a first look at the structure of the wave pouch during the 2009 predict grip dry runs over the atlantic abstractin support of the national science foundation pre depression investigation of cloud systems in the tropics nsf predict and national aeronautics and space administration genesis and rapid intensification processes nasa grip dry run exercises and national oceanic and atmospheric administration hurricane intensity forecast experiment noaa ifex during the 2009 hurricane season a real time wave tracking algorithm and corresponding diagnostic analyses based on a recently proposed tropical cyclogenesis model were applied to tropical easterly waves over the atlantic the model emphasizes the importance of a lagrangian recirculation region within a tropical wave critical layer the so called pouch where persistent deep convection and vorticity aggregation as well as column moistening are favored for tropical cyclogenesis distinct scenarios of hybrid wave vortex evolution are highlighted it was found that easterly waves without a pouch or with a shallow pouch did not develop although not all wav

extratropical impacts on atlantic tropical cyclone activity abstractwith warm sea surface temperature sst anomalies in the tropical atlantic and cold sst anomalies in the east pacific the unusually quiet hurricane season in 2013 was a surprise to the hurricane community the authors analyses suggest that the substantially suppressed atlantic tropical cyclone tc activity in august 2013 can be attributed to frequent breaking of midlatitude rossby waves which led to the equatorward intrusion of cold and dry extratropical air the resultant mid to upper tropospheric dryness and strong vertical wind shear hindered tc development using the empirical orthogonal function analysis the active rossby wave breaking in august 2013 was found to be associated with a recurrent mode of the midlatitude jet stream over the north atlantic which represents the variability of the intensity and zonal extent of the jet this mode is significantly correlated with atlantic hurricane frequency the correlation coefficient is comparable to the correlation of atlantic hurricane fre

the effect of vertical shear orientation on tropical cyclogenesis the effect of the relative orientation of the vertical wind shear to the surface wind on tropical cyclogenesis is explored in environments of radiative convective equilibrium rce through numerical simulation this study serves as a companion paper to an earlier study on the thermodynamics of genesis in rce it is found when the mean surface wind and shear are aligned a negative surface wind anomaly arises from the superposition of the mean and vortex surface flows left of the shear vector the resulting weak surface enthalpy fluxes and up shear quasi balanced subsidence leads to dry air being located cyclonically down wind of the down shear convective anomaly thus convection is inhibited from propagating cyclonically around the core leading to a large down shear vortex tilt conversely in a counter aligned orientation the negative surface wind anomaly and driest air is found right of the shear vector hence the driest air rotates into the down shear flank where it moistened by shear organized convection furthermore the boundary layer is relatively moist left of shear due to the positive surface wind anomaly therefore promoting the cyclonic propagation from down shear and constraining the magnitude of the vortex tilt genesis is intimately tied to the magnitude of the tilt and is found to occur once the mid level vortex has precessed into the up shear flank for smaller values of maximum tilt vortex precession is comparatively rapid aided by showerhead moistening provided by the up shear advection of frozen condensate aloft with the up shear flank pre moistened rapid precession of the mid level vortex at smaller radii leads to near saturation on the mesoscale and the onset of rapid intensification when the magnitude of the tilt is quite large precession is much slower and the showerhead effect is significantly reduced until just prior to the emergence of the mid level vortex in the up shear flank copyright 2011 royal meteorological society

a balanced tropical cyclone test case for agcms with background vertical wind shear abstractthis paper presents a balanced tropical cyclone tc test case designed to improve current understanding of how atmospheric general circulation model agcm configurations affect simulated tc development and behavior it consists of an analytic initial condition comprising two independently balanced components the first provides a vortical tc seed while the second adds a planetary scale zonal flow with height dependent velocity and imposes background vertical wind shear vws on the tc seed the environmental flow satisfies the steady state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables e g temperature surface geopotential the evolution of idealized tcs in the test case framework is illustrated in 10 day simulations performed with the community atmosphere model version 5 1 1 cam 5 1 1 environmental wind profiles with different magnitudes directions and vertical inflection points are applied to ensure that the technique

