transition from an eastern pacific upper level mixed rossby gravity wave to a western pacific tropical cyclone 1 the ancestor of unseasonal typhoon nanmadol 2004 over the western north pacific is traced back to the eastern pacific near 120 w as an upper tropospheric counter clockwise rotating mixed rossby gravity mrg wave the temporal and spatial evolution from an equatorial trapped mrg wave type disturbance to an off equatorial tropical depression is documented by utilizing nogaps navy s operational global atmospheric prediction system analysis data it is found that the mrg wave moved away from the equator after a dramatic reduction in its zonal dimension and downward development and amplification in the lower troposphere these dramatic changes in mrg wave properties are attributed to the modulation of the easterly vertical shear low level westerly easterly confluence in the large scale background flows and convective coupling as well as underlying high sea surface temperature sst the boundary layer convergence associated with asymmetric pressure field of the mrg wave is likely responsible for the transition from an equatorial mrg to an off equatorial tropical disturbance this case study addresses the possibility that upper tropospheric mrg waves over the far eastern pacific may provide seeds for tropical cyclogenesis over the western north pacific

2 3 day convective variability in the tropical western pacific abstract this paper is an examination of 2 3 day convective variability in the tropical pacific region the initial focus of the paper is on the western tropical pacific during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period iop high spatial and temporal resolution outgoing longwave radiation olr data and sea surface temperatures are filtered to eliminate diurnal and lower frequency variability the propagation of the 2 3 day convective variability is also studied westward propagation appears to be favored in some regions indicative of the events being influenced by westward propagating inertio gravity waves however many regions have 2 3 day events that divide fairly equally into eastward and westward propagations indicating that both eastward and westward propagating inertio gravity waves are influencing the oscillation the sst data during the 4 month iop dataset show evidence of a 2 3 day variability during those con

observations of variability on synoptic timescales in the east pacific itcz abstract data obtained in the eastern pacific intertropical convergence zone itcz during the tropical eastern pacific process study tepps show a 3 6 day variability the noaa ship ronald h brown collected surface meteorological observations c band doppler radar volumes atmospheric soundings and rainfall data while on station at 7 8 n 125 w from 8 23 august 1997 the 3 6 day variability was a prominent timescale in the meridional wind and humidity data the maxima of the surface to 700 mb meridional wind anomalies were 5 12 m s 1 maxima of the moisture anomalies at the same levels were 1 3 g kg 1 in phase with the low level southerlies while upper level moisture lagged the southerlies by less than a day the radar indicated a close connection between precipitation in the vicinity of the ship and the meridional wind with the precipitation occurring when the surface southerlies were strongest the meridional and zonal wind components had a maximum of 850 450 mb wind shear during the southerly e

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

a spectrum analysis of synoptic scale disturbances in the itcz abstract spectral characteristics of convective signals in synoptic scale disturbances along the intertropical convergence zone itcz are examined using a 20 yr daily outgoing longwave radiation dataset a new analysis method which combines conventional wavenumber frequency spectrum analysis and wavelet analysis is developed to explore the longitudinal seasonal and interannual variations in these disturbances within the itcz whose seasonal migration varies in different parts of the tropics the analysis focuses on three longitudinal sectors where the itcz can be clearly identified the western central pacific the central eastern pacific and the atlantic west africa the most striking results are the evident zonal variability in the spectral properties of westward propagating synoptic scale disturbances the zonal variability exists not only in their dominant frequencies and zonal wavenumbers but also in their seasonal and interannual variations eastward propagating synoptic scale disturbances in

synoptic settings of westerly wind bursts the morphology of westerly wind bursts wwbs during the 1980s is investigated using 1000 mbar winds analyzed by the european center for medium range weather forecasts ecmwf the variety of synoptic situations in which wwbs occur are explored so that the dynamics of wwb generation and maintenance can be studied and so that those interested in short and long term forecasts of conditions over the equatorial pacific will have an increased knowledge of those elements associated with wwbs wwbs are identified by searching for episodes in which the zonal wind was at least 5 m s 1 over at least 10 longitude for two or more days this definition based on surface winds rather than elevated winds or wind anomalies reflects the impact wwbs have on air sea interaction processes the spatial and temporal criteria provide a synoptic scale envelope for such interactions and mitigate against erroneous analyses according to these criteria 131 distinct wwbs occurred during the 1980s a new two dimensional classification scheme has been developed the nine patterns in it describe the near surface flow during 90 of these wwbs a single cyclone or a series of cyclones in one or both hemispheres and several different types of cross equatorial flow are the major components of the patterns only 8 of the bursts were associated with concurrent cyclones in both the northern and southern hemispheres four bursts involving cross equatorial flow are subjected to further study the flow is decomposed into barotropic and baroclinic parts and into rotational and divergent baroclinic components one of the bursts was predominantly barotropic and another predominantly baroclinic the cross equatorial flow in all four cases was predominantly divergent in nature the information from these cases coupled with the typical vertical structures and small meridional length scales associated with the various synoptic patterns suggests that simple baroclinic models of circulations driven by near equatorial heating are not adequate to describe the dynamics during wwbs

observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

the equatorial response to higher latitude forcing abstract the classic view following charney and webster and holton is that significant midlatitude forcing of the tropics can be expected only in regions with westerly winds in the upper troposphere because it is only in these regions that stationary rossby waves will be able to propagate toward the equator here it is shown that higher latitude forcing can project directly onto equatorial waves and give a significant tropical response in both easterly and westerly tropical flow the equatorial response to higher latitude forcing is considered in the context of a dry atmosphere and a localized higher latitude forcing with eastward or westward phase speed previous ideas of the doppler shifting of equatorial waves by zonal flows are extended to include consideration of a forcing involving a range of zonal wavenumbers a gill type model suggests that there can be significant forcing of equatorial waves by either vorticity forcing or heating in higher latitudes in agreement with the theory the kelvin wav

