core mantle boundary shape constraints inferred from the pressure torque acting between the core and the mantle summary in the last few years models of the flow at the top of the earth s core and of the related pressure field have been calculated from the secular variation of the geomagnetic field and core mantle topographies have been computed by seismologists a pressure torque results from the action of the pressure field on the core topography which can theoretically be computed from models of both the pressure field and the core mantle interface small scale features of the flow and of the topography are shown to be capable of contributing strongly to the pressure torque it is thus impossible to calculate the exact value of the torque from the knowledge of only the long wavelength components of the models but the interaction between the large scale components generates by itself torques two orders of magnitude larger than the torques inferred from the irregularities of the length of the day it is nevertheless possible to reconcile the topographic coupling mechanism with the length of the day observations keeping the amplitude of the core topography proposed by seismologists if an orthogonality relation between the geometry of the fluid upwellings and downwellings at the top of the core and the topography is satisfied it is shown how to compute such a topography for a given flow and close to an original topography provided by seismic tomography some consequences of the so inferred link between the fluid flow at the top of the core and the core mantle boundary topography are discussed

rapidly intensifying hurricane guillermo 1997 part i low wavenumber structure and evolution abstract the structure and evolution of rapidly intensifying hurricane guillermo 1997 is examined using airborne doppler radar observations in this first part the low azimuthal wavenumber component of the vortex is presented guillermo s intensification occurred in an environmental flow with 7 8 m s 1 of deep layer vertical shear as a consequence of the persistent vertical shear forcing of the vortex convection was observed primarily in the downshear left quadrant of the storm the greatest intensification during the 6 h doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left of shear semicircle of the eyewall some of the strongest convective bursts were triggered by azimuthally propagating low wavenumber vorticity asymmetries mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to guillermo s structural evol

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

multiscale structure and evolution of hurricane earl 2010 during rapid intensification abstractthe structure and evolution of hurricane earl 2010 during its rapid intensification as sampled by aircraft is studied here rapid intensification occurs in two stages during the early stage covering 24 h earl was a tropical storm experiencing moderate northeasterly shear with an asymmetric distribution of convection and the symmetric structure was shallow broad and diffuse the upper level circulation center was significantly displaced from the lower level circulation at the beginning of this stage deep vigorous convection termed convective bursts was located on the east side of the storm and appeared to play a role in positioning the upper level cyclonic circulation center above the low level center by the end of this stage the vortex was aligned and extended over a deep layer and rapid intensification began during the late stage rapid intensification continued as earl intensified 20 m s 1 during the next 24 h the vortex remained aligned in the presence of weaker vertical shear

distributions of shallow to very deep precipitation convection in rapidly intensifying tropical cyclones abstractshear relative distributions of four types of precipitation convection in tropical cyclones tcs are statistically analyzed using 14 years of tropical rainfall measuring mission trmm precipitation radar pr data the dataset of 1139 trmm pr overpasses of tropical storms through category 2 hurricanes over global tc prone basins is divided by future 24 h intensity change it is found that increased and widespread shallow precipitation defined as where the 20 dbz radar echo height 6 km around the storm center is a first sign of rapid intensification ri and could be used as a predictor of the onset of ri the contribution to total volumetric rain and latent heating from shallow and moderate precipitation 20 dbz echo height between 6 and 10 km in the inner core is greater in ri storms than in non ri storms while the opposite is true for moderately deep 20 dbz echo height between 10 and 14 km and very deep precipitation 20 dbz echo height 14 km the authors argue that ri is more likely

azimuthal distribution of deep convection environmental factors and tropical cyclone rapid intensification a perspective from hwrf ensemble forecasts of hurricane edouard 2014 abstractforecasts from the operational hurricane weather research and forecasting hwrf based ensemble prediction system for hurricane edouard 2014 are analyzed to study the differences in both the tropical cyclone inner core structure and large scale environment between rapidly intensifying ri and non intensifying ni ensemble members an analysis of the innercore structure reveals that as deep convection wraps around from the downshear side of the storm to the upshear left quadrant for ri members vortex tilt and asymmetry reduce rapidly and ri occurs for ni members deep convection stays trapped in the downshear downshear right quandrant and storms do not intensify the budget calculation of tangential wind tendency reveals that the positive radial eddy vorticity flux for ri members contributes significantly to spinning up the tangential wind in the middle and upper levels and reduces vortex tilt the negative eddy vorticity flux for ni members spins down the tangential wind in the middle and u

