Showing papers on "Longitude published in 1994"

Statistical study of ELF/VLF emissions recorded by a low‐altitude satellite during seismic events

Abstract: This paper presents a statistical study of low-altitude satellite data linked to seismic events. Data of the satellite AUREOL 3 are considered during 24-hour windows around the time of 325 earthquakes with Ms > 5. Amplitudes at the output of different frequency filters in the ELF/VLF range, connected to electric or magnetic components, were stored in a file. This file is organized as functions of three parameters: Δt, the difference between the time of the earthquake and the time of the satellite data; ΔLong, the difference between the longitude of the earthquake and the longitude of the satellite; and ΔInv.Lat, the difference between the invariant latitude of the earthquake and the invariant latitude of the satellite. When all data are averaged over time, the amplitude is maximum in the interval ΔLong < 10° regardless of ΔInv.Lat. This indicates that, due to propagation, waves related to seismic processes can be observed all along the magnetic meridian passing over the epicenter of an earthquake. However, as the AUREOL 3 data were not continuously recorded, thus providing a limited number of events, it was impossible to carry out a complete statistical study.

Long‐term geometry of the geomagnetic field for the last five million years: An updated secular variation database

Abstract: Lee [1983] assembled more than two thousand paleomagnetic directional data from lava flows in 65 sampling sites with ages spanning the last 5 million years. Constable [ 1992] recently suggested that the virtual geomagnetic poles (VGP) derived from this data base have been preferentially located within two antipodal bands of longitude. We have reanalyzed and updated the Lee data base, yielding a total of 3179 data from 86 distinct sites. Neither the total data set, nor various subsets of the data unambiguously show any large and clear maxima in the longitude distribution of VGPs. The shape of the common site longitude distribution is far more striking with a pronounced (and robust) minimum close to the common site longitude and secondary maxima about 120 o away from it. The former (first order) feature is equivalent to the far-sided effect discovered by Wilson [1970] and corresponds to a persistent axial quadrupole amounting to about 5% of the axial dipole, as previously found by several authors. The latter (second order) feature could correspond to the VGP biasing effect described by Egbert [1992] although its observed amplitude appears larger than predicted. Part of this effect (an asymmetry in the maxima) may also correspond to Wilson's [1971] right-handed effect. Given only a small axial quadrupolar component and the very uneven actual site distribution, the expected longitude distribution of VGPs can be calculated: this is found to be in good agreement with the paleomagnetic observations (i.e. rather flat with a moderate maximum near 120oE). This study emphasizes problems related to the unsatisfactory distribution of sites. The amplitude and significance of other terms, beyond the dominant axial dipole and significant axial quadrupole contribution, remain to be assessed.

Inference of Subsurface Thermohaline Structure from Fields Measurable by Satellite

Abstract: Satellites now provide global measurements of the ocean's surface height and temperature. Ocean climatologies for the northwest Pacific and northwest Atlantic Oceans that relate sea surface height, sea surface temperature, day of the year, latitude, and longitude to temperature and salinity profiles were produced using least-squares regression. These analyses use over 33,000 profiles of historical temperature and salinity data and are considerably streamlined and compacted by expressing each profile in terms of empirical orthogonal functions. Evaluations and error analyses of the climatologies, including a comparison to the navy's Generalized Digital Environmental Model, were performed and differences between the regions are discussed. Two sample vertical sections are shown to be closely reproduced with the climatologies. Climatologies based on surface height and temperature are found to offer considerable improvement over climatologies based only on position.

A 57 Ma Pacific plate palaeomagnetic pole determined from a skewness analysis of crossings of marine magnetic anomaly 25r