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

effects of vertical shears and midlevel dry air on tropical cyclone developments abstracta set of idealized experiments using the weather research and forecasting model wrf were designed to investigate the impacts of a midlevel dry air layer vertical shear and their combined effects on tropical cyclone tc development compared with previous studies that focused on the relative radial position of dry air with no mean flow it is found that the combined effect of dry air and environmental vertical shear can greatly affect tc development moreover this study indicates the importance of dry air and vertical shear orientations in determining the impact the background vertical shear causes the tilting of an initially vertically aligned vortex the shear forces a secondary circulation fsc with ascent descent in the downshear upshear flank hence convection tends to be favored on the downshear side the fsc reinforced by the convection may overcome the shear induced drifting and restore the vertical alignment when dry air is located in the downshear right quadrant of the ini

formation of high δ18o fayalite bearing a type granite by high temperature melting of granulitic metasedimentary rocks southern china comment huang et al 2011 1 describe a granite that they interpret as crystallized from an a type magma derived from a metasedimentary protolith sun et al 2011 2 had already described a similar example with high initial 87sr 86sr and low nd the important question is whether these a types

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

physical processes controlling earlier and later onset of a typhoon season in the western north pacific the interannual variability of typhoon onset date in western north pacific wnp during 1979 2015 is investigated the average date in the earlier later onset group is early april late july a diagnosis of the genesis potential index shows that the key factor affecting the earlier and later onset lies in the background moisture field according to their evolution feature the earlier onset cases are further divided into two sub groups in the first sub group positive specific humidity anomalies were confined in the western wnp and caused primarily by circulation anomalies associated with a la nina in the equatorial eastern pacific in the second sub group positive specific humidity anomalies were confined in the eastern wnp and caused by anomalous convection associated with the pacific meridional mode pmm in the tropical and subtropical eastern pacific in the later onset composite negative specific humidity anomalies appear in the wnp and were accompanied by an anomalous anticyclone in situ and a v shape negative ssta pattern in the western pacific in addition the change of background vertical wind shear vws also influences the tc onset date a decrease increase in the vws magnitude and an easterly westerly shear anomaly occur in the earlier later onset composite physically it is argued that both the magnitude of the vws and the sign of anomalous zonal wind shear may affect tc formation in the wnp

impacts of radiation and cold pools on the intensity and vortex tilt of weak tropical cyclones interacting with vertical wind shear abstractidealized numerical simulations of weak tropical cyclones e g tropical depressions and tropical storms in sheared environments indicate that vortex tilt reduction and convective symmetr

potential vorticity diagnosis of a simulated hurricane part ii quasi balanced contributions to forced secondary circulations although the forced secondary circulations fscs associated with hurricane like vortices have been previously examined understanding is still limited to idealized axisymmetric flows and forcing functions in this study the individual contributions of latent heating frictional and dry dynamical processes to the fscs of a hurricane vortex are separated in order to examine how a hurricane can intensify against the destructive action of vertical shear and how a warm cored eye forms this is achieved by applying a potential vorticity pv inversion and quasi balanced omega equations system to a cloud resolving simulation of hurricane andrew 1992 during its mature stage with the finest grid size of 6 km it is shown that the latent heating fsc tilting outward with height acts to oppose the shear forced vertical tilt of the storm and part of the upward mass fluxes near the top of the eyewall is detrained inward causing the convergence aloft and subsidence warming in the hurricane eye the friction fsc is similar to that of the ekman pumping with its peak upward motion occurring near the top of the planetary boundary layer pbl in the eye about 40 of the pbl convergence is related to surface friction and the rest to latent heating in the eyewall in contrast the dry dynamical forcing is determined by vertical shear and system relative flow when an axisymmetric balanced vortex is subjected to westerly shear a deep countershear fsc appears across the inner core region with the rising sinking motion downshear upshear and easterly sheared horizontal flows in the vertical the shear fsc is shown to reduce the destructive roles of the large scale shear imposed as much as 40 including its forced vertical tilt moreover the shear fsc intensity is near linearly proportional to the shear magnitude and the wavenumber 1 vertical motion asymmetry can be considered as the integrated effects of the shear fscs from all the tropospheric layers the shear fsc can be attributed to the laplacian of thermal advection and the temporal and spatial variations of centrifugal force in the quasi balanced omega equation and confirms the previous finding of the development of wavenumber 1 cloud asymmetries in hurricanes hurricane eye dynamics are presented by synthesizing the latent heating fsc with previous studies the authors propose to separate the eye formation from maintenance processes the upper level inward mass detrainment forces the subsidence warming and the formation of an eye the surface pressure fall and increased rotation in the eyewall this increased rotation will induce an additional vertical pressure gradient force to balance the net buoyancy generated by the subsidence warming for the maintenance of the hurricane eye in this sense the negative vertical shear in tangential wind in the eyewall should be considered as being forced by the subsidence warming and maintained by the rotation in the eyewall

