remote trigger of deep convection by cold outflow over the taiwan strait in the mei yu season a modeling study of the 8 june 2007 case abstractin this study the heavy rainfall event over central taiwan during the mei yu season on 8 june 2007 is investigated with an emphasis on the triggering mechanism for the deep convection that produced the rain observations indicate that there existed two lines of forcing with convection prior to the rain one over the northern taiwan strait along the mei yu front and the other over the southern taiwan strait yet the convection in question developed over the central strait between these two lines in an unstable environment with strong westerly vertical wind shear this motivated the authors to carry out the present study the cloud resolving storm simulation cress of nagoya university was used and the event was reproduced at a horizontal grid size of 2 km including the initiation of new convection over the central strait at the correct location and time the model results suggest a crucial role played by the series of active persistent and propagating storms in the southern strait along the

observations of mesocale wave disturbances during the genesis of atlantic lows experiment abstract the portable automated mesonet pam data obtained during the genesis of atlantic lows fxperiment gale are used to document mesoscale wave activity during the 3 day period from 4 to 6 february 1986 from the surface pressure analyses four cases of wave activity are identified with wavelengths of 200 400 km phase speeds of 20 40 m s 1 and trough to crest pressure amplitudes of 0 5 3 5 mb precipitation was associated with the waves in two of the four cases detailed analyses of the horizontal structure show that the waves do not have the pressure wind relationship expected from linear gravity wave theory the wind vectors are oriented from high to low pressure with a maximum amplitude between the high and low pressure areas low level inversions were present in three of the four cases in the raw without a low level inversion the amplitude rapidly decreased as the wave moved towards the east in the case which lasted for the longest time period at least 8 h and had the largest pressure amp

assessment of earthquake hazard in the tokyo area japan abstract the probability of occurrence of an inland earthquake originating beneath the tokyo area is evaluated for a 10 year period from 1991 on the basis of an earthquake catalogue containing some 40 earthquakes which caused some damage to edo now tokyo over a period of 400 years the parameters of the weibull and lognormal probability distributions applied to recurrence interval statistics are estimated with these parameters it is concluded that an earthquake directly beneath the capital the magnitude of which is equal to or greater than 6 0 occurs with a probability of 0 40 for the period in question when the magnitude threshold is assumed as 6 4 and 7 0 the probabilities become 0 17 and 0 049 respectively these probability evaluations are extended to those for the seismic intensity at typical sites in the area although no accurate evaluation is possible because the exact focal depths of historical earthquakes are not known on the assumption that these earthquakes occur near the upper surface of the down going philippine sea plate however a typical depth of 30 km or so is suggested should an earthquake having a mean magnitude of 6 4 say and at a mean location of past earthquakes occur the probability of seismic intensity at typical sites in the capital area exceeding 5 on the japan meteorological agency jma scale would amount to 0 17 the possibility of having a highly damaging earthquake of intensity 6 on the jma scale also cannot be ruled out judging from earthquake disasters in the past although the probability does become lower to summarize it may be said that the probability of japan s capital area being hit by a damaging earthquake in the foreseeable future is not particularly low

cloud resolving model simulations of multiply banded frontal clouds an idealized two dimensional cloud resolving model is used to investigate the formation and temporal evolution of multiply banded clouds in frontal zones radar observations often show both upright and slantwise convection in the circulations associated with such bands the aim is to examine the interaction between upright and slantwise convection and to determine the mechanisms leading to multiple banding a warm bubble is used to initiate convection in the frontal zone which has an initial thermodynamic profile based on observations further triggering occurs and banded clouds evolve the initially upright plumes become tilted due to the so called am adjustment process upscale development observed multiple bands in frontal zones are frequently attributed to the release of conditional symmetric instability csi however in these simulations there is no evidence of the release of csi despite the fragmentation of slantwise bands into multiple layers in the mid troposphere successive triggering of upright convection is instead associated with a spreading cold pool driven by evaporative cooling in the slanted downdraughts triggering can occur on both the warm and cold air sides of the frontal zone and is sensitive to the microphysical parametrization used

