empirical relationship of t wave energy and fault parameters of northeast pacific ocean earthquakes a total of 179 northeast pacific ocean earthquakes that occurred between 1992 1998 are used to investigate the relationship of t wave acoustic energy and earthquake fault parameters the moderate sized 3 7 mw 6 9 earthquakes were recorded by ocean hydrophones and had their source parameters estimated by land based seismic networks the acoustic energy release at the seafloor water interface of each earthquake was estimated by removing the signal attenuation along the propagation path and instrument gain from the hydrophone signal there appears to be a relationship where for a given magnitude earthquake t wave energy is lower for normal and reverse fault earthquakes than strike slip events a more detailed comparison indicates acoustic energy of the earthquake will often decrease as the component of dip slip motion increases these observations suggest fault parameter information is contained within the t wave signal packet

krýsuvik high temperature geothermal area in sw iceland geological setting and 3d inversion of magnetotelluric mt resistivity data abstract the kr suvik area in sw iceland is characterized by a 40 km long and around 6 8 km wide fissure swarm and two ne sw trending tindars complexes associated with the fissure swarms are fumarole fields located primarily on parallel postglacial eruptive fissure segments there are indications that kr suvik hosts a buried caldera and an intrusion complex in its roots the geothermal surface manifestations cover an area of around 50 60 km2 and has potential for future exploitation faulting accompanies the ridges and postglacial volcanic fissures with normal faults and open fissures with a maximum throw of 10 m a 3d inversion was performed of the static shift corrected off diagonal impedance tensor elements of 102 magnetotelluric mt resistivity soundings from the greater kr suvik geothermal area in the inversion 21 periods were used evenly distributed from 0 01 to 100 s on a logarithmic scale the robustness of the inversion was tested by using three different initial models a model compiled from a joint 1d inversion of tem and mt soundings with a homogeneous earth of resistivity 100 m and a homogeneous earth of resistivity 10 m a flat topographic surface was assumed in the 3d inversion the resulting models were later elevation corrected the results of the 1d inversion and the 3d inversion are strikingly similar where the 1d inversion reproduces the main resistivity structures while the 3d inversion shows considerably more details an analysis of the electrical strike directions based on the vertical magnetic field data is in fairly good agreement with the final resistivity model the subsurface resistivity structure in kr suvik has the same main features as other high temperature areas in iceland and in general where the host rocks are basaltic above a shallow conductive cap a high resistivity zone is seen reflecting unaltered rock the conductive cap reflects smectite hydrothermal mineral alteration below the low resistivity cap a resistive core is found reflecting chlorite epidote alteration good correlation is observed in the kr suvik field between the subsurface resistivity structure and the hydrothermal alteration revealed by boreholes cuttings parts of the field have cooled down and therefore the resistivity structure indicates alteration mineralogy but not necessarily the present rock temperature the geothermal up flow zones are therefore most likely where the hydrothermal alteration and the resistive core reach the highest elevation the 3d inversion shows an indication of a relatively deep seated conductive body below the central part of the high temperature area this body coincides horizontally with the centre of the 2010 2011 inflation source at 4 5 km depth it has been suggested that the 2007 2016 inflation deflation periods are linked to gas flux as no signs of s wave attenuation have been found it is therefore unlikely that the deep seated conductive body resolved by our resistivity models comprises partial melt the body is probably connected to the heat source of the geothermal field and could be due to emission of gas or dehydration

elevated potential instability in the comma head distribution and development abstractthe development of elevated potential instability within the comma head of a continental winter cyclone over the north central united states is examined using a 63 h weather research and forecasting wrf model simulation the simulation is first compared to the observed cyclone the distribution of most unstable convective available potential energy mucape within the comma head is then analyzed the region with positive mucape was based from 2 to 4 km altitude with mucape values up to 93 j kg 1 backward trajectories from five sublayers within the region of elevated convection in the comma head were calculated to investigate how elevated potential instability developed air in the lowest sublayer the source air for convective cells originated 63 h earlier near baja california at elevations between 2 25 and 2 75 km altitude air atop the layer where convection occurred originated at altitudes between 9 25 and 9 75 km in the arctic 5000 km away from the origin of air in the lowest sublayer

the role of moist processes in the formation and evolution of mesoscale snowbands within the comma head of northeast u s cyclones abstract the role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast u s cyclones is investigated using piecewise potential vorticity pv inversion modeling experiments and potential temperature tendency budgets snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700 hpa low this 700 hpa trough was associated with intense frontogenetical forcing for ascent a variety of pv evolutions among the cases contributed to midlevel trough formation and associated frontogenesis however in each case the induced flow from diabatic pv anomalies accounted for a majority of the midlevel frontogenesis during the band s life cycle highlighting the important role that latent heat release plays in band evolution simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band however changes in the meso

