concentric eyewall formation in typhoon sinlaku 2008 part iii horizontal momentum budget analyses abstract this is a follow up work to two prior studies examining secondary eyewall formation sef in typhoon sinlaku 2008 this study shows that in the sef region the majority of the elevated

rapid filamentation zones in intense tropical cyclones intense tropical cyclones often possess relatively little convection around their cores in radar composites this surrounding region is usually echo free or contains light stratiform precipitation while subsidence is typically quite pronounced in this region it is not the only mechanism suppressing convection another possible mechanism leading to weak echo moats is presented in this paper the basic idea is that the strain dominated flow surrounding an intense vortex core creates an unfavorable environment for sustained deep moist convection strain dominated regions of a tropical cyclone can be distinguished from rotationdominated regions by the sign of s 2 s 2 2 where s1 ux y and s2 x uy are the rates of strain and x uy is the relative vorticity within the radius of maximum tangential wind the flow tends to be rotation dominated 2 s 2 s 2 so that coherent structures such as mesovortices can survive for long periods of time outside the radius of maximum tangential wind the flow tends to be strain dominated s 2 s 2 2 resulting in filaments of anomalous vorticity in the regions of strain dominated flow the filamentation time is defined as fil 2 s 2 s 2 2 1 2 in a tropical cyclone an approximately 30 kmwide annular region can exist just outside the radius of maximum tangential wind where fil is less than 30 min and even as small as 5 min this region is defined as the rapid filamentation zone since the time scale for deep moist convective overturning is approximately 30 min deep convection can be significantly distorted and even suppressed in the rapid filamentation zone a nondivergent barotropic model illustrates the effects of rapid filamentation zones in category 1 5 hurricanes and demonstrates the evolution of such zones during binary vortex interaction and mesovortex formation from a thin annular ring of enhanced vorticity

spectral optical backscatter of sand in suspension effects of particle size composition and colour abstract optical backscatter sensors obs have been used to estimate in situ concentrations of suspended particulate matter spm in aquatic systems for about 20 years the logical next step is to use the differential responses to varying sizes and composition of the particles across a range of wavelengths to characterize discrete mixtures of sediments to do this we examined the response of the backscatter coefficients in the optical range 442 671 nm to defined mixtures of suspended quartz and carbonate sands in a turbulent jet we found positive linear responses of the backscatter coefficient to the amount of suspended sand at all wavelengths the regressions differed among the wavelengths for mixture constituents but analyses of error propagation indicated that concentration prediction using mixture component calibration curves was problematic when the colour of the sand was changed the response of backscatter to concentration at some of the wavelengths changed and errors in prediction of mixture concentration were low thus the differential optical backscatter response of sediment components can provide a means to estimate suspended sediment concentrations in the field from individual calibration equations when the components are different colours under certain conditions this approach can be used as an alternative to the traditional calibration procedure which uses sediment collected from the sampling site during the obs measurements

the concentric eyewall cycle of hurricane gilbert abstract hurricane gilbert of 1988 formed an outer eyewall as it intensified rapidly toward a record minimum pressure of 888 hpa in the western caribbean the outer eyewall strengthened and contracted while the inner eyewall showed some signs of weakening before landfall on the yucatan peninsula remarkably both eyewalls survived passage over land but the storm was much weaker when it entered the gulf of mexico although the primary cause of weakening was passage over land the effect of the contracting outer eyewall may have contributed later the outer eyewall completely replaced the inner eyewall subsequently it contracted steadily but slowly as gilbert maintained nearly constant intensity over the cooler waters of the gulf before final landfall on the mainland of mexico

