low latitude ionospheric d region dependence on solar zenith angle phase and amplitude measurements of vlf radio signals on a short nearly all sea path between two hawaiian islands are used to find the height and sharpness of the lower edge of the daytime tropical d region as a function of solar zenith angle sza the path used was from u s navy transmitter npm 21 4 khz on oahu to keauhou 306 km away on the west coast of the big island of hawaii where ionospheric sensitivity was high due to the destructive interference between the ionospherically reflected wave and the ground wave particularly around the middle of the day the height and sharpness are thus found to vary from h 69 3 0 3km and 0 49 0 02 km 1 for sza 10 at midday to h 80 km and 0 30 km 1 as the sza approached 70 90 near dawn and dusk for this tropical path additional values for the variations of h and with solar zenith angle are also found from vlf phase and amplitude observations on other similar paths the short path nwc to karratha in nw australia and the long paths nwc to kyoto in japan and nau puerto rico to st john s canada significant differences in the sza variations of h and were found between low and middle latitudes resulting from the latitudinally varying interplay between lyman and galactic cosmic rays in forming the lower d region both latitude ranges showed 0 30 km 1 during sunrise sunset conditions 1

geodetic observations during the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano about 160 km to the sw of anchorage alaska began its most recent explosive eruption deformation induced by this event was recorded by a gps campaign network consisting of 14 benchmarks which had been established in 1991 after the previous eruption the network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period in response to precursory unrest starting in january 2009 the alaska volcano observatory temporarily deployed continuously recording gps instruments at four of the campaign benchmarks only days before the onset of explosive activity in march 2009 the only gps instrument recording continuously during the months prior to the eruption was the plate boundary observatory pbo station ac17 about 28 km northeast of the volcano s summit data from this station reveals subtle motion radially outward from the volcano beginning as early as may 2008 which reversed with the onset of explosive activity using simple analytical models we link the precursory activity to a point source intrusion of 0 0194 0 03400 0092 km3 in volume at 13 50 17 3310 17 km below sea level bsl superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95 level during the explosive phase about 0 05 0 10 028 km3 of magma was evacuated from a prolate spheroid with its centroid at 9 17 15 176 92 km bsl a semimajor axis of 4 50 10 001 25 km length and a semi minor axis of 0 475 4 00 3 km the effusive activity is inferred to come from the same source decreasing in volume by 0 0167 0 02280 0106 km3 including observations from seismology and petrology we hypothesize a mid crustal two reservoir system with material sourced from 20 km flowing in at about 13 5 km depth and reheating residual material in the proposed spheroid the mixture migrated to shallower depth 2 4 5 km bsl and reheated material there as this residual magma erupted it was replaced by the material from the spheroidal reservoir at 7 11 5 km depth which renders the shallow source undetectable for geodetic instruments in addition to long term displacements we investigate sub daily kinematic positioning solutions and find that large short term positioning offsets correlate with large explosive events spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite station geometry which may be of use in volcano monitoring

initial testing of a numerical ocean circulation model using a hybrid quasi isopycnic vertical coordinate abstract an ocean circulation model developed for the study of mesoscale to gyre scale circulation and heat transport is described and tested the model employs density as vertical coordinate except in the immediate vicinity of possible coordinate surface intersections with the ocean surface test simulations are carried out for a double gyre ocean basin of the type used by holland 1978 but with better resolution in the upper 1000 m of the model ocean the final state of a 5 year coarse mesh 50 km resolution on a 2400 km 1200 km domain spin up is used as the initial state for mesoscale experimentation on a 25 km mesh basin energetics as well as mean mass transport streamfunction and mean potential vorticity fields are given for three mesoscale experiments in which the magnitude and formulation of lateral dissipation are varied each of these experiments run for approximately five years exhibits vigorous mesoscale activity associated with western boundary current separation and the free jet

preface to seasat ii seasat the first satellite designed to assess the value of microwave sensors for remote sensing of the world s oceans was launched on june 27 1978 the satellite operated successfully until october 10 1978 when a power failure brought transmission to a stop despite its short lifetime seasat acquired a wealth of data on sea surface winds and temperatures ocean wave heights internal waves atmospheric water content sea ice topography of the ocean surface and shape of the marine geoid analysis of these data has demonstrated the success of seasat in accurately measuring on a global scale important oceanographic parameters from space the seasat sensors included a radar altimeter a scanning multi channel radiometer a synthetic aperture radar a windfield scatterometer and a visual and infrared radiometer from these instruments have come the first global maps of the variability of ocean currents surface wind speed surface temperature wave height and water vapor in the atmosphere the success of seasat has been the major impetus for plans in the united states europe and japan to launch microwave ocean monitoring satellites in the late 1980s this is the second of two special issues of the journal of geophysical research dedicated to the seasat mission the first issue vol 87 no c5 april 30 1982 focused on the processing algorithms used for converting sensor data into geophysically useful information this issue emphasizes cientific results from the seasat sensors scientists from numerous government centers and universities from the united states and abroad have performed oceanographic and geodetic studies with seasat data however much research still remains to be done particularly in the application of the global scatterometer windfie ds to weather prediction and the use of altimeter data to refine knowledge of the marine geoid and global ocean circulation patterns this issue is a demonstration of the increasingly important role that satellites play in oceanography and geodesy the papers were processed through normal jgr review procedures we thank the authors associate editors and reviewers for their contributions and assistance in preparing this issue