Abstract: SUMMARY An increase in the accuracy and age resolution of the apparent polar wander path of the Pacific plate could be important for testing reconstructions that relate the motion of Pacific basin plates to other plates, for testing if hotspots in different ocean basins are stationary relative to one another, and for estimating the motion of hotspots relative to the spin axis. With these goals in mind, herein we investigate how accurately a palaeomagnetic pole can be estimated from skewness analysis of many crossings of a single magnetic anomaly on the Pacific plate. Apparent effective remanent inclinations of the sea-floor magnetization were estimated from the skewnesses of 132 useful (out of 149 total) crossings of anomaly 25r (56.5–57.8 Ma) distributed over a distance of more than 11000 km across the Pacific plate. These estimates were inverted to obtain a best-fitting palaeomagnetic pole latitude, pole longitude, and anomalous skewness for this single reversed-polarity chron. The best-fitting model gives a pole of 78.2°N, 4.8°E with a 95 per cent confidence ellipse having a 6.4° major semi-axis oriented 93° clockwise of north and a 4.1° minor semi-axis; anomalous skewness is 16.2°± 4.6° (95 per cent confidence limits). We also investigated the effect of the dependence of anomalous skewness on spreading rate by correcting our data using an empirical model. The pole obtained from the inversion of this alternative data set lies a statistically insignificant 0.6° from the pole obtained using no correction. That a pole with usefully compact confidence limits and a narrowly resolved, precisely estimated age can be so determined suggests that an accurate apparent polar wander path with a fine-age resolution can be determined for the Pacific plate by applying the same approach to the shapes of other marine magnetic anomalies. Comparison of our chron 25r pole with other Pacific palaeomagnetic and palaeoequatorial sediment facies data indicates that the Pacific plate remained nearly stationary relative to the spin axis during the Eocene (-0.05°Myr−1± 0.28° Myr−1), but probably moved rapidly northward during the Paleocene (0.83° Myr−1± 0.46° Myr−1). Comparison of these data to latitudes of dated volcanic edifices along the Hawaiian-Emperor chain indicates that the Hawaiian hotspot drifted southward by 10.2°± 3.4° (95 per cent confidence limits) since 57 Ma, but only by 1.7°± 1.9° since 39 Ma, which gives a southward displacement of 8.5°± 3.9° (95 per cent confidence limits) between 57 and 39 Ma, corresponding to a rate of southward motion of 52°24mm yr−1. Incorporation of realistic uncertainties of volcano ages would increase these uncertainties considerably, however. We also examined the distance between the crossings of anomalies 25 and 27 on all the profiles we analysed; along the palaeo-Pacific-Farallon boundary these distances are inconsistent with the joint hypotheses of symmetric spreading and single Pacific and Farallon plates between 62 and 56 Ma, indicating that the evidence for a single Pacific plate in early Tertiary time is not as compelling as it had previously seemed.

Studies of African Wave Disturbances with the GISS GCM

Abstract: Simulations made with the general circulation model of the NASA/Goddard Institute for Space Studies (GISS GCM) run at 4 deg latitude by 5 deg longitude horizontal resolution are analyzed to determine the model's representation of African wave disturbances. Waves detected in the model's lower troposphere over northern Africa during the summer monsoon season exhibit realistic wavelengths of about 2200 km. However, power spectra of the meridional wind show that the waves propagate westward too slowly, with periods of 5-10 days, about twice the observed values. This sluggishness is most pronounced during August, consistent with simulated 600-mb zonal winds that are only about half the observed speeds of the midtropospheric jet. The modeled wave amplitudes are strongest over West Africa during the first half of the summer but decrease dramatically by September, contrary to observational evidence. Maximum amplitudes occur at realistic latitudes, 12 deg - 20 deg N, but not as observed near the Atlantic coast. Spectral analyses suggest some wave modulation of precipitation in the 5-8 day band, and compositing shows that precipitation is slightly enhanced east of the wave trough, coincident with southerly winds. Extrema of low-level convergence west of the wave troughs, coinciding with northerly winds, were not preferred areas for simulated precipitation, probably because of the drying effect of this advection, as waves were generally north of the humid zone. The documentation of African wave disturbances in the GISS GCM is a first step toward considering wave influences in future GCM studies of Sahel drought.

Stationkeeping of geostationary satellites with simultaneous eccentricity and longitude control

Abstract: Because of increasingly stringent deadband requirements (±0.05°) in conjunction with larger solar radiation perturbations caused by higher area-to-mass ratios on current and future satellites, east/west Stationkeeping has become significantly more complicated. An algorithm that simultaneously controls the mean eccentricity and longitudinal motion of a geostationary satellite placed at any station longitude is developed. Eccentricity control is achieved based upon an expanded version of the sun pointing perigee method to include the long-period luni-solar effects in the eccentricity vector targeting scheme. Simultaneous control of the longitudinal motion is achieved by apportioning the required AV for eccentricity control amongst N maneuvers to maintain longitude within a ±0.05° deadband. Upon completing the Mh maneuver, the satellite begins a period of free drift with starting conditions coinciding with the optimal free-drift cycle initial conditions. Modeling of the sun, Earth, and moon effects on the satellite's motion allows for an arbitrary station longitude (and in particular for longitudes at or near an equilibrium point). A detailed simulation of the spacecraft's operating environment incorporating the maneuver strategy was used to verify the feasibility of the algorithm and to illustrate its robustness in the presence of measurement and execution errors.