secondary eyewall formation in an idealized tropical cyclone simulation balanced and unbalanced dynamics abstractthe secondary eyewall formation sef in an idealized simulation of a tropical cyclone tc is examined from the perspective of both the balanced and unbalanced dynamics and through the tangential wind vt budget analysis it is found that the expansion of the azimuthal mean vt above the boundary layer occurs prior to the development of radial moisture convergence in the boundary layer the vt expansion results primarily from the inward angular momentum transport by the mid to lower tropospheric inflow induced by both convective and stratiform heating in the spiral rainbands in response to the vt broadening is the development of radial inflow convergence and the supergradient flow near the top of the inflow boundary layer results from the vt budget analysis show that the combined effect of the mean advection and the surface friction is to spin down vt in the boundary layer while the eddy processes eddy radial and vertical advection contribute positively to the spinup of vt in the sef region

acoustic inversions for measuring boundary layer suspended sediment processes although sound has been applied to the study of sediment transport processes for a number of years it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters in particular when the attenuation due to the suspension becomes significant the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension to study this attenuation propagation problem numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters the results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters which become increasingly erroneous with range as the sound propagates through the suspension to address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion this approach is not subject to the accumulation of errors and has an explicit solution here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion

seasonal variations of high latitude field aligned currents inferred from orsted and magsat observations 1 in this paper we report on field aligned currents inferred from high precision three component geomagnetic field observations made on board the danish satellite orsted over polar regions because of a slow drift in local time of the satellite orbit through the noon midnight sector we were able to study the seasonal dependence of the dynamic properties of the dayside and nightside field aligned current systems over the northern and southern hemispheres we find an average over the pole distance between dayside and nightside currents of 32 during summer but 37 during winter and 36 during equinox the decrease in the size of the summer polar cap is caused by a shift of both daytime and nighttime current systems to higher magnetic latitudes for comparison the dawn dusk cross polar distance of the region 1 region 2 field aligned currents has been determined from high precision data observed by magsat a satellite flown in 1979 1980 in a dawn dusk orbit the latter results show that the dawn dusk distance between r1 r2 currents exhibits little seasonal dependence and amounts to 34 for all seasons in both polar caps the seasonal dependence is confirmed for the high latitude field aligned intensities they are larger by a factor of 1 5 1 8 in the sunlit summer polar cap in comparison with the winter hemisphere our results suggest that the r1 r2 and dayside field aligned currents are well balanced between the pairs of downward upward currents for all seasons as well as between hemispheres during equinox we were not able to confirm results reported in earlier studies that the net currents tend to increase with an enhancement of ionospheric conductivity caused by the solar illumination or substorm activity

a numerical study of the genesis of concentric eyewalls in hurricanes we use two axisymmetric numerical models to explore the dynamics of concentric eyewalls in hurricanes the first is a simple two layer model using balanced dynamics and parametrized convection while the second is a cloud resolving non hydrostatic model in the case of the balanced model infinitesimal disturbances amplify into secondary eyewalls provided the lower troposphere is sufficiently moist otherwise finite amplitude perturbations are necessary to initiate amplifying structures but experiments with the full physics model show that finite amplitude disturbances are always necessary to initiate secondary eyewalls regardless of the initial humidity of the lower troposphere experiments with both models in which the surface wind is held constant in the surface flux formulations fail to develop secondary eyewalls demonstrating that in these models the disturbances once initiated grow through the wind induced surface heat exchange wishe mechanism based on this work we hypothesize that real secondary eyewalls result from a finite amplitude wishe instability triggered by external forcing such as interaction of the tropical cyclone with baroclinic eddies topography or local perturbations in sea surface temperature copyright 2003 royal meteorological society

rapid filamentation zone in a numerically simulated tropical cyclone abstract in a recent study rozoff et al proposed a possible mechanism to explain the formation and maintenance of the weak echo annulus or moat outside of the primary eyewall of a tropical cyclone observed in radar images by this mechanism the moat is determined to be a region of the strain dominated flow outside of the radius of maximum wind in which essentially all fields are filamented and deep convection is hypothesized to be highly distorted and even suppressed this strain dominated region is defined as the rapid filamentation zone wherein the filamentation time is shorter than the overturning time of deep convection an attempt has been made in this study to test the hypothesis in a full physics tropical cyclone model under idealized conditions and to extend the concept to the study of the inner core dynamics of tropical cyclones the foci of this paper are the evolution of the rapid filamentation zone during the storm intensification the potential roles of rapid filamentation in the organiz