earthquakes recurrence and interoccurrence times the purpose of this paper is to discuss the statistical distributions of recurrence times of earthquakes recurrence times are the time intervals between successive earthquakes at a specified location on a specified fault although a number of statistical distributions have been proposed for recurrence times we argue in favor of the weibull distribution the weibull distribution is the only distribution that has a scale invariant hazard function we consider three sets of characteristic earthquakes on the san andreas fault 1 the parkfield earthquakes 2 the sequence of earthquakes identified by paleoseismic studies at the wrightwood site and 3 an example of a sequence of micro repeating earthquakes at a site near san juan bautista in each case we make a comparison with the applicable weibull distribution the number of earthquakes in each of these sequences is too small to make definitive conclusions to overcome this difficulty we consider a sequence of earthquakes obtained from a one million year virtual california simulation of san andreas earthquakes very good agreement with a weibull distribution is found we also obtain recurrence statistics for two other model studies the first is a modified forest fire model and the second is a slider block model in both cases good agreements with weibull distributions are obtained our conclusion is that the weibull distribution is the preferred distribution for estimating the risk of future earthquakes on the san andreas fault and elsewhere

role of gravity waves in triggering deep convection during toga coare the role of gravity waves in the initiation of convection over oceanic regions during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare experiment is investigated first an autocorrelation method is applied to infrared temperature observations of convective events from satellite images it reveals that new deep convective cells often occur a few hours after a previous intense event at a typical distance of a few hundred kilometers such fast moving modes faster than 15 m s 21 are interpreted as the trace of gravity waves excited by previous convection and contributing to trigger further convection second the specific case of 11 12 december 1992 during which an active squall line is generated after the collapse of a previous mesoscale convective system mcs nearby is analyzed with a nonhydrostatic model the triggering of the second mcs is well reproduced explicitly owing to the use of the two way interactive grid nesting the convective source appears to emit pulses of gravity waves on a wide range of small scales on the contrary the troposphere response to the convective source exhibits a spectral simplicity a slowly evolving mode characterized by an ascent in the pbl and a compensating subsidence in the free troposphere favors shallow convection and inhibits deep convection respectively traveling modes propagating away from the convective source are characterized by a fast mode 50 m s21 and a slower mode 25 ms 21 associated with the convective and stratiform development of the source respectively in agreement with previous studies a budget analysis reveals the different factors leading to the deep convection triggering first an active pbl characterized by strong surface fluxes and mean ascent initiates shallow convection lasting about 2 h inhibited above by the subsiding motions maintaining a dry layer second horizontal advection of moist and cooler air at midlevels and detrainment from cumuli contribute to destroy the dry air layer capping the shallow convective layer finally vertical advection induced by the gravity waves passage modulates the vapor and temperature evolution ascending phases favor moistening and cooling whereas subsiding phases stop these effects delaying the deep convection onset the triggering occurs after a strong subsidence when the ascent phases of deep and shallow modes are combined

numerical modelling of the destructive meteotsunami of 15 june 2006 on the coast of the balearic islands a destructive tsunami like event locally known as rissaga waves occurring on 15 june 2006 in ciutadella harbour menorca balearic islands is reproduced by a numerical model forced by a travelling atmospheric disturbance the disturbance is reconstructed from microbarograph measurements being the only available instrumental data at the time of the event the model is verified based on two weaker 1997 events which were recorded by a number of bottom pressure recorders operating at that time on the menorca shelf in ciutadella inlet and adjacent platja gran inlet both 1997 events are numerically simulated and good agreement is achieved with observations in time frequency including eigenfrequencies of the affected inlets and wave heights subsequently the same model is applied to simulate the 2006 event the vigorous currents with speeds up to 400 cm s are found to occur specifically at those areas of the harbour where the most severe damage and sinking of boats had been reported maximum simulated sea level heights of 2 5 m were about one half of those reported by eyewitnesses this difference is apparently caused by quality and spatial resolution of bathymetry data however in general the model is capable of reproducing the event fairly well and can probably be used for future assessment and mitigation activities on the coasts of the balearic islands

