Showing papers on "Longitude published in 1980"

An empirical model of quiet-day ionospheric electric fields at middle and low latitudes

Abstract: Seasonally averaged quiet-day F region ionospheric E × B drift observations from the Millstone Hill, St. Santin, Arecibo, and Jicamarca incoherent scatter radars are used to produce a model of the middle and low-latitude electric field for solar minimum conditions. A function similar to an electrostatic potential is fitted to the data to provide model values continuous in latitude, longitude, time of day, and day of the year. This model is intended to serve as a reference standard for applications requiring global knowledge of the mean electric field or requiring information at some location removed from the observing radars. This article contains supplementary material.

Monthly Mean Wind Fields for the South Atlantic Bight

Abstract: A total of 339 389 marine weather observations have been analyzed to Produce Monthly mean wind fields for the South Atlantic Bight. The results of plotting wind vectors on a 1/2° latitude by 1/2° longitude grid yields four traditional seasonal flow regimes (winter, spring, summer and fall) and an additional regime designated as mariners’ fall. These seasonal wind regimes are discussed and related to the monthly mean ocean circulation in the Bight.

Discovery of a longitudinal asymmetry in the H Lyman‐alpha brightness of Jupiter

Abstract: A strong longitude variation in the midlatitude Lyman-alpha brightness of Jupiter has been discovered using data from the Voyager ultraviolet spectrometers. A minimum brightness of 14.4 kR was observed in the System III (1965) west longitude range 200-300 deg. The intensity rises to a broad peak of 19.6 kR near a longitude of 110 deg, a 36% increase over the minimum. This intensity 'bulge' was observed to rotate with the planet and appeared at the same longitude during both Voyager encounters, four months apart. This is a surprising discovery; no other planet studied to date has such a characteristic and the upper levels of the Jovian atmosphere were expected to be uniform in longitude. It is likely that a longitudinal asymmetry in charged particle precipitation leads to selective heating of the upper atmosphere and increased dissociation of H2, increasing the hydrogen column abundance. The resulting increase in resonant scattering could produce the observed intensity bulge.

Comparisons of magnetic anomalies of lithospheric origin measured by satellite and airborne magnetometers over western Canada

Abstract: Crustal magnetic anomaly data from the OGO 2, 4 and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 50 deg -85 deg N latitude and 220 deg - 260 deg E longitude. Agreement is good both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill province. No features are present to indicate a magnetic boundary between Slave and Bear provinces, but a trend change is evident between Slave and Churchill provinces. South of 60 deg latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization.

The morphology of high-latitude VHF scintillation near 70°W

Abstract: The long-term VHF scintillation data from ATS 3 obtained at three stations situated in the North Atlantic sector at auroral and subauroral locations during the period 1968–1974 are used to determine the morphology of high-latitude scintillations near the 70°W longitude sector. The variation of the average level of scintillation at each observatory is studied as a function of time of day, season, and magnetic activity in a manner suitable for incorporation into statistical models of scintillation occurrence. The most prominent feature of the data is a seasonal dependence of scintillations with a 2:1 variation from northern summer to winter under quiet magnetic conditions. This also causes a large variation in the latitudinal gradient of scintillations from 2 dB per degree in summer to 1 dB per degree in winter for latitudes >60° invariant. The observed seasonal control of scintillations is related to the variation of the tilt angle of the earth's magnetic dipole and consequent modulation of the particle precipitation in the North Atlantic sector of the auroral oval.

Multisatellite Observations of Geomagnetic Pulsations

Abstract: The technique of using simultaneous data from more than one spacecraft to study hydromagnetic waves in space is proving to be a very powerful one which will undoubtedly become more widespread in the future. We review the results obtained using this technique thus far. All of the work has involved longer period (>20 s) pulsations and most of the data has come from near geostationary orbit. Attempts to measure the thickness of field line resonance regions have not so far been conclusive, but they suggest that values of about (l/2)R E are typical. Signals in the Pc3 and 4 bands in the morning are coherent over at least 20° of longitude while in the afternoon they are much more localized. One afternoon source is resonance with hot ions. Pi 2’s on the nightside can also be confined to small regions of longitude.