a laboratory evaluation of optical backscatterance suspended solids sensors exposed to sand mud mixtures abstract optical suspended solids sensors were studied in the laboratory in order to obtain calibration factors and evaluate the general behavior of the instrument when exposed to suspensions of mud and sand the sensors were found to be capable of measuring the time averaged concentration of either suspended sand or suspended mud but the relative sensitivity of the sensor to these two different types of sediment varied by approximately an order of magnitude in mixtures with a constant or known mud concentration the instrument response to the mud may be treated as an offset and gains appropriate to sand may be used to estimate the suspended sand concentrations semi quantitative observations of the effects of flow direction relative to sensor orientation indicate that significant concern is warranted

on the dynamics of the secondary eyewall genesis in hurricane wilma 2005 1 the weather research and forecast model is used to simulate the secondary eyewall genesis seg and evolution in hurricane wilma 2005 the structure and time evolution of the secondary eyewall are well captured the theory of empirical normal modes is then applied to study the seg for azimuthal wavenumber 1 anomalies the wave activity spectra indicate that the leading modes 1 and 2 are vortex rossby waves vrws the eliassen palm ep theorem is used to diagnose the impact of the propagating waves on the formation of the secondary eyewall analysis of the ep flux and its time mean divergence show that in the lower troposphere the vrws propagate outward outside the primary eyewall the fact that the critical radius of the leading modes is located close to the region where the secondary eyewall eventually develops suggests that vrws play an important role in seg

comments on convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstractin a previous paper judt and chen propose that secondary eyewall formation can be the result of the accumulation of convectively generated potential vorticity in the rainbands they argue that secondary potential vorticity maxima precede the development of the secondary wind maximum and conclude that vortex rossby waves do not contribute to the formation of the secondary eyewall amidst examination of their thought provoking study some questions arose regarding their methodology interpretation and portrayal of previous literature here the authors inquire about aspects of the methodology for diagnosing vortex rossby waves and assessing their impact on their simulation inaccuracies in the literature review are noted and further analysis of existing three dimensional full physics numerical hurricane integrations that exhibit canonical secondary eyewalls are encouraged

seasonal and diurnal variations in ampere observations of the birkeland currents compared to modeled results we reduce measurements made by the active magnetosphere and planetary electrodynamics response experiment ampere to give the total birkeland field aligned current flowing in both hemispheres in monthly and hourly bins we analyze these totals using 6 years of data 2010 2015 to examine solar zenith angle driven variations in the total birkeland current flowing in both hemispheres simultaneously for the first time a diurnal variation is identified in the total birkeland current flowing consistent with variations in the solar zenith angle a seasonal variation is also identified with more current flowing in the northern southern hemisphere during bartels rotations in northern southern summer for months close to equinox more current is found to flow in the northern hemisphere contrary to our expectations we also conduct the first test of the milan 2013 model for estimating birkeland current magnitudes with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the birkeland currents with season and time of day the modified model using the value of d averaged by bartels rotation scaled by 1 7 is found to agree with the observed ampere currents with a correlation of 0 87 in the northern hemisphere and 0 86 in the southern hemisphere the improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model the correlation of the residuals is found to be consistent with more current flowing in the northern hemisphere this new observation of systematically larger current flowing in the northern hemisphere is discussed in the context of previous results which suggest that the northern hemisphere may react more strongly to dayside reconnection than the southern hemisphere