A fine grid two-dimensional M2 tidal model of the East China sea

Abstract: The previous two-dimensional non-linear tidal model of the East China Sea (Chung, 1986) has been further refined to resolve the flow over the continental shelf in more detail. The mesh resolution of the present finite-difference grid system used is 4 minutes latitude by 5 minutes longitude over the entire shelf. The developed fine grid two-dimensional model was utilized to reproduce the M{sub 2} tide and M{sub 4} tide for the East China Sea continental shelf. There is general agreement between the model results and the current observation made in the Eastern Yellow Sea, which supports the calculated tidal regime over the shelf. Some preliminary results on maximum bottom stress and tidally-induced residual current were also examined and discussed.

Crash position predicting/alarming equipment for mobile

Abstract: PURPOSE:To predict the danger of crash by detecting an obstacle based on the data from a navigation system for attaining the position of a mobile including the longitude, latitude, etc. thereof and a memory for storing a map data including the topography, the longitude, latitude, etc., of an artificial obstacle and then calculating the distance and the variation rate thereof. CONSTITUTION:A navigation system 1 receives a signal from a GPS and delivers the positional data (longitude, latitude, altitude, speed and course) thereof to a crash avoidance computer 3. A map data memory 2 comprises a topographic data storing section 2a and an artificial obstacle data storing section 2b and delivers the stored data to the computer 3. The memory section 2a stores the fixed data of natural topography, e.g. the longitude and latitude, whereas the memory section 2b stores an arbitrary input data representative of the longitude, latitude, height and size of a building obstacle. The computer 3 detects the ground height and the position of the obstacle with respect to a predicted course, predicts the crash time, decides the necessity of alarm, and presents them on a display 4.

Method for taking directions and timepiece intended to make use of this method

Abstract: According to this method the longitude of the place where one is situated on the surface of the earth is determined by comparing the local time with the time of a reference time zone, and the latitude of the place where one is situated is determined by measuring the inclination of the earth's magnetic field in relation to the horizontal.

GLACIER TRENDS IN THE CAUCASUS, 1960s TO 1980s

Abstract: Records of terminus positions for the 1960s to 1980s have been obtained for 51 glaciers in the Greater Caucasus Mountains between the Black Sea and Caspian Sea, between latitude 40° and 44° N and longitude 40° and 49° E. These records have been analyzed as percentage of glaciers observed retreating, advancing, and stationary, displayed as a five-year moving average. The main result is the absence of the clear trend towards glacier advance found in the Alps between the 1960s and 1980s by both Patzelt (1985) and Wood (1988), suggesting a phase difference in the climates of the Alps and the Caucasus. [Key words: glaciers, glaciology, Greater Caucasus Mountains, Alps.]

Spatial Variability of Outgoing Longwave Radiation.

Abstract: Data from the Earth Radiation Budget Experiment scanning radiometer aboard the NOAA-9 operational meteorological satellite are used to investigate the spatial variability of Outgoing Longwave Radiation (OLR). Daily and monthly radiation maps at 2.5 deg latitude-longitude scale are used as a basis for the study. The regions of greatest variability are in the tropics and subtropics. Storm tracks such as the South Pacific convergence zone appear as regions of high OLR variability. Spatial spectra in longitude show two regimes of OLR. At large scales (wavenumbers less than 6), the spatial spectrum is flat. For wavenumbers greater than 10, the spectra decrease as wavenumber to the -3 power. The spatial spectrum of daily anomalies from the mean is a strong function of latitude and season, with interesting features. Correlations of daily anomalies from the monthly mean decrease exponentially in latitude but have a damped-wave structure in longitude. The spatial variability of the daily maps, as measured by degree variance, have 10 times the power at degree 24 than the monthly maps, but at scales between 1 and 10, the degree variance is practically the same for daily as for monthly.