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

airborne doppler observations of the inner core structural differences between intensifying and steady state tropical cyclones abstractdifferences in the inner core structure of intensifying in intensity increase of at least 20 kt 24 h 1 where 1 kt 0 51 m s 1 and steady state ss intensity remaining between 10 kt 24 h 1 tropical cyclones tcs are examined using composites of airborne doppler observations collected from noaa p 3 aircraft missions the in dataset contains 40 eyewall passes from 14 separate missions while the ss dataset contains 53 eyewall passes from 14 separate missions intensifying tcs have a ringlike vorticity structure inside the radius of maximum wind rmw lower vorticity in the outer core a deeper stronger inflow layer and stronger axisymmetric eyewall upward motion compared with steady state tcs there is little difference in the vortex tilt between 2 and 7 km and both in and ss tcs show an eyewall precipitation and updraft asymmetry whose maxima are located in the downshear and downshear left region the azimuthal coverage of eyewall and outer core precipitation is greater for in tcs

variations of the earth s figure axis from satellite laser ranging and grace 1 satellite laser ranging slr data were used to determine the variations in the earth s principal figure axis represented by the degree 2 and order 1 geopotential coefficients c21 and s21 significant variations at the annual and chandler wobble frequencies appear in the slr time series when the rotational deformation or pole tides i e the solid earth and ocean pole tides were not modeled the contribution of the ocean pole tide is estimated to be only 8 of the total annual variations in the normalized coefficients based on the analysis of slr data the amplitude of the nontidal annual variation of is only 30 of from the slr time series the estimates of the annual variation in from slr the gravity recovery and climate experiment grace and polar motion excitation function are in a good agreement the nature of the linear trend for the earth s figure axis determined by these techniques during the last several years is in general agreement but does not agree as well with results predicted from current glacial isostatic adjustment gia models the fluid love number for the earth is estimated to be 0 9 based on the position of the mean figure axis from the grace gravity model ggm03s and the mean pole defined by the iers 2003 conventions the estimate of from grace and slr provides an improved constraint on the relative rotation of the core the results presented here indicate a possible tilt of the inner core figure axis of 2 and 3 arc sec displacement for the figure axis of the entire core

low wavenumber structure and evolution of the hurricane inner core observed by airborne dual doppler radar abstract the asymmetric dynamics of the hurricane inner core region is examined through a novel analysis of high temporal resolution three dimensional wind fields derived from airborne dual doppler radar seven consecutive composites of hurricane olivia s 1994 wind field with 30 min time resolution depict a weakening storm undergoing substantial structural changes the symmetric and asymmetric mechanisms involved in this transformation are considered separately to zeroth order the weakening of the primary circulation is consistent with the axisymmetric vortex spindown theory of eliassen and lystad for a neutrally stratified atmosphere vertical shear however increased dramatically during the observation period leading to a strong projection of the convection onto an azimuthal wavenumber 1 pattern oriented along the maximum vertical shear vector recent theoretical ideas elucidating the dynamics of vortices in vertical shear are used to help explain this asymmetry the role of asymmetric vorticity d

the relationship between storm motion vertical wind shear and convective asymmetries in tropical cyclones abstract the influence of the direction of storm motion on the azimuthal distribution of electrified convection in 35 atlantic basin tropical cyclones from 1985 to 1999 was examined using data from the national lightning detection network in the inner 100 km flashes most often occurred in the front half of storms with a preference for the right front quadrant in the outer rainbands r 100 300 km flashes occurred predominantly to the right of motion although the maximum remained in the right front quadrant the results are shown to be consistent with previous studies of asymmetries in rainfall radar reflectivity and vertical motion with respect to tropical cyclone motion the motion effect has been attributed to the influence of asymmetric friction in the tropical cyclone boundary layer the authors previously found a strong signature in the azimuthal distribution of lightning with respect to vertical wind shear because both effects show clearly vertical wind shear and storm motion must themse

how does hurricane edouard 2014 evolve toward symmetry before rapid intensification a high resolution ensemble study abstracta 14 member high resolution ensemble of edouard 2014 a moderately sheared tropical storm that underwent rapid intensification ri is used to determine causes of vortex alignment and pr