observations of internal tides off the coast of shandong peninsula china abstract bottom mounted platforms equipped with current profilers meters temperature salinity and turbidity sensors were deployed for about 10 days in august 2017 over an elongated deposit off the coast of shandong peninsula in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer in total semidiurnal barotropic tides dominate the measured currents accounting for 90 of total variance however in the cross shore direction greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents both the empirical orthogonal functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode 1 internal tides i e the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle although the bottom slope is subcritical in most area of the deposit the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0 5 suitable for local internal tide generation the internal tides generated from the deposit are especially significant considering that the shelf of the yellow sea is usually broad and flat the quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides 6 44 10 4 m3 s 3 is greater than the internal tides 0 95 10 4 m3 s 3 and the total dissipation rate due to bottom drag is 5 49 10 4 m3 s 3 which is much greater than the interior one due to internal tides 2 69 10 4 m3 s 3 the internal tidal current alone is not energetic enough to resuspend the local fine grained sediments however in the cross shore direction the sediment flux due to internal tides is twice as much as the barotropic component resulting in a net onshore sediment flux thus highlighting the advection effect of internal tides in the coastal mass transport

new instrumentation for the investigation of sediment suspension processes in the shallow marine environment abstract an instrumentation system has been developed that continuously measures flow velocity water depth and suspended sediment concentration profiles in the nearshore zone the system consists of four components 1 an array of electronic sensors including an electromagnetic current meter a surface piercing resistance wave gauge and a five element array of optical back scatterance sensors 2 a signal processing electronics unit 3 a guyed mast support structure and 4 a data acquisition system the small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves 2 m results from an experiment on an exposed ocean beach on the coast of washington u s a indicate that sand suspension events of long duration 15 40 sec relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift work is now in progress to modify the system for self contained operation on the continental shelf field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation

the 1991 coccolithophore bloom in the central north atlantic 1 optical properties and factors affecting their distribution optical scattering and absorption were measured in the central north atlantic ocean during a mesoscale bloom of the coccolithophorid emiliania huxleyi the chlorophyll specific absorption was similar to previously measured levels for this species in laboratory cultures suspended coccoliths were responsible for 80 of the total backscattering in the center of the bloom and the greatest calcite dependent backscattering was observed just below the base of the mixed layer areal maps of calcite dependent backscattering and reflectance were similar because of the dominance of backscattering over absorption calculated reflectance at 440 and 550 nm reached 24 which is slightly less than what has been observed previously in gulf of maine blooms total scattering b was also calculated as the difference between beam attenuation and absorption the ratio b backscattering divided by total scattering was 0 01 0 02 at 440 and 550 nm at the most turbid parts of the coccolithophore bloom b l 3 m l as total scattering decreased below 1 m l bb increased the behavior of b was compared for coccolith dominated vs chlorophyll dominated waters vertical profiles of calcite dependent scattering combined with satellite remote sensing data were used to assess the factors responsible for vertical transport of calcite the subsurface peak in calcite dependent scattering did not result from detached coccoliths sinking but resulted either from plated coccolithophores sinking and then detaching their plates or from deep coccolithophores producing and detaching their plates in situ

concentric eyewall formation in typhoon sinlaku 2008 part ii axisymmetric dynamical processes abstractin part i of this study the association between the secondary eyewall formation sef and the broadening of the outer swirling wind in typhoon sinlaku 2008 was documented the findings from part i help lay the groundwork for the application of a newly proposed intensification paradigm to sef part ii presents a new model for sef that utilizes this new paradigm and its axisymmetric view of the dynamics the findings point to a sequence of structure changes that occur in the vortex s outer core region culminating in sef the sequence begins with a broadening of the tangential winds followed by an increase of the corresponding boundary layer bl inflow and an enhancement of convergence in the bl where the secondary eyewall forms the narrow region of strong bl convergence is associated with the generation of supergradient winds in and just above the bl that acts to rapidly decelerate inflow there the progressive strengthening of bl inflow and the generation of an effective adverse radial force

