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.

Observations of the F region height redistribution in the storm‐time ionosphere over Europe and the USA using GPS imaging

Abstract: [1] Ionospheric imaging with GPS provides a near-global view of the three-dimensional time-evolving ionosphere. This is of particular interest during storms. The focus of this paper is on the height redistribution of the plasma and in particular the longitudinal and latitudinal variations in the time of plasma uplifts. Three storms, 15 July 2000, 30 October 2003 and 20 November 2003, are studied here. Dramatic elevation of the F layer by more than one hundred kilometers was seen in the images during daytime over Europe and the USA for all three storms. All three showed an east-west time delay of around one hour in the peak-height elevation over some 85° longitude. The 20 November 2003 storm also showed a north-south time delay in the change in the F-region height with the uplift seen first at high latitudes and then low latitudes. Independent evidence from other instruments and techniques are provided as supporting evidence that the peak-height uplifts occurred. Candidate mechanisms of the peak height changes are electric fields and neutral winds and the roles of these drivers will be investigated in future modelling studies.

Variations in the strength of the Sq current system

Abstract: The strength of the Sq current system is measured by taking the difference between magnetic variations on either side of the current system focus. This is carried out for several longitude sectors. A distinct semiannual variation is sometimes found but its incidence varies with longitude, local time and hemisphere. Other semiannual effects in the ionosphere are reviewed and the possibility of a diurnal modulation of the strength of the 12-h tide is suggested.

Correlation between the global occurrences of ionospheric irregularities and deep atmospheric convective clouds in the intertropical convergence zone (ITCZ)

Abstract: To study the seeding mechanism of ionospheric irregularity occurrences, a correlation study has been carried out between the global monthly/latitudinal (m/l) distributions of irregularity occurrences and the deep atmospheric convective clouds in the intertropical convergence zone (ITCZ) indicated by the outgoing longwave radiation (OLR) measurements. Seven longitude sectors - the African, Indian, West Pacific, Central Pacific, East Pacific, South American, and Atlantic sectors - are selected to study the correlations between the two distributions. The results indicate that good correlations exist only in the South American sector and to some extent in the African sector. For the other five sectors, no correlations are found in the m/l distributions between the irregularities and OLRs. This implies that the gravity wave induced in the ITCZ cannot be the sole seeding agent for the Rayleigh-Taylor (RT) instability in the global irregularity occurrences every season. We suspect that the post-sunset ionospheric electrodynamic perturbations could be the prevailing seeds for the RT instability globally year long. Together with the favorable post-sunset ionospheric condition, the global m/l distributions of irregularity occurrences could be adequately explained.

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.