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Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.


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Journal ArticleDOI
TL;DR: In this article, the Haystack radar was used to determine the topography in a belt near the equator of the planet Mars during the 1969 opposition, and the results showed that the variation of surface height with longitude between latitudes 3°N and 12°N is similar to that measured for latitudes near 22°N during the 1967 opposition.
Abstract: During the period surrounding the 1969 opposition, the planet Mars was observed with the Haystack radar to determine the topography in a belt near the equator. Elevation values obtained for the same surface location on Mars on different days of observation agree, for high signal-to-noise ratio cases, to within about 100 meters. Preliminary results show that the variation of surface height with longitude between latitudes 3°N and 12°N is similar to that measured for latitudes near 22°N during the 1967 opposition. The most notable difference is found near 215° longitude, where at 22°N there is a highland at Elysium, although at 5°N a lowland is found. Optically dark regions often have a high radar cross section. However, the topography shows no significant correlation with either the visual or the radar brightness.

40 citations

Journal ArticleDOI
TL;DR: In this paper, a simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration.
Abstract: The longitude of the western limit of the equatorial Pacific upwelling is a key parameter for studies of carbon budget and pelagic fisheries variability. Although it is well defined at the surface on the equator by a salinity front and a sharp variation of the partial pressure of CO2, data from two equatorial cruises make it clear that this hydrological limit does not necessarily coincide with the boundary of the nitrate and chlorophyll enriched area. In January-February 1991 during a non-El Nino period, when trade winds and the South Equatorial current (SEC) were favorable to upwelling, the two limits were at the same longitude. Conversely, in September-October 1994 during El Nino conditions, when the equatorial upwelling had stopped, the nitrate and chlorophyll enriched zone was found a few degrees of longitude east of the hydrological boundary (5.5° at the surface and 2.5° for the 50 m upper layer), whereas no such offset was observed for zooplankton biomass. A simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration. The model results support the hypothesis that zonal separation of the limits arises from biological processes (i.e. nitrate uptake and phytoplankton grazing) achieved during that upwelling break.

40 citations

Journal ArticleDOI
TL;DR: In this article, the first observations of meter-scale equatorial 150km plasma irregularities outside the American longitude sector were reported, conducted at Pohnpei (western Pacific) with a wind profiling ST radar demonstrate the feasibility of making ionospheric electric field measurements with low cost instruments and also reveal a potentially important anisotropy in the angular distribution of 150km VHF radar echoes.
Abstract: First observations of meter-scale equatorial 150-km plasma irregularities outside the American longitude sector are reported. The observations conducted at Pohnpei (western Pacific) with a wind profiling ST radar demonstrate the feasibility of making ionospheric electric field measurements with low cost instruments and also reveal a potentially important anisotropy in the angular distribution of 150-km VHF radar echoes.

40 citations

Journal ArticleDOI
TL;DR: In this article, the motion in longitude of a nominally geostationary satellite due to the tesseral harmonics is investigated, and the necessary formulae to describe the motion, and to find the corrective impulses required etc., have been developed for the principal J2.2 term.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25°16′N, Longitude 82°59′E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographical latitude 17°20′ N, longitude 78°30′
Abstract: The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25°16′ N, Longitude 82°59′ E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographic latitude 17°20′ N, longitude 78°30′ E) and Bangalore (Geographic latitude 12°58′ N, longitude 77°33′ E) in India. We describe the diurnal and seasonal variations of total electron content (TEC), and the effects of a space weather related event i.e. a geomagnetic storm on TEC. The mean diurnal variation during different seasons is brought out. It is found that TEC at all the three stations is maximum during equinoctial months (March, April, September and October), and minimum during the winter months (November, December, January and February), while obtaining intermediate values during summer months (May, June, July and August). TEC shows a semi-annual variation. TEC variation during geomagnetic quiet as well as disturbed days of each month and hence for each season from May 2007 to April 2008 at Varanasi is examined and is found to be more during disturbed period compared to that in the quiet period. Monthly, seasonal and annual variability of GPS-TEC has been compared with those derived from International Reference Ionosphere (IRI)-2007 with three different options of topside electron density, NeQuick, IRI01-corr and IRI 2001. A good agreement is found between the GPS-TEC and IRI model TEC at all the three stations.

39 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023240
2022432
202142
202042
201960
201851