共查询到20条相似文献,搜索用时 250 毫秒
1.
A. V. Rodin N. A. Evdokimova R. O. Kuzmin A. A. Fedorova O. I. Korablev J. -P. Bibring 《Cosmic Research》2010,48(2):150-156
Channel C of the orbital hyperspectrometer OMEGA onboard Mars Express spacecraft has delivered data on the distribution and seasonal variability of water ice spectral features at 1.25, 1.5, 2.0
μm, based on which one may conclude about the thickness of ice coverage and microstructure of the upper, optically active
ice layer on the Martian surface. Data covering polar regions during spring-to-summer periods of both hemispheres have been
analyzed. Microstructure of the North polar cap, as well as the residual frost deposits of the seasonal South polar cap, have
revealed remarkable zonal variations with regularly located maxima. Based on the comparison with the atmospheric general circulation
model results, it has been proposed that these variations result from the impact of mesoscale inertial waves in the circumpolar
vortex on water exchange processes between the atmosphere and planetary surface. 相似文献
2.
The evolution of seismo-ionospheric disturbances accompanied strong destructive earthquakes in the region of Kuril and Japan
Islands on October 4, 1994, September 25, 2003, and November 15, 2006 is studied in the paper. For determination of the dynamics
of spatial-temporal and amplitude parameters of disturbances in the total electron content (TEC) on the basis of the Japan
network of receiving GPS stations GEONET and Korean network KGN, the method of drawing “distance-time” diagrams and quasi-optimal
algorithm of spatial-temporal processing of the GPS network data was used. The ionospheric response was detected at a distance
D from the epicenter up 2500 km. The maximal value of the disturbance amplitude is observed at D = 400–600 km. For the September 25, 2003 and November 15, 2006 earthquakes, the velocity V of propagation of the dominant disturbance mode is independent of the distance and equal to 850 and 1100 m/s, respectively.
At a distance D ∼ 600 km, the wave disturbance from the main shock of the October 4, 1994 earthquake is split into two modes: the velocity
of the “fast mode” of the disturbance increases with distance from 1500 to 2400 m/s, while the velocity of the “slow mode”
V = 600 m/s does not depend on D. Possible interpretation of the obtained results is given. 相似文献
3.
The influence of auroral electojets and solar wind parameters on variations in low-latitude geomagnetic disturbances and D
st
during strong magnetic storms on November 7–8, 2004 with D
st
≈ −380 nT and on November 9–10, 2004 with D
st
≈ −300 nT is studied on the basis of global geomagnetic observations. It is found that the impulsive variations of the western
electrojet intensity with a duration of Δt ≈ 1–2 h (probably, substorm disturbances) lead to positive low-latitude disturbances of ΔH at Φ′ ≈ 10°–30° and to disturbances of the same durations with an amplitude +ΔH ∼ 30–100 nT at latitudes of the polar cap (Φ′ ≈ 75°–80°). More durable (with Δt ≥ 10 h) convection electrojets whose centers are shifted to latitudes of ∼50°–55° in the process of storm development are
the main cause of the increase in negative values of ΔH at low latitudes and D
st
. It is shown that meridional dynamics of position of the center of electrojets and the equatorial boundary of the auroral
oval is governed by variations (increase or decrease) in the intensity of negative values of the IMF B
z
component. It is assumed that in these storms the intensification of the magnetospheric partially ring current closes the
circuit to the ionosphere with the help of field-aligned currents at the equatorial boundary of the auroral oval is the main
cause of the magnetic field depression at low latitudes. 相似文献
4.
We consider the issues of modeling the moments of aerodynamic forces acting upon a satellite with gravitational system of
stabilization. It is assumed that satellite orbits are almost circular with heights in the range 550–750 km. Simplified analytical
expressions are suggested for the aerodynamic moment in the case when a satellite moves in the regime of gravitational orientation.
Accuracy of the obtained expressions is estimated to be compared with that of expressions derived under the assumption of
constant coefficient of frontal resistance. An analysis is made of short-periodic variations of the atmosphere density occurring
due to orbital motion of a satellite. It is demonstrated that these variations can result in a substantial change of the aerodynamic
moment, and their approximation by a truncated Fourier series is suggested. Estimates of the accuracy of the suggested approximation
are given. 相似文献
5.