vertical velocity and physical structure of generating cells and convection in the comma head region of continental winter cyclones abstractthe vertical motion and physical structure of elevated convection and generating cells within the comma heads of three continental winter cyclones are investigated using the wyoming w band cloud radar mounted on the national science foundation national center for atmospheric research nsf ncar c 130 supplemented by analyses from the rapid update cycle model and weather surveillance radar 1988 doppler wsr 88d data the cyclones followed three distinct archetypical tracks and were typical of those producing winter weather in the midwestern united states in two of the cyclones dry air in the middle and upper troposphere behind the pacific cold front intruded over moist gulf of mexico air at lower altitudes within the comma head separating the comma head into two zones elevated convection in the southern zone extended from the cold frontal surface to the tropopause the stronger convective updrafts ranged from 2 to 7 m s 1 and downdrafts ranged from 2 to 6 m s 1 the horizontal scale of the

quasigeostrophic forcing of ascent in the occluded sector of cyclones and the trowal airstream a numerical model based analysis of the quasigeostrophic forcing for ascent in the occluded quadrant of three cyclones is presented based upon a natural coordinate partitioning of the q vector into its along and acrossisentrope components qs and qn respectively the qn component describes the geostrophic contribution to the rate of change of the magnitude of pu traditional frontogenesis whereas the qs component describes the geostrophic contribution to the rate of change of direction of pu rotational frontogenesis it is shown that convergence of qs simultaneously creates the isobaric thermal ridge characteristic of the thermal structure of occluded cyclones and provides the predominant dynamical support for ascent within the occluded quadrant the absence of significant qn convergence there suggests that quasigeostrophic q g frontogenesis plays a subordinate role both in forcing vertical motions and in affecting three dimensional structural changes in the occluded sector of post mature phase midlatitude cyclones a cyclonically ascending cloud and precipitation producing airstream that originates in the warm sector boundary layer and flows through the trowal portion of the occluded structure is supported by the upward vertical motions implied by the identified q g forcing this airstream is referred to as the trowal airstream and it is shown to be responsible for the production of the wrap around cloud and precipitation commonly associated with occluded systems the relationship of the trowal airstream to previously identified cloud and precipitation producing airflows in cyclones is discussed

high resolution observations of the trowal warm frontal region of two continental winter cyclones abstract this paper compares the structure of the trough of warm air aloft trowal warm frontal region of two continental wintertime cyclones the cyclones were observed over the central great lakes region during the lake induced convection experiment snowband dynamics project field campaign the cyclones had different origins with the first forming east of the colorado rockies and the second forming over the gulf of mexico they were associated with different upper level flow regimes one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet both storms produced heavy swaths of snow across the states of illinois wisconsin and michigan high resolution observations of frontal structure were made during flights of the national center for atmospheric research electra aircraft using dropsondes and the electra doppler radar tail radar system the high resolution observations suggest a different arrangement of air masses in the trowal region compared with the

the structure and evolution of a simulated midlatitude cyclone over land abstract using output from a mesoscale model simulation this paper describes the evolution of the three dimensional temperature and humidity structures of an intense cyclone that developed over the eastern half of the united states during 14 16 december 1987 some specific findings include the following the occlusion process at the surface appeared similar to the classical paradigm with the cold front catching up with the warm front aloft a warm type occlusion structure formed as an upper baroclinic zone merged with the surface based occluded front the frontogenesis associated with the cold and warm fronts was initially continuous but as the system evolved a break in the frontogenesis along the northern section of the cold front developed a single frontogenesis feature appeared to support both the warm and occluded fronts a quasi linear region of convective activity was observed in advance of the surface cold front this convective line was associated with an upper level humidity front wh

earthquakes stress and strain along an obliquely divergent plate boundary reykjanes peninsula southwest iceland earthquakes stress and strain along an obliquely divergent plate boundary the reykjanes peninsula southwest iceland

evolution of mesoscale precipitation band environments within the comma head of northeast u s cyclones abstract this paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32 km north american regional reanalysis hourly 20 km rapid update cycle analyses and 2 km composite radar reflectivity data a statistical and composite analysis of 36 banded events occurring during the 2002 08 cool seasons reveals a common cyclone evolution and associated band life cycle a majority 61 of banded events develop along the northern portion of a hook shaped upper level potential vorticity pv anomaly during the 6 h leading up to band formation lower tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced the frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough this trough extends poleward of the 700 hpa low and is the vertical extension of the surface warm front and surface

organization and structure of clouds and precipitation on the mid atlantic coast of the united states part v the role of an upper level front in the generation of a rainband abstract the origins of a rainband of moderate intensity that occurred over the eastern carolinas is investigated it is concluded that the band formed in the updraft portion of a thermodynamically direct vertical circulation about an upper level frontal zone in a region of conditional symmetrical instability csi the release of csi is presumed to have been responsible for the dimensions of the band and its orientation relative to the shear vector an adiabatic mechanism for destabilization of the environment of the upper level front to csi was explored but found to be insignificant in this case