quadrant distribution of tropical cyclone inner core kinematics in relation to environmental shear abstractairborne doppler radar data collected in tropical cyclones by national oceanic and atmospheric administration wp 3d aircraft over an 8 yr period 2003 10 are used to statistically analyze the vertical structure of tropical cyclone eyewalls with reference to the deep layer shear convective evolution within the inner core conforms to patterns shown by previous studies convection initiates downshear right intensifies downshear left and weakens upshear analysis of the vertical distribution of radar reflectivity and vertical air motion indicates the development of upper level downdrafts in conjunction with strong convection downshear left and a maximum in frequency upshear left intense updrafts and downdrafts both conform to the shear asymmetry pattern while strong updrafts occur in the eyewall intense downdrafts show far more radial variability particularly in the upshear left quadrant though they concentrate along the eyewall edges strong updrafts are collocated with low level inflow and

limits on lateral pressure gradients in the outer core from geodetic observations abstract lateral variations in pressure associated with flow at the core mantle boundary will produce deformations of the mantle it is shown here that geostrophically plausible pressure gradients are sufficient to produce measurable changes in the length of day polar motion j2 sea level tilt gravity and strain of these polar motion is the most discriminating and limits intra annual variations in the lateral pressure field at planetary wavelength to less than 104 pa satellite observations of changes in j2 are potentially even more useful however at present the time span of observations is short and the separation of a residual which might be due to a change in the distribution of pressure at the core mantle boundary from other causes such as post glacial rebound is ambiguous it is suggested that not more than 10 of the decade variations in the length of day may be caused by pressure fluctuations at the core mantle boundary

idealized tropical cyclone responses to the height and depth of environmental vertical wind shear abstractthree sets of idealized cloud resolving simulations are performed to investigate the sensitivity of tropical cyclone tc structure and intensity to the height and depth of environmental vertical wind shear in the first two sets of simulations shear height and depth are varied independently in the third set orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis despite all simulations having the same westerly deep layer 200 850 hpa shear of 10 m s 1 different intensity and structural evolutions are observed suggesting the deep layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on tcs in general vertical wind shear that is shallower and lower in the troposphere is more destructive to model tcs because it tilts the tc vortex farther into the downshear left quadrant the vortices that tilt the most are unable to precess upshear and realign resulting in their failure to intensify shear height appears to

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

an expanded dataset of hurricane eyewall sizes and slopes abstractusing airborne doppler radar data from 39 flights into hurricanes from 2004 to 2010 the authors examine the outward slope of the eyewall revisiting the recent studies of stern and nolan the slope of the radius of maximum winds rmw is found to increase nearly linearly with size and is uncorrelated with intensity the slope of the eyewall absolute angular momentum surface m increases with increasing size strong correlation and decreases with increasing intensity weak to moderate correlation two other measures of eyewall slope are also investigated the 20 dbz reflectivity isosurface dbz20 and the radius of maximum azimuthal mean updraft rwmax the slopes of both dbz20 and rwmax increase with their size the slope of dbz20 decreases with intensity though the correlation is weak while the slope of rwmax is uncorrelated with intensity the absolute angular momentum decreases on average along the rmw by 9 from 2 to 8 km heights with this larger dataset the previous results are genera

fluid flow near the surface of earth s outer core maps of the fluid flow at the core surface are important for a number of reasons foremost they may provide some insight into the workings of the geodynamo and may place useful constraints on geodynamo models from the flow the force balance at the top of the core can at least in part be deduced the flow can provide short term predictions of the secular variation the flow is important in understanding changes in the length of day and constraints on lateral temperature variations and topography at the core mantle boundary may be derived unlike the case of mantle convection only very small lateral variations in core density are required to drive the flow these density variations are too small by several orders of magnitude to be imaged seismically so instead we use the geomagnetic secular variation to infer the flow despite considerable recent progress in mapping the core flow substantial differences exist between maps produced by different researchers here we examine the possible underlying reasons for these differences paying particular attention to the inherent problems of nonuniqueness we focus on the aspects of the flow which do seem to be well determined and discuss their geophysical implications

the rotation of the earth earth rotation studies are reviewed for the 1987 1990 time period it is noted that the emphasis in these studies has shifted from improvements in the observational techniques to interpreting and gaining greater understanding of the variations of the earth rotations there have been progressive improvements in the accuracy and the temporal resolution of earth rotation measurements