satellite tracked drift buoy observations of the near surface flow in the eastern mid latitude north pacific the surface and near surface 30 m currents of the eastern mid latitude pacific obtained from 32 satellite tracked drifting buoys during the period june 1976 through august 1977 are discussed these observations of oceanic currents are merged with and are compared to fleet numerical weather center s daily estimates of surface winds for the same period statistical comparisons of these data sets reveal that the drifters move systematically approximately 30 to the right of the surface wind at approximately 1 5 of the wind speed this relationship between drifter movement and surface winds occurs during the entire period except for the summer months of 1976 when independent of the surface winds the buoy trajectories indicate mesoscale eddy motions with 100 km and 30 day time and space scales respectively drifter liftimes exceeded that of the 9 m diameter parachute drogues set at 30 m depth thus enabling a comparison of the currents derived from the drifter motions at the surface and 30 m these comparisons reveal no systematic difference in the drifter motions with and without drogues these results suggest a rather uniform flow in the upper 30 m during periods of steady winds the estimates of the nature of near surface currents obtained from the drifters differ from those predicted by ekman s classical theory of wind driven flow in that there is no evidence of either a reduction in speed or change in direction of the currents over the upper 30 m

detection of seamount signatures in seasat altimeter data using matched filters matched filter techniques are described for the detection of characteristic geoid undulation signatures of seamounts in seasat radar altimeter data the technique requires models of the expected undulation signatures and a statistical description of the background seamount free data examples are given of the detection of 11 known seamounts on four distinct tracks further extensions and applications of the matched filter methods are discussed

tropical daytime lower d region dependence on sunspot number 1 observed phases and amplitudes of vlf radio signals propagating on near tropical all sea paths both short 300 km and long 10 mm are used to find daytime parameter changes for the lowest edge of the d region of the earth s ionosphere as the solar cycle advanced from a very low sunspot number of 5 up to 60 in the period 2009 2011 the vlf phases relative to gps 1 s pulses and amplitudes were measured 100 km from the transmitter where the direct ground wave is very dominant 300 km from the transmitter near where the ionospherically reflected waves form a modal minimum with the ground wave and 10 mm away where the lowest order waveguide mode is fully dominant most of the signals came from the 19 8 khz 1 mw transmitter nwc north west cape australia propagating ene mainly over the sea to the vicinity of karratha and dampier on the nw coast of australia and then on to kauai hawaii 10 6 mm from nwc observations from the 8 1 mm path npm 21 4 khz hawaii to dunedin nz are also used the sunspot number increase from 5 to 60 was found to coincide with a decrease in the height h of the midday tropical ionosphere by 0 75 0 25 km from h 70 5 km to h 69 7 km while the sharpness increased by 0 025 0 01 km 1 from 0 47 km 1 to 0 49 km 1 where h and are the traditional height and sharpness parameters used by wait and by the u s navy in their earth ionosphere vlf radio waveguide programs

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

absolute measurement by satellite altimetry of dynamic topography of the pacific ocean satellites are the only foreseeable possibility for obtaining observations of the ocean circulation on the basin and global scales required to understand it such observations are essential for an understanding of the role of the ocean in various important problems for example climate the 3 month seasat mission1 has demonstrated2 3 that altimetry is capable of providing global observations of oceanic variability we show here that the data from this short sub optimum mission are also adequate for a determination of the absolute sea surface topography of the ocean on large scales a much more difficult4 and even more valuable measurement an absolute determination of the subtropical gyre of the north pacific ocean has been obtained we believe this to be the first direct measurement showing the existence of such a feature that does not depend on conventional hydrography and a series of assumptions