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

a case study of the interaction of a mesoscale gravity wave with a mesoscale convective system abstractthis study documents the high amplitude mesoscale gravity wave mgw event of 7 march 2008 in which two mgws strongly impacted the sensible weather over a large portion of the southeast united states these mgws exhibited starkly contrasting character despite propagating within similar environments the primary i e long lived mgw was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming while the secondary short lived mgw was manifest by a solitary wave of elevation mgwel dominated by rising motion and moist adiabatic cooling genesis of the primary mgw occurred as a strong cold front arrived at the foot of mexico s high terrain and perturbed the appreciable overriding flow the resulting gravity wave became ducted in the presence of a low level frontal stable layer and caused surface pressure falls up to 4 hpa the mgw later amplified as it became coupled with a stratiform precipitation system which led to its evolution into an intense

an application of l band synthetic aperture radar to tide height measurement a method for measuring the tide height near the coast from l band synthetic aperture radar sar data is presented twenty one coherent interferograms have been successfully constructed from japanese earth resources satellite 1 jers 1 sar data obtained over oyster sea farming structures a coherence analysis of the 21 interferometric pairs showed that a perpendicular baseline of less than 3 km with a temporal baseline within 500 days are required to obtain a coherent pair with a coherence higher than 0 25 in the study area the coherent phases preserved in the interferograms showed a close relation with the sea level the problem of phase unwrapping to restore an absolute tide height was overcome by introducing normalized image intensities the radar measurements estimated by the proposed method were verified using tide gauge data and comparison of the two datasets yielded a correlation coefficient r sup 2 of 0 91 with a root mean square error of 5 76 cm the results demonstrate that radar interferometry can be applied for a tide height measurement near the coast given sufficient structures that return off nadir radar pulses to the antenna the multipolarized l band sar system will provide better results using only double bounced signals in the future

inertia gravity waves spontaneously generated by jets and fronts part i different baroclinic life cycles abstract the spontaneous generation of inertia gravity waves in idealized life cycles of baroclinic instability is investigated using the weather research and forecasting model two substantially different life cycles of baroclinic instability are obtained by varying the initial zonal jet the wave generation depends strongly on the details of the baroclinic wave s development in the life cycle dominated by cyclonic behavior the most conspicuous gravity waves are excited by the upper level jet and are broadly consistent with previous simulations of o sullivan and dunkerton in the life cycle that is dominated by anticyclonic behavior the most conspicuous gravity waves even in the stratosphere are excited by the surface fronts although the fronts are no stronger than in the cyclonic life cycle the anticyclonic life cycle also reveals waves in the lower stratosphere above the upper level trough of the baroclinic wave these waves have not been previously identified in idealized simulations the sensiti

large amplitude pressure oscillations in the western mediterranean pressure oscillations with unusually large amplitude of some 3 mb and periods of about 50 min have been registered in the balearic islands western mediterranean sea during summer 1989 these large pressure oscillations are maintained over several hours and have been recorded on several occasions the synoptic pattern and vertical structure of the atmosphere simultaneous with these oscillations is described the large amplitude waves described here do not appear to be directly related to convective activity some of the characteristics of these waves are described however their source mechanism remains unclear

evidence of very large amplitude solitary waves in the atmosphere atmospheric solitary waves are gravity waves that retain their integrity over long periods because of a near balance between nonlinearity and dispersion they have been observed on various scales in many regions of the world1 3 but we present here detailed measurements of solitary waves with amplitudes comparable to the scale height of the lower troposphere two such waves were generated downstream of intense mid tropospheric pressure troughs over the central united states they propagated over 1 000km several times their wavelength with no appreciable change in structure within a waveguide formed by surface inversion and a middle tropospheric critical level fluctuations in surface pressure associated with the two waves exceeded 6 mbar and 10 mbar the waves caused banded patterns of precipitation and significantly influenced other meteorological phenomena the restoration of balance between pressure driven air flow and the coriolis force geostrophic adjustment seems to have a prominent role in the formation of these solitary waves

pressure forced seiches of large amplitude in inlets of the balearic islands 2 observational study in part 1 of this study gomis et al 1993 proposed a possible mechanism for the generation of large amplitude seiches observed in inlets of the balearic islands in part 2 we revise the proposed mechanism in light of recent observations these consist of simultaneous records of sea level bottom pressure measured at three locations inside and outside ciutadella inlet and atmospheric pressure measured at four sites inland nearby first results that support the existence of offshore surface waves of atmospheric origin are shown next a detailed analysis of atmospheric data reveals the passage of non dispersive waves with a predominant direction and phase speed that seem to be about the same during seiche events finally coherence phase difference and admittance functions estimated for different pairs of instruments are compared with the theoretical results all observations indicate that large amplitude seiches observed in ciutadella are likely the result of a resonant coupling between offshore surface waves generated by atmospheric disturbances and the fundamental mode of that inlet as suggested in part 1 however the analytical model used in part 1 is clearly too simple to explain the observed characteristics of the offshore surface waves