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

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

buoyancy of convective vertical motions in the inner core of intense hurricanes part ii case studies abstract this is the second of two papers on the buoyancy of convective vertical motions in the inner core of intense hurricanes this paper uses extensive airborne radar dropwindsonde and flight level observations in hurricanes guillermo 1997 and georges 1998 to illustrate typical azimuthal distribution of buoyant convection and demonstrate that the low level eye can be an important source region for buoyant eyewall convection in both hurricanes eyewall vertical velocity and radar reflectivity are asymmetric and exhibit persistent relationships with the direction of the environmental vertical wind shear mesoscale vertical motions exhibit a wavenumber 1 structure with maximum ascent downshear and weak descent upshear the mesoscale reflectivity maxima are located left of shear buoyant eyewall updraft cores and transient convective scale reflectivity cells are predominantly downshear and left of shear most eyewall downdraft cores that transport significant mass downward are located upshear nega

the relationship between spatial variations in the structure of convective bursts and tropical cyclone intensification as determined by airborne doppler radar abstractthe relationship between radial and azimuthal variations in the composite characteristics of convective bursts cbs that is regions of the most intense upward motion in tropical cyclones

rapidly intensifying hurricane guillermo 1997 part ii resilience in shear this paper examines the structure and evolution of a mature tropical cyclone in vertical wind shear vws using airborne doppler radar observations of hurricane guillermo 1997 in part i the modulation of eyewall convection via the rotation of vorticity asymmetries through the downshear left quadrant was documented during rapid intensification here the focus is on the relationship between vws vortex tilt and associated asymmetry within the tropical cyclone core region during two separate observation periods a method for estimating local vws and vortex tilt from radar datasets is further developed and the resulting verticalstructureanditsevolutionaresubjectedtostatisticalconfidencetests guillermowasahighlyresilient vortex evidenced by its small tilt magnitude relative to the horizontal scale of the vortex core the deep layer tilt was statistically significant oriented on average 608 left of shear large scale vorticity and thermal asymmetries oriented along the tilt direction support a response of guillermo to shear forcing that is consistent with balanced dynamics the time averaged vertical motion asymmetry within the eyewall exhibited maximum ascent values 408 left of the deep layer shear or in this case right of the deep layer tilt the observation based analysis of guillermo s interaction with vws confirms findings of recent theoretical and numerical studies and serves as the basis for a more comprehensive investigation of vws and tropical cyclone intensity change using a recently constructed multistorm database of doppler radar analyses

vertical structure of hurricane eyewalls as seen by the trmm precipitation radar abstractstatistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones shown by the tropical rainfall measurement mission trmm precipitation radar pr shows that the eyewall contains high reflectivities and high echo tops with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure the overall echo strength height of echo top and presence of intense echo perturbations all increase with vortex strength intense echo perturbations decrease in frequency with low sea surface temperatures when the pr data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear the nature of convective processes in different parts of the eyewall becomes apparent the normalized statistics of the echo intensity brightband structure and maximum echo top height show that processes generating convective precipitation are generally favored in the dow

a statistical perspective on wind profiles and vertical wind shear in tropical cyclone environments of the northern hemisphere abstracta statistical analysis of tropical cyclone tc environmental wind profiles is conducted in order to better understand how vertical wind shear influences tc intensity change the wind profiles are computed from global atmospheric reanalyses around the best track locations of 7554 tc cases in the northern hemisphere tropics mean wind profiles within each basin exhibit significant differences in the magnitude and direction of vertical wind shear comparisons between tc environments and randomly selected non tc environments highlight the synoptic regimes that support tcs in each basin which are often characterized by weaker deep layer shear because weaker deep layer shear may not be the only aspect of the environmental flow that makes a tc environment more favorable for tcs two new parameters are developed to describe the height and depth of vertical shear distributions of these parameters indicate that in both tc and non tc environments vertical shear most frequently occurs in shallow layer