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

midlatitude ionospheric d region height sharpness and solar zenith angle vlf radio amplitude and phase measurements are used to find the height and sharpness of the d region of the ionosphere at a mid to high geomagnetic dip latitude of 52 5 the two paths used are both from the 23 4 khz transmitter dho in north germany with the first path being northwards and mainly over the sea along the west coast of denmark over a range of 320 425 km and the second also mainly all sea to a single fixed recording receiver at eskdalemuir in scotland 750 km from plots of the measured amplitudes and phases versus distance for the first of these paths compared with calculations using the us navy code modefinder the wait height and sharpness parameters of the d region at midday in summer 2015 are found to be h 72 8 0 2 km and s 0 345 0 015 km 1 at a solar zenith angle 33 from phase and amplitude measurements at other times of day on the second path the daytime changes in h and s as functions of solar zenith angle are determined from shortly after dawn to shortly before dusk comparisons are also made between the modal modefinder calculations and wave hop calculations with both giving similar results the parameters found here should be useful in understanding energy inputs to the d region from the radiation belts solar flares or transient luminous events the midday values may be sufficiently precise to be useful for monitoring climate change

cascades of dense water around the world ocean dense water overflow off continental shelves cascading is one of the contributing processes of shelf deep ocean exchange and of topical interest to climate studies and nutrient fluxes dense water originating from cooling evaporation freezing and salinization on a shallow shelf spills over the shelf edge and may develop as near bottom gravity current or an intermediate depth intrusion it is difficult to observe in nature due to its intermittent character this paper provides an extensive inventory of observed cases of water cascades around the world ocean summarises their locations and individual properties and provides statistics of the identified cases the search for cascading was carried out using oceanographic databases and a literature review this study identified 61 confirmed cases world wide including 25 cases in the arctic seas 12 at mid latitudes seven in sub tropical and tropical regions and 17 off the antarctic shelves eighteen cascades had not been reported before we analyze a set of numerical parameters of dense water cascades allowing us to quantify compare and contrast the properties of water cascades the overall average density contrast between the confirmed cascades and ambient water is 0 37 kg m3 it can be as much as 2 kg m3 on some arctic shelves frequently initiated by strong cooling at the surface cascades often remain colder through the descent thus supplying the deep ocean with colder and fresher water in non dimensional variables the data from all climate zones fit well to a unique curve which represents a relationship between a cascade s internal structure and the parameters describing its forcing on average the down slope volumetric flux provided by dense water cascades is estimated as 0 05 to 0 08 sv per 100 km of shelf edge regional terms arctic antarctic north atlantic ocean barents sea mediterranean sea skagerrak tasman sea sea of okhotsk

a demonstration of ocean acoustic tomography over the past decade oceanographers have become increasingly aware of an intense and compact ocean mesoscale eddy structure the ocean weather that is superimposed on a generally sluggish large scale circulation the ocean climate traditional ship based observing systems are not adequate for monitoring the ocean at mesoscale resolution a 1981 experiment mapped the waters within a 300 300 km square south west of bermuda using a peripheral array of moored midwater acoustic sources and receivers the variable acoustic travel times between all source receiver pairs were used to construct the three dimensional time variable eddy fields using inverse theory preliminary results from inversions are consistent with the shipborne and airborne surveys

daytime tropical d region parameters from short path vlf phase and amplitude 1 observed phases and amplitudes of vlf radio signals propagating on a short 300 km path are used to find improved parameters for the lowest edge of the d region of the earth s ionosphere the phases relative to gps 1 s pulses and the amplitudes were measured both near 100 km from the transmitter where the direct ground wave is very dominant and at distances of 300 km near where the ionospherically reflected waves form a modal minimum with the direct ground wave the signals came from the 19 8 khz 1 mw transmitter nwc on the north west cape of australia propagating 300 km ene mainly over the sea to the vicinity of karratha dampier on the n w coast of australia the bottom edge of the mid day tropical equatorial ionosphere was thus found to be well modeled by h 70 5 0 5 km and 0 47 0 03 km 1 where h and are the traditional height and sharpness parameters as used by wait and by the u s navy in their earth ionosphere vlf radio waveguide programs u s navy modal waveguide code calculations are also compared with those from the wave hop code of berry and herman 1971 at least for the vertical electric fields on the path studied here the resulting phase and amplitude differences between the 100 km and 300 km sites agree very well after just a small adjustment of 0 2 km in h between the two codes such short paths also allow more localization than the usual long paths here this localization is to low latitudes

a real time dynamical forecast of ocean synoptic mesoscale eddies energetic eddy currents are the oceanic analogue of atmospheric weather and have time scales of days to weeks and space scales of tens to hundreds of kilometres1 we have predicted their evolution in time by internal dynamical processes for the forecasts we transferred initialization data from ship to shore based computers during two 2 week periods in june and july of 1983 from an approximately 150 km 2 region in the deep north east pacific off california this is to the best of our knowledge the first such real time forecast at sea the results were substantially successful the dynamics predicted a prominent zonal jet absent in the initial flow also the model forecast revealed a strong eddy merger event otherwise obscured in the data prospects are encouraging for future forecasting which should have important implications for research and practical operations at sea2