deep tropospheric gravity waves created by leeside cold fronts abstract the water vapor channel of the geostationary operational environmental satellite goes 8 reveals narrow 30 km wide elongated 500 1000 km bands that propagate southward on the eastern side of the rocky mountains from colorado to texas two events in which surface and wind profiler observations show that these bands are associated with leeside cold fronts are documented in detail and several other cases are summarized the wind profilers observe vertical motions exceeding 1 m s 1 in narrow plumes at the leading edge of the fronts in broader zones in the upper troposphere and in the lower stratosphere these cause vertical displacements of up to 1 km and are responsible for the signature in water vapor images the bands occur when the rocky mountains block either arctic leeside cold fronts coming from the north or northeast or pacific cold fronts coming from the northwest the blocking changes the frontal orientation and disrupts geostrophic thermal wind balance near the terrain modified fron

determination of earthquake early warning parameters τ c and pd for southern california summary we explore a practical approach to earthquake early warning in southern california by determining a ground motion period parameter c and a high pass filtered displacement amplitude parameter pd from the initial 3 s of the p waveforms recorded at the southern california seismic network stations for earthquakes with m 4 0 at a given site we estimate the magnitude of an event from c and the peak ground motion velocity pgv from pd the incoming threecomponent signals are recursively converted to ground acceleration velocity and displacement the displacements are recursively filtered with a one way butterworth high pass filter with a cut off frequency of 0 075 hz and a p wave trigger is constantly monitored when a trigger occurs c and pd are computed we found the relationship between c and magnitude m for southern california and between pd and pgv for both southern california and taiwan these two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the p wave when the station density is high the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach in an ideal situation such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

polarimetric features of oyster farm observed by airsar and jers 1 the polarimetric features of an oyster farm in a coastal area are analyzed to verify the applicability of radar polarimetry and interferometry l band airborne synthetic aperture radar airsar data and japan earth resources satellite jers 1 data are used to examine the unique structure of an oyster farm located in south korea a specific feature of the oyster farm is the presence of numerous arrays of structures of various orientations that consist of exercise bar shaped poles protruding above sea level this paper demonstrates that tide level is strongly correlated with the double bounce scattering power from the vertical pole structures this phenomenon is also verified by laboratory measurements using a network analyzer in the laboratory experiment double bounce scattering and total power showed increasing trends with increased height of the vertical poles single bounce scattering is sensitive to the orientation of horizontal poles relative to antenna orientation hh polarization is the most effective technique for imaging oyster farms from l band polarimetric airsar data the authors were able to use a three component decomposition of the airsar data to distinguish an exposed tidal flat from a submerged tidal flat the characteristics of the exposed tidal flat are similar to those of the carbon sponge in the laboratory test except that the double bounce scattering power is slightly greater in the real world example the single bounce scattering component in airsar data is generally greater than that in laboratory measurements because of sea surface conditions and oyster growth when the horizontal pole was aligned normal to the radar look direction single bounce scattering was greater than the double bounce scattering even under water covered conditions while a difference in tide height of 10 cm contributed approximately 3 0 db in the laboratory experiment a difference in tide height of 20 cm contributed to only approximately 1 7 db in the jers 1 sar image intensity jers 1 sar image intensity for areas dominated by double and single bounce scattering was 0 78 and 0 56 respectively results confirm that polarimetric sar data are useful in selecting areas dominated by double bounce scattering in oyster farms