a dynamical model of high latitude convection derived from superdarn plasma drift measurements 1 a discrete set of climatological patterns of high latitude ionospheric convection are derived using line of sight plasma drift data from the super dual auroral radar network superdarn the patterns are derived independently for the northern hemisphere and southern hemisphere and for varying solar wind interplanetary magnetic field imf and dipole tilt angle conditions by interpolating between discrete patterns a dynamical model of convection is obtained which can uniquely specify the high latitude electrostatic potential distribution for a wide range of solar wind imf and dipole tilt parameter values accounting for solar wind velocity dependencies in convection leads to better resolving the large scale convection pattern as compared to previous statistical models based on superdarn data it is shown that the mesoscale features of the climatological model compare favorably to the features seen in instantaneous patterns of convection observed with superdarn comparison of the model to other statistical or empirical models derived from ground and space based measurements shows good agreement with most models

reexamining the near core radial structure of the tropical cyclone primary circulation implications for vortex resiliency abstract recent theoretical studies based on vortex rossby wave vrw dynamics have established the importance of the radial structure of the primary circulation in the response of tropical cyclone tc like vortices to ambient vertical wind shear linear vrw theory suggests in particular that the degree of broadness of the primary circulation in the near core region beyond the radius of maximum wind strongly influences whether a tilted tc vortex will realign and resist vertical shear or tilt over and shear apart fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex this raises the question of how well the true nature of a tc s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies in this paper the swirling wind structure of tcs is reexamined by utilizing flight level observations collected from atlantic and eastern pacific storms during 1977 2

the large scale current system during auroral substorms we present an empirical model of the equivalent current system in the ionosphere during the peak of a classical bulge type auroral substorm this model is derived from measurements made by 110 ground magnetometer stations during 116 substorms the data are temporally and spatially organized using global auroral images obtained by the polar visible imaging system earth camera the empirical equivalent current system displays three key features a poleward shift of the westward electrojet connecting the postmidnight and premidnight components a polar cap swirl and significantly different magnitudes of the postmidnight and premidnight westward electrojets this leads us to propose a two wedge current system linking the ionosphere to the magnetosphere the bulge current wedge is located in the premidnight region just equatorward of the open closed field line boundary while another three dimensional current system is located in the postmidnight region well within the auroral oval we use biot and savart calculations and tsyganenko mapping and show that this new model is a likely solution for the large scale current system

altitude adjusted corrected geomagnetic coordinates definition and functional approximations analysis of the functional approximations used to transform between geo graphic and altitude adjusted corrected geomagnetic aacgm coordinates reveals that errors of 50 km can occur in the auroral and polar regions these errors are the result of efforts to better approximate aacgm coordinates near the magnetic equator and the south atlantic anomaly in these regions aacgm coordinates are not defined and alternate coordinates have been used this augmentation and emphasis on the so lution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions in response a new set of spherical harmonic coefficients have been derived that better represent aacgm coordinates in these regions these new aacgm coefficients are limited to below 2000 km in altitude in order to ensure accuracy for altitudes above 2000 km a magnetic field line tracing solution is recommended a software package developed to take advantage of the new aacgm coefficients provides the capability of tracing magnetic field lines at any altitude for improved accuracy in addition linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 present the intent of this work is to provide a more accurate procedure for de termining aacgm coordinates in the auroral and polar regions for the study of mag netospheric and ionospheric processes

the kinematic structure of a hurricane with sea level pressure less than 900 mb abstract a national oceanic and atmospheric administration aircraft recorded the first doppler radar data in a tropical cyclone with a minimum sea level pressure mslp 50 m s 1 extended to 12 km higher than has been reported in previous hurricanes the inner eyewall contained weak

laboratory apparatus for calibrating optical suspended solids sensors abstract an apparatus for testing and calibrating miniature to medium sized optical suspended solids sensors is described stable suspensions of sedimentary particles ranging in size from 10 6 to 4 10 3 m can be produced in water with concentrations exceeding 100 g 1 1 flow velocities in the test volume can be varied continuously from 0 1 to 1 5 m s 1 and samples of suspensions can be withdrawn directly with a peristaltic pump for gravimetric and particle size analyses the apparatus has been used to evaluate the effects of particle size flow speed and air bubbles on the performance of optical backscatterance sensors and transmissometers