Beaming Geometry of the IO-Related Decametric Radiation

Abstract: The geometrical beam modeling of a component of Jovian Io-related decametric radiation (so-called Io-B) is made on the basis of the 22.2 MHz occurrence probability data from University of Texas Radio Astronomy Observatory. To see the emission directions of the 22.2 MHz radiation with respect to the orbital position of Io, the 22.2 MHz occurrence probability is plotted as a function of the sub-Io longitude and the difference between the sub-Io longitude and the sub-observer longitude (referred to as a “longitude difference”). In such a plot the longitude difference of the Io-B main region increases with increasing sub-Io longitude. A simulation of the drift of the longitude-difference is made on the basis of a hollow cone beaming model using the 04 magnetic field model. It is assumed that the disturbance caused by the Io’s motion propagates to the 22.2 MHz source location just above the cloud tops of the planet to excite the radiation. The effect of the propagation time of the disturbance to the 22.2 MHz source is taken into account by a lead angle of the Io-excited flux tube with respect to the orbital position of Io. It is also assumed that the radiation is emitted into a sector of a hollow cone, the axis of the cone being aligned with the magnetic field at the emission point. By fitting the simulated longitude-difference drift curve to the observation, the best fit lead angle and cone half-angle are estimated to be about 40o±10o and 65o∓5o, respectively. The result of the simulation is discussed in relation to the O4 field model.

Controlling method for satellite

Abstract: PURPOSE:To safely position many satellites in the space at substantially the same longitude position on the geostationary orbit. CONSTITUTION:To control at least three, e.g. four satellites, a, b, x, y, the orbital plane.eccentricity separation system for separating the inclination of orbit vector of the satellite orbit from the eccenstricity vector is used in a combination with the longitude separation system for separating longitude. Separation arrangement a-b, x-y by the orbital plane. eccentricity separation system, separation arrangement a-x, b-y by the longitude separation system, and separation arrangement a-y, b-x by both the systems are done for every two-satellite combination.

Interannual variability in global wave climate from satellite data

Abstract: This paper presents an analysis of altimeter wave height data, spanning a period of 9 years, provided by the Geosat, ERS-a and Topex/Poseidon satellite programs. Monthly means are derived for 2 degree latitude by 2 degree longitude bins from data for each of the three satellites, and these data sets are then intercompared with each other and against NOAA buoy wave height month means. Consistent differences are shown to exist between the various data sets, and correction factors to adjust the satellite data to the buoy measurements are suggested. These correction factors are applied to the monthly mean satellite data, which are then analyzed to investigate interannual variability since 1986. Analysis of Geosat data (for 1986- 1989) has suggested the possibility of a negative correlation between the mean winter wave heights in the NE Atlantic and the NE Pacific, and a positive correlation between the NE Atlantic values and the El Nino Southern Oscillation Index. As preliminary study with ERS-1 and TOPEX data has shown similar wave climate patterns over the period 1991-1994.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Observation of interannual sea level oscillations in the Indian Ocean using Geosat altimeter data

Abstract: Similar to the atmosphere, intermediate frequency oscillations are also present in oceanographic parameters. In this study, sea level variations derived from Geosat altimeter data were analyzed during 1986 to study the 40‐ to 60‐day oscillations in sea level height over the Indian Ocean. A time series of 256 points starting from January 1, 1986, was analyzed over the 2° longitude, 1° latitude grid points. A prominent mode of 42‐ to 64‐day oscillations was observed along the coastal regions.

Method for fixing the geographical position and timepiece for implementing this method

Abstract: According to this method the longitude of the place at which one is located on the surface of the Earth is determined by comparing the local time with the time of a reference time zone, and the latitude of the place at which one is located is determined by measuring the inclination of the Earth's magnetic field with respect to the horizontal.

Communication distance azimuth measuring instrument

Abstract: PURPOSE:To measure the distance and azimuth of a communication destination automatically and with a simple operation. CONSTITUTION:The latitude and longitude of a current position are input from a current position measurement position 10 such as a GPS receiver and a grid locator value (GL) such as a communication destination is set by a GL value setting part 12. The latitude and longitude of the center point of the set GL value are calculated by a center latitude/longitude calculation part 14 and are input to a distance azimuth calculation part 16 as destination/latitude. The distance azimuth calculation part 16 calculates the distance/azimuth of the communication destination, etc., from the latitude/longitude of the current position measurement part 10 and that of the center latitude/longitude calculation part 14 and then a display part 18 displays the obtained communication distance/ azimuth.