kinematic parameters horizontal divergence and vorticity as well as satellite clouds and rainfall estimations the conditional instability of the second kind cisk process was suggested to be responsible for the intensification of the mei yu front and the frontal disturbance over the ocean under the influence of island topography

hydrocarbons in mississippi fan and intraslope basin sediments abstract aliphatic and aromatic hydrocarbons in sediments of the middle and lower mississippi fan and two intraslope basins in the gulf of mexico are derived from terrestrial organic matter and thermogenic mature hydrocarbons the terrestrial hydrocarbon component consists primarily of terrigenous plant biowaxes n alkanes with 21 to 33 carbons the occurrence of thermogenic hydrocarbons in immature near surface sediments their molecular distributions and concentration variations with depth suggest that the majority of these mature hydrocarbons have migrated from a source much deeper in the sediment column a portion of the thermogenic hydrocarbons may be derived from recycled material and includes phenanthrene methyl phenanthrenes chrysene and benzopyrenes the migrated thermogenic hydrocarbons include normal and isoprenoid alkanes with less than 21 carbons naphthalene methyl naphthalenes ethyl naphthalenes and other aromatics of similar volatility i e biphenyl acenaphthene and fluorene triterpane sterane and aromatized sterane distributions suggest that the thermogenic hydrocarbons at both sites have a common source and are overprinted with immature sediment hydrocarbons the biomarker distributions and carbon isotopic compositions of the thermogenic hydrocarbons are atypical for petroleum produced in the gulf of mexico molecular distributions of the hydrocarbons are constant regardless of the present depth of occurrence suggesting that they have migrated in a separate phase the upward migration of hydrocarbons from deeper sources is a wide spread phenomenon in the gulf of mexico with several documented cases of massive seepage visible oil as well as the more diffuse permeation of pleistocene sediments of the mississippi fan and two intraslopes reported here

analysis of a heavy rainfall event during tamex abstract a heavy rainfall event during the taiwan area mesoscale experiment intensive observing period 13 has been studied using upper air surface mesonet and dual doppler radar data the heavy rainfall 231 mm day 1 occurred over northwestern taiwan with the maximum rainfall along the northwestern coast and was caused by a long lived convective rainband in the prefrontal atmosphere it occurred in an upper level divergence region and along the axis of the maximum equivalent potential temperature at the 850 hpa level as a mei yu front advanced southeastward the postfrontal cold air in the lowest levels was retarded by the hilly terrain along the southeastern china coast as a result a low level wind shift line associated with a pressure trough at the 850 hpa level moved over the taiwan strait before the arrival of the surface front the westerly flow behind the trough interacted with a barrier jet along the northwestern coast of taiwan the barrier jet is caused by the interaction between the pref

climatology and dynamics of the link between dry intrusions and cold fronts during winter part ii front centred perspective the conceptual picture of an extratropical cyclone typically includes a cold front and a dry intrusion di behind it by objectively identifying fronts and dis in ecmwf era interim data for 1979 2014 part i quantified the climatological relationship between cold fronts and dis driven by the finding that front intensity and frontal precipitation are enhanced in the presence of dis here we employ a front centred perspective to focus on the dynamical and thermodynamical environment of cold fronts with and without dis in the northern hemisphere winter distinguishing between trailing fronts that connect to a parent cyclone and isolated fronts examples of dis behind each type illustrate the baroclinic environment of the trailing front and the lack of strong temperature gradients across the isolated front composite analyses of north atlantic and north pacific fronts outline the major differences in the presence of dis compared to similar fronts but without dis in their vicinity the magnitude and spatial structure of the modification by dis depends on the front intensity yet generally with dis trailing fronts occur with stronger slp dipole deeper upper tropospheric trough stronger 10 m wind gusts enhanced ocean sensible and latent heat fluxes in the cyclone cold sector and heavier precipitation isolated weak fronts exhibit similar behaviour with different spatial structure this study highlights the central role of dis for shaping the variability of fronts and their associated environment and impact

a diagnostic case study of mei yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment abstract during 6 7 june 2003 a mei yu front over southern china with active mesoscale convective systems mcss along it and to its south intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1 7 10 4 s 1 and a low level jet llj of 22 5 m s 1 at 850 hpa moreover both the mass and wind fields and convection developed a wavelike structure at meso scale along the front using mainly gridded analyses from the european centre for medium range weather forecasts ecmwf the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity pv inversion results indicate that this mei yu front was characterized by strong horizontal shear and moderate temperature gradient and its development was not baroclinic in nature the initiation of a wavelike structure along the frontal shear zon

a case study of subtropical frontogenesis during a blocking event abstract during 8 14 june 2000 a 500 hpa blocking event occurred over mongolia and northern china near 45 n 108 e which was the only case over this region in june since 1981 as the block developed the initially weak low level mei yu front over southern china evolved into a system with strong baroclinity and subsequently moved south the frontal passage over taiwan caused temperatures to drop by 10 c the largest in june over two decades using gridded analyses manually analyzed weather maps and satellite and surface data the present study investigates the evolution of this mei yu front under the influence of the block the 925 hpa frontogenetical function is computed and effects of different processes are discussed as the blocking event developed concurrent ridge trough amplification in the lower midtroposphere produced a reversed thermal pattern the lower tropospheric high moved southward and large scale confluence and deformation were enhanced between the northerly flow and the prefrontal