the measurement of constituent concentrations in nonhomogeneous sediment suspensions using optical backscatter sensors abstract a method is proposed for estimating the concentrations of the constituents of nonhomogeneous sediment suspensions using optical backscatter sensors the method is predicated on the assumption that constituent interaction e g grain shielding and multiple scattering does not significantly affect sensor response this fundamentally linear approach was verified by laboratory tests of a backscatter sensor in a range of silt sand mixtures implementation of the method will require further development of the optical backscatter sensor or possibly the pairing of an acoustic backscatter sensor with an optical sensor the method has the potential for resolving small scale spatial and temporal changes in the suspended sediment population and therefore could be employed in studies of winnowing and bed armouring for example

a new tool for determining ionospheric currents from magnetic satellite data an algorithm for determining ionospheric currents at high latitudes from magnetic measurements made by low altitude satellites is presented and illustrated using magsat data the ionospheric currents are assumed to flow in a height of 115 km perpendicular to the orbit plane of the satellite which corresponds to east west direction in the case of the dawn dusk magsat orbit the method allows for studying the time development of both the strength and the location of the auroral electrojets application to 13 days of magsat data in winter 1979 yields a correlation coefficient of r 0 88 between the ae index and the strength of the auroral electrojets their latitudinal location moves southward with increasing magnetospheric ring current as measured by the dst index

on the secondary eyewall formation of hurricane edouard 2014 abstracta first observationally based estimation of departures from gradient wind balance during secondary eyewall formation is presented the study is based on the atlantic hurricane edouard 2014 this storm was observed during the national aeronautics and space administration s nasa hurricane and severe storm sentinel hs3 experiment a field campaign conducted in collaboration with the national oceanic and atmospheric administration noaa a total of 135 dropsondes are analyzed in two separate time periods one named the secondary eyewall formation period and the other one referred to as the decaying double eyewalled storm period during the secondary eyewall formation period a time when the storm was observed to have only one eyewall the diagnosed agradient force has a secondary maximum that coincides with the radial location of the secondary eyewall observed in the second period of study the maximum spinup tendency of the radial influx of absolute vertical vorticity is within the boundary la

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

long lived concentric eyewalls in typhoon soulik 2013 abstractthe authors report on western north pacific typhoon soulik 2013 which had two anomalously long lived concentric eyewall ce episodes as identified from microwave satellite data radar data and total precipitable water data the first period was 25 h long and occurred while soulik was at category 4 intensity the second period was 34 h long and occurred when soulik was at category 2 intensity a large moat and outer eyewall width were present in both ce periods and there was a significant contraction of the inner eyewall radius from the first period to the second period the typhoon intensity decrease was partially due to encountering unfavorable environmental conditions of low ocean heat content and dry air even though inner eyewall contraction would generally support intensification the t vmax diagram where t is the brightness temperature and vmax is the best track estimated intensity is used to analyze the time sequence of the intensity and convective activity the convective activity

vertical structure of tropical cyclones with concentric eyewalls as seen by the trmm precipitation radar ten years of data from the tropical rainfall measurement mission satellite s precipitation radar are analyzed to determinethe typical vertical structure of the concentric eyewalls of tropical cyclones undergoing eyewall replacement the vertical structure of the secondary outer eyewall is different from the primary inner eyewall and also different from the eyewall of single eyewall storms the upper troposphere portions of the outer eyewalls are like the rainbands from which they evolve their lower tropospheric portions are more intense and more uniform than rainbands of single eyewall storms suggesting that these secondary eyewalls are forming from rainbands undergoing axisymmetrization and building from below the inner concentric eyewalls are more strongly affected by shear than are the eyewalls of single eyewall storms while the outer eyewalls are relativelyunaffectedby shear which suggeststhe outereyewall is amplifyingthe shearinduced asymmetry of the inner eyewall

