Brazilian Geomagnetic Anomaly Research Articles

Correlation properties of a forecast of secular variation in the main geomagnetic field

The statistical and correlation characteristics for a forecast of secular variation (SV) in the Earth’s main magnetic field were derived for the territory of Russia and the adjacent water areas in comparison with other regions of the terrestrial globe. The spatial structure of the SV forecast was found to correlate best with the SV of the preceding epoch. SV is forecasted with the largest error for the Russian territory and the adjoining equatorial area. The existence of small-size SV anomalies that vary over time in the spatial structure is characteristic for both regions. The presence of a large anomaly, such as the Brazilian Geomagnetic Anomaly, influences the error level in forecasting the mean and relative standard deviation. The absolute values of the forecast error in this case are comparable in magnitude with the values obtained for the other regions. The spatial structure of the SV forecast error points to the integral nature of SV anomalies and the independent change in the parameters of different-scale flows in the liquid core that determine them. When the methods of coefficient extrapolation are used for the SV forecast, its accuracy can be improved only by updating forecast coefficients with an interval of no more than two years on the basis of data from magnetic observatories and repeat stations.

Energetic particle precipitation in the Brazilian geomagnetic anomaly during the “Bastille Day storm” of July 2000

Abstract Ionospheric absorption associated with a great geomagnetic storm on July 15–16, 2000 (the “Bastille Day storm”) was observed in the Brazilian geomagnetic anomaly using a two-dimensional 4 × 4 imaging riometer (IRIS). In the afternoon of July 15, weak absorption (≈0.2 dB) was observed during the initial phase of the storm; large spatial-scale absorption exceeded the IRIS field of view (330×330 km). During the sharp magnetic decrease in the main phase of the storm, absorption was intensified (<0.5 dB) in the evening, showing a sheet structure with ≈150 km latitudinal width and >330 km longitudinal elongation. Subsequently, absorption was intensified (≈1 dB), having a small spatial-scale (≈150 km) in the background sheet structure and a pronounced westward drift (≈570 m s-1). In association with large magnetic fluctuations in the Bz component of the interplanetary magnetic field (IMF), the ground magnetic variation in the night sector showed large positive swings during the initial to main phases of the storm. With the subsequent southward turning of the IMF Bz, the ground magnetic variation in the evening sector showed rapid storm development. Particle fluxes measured by a geosynchronous satellite (L =≈6.6) demonstrated large enhancements of low-energy protons (50–400 keV) and probably electrons (50–225 keV) during the storm’s initial phase. Particle fluxes from the low-altitude NOAA satellite (≈870 km) indicated the invasion of low-energy particles into the region of L < 2 during the main phase of the storm. These results indicate that low-energy particles injected into the outer radiation belt in association with frequent and strong substorm occurrences, were transported into the inner radiation belt through direct convective access by the storm-induced electric fields during the storm’s development. These particles then precipitated into the ionosphere over the Brazilian geomagnetic anomaly. Notably, the most intense absorption could be dominantly caused by proton precipitation with energies of ≈40 keV. Key words: Bastille Day storm, Brazilian geomagnetic anomaly, energetic particle precipitation, imaging riometer.

Change of earth environment due to the decreasing geomagnetic field -The necessity of observation in Brazilian geomagnetic anomaly region-

Change of earth environment due to the decreasing geomagnetic field -The necessity of observation in Brazilian geomagnetic anomaly region-

Comment on “Modeling the ion chemistry of the D region: A case study based upon the 1966 total solar eclipse” by Sears et al.

