Showing papers on "Longitude published in 1990"
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TL;DR: In this article, a global climatology of mean monthly surface air temperature has been compiled using terrestrial observations of shelter-height air temperature and shipboard measurements, and the combined data base consists of 17 986 independent terrestrial station records and 6 955 oceanic grid-point records.
Abstract: Using terrestrial observations of shelter-height air temperature and shipboard measurements, a global climatology of mean monthly surface air temperature has been compiled. Data were obtained from ten sources, screened for coding errors, and redundant station records were removed. The combined data base consists of 17 986 independent terrestrial station records and 6 955 oceanic grid-point records. These data were then interpolated to a 0.5° of latitude by 0.5° of longitude lattice using a spherically-based interpolation algorithm. Spatial distributions of the annual mean and intra-annual variance are presented along with a harmonic decomposition of the intra-annual variance.
626 citations
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TL;DR: In this paper, two years of Geosat data were used to systematically investigate the mesoscale variability and spatial scales of the North Atlantic, and it is believed that the total error budget is globally below that of the oceanic signal.
Abstract: Two years of Geosat data were used to systematically investigate the mesoscale variability and spatial scales of the North Atlantic. We first calculated sea surface height variability and eddy kinetic energy. These compare well with the eddy kinetic energy obtained with surface drifters. Then the spatial scales of mesoscale variability were characterized in 10° (latitude) × 10° (longitude) areas by their wave number spectra and autocorrelation functions. Comparison with existing in situ data shows good agreement, and it is believed that the total error budget is globally below that of the oceanic signal. The wave number spectra show significant differences as a function of latitude and longitude, and these can be related to different types of forcing (instability of a mean current or fluctuating wind). Scales typically decrease from west to east and south to north. Simple proportionality with respect to the first internal Rossby radii does not apply everywhere.
141 citations
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TL;DR: In this paper, an interhemispherically coupled model of airglow emissions of the O(+) (2P) metastable state (7320 A) and the 0-0 band of the N2 second positive system (3371 A), covering mid- and low-latitudes, is presented.
Abstract: This paper presents an interhemispherically coupled model of airglow emissions of the O(+) (2P) metastable state (7320 A) and the 0-0 band of the N2 second positive system (3371 A), covering mid- and low-latitudes. The model produces volume emission rates as a function of altitude, latitude, longitude, and local time for any selected data and solar and magnetic conditions, and, thus, can be used to provide three-dimensional maps of the selected emission for comparison with data obtained from orbiting vehicles. The semiglobal graphical maps of the 7320 A and 3371 A emissions illustrate the seasonal, diurnal, and solar cyclic variations on a scale that covers mid- and low-latitudes, as well as the effects of interhemispheric coupling (conjugate photoelectrons). It is shown that, in both cases, conjugate photoelectrons result in excitation at mid- to high- nighttime-latitudes in the winter hemisphere.
139 citations
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TL;DR: In this article, Geosat data are processed and analyzed into sea-level variations over the tropical Pacific Ocean during the first 26 months of the Exact Repeat Mission from November 15, 1986 to January 15, 1989.
Abstract: Geosat data are processed and analyzed into sea-level variations over the tropical Pacific Ocean during the first 26 months of the Exact Repeat Mission from November 15, 1986 to January 15, 1989. The resolution is 1 deg latitude and longitude and 10 days. The frequency and wavenumber spectra of these sea-level variations show much more energy in the northeastern than in the western or southern Pacific. Energy highs of 8000 sq cm per (cycle per day) per (cycle per deg longitude) are clearly identified along 5 deg N for periods of 28-40 days and wavelengths of 1000-2200 km (band 1), and along 12 deg N for periods of 50-90 days and wavelengths of 630-950 km (band 2).
62 citations
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TL;DR: In this paper, the column density of hydrocarbons above the altitude of the FUV auroral emission was analyzed to determine column density above the IUE spectra of the north Jovian aurora, and it was found that the hydrocarbon column density exhibited a consistent dependence on magnetic longitude, with peak density occurring approximately coincident with the peak in the observed auroral intensity.