radar observations of a 3 day kelvin wave in the equatorial mesosphere mesospheric radars are used to investigate the characteristics of a kelvin wave from two equatorial sites jakarta indonesia in the western pacific and christmas island in the central pacific our study focuses on the time span from mid january through mid october 1993 a kelvin wave with a period near 3 days was detected throughout this 9 month duration although it underwent deep amplitude modulations on a 20 day timescale a fitting procedure is applied to study the phase amplitude behavior of the wave the vertical wavenumber was measured by the radars and found to be small wandering around zero with only a weak bias toward downward phase progression the long vertical wavelength suggests that the wave was predominantly zonal wavenumber 1 the amplitude of the wave measured by the jakarta meteor scatter radar was much larger than the amplitude measured by the mf partial reflection radar at christmas island the smaller wave amplitude at christmas island could at least partially be due to a measurement bias associated with mf radars the radar at jakarta is a vhf meteor scatter radar and is not susceptible to this bias however the mean velocities and the amplitudes of the tidal and quasi 2 day wave components were in good agreement at the two sites the estimated 9 month averaged zonal acceleration was 0 67 ms 1 day 1 over jakarta at 94 98 km and only about half as large over christmas island the magnitude of the zonal acceleration occasionally showed large enhancements which suggest the importance of refractive effects associated with vertical and temporal variations in the mean winds the larger 3 day wave amplitudes and inferred acceleration at jakarta may reflect its location in the western pacific a region of high convection and hence an excitation region for equatorial waves the relative phase of the wave between the two radar sites gradually shifted over a timescale of weeks these smooth variations in relative phase are suggestive of a superposition of waves with different zonal wavenumbers perhaps radiating preferentially from one longitude the phase of the wave as a function of altitude and time was much more disordered at jakarta than at christmas island the conjecture can be made that the more chaotic phase structure observed over jakarta is due to higher order zonal wavenumber components which weaken as they propagate eastward

total moment spectra of fourteen large earthquakes total moment spectra mt m where m is the moment rate tensor are computed for 14 large earthquakes recorded by the international deployment of accelerometers ida network using the scalar moment retrieval method proposed by silver and jordan 1982 for each event we obtain estimates of mt averaged over the 10 disjunct 1 mhz intervals in the low frequency band 1 11 mhz typical ida record sets from events with mt 0 2 a 1 a 1027 dyne cm yield standard errors on the 1 mhz averages that are generally less than 20 our multiple band estimates of mt are usually consistent with comparable single band values found by other investigators from the total moment spectra we derive the zero frequency static moment mt 0 and the characteristic source duration c 2 var f t where f t is the time function of the moment rate tensor assumed to be the same for all components the parameter c formally depends on the second degree temporal spatial and mixed spatial temporal moments of an extended source but calculations with realistic source geometries indicate that the interpretation of tc strictly in terms of the second temporal moment leads to very little error a plot of c against shows considerable scatter some events lie significantly above the empirical scaling curve of kanamori and given 1981 slow earthquakes and some below fast earthquakes examples of the former include all three deep focus events analyzed here as well as the 1970 colombia and 1963 peru bolivia deep focus earthquakes whose total moment spectra are calculated from the moment tensor solutions of gilbert and dziewonski 1975 an example of the latter is the great sumbawa earthquake of august 9 1977 24 3 a which is inferred to have a relatively shallow spatial centroid 20 km and a nearly flat moment spectrum suggesting that the faulting was confined to the upper more brittle portion of the oceanic lithosphere three other large earthquakes tonga june 22 1977 23 2 a kuril islands december 6 1978 3 6 0 2 a and tumaco december 12 1979 25 2 a exhibit moment spectra which significantly decrease toward higher frequencies indicating larger values of c the aftershocks of both the tonga and kuril islands events are distributed over a considerable range of depths consistent with rupture into the lower more ductile portions of the oceanic lithosphere we speculate that the characteristic source duration may be causally related to the depth of coseismic rupturing within the lithosphere

rupture dimensions of the 1998 antarctic earthquake from low frequency waves we inverted frequency dependent phase and amplitude measurements from 1st orbit rayleigh waves at global stations for the 1st and 2nd degree polynomial moments of the stress glut rate tensor the higher moments of the slip rate distribution determine the fault plane and approximate rupture dimensions the results show strong rupture propagation to the west with an average velocity of the instantaneous centroid of 3 6 1 km s the rupture had a characteristic length of 178 46 km in the east west direction and a characteristic duration of 48 2 s the results are consistent with unilateral rupture on the east west fault plane of the focal mechanism and rule out significant rupture on the north south nodal plane

space time spectral analysis of the moist static energy budget equation abstractthe budget of column integrated moist static energy mse is examined in wavenumber frequency transforms of longitude time sections over the tropical belt cross spectra with satellite deri

re visiting the tectonics of the oceanic intraplate earthquake of march 25 1998 m 8 1 in the balleny sea offshore antarctica abstract the antarctic plate earthquake of march 25 1998 m 8 1 and its aftershocks are re visited to evaluate the role of the associated tectonics in stress concentration due to ambient horizontal crustal motion caused by deglaciation in antarctica using a numerical technique called the distinct element method a two dimensional structural model of the epicentral region is developed and tectonically loaded for a year along the inferred direction of the motion a spatial correlation is observed between the resulting locations of relatively high shear stresses and those of the main shock and associated aftershocks in particular seismicity is concentrated at and near the intersections of the main fault carey and gambier fracture zones where the shear stresses are significantly elevated and whose sign duplicate the inferred sense of movement along them the modeling results suggest that stress concentrations near pre existing intersecting fault and fracture zones due to a possible deglaciation induced horizontal crustal force may have been a cause of this enigmatic earthquake

modulation of seasonal precipitation over the tropical western central pacific by convectively coupled mixed rossby gravity waves abstractthe relationship between the interannual variations of the activity of convectively coupled equatorial waves and seasonal mean precipitation in the tropical western to central pacific ocean is investigated it is found that the convectively coupled mixed rossby gravity mrg waves are highly and negatively correlated with the seasonal precipitation near the equator in boreal summer it is suggested that the mrg waves which have convection centers off the equator suppress the equatorial precipitation the relation is insignificant in the other seasons when the interannual variation of sea surface temperature near the equator is greater than in boreal summer also a similar relation is not found in the eastern pacific in any season

the coupling of mixed rossby gravity waves with diabatic heating during the trmm kwajex field campaign composite dynamic and thermodynamic structures of mixed rossby gravity mrg waves are presented with their coupling with diabatic heating and moisture sources sinks using tropical rainfall measuring mission kwajalein experiment trmm kwajex field campaign data a significant departure of convectively coupled waves from dry waves exists in the phases of wave component maximum low level wind convergence is accompanied by midtropospheric divergence and upper tropospheric convergence that is preceded by increase of moisture in the boundary layer these phases correspond to surface turbulent transport shallow and midlevel convections that cause moistening and heating of the lower and middle troposphere they are followed by deep convection with maximum heating centered in the upper troposphere the deep convective heating evolves to stratiform like upper tropospheric heating and lower tropospheric cooling that precedes the quick demise of convection such a structure on convectively coupled mrg waves is summarized by four phases which sheds lights on how tropical waves are coupled with convective processes in all their phases