a study of the interaction between typhoon francisco 2013 and a cold core eddy part i rapid weakening abstracttyphoon francisco 2013 experienced unusually rapid weakening rw with its maximum surface wind decreasing by 45 kt 1 kt 0 51 m s 1 over 24 h as measured from the satellite derived ad

thermodynamic aspects of tropical cyclone formation abstractthe thermodynamic aspects of tropical cyclone tc formation near the center of the wave pouch a region of approximately closed lagrangian circulation within the wave critical layer are examined through diagnoses of a high resolution numerical simulation and dropsonde data from a recent field campaign it is found that the meso area near the pouch center is characterized by high saturation fraction small difference in equivalent potential temperature e between the surface and the middle troposphere and a short incubation time scale updrafts tend to be more vigorous in this region presumably because of reduced dry air entrainment while downdrafts are not suppressed the thermodynamic conditions near the pouch center are thus critically important for tc formation the balanced responses to convective and stratiform heating at the pregenesis stage are examined using the sawyer eliassen equation deep convection is concentrated near the pouch center the strong radial and vertical gradients o

thermodynamic and kinematic influences on precipitation symmetry in sheared tropical cyclones bertha and cristobal 2014 abstractprior studies have shown an association between symmetrically distributed precipitation and tropical cyclone tc intensification although environmental vertical wind shear typically forces an asymmetric precipitation distribution in tcs the magnitude of this asymmetry can exhibit considerable variability even among tcs that experience similar shear magnitudes this observational study examines the thermodynamic and kinematic influences on precipitation symmetry in two such cases bertha and cristobal 2014 consistent with the impact of the shear both tcs exhibited a tilted vortex as well as a pronounced azimuthal asymmetry with the maximum precipitation occurring in the downshear left quadrant however bertha was characterized by more symmetrically distributed precipitation and relatively modest vertical motions while cristobal was characterized by more azimuthally confined precipitation and much more vigorous vertical motions observations showed three potential hindrances to precipitat

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part ii numerical simulations abstract the cyclogenesis events associated with the tropical cyclone tc energy dispersion are simulated in a 3d model a new tc with realistic dynamic and thermodynamic structures forms in the wake of a preexisting tc when a large scale monsoon gyre or a monsoon shear line flow is present maximum vorticity generation appears in the planetary boundary layer pbl and the vorticity growth exhibits an oscillatory development this oscillatory growth is also seen in the observed rainfall and cloud top temperature fields the diagnosis of the model output shows that the oscillatory development is attributed to the discharge and recharge of the pbl moisture and its interaction with convection and circulation the moisture convection feedback regulates the tc development through controlling the atmospheric stratification raindrop induced evaporative cooling and downdraft pbl divergence and vorticity generation on one hand ascending motion associated with deep convection transports moisture upward and le