solar wind control of ionospheric equivalent currents and their time derivatives a solid understanding of the solar wind control of ground magnetic field disturbances is essential for utilizing the existing long time series of ground data to obtain information on solar wind magnetosphere ionosphere coupling we have used 20 years of international monitor for auroral geomagnetic effects magnetometer data 54 76 magnetic latitude to study the solar wind control of the ionospheric equivalent current density and its time derivative we found that peaks at the premidnight and prenoon ends of the westward electrojet the prenoon peak was most intense during fast solar wind and radial interplanetary magnetic field imf the location of the peak was not affected by the imf orientation but persisted at 8 10 magnetic local time and 70 75 latitude near the boundary between the westward and eastward electrojets sensitivity of this boundary to disturbances was suggested as a possible explanation for the persistent prenoon location of the peak the premidnight peak was most intense during southward imf orientation while faster solar wind mainly resulted in more intense in the premidnight sector stronger imf caused the region of intense to spread to the postmidnight dawn and dusk sectors a good correspondence was found between development of the nightside intensification and average substorm bulge and oval aurora as determined by gjerloev et al 2007 the bulge aurora covered the western end of the westward electrojet where the equivalent current also had a significant poleward component the substorm oval aurora on the other hand extended eastward along the westward electrojet

western north pacific typhoons with concentric eyewalls abstract this study examines the intensity change and moat dynamics of typhoons with concentric eyewalls using passive microwave data and best track data in the western north pacific between 1997 and 2006 of the 225 typhoons examined 55 typhoons and 62 cases with concentric eyewalls have been identified the data indicate that approximately 57 of category 4 and 72 of category 5 typhoons possessed concentric eyewalls at some point during their lifetime while major typhoons are most likely to form concentric eyewalls the formation of the concentric structure may not be necessarily at the lifetime maximum intensity approximately one third of concentric eyewall cases are formed at the time of maximum intensity the moat is known to be heavily influenced by the subsidence forced by the two eyewalls rozoff et al proposed that the rapid filamentation dynamics may also contribute to the organization of the moat this paper examines the possibility of rapid filamentation dynamics by devising a filamentati

outer rainbands driven secondary eyewall formation of tropical cyclones abstractsecondary eyewall formation sef could be considered as the aggregation of a convective ring coupling with a tangential wind maximum outside the primary eyewall of a tropical cyclone tc

hurricane intensity and eyewall replacement observations made during the historic 2005 hurricane season document a case of eyewall replacement clouds outside the hurricane eyewall coalesce to form a new eyewall at a greater radius from the storm center and the old eyewall dies the winds in the new eyewall are initially weaker than those in the original eyewall but as the new eyewall contracts the storm reintensifies understanding this replacement mechanism is vital to forecasting variations in hurricane intensity processes in the moat region between the new and old eyewall have been particularly unclear aircraft data now show that the moat becomes dynamically similar to the eye and thus is converted into a region inimical to survival of the inner eyewall we suggest that targeting aircraft to key parts of the storm to gain crucial input to high resolution numerical models can lead to improvements in forecasting hurricane intensity

secondary wind maxima in hurricanes airflow and relationship to rainbands abstract aircraft flight level data from 787 radial legs in 20 hurricanes are analyzed to identify the composite kinematic structure in the hurricane eyewall and especially with secondary horizontal wind maxima shwm that occur outside the eyewall similar to previous studies analysis of the flight level wind data in the eyewall reveals radial convergence near the radius of maximum wind rmw and the highest frequency of updraft and the largest upward mass transport radially inward of the rmw more than 20 of the flight legs contain substantial secondary horizontal wind maxima of specified strength and length the kinematic structure associated with shwm is similar to that of the hurricane eyewall with radial convergence near the radius of maximum wind and a preferred location for maximum upward motions and upward mass transport just inside the rmw statistical analysis confirms the similarity in characteristics between radial and vertical velocities of the eyewall and near the shwm in addition for