interannual variations in mixed rossby gravity waves and their impacts on tropical cyclogenesis over the western north pacific abstract the present study investigates the transition from mixed rossby gravity mrg waves to tropical depression td type disturbances and its interannual variations over the western north pacific wnp using ecmwf high resolution data for the years of 1980 2001 as the equatorially trapped mrg waves propagate westward into the wnp the mrg waves transit to td type disturbances because of background flow change interannual variations in the transition of mrg waves are related to monsoon circulation change in response to tropical convective heating over the warm pool wp region when the wp is in a warm state convective heating is enhanced in the western part of the wnp and the monsoon trough retreats westward which induces a westward shift of the wave transition zone in contrast when the wp is in a relatively cold state the eastward penetration of convection and monsoon trough shifts the wave transition to the eastern part of the wnp the zonal wind convergence and shear in the monsoon trough

synoptic scale disturbances near the equator abstract a spectral analysis of winds analyzed and initialized at the european centre for medium range weather forecasts reveals an abundance of power in the 850 mb meridional wind along the equator with periods near four days the power is mostly in the westward propagating component using high pass filtered data it is shown that the waves have westward phase and eastward group propagation relative to the mean wind the longest wavelengths are found over the pacific ocean while the shortest are found over the convectively variable regions of indonesia south america and africa mean phase speeds at 850 mb are positively correlated with the mean wind on the equator at 500 mb and below and negatively correlated with the mean wind above that level the effective advecting zonal wind of the disturbances seems to be the density weighted average of the lower troposphere the structure of the disturbances bears resemblance to the expected structure of an equatorially trapped mixed rossby gravity wave over t

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

synoptic scale waves in sheared background flow over the western north pacific abstracttropical depression td type waves are the dominant mode of synoptic scale fluctuations over the western north pacific by applying spatiotemporal filters to the observed olr data and the ncep doe amip ii reanalysis data for 1979 2013 this study reveals the characteristics and energetics of convectively coupled td type waves under the effects of different circulation patterns in association with vertical wind shear results exhibit that different ambient sheared flows significantly affect the vertical structure of westward propagating td type waves with a lower tropospheric mode in an easterly sheared background and an upper tropospheric mode in a westerly sheared background energetic diagnoses demonstrate that when the disturbance is trapped in the lower upper level by easterly westerly shear the horizontal mean flow in the lower upper level favors wave growth by converting energy from the shear of the zonal mean flow from the convergence of the meridional mean flow during the penet

on the interpretation of subevents in teleseismic waveforms the 1994 bolivia deep earthquake revisited we evaluate the methodologies that aim at resolving the space time slip distribution during large earthquakes in one common approach the source process of an event is assumed to be composed of a series of subevents critical points in teleseismic body waves such as peaks and coherent arrivals are viewed as discrete points in the spatiotemporal history of an earthquake we show that these features can be interpreted as the instantaneous centroid locations of the moment release history we demonstrate this result with an analysis of the mw 8 2 bolivia 1994 deep event we reconstruct the slip distribution in two contrasting ways first broadband p waves are interpreted as being composed of subevents five peaks in the moment release rate are located relative to the onset of the rupture using the azimuthal variations of onset to peak times second we invert broadband p waves for the slip distribution on a subhorizontal fault we use a nonlinear tomographic imaging technique called simulated annealing and an l1 misfit norm rupture velocities appear to be 2 km s 1 and largest slip values are found to the east and north of the onset in a 40 by 50 km region the instantaneous centroids of the moment release history correspond closely to the locations found using the subevent analysis however especially near the middle and the end of the rupture the instantaneous centroid locations are in regions of little moment release we discuss how the subevent analysis and the instantaneous centroid approach lead to dissimilar interpretations of rupture processes especially for events with length to width ratios near unity another result of this study is that the rupture of the 1994 bolivia event appears to end 50 km to the northwest of the onset implying that the slip area is larger that previously thought comparing the slip distribution with the aftershock distribution suggests that more than one physical mechanism is necessary to account for the rupture process of this great deep event

generation of african easterly wave disturbances relationship to the african easterly jet abstract the relationship between african easterly waves and the background climatology in which they form is studied using a regional climate model the surface and lateral boundary conditions in the model are manipulated to modify the background climatology especially the african easterly jet and the itcz and the behavior of the waves in these different settings is evaluated three climate simulations are presented with monthly mean lateral and surface boundary conditions one has a strong jet and a strong itcz the second has a strong jet and a weak itcz and the third has a weak jet and a strong itcz in these simulations the presence of wave activity is more closely associated with the concentration of the itcz than the strength of the african easterly jet in particular the simulation with a strong jet accompanied by a weak itcz does not produce significant wave activity but a weak jet with a strong itcz has realistic wave disturbances both the charney stern and the fjortoft necessary conditi

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

a vortex based perspective of eastern pacific tropical cyclone formation tropical cyclone formation over the eastern pacific during 2005 and 2006 was examined using primarily global operational analyses from the national centers for environmental prediction this paper represents a vortex view of genesis adding to previous work on tropical cyclone formation associated with tropical waves between 1 july and 30 september during 2005 and 2006 vortices at 900 hpa were tracked and vortex following diagnostic quantities were computed vortices were more abundant during periods of an enhanced hadley circulation with monsoon westerlies around 10 n in the lower troposphere this zonally confined hadley circulation was significantly stronger during the genesis of developing vortices developing vortices were stronger at the outset with a deeper potential vorticity maximum compared to nondeveloping vortices this implies that developing disturbances were selected early on by favorable synoptic scale features the characteristic time mean reversal of the meridional gradient of absolute vorticity in the lower troposphere was found to nearly vanish when the aggregate contribution of strong vortices was removed from the time mean vorticity this finding implies that it is difficult to unambiguously attribute development to a preexisting enhancement of vorticity on the synoptic scale the time mean enhancement of cyclonic vorticity primarily results from the accumulated effect of vortices it is suggested that horizontal deformation in the background state helps distinguish developing vortices from nondevelopers and also biases the latitude of development poleward of the climatological itcz axis

frequency distribution of daily itcz patterns over the western central pacific abstract this study attempts to explore a comprehensive and compact approach for delineating the multiscale and multivariate characteristics of the itcz over the western central pacific based on daily satellite observations of precipitation ssts and surface winds essentially six distinct itcz spatial patterns namely the north south equator double full and weak are identified according to the daily percentage coverage of deep convection within different latitudinal bands on and off the equator over the western central pacific the evolving structure of the itcz over the western central pacific is investigated with a focus on the transient statistical characteristics the relationship between these daily itcz patterns and ssts and near surface winds is also examined the north 37 south 24 and weak 24 itczs represent the three major itcz daily patterns over the western central pacific and combined they account for almost 85 of the total number of days within a 10 yr period the other