Measurements of inner zone electron precipitation

Abstract: Energetic electron (≳0.16 MeV) data taken from November 1972 to April 1973 from over 1000 passes of a low-altitude (∼750 km) noon-midnight polar-orbiting satellite across the L=1.75 field line in both the northern and southern hemispheres have been analyzed for evidence of the longitude and local time distributions in electron precipitation on that field line. The precipitation processes were observed to be weak, at least near local noon and midnight, as evidenced from the negligible fluxes observed at all pitch angles when the conjugate point is below sea level and from the absence of any direct observation of electrons at L=1.75 in the bounce loss cone at all longitudes. By observing quasi-trapped fluxes with a spectrometer having a large geometric factor, a high sensitivity was achieved for detecting electron precipitation and measuring the energy spectra with fine resolution. The data have been analyzed and found to show that prounounced precipitation events near local noon and midnight were a rare occurrence between ∼60°E and ∼100°E. In the ∼100°E to ∼180°E longitude region, significant fluxes of quasi-trapped electrons were often observed with a very pronounced noon-midnight asymmetry. The quasi-trapped fluxes observed locally in this region were often large near midnight but seldom significant near noontime. At longitudes east of 180°E, to the western edge of the South Atlantic Anomaly, the local noontime fluxes of quasi-trapped electrons displayed an abrupt increase and, on the average, were higher than the midnight intensities. In this region the energy spectra of quasi-trapped electrons observed at midnight displayed L-dependent peaks less often than those observed at noontime. These very pronounced longitude and local time variations in the quasi-trapped population provide conclusive evidence that the effectiveness of the electron precipitation mechanism(s) is dependent upon local time, (although without further information, detailed local time distributions in the precipitation mechanisms were not derived). From the electron data it was found that within a given local time and longitude interval the fluxes were widely variable, indicating that the precipitation mechanism(s) were not steady in time. Also, during the time period of observation, the average intensities of the quasi-trapped electrons were higher at times of high negative Dst.

Surface meteorology over the gate a-scale

Abstract: A method of analysis for the surface motion field based on a mix of observations from research ships, merchant ships and low-cloud motion vectors from geostationary satellites is proposed in this paper. The proposed scheme permits a turning of wind with height between the cloud wind level and the surface. This turning is incorporated via a successive correction procedure which enables us to utilize fully the low-cloud winds. The method does not depend on the selection of a level of best fit for the cloud winds and thus is not dependent on a predetermined theory. The analysis of the surface wind field is carried out for the 100 days of the GARP Atlantic Tropical Experiment (GATE) for two observation periods per day (00Z, 12Z) over a wide domain. This paper illustrates i) time-averaged geometry of the motion field during GATE, and ii) time-averaged fields of the zonal and the meridional stresses as well as of the curl of the wind stress. Finally, we examine the spectral analysis of the motion field and the stresses over the trade wind belts of the summer and winter hemisphere. Our study emphasizes the importance of two modes of oscillation, one around 3 to 6 days and the other around 10 to 15 days. While the former is identified with African v/aves, the scale and speed of propagation of the latter is determined from x–t diagrams and is identified as a westward propagating wave, whose scale is of the order of 40° longitude and speed of propagation is around 3° longitude/day. This study emphasizes the possible usefulness of this approach during the GARP Global Experiment when a global coverage from geostationary satellites is expected.