detection of oyster habitat in tidal flats using multi frequency polarimetric sar data abstract exposed oyster reefs in tidal flats have complex and rough surfaces because of their unique surface texture which are quite distinct from the surrounding mud or sand flats here we investigate the microwave signatures backscattered from naturally distributed oyster reefs in tidal flats utilizing the polarimetric analysis techniques to fully polarimetric radarsat 2 c band and alos palsar l band data the study areas include the tidal flats around jebu island and hampyung bay on the west coast of the korean peninsula we analyzed the microwave scattering mechanisms associated with oyster reefs and surrounding areas using the polarimetric target decomposition theorem and quantitatively measu hhvv red target depolarization effects the cross polarized ratio hv vv the co polarized correlation coefficient hhvv and the co polarized phase difference between hh and vv on the basis of a large increase in the cross polarized backscattering hv in the c band sar data one can observe strong volume or multiple scattering and depolarization effects over oyster reefs areas whereas only surface scattering was dominant in most parts of the background tidal areas in oyster reefs the proportion of volume scattering and the cross polarized ratio were greater than 0 7 and 8 db respectively these scattering characteristics were also verified from in situ measurements in the field using a ground based polarimetric scatterometer system however almost no difference was observed between the scattering signatures of oyster reefs and background mudflat areas from l band data which have a considerably longer wavelength than c band the study clearly suggests that multi frequency c and l band polarimetric sar systems can be used to detect the naturally distributed oyster reefs in tidal flats

the role of gravity waves in slowly varying in time mesoscale motions abstract pressure oscillations with amplitudes of the deviations from the horizontal mean and periods considerably less than those for the large scale case have been observed in a number of summer and winter storms however there is conflicting evidence about the role of these waves in mesoscale storms in the case of mesoscale heating that is a prescribed function of the independent variables it has been proven that the dominant component of the corresponding slowly varying in time solution is accurately described by a simple dynamical reduced system in which gravity waves play no role this paper proves that large spatial scale gravity waves with amplitudes and periods of the pressure perturbations the same as the reduced system component of the solution can be generated by mesoscale storms because the amplitudes and the periods of the pressure perturbations for the two components of the solution are similar it is difficult to distinguish between them using temporal plots of the pressure at a sing

impact of fault parameter uncertainties on earthquake recurrence probability examined by monte carlo simulation an example in central taiwan abstract the region around taiwan is well known for its unique geological setting which has resulted in a high seismicity the central geological survey taiwan cgst has launched a series of investigation on characterizing the active faults on the island the cgst revealed that there are 33 active faults and their fault parameters are suggested in the latest publication in 2010 however the uncertainties of return period and earthquake magnitude are not provided the main objective of the paper is to study the impact of unspecified parameter uncertainties on recurrence earthquake probabilities in addition a numerical approach involving the use of monte carlo simulation was proposed to estimate the exceedance probabilities in which the parameter uncertainties were taken into account the meishan fault in central taiwan with the best estimate return period of 162 years and earthquake magnitude of 7 1 was used as an example the analyses verified the impact of parameter uncertainties on the exceedance probability in fault induced earthquake recurrence when uncertainty is high the exceedance probability associated with large magnitudes is high it was also observed that the probabilistic analysis in this study can generate a realistic continuous distribution of exceedance probabilities that cannot be obtained by a deterministic approach the best estimate distribution of exceedance probability was established by enveloping the curves estimated by both deterministic and probabilistic approaches accordingly the best estimate exceedance probability for a 7 5 magnitude earthquake recurring in 2011 2060 induced by the meishan fault in central taiwan was estimated as 11

modelling earthquake rupture rates in fault systems for seismic hazard assessment the eastern betics shear zone abstract earthquake surface fault ruptures can show very complex geometries and involve different faults simultaneously consequently modern fault based probabilistic seismic hazard assessments psha need to account for such complexities in order to achieve more realistic modellings that treat fault systems as a whole and consider the occurrence of earthquake ruptures as aleatory uncertainties we use sherifs a recent approach of modelling annual rates of complex multi fault ruptures to obtain system level magnitude frequency distributions mfds for the eastern betics shear zone ebsz spain considering four fault rupture hypotheses we then analyze the consistency of each scenario based on data from the earthquake catalogue and paleoseismic studies the definition of the different rupture hypotheses was discussed within the frame of fault2sha esc working group and critical fault input data is extracted from previous published studies the four rupture hypotheses are defined as incremental scenarios based on fault geometry and kinematics with lengths varying from minimal fault sections to a rupture of nearly the whole system the results suggest that multi fault ruptures involving lengths up to single to several whole faults are consistent with the annual rates from both the instrumental catalogue and paleoseismic record the method does not allow to completely discard any hypothesis but it allows to weight the different models in a logic tree for seismic hazard assessment the approach is revealed as a practical tool for obtaining fault system mfds and as a useful tool for highlighting limitations and uncertainties in geological and paleoseismic data to be assessed this study aims to constitute a step forward in the consideration of complex multi fault ruptures for future seismic hazard assessments in the region