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

new constraints on the rupture process of the 1999 august 17 izmit earthquake deduced from estimates of stress glut rate moments summary this paper illustrates the use of integral estimates given by the stress glut rate moments of total degree 2 for constraining the rupture scenario of a large earthquake in the particular case of the 1999 izmit mainshock we determine the integral estimates of the geometry source duration and rupture propagation given by the stress glut rate moments of total degree 2 by inverting long period surface wave lpsw amplitude spectra kinematic and static models of the izmit earthquake published in the literature are quite different from one another in order to extract the characteristic features of this event we calculate the same integral estimates directly from those models and compare them with those deduced from our inversion while the equivalent rupture zone and the eastward directivity are consistent among all models the lpsw solution displays a strong unilateral character of the rupture associated with a short rupture duration that is not compatible with the solutions deduced from the published models with the aim of understand this discrepancy we use simple equivalent kinematic models to reproduce the integral estimates of the considered rupture processes including ours by adjusting a few free parameters controlling the western and eastern parts of the rupture we show that the joint analysis of the lpsw solution and source tomographies allows us to elucidate the scattering of source processes published for this earthquake and to discriminate between the models our results strongly suggest that 1 there was significant moment released on the eastern segment of the activated fault system during the izmit earthquake 2 the apparent rupture velocity decreases on this segment

synoptic scale dual structure of precipitable water along the eastern pacific itcz abstractusing 10 yr high resolution satellite and reanalysis data the synoptic scale dual structure of precipitable water pw in which the southern and northern bands straddled at the itcz produce zonally propagating meridional dipoles is observed over the eastern pacific ep during boreal summer and fall composites indicate that the pw dipole concurrent with the dipole like filtered divergence has a shift to the west of the anomalously cyclonic circulation the vertical structure of filtered meridional wind is characterized by a wavenumber 1 baroclinic mode and the vertical motion has two peaks situated at 850 and 300 hpa respectively to the east of the pw dipole the shallow convection is embedded within the deep convection forming a multilevel structure of meridional wind on the itcz equatorward side to the west of the pw dipole the deep convection tends to be suppressed because of the invasion of midlevel dry air advected by northerly flows the generation and propagation of the dual pw

climatology of sign reversals of the meridional potential vorticity gradient over africa and australia abstract a 10 yr climatology 1986 95 was performed using ecmwf gridded analyses on isentropic surfaces to identify regions where the lower tropospheric meridional potential vorticity pv gradient changes sign across africa and australia during their respective summer seasons while an african sign reversal has been documented no similar study has been performed for the australian region which also has desert on the poleward side of open ocean in each hemisphere a northward decrease of pv is sufficient to produce a sign reversal it was found that pv decreases northward in the lower troposphere across northern australia with the maximum reversal on the 315 k surface it had comparable magnitude but smaller zonal extent 3000 km than that on the 320 k surface in africa 5000 km in each region the sign reversal was associated with cyclonic pv anomalies on the equatorward side and anticyclonic anomalies on the poleward side olr was used as a proxy for deep convective heating in order to evaluate

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

consistent changes in the sea ice seasonal cycle in response to global warming the northern hemisphere sea ice cover has diminished rapidly in recent years and is projected to continue to diminish in the future the year to year retreat of northern hemisphere sea ice extent is faster in summer thanwinter whichhasbeenidentifiedasoneofthemoststrikingfeaturesof satellite observations aswellasof state of the art climate model projections this is typically understood to imply that the sea ice cover is most sensitive to climate forcing in summertime and previous studies have explained this by calling on factors such as the surface albedo feedback in the southern hemisphere however it is the wintertime sea ice extent that retreats fastest in climate model projections here it is shown that the interhemispheric differences in the model projections can be attributed to differences in coastline geometry which constrain where sea ice can occur after accounting for coastline geometry it is found that the sea ice changes simulated in both hemispheres in most climate models are consistent with sea ice retreat being fastest in winter in the absence of landmasses these results demonstrate that despite the widely differing rates of ice retreat among climate model projections the seasonal structure of the sea ice retreat is robust among the models and is uniform in both hemispheres

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

aftershock zone scaling we investigate the distribution of aftershock zones for large earthquakes scalar seismic moment m 10 19 5 n m moment magnitude m 7 mainshocks are selected from the harvard centroid moment tensor catalog and aftershocks are selected from the preliminary determination of epicenters neic catalog the aftershock epicenter maps are approximated by a two dimensional gaussian distribution the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size the dependence of zone length l on earthquake size is studied for three representative focal mechanisms thrust normal and strike slip although the numbers of mainshocks available for analysis are limited maximum a few tens of events in each case all earthquakes show the same scaling m l 3 no observable scaling break or saturation occurs for the largest earthquakes m 10 21 n m m 8 therefore it seems that earthquake geometrical focal zone parameters are self similar

mixed rossby gravity waves and western pacific tropical cyclogenesis part i synoptic evolution abstract a large amplitude mixed rossby gravity wave packet is identified in the western pacific using 6 10 day bandpass filtered winds individual disturbances of 2300 3000 km wavelength propagated westward as the packet moved slowly eastward the packet first appeared and subsequently amplified within a region of active convection associated with the madden julian oscillation mjo which was isolated by low pass filtered outgoing longwave radiation the packet lasted about 5 weeks then rapidly dispersed as the active mjo moved away from it to the east west of 150 e individual disturbances within the packet turned northwestward away from the equator indicating an apparent transition from mixed rossby gravity waves to off equatorial tropical depression td type disturbances cyclones filled with cloud and anticyclones cleared during the transition nevertheless convective structure consistent with mixed rossby gravity waves remained outside the circulation centers and three tropical cyclones for

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

upper tropospheric equatorial waves in ecmwf analyses tropical wind fields from the european centre for medium range weather forecasts operational analyses are analysed to search for equatorially trapped waves in the upper troposphere data are studied for 1980 87 zonal wind spectra show a predominance of power at low zonal wave numbers and low frequencies these data do not show distinct spectral peaks corresponding to eastward propagating kelvin waves or westward propagating equatorially trapped rossby waves the zonal wind spectra do show episodic evidence for westward propagating 5 day zonal wave 1 features with maxima over the equator these are likely related to rossby normal mode oscillations previously reported meridional wind spectra show a predominance of westward propagating power in the 6 to 10 day period range primarily concentrated in zonal waves 4 7 enhanced meridional wind activity at the equator occurs episodically in time with events persisting for one to several months duration wave packets are longitudinally localized with preferred occurrence over the eastern pacific ocean most cases show evidence of meridional wind maxima in the tropics suggesting a degree of equatorial trapping the horizontal structure of these oscillations is that of mixed rossby gravity waves although they are not necessarily centred directly over the equator these waves have largest amplitudes in the upper troposphere showing weak coherence with the surface they appear to be fundamentally distinct from fast 4 to 5 day rossby gravity waves observed in the western pacific a detailed study of a group of intense rossby gravity waves observed over the eastern pacific during august september 1985 is presented the reality of these features is confirmed in direct rawinsonde observations correlations are found between bursts of equatorial wave activity and enhanced meridional momentum fluxes from the subtropics suggesting extratropical forcing as at least one mechanism for their generation the waves are also strongly coupled to the upper tropospheric zonal wind field which likely accounts for their longitudinal and temporal confinement