stability and charging characteristics of the comma head region of continental winter cyclones abstractthis paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16 storm climatology analyzing the distribution of lightning within the comma head a case study of a deep cyclone is presented illustrating how upper tropospheric dry air associated with the dry slot can intrude over moist gulf air creating two zones of precipitation within the comma head a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection lightning when it occurred originated from the elevated convection a second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection updrafts within convective cells in both storms approached 6 8 m s 1 and convective available potential energy in the cell environment reached approximately 50 250 j kg 1 radar measurements obtained in convective updraft regions showed enhanced spectral

the role of cloud top generating cells and boundary layer circulations in the finescale radar structure of a winter cyclone over the great lakes abstractdata from airborne w band radar are used in conjunction with thermodynamic fields from the weather research and forecasting model and air parcel back trajectories from the hysplit model to investigate the finescale reflectivity vertical motion and airmass structure of the comma head of a winter cyclone in the vicinity of the great lakes cloud top generating cells formed along an upper level frontal boundary vertically separating dry air which 48 h earlier was located in the upper troposphere over south central canada from moist air which was located in the lower troposphere over the southeast united states the stronger updrafts within the generating cells had vertical velocities ranging from 1 to 3 m s 1 the generating cells were important to precipitation production within the comma head precipitation trails formed within the generating cells could sometimes be followed to the boundary layer before merging boundary layer air beneath the cyclone s comma head exhibited convective circulati

dynamical forcing and mesoscale organization of precipitation bands in a midwest winter cyclonic storm abstract a winter snowstorm developed on 10 11 february 1988 over the midwestern united states and produced several inches of snowfall locally over east central illinois analysis of the mesoscale organization of the storm revealed the presence of complex banded structure throughout its 17 h evolution three distinct types of mesoscale precipitation bands were identified during the course of the storm using a 10 cm doppler radar as part of the university of illinois winter precipitation program the bands had different orientations directions of movement relationships to synoptic scale frontal zones and mechanisms for development the mesoscale organization of this storm system is reviewed mesoscale synoptic scale and doppler analyses of the storm structure are presented the role of boundary layer convergence conditional symmetric instability and frontogenetical forcing in the formation and maintenance of the different mesoscale precipitation bands is discussed

statistical analysis and updated climatology of explosive cyclones abstract a statistical analysis of 12 and 24 hour deepening rates for all surface lows analyzed on at least two successive nmc 12 hourly front half hemispheric surface charts was performed for one year of data both 12 and 24 hour deepening distributions showed statistically significant at the 5 level departures from normality with the largest deviations occurring along the tail of the distribution associated with most rapid deepening the sum of two normal curves of different means and standard deviations was successfully fitted to the deepening distributions suggesting that most cases of explosive cyclogenesis are the result of some additional physical mechanism distinct from ordinary baroclinic instability the climatology of explosive cyclones sanders and gyakum was updated to include the 1979 82 cold seasons and compared to the previous three year sample in addition a climatology of formation positions maximum deepening positions and dissipation positions for all cyclones in a one year d

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part i multiscale case study abstract the long standing observational view of cyclogenesis involves an interaction between tropopause and surface based finite amplitude disturbances there are however instances where more than one upper level disturbance contributes to low level development a subset of these events involves wave or trough merger which has been defined as the amalgamation of two or more distinct 500 hpa vorticity maxima an example of this phenomenon involving a case of very intense continental cyclogenesis 25 26 january 1978 over the eastern united states is selected to elucidate the origin and evolution of precursor disturbances from the planetary scale to the mesoscale the analysis of this event reveals that the two well defined tropopause based disturbances that contribute to cyclogenesis have distinctly different origins and are brought together by confluent planetary scale flow one of these disturbances originates over the western north pacific ocean 10 days prior to cyclogenesis and tracks eastward