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

osmium isotope systematics of ureilites abstract the 187 os 188 os for 22 ureilite whole rock samples including monomict augite bearing and polymict lithologies were examined in order to constrain the provenance and subsequent magmatic processing of the ureilite parent body or bodies the re os ratios of most ureilites show evidence for a recent disturbance probably related to re mobility during weathering and no meaningful chronological information can be extracted from the present data set the ureilite 187 os 188 os ratios span a range from 0 11739 to 0 13018 with an average of 0 1258 0 0023 1 similar to typical carbonaceous chondrites and distinct from ordinary or enstatite chondrites the similar mean of 187 os 188 os measured for the ureilites and carbonaceous chondrites suggests that the ureilite parent body probably formed within the same region of the solar nebula as carbonaceous chondrites from the narrow range of the 187 os 188 os distribution in ureilite meteorites it is further concluded that re was not significantly fractionated from os during planetary differentiation and was not lost along with the missing ureilitic melt component the lack of large re os fractionations requires that re os partitioning was controlled by a metal phase and thus metal had to be stable throughout the interval of magmatic processing on the ureilite parent body

a modified kain fritsch scheme and its application for the simulation of an extreme precipitation event in vietnam abstract from 24 to 26 november 2004 an extreme heavy rainfall event occurred in the mountainous provinces of central vietnam resulting in severe flooding along local rivers the regional atmospheric modeling system version 4 4 is used to simulate this event in the present study the convective parameterization scheme includes the original kain fritsch scheme and a modified one in which a new diagnostic equation to compute updraft velocity closure assumption and trigger function are developed these modifications take the vertical gradient of the exner function perturbation into account with an on off coefficient to account for the role of the advective terms according to the event simulations the simulated precipitation shows that the modified scheme with the new trigger function gives much better results than the original one moreover the interaction between convection and the larger scale environment is much stronger near the midtroposphere where the return flow associated with lower level

observations of a subtropical cold front in a region of complex terrain abstract the passage of shallow cold fronts during the late spring and early summer months over the island of taiwan is often accompanied by heavy rainfall and occasional flash flood episodes previous studies have emphasized the weak baroclinicity of these fronts and their possible modification by fluxes from the air sea interface in this study a cold frontal passage in the vicinity of taiwan is analyzed using data gathered during the taiwan area mesoscale experiment tamex on 8 june 1987 at the northern extent of the tamex network the cold front was shallow 1 2 km deep and moderately baroclinic with 5 7 c temperature contrasts at the surface a doppler radar cross section of radial velocity reveals a structure similar to that of a density current at the leading edge of the shallow front the postfrontal air man was substantially modified by oceanic heat fluxes as it moved southward over the warm ocean waters this led to a 60 70 decrease in the temperature contrast across the front between ocean

airborne doppler observations of a cold front in the vicinity of vancouver island abstract this study uses airborne doppler radar and flight level measurements from the coastal observations and simulations with topography experiment to examine the detailed mesoscale structure of an oceanic cold front upstream of vancouver island on 13 december 1993 these aircraft observations show that there were dramatic differences in frontal structure and movement between nearshore and offshore regions presumably due to the effects of blocking by the terrain the aircraft observations are considered in two parts since the behavior of the front evolved over the flight period during the early and middle portion of the flight the low level flow east of the front was out of the south southeast in the nearshore region rather than southerly as found farther offshore the nearshore segment of the front was oriented south north and appeared to be stationary the zone of orographic influence was found to extend to a region 20 km offshore and confined primarily to the lowest 1 5 km msl in distinct c

case study of an unusually heavy rain event over eastern taiwan during the mei yu season abstract a heavy rain event during the mei yu season was observed over eastern taiwan on 28 may 2001 under a potentially unstable environment with high cape and copious moisture this event with an unusually high daily rainfall maximum of 307 mm was observed in the ilan area over northeastern taiwan the retrogression of a mei yu front over the nearby ocean collocated with a short wave trough provided favorable large scale conditions for the production of localized heavy rainfall latent heating was suggested to be responsible for the retrogression and the development of the mei yu front over the nearby ocean to the east of taiwan in addition to the large scale forcings the local circulations and local topography modulated the rainfall distribution over the ilan area during the daytime hours the strengthened onshore wind component due to the intensified mei yu frontal circulation and orographic lifting provided enhanced rising motion over the windward slopes of the mountain to produce the significan