influence of equatorial waves on the genesis of super typhoon haiyan 2013 abstractthe influence of equatorial wave disturbances on the genesis of super typhoon haiyan 2013 is investigated through spectral composite and ensemble sensitivity analysis of various observational datasets in combination with predictions from an operational ensemble under the favorable large scale environmental conditions of the asian monsoon combined with the madden julian oscillation mjo the incipient haiyan develops from a cyclonic disturbance that originates from a train of westward propagating mixed rossby gravity mrg waves haiyan eventually develops in the monsoon trough region at the leading edge of the moist mjo phase that has strong low level convergence high moisture content and weak shear along with high sea surface temperature these favorable environmental conditions promote the intensification of deep moist convection that facilitates the development of the cyclonic disturbance from an mrg wave into a tropical depression which later intensifies rapidly into super typhoon ha

the role of trade wind surges in tropical cyclone formations in the western north pacific abstract a total of 40 out of 531 tropical cyclones that formed in the western north pacific during 1986 2005 have accompanied trade wind surges located 5 15 latitude to the north of the pretropical cyclone disturbance centers composite and empirical orthogonal function analyses indicate that the trade wind surges are related to a midlatitude eastward moving high pressure system often found during the east asian winter monsoon therefore these trade wind surge tropical cyclones tend to occur in late season with one third of them in december and at lower latitudes 7 latitude lower than the climatological average formation position the evolution of mesoscale features during formation of trade wind surge tropical cyclones is examined various satellite datasets show similar mesoscale patterns during their formations a few convective lines form by convergence between the trade wind surges and the strengthening cyclonic circulation associated with incipient vortex within the 24 h before formation

large scale circulation associated with westerly wind bursts and deep convection over the western equatorial pacific the relationship between deep equatorial convection over the western pacific and atmospheric circulation during november to february 1986 1992 is studied using cross correlations between outgoing longwave radiation olr and national meteorological center global analyses we focus on intraseasonal convective events on the 6 to 30 day timescale over two regions just east of borneo and over the tropical ocean and global atmosphere toga coupled ocean atmosphere response experiment coare domain to the northeast of new guinea although comparatively little work has been done on this timescale we show that the bulk of the intraseasonal variability in both convection and low level circulation over the tropical western pacific occurs in this period range as a comparison with these higher frequency events the evolution of coare convection on the 30 to 70 day timescale is also considered the results of the historical data analysis are compared to a case study of deep convection associated with strong surface westerly winds during november 1989 this analysis is meant to serve as a benchmark for future case studies from the tropical ocean global atmosphere coare experiment and other periods in general 6 to 30 day equatorial convection in the regions studied occurs in conjunction with low level equatorial westerly wind anomalies paired anomalous cyclonic circulations straddling the equator and a strengthening of the sea level pressure gradient along the equator the increase in the pressure gradient appears most often tied to the simultaneous equatorward movement of high pressure systems originating over southeastern asia and australia a surge of trades over the central pacific also accompanies the development of convection over both study regions following the convective peak the low level westerlies slowly decay as the northern cyclone moves northwestward away from the equator in a track characteristic of a tropical depression it is also observed that low level westerly anomalies occur frequently without deep convection the vertical structure during convective events along the equator on the 30 to 70 day timescale and over indonesia in the 6 to 30 day band is baroclinic with easterly anomalies at upper levels overlying low level westerlies at 200 mbar a strengthened meridional outflow from the olr signal into a wave train on the equatorward side of the asian jet is observed to develop following the convective peak suggesting forcing of this circulation by the convection over the coare domain there is evidence that 6 to 30 day convection often occurs in conjunction with deep westerly flow it is suggested that these types of events are frequently characterized by vertical propagation of westerlies from the surface to the upper troposphere as is shown for a case study from november 1989 this westerly burst episode is shown to have many features in common with the typical case as defined from historical data

effect of enso and the mjo on western north pacific tropical cyclones prior work has suggested that rossby wave accumulation in the lower troposphere may be an important mechanism for the development of synoptic scale disturbances in the western north pacific in northern summer this work examines the intraseasonal and interannual variability of wave accumulation by computing the barotropic wave activity flux divergence at 850 hpa for different phases of the madden julian oscillation mjo and el nino southern oscillation enso indirectly and without ruling out other influences the results suggest a physical mechanism behind previously identified relationships between tropical cyclogenesis statistics and these two modes of variability mjo and enso

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

monsoonal influence on typhoon morakot 2009 part i observational analysis abstracttyphoon morakot made landfall on taiwan with a record rainfall of 3031 5 mm during 6 13 august 2009 while previous studies have emphasized the influence of southwesterly winds associated with intraseasonal oscillations and monsoon surges on moisture supply the interaction between morakot and low frequency monsoon flows and the resulting influence on the slow movement and asymmetric precipitation structure of the typhoon were examined observationally embedded in multi time scale monsoonal flows morakot generally moved westward prior to its landfall on taiwan and underwent a coalescence process first with a cyclonic gyre on the quasi biweekly oscillation time scale and then with a cyclonic gyre on the madden julian oscillation time scale the coalescence enhanced the synoptic scale southwesterly winds of morakot and thus decreased its westward movement and turned the track northward leading to an unusually long residence time in the vicinity of taiwan the resulting slow movement and collocation

scale interactions involved in the initiation structure and evolution of the 15 december 1992 mcs observed during toga coare part i synoptic scale processes this paper the first of a series examines the synoptic scale mechanisms involved in the initiation structure and evolution of a mesoscale convective system observed during toga coare this study relies upon the use of the japanese geosynchronous meteorological satellite 4 imagery and ecmwf model outputs from which diagnostic parameters are derived and interpreted this mesoscale convective system consists initially of two groups of convective entities that progressively move toward each other and merge it is shown that the synoptic scale flow creates a favorable environment for the formation of this large convective system through the production of convective available potential energy cape by horizontal advection and the enhancement of low level convergence in the region where the convective system formed moreover the general evolution of the system is found to be governed by the synoptic scale circulation and more precisely by the temporal evolution of cape and low level convergence the mechanisms leading to the initiation and general evolution of the system are examined the easterly equatorial jet at 500 hpa triggered positive potential vorticity areas that propagated westward and generated an anticyclonic circulation this anticyclonic circulation was enhanced during the development phase of the convective system through vortex stretching and tilting which accelerated the low level westerlies corresponding to the southern branch of this circulation and enhanced the low level convergence associated with the studied convective system in a companion paper the mesoscale and convective scale processes involved in the internal organization of this mesoscale convective system are examined using the airborne doppler radar dataset collected within the system from 1700 to 2100 utc the downscale interactions i e from synoptic scale to mesoscale and convective scale are scrutinized using both the synoptic scale context described in this paper and the mesoscale and convective scale characteristics derived from the airborne radar observations