Abstract: The wavelength-dependent absorption apparent in IUE spectra of the north Jovian aurora is analyzed to determine the column density of hydrocarbons above the altitude of the FUV auroral emission. Both the magnetotail and torus auroral zone models are considered in estimating zenith angles, with very similar results obtained for both models. It is found that the hydrocarbon column density above the FUV emission displays a consistent dependence on magnetic longitude, with the peak density occurring approximately coincident with the peak in the observed auroral intensity. Two distinct scenarios for the longitude dependence of the column density are discussed. In one, the Jovian upper atmosphere is longitudinally homogeneous, and the variation in optical depth is due to a variation in penetration, and thus energy, of the primary particles. In the other, the energy of the primaries is longitudinally homogeneous, and it is aeronomic properties which change, probably due to auroral heating.
59 citations
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TL;DR: The attributes for the simulation of tropical intraseasonal oscillations in the 30 to 60 day range by three GCMs are compared with analyses of the European Center for Medium-Range Weather Forecasts as mentioned in this paper.
Abstract: The attributes for the simulation of tropical intraseasonal oscillations in the 30 to 60 day range by three GCMs are compared with analyses of the European Center for Medium-Range Weather Forecasts. Models under consideration include the Goddard Laboratory of Atmospheric sciences (GLAS), Goddard Laboratory for Atmospheres (GLA), and UCLA GCMs. They are characterized by the same resolutions of four degrees latitude by five degrees longitude with 9 levels. Observations reveal that the eastward traveling planetary scale structure becomes more stationary over the Indonesian region and accelerates over the Central Pacific. In the tropics a Kelvin wave-type structure is found to be dominant near the center of the oscillation. The simulated winds are realistic although the meridional component is too strong, especially in the GLA GCM. The differences in the structure of the oscillation in the GLAS GCM and GLA GCM are considered to be a consequence of the different numerical schemes used. The GCMs are characterized by preferred zones for diabatic heating, with a turn-on heating occurring when the rising branch of the intraseasonal oscillation passes over these convective regions.
39 citations
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TL;DR: In this article, a model describing the physical libration in longitude and latitude for Phobos is derived and the major effect is the well-known longitude variation with the anomalistic orbital period and amplitude.
Abstract: A model describing the physical libration in longitude and latitude for Phobos is derived. The major effect is the well-known longitude variation with the anomalistic orbital period and amplitude. Several additional meter-sized periodic librations in longitude exist. The latitude variation is dominated by the forced precession of Phobos' figure axis with the precession of Phobos' orbital plane. The contribution of Phobos' topography to its gravity field is estimated using the control network model of Duxbury and Callahan (1989).
36 citations
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TL;DR: In this paper, vertical and horizontal ion drift velocities for 1977-1979 from the Unified Abstract files of the satellite Atmosphere Explorer E were used in preliminary studies of the behavior of the low-latitude (−20° to 20° degree) F region.
Abstract: Vertical and horizontal ion drift velocities for 1977-1979 from the Unified Abstract files of the satellite Atmosphere Explorer E were used in preliminary studies of the behavior of the low-latitude ({minus}20{degree} to 20{degree} dip latitude) F region. Sample diurnal variations obtained during 1978-1979 equinox time periods are very similar to those measured by the incoherent scatter radar at Jicamarca, Peru. Latitude profiles of the vector drift values clearly show the classic fountain effect responsible for the Appleton anomaly during the day. Investigation of longitude effects revealed that the average perpendicular (approximately vertical) drift velocity V{sub perp} is independent of longitude, implying that the average east-west electric field is proportional to B and thus is likely derived from classical dynamo winds.
34 citations
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TL;DR: In this paper, the authors used complex demodulation to describe the year-to-year modulation of the phase and amplitude of the annual cycle of sea level along the mere axis of the North Equatorial Countercurrent (NECC) sea level trough in the western Pacific.