analytical studies of low level internal gravity waves over the kanto plain associated with a stationary front abstract an observational analysis of the low level internal gravity waves over the kanto plain in japan on 17 october 1998 was performed the data from the doppler radar for airport weather draw as well as aircraft communications addressing and reporting system acars data of wind and temperature provided unique observations with high spatial and temporal resolutions and were used to analyze detailed wave structures and environmental conditions especially the wave trapping mechanism according to the data analysis the horizontal wavelength was approximately 7 km the ground relative phase speed of the waves was approximately 1 m s 1 and the direction of propagation was toward 50 ne the profiles from acars revealed that the scorer parameter decreased rapidly with height above 1500 m agl and became less than the horizontal wavenumber near 2600 m agl these results indicate that the atmosphere acts as a duct and the waves were trapped vertically and reflected downward the observed horizontal wa

evaluation of terrasar x observations for wetland insar application this paper assesses the potential of using spaceborne x band synthetic aperture radar sar data for monitoring water level changes over wetlands our analysis is based on three sets of terrasar x tsx observations acquired over south florida s everglades wetlands during an eight month period in 2008 the first set was acquired in single hh polarization stripmap mode over our northern study area consisting of managed wetlands and urban environments the second set was acquired in dual polarization stripmap mode over the western half of the same area consisting mostly of managed wetlands the third set was also acquired with dual polarization stripmap mode over our southern study area consisting of natural flow freshand salt water wetlands in the southern everglades the first data set was used for a proof of concept study to verify that x band data can generate coherent interferograms in wetland areas interferometric processing of this data set shows a high level of coherence 0 35 over both wetland and urban regions maintaining interferometric phase in all three interferograms spanning 11 days surprisingly phase is maintained over some of the wetlands even for interferograms spanning 33 days the other two data sets were used to evaluate interferometric coherence of all four polarization modes and to determine dominant scattering mechanism in each wetland environment our results show high coherence values 0 4 in all polarization modes with highest values in hh then vv and lowest in hv or vh interferograms calculated from multipolarization data show very similar fringe patterns regardless of the polarization type suggesting that the phase information in all polarization data reflects water level changes in wetlands and that volume scattering may be less important than commonly believed we also used the two multipolarization data sets to conduct the pauli decomposition finding a strong dependence of scattering mechanism on vegetation type the high interferometric coherence level of all polarization data suggests that a significant part of the x band scattered signal interacts with lower sections of the vegetation trunks and branches because scattering from wind affected canopies cannot support such a high coherence level the high spatial resolution of tsx combined with its 11 day repeat orbit makes this x band sensor surprisingly suitable for wetland interferometric sar applications

gravity wave observations using an array of microbarographs in the alearic islands time series of surface pressure from an array of microbarographs in the balearic islands western mediterranean are used to obtain wavelength phase speed and direction of propagation of gravity waves on the balearic islands these pressure waves are commonly found during the summer and they force the large seal level oscillations observed in the inlet of ciutadella a phenomenon locally known as rissaga four events are described here each of which has a duration of between 30 and 48 hours radiosonde data from palma de mallorca are used to relate the waves to the vertical structure of the atmosphere the various source mechanisms of these waves and also the possibility of the existence of a duct layer trapping the wave energy near the surface are discussed the waves are found to have no significant variation of phase speed with frequency and so they are basically non dispersive this is an indicator pointing either to a local generation of gravity waves by wind shear instability or to the existence of neutral trapped waves in the lower troposphere

mesoscale dynamics in the palm sunday tornado outbreak abstract radar and satellite imagery suggest that strong mesoscale forcing occurred in the palm sunday tornado outbreak on 27 march 1994 parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in mississippi and alabama on this date analyses of routine meteorological observations barograph data and forecasts from the eta and ngm models and a mesoscale research model mass are used to examine the relative roles of large scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection quasigeostrophic forcing was absent in the outbreak region likewise a thermally direct circulation system transverse to the upper level jet that was present to the northwest of the outbreak region was decoupled from the strong low level ascent occurring in northern alabama and mississippi at the time of the outbreak strong ageostrophic frontogenesis in the presence of conditional symmetric instability csi was the chief