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

the march 25 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake mw 8 1 occurred 250 km from the nearest plate boundary in oceanic lithosphere with an age of 35 55 my analysis of aftershock patterns shows that the earthquake ruptured a fault or series of strike slip fault segments nearly 300 km long the strike of the fault s is nearly perpendicular to the north south trending fossil fracture zones which are the most marked bathymetric features of this region moment release during the mainshock was concentrated in two large subevents clearly visible in the teleseismic body wave waveforms modeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation on the eastern end of the fault with the second large subevent occurring 220 280 km to the west the two pulses of moment release are found to be separated in time by 65 s comparison of the relative s wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by 10 occurred between the two subevents

origin of the summertime synoptic scale wave train in the western north pacific abstract the origin of the summertime synoptic wave train in the western north pacific is investigated with a multilevel nonlinear baroclinic model a realistic three dimensional summer mean state is specified and eigenvectors are calculated by introducing small perturbation initially to the model numerical experiments indicate that the origin of the synoptic wave train may arise from instability of the summer mean flow in the presence of a convection frictional convergence cfc feedback in the lack of the cfc feedback the summer mean flow supports only a least damped mode characterized by a northwest southeast oriented wave train pattern with a zonal wavelength of 2500 km in the presence of both the realistic summer mean flow and the cfc feedback the model reproduces a fast growing mode whose structure and propagation characters are similar to the observed sensitivity experiments with different initial perturbation patterns indicate that the model solution is not sensitive to initial conditions

are tropical cyclones less effectively formed by easterly waves in the western north pacific than in the north atlantic abstract it has been observed that the percentage of tropical cyclones originating from easterly waves is much higher in the north atlantic 60 than in the western north pacific 10 20 this disparity between the two ocean basins exists because the majority 71 of tropical cyclogeneses in the western north pacific occur in the favorable synoptic environments evolved from monsoon gyres because the north atlantic does not have a monsoon trough similar to the western north pacific that stimulates monsoon gyre formation a much larger portion of tropical cyclogeneses than in the western north pacific are caused directly by easterly waves this study also analyzed the percentage of easterly waves that form tropical cyclones in the western north pacific by carefully separating easterly waves from the lower tropospheric disturbances generated by upper level vortices that originate from the tropical upper tropospheric trough tutt it is observed that 25 of easterly waves form tropical cyclones in thi

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

a combined wave number frequency and time extended eof approach for tracking the progress of modes of large scale organized tropical convection an algorithm combining filtering in the wave number frequency domain with time extended empirical orthogonal function eeof analysis is developed and applied to diagnose and track signals associated with modes of organized moist deep convection in the tropics the wave number frequency spectrum of outgoing long wave radiation olr is broken down into five broad filter bands in order to concentrate signals associated with the madden julian oscillation convectively coupled equatorial rossby kelvin and mixed rossby gravity waves easterly waves and low frequency variations such as the el nino southern oscillation enso the eeof patterns are obtained from analysis of the filtered data and principal component pc time series are generated by projection of temporally smoothed but otherwise unfiltered data onto the eeof patterns filtered data are reconstructed by taking the product of the eeof patterns and the corresponding pcs these reconstructed data compare well with unfiltered olr anomalies and with olr anomalies filtered in the wave number frequency domain for the same modes the method is easily applied in real time since results are not influenced by the proximity to the end of the dataset copyright 2009 royal meteorological society

dispersion characteristics and circulation associated with boreal summer westward traveling mixed rossby gravity wave like disturbances abstractan algorithm has been developed to track synoptic scale westward traveling mixed rossby gravity mrg wave like disturbances with a cross equatorial component applied to space time filtered meridional wind data this algorithm finds locations with gaussian shaped wind structures stated in the solutions of shallow water equations swes based on 850 hpa meridional wind from the global national centers for environmental prediction ncep climate forecast system reanalysis cfsr dataset local and instantaneous wave properties including the occurrence time wavenumber intrinsic frequency and magnitude were examined it was found that these low level mrg wave like disturbances can be classified into a longer wavelength group and a shorter wavelength group while most waves identified in the eastern pacific give longer wavelengths disturbances in the western pacific tend to have a wider range of wavenumbers composite analysis revealed that east of 140 e low level disturbances are characterize

ongoing deformation of antarctica following recent great earthquakes antarctica s secular motion is thought to be almost everywhere governed by horizontal rigid plate rotation plus three dimensional deformations due to past and present changes in ice ocean loading known as glacial isostatic adjustment gia we use geodetic data to investigate deformation following the 1998 m 8 2 antarctic intraplate earthquake and show sustained three dimensional deformation along east antarctica s coastline 600 km from the rupture location using a model of viscoelastic deformation we are able to match observed northward velocity changes and either east or height but not all three directions simultaneously apparently partly due to lateral variations in mantle rheology our modeling predicts that much of antarctica may still be deforming with further deformation possible from the 2004 m 8 macquarie ridge earthquake this previously unconsidered mode of antarctic deformation affects geodetic estimates of plate motion and gia its viscous nature raises the prospect of further present day deformation due to earlier great earthquakes

application of the marsupial paradigm to tropical cyclone formation from northwestward propagating disturbances awave trackingalgorithmisdevelopedfornorthwestward propagatingwavesthat onoccasion playarole in tropical cyclogenesis over the western oceans to obtain the lagrangian flow structure the frame of reference is translated obliquely at the same propagation speed with the precursor disturbance trajectory analysis suggests that streamlines in the obliquely translated frame of reference can be used to approximate flow trajectories the algorithm was applied to super typhoon nakri 2008 tropical cyclone erika 2009 and a few other examples diagnoses of meteorological analyses and satellite derived moisture and precipitation fields show that the marsupial framework for tropical cyclogenesis in tropical easterly waves is relevant also for northwestward propagating disturbances as are commonly observed in the tropical western atlantic the gulf of mexico and the western north pacific finally it is suggested that analysis of the global model data and satellite observations in the marsupial framework can provide useful guidance on early tropical cyclone advisories