Abstract: The annual cycle of sea level variability is examined for the period 1976–1985 at seven stations that lie along the mere axis (near 7°N)) of the north equatorial countercurrent (NECC) sea level trough in the western Pacific. The technique of complex demodulation is used to describe the year to year modulation of the phase and amplitude of the annual cycle of sea level along this line. This technique reveals differences in the character of the annual cycle that are related to the occurrence of the El Nino/Southern Oscillation (ENSO) phenomenon. During non-ENSO time periods, the amplitude of the annual cycle averages 4–5 centimeters and increases towards the west at approximately 1 mm per degree of longitude. The annual cycle during thew periods also shows a phase propagation towards the west at about 50 cm/s, which is comparable to the Rossby wave phase speed at this latitude. During the ENSO events, the amplitude of the annual cycle averages 7–8 centimeters and increases towards the west at about...
21 citations
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TL;DR: In this paper, the authors show that the longitude effect is the same as that contained in the Utah State University time-dependent ionospheric model and that magnetic activity dependency is associated with the westward convection in the afternoon sector.
Abstract: The nighttime main F region trough extends into the sunlit afternoon sector. This trough feature exhibits both a strong magnetic activity dependence and a longitude (UT) dependence. Whalen (1987), using International Geophysical Year (IGY) ionosonde data, showed that both of these effects are readily extracted from f{sub 0}F{sub 2} observations. In this study the authors show that the longitude effect is the same as that contained in the Utah State University time-dependent ionospheric model. It arises from the offset of the geomagnetic axis from the geographic axis. The magnetic activity dependency is associated with the westward convection in the afternoon sector. It is also contained in the ionospheric model via the empirical magnetospheric convection model. This one-to-one observational-model agreement is unique; to date no other magnetic activity dependent ionospheric feature has been simulated this systemtically.
20 citations
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TL;DR: In this paper, compositing methods were applied to ECMWF model analyses during July and August 1981 to determine the structure of synoptic scale waves with periods of 6-9 days.
Abstract: This study applies compositing methods to ECMWF model analyses during July and August 1981 to determine the structure of synoptic scale waves with periods of 6–9 days. Over northern Africa, these ware intermittent in time, are most regular in period and amplitude west of the Greenwich meridian in a narrow longitude band, though there is a suggestion of their existence between 15°E and 0°. The average wavelength is 5000 km and the westward velocity is 6°–7° longitude day−1. The horizontal wind pattern in midtroposphere (700 and 500 hPa) consists of two vortices of opposite signs on either side of 12.5°N, with maximum perturbation of the zonal wind component at this latitude, and maximum perturbation of the meridional wind component at 5°–7.5°N and at 17.5°–20°N. Temperature is modulated by the passage of the waves throughout the troposphere. This structure is very different from that of the 3‐4 day African wave.
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TL;DR: In this paper, the authors describe properties of large-scale fluctuations in the wind field represented by two analyses (FNOC and NOAA ATOLL) and in the SST fields represented by maps derived from 5-day composite AVHRR images, within an 11° longitude by 10° latitude domain during FASINEX (January through June 1986).
Abstract: We describe properties of large-scale fluctuations in the wind field represented by two analyses (FNOC and NOAA ATOLL), and in the SST field represented by maps derived from 5-day composite AVHRR images, within an 11° longitude by 10° latitude domain during FASINEX (January through June 1986). FNOC and ATOLL wind and wind stress time series were highly correlated with each other (<0.8) over the entire domain, and they were also highly correlated with time series measured at the FASINEX site ≥0.89. At periods of 2–13 days, clockwise →τ energy exceeded anticlockwise energy by an order of magnitude, while the energy was nearly partitioned equally at periods of 13–40 days. Mean ATOLL winds were everywhere more eastward than mean FNOC winds, probably in part because the ATOLL (FNOC) analyses are intended to represent 850 mb (19.5 m) winds. The 850 mb winds are expected to be more eastward due to the thermal wind balance with the mean southward air temperature gradient. The SST maps represented large-s...
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TL;DR: In this paper, the structure and variability of tides in the 80-120 km height region are reviewed and seasonal-latitudinal variations in the vertical structure of diurnal and semidiurnal winds between 70-100 km as measured by meteor and partial reflection drift radars, and tidal temperatures determined by incoherent scatter radars between 100 and 140 km.