a case study of gravity waves convective storms interaction 9 may 1979 abstract an analysis is presented of a series of severe storms which occurred in the north central united states on 9 may 1979 and whose spatial distribution and movement correlate well with observed gravity waves two gravity wave trains of 2 1 3 mb amplitude 2 5 3 3 h period and 240 265 km horizontal wavelength were isolated through power spectra analysis and cross correlation techniques applied to national weather service barograph traces the wave trains propagated in the 200 direction which coincided with the jet axis with a phase velocity of 20 30 m s 1c and within a 300 km wide band the storms were identified on enhanced infrared goes satellite pictures with the help of radar summaries these convective systems initially developed in nebraska and propagated north northeast at 25 m s 1 revealing wave like characteristics with a separation of 300 400 km the convective systems were closely linked to the observed wave trains with cell intensity height and associated rainfall maximized at the wa

extreme value distribution of earthquake magnitude abstract probability distribution of maximum earthquake magnitude is first derived for an unspecified probability distribution of earthquake magnitude a model for energy release of large earthquakes similar to that of adler lomnitz and lomnitz is introduced from which the probability distribution of earthquake magnitude is obtained an extensive set of world data for shallow earthquakes covering the period from 1904 to 1980 is used to determine the parameters of the probability distribution of maximum earthquake magnitude because of the special form of probability distribution of earthquake magnitude a simple iterative scheme is devised to facilitate the estimation of these parameters by the method of least squares the agreement between the empirical and derived probability distributions of maximum earthquake magnitude is excellent

a three component scattering model for polarimetric sar data an approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric sar observations the mechanisms are canopy scatter from a cloud of randomly oriented dipoles evenor double bounce scatter from a pair of orthogonal surfaces with different dielectric constants and bragg scatter from a moderately rough surface this composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers the model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from nasa jet propulsion laboratory s jpls airborne polarimetric synthetic aperture radar airsar system the model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas for example the model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature an advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric sar images furthermore it is shown that the contributions of the three scattering mechanisms to the hh hv and vv backscatter can be calculated from the model fit finally this model fit approach is justified as a simplification of more complicated scattering models which require many inputs to solve the forward scattering problem

a 4 yr climatology of pressure disturbances using a barometer network in central illinois this paper presents a climatology of coherent disturbances detected during 1991 95 by a network of barometers with a diameter of about 50 km located in a very flat terrain centered on the flatland atmospheric observatory in east central illinois an automatic wavelet based adaptive filter is used to extract the waveforms of all disturbance events with amplitudes larger than a frequency dependent threshold the extracted events cover characteristic temporal scales from about 30 min to 6 h that is the range that includes mesoscale disturbances that affect the weather and the forecasts the analysis resulted in two classes of events one class called coherent events or ces consists of disturbances that propagated coherently through the barograph network and for which the phase propagation velocity dominant period and horizontal wavelength could be estimated with good accuracy the propagation directions of 97 of the ces were between 08 and 1808 i e had an eastward component and the speeds of 96 were between 10 and 50 ms 21 with a mode at 25 30 m s21 the other class called incoherent events or ies consists of disturbances that had significant amplitudes but that did not propagate coherently across the network so that the propagation velocity could not be estimated this class consists of localized disturbances and wave packets with short periods and or wavelengths or with pressure signatures that were too different at the network stations the extracted events are attributed to gravity waves wave packets gravity currents pressure jumps solitary waves bores etc the rate of occurrence of events had a strong seasonal dependence with a maximum in fall and winter and a minimum in summer the ces occurred about 20 21 of the total time in fall and winter and 12 in summer while all events occurred 34 in both fall and winter and 23 in summer the seasonal dependence of events confirms the strong relation of these disturbances to the baroclinicity of the atmosphere concurrent vertical velocity fluctuations observed by the 50 mhz radar at the flatland atmospheric observatory showed that many of the large amplitude events extended up to at least 7 km the highest altitude reliably observed by the radar