an observational and numerical study of a cold front interacting with the olympic mountains during coast iop5 abstract this paper documents the three dimensional flow and precipitation structures associated with a weak cold front interacting with the olympic mountains and the subsequent development of a puget sound convergence zone this study utilizes data collected during coast iop5 the fifth intensive observing period of the coastal observation and simulation with topography field experiment that took place on 11 12 december 1993 one of the most important data sources was a noaa p 3 aircraft which provided flight level data radar reflectivity and doppler winds as it circumnavigated the olympics initially frontal passage along the western foothills of the olympics was accompanied by a 2 3 c temperature drop a rapid wind shift to northwesterlies and an intense line of precipitation 35 45 dbz however the wind shift and associated precipitation structures attenuated when the front began to ascend the windward slopes of the olympics surface and p 3 observations document the deformation of the front

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

the role of offshore convergence on coastal rainfall during tamex iop 3 abstract the role of offshore convergence on the coastal rainfall maximum along the northwestern coast of taiwan is analyzed based on tamex taiwan area mesoscale experiment data and numerical experiments using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 from a case study during tamex iop 3 moderate rainfalls 40 mm h 1 are observed along the northwestern coast of taiwan associated with the arrival of three rainbands in succession during 1000 1600 lst these rainbands form over the taiwan strait with northeast southwest or north south orientation they intensify off the northwestern coast there is a tendency for the most intense echoes to align in a northeast southwest orientation off the northwestern coast an orographically enhanced convergence zone with a northeast southwest orientation occurs in the area where the deflected southerly flow converges with the prevailing southwesterly flow that is modified by the storm

potential vorticity diagnostics of a mei yu front case abstract the present study selects the mei yu frontal case of 12 13 june 1990 over southeastern china and performs potential vorticity pv diagnostic analysis to discuss the mechanism responsible for the intensification and maintenance of frontal vorticity the mei yu front had typical characteristics at the western section and was shallow with weak baroclinity but strong horizontal shear vorticity for this particular case results of piecewise pv inversion indicate that latent heat release associated with both deep convections and stratiform clouds was responsible for the frontal vorticity and the apparent frontogenesis near 0000 utc 13 june was driven almost entirely by an outbreak of deep convections along the front through the conditional instability of the second kind cisk mechanism proposed by cho and chen the positive feedback between the mei yu frontogenesis and cumulus latent heating in which the front provided low level convergence and helped organize the convection while latent heatin

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

topographic effects on a wintertime cold front in taiwan abstract this paper describes an observational and numerical study of an intense wintertime cold front that occurred in taiwan on 8 january 1996 the front was associated with rope clouds at the leading edge and a broad area of stratiform clouds behind the front was blocked by the central mountain range of taiwan and divided into two sections on each side of the mountain range as the cold air moved southward along the east coast the increasing westward coriolis force induced a landward acceleration after the cold air piled up against the mountains a coastal pressure ridge developed the cold air damming yielded a geostrophic balance between the westward coriolis force and the eastward component of the pressure gradient force in the x direction and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component over the taiwan strait southward pressure gradient forces increased when the low level stable cold air was confined over the taiwan strait lead

initiation maintenance and properties of convection in an extreme rainfall event during scmrex observational analysis a long lived mesoscale convective system mcs with extreme rainfall over the western coastal region of guangdong on 10 may 2013 during the southern china monsoon rainfall experiment scmrex is studied the environmental conditions are characterized by little convective inhibition low lifting condensation level moderate convective available potential energy and precipitable water and lack of low level jets from the tropical ocean repeated convective back building and subsequent northeastward echo training of convective cells are found during the mcs s development stages however the initiation maintenance factors and organization of convection differ significantly during the earlier and later stages from midnight to early morning convection is continuously initiated as southeasterly flows near the surface impinge on the east side of mesoscale mountains near the coastal lines and then moves northeastward leading to formation of two quasi stationary rainbands from early morning to early afternoon new convection is repeatedly triggered along a mesoscale boundary between precipitation induced cold outflows and warm air from south china sea and gulf of tokin resulting in the formation of band training of several parallel rainbands that move eastward in a later time i e two scales of training of convective elements are found as the mcs dissipates a stronger squall line moves into the region from the west and passes over within about 3 5 h contributing about 10 15 to the total rainfall amount it is concluded that terrain near surface winds warm advection from the upstream ocean in the boundary layer and precipitation generated cold outflows play important roles in initiating and maintaining the extreme rain producing mcs