Estimate of wind stressed sea level excitation of the Earth's annual wobble

Abstract: Summary. This article estimates the contribution to the Earth's annual wobble caused by the wind stressed non-isostatic sea level variations in the oceans. Since there is a lack of data on these sea level changes, an analytic approach is taken. An ocean basin is assumed to be bounded by two meridians of longitude and two parallels of latitude, and is symmetric about the equator. A simple zonal wind stress profile based on observed data represents the seasonal changes in each hemisphere with a simple annual cosine variation. The one layer barotropic ocean has a frictionally controlled boundary layer giving rise to a western boundary current. From the equations of motion a stream function and vorticity equation are developed. The ocean is assumed to be always in adjustment to the wind stress forcing so that the steady state solution yields the velocity and height fields. Model parameters are adjusted so that these sea level changes correspond to estimates of nonisostatic sea level changes. The expression for the annual height field changes caused by the wind stress forcing is substituted into the equations governing the wobble excitation. From the resulting expression it is seen that for an ocean basin and wind regime symmetric about the equator, the contributions to the excitation of wobble from the northern and southern oceans add, while the contributions to the length of day cancel. The pole of excitation for the resultant of all oceans moves along an ellipse of eccentricity unity (line segment), aligned nearly along the Greenwich meridian, with semi-major axes of 19 cm, and is farthest from the pole of reference along 11° E longitude in mid-February. This indicates that the major contribution to the sea level excitation comes from the set up in the western Pacific. The positive annual frequency vector is calculated to be (1.2–0.8i)×10−8 rad. Comparisons with the results of Wilson & Haubrich (1976a) show that this wind stressed sea level excitation of wobble is of the phase and probable magnitude to significantly reduce the discrepancy between the astronomically observed excitation and the calculated geophysical excitations due to air mass redistribution, continental water storage and mountain torque.

The longitudinal variation of the thermal inertia and of the 2.8 centimeter brightness temperature of Mars

Abstract: The spatial variations on Mars of the surface thermal inertia and radiometric albedo are used to predict the variation with sub-earth longitude of the 2.8 cm whole-disk brightness temperature. The maximum variation predicted, about 8 K, agrees well with observations. The sub-earth longitudes at which the temperature maxima and minima are predicted to occur nearly agree with the observations. There are, however, differences in the overall form of the variation with longitude. These discrepancies can be reduced by an ad hoc assumption of spatial variations in either the fraction of the surface covered by rock or the amount of atmospheric dust.

Relationship between Terrestrial and Satellite Doppler Systems

Abstract: Classical horizontal geodetic networks are commonly combined with space observations, mostly satellite Doppler, in order to optimize the accuracy of geodetic control points and, thus, satisfy as many types of users as possible Since satellite Doppler observations refer to a fully defined three-dimensional reference system and terrestrial observations, through the presence of Laplace stations (astronomical longitude and azimuth), contribute also to the pole and longitude orientations, it is imperative to ensure the highest possible degree of compatibility between the astronomical and satellite Doppler systems to maintain optimization of the accuracy of control points Since gravity and geopotential (in the form of spherical harmonics) data are usually combined to evaluate geoid undulations and deflections of the vertical which are in turn used to reduce terrestrial angular and range observations, it is equally imperative to ensure that the satellite Doppler system and that of the geopotential solution are truly geocentric and thus compatible with the gravity data which should refer to a single equipotential surface In order to estimate the degree of compatibility in terms of longitude orientation between satellite Doppler and geodetic astronomical systems as realized by current observations, astrogeodetic (based on CIO pole, BIH longitudes, and NWL9D satellite Doppler system) and gravimetric deflections of the vertical were compared at several hundred stations of the Canadian geodetic framework and US transcontinental traverse It was found that, when using the US data subset only, incompatibility between the zero geodetic meridian plane of the NWL9D system and the zero astronomic meridian plane of the BIH was of the order of 078, which is in good agreement with previous results However, inter-comparisons between various North American subsets revealed inconsistencies between areas of up to 078 (between Canadian and US geodetic astronomical longitude observations) These results are based on the assumption that gravimetric deflections are bias free The geocentricity of the NWL9D system with respect to other systems such as the Goddard Earth Models and SAO Standard Earths is also analyzed by comparing satellite Doppler derived geoid undulations with GEM and SAO SE undulations An incompatibility of 4 m in Z (axis) exists between the origin of the NWL9D system and that of the other systems

The position angle of Jupiter's linearly polarized synchrotron emission – observations extending over 16 years

Abstract: Parkes, Owens Valley and Goldstone measurements are presented, showing the variation with central meridian longitude of the position angle of Jupiter's linearly polarized synchrotron emission at wavelengths of 21, 13, 11 and 6 cm; the observations span a total time interval greater than one Jovian orbital period. The form of the position angle versus longitude curve shows a slight dependence on wavelength and epoch. The epoch dependence appears to reflect Jupiter's changing aspect with respect to the earth. The observations yield a Jovian rotation period agreeing to within about 0.02 s with that derived from the decametric burst measurements, implying a highly stable inner magnetic field configuration.