a lagrangian trajectory view on transport and mixing processes between the eye eyewall and environment using a high resolution simulation of hurricane bonnie 1998 the transport and mixing characteristics of a large sample of air parcels within a mature and vertically sheared hurricane vortex are examined data from a high resolution 2 km horizontal grid spacing numerical simulation of real case hurricane bonnie 1998 are used to calculate lagrangian trajectories of air parcels in various subdomains of the hurricane namely the eye eyewall and near environment to study the degree of interaction transport and mixing between these subdomains it is found that 1 there is transport and mixing from the low level eye to the eyewall that carries air possessing relatively high values of equivalent potential temperature e which can enhance the efficiency of the hurricane heat engine 2 a portion of the low level inflow of the hurricane bypasses the eyewall to enter the eye and this air both replaces the mass of the low level eye and lingers for a sufficient time order 1 h to acquire enhanced entropy characteristics through interaction with the ocean beneath the eye 3 air in the mid to upper level eye is exchanged with the eyewall such that more than half the air of the eye is exchanged i n5hi nthis case of a sheared hurricane and 4 that one fifth of the mass in the eyewall at a height of 5 km has an origin in the mid to upper level environment where e is much less than in the eyewall which ventilates the ensemble average eyewall e by about 1 k implications of these findings for the problem of hurricane intensity forecasting are briefly discussed

the dynamics of intensification in a hurricane weather research and forecasting simulation of hurricane earl 2010 we use a high resolution numerical simulation of atlantic hurricane earl 2010 to increase our understanding of earl s intensification in relatively strong vertical shear in the context of a recent paradigm for tropical cyclone intensification the integrity of the simulation is judged by comparing analyses thereof with those of the unprecedented observational data gathered in earl consistent with the classical view of spin up the amplification of the tangential wind field above the boundary layer is found to occur as the absolute angular momentumsurfaces are drawn inwards by the aggregate heating of the rotating convective clouds in the interior of the vortex in addition to this classical pathway spin up occurs within the inner core boundary layer where the maximum tangential winds occur the latter is another element of the new paradigm despite the detrimental influence of the shear on the vortex alignment and on depressing the pseudo equivalent potential temperature outside the developing eyewall the combined eddy processes associated with the vortical plume structures in and around the developing eyewall region are shown to contribute to an enhanced overturning circulation and an intensifying storm these eddy processes are distinctly agradient effects that are not features of the classical spin up mechanism it remains to be understood how the rotating convective updraughts combine to produce the diagnosed structures of the eddy terms themselves and how vortex rossby waves and other eddies contribute to the alignment of the vortex during intensification

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

structural changes preceding rapid intensification in tropical cyclones as shown in a large ensemble of idealized simulations abstractstructural changes that precede rapid intensification ri of tropical cyclones tcs are examined in a full physics model by conducting a large ensemble 270 of idealized tc simulations the processes leading to ri in a representative case with moderate shear are consistent with previous studies for weakly sheared cases the most distinct changes are that the vortex tilt and the vortex size begin to decrease more rapidly 6 h before the onset of ri a vorticity budget analysis for the upper layer around the low level center reveals that the vertical vorticity is increased by vertical advection stretching and tilting terms before ri whereas the horizontal advection is small thus the upright vortex structure is not achieved through a vortex alignment process but rather is built upward by deep convection the ensemble simulations are generated by changing the intensity and size of the initial vortex the magnitude of vertical wind shear and the translation speed the ensemble members that show

the earth s c21 and s21 gravity coefficients and the rotation of the core summary observational results for the earth s c21 and s21 gravity coefficients can be used to constrain the mean equatorial rotation of the core with respect to the mantle current satellite gravity solutions suggest the equatorial rotation rate is no larger than 1 x 10 7 times the earth s diurnal spin rate a limit more than one order of magnitude smaller than the polar rotation rate inferred from the westward drift of the earth s magnetic field the next generation gravity solutions should improve this constraint by more than one order of magnitude implications for the fluid pressure at the core mantle boundary and for the shape of that boundary are discussed

decay of polar cap patch 1 we report an event in which a polar cap patch was detected with an all sky imager asi at resolute bay canada 74 73 n 265 07 e aacgm latitude 82 9 on the nightside the patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the asi for more than 1 h when the patch stagnated its luminosity decreased gradually which allows us to investigate how the patch plasma decayed in a quantitative manner the decay of the patch can be quantitatively explained by the loss through recombinations of o with ambient n2 and o2 molecules if we assume the altitude of the optical patch to be around 295 km the derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the msis e90 and iri 2007 models indicating that climatological models such as iri are not suitable for describing the actual density profile of patches this is probably because the loss process was much faster in the lower altitude part of the patch thus the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the f region this suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap such information is important when we compare the optical data with other instruments such as coherent radars and gps scintillation measurements by mapping the all sky image on the geographic coordinate system with an assumption of the patch emission altitude

