Reduction to the pole at low magnetic latitude using a stabilized filter

1992 ◽  
Author(s):  
Carlos A. Mendonça ◽  
J. B. C. Silva
Keyword(s):  
Magnetic Latitude ◽  
Reduction To The Pole

scholarly journals Estimation of the total magnetization direction of approximately spherical bodies

2014 ◽  
Vol 1 (2) ◽  
pp. 1465-1507
Author(s):  
V. C. Oliveira ◽  
D. P. Sales ◽  
V. C. F. Barbosa ◽  
L. Uieda
Keyword(s):  
Synthetic Data ◽  
Magnetization Vector ◽  
Spherical Shape ◽  
Time Interval ◽  
Alkaline Complex ◽  
Multiple Sources ◽  
Geological Time ◽  
Magnetization Direction ◽  
Reduction To The Pole ◽  
Horizontal Grid

Abstract. We have developed a fast total-field anomaly inversion to estimate the magnetization direction of multiple sources with approximately spherical shape and known centres. Our method can be applied to interpret multiple sources with different magnetization directions. It neither requires the prior computation of any transformation like reduction to the pole nor the use of regularly spaced data on a horizontal grid. The method contains flexibility to be implemented as a linear or non-linear inverse problem, which results, respectively, in a least-squares or robust estimate of the components of the magnetization vector of the sources. Applications to synthetic data show the robustness of our method against interfering anomalies and errors in the location of the sources' centre. Besides, we show the feasibility of applying the upward continuation to interpret non-spherical sources. Applications to field data over the Goiás Alkaline Province (GAP), Brazil, show the good performance of our method in estimating geological meaningful magnetization directions. The results obtained for a region of the GAP, near from the alkaline complex of Diorama, suggest the presence of non-outcropping sources marked by strong remanent magnetization with inclination and declination close to -70.35° and -19.81°, respectively. This estimated magnetization direction leads to predominantly positive reduced-to-the-pole anomalies, even for other region of the GAP, in the alkaline complex of Montes Claros de Goiás. These results show that the non-outcropping sources near from the alkaline complex of Diorama have almost the same magnetization direction of that ones in the alkaline complex of Montes Claros de Goiás, strongly suggesting that these sources have emplaced the crust almost within the same geological time interval.

scholarly journals Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

2014 ◽  
Vol 32 (2) ◽  
pp. 69-75 ◽  
Author(s):  
W. R. Coley ◽  
R. A. Stoneback ◽  
R. A. Heelis ◽  
M. R. Hairston
Keyword(s):  
Solar Activity ◽  
Local Time ◽  
Geomagnetic Field ◽  
General Pattern ◽  
Magnetic Latitude ◽  
Ion Drifts ◽  
F Region ◽  
Westerly Flow ◽  
Solar Local Time ◽  
Ion Velocity

Abstract. The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400–850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009–2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130–150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

scholarly journals A statistical study of the motion of pulsating aurora patches: using the THEMIS All-Sky Imager

2017 ◽  
Vol 35 (2) ◽  
pp. 217-225 ◽  
Author(s):  
Bing Yang ◽  
Eric Donovan ◽  
Jun Liang ◽  
Emma Spanswick
Keyword(s):  
Statistical Study ◽  
Accurate Method ◽  
Auroral Electrojet ◽  
Large Database ◽  
Ionospheric Convection ◽  
Magnetic Latitude ◽  
Magnetospheric Convection ◽  
Ae Index ◽  
Sky Imager ◽  
Remotely Sense

Abstract. Previous studies of the motion of patches that comprise patchy pulsating aurora (PPA) have been based on a limited number of events. In this study, we use a large database of PPA patches obtained from the THEMIS all-sky imager at Gillam (66.18° magnetic latitude, 332.78° magnetic longitude) between May 2006 and July 2013 to explore the velocity of the PPA patches. Our results show that PPA patches mainly drift eastward after midnight and westward before midnight. In addition, we found that patch velocities are in the expected range of convection given the magnetic latitude and that the velocities do not seem to depend on auroral electrojet (AE) index. The results suggest that the drifts of auroral patches could be a proxy for the ionospheric convection, and possibly provide a convenient and accurate method to remotely sense the magnetospheric convection.

Location in magnetic latitude and local time of the tropical ultraviolet bands seen from Apollo 16

1973 ◽  
Vol 35 (10) ◽  
pp. 1905-IN3 ◽  
Author(s):  
B.A Tinsley ◽  
A.B Christensen ◽  
Jane M Broadt ◽  
C.L Hammond
Keyword(s):  
Local Time ◽  
Magnetic Latitude

Differential reduction of magnetic anomalies to the pole on a massively parallel computer

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1945-1951 ◽  
Author(s):  
Richard S. Lu ◽  
John Mariano ◽  
Dennis E. Willen
Keyword(s):  
Filter Design ◽  
Finite Impulse Response ◽  
Mineral Exploration ◽  
Magnetic Anomalies ◽  
Parallel Computer ◽  
Massively Parallel ◽  
Central Location ◽  
Differential Reduction ◽  
Reduction To The Pole ◽  
The Difference

A finite‐impulse‐response filter was implemented on a computer with massively parallel processors to reduce a magnetic anomaly map to the magnetic pole, allowing each grid node to have a different inclination and declination (differential reduction to the pole, DRTP). The dramatic speed improvement of such an implementation for the filter design and application via space‐domain convolution makes DRTP a practical tool for hydrocarbon and mineral exploration. Application of this tool to magnetic anomalies in east China reveals that the northward shift in position of the anomaly maximum generated by DRTP is 6 km for anomalies with dominant wavelengths of approximately 25 km in the northernmost part of the study area. The shift increases as the anomaly wavelength increases. Shifts for all anomaly wavelengths are even larger in the southern part of the study area, where the magnetic inclination is lower. The shift in position of the anomaly maximum for anomalies of wavelengths 25 km in the northernmost area produced by DRTP is 2 km less than that produced by a conventional reduction to the pole using the inclination and declination at the central location of the study area. Once again, such differences in shifts are larger for anomalies of longer wavelengths. The farther away from the central location, the greater is the absolute value of the difference.

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