Observation of long period sea surface temperature variability during gate

Abstract: —Current meter observations in the equatorial Atlantic during GATE yielded a temporal spectrum rich in longer period (< 1 week) variability. Observation siting does not permit generation of accurate spatial scales. A method is developed which yields the time and space scales as well as the phase sense for equatorial disturbances from sea surface temperature observations. The method is based on performing a two-dimensional (longitude, time) auto-covariance calculation on latitude sections of sea surface temperature obtained during GATE from satellite and ship platforms. Observations at 3 N show considerable variability with spatial-temporal scales attributable to equatorially trapped phenomena. Time series as determined from concurrent current meter observations along the meridians of 10, 20 and 23.5°W agree well with the periodicities derived from sea surface temperature. The most pronounced variability in the sea surface temperature along 3°N occurs at periods of about one month. This is interpreted as a meridional motion of the South Equatorial Current – North Equatorial Counter current sea surface temperature front. Typical parameters for this north-south motion of the sea surface temperature front (separating the South Equatorial Current and the North Equatorial Countercurrent) east of 20°W are ±.5° C temperature, ±.75° latitude; 33 ± 2 days period, 1000 ± 200 km wavelength for westward phase propagation and 25 ± 3 days period, 1400 ± 300 km wavelength for eastward phase propagation.

North Pacific Sea Surface Temperature Observations: A History

Abstract: For more than the past five years I have been trying to understand why the sea surface temperature has the marked variation with longitude on a scale of several thousand kilometers which is observed in the North Pacific, particularly at mid-latitudes, and what causes its time variations. This interest led me to the present short history of sea surface temperature observations. I have attempted to assemble the early observations, descriptions, and thinking about the large-scale surface temperature distribution of the North Pacific Ocean.

Energetic particle recurrence and escape during solar cycle 20

Abstract: Low-energy solar particle data have been combined from a multi-spacecraft near-earth data set covering most of solar cycle 20 (1966-1976) Particle intensity profiles have been ordered in the natural heliographic coordinate system of the estimated high coronal connection longitude of the foot point of the interplanetary field line The recurrence trends of approximately 1-MeV solar particles become more apparent in this coordinate system than when plotted versus time, and thereby extend the evidence for regions of continual injection and escape from the corona Intercomparison of solar particles and solar wind streams in heliographic longitude suggests that the origin of stream-associated spatial particle events seen at 1 AU is solar rather than interplanetary

Recorder for following wake

Abstract: PURPOSE:To obtain wake record easily with high precision by setting and memorizing two reference points on a piece of recording paper and by automatically processing the movement of a recording pen on the basis of the displacement of two points corresponding to the reduced scale of a map. CONSTITUTION:With regard to the pen position of recording pen 2 on recording paper 3, position signals are output from output terminals Px1 and Py1. Positions of reference points P0(X0, Y0) and P1(X1, Y1) on recording paper 3 are stored in memory circuits Mx0 and My0, and Mx1 and My1. As for the recording extent of a navigating position to be recorded, on the other hand, setting circuit 6 sets the longitude direction and setting circuit 7 the latitude direction. The set longitude and set latitude obtained by those circuits 6 and 7 are supplied to Y-position converting circuit 8 and X-position converting circuit 9. On the other hand, the measured result of the navigating position from navigating unit 10 is supplied to longitude/ latitude converting circuit 11, which supplies the converted longitude output to circuit 8 and the latitude output to circuit 9, so that the longitude and latitude of the measured navigating position will be shown at the corresponding position on recorder 1.