the structure and evolution of a continental winter cyclone part i frontal structure and the occlusion process the frontal structure and occlusion process in a cyclone of moderate intensity that affected the central united states in january 1995 is examined the deep warm frontal zone associated with this cyclone had a lateral extension to the southwest of the sea level pressure minimum that although characterized by cold air advection near the surface had many of the characteristics of a warm front aloft in fact this feature had a structure similar to the so called bent back fronts previously documented only in association with explosively deepening maritime cyclones the development of a warm occluded structure was investigated with the aid of a numerical simulation of the event performed using the university of wisconsin nonhydrostatic modeling system the development of the warm occluded structure was asynchronous in the vertical occurring first at midtropospheric levels and later near the surface in contrast to the classical occlusion process near the surface the warm occluded front was formed as the warm front was overtaken by the frontogenetically inactive portion of the historical coldfrontal zone at midtropospheric levels the warm occluded structure formed as a result of the cold frontal zone approaching and subsequently ascending the warm frontal zone in accord with a component of the classical occlusion mechanism the observed asynchronous evolution of the occluded structure is proposed to result from the vertical variation in vortex strength associated with the upper level potential vorticity pv anomaly that controls the cyclogenesis it is suggested that the occlusion process begins aloft where the associated vortex strength is greatest and gradually penetrates downward toward the surface during the cyclone life cycle additionally a characteristic treble clef shape to the upper level pv anomaly is shown to be a sufficient condition for asserting the presence of a warm occluded structure in the underlying troposphere

the structure and evolution of a continental winter cyclone part ii frontal forcing of an extreme snow event abstract the production of a narrow heavy occasionally convective snowband that fell within a modest surface cyclone on 19 january 1995 is examined using gridded model output from a successful numerical simulation performed using the university of wisconsin nonhydrostatic modeling system it is found that the snowband was produced by a thermally direct vertical circulation forced by significant lower tropospheric warm frontogenesis in the presence of across front effective static stability differences as measured in terms of the equivalent potential vorticity pve the sometimes convective nature of the snowband resulted from the development of freely convective motions forced by frontal lifting of the environmental stratification model trajectories demonstrate that a stream of warm moist air ascended through the trowal portion of the warm occluded structure that developed during the cyclone life cycle the lifting of air in the trowal was in this case forced by lower tropospheric frontogenesis occ

mesoscale structure in the megalopolitan snowstorm of 11 12 february 1983 part i frontogenetical forcing and symmetric instability abstract a cyclone moving northeastward off the coast of the northeastern united states on 11 12 february 1983 was accompanied by a band of heavy snow across all the major cities of this region from washington to boston frontegenetical forcing and symmetric instability are discussed as possible explanations of the intense precipitation rawinsonde data were analyzed to investigate the roles of these effects in this case we found that intense ascent was part of a thermally direct transverse circulation to be expected in response to frontogenetical forcing when the symmetric stability in the warmer air is small symmetric instability per se in the saturated major cloud mass may have been responsible for pulselike oscillations in its top these were men in satellite imagery elongated in the direction of the tropospheric thermal wind

frontogenesis and symmetric stability in a major new england snowstorm abstract synoptic and doppler radar data are used to study the roles of large scale frontogenetical forcing and of moist symmetric instability in the new england snowstorm of 5 6 december 1981 associated with an explosively intensifying cyclone offshore radar reflectivity patterns showed a tendency toward banded structure particularly near the leading northwestern edge of the storm only a minor portion of the snowfall however was associated with this pronounced bandedness from a set of constant pressure analyses the frontogenetical forcing was measured from the variation along the temperature gradient of the geostrophic wind component in the direction of this gradient over southeastern new england maximum forcing found near 500 mb at the outset of the storm descended to the layer between 850 and 700 mb 24 h later magnitudes were 3 7 10 10 deg m 1 s 1 observed rates of strengthening of temperature gradient were less than half this value implying relative adiabatic cooling in the rising

mesoscale dynamics of the trowal and warm frontal regions of two continental winter cyclones abstract the dynamic and thermodynamic structure and associated frontal circulations within the trowal and warm frontal regions of two extratropical winter cyclones are examined using numerical simulations in each cyclone the warm moist airstream originating in the warm sector was found to bifurcate upon reaching the warm front one branch of the flow turned anticyclonically eastward corresponding to the warm conveyor belt while the second branch turned cyclonically westward becoming the trowal airstream the dynamic forcing of vertical motion within the two airstreams was investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 both from an analysis of the sawyer eliassen se equation in two dimensions and from complete model solutions shearing deformation associated with the jet stream and the low level cyclonic flow dominated confluent deformation near the trowal in both cases the shearing deformation was accompanied

frontogenesis in the presence of small stability to slantwise convection abstract it is often observed that despite the existence of near neutrality to slantwise convection rainbands and snowbands can persist for long periods with narrow intense updrafts producing large quantities of precipitation in many cases this is probably due to the presence of active frontogenesis which as shown here maintains such structures in order to investigate this process we use two dimensional semigeostrophic theory to solve the deformation forced frontogenesis problem for a circumstance in which the stability to moist slantwise convection is small but positive in this case numerical simulation is necessary to determine the evolution of the front several previous studies have described the role of diabatic forcing in modifying the cross frontal circulation by use of the sawyer eliassen equation in particular analytic solutions of that equation for the case of small moist symmetric stability show that a narrow updraft should occur ahead of the maximum geostrophic frontogenesis numeri