geographic muting of changes in the arctic sea ice cover the seasonal cycle in arctic sea ice extent is asymmetric its amplitude has grown in recent decades as the ice has retreated more rapidly in summer than in winter these seasonal disparities have typically been attributed to different physical factors operating during different seasons here we show instead that the seasonal asymmetries in arctic sea ice extent are a geometric consequence of the distribution of continents coastlines block southward ice extension during winter thereby muting changes in ice extent but they have relatively little effect at the time of summer minimum extent we suggest that the latitude of the arctic sea ice edge averaged zonally over locations where it is free to migrate is the most readily interpretable quantity to describe the northern hemisphere sea ice cover we find that the zonal mean sea ice edge latitude during the 1978 present era of satellite measurements has been following an approximately sinusoidal seasonal cycle that has been migrating northward at an approximately annually constant rate of 8 km year these results suggest a change in perspective of the most critical quantities for understanding changes in arctic sea ice

equatorial atmospheric waves and their association to convection equatorial wave systems and their relationships with convective activity are analyzed in the western and central pacific regions during the coupled ocean atmosphere response experiment coare intensive observation periods the study uses geostationary meteorological satellite infrared temperature observations and the operational european centre for medium range weather forecasts analyses supplemented with coare observations spectral and complex principal component analysis are applied to the data using the linear theory of equatorially trapped waves as a guideline the existence of three types of waves is detected in the 7 10 day period range n 5 1 rossby waves are found to the east of the date line in a region of weak convective activity over the western equatorial pacific where intense convection occurs the 7 10 day waves do not possess the general characteristics of linear rossby waves but they are strongly linked to the active phases of westerly wind bursts and of convection analysis of the meridional wind reveals intense mixed rossby gravity waves with a mean 5 day period and westward phase and eastward group velocities over the western pacific the convection is found to be strongly correlated with the antisymmetric structure of the divergent field as predicted by the linear theory in the 200 hpa divergence field n 5 1 gravity waves are visible having periods shorter than 2 5 days they rapidly propagate about 25 m s21 both westward and eastward and have strong correlations with convective clusters

cluster analysis of typhoon tracks part ii large scale circulation and enso abstract a new probabilistic clustering method based on a regression mixture model is used to describe tropical cyclone tc propagation in the western north pacific wnp seven clusters were obtained and described in part i of this two part study in part ii the present paper the large scale patterns of atmospheric circulation and sea surface temperature associated with each of the clusters are investigated as well as associations with the phase of the el nino southern oscillation enso composite wind field maps over the wnp provide a physically consistent picture of each tc type and of its seasonality anomalous vorticity and outgoing longwave radiation indicate changes in the monsoon trough associated with different types of tc genesis and trajectory the steering winds at 500 hpa are more zonal in the straight moving clusters with larger meridional components in the recurving ones higher values of vertical wind shear in the midlatitudes also accompany the straight moving tracks compared to

genesis of twin tropical cyclones as revealed by a global mesoscale model the role of mixed rossby gravity waves 1 in this study it is proposed that twin tropical cyclones tcs kesiny and 01a in may 2002 formed in association with the scale interactions of three gyres that appeared as a convectively coupled mixed rossby gravity ccmrg wave during an active phase of the madden julian oscillation mjo this is shown by analyzing observational data including ncep reanalysis data and meteosat 7 ir satellite imagery and performing numerical simulations using a global mesoscale model a 10 day control run is initialized at 0000 utc 1 may 2002 with grid scale condensation but no sub grid cumulus parameterizations the ccmrg wave was identified as encompassing two developing and one non developing gyres the first two of which intensified and evolved into the twin tcs the control run is able to reproduce the evolution of the ccmrg wave and thus the formation of the twin tcs about two and five days in advance as well as their subsequent intensity evolution and movement within an 8 10 day period five additional 10 day sensitivity experiments with different model configurations are conducted to help understand the interaction of the three gyres leading to the formation of the tcs these experiments suggest the improved lead time in the control run may be attributed to the realistic simulation of the ccmrg wave with the following processes 1 wave deepening intensification associated with a reduction in wavelength and or the intensification of individual gyres 2 poleward movement of gyres that may be associated with boundary layer processes 3 realistic simulation of moist processes at regional scales in association with each of the gyres and 4 the vertical phasing of low and mid level cyclonic circulations associated with a specific gyre

mechanisms of some tropical intraseasonal oscillations an underlying mechanism for two westward propagating tropical intraseasonal oscillations is discovered destabilization of equatorial normal modes by moist feedbacks in particular by evaporation wind feedback is responsible for both of them the westward propagating 4 5 day oscillation and the quasi biweekly oscillation result from destabilization of the mixed rossby gravity mrg wave by the evaporation wind feedback the frequency and scale selection of the unstable mrg wave depend critically on the background mean wind in mean easterlies as in the pacific and the atlantic it results in the 4 5 day oscillation while in mean westerlies as in the indian ocean during northern summer it results in the quasi biweekly mode

convection and easterly wave structures observed in the eastern pacific warm pool during epic 2001 abstract during september october 2001 the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 intertropical convergence zone itcz field campaign focused on studies of deep convection in the warm pool region of the eastern pacific this study combines c band doppler radar sounding and surface heat flux data collected aboard the r v ronald h brown during epic to describe the kinematic and thermodynamic states of the itcz environment together with tendencies in convective structure lightning rainfall and surface heat fluxes as a function of 3 5 day easterly wave phase three easterly waves were observed at the location of the r v brown during epic 2001 wind and thermodynamic data reveal that the wave trough axes exhibited positively correlated u and winds a slight westward phase tilt with height and relatively strong weak northeasterly tropospheric shear following the trough ridge axis temperature and humidity perturbations exhibited mid to

influence of the basic state zonal flow on convectively coupled equatorial waves observational data are used to test the hypothesis that the basic state modulates the dispersion properties of convectively coupled equatorial waves ccews this hypothesis is based on shallow water theory which predicts that the zonal speed of propagation of such tropospheric equatorial modes is altered by the equivalent depth and the basic zonal flow localized space time spectra are calculated to investigate how ccew spectral peaks vary across the tropics and how they are affected by the variations in zonal wind observed geographically and by season doppler shifting by the basic state barotropic zonal flow is readily identified once this doppler shifting is taken into account the equivalent depths of ccews inferred from global power spectra are surprisingly uniform both geographically and temporally however there are also detectable modulations that appear consistent with changes in vertical shear of the zonal flow along with other shifts that are not as easily explained

eastward propagating 2 to 15 day equatorial convection and its relation to the tropical intraseasonal oscillation anomalies of outgoing longwave radiation olr in 1980 1989 were examined in a narrow latitude band about the equator to elucidate the propagation and interaction of tropical intraseasonal oscillations tios and synoptic scale convective activity hovmoller diagrams of olr data reconstructed from two frequency bands corresponding to periods of 30 60 days and 2 15 days respectively revealed a clear distinction between the phase speed of eastward moving tios 3 7 m s 1 and that of eastward synoptic scale convection 10 13 m s 1 coherent propagation of tios from the indian to the western pacific oceans was often observed with temporary diminution of amplitude over the maritime continent propagation of high frequency anomalies was generally confined to an individual basin dominance of eastward propagating synoptic scale convection in the equatorial zone contrasts sharply with the westward propagation of off equatorial convergence zones interaction between the tio and high frequency activity resolved by daily olr was visible as a modest enhancement of eastward synoptic scale events and of high frequency activity in general during the convectively active phase of the tio