Equatorial waves in the satellite-observed cloud velocity field over the Pacific

Abstract: A space-time spectral analysis is applied to the 900-mbar meridional wind component over the equatorial Pacific Ocean. Cloud drift vectors, in the form of movie loops derived manually from cloud-tracking satellites, constitute the data base for this investigation. The major conclusions are as follows: (1) The maximum energy density levels of the wind occur at low wave numbers over a broad range of frequencies. These disturbances appear to manifest themselves as fluctuations occurring simultaneously over a large span of longitude. (2) Investigation of the high frequency-high wave number structure is difficult because of the general shortage of reliable data and the uneven satellite sampling intervals. Selection of spectral parameters becomes a compromise between the problems of high aliasing and low reliability. A high frequency-low wave number (time lag of 5 hours and space separation of 2.1° longitude) study was selected. (3) There was no indication of a distinct 4-day signal in our spectra. (4) There appears to be less high-frequency energy in the equatorial band (1.05°S to 1.05°N) than in the other two more southerly bands (5.25°S to 3.15°S and 3.15°S to 1.05°S).

Rate of Change Methods in Astronomical Surveying

Abstract: A method is described whereby longitude, latitude and azimuth can be obtained by taking sights on the sun at short timed intervals. Both rate of change of altitude with time and rate of change of bearing with altitude can be used to calculate the observer’s position and the direction of the meridian. A calculator can be programmed with monthly data from the \IStar Almanac for Land Surveyors\N to correct for refraction and carry out the necessary calculations from the raw observations. No previous knowledge of position is required.

Ionospheric Variations during the 13 September 1967 Storm: Incoherent Scatter Radar Results

Abstract: The storm time variations in Ne, Te, and ion drifts are studied for a mid-latitude station, St. Santin (44.11°N, 2.3°E) using incoherent scatter radar data. It is observed that there is an increase in Ne with a corresponding decrease in Te at 350km and the drifts are upward when compared with the quiet time drifts. These drifts are shown to be related to changes in magnetic field and hence they may be due to an electrodynamic effect. It is established from the Ne and Te profile changes that the differences in the ionospheric effects at different times reported earlier by the authors for the same storm are due to the storm-time effect and not due to a longitude effect.

John Churchman and the Longitude Problem

Abstract: In the early days of ocean navigation the problem of finding longitude, apart from the crude methods of dead reckoning, commanded considerable attention until practical solutions were found at mid-eighteenth century. In the initial phase of Atlantic voyaging it was realized that variation changes with longitude. This led to the suggestion that the crucial problem of east-west navigation might be solved from variation observations. Under an Act of Parliament (12 Anne, cap.xv) of 1714, which provided for a handsome monetary prize for the ‘discovery of the longitude’, a committee known as the Board of Longitude was formed. The Board continued, until its dissolution in 1828, to examine proposals for improving navigation after the principal problem had been solved. The 1714 Act led to numerous proposals from cranks and crackpots as well as men of science, and many of these proposals concerned ‘longitude by variation’. John Churchman, a land-surveyor and citizen of Philadelphia, communicated with the Board of Longitude on his scheme for finding longitude by variation for seventeen years from 1787 to 1804. During this time he persisted, with unshaken faith, that he had solved the problem. This paper deals with Churchman's proposals with special reference to his correspondence with the Board of Longitude.

Spectrum of Latitude Variations in the Frequency Range 1.4-2.2 Cpy and a Search for Nearly Diurnal Free Polar Motion

Abstract: Astronomical latitude observations of the ILS stations seem to indicate the existence of both a retrograde and a direct component of nearly diurnal polar motion with close frequencies (Yatskiv et al. 1975). The latter would manifest itself as a latitude variation with a period of about 204 mean days (m.d.) and with a phase depending on the double longitude of station.

An empirical model of night equatorial ionosphere on data from rpa on ogo-6 satellite

Abstract: An empirical model for the density distribution of o+ ions is constructed from 98 transits of OGO-6 satellite over the period Febr. l-ll 1970.The local time refers to the universal 22h 30m-00h 30m, and the satellite altitude over the equator is 600 km on average. Density is taken down at intervals of 5° dip latitude and 10° geographic longitude. Mathematical expressions are derived for distribution and variations of the ion density and temperature through a statistical analysis of a file of 7000 points as a function of dip latitude and magnetic declination.