evolution of multiscale vortices in the development of hurricane dolly 2008 abstract as a follow up to a previously published article on the initial development and genesis of hurricane dolly 2008 this study further examines the evolution of and interactions among multiscale vortices ranging from the system scale main vortex l 150 km to the intermediate scale cloud clusters 50 km l 150 km and individual vorticity rich convective cells l 50 km it is found that there are apparent self similarities among these vortices at different scales each of which may undergo several cycles of alternating accumulation and release of convective available potential energy enhanced surface fluxes below individual cyclonic vortices at each scale contribute to the sustainment and reinvigoration of moist convection that in turn contributes to the maintenance and upscale growth of these vortices spectral analysis of horizontal divergence and relative vorticity further suggests that the cloud cluster scale and system scale vortices are predominantly balanced while the individual

separate tree ring reconstructions of spring and summer moisture in the northern and southern great plains the two most severe droughts to impact the great plains in the twentieth century the 1930s dust bowl and 1950s drought were the result of multiyear moisture deficits during the spring and especially the summer season tree ring reconstructions of the palmer drought severity index indicate similar droughts in magnitude have occurred in previous centuries but these reconstructions do not capture the potential distinct seasonal drought characteristics like those of the 1930s and 1950s separate tree ring reconstructions of the spring and summer z index based on earlywood latewood and adjusted latewood width chronologies have been developed for two regions in the northern and southern great plains of the us the reconstructions extend from 1651 to 1990 and 1698 1990 respectively with instrumental data added from 1991 to 2017 the four reconstructions explain from 39 to 56 of the variance during the 1945 1990 calibration interval and are significantly correlated with independent moisture balance observations during the 1900 1944 validation period the reconstructions reproduce similar seasonal sea surface temperature and 500 mb geopotential height spatial correlation patterns detected with the instrumental data the 1930s is estimated to have been the most extreme decadal summer drought to impact the two regions concurrently in the last few centuries on average spring moisture deficits were more severe during the multidecadal droughts of the mid to late nineteenth century but the timing of drought onset and termination differed between the study regions in the recent two decades the spring moisture balances for the two study regions have largely been opposite and this has been one of the most extreme periods of anti phasing in the last few centuries seasonal moisture reversals are not randomly distributed in time based on the reconstructed estimates and are related to sea surface temperature anomalies in the tropical pacific and to mid tropospheric circulation changes over the north pacific north american sector during may and june

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

simulation and interpretation of the genesis of tropical storm gert 2005 as part of the nasa tropical cloud systems and processes experiment abstract several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones this paper examines high resolution simulations of tropical storm gert 2005 which formed in the gulf of mexico during nasa s tropical cloud systems and processes experiment to investigate the development of low level circulation and its relationship to the precipitation evolution two simulations are examined one that better matches available observations but underpredicts the storm s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm the roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed gert are discussed during 21 25 july two episodes of convective system development occurred in each precipitation system evolution was characterized by i

a numerical study on rapid intensification of typhoon vicente 2012 in the south china sea part ii roles of inner core processes abstractin part i of this study the role of environmental monsoon flow in the onset of rapid intensification ri of typhoon vicente 2012 was discussed in this part ii key inner core processes that effectively resist environmental vertical wind shear during ri onset are investigated the convective precipitation shield cps embedded in the downshear convergence zone plays a vital role in preconditioning the tropical cyclone tc vortex before ri the cps induces a mesoscale positive vorticity band pvb characterized by vortical hot tower structures upstream and shallower structures 4 km downstream multiple mesovortices form successively along the pvb and are detached from the pvb at its downstream end rotating cyclonically around the tc center the sufficient amount of vorticity anomalies in the pvb facilitates the upscale growth of a mesovortex into a reformed inner vortex which eventually replaces the parent tc vortex i e downshear reformation leading to ri onset the timing of downshe

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