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TL;DR: In this article, the first map of the horizontal flows as a function of depth and heliocentric position in the solar convection zone is presented, which is inferred from a least-squares smoothness-constrained inversion of velocities measured from ring diagrams of the solar p-mode oscillations.
Abstract: The first map of the horizontal flows as a function of depth and heliocentric position in the solar convection zone is presented. The map is inferred from a least-squares smoothness-constrained inversion of velocities measured from ring diagrams of the solar p-mode oscillations. The data provide information in four longitude regions at a latitude just south of the solar equator. The presence of several features is suggested by the results:
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A prograde directed longitudinal jet between the hydrogen and first helium ionization zone, reversing direction to retrograde below the second helium ionization zone.
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A equatorward directed latitudinal flow above the second helium ionization zone.
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A poleward latitudinal flow below the second helium ionization zone, but only in one of the four longitude bands. A large active region was present in this band, but not in two of the other bands, suggesting a possible relationship between the activity and the different flow pattern.
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TL;DR: In this paper, the effect of the Macquarie Ridge earthquake on the earth's length of day, polar motion, and low-degree harmonic coefficients of the gravitational field are compared, and it is found that this earthquake should have caused the length-of-day to decrease by 0.06, the position of the mean rotation pole to shift 0.11 milliarcsec towards 323 E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10 to the 13th.
Abstract: The coseismic effect of the Macquarie Ridge earthquake on the earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are compared. It is found that this earthquake should have caused the length-of-day to decrease by 0.06, the position of the mean rotation pole to shift 0.11 milliarcsec towards 323 E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10 to the 13th.
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TL;DR: In this article, a method is developed to compare the location of the recorded minimum cosmic ray intensity with that of the predicted minimum along a route as calculated from cutoff rigidities, and it is found that the positions of the minima in cosmic ray intensities obtained from a survey across the equator and those derived from the interpolated cutoff rigidity along the survey route are mutually consistent.
Abstract: Since the cutoff rigidity at the cosmic ray equator varies with longitude, the location of the minimum cosmic ray intensity obtained during a latitude survey depends on the direction by which the geographic equator is crossed. A method is developed to compare the location of the recorded minimum cosmic ray intensity with that of the predicted minimum along a route as calculated from cutoff rigidities. The data of several surveys, covering the period 1954–1986/1987, are used. Instead of the accurate but computer intensive trajectory-tracing method, cutoff rigidities for every location and instant are interpolated from 5°×15° world grids. It is found that the positions of the minima in cosmic ray intensities obtained from a survey across the equator and those derived from the interpolated cutoff rigidities along the survey route are mutually consistent. The rms difference between the experimental and calculated positions of the cosmic ray minima for all the surveys amounts to only 0.32°. Major secular changes in cutoff rigidities occur in the Atlantic Ocean region. Whereas a fast northerly shift of the cosmic ray equator is evident between 320° and 345° longitude, the data points from different epochs within this longitude range show a negligible difference between the simulated and experimental positions of the route-dependent cosmic ray equator. This indicates that the secular variation in cutoff rigidity is well accounted for by the grid values derived from the International Geomagnetic Reference Fields for 1955.0, 1965.0, and 1980.0, even when the values are extrapolated linearly beyond 1980.0 through to 1987 in equatorial regions.