Journal of Geophysical Research: Space PhysicsVolume 89, Issue A4 p. 2406-2408 CommentariesFree Access Comment on “Modeling the ion chemistry of the D region: A case study based upon the 1966 total solar eclipse” by Sears et al. M. A. Abdu, M. A. AbduSearch for more papers by this authorJ. H. A. Sobral, J. H. A. SobralSearch for more papers by this authorI. S. Batista, I. S. BatistaSearch for more papers by this author M. A. Abdu, M. A. AbduSearch for more papers by this authorJ. H. A. Sobral, J. H. A. SobralSearch for more papers by this authorI. S. Batista, I. S. BatistaSearch for more papers by this author First published: 1 April 1984 https://doi.org/10.1029/JA089iA04p02406AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Abdu, M. A., I. S. Batista, J. H. A. Sobral, Particle ionization rates from total solar eclipse rocket ion composition results in the south Atlantic geomagnetic anomaly, J. Geophys. Res., 84, 4328– 4334, 1979. Abdu, M. A., I. S. Batista, L. R. Piazza, O. Massambani, Magnetic storm associated particle precipitation in the south Atlantic anomaly: Evidence from VLF phase measurements, J. Geophys. Res., 86, 7533– 7542, 1981. Batista, I. S., M. A. Abdu, Magnetic storm associated delayed sporadic E enhancements in the Brazilian geomagnetic anomaly, J. Geophys. Res., 82, 4777– 4783, 1977. Gledhill, J. A., R. A. Hoffman, Nighttime observations of 0.2–25 keV electrons in the south Atlantic anomaly made by Atmospheric Explorer-C, J. Geophys. Res., 86, 6739– 6744, 1981. Lyons, L. R., A. D. Richmond, Low-latitude E region ionization by energetic ring current particles, J. Geophys. Res., 83, 2201, 1978. Mechtly, E. A., K. Seino, L. G. Smith, Lower ionosphere electron densities measured during the solar eclipse of November 12, 1966, Radio Sci., 4, 371– 375, 1969. Mizera, P. F., J. B. Blake, Observations of ring current protons at low latitude, J. Geophys. Res., 78, 1058, 1973. Narcisi, R. S., A. D. Bailey, L. E. Wlodyka, C. R. Philbrick, Ion composition measurements in the lower ionosphere during the November 1966 and March 1970 solar eclipse, J. Atmos. Terr. Phys., 34, 647– 658, 1972. Ogawa, T., T. Tohmatsu, Photoelectronic processes in the upper atmosphere, II, The hydrogen and helium ultraviolet glow as an origin of the nighttime ionosphere, Rep. Ionos. Space Res. Jpn., 20, 395– 417, 1966. Pfitzer, K. A., J. R. Winkler, Experimental observation of a large addition to the electron inner radiation belt after solar flare event, J. Geophys. Res., 73, 5899– 5797, 1968. Rees, M. H., Auroral ionization and excitation by incident energetic electrons, Planet. Space Sci., 11, 1209– 1218, 1963. Sears, R. D., M. G. Heaps, F. E. Niles, Modeling the ion chemistry of the D region: A case study based upon the 1966 total eclipse, J. Geophys. Res., 86, 10,073– 10,086, 1981. Tinsley, B. A., Evidence that the recovery phase ring current consists of helium ions, J. Geophys. Res., 81, 6193, 1976. Ulwick, J. C., Eclipse rocket measurements of charged particle concentration, J. Atmos. Terr. Phys., 34, 659– 665, 1972. Volume89, IssueA41 April 1984Pages 2406-2408 ReferencesRelatedInformation

Magnetic storm associated delayed sporadic E enhancements in the Brazilian Geomagnetic Anomaly

Sporadic E layer behavior over Cachoeira Paulista (11°57′S, 22°32′E geomagnetic coordinates), located near the center of the Brazilian Geomagnetic Anomaly, is investigated during magnetically disturbed periods. Significant enhancements in the Es layer parameters, ftEs and fbEs take place for short periods (2–3 hours) following a magnetic disturbance of moderate intensity. The enhancements, however, are delayed by 1–3 days with respect to the initiation of a disturbance. The electron density enhancement in the Es layer inferred from fbEs during such events are at times an order of magnitude larger than undisturbed values. Also, during some night events the ambient E region electron densities appear comparable to the regular daytime maximum values. The Es traces in the ionograms during these events exhibit range spread in the echoes resembling the a-type Es, know to occur over auroral latitudes under disturbed conditions. These results are interpreted as evidence of enhanced charged particle precipitation in the E region over the geomagnetic anomaly following magnetic disturbances. The results also provide evidence that the E region response over our station is delayed with respect to magnetic activity.

