CONJUGATE POINT OBSERVATIONS AT A VARIETY OF HIGH GEOMAGNETIC LATITUDES

1964 ◽  
pp. 27-38 ◽  
Author(s):  
H.J.A. CHIVERS
Keyword(s):  
2014 ◽  
Vol 119 (1) ◽  
pp. 375-383 ◽  
Author(s):  
M. A. Abdu ◽  
E. A. Kherani ◽  
I. S. Batista ◽  
B. W. Reinisch ◽  
J. H. A. Sobral
Keyword(s):  

Author(s):  
Kurt Kreith ◽  
Charles A. Swanson

SynopsisWirtinger-type inequalities of order n are inequalities between quadratic forms involving derivatives of order k ≦ n of admissible functions in an interval (a, b). Several methods for establishing these inequalities are investigated, leading to improvements of classical results as well as systematic generation of new ones. A Wirtinger inequality for Hamiltonian systems is obtained in which standard regularity hypotheses are weakened and singular intervals are permitted, and this is employed to generalize standard inequalities for linear differential operators of even order. In particular second order inequalities of Beesack's type are developed, in which the admissible functions satisfy only the null boundary conditions at the endpoints of [a, b] and b does not exceed the first systems conjugate point (a) of a. Another approach is presented involving the standard minimization theory of quadratic forms and the theory of “natural boundary conditions”. Finally, inequalities of order n + k are described in terms of (n, n)-disconjugacy of associated 2nth order differential operators.


2021 ◽  
Vol 44 ◽  
pp. 63-66
Author(s):  
V.B. Belakhovsky ◽  
◽  
V.A. Pilipenko ◽  
K. Shiokawa ◽  
Y. Miyoshi ◽  
...  

The physical nature of Pg (pulsation giant) pulsations, which were observed in the magnetosphere by the Japanese satellite Arase, geostationary satellites GOES, and ground stations of the THEMIS and CARISMA networks, was investigated in this work. Pg pulsations belong to the Pc4 frequency range and are characterized by a very monochromatic shape. For the event on 5 June, 2018, according to the data from the Arase satellite, the Pg pulsation wave packet was recorded in the dawn sector during 3 hours. The pulsations are most pronounced in the radial component of the geomagnetic field, their frequency was about 11 mHz. Pg pulsations observed in the magnetosphere were accompanied by pulsations with the same period according to data from a number of ground-based magnetic stations located near the conjugate point. According to the data of ground stations, the pulsations were most strongly expressed in the Y-component of the geomagnetic field. Pg pulsations were accompanied by pulsations in electron and proton fluxes according to the Arase, GOES satellite observations. There are no clear phase relationships between geomagnetic pulsations and pulsations in charge particle fluxes. Pg pulsations were excited under quiet geomagnetic conditions (SYM-H = -10 nT, AE = 100-400 nT) on the recovery phase of the small geomagnetic storm. It is assumed that the expansion of the plasmasphere at low geomagnetic activity leads to an increase in the plasma density in the region of the geostationary orbit, which creates favorable conditions for the excitation of Pg pulsations due to the drift-bounce resonance of protons with the geomagnetic field lines oscillations in the magnetosphere.


2018 ◽  
Vol 61 (7) ◽  
pp. 1636-1651 ◽  
Author(s):  
C. Martinis ◽  
J. Baumgardner ◽  
J. Wroten ◽  
M. Mendillo

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Charles S. Carrano ◽  
Cesar E. Valladares ◽  
Keith M. Groves

Previous authors have reported on the morphology of GPS scintillations and irregularity zonal drift during the 2002 Conjugate Point Equatorial Experiment (COPEX) in Brazil. In this paper, we characterize the turbulent ionospheric medium that produced these scintillations. Using 10 Hz GPS carrier-to-noise measurements at Boa Vista (2.9°N, 60.7°W), Alta Floresta (9.9°S, 56.1°W), and Campo Grande (20.5°S, 54.7°W), we report on the variation of turbulent intensity, phase spectral index, and irregularity zonal drift as a function of latitude and local time for the evening of 1-2 November 2002. The method of analysis is new and, unlike analytical theories of scintillation based on the Born or Rytov approximations, it is valid when the scintillation index saturates due to multiple-scatter effects. Our principal findings are that (1) the strength of turbulence tended to be largest near the crests of the equatorial anomaly and at early postsunset local times, (2) the turbulent intensity was generally stronger and lasted two hours longer at Campo Grande than at Boa Vista, (3) the phase spectral index was similar at the three stations but increased from 2.5 to 4.5 with local time, and (4) our estimates of zonal irregularity drift are consistent with those provided by the spaced-receiver technique.