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TL;DR: In this paper, the authors analyzed the global mean of the annual net air-sea heat flux is not in equilibrium, but shows a relatively small loss of 5 W m−2 for the ocean (instead of a 40 Wm−2 gain in an older ECMWF analysis), while the meridional oceanic net heat transport is consistent with other climatological estimates (Hastenrath 1982) in the northern hemisphere, but less consistent with estimates from the southern hemisphere, Seasonal variability of the net heat flux at the airsea interface was studied over two
Abstract: Twelve months of data on surface heat fluxes (shortwave radiation, longwave radiation, latent heat and sensible heat, from August 1985 to July 1986), obtained from the European Center for Medium-Range Weather Forecast (ECMWF) on a grid of 1.125° latitude by 1.125° longitude were analyzed. Comparison with older data from ECMWF (Simonot and Le Treut, 1987) indicates the occurrence of significant improvements in global and local distributions of the fluxes over oceans (mainly the latent and net heat fluxes), except for the shortwave radiative heat flux, which seems degraded. The global mean of the annual net air-sea heat flux is not in equilibrium, but shows a relatively small loss of 5 W m−2 for the ocean (instead of a 40 W m−2 gain in an older ECMWF analysis). Meridional oceanic net heat transport is consistent with other climatological estimates (Hastenrath 1982) in the northern hemisphere, but less consistent with estimates from the southern hemisphere, Seasonal variability of the net heat flux at the air-sea interface was studied over two limited mid-latitude ocean basins: the North and the South Atlantic. Annual mean and low frequency rms are discussed. Fair agreement is found with climatological studies from Bunker (1976, 1988), Esbensen and Kushnir (1981), and Hsiung (1986), with discrepancies being large enough in the tropical South Atlantic to explain the deviation from climatology in the meridional oceanic heat transport in the southern hemisphere. Large-scale variability of low-frequency perturbation net heat flux was investigated by means of empirical orthogonal function (eof) analysis. For each ocean, the first eof accounts for a large amount of the total variance in the data (41% in the North Atlantic and 61% in the South Atlantic), and is characterized by basin-sized oscillations with annual and semiannual cycles. Comparison of our data with a climatology of the Agulhas retroflection area (Walker and Mey, 1988) indicates the good quality of ECMWF analyses in regions where air-sea exchanges are large; but large relative uncertainties remain among estimates in regions where fluxes are weak.
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TL;DR: In this article, the authors investigated the relationship between sunspot activity in heliographic longitude and coronal holes for the period corresponding to Cycle 21 (Carrington rotations 1623-1779).
Abstract: The relationship between sunspot activity in heliographic longitude and coronal holes is investigated for the period corresponding to Cycle 21 (Carrington rotations 1623–1779). The major result is that, based on He i 10830 A data, a strong inverse association is found between the longitudinal positions of sunspot groups and the size and number of coronal holes (especially, the equatorial extensions of polar holes). Frequencies of coincidences in longitude were determined for both types of activity and the evolution of coronal holes over Cycle 21 is depicted in the form of a ‘butterfly diagram’ displaying their latitudinal and longitudinal extents. A tabular listing identifies average longitude and persistence of sunspot active longitudes.
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TL;DR: In this paper, a satellite-borne x ray imager was used to detect electron precipitation at latitudes near the midnight trapping boundary with a single pass of the satellite spin motion, and it was shown that in situ electron precipitation was generally fairly uniform over a median longitude interval of at least 45°.
Abstract: Electron precipitation occurring at latitudes near the midnight trapping boundary was measured remotely with a satellite-borne x ray imager (>21 keV). This investigation has demonstrated for the first time the repetitive mapping of precipitation at the trapping boundary with x rays. The satellite spin motion (5.5 second period) provided repeated scans of each scene during a single pass of the satellite. When the in situ electron precipitation, measured directly with a spectrometer (>68 keV) on the same satellite, was limited to a narrow region at the trapping boundary the precipitation inferred from the x rays was generally fairly uniform over a median longitude interval of at least 45°. Significant decreases of x rays at longitudes away from the satellite crossing seldom occurred, but significant increases at certain longitudes were sometimes observed. The widespread arc patterns of the precipitation have important implications for both understanding the nature of the responsible loss mechanisms and for assessing the atmospheric effects.
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TL;DR: In this paper, a set of mid-latitude European observatories, using International Quiet Sun Years (IQSY) data, were used to analyze the longitude variations with longitude of the geomagnetic tides.
Abstract: SUMMARY
Night-time lunar geomagnetic tides have been analysed for a set of mid-latitude European observatories, using International Quiet Sun Years (IQSY) data. It is found that the variations with longitude are consistent with those expected on the Chapman–Kendall theory for a tidally induced electric current flowing north–south in the Atlantic Ocean together with an image current induced in the solid Earth.