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

observations of the structure and evolution of hurricane edouard 2014 during intensity change part ii kinematic structure and the distribution of deep convection abstractthe structural evolution of the inner core and near environment throughout the life cycle of hurricane edouard 2014 is examined using a synthesis of airborne and satellite measurements this study specifically focuses on differences in the distribution of deep convection during two periods when edouard intensified toward hurricane status and when edouard peaked in intensity and began to weaken while both periods saw precipitation maximized in the downshear left and upshear left quadrants deep convection was only seen from the aircraft during the intensifying period deep convection was located farther inside the radius of maximum winds rmw during the intensifying period than the weakening period this convection is traced to strong updrafts inside the rmw in the downshear right quadrant tied to strong low level convergence and high convective available potential energy cape as the storm remained over warm water in a moist environment strong updrafts persisted upshear left and were collo

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

environmental flow impacts on tropical cyclone structure diagnosed from airborne doppler radar composites abstractfollowing a recent demonstration of multicase compositing of axisymmetric tropical cyclone tc structure derived from airborne doppler radar measurements the authors extend the analysis to the asymmetric structure using an unprecedented database from 75 tc flights in particular they examine the precipitation and kinematic asymmetry forced by the tc s motion and interaction with vertical wind shear for the first time they quantify the average magnitude and phase of the three dimensional shear relative kinematic asymmetry of observed tcs through a composite approach the composite analysis confirms principal features of the shear relative tc asymmetry documented in prior numerical and observational studies e g downshear tilt downshear right convective initiation and a downshear left precipitation maximum the statistical significance of the composite shear relative structure is demonstrated through a stratification of cases by shear magnitude the impact of storm motion on eyewall convect

convective bursts downdraft cooling and boundary layer recovery in a sheared tropical storm abstracttropical storm edouard 2002 experienced episodic outbreaks of convection downshear within the storm core in the presence of 11 15 m s 1 of ambient vertical wind shear these outbreaks lasted 2 6 h and were followed by long periods with no deep convection flights from u s air force reconnaissance aircraft within the boundary layer were used to investigate the cause of one such oscillation low equivalent potential temperature e air filled the boundary layer as convection ceased creating a 4 6 k deficit in e within the convective region soundings within 110 km of the center were supportive of convective downdrafts with midlevel relative humidity below 15 and large downdraft cape deep convection ceased within 75 km of the center for more than 8 h tangential velocity reached hurricane force locally during the convective outbreak then became nearly symmetric after convection stopped arguably as a result of axisymmetrization and the storm weakened nevertheless the corresponding lack of

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

evaluation of tropical cyclone center identification methods in numerical models abstractidentifying the center of a tropical cyclone in a high resolution model simulation has a number of operational and research applications including constructing a track calculating azimuthal means and perturbations and diagnosing vortex tilt this study evaluated several tropical cyclone center identification methods in a high resolution weather research and forecasting wrf model simulation of a sheared intensifying asymmetric tropical cyclone the simulated tropical cyclone tc contained downshear convective cells and a mesovortex embedded in a broader tc vortex complicating the identification of the tc vortex center it is shown that unlike other methods the pressure centroid method consistently 1 placed the tc center within the region of weak storm relative wind 2 produced a smooth track 3 yielded a vortex tilt that varied smoothly in magnitude and direction and 4 was insensitive to changes in horizontal grid resolution based on these results the authors recommend using the pr

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

the convective evolution and rapid intensification of hurricane earl 2010 abstractthe relationship between an inner core r 100 km lightning outbreak and the subsequent rapid intensification ri of hurricane earl 2010 is examined using lightning strikes recorded by the world wide lightning location network wwlln and in situ observations from various aircraft missions moderate 8 4 m s 1 northeasterly deep layer 850 200 hpa vertical wind shear caused by outflow from hurricane danielle existed over earl at the beginning of a prolonged period of ri over 70 of the lightning strikes within a 500 km radius occurred downshear with a preference toward downshear right in the outer rainbands in agreement with previous studies the location of inner core strikes in earl differed markedly from previous studies the inner core lightning activity precessed from left of shear to upshear an extremely rare event beginning just prior to the onset of ri diagnosis of the vortex tilt midway through the lightning precession showed this convection was occurring downtilt in the ups