Author(s):  
Charles F. Kennel

Studies using data from the ATS-5 geosynchronous spacecraft revealed a clear relationship between midnight region injection events near the spacecraft and auroral displays near the ATS magnetic conjugate point (Hones et al., 1971a; Mende et al., 1972; Eather et al., 1976; Mende and Shelley, 1976). A comparison of ATS-5 particle and magnetic field data with all-sky photographs taken at the conjugate point, Great Whale River, indicated that an injection at geostationary orbit generally corresponded to the brightening of the onset arc when the spacecraft was in the midnight sector (Akasofu et al., 1974). Results such as this whetted the collective appetite. How closely can the initial onset and injection be related to one another in time, do the onset and injection start on the same field field line, does the westward propagation of dipolarization correspond to the westward surge, can one relate the fine structures of the auroral expansion and the dipolarization? As time passed, increasingly precise answers have been given to these and similar questions, and auroral and geosynchronous substorm phenomenology has become more tightly integrated. In this chapter, we sample some of the evidence that supports this statement. The GEOS 2 spacecraft was stationed with its magnetic conjugate point near Kiruna, Sweden, so that the conjugate aurora could be studied with the extensive network of ground-based observatories in Scandinavia (Knott, 1975; Knott et al., 1979). In the first part of this chapter, we review some of the correlation studies carried out in the GEOS 2 project. In one particular series of four substorms, it was found that the dipolarization occurred at the same time as the aurora brightened and expanded poleward over the ground conjugate region (Section 14.2). In another case, a dispersionless injection at GEOS 2 corresponded to an intensification of the auroral X-ray band in Scandinavia (Section 14.2). Westward surges at the auroral conjugate point were associated with dipolarization at the spacecraft on a statistical basis (Section 14.3). Finally, the close relationship between both the auroral and geostationary substorm phenomena was extended to small spatio-temporal scales.


2019 ◽  
Vol 11 (23) ◽  
pp. 2737 ◽  
Author(s):  
Minsu Kim ◽  
Seonkyung Park ◽  
Jeffrey Danielson ◽  
Jeffrey Irwin ◽  
Gregory Stensaas ◽  
...  

The traditional practice to assess accuracy in lidar data involves calculating RMSEz (root mean square error of the vertical component). Accuracy assessment of lidar point clouds in full 3D (three dimension) is not routinely performed. The main challenge in assessing accuracy in full 3D is how to identify a conjugate point of a ground-surveyed checkpoint in the lidar point cloud with the smallest possible uncertainty value. Relatively coarse point-spacing in airborne lidar data makes it challenging to determine a conjugate point accurately. As a result, a substantial unwanted error is added to the inherent positional uncertainty of the lidar data. Unless we keep this additional error small enough, the 3D accuracy assessment result will not properly represent the inherent uncertainty. We call this added error “external uncertainty,” which is associated with conjugate point identification. This research developed a general external uncertainty model using three-plane intersections and accounts for several factors (sensor precision, feature dimension, and point density). This method can be used for lidar point cloud data from a wide range of sensor qualities, point densities, and sizes of the features of interest. The external uncertainty model was derived as a semi-analytical function that takes the number of points on a plane as an input. It is a normalized general function that can be scaled by smooth surface precision (SSP) of a lidar system. This general uncertainty model provides a quantitative guideline on the required conditions for the conjugate point based on the geometric features. Applications of the external uncertainty model were demonstrated using various lidar point cloud data from the U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) library to determine the valid conditions for a conjugate point from three-plane modeling.


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