generation of seiches by cold fronts over the southern north sea 1 seiches affecting the port of rotterdam are generated in the southern north sea their generation is investigated with observations and numerical simulations a wavelet analysis of the observations both at sea and in the harbor shows that low frequency energy 0 1 2 0 mhz does indeed occur at sea prior to each seiche event in rotterdam an analysis of 6 years of weather charts indicates that all 51 seiche events in this period with amplitude exceeding 0 25 m coincided with the passage of a low pressure weather system some of these low pressure systems included a sharp cold front classical or ana whereas others included a more diffuse cold front split or kata numerical simulations with a hydrodynamic model driven by meteorological observations reproduced the seiches for situations with the sharp cold fronts correctly the seiches that were simulated for situations with the gradual cold fronts do not agree with the observations which is ascribed to the inadequate atmospheric forcing of the hydrodynamical model

convection waves observations of gravity wave systems over convectively active boundary layers widespread gravity wave systems have been found to exist over convectively active boundary layers cbls in the presence of vertical wind shear in contrast to mountain waves these convection waves occur over flat terrain and are ubiquitous over fields of shallow fair weather cumuli or clear air thermals they extend vertically to at least 9km a m s l probably to the tropopause first discovered by glider pilots as thermal waves they have now been systematically investigated by research aircraft during the ncar convection wave project which also incorporates an effort in numerical simulation the flight results are reported in this paper while the numerical simulations are described in a companion paper typical wavelengths of convection waves were found to range from 5 to 15 km average 9 km and typical vertical motion amplitudes from 1 to 3 m s 1 in all cases vertical wind shear exceeded 3 10 3s 1 under these conditions cloud tops were measured to move with relative velocities of 8 to 10 m s 1 against their environment hence they present an obstacle to the surrounding airflow the analogy to mountainous obstacles launching gravity waves into the atmosphere is suggestive and borne out by the aforementioned numerical simulations which describe this process step by step the interaction between the cbl and the overlying stable layers is studied by spectral and cross spectral analysis of aircraft data including coherence and phase relations between wave motions and cloud population underneath consideration is given to other potential sources of the observed gravity waves at this stage the conclusions of our pilot study may be considered tentative some implications for further research are also discussed

pressure forced seiches of large amplitude in inlets of the balearic islands large amplitude harbor seiches usually occur in summer in the balearic islands a significant correlation between sea level oscillations and atmospheric pressure disturbances has been found though a proved physical mechanism to account for this atmosphere ocean interaction is still missing using a flat bottom shallow water model we show that a direct coupling between atmospheric pressure and the free mode of an inlet is unlikely but that an oceanic wave of atmospheric origin can act as an intermediate mechanism and adequately force the inlet by resonance the phase relationship derived from this mechanism is in good agreement with observations provided the whole spectrum of oceanic waves is in opposite phase to the generating atmospheric disturbance we also show that the very large oscillations observed at ciutadella an elongated shallow inlet in the west coast of menorca balearic islands can be explained in terms of the particular shape of this inlet

study of the polarimetric characteristics of mud flats in an intertidal zone using c and x band spaceborne sar data abstract the polarimetric characteristics of a mud flat area in the intertidal zone near jiangsu china are analyzed under different environmental conditions using x band and c band spaceborne synthetic aperture radar sar data from the terrasar x tsx and radarsat 2 r2 satellites the dominant scattering mechanisms of different objects including mud flats and aquaculture facilities in the intertidal zone are studied based on the polarimetric target decomposition of fully polarimetric r2 data the polarimetric characteristics of different objects in the intertidal zone are quantitatively compared using the depolarization parameters derived from the r2 data which indicate that tides have different effects on the dominant scattering mechanisms of the mud flats and aquaculture farms furthermore comparisons of the c band and x band polarimetric characteristics of the mud flats and aquaculture farms in the intertidal zone are analyzed by combining the tsx and r2 data the results show that surface scattering is the dominant mechanism of the mud flats whereas different dominant mechanisms occur in the aquaculture areas present during different tides interestingly strikingly similar polarimetric characteristics of mud flats and aquaculture in x band and c band sar are observed and these novel results were achieved through a depolarization analysis based on the tsx and r2 data in synergy

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du