Sporadic E-layer phenomena in the Brazilian geomagnetic anomaly: evidence for a regular particle ionization source

A study of Sporadic E-layer phenomena over Cachoeira Paulista (22.6°S, 45°W), located in the vicinity of the Brazilian geomagnetic anomaly centre is presented. Monthly average diurnal behaviour of the Es occurrence presented for summer, winter and equinoctial months shows that the simidiurnal tidal component dominates in some months while others show a single diurnal maximum. The night-to-day ratio in the occurrence rate of Es appears to be greatly enhanced over our station in relation to middle latitude stations. This and the frequent night occurrence of high blanketing frequencies ( fbEs) are interpreted as evidence of a regular night-time ionization source in the geomagnetic anomaly. From considerations based upon the theory of redistribution of ionization by neutral winds a lower limit in the ambient ionization needed to produce the observed fbEs is determined and a corresponding precipitating electron flux is estimated.

Enhanced low-energy gamma rays at balloon altitude in the Brazilian magnetic anomaly

THE region of the Brazilian geomagnetic anomaly presents an interesting opportunity for the study of precipitation of charged particles of the inner radiation belt into the atmosphere below. Some recent studies based on direct and indirect observations (refs 1–3 and our unpublished work) show that the precipitating flux increases appreciably during the period of a geomagnetic storm. The present note provides another evidence in this direction.

Particle precipitation in Brazilian geomagnetic anomaly during magnetic storms

Particle precipitation in Brazilian geomagnetic anomaly during magnetic storms is investigated using riometer and VLF propagation data. It is found that during large storms the changes in the ionosphere caused by particle precipitation are detectable. There is a good correlation between the behavior of the absorption and the variations of the magnetic field intensity during different phases of a storm. In particular, there seems to be a close relationship between the precipitation of high energy particles and short-period fluctuations of the magnetic field intensity of the order of 5–6 min. During the main phase of the storm, when the field intensity reaches its minimum, the flux of soft electrons also plays a significant role in producing absorption. The nature of precipitation associated with a sudden commencement appears to be more complex; the predominance of low or high energy particle flux may depend on the magnitude of the field increase. The amplitude and phase records of VLF signals also show the effect of the disturbance, but it is difficult to correlate the changes in these records with the features observed on the magnetogram, because only a small part of the propagation path lies in the region of the anomaly. A more detailed analysis of riometer data from different stations and VLF phase and amplitude records for different paths will be helpful in understanding the mechanism of particle precipitation associated with magnetic disturbances. In future experiments it may also be fruitful to look for detectable radiation emitted by the precipitating electrons, for example, Cherenkov and synchrotron radiation.

Geographical and solar activity variations in the electron temperature of the upper F -region

Electron temperature observations obtained in April-July 1962 on the Ariel I satellite have been further analysed by a statistical method. The general increase of electron temperature with latitude (amounting to about 500 degK) and with altitude between 400 and 1200 km, ( ca . 600 degK) previously reported, are confirmed. In addition, the dawn maximum of electron temperature found by other workers, which at the period of these observations is only a minor effect at 40° geomagnetic latitude, is found to become more pronounced near the magnetic equator. The geographical variations of electron temperature are shown to divide into distinct patterns characteristic of noon, dawn and midnight. The dawn pattern consists essentially of a longitude variation in the amplitude of the dawn maximum. All three patterns are closely associated with the geographical variations of electron density, and by examining the detailed correlation of temperature and density it is shown that the temperature variations result from changes in the collisional cooling rate of the electrons. This provides confirmation of the explanation of the dawn maximum suggested by Dalgarno, McElroy & Moffat (1963). Temperature variations due to changes in the far u.v. emission of the sun are considered. By day it is found that the electron temperature increases with 2800 Mc/s solar emission at a rate of (4.6 ± 2.3) degK per flux unit of 10 -22 Wcm -2 s -1 (c/s) -1 , while at night it decreases at a rate of 2.3 ± 2.7 degK/flux unit. Temperature variations in magnetic storms are compared with density enhancements described by Willmore & Henderson (1965). Electron density increases in the storm are always accompanied by a temperature reduction of about 180 degK, the storm-time changes showing a distinct magnetic shell structure. An instance of a temperature increase near the Brazilian geomagnetic anomaly is also given. Finally it is shown that these results lend support to the suggestion of a departure from thermal equilibrium in the night-time ionosphere.