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.

On the theory of the Solar diurnal variation of the Earth’s magnetism

Abstract: 1. The most likely explanation of the solar diurnal magnetic variation (conveniently denoted by S) has for more than a generation seemed to be that afforded by the "dynamo ” theory, originally proposed by Balfour Stewart and further developed by Schuster and the writer. It attributes S to overhead electric currents, induced by convective motion of the air across the earth’s magnetic field. The form and intensity of the current-system can be inferred from the spherical harmonic analysis of S; J. Bartels, on the basis of the writer’s analysis, has drawn the current-diagram reproduced in the figure (p. 383). It will be seen that the current-system consists of four circuits, two north and two south of the equator, each flowing round a centre or focus. At the equinoxes, to which the figure refers, the system is approximately symmetrical with respect to the equator. The principal pair of circuits are situated in the sunlit hemisphere, and each circuit of this pair carried 62,000 amperes at sun­spot minimum; their foci lie approximately on the 11 hour meridian. The other pair of circuits, each carrying 32,000 amperes, are less intense but more extensive, covering about 15 hours in longitude. The equatorial current-intensity, per centimetre measured along the meridian, has an eastward maxi­mum of 2 .10-5 e. m. u. at about 11h, and a westward maximum of 10-5 e. m. u. at about 17h. 2. The dynamo theory can give a good account of the general form of this current-system, but meets serious difficulties when it attempts to explain the phase and intensity of the currents. This is because the convective motion which induces the currents, and the total conductivity of the layer in which they flow, are unknown. But if it is assumed that the convective motion is the same as at ground level, it appears that the day current-foci should be on the meridian 13h or 14h, distinctly later than the observed position. Further, the total electric conductivity (or ∫ σ dh , the integral of the specific conduc­tivity σ throughout the thickness of the layer) must be large, of the order 10-5 e. m. u.

Using ionospheric scintillation observations for studying the morphology of equatorial ionospheric bubbles

Abstract: [1] For a study of the equatorial ionosphere, ionospheric scintillation data at VHF and L-band frequencies have been routinely collected by ground-based receivers at Ancon, Peru, Antofagasta, Chile, and Ascension Island, UK, since May 1994. The receivers routinely monitor VHF transmissions from two geosynchronous satellites located at 100°W longitude and 23°W longitude, and L-band signals from satellites located at 75°W longitude and 15°W longitude. This combination provides a network of seven usable, reasonably separated links for monitoring ionospheric equatorial bubble activity in the South American longitude sector. A data set of seven years covering the period from 1995 to 2001 was studied to determine the temporal, diurnal, and seasonal behavior of equatorial bubbles. The results of our statistical study are presented here. In general the equatorial ionospheric bubble activity shows a strong systematic and primary dependence in temporal, diurnal, and seasonal variation, and a secondary weak dependence on geomagnetic and solar flux activity. At present, the dependence on solar and magnetic activity is not usable for near-time and short-term prediction of the equatorial bubble activity. Equatorial bubbles usually start 1 hour after sunset, the activity peaks before local midnight, and vanishes by early morning. The activity peaks in the months of November and January–February and is practically absent (weak) from May to August. On a daily basis on the average one sees 1 to 3 bubbles. The duration of bubbles is about 70 min, and the time spacing between the bubbles is 1 to 2 hours. The bubble activity in general follows the phase of solar cycle activity. The observed systematic behavior of the equatorial bubbles allows for a now cast and short-term forecast of the bubble activity in the South American sector.

Characteristics of equatorial ionization anomaly (EIA) in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

Abstract: . The poleward gradient of the equatorial ionization anomaly (EIA) introduces more intense propagation effects on transionospheric satellite links in comparison to the equatorward gradient. Characterization of the poleward gradient was performed during March–April, August–October 2011 and March–April 2012 using GPS total electron content (TEC) recorded from a chain of stations located more or less along the same meridian (88.5° E) at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50° at 14:00, 15:00 and 16:00 LT were found to have a strong correlation with GPS S4 observed from Calcutta during post-sunset-to-midnight hours. A threshold value of poleward TEC gradient is calculated above which there is a probability of scintillation at Calcutta with S4 ≥ 0.4.