03 May 1990
TL;DR: In this paper, the authors present an extension and modifications to ICED that provide a global specification, in effect a GLOBAL ICED, that includes electron and ion density profiles.
Abstract: At the Fifth Ionospheric Effects Symposium, a paper was presented and published that described an operational Air Force Weather Service (AWS), near real-time, ionospheric specification model called Ionospheric Conductivity and Electron Density (ICED) That version of the model specified primarily the northern hemisphere midlatitude and auroral zone ionospheric regions and did not cover either the low latitude or high latitude/polar cap regions We are making extensions and modifications to ICED that provide a global specification - in effect a GLOBAL ICED Major additions include (1) specifications of electron and ion density profiles (90 to 1000 km) in the high latitude trough, auroral oval, and polar cap ionosphere in both northern and southern hemispheres, (2) midlatitude electron and ion density profiles that include magnetic declination effects, and (3) low latitude ionospheric specification that accounts for longitude control through differences in vertical E x B drift patterns Since this model is driven by real-time data, we describe the various input parameters and how they are incorporated
01 Jan 1990
TL;DR: Based on June to September 1981 ECMWF grid datasets analysis is done of the characteristics of the propagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia, revealing that the oscillation of the zonal winds is quasi-geostrophic in pature and in phase in the high and low levels.
Abstract: Based on June to September 1981 ECMWF grid datasets analysis is done of the characteristics of thepropagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia. Results show aseparating (confluence) belt for the meridional propagation of low-frequency zonal (meridional) winds at higher(lower) levels over subtropical latitudes at 120°E, revealing that the oscillation of the zonal winds is quasi-geostrophic in pature and in phase in the high- and low-level. It is also found that the eastward propagationof the high-level zonal winds around 35°N in East Asia is the result of eastward march of midlatitude low-frequency waves with 60--90 longitude wavelength and speed of 1.5--2.0 longitudes per day. In addition, suchlow-frequency vortices, when moving over the coastwise region, tend to develop, accompanied by sharp oscil-lation in the westerly jetstream over eastern Asia.
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19 Feb 1990
TL;DR: In this article, a position display radar equipment is provided, and it is moved on a display screen so that a display position of a target whose latitude/longitude position is known in advance in an image of radar echo information coincides with correct latitude and longitude.
Abstract: PURPOSE:To display a correct a latitude/longitude line by moving the latitude/ longitude line so that an image of a target whose latitude/longitude position on a display screen is known is positioned correctly against the displayed latitude/longitude line, and calculating an error from the moving amount. CONSTITUTION:On a position display radar equipment, a correction control part 42 is provided, and it is moved on a display screen so that a display position of a target whose latitude/longitude position is known in advance in an image of radar echo information coincides with correct latitude and longitude. From a shift of the longitude and the latitude before the movement and the longitude and the latitude after the movement, an error of measured position information stored in a position information storage part 16 is derived, and error information is stored in a storage part 43 of an arithmetic part 22. Subsequently, the measured position information is read out of the storage circuit 16, and a parameter operation of latitude and longitude lines is executed, while correcting the information by error information of the storage part 43.
01 Jan 1990
TL;DR: In this article, the authors presented data on the atmospheric circulation of Venus, obtained by the Mariner 10 (1974) and Pioneer (1979-1986) observations, which yielded evidence of relatively stable zonal circulation at the cloud level.
Abstract: This paper presents data on the atmospheric circulation of Venus, obtained by the Mariner 10 (1974) and Pioneer (1979-1986) observations. The results yielded evidence of relatively stable zonal circulation at the cloud level. On the other hand, changes on a yearly time scale appear in both the zonal and the meridional components of motion. Solar thermal tides and large-scale planetary waves are also seen in averaged zonal and meridional cloud motions. The relationship between the large-scale circulation and global cloud structure is discussed.
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TL;DR: In this paper, the longitude effect upon foF2 over the dip equator is anticorrelated with the total electrojet current, and also to some extent with the build-up of the northern and southern crests.
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