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

development of synoptic scale disturbances over the summertime tropical northwest pacific abstract this study addresses the origin of the synoptic scale disturbances that occur in the tropical western north pacific ocean wp region in northern hemisphere summer these have been called easterly waves and tropical depression type td disturbances this analysis uses the national center for environmental prediction national center for atmospheric research reanalysis dataset by performing a regression analysis on several terms in the vorticity equation at 850 hpa it is shown that the td disturbances propagate approximately as barotropic rossby waves at 850 hpa given this ray tracing calculations and the wave activity diagnostic introduced by plumb are used to show that wave accumulation is a promising candidate for the initial development mechanism of the td disturbances the expected local growth rate from this mechanism is simply the convergence of the group velocity which reaches values corresponding to a growth timescale of 3 days this convergence is dominated by but somewhat lar

origins and mechanisms of eastern pacific tropical cyclogenesis a case study the genesis of hurricane hernan 1996 in the eastern pacific was investigated using gridded analyses from the european centre for medium range weather forecasts and gridded outgoing longwave radiation hernan developed in association with a wave in the easterlies that could be tracked back to africa in longitude time plots of the filtered y component of the wind 2 6 day period at 700 mb the wave crossed central america near lake nicaragua with little change in its southwest northeast tilt but the most intense convection shifted from near the wave axis in the caribbean to west of the wave axis in the pacific the wave intensified as it moved through a barotropically unstable background state defined by a low pass filter with a 20 day cutoff in the western caribbean and eastern pacific a surge in the southwesterly monsoons and enhanced convection along 108n occurred to the west of the 700 mb wave in the pacific and traveled with the wave this had the effect of enhancing low level vorticity over a wide region ahead of the 700 mb wave available evidence suggests that additional low level vorticity was produced by enhanced flow from the north through the isthmus of tehuantepec as the 700 mb wave approached depression formation did not occur until 6 12 h after the 700mb wave reached this region of large low level vorticity in the gulf of tehuantepec eastern pacific sst and vertical wind shear magnitude are typically favorable for tropical cyclone development in northern hemisphere summer and early fall because the favorable mountain interaction and the surge in the low level monsoons appear to relate directly to the wave in the easterlies it is argued that the strength of such waves reaching central america from the east is the single most important factor in whether subsequent eastern pacific cyclogenesis occurs possible parallels with western pacific cyclogenesis are discussed

isolating spatiotemporally local mixed rossby gravity waves using multi dimensional ensemble empirical mode decomposition tropical waves have relatively large amplitudes in and near convective systems attenuating as they propagate away from the area where they are generated due to the dissipative nature of the atmosphere traditionally nonlocal analysis methods such as those based on the fourier transform are applied to identify tropical waves however these methods have the potential to lead to the misidentification of local wavenumbers and spatial locations of local wave activities to address this problem we propose a new method for analyzing tropical waves with particular focus placed on equatorial mixed rossby gravity mrg waves the new tropical wave analysis method is based on the multi dimensional ensemble empirical mode decomposition and a novel spectral representation based on spatiotemporally local wavenumber frequency and amplitude of waves we first apply this new method to synthetic data to demonstrate the advantages of the method in revealing characteristics of mrg waves we further apply the method to reanalysis data 1 to identify and isolate the spatiotemporally heterogeneous mrg waves event by event and 2 to quantify the spatial inhomogeneity of these waves in a wavenumber frequency energy diagram in this way we reveal the climatology of spatiotemporal inhomogeneity of mrg waves and summarize it in wavenumber frequency domain the indian ocean is dominated by mrg waves in the period range of 8 12 days the western pacific ocean consists of almost equal energy distribution of mrg waves in the period ranges of 3 6 and 8 12 days respectively and the eastern tropical pacific ocean and the tropical atlantic ocean are dominated by mrg waves in the period range of 3 6 days the zonal wavenumbers mostly fall within the band of 4 15 with indian ocean has larger portion of higher wavenumber smaller wavelength components mrg waves

two contrasting african easterly wave behaviors abstractthe dominant structural variability of african easterly waves aews is explored using an empirical orthogonal function eof approach the structure of aews is obtained by projecting the w

characteristics and origin of quasi biweekly oscillation over the western north pacific during boreal summer 1 this study investigates the structure energetic and origin of quasi biweekly oscillation qbwo over the western north pacific wnp using ncep reanalyses for the years 2000 2007 in the context of vorticity there appears to be a significant qbwo mode over the wnp during the summer qbwo emerges from the equatorial region and propagates northwestward its horizontal structure exhibits a slight southwest northeast tilt but mainly longitudinal elongation in the vertical the qbwo has a northwest tilt with height that gives rise to a structure of the first baroclinic mode the centers of vorticity and vertical motion near the equator show a phase lag of about one quarter wavelength consistent with the characteristics of equatorial waves whereas the cyclonic circulation is tightly coupled with anomalous convection as the wave moves away from the equator energetic analysis of the qbwo reveals that diabatic heating in the tropics and baroclinic processes in the subtropics play important roles in the generation of eddy available potential energy eape in turn the conversion from eape to eddy kinetic energy eke and the barotropic conversion are major sources for eke to compensate the loss by eke redistribution and dissipation tracing the qbwo to equatorial disturbances our results show some features of equatorially trapped n 1 rossby mode such as phase speed and group velocity this mode is generally characterized by a zonal planetary wave number of about 6 and nearly symmetric circulation about the equator a typical case from 2002 is chosen to illustrate that the origin of the qbwo is closely associated with the theoretical equatorial rossby wave

non double couple moment tensor of the march 25 1998 antarctic earthquake composite rupture of strike slip and normal faults the 1998 antarctic intraplate earthquake mw 8 1 has a significant non double couple component in the moment tensor solution as determined from long period surface waves in the teleseismic p and sh wave forms there are two distinctive wave packets that can be explained by multiple strike slip subevents we propose a composite rupture model comprising two different episodes two predominant clusters of en echelon strike slip segments 16 1020 nm and normal faulting with a long duration of approximately 100 s 4 1020 nm this model agrees with observations of both teleseismic body waves and long period surface waves including the large non double couple component the normal faulting with as long a duration as the main strike slip rupture might be secondarily induced by the en echelon segments of strike slip faulting