some dynamical aspects of tropical cyclone concentric eyewalls the intensification of tropical cyclones is often interrupted by an eyewall replacement cycle a process in which an outer eyewall forms contracts and replaces an inner eyewall the radial distributions of inertial stability and diabatic heating change during such events impacting the transverse circulation to examine the effects of such changes an analytical solution of the transverse circulation equation associated with a balanced vortex model is derived using a parameterization that distinguishes five radial regions subdividing the domain by each region s values of inertial stability and diabatic heating these regions define the eye inner eyewall moat outer eyewall and far field in mature concentric eyewall situations the solutions do not support the hypothesis that the inner eyewall collapses as a direct result of subsidence from the outer eyewall however the results suggest subsidence and warming temperatures in the moat are governed by enhanced inertial stability associated with a strengthening outer eyewall the model solutions also illustrate how the diabatic heating in the inner eyewall imbedded in a region of high inertial stability induces larger temperature tendencies than the diabatic heating in the outer eyewall which borders the far field region of low inertial stability thus as the inner eyewall dies the storm temporarily loses its ability to produce an intense localized warm region this ability is restored during the contraction and intensification of the outer eyewall these results provide a partial dynamical explanation of how an eyewall replacement cycle can act as a temporary brake on tropical cyclone intensification copyright 2008 royal meteorological society

secondary eyewall formation and concentric eyewall replacement in association with increased low level inner core diabatic cooling abstractthe role of increased diabatic cooling in secondary eyewall formation sef and eyewall replacement cycle erc is examined using idealized numerical simulation the experiment with the low

the effect of air bubbles on optical backscatter sensors the sensitivity of an optical backscatter sensor obs to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies over 1200 one minute runs were performed in a stirred test tank by altering the bubbler type water type air flow rate and sand or mud concentration the laboratory data shows a strong dependence of obs response to bubble size and concentration for sand or mud sediments the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect the effect was more pronounced in salt water than fresh water we conservatively report that obs output voltage is increased due to the presence of bubbles by 25 for the trials undertaken here in the cases performed in vigorously stirred salt and synthetic salt water bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring it was found in those cases that the bubble effect on obs was larger than the 25 reported here but the extension of this finding to a natural setting such as in the direct vicinity of the breakpoint or a bore is not known

the axisymmetric and asymmetric aspects of the secondary eyewall formation in a numerically simulated tropical cyclone under idealized conditions on an f plane abstractthe axisymmetric and asymmetric aspects of the secondary eyewall formation sef in a numerically simulated tropical cyclone tc under idealized conditions were analyzed consistent with p

secondary eyewall formation and eyewall replacement cycles in a simulated hurricane effect of the net radial force in the hurricane boundary layer abstractmultiple secondary eyewall formations sefs and eyewall replacement cycles ercs are simulated with the fifth generation pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 at horizontal grid spacing of 0 67 km the simulated hurricane is initialized from a weak synthetic vortex in a quiescent environment on an f plane after spinup and rapid intensification the hurricane enters a mature phase during which the intensity change is relatively slow convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane s primary eyewall this secondary eyewall se then contracts and strengthens the primary eyewall weakens and is eventually replaced by the se the hurricane grows in size and the radius of maximum wind rmw increases as similar ercs repeat 5 times during the simulation two existing hypotheses on sef are evaluated using the simulation output then model diagnostics are used to revea

temporal changes of the primary circulation in tropical cyclones abstract more than 900 radial profiles of in situ aircraft observations collected in 19 atlantic hurricanes and tropical storms over 13 years confirm that the usual mechanism of tropical cyclone intensification involves contracting maxima of the axisymmetric swirling wind radar shows that annuli of convective echoes accompany the wind maxima these features called convective rings exist and move inward because latent heat released in the rings leads to descent adiabatic warming and rapid isobaric height falls in the area they enclose the radial change in rate of isobaric height fall is concentrated at the inner edge of the wind maximum causing the gradient wind to increase there and the maximum to contract vigorous convection organized in rings invariably causes well defined inward moving wind maxima but when convection is weak the rings are also weak or even absent in this case the swirling wind may be nearly constant with radius and change slowly in time hurricanes that have a single vigor