a simulation of bomb tritium entry into the atlantic ocean abstract tritium is used in a model calibration study that is aimed at developing three dimensional ocean circulation and mixing models for climate and geochemical simulations the north atlantic tritium distribution is modeled using a three dimensional advective field predicted by a primitive equation ocean circulation model the effect of wintertime convection is parameterized by homogenizing the tracer to the observed march mixed layer depth mixing is parameterized by horizontal and vertical fickian diffusivities of 5 10 6 cm2 s 1 and 0 5 cm2 s 1 respectively the spreading of tritium in the model is dominated by advection in the horizontal and by wintertime convection and advection in the vertical the horizontal and vertical mixing provided by the model have negligible effect a comparison of the model tracer fields with observations shows that most of the basic patterns of the tritium field are reproduced the model s mean vertical penetration of 543 m in 1972 is comparable to the 592 m penetra

a numerical model of the ventilated thermocline abstract a steady state numerical solution is found for an idealized rectangular ocean basin driven by wind and surface buoyancy flux a three dimensional primitive equation model is used in agreement with recent analytical modeling the thermocline in the numerical solution consists of three regions quite distinct in their ventilation characteristics forming the greater part of the subtropical thermocline is an unventilated pool zone located in the core of the subtropical gyre and a ventilated zone to the east the unventilated shadow zone lies farther east and toward the equator analysis of potential vorticity on constant density surfaces is used to study the structure of the thermocline a small but intense zone of convection located in the western boundary outflow caused by rapid heat loss to the atmosphere produces source water for the ventilated zone this water of extremely low potential vorticity mode water is distributed widely into the subtropical thermocline the pool forms equ

the world ocean circulation experiment the international oceanographic community is preparing for an ambitious five year experiment starting in 1990 it will provide the first comprehensive global survey of physical properties of the oceans the resulting data set will be used to test computer models of the ocean circulation needed for predicting decadal climate change the results will also benefit research in marine chemistry biology and geology this review looks at the climatalogicalproblems that motivated the project and discusses new observing techniques from space and in situ which make it timely to embark on this major step in physical exploration of the ocean

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

daytime midlatitude d region parameters at solar minimum from short path vlf phase and amplitude 1 observed phases and amplitudes of vlf radio signals propagating on a short 360 km path are used to find improved parameters for the lowest edge of the d region of the earth s ionosphere at a geomagnetic latitude of 53 5 in midsummer near solar minimum the phases relative to gps 1 s pulses and the amplitudes were measured both near 110 km from the transmitter where the direct ground wave is very dominant and at distances of 360 km near where the ionospherically reflected waves form a modal minimum with the direct ground wave the signals came from the 24 0 khz transmitter naa on the coast of maine near the u s canada border propagating 360 km e ne mainly over the sea to saint john and prince edward island the bottom edge of the midday midsummer ionosphere at 53 5 geomagnetic latitude was thus found to be well modeled by h 71 8 0 6 km and 0 335 0 025 km 1 where h and are wait s traditional height and sharpness parameters used by the u s navy in their earth ionosphere vlf radio waveguide programs the variation of with latitude is also estimated with the aid of interpolation using measured galactic cosmic ray fluxes

dynamics of the oceanic general circulation the potential vorticity field the general circulation of the oceans is determined by vorticity temperature and salinity the theory of large scale circulation puts a strong constraint on the fields of potential vorticity q new calculations and observations of the north atlantic and north pacific using the field of potential vorticity as a point of comparison reveal strong similarities in particular the observations can be modelled by gyres around which geostrophic contours deform to follow the circulation and within which q is uniform the effects of injected waters with relatively low potential vorticity are significant

summary of the jasin 1978 field experiment jasin was designed to observe the physical processes causing mixing and to quantify aspects of the heat and momentum budgets in mid latitude oceanic and marine atmospheric boundary layers the multiplicity of processes to be sampled necessitated a large experiment and jasin involved 14 ships and 3 aircraft with more than 50 teams of investigators from 9 countries the experiment took place from july to september 1978 in the north rockall trough an area of deep water several hundred kilometres off the west coast of scotland hydrographic surveys revealed eddies 100 km across and intensive measurements on smaller scales revealed fronts in the confluence zones of the eddy field the development of the mixing layer and seasonal thermocline internal and inertial wave fields and the ekman response to winds are all complicated by the fronts and eddies the atmospheric boundary layer on scales of 200 km was non steady and inhomogeneous surface generated turbulence occupied the subcloud layer and transfers through the cloud layer occurred on scales greater than 50 km or intermittently possible driving factors were the variability in surface fluxes near the oceanic mesoscale eddies radiative processes in the cloud layer and condensation processes the lifting of warm sector boundary layer air from widely differing sources into the free atmosphere at a front resulted in well mixed moist layers that exhibited near thermal wind equilibrium