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121.
The organization principles of constructing the European system of warning about dangerous situations in the outer space are
considered in the paper. 相似文献
122.
First results of operational ionospheric dynamics prediction for the Brazilian Space Weather program
Adriano Petry Jonas Rodrigues de Souza Haroldo Fraga de Campos Velho André Grahl Pereira Graham John Bailey 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
It is shown the development and preliminary results of operational ionosphere dynamics prediction system for the Brazilian Space Weather program. The system is based on the Sheffield University Plasmasphere–Ionosphere Model (SUPIM), a physics-based model computer code describing the distribution of ionization within the Earth mid to equatorial latitude ionosphere and plasmasphere, during geomagnetically quiet periods. The model outputs are given in a 2-dimensional plane aligned with Earth magnetic field lines, with fixed magnetic longitude coordinate. The code was adapted to provide the output in geographical coordinates. It was made referring to the Earth’s magnetic field as an eccentric dipole, using the approximation based on International Geomagnetic Reference Field (IGRF-11). During the system operation, several simulation runs are performed at different longitudes. The original code would not be able to run all simulations serially in reasonable time. So, a parallel version for the code was developed for enhancing the performance. After preliminary tests, it was frequently observed code instability, when negative ion temperatures or concentrations prevented the code from continuing its processing. After a detailed analysis, it was verified that most of these problems occurred due to concentration estimation of simulation points located at high altitudes, typically over 4000 km of altitude. In order to force convergence, an artificial exponential decay for ion–neutral collisional frequency was used above mentioned altitudes. This approach shown no significant difference from original code output, but improved substantially the code stability. In order to make operational system even more stable, the initial altitude and initial ion concentration values used on exponential decay equation are changed when convergence is not achieved, within pre-defined values. When all code runs end, the longitude of every point is then compared with its original reference station longitude, and differences are compensated by changing the simulation point time slot, in a temporal adjustment optimization. Then, an approximate neighbor searching technique was developed to obtain the ion concentration values in a regularly spaced grid, using inverse distance weighting (IDW) interpolation. A 3D grid containing ion and electron concentrations is generated for every hour of simulated day. Its spatial resolution is 1° of latitude per 1° of longitude per 10 km of altitude. The vertical total electron content (VTEC) is calculated from the grid, and plotted in a geographic map. An important feature that was implemented in the system is the capacity of combining observational data and simulation outputs to obtain more appropriate initial conditions to the ionosphere prediction. Newtonian relaxation method was used for this data assimilation process, where ionosonde data from four different locations in South America was used to improve the system accuracy. The whole process runs every day and predicts the VTEC values for South America region with almost 24 h ahead. 相似文献
123.
Tshimangadzo Merline Matamba John Bosco Habarulema 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):777-787
The ionospheric responses to High-Intensity Long Duration Continuous Auroral Electrojet Activity (HILDCAA) event which happened following the CIR-driven storm were studied over the southern hemisphere mid-latitude in the African sector. The 13–15 April 2005 event was analysed to understand some of the mechanisms responsible for the ionospheric changes during HILDCAA event. The ionosonde critical frequency of F2 layer (foF2) and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) were used to analyse the ionospheric responses. The daytime increase in foF2 and TEC values were observed on 13 April 2005. The TEC and foF2 enhancement could be attributed to Large Scale Traveling Ionospheric Disturbances (LSTIDs), increase in thermospheric neutral composition changes, Prompt Penetration Electric Field (PPEF) and an expansion of Equatorial Ionization Anomaly (EIA) to the mid-latitude. 相似文献
124.
125.
Chubb Elliott Grindon John R. Venters David C. 《IEEE transactions on aerospace and electronic systems》1967,(2):250-256
A system for providing near-instantaneous determination of the azimuthal angle of arrival of a received signal has been designed and fabricated at L band. Direction is determined by phase measurement of the outputs of a multimode antenna, which has no moving parts. Effects of multipath interference are reduced to a minimum through a combination of signal processing techniques. The position of the transmitting source is presented on a PPI display. 相似文献
126.
Bieber John W. Eroshenko Eugenia Evenson Paul Flückiger Erwin O. Kallenbach Reinald 《Space Science Reviews》2000,93(1-2):1-9
Cosmic rays provide a diagnostic tool to analyze processes in interplanetary space and at the Sun. Cosmic rays also directly
affect the terrestrial environment and serve as indicators of solar variability and non anthropogenic climatic changes on
Earth at present and in the distant past.
After the invention of the neutron monitor by John A. Simpson in 1948, an international network of cosmic ray detectors developed
in a cooperative effort to examine temporal and spatial variations in our space environment. The resulting datasets represent
the longest continuous, high time resolution series of particle radiation measurement in space science. At present, the neutron
monitor network is complemented by spacecraft instrumentation to study solar-terrestrial correlated phenomena.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
127.
The invention of the neutron monitor pile for the study of cosmic-ray intensity-time and energy changes began with the discovery
in 1948 that the nucleonic component cascade in the atmosphere had a huge geomagnetic latitude dependence. For example, between
0° and 60° this dependence was a ∼ 200–400% effect – depending on altitude – thus opening the opportunity to measure the intensity
changes in the arriving cosmic-ray nuclei down to ∼1–2 GeV nucl−1 for the first time. In these measurements the fast (high energy) neutron intensity was shown to be a surrogate for the nuclear
cascade intensity in the atmosphere.
The development of the neutron monitor in 1948–1951 and the first geomagnetic latitude network will be discussed. Among its
early applications were:
(1) to prove that there exists interplanetary solar modulation of galactic cosmic-rays (1952), and;
(2) to provide the evidence for a dynamical heliosphere (1956).
With the world-wide distribution of neutron monitor stations that are presently operating (∼ 50) many novel investigations
are still to be carried out, especially in collaborations with spacecraft experiments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
128.
John A. Wood 《Space Science Reviews》2000,92(1-2):97-112
Radiometric dating shows that the earliest steps in forming the substance of meteorites and assembling it into planetesimals
occurred in a very short interval of time, 1–2 Ma. This study shows that rapid formation is also dictated by the need to use
short-lived 26Al (half-life T
1/2=0.74 Ma) as a heat source to metamorphose and in some cases melt the meteorite parent bodies after they accreted. The earliest
events in solar system history dated by cosmochemists, formation at high temperatures of the Ca,Al-rich inclusions that occur
in chondritic meteorites, probably occurred during the most energetic stage of protosolar disk evolution, as the protosun
neared its present mass and infall drew to a close.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
129.
130.
Margarita Karovska Brian E. Wood John W. Cook Russell A. Howard Guenter E. Brueckner 《Space Science Reviews》1999,87(1-2):219-222
We present the results from a study of the dynamical properties of polar jets in the Sun's polar regions using LASCO C2 coronagraph
and EIT observations. In the simplest impulsive acceleration scenarios for jets, gravity is expected to be the dominant force
on the jet following the initial acceleration, especially in the Sun's polar regions where the open magnetic fields should
not significantly impede the jet's motion. Our analysis shows that although at low heights the kinematics of the jets could
be consistent with a gravitational deceleration of the ejected plasma, at higher heights their motions may simply follow the
ambient solar wind outflow. If so, the polar jets can be used as tracers of the solar wind in coronal holes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献