Low fluxes of protons with energies 0.3–10 MeV were studied during 21–23 solar cycles as a function of the MgII index using the data of the instruments CPME, EIS (IMP8), and EPHIN (SOHO). It has been shown that a) during quiet time of solar activity the fluxes of protons (background protons) have a positive
correlation with the MgII index value throughout the solar cycle, b) specific features of variations of the MgII index during the solar minima of 1986–1987 and 1996–1997 can be considered, as well as variations of background fluxes of
low energy charged particles, to be manifestations of the 22-year magnetic cycle of the Sun, and c) periods of the lowest
value of the MgII index are also characterized by the smaller values of the ratio of intensities of protons and helium nuclei than in other
quiet periods. A hypothesis is put forward that acceleration in a multitude of weak solar flares is one of the sources of
background fluxes of low energy particles in the interplanetary space. 相似文献
6.
7.
Altitude—temporal cross-sections q(z, t) of atmospheric ionization rates by solar protons above the polar regions were calculated using the GOES-10 satellite data on solar proton fluxes for the period of solar proton flare (SPF) on July 14, 2000. The values of q(z, t) were used further in calculations of variations of the atmospheric chemical composition during the flare in the northern
and southern polar regions (70°N and 70°S) by two different 1D photochemical models of the atmosphere (neutral and charged
components). The calculation results have shown considerable variation of the ozone content after SPF: a decrease of [O3]
was about 80% at altitudes of 65–75 km above northern and 25% in the layer of 55–65 km above the southern polar region. Such
decrease of the ozone content is a result of reactions with [NO] and [OH] whose concentrations have grown substantially during
SPF. According to calculations, the increase of electron concentration during SPF has reached 3–4 orders of magnitude at altitudes
of 50–80 km. A comparison of the calculation results with the observational data on [NO], [NO2], and [O3] from the UARS and HALOE satellites for 70°N have shown a good qualitative correspondence, however, for variations of nitric oxides there are quantitative
discrepancies. 相似文献
8.
9.
On the basis of numerical experiments, we have shown the principal possibility of long (more than 1 month) and extremely long
(more than 1 year) orbit lifetime of technogenic microparticles with radii from 1 to 100 μm injected into the near-Earth space
in highly elliptical orbits with low perigee, including the case of an orbit with parameters corresponding to the orbital
parameters of the Molniya satellite. Calculations are performed taking into account the perturbing effect on the orbital microparticle motion in the
near-Earth space of gravitational perturbation caused by the Earth’s polar oblateness, the solar pressure force (calculated
using methods of the Mie theory), and the drag force of neutral component of the background gas under conditions of low, medium,
and high levels of solar and geomagnetic activities. 相似文献
10.
As a result of processing long (up to 144 h) series of sunspot magnetograms obtained on the SOHO (Solar and Heliospheric Observatory) spacecraft with the MDI (Michelson Doppler Imager) instrument it is shown that the mode
with a period of 800–1300 min is a limiting low-frequency oscillation mode of the magnetic field of a sunspot as a whole.
Its period is essentially and nonlinearly depends on the sunspot magnetic field strength. In addition to this mode, higher
harmonics are also revealed in the sunspot oscillation spectra in the bands 40–45, 60–80, 135–170, 220–250, and 480–520 min.
The oscillation power in these bands monotonically and rapidly decreases with increasing frequency, which is characteristic
for overtones arising due to the nonlinear nature of oscillations. The limiting oscillation mode stably exists in sunspots
for 1.5–2 days, which coincides with the average lifetime of a supergranular cell. The mode with the period of 35–48 h observed
in the power spectrum is not an eigen mode of sunspots, because its period is independent of its magnetic field strength.
Probably, it occurs as a quasiperiod of an external exciting force caused by disturbances from supergranular cells surrounding
the sunspot. 相似文献
11.
Based on the results of plasma and magnetic measurements at three different points of the heliosphere and telescopic observations
of the Sun from these points we study simultaneously high-speed streams (HSS) of the solar wind (SW) near the Earths’s orbit
and coronal holes (CH) that have generated them. The data from spacecraft STEREO-A, STEREO-B, ACE, and SOHO are used together with ground-based observations from March 2007 to May 2008. In this period there existed HSS whose sources
represented CH of various polarity, geometry, and location relative to the heliographic and heliomagnetic equators. Dependence
of SW parameters on mutual positions of spacecraft with respect to CH and heliospheric current sheet, and also on heliolatitude
and geometry of the CH is revealed. A difference of more than 5° in locations of spacecraft with respect to the heliospheric
current sheet in November 2007 allowed us to discover a heliolatitude velocity gradient of the SW streams between the STEREO-A and STEREO-B spacecraft. On the average this gradient at that time was equal to 20 km/s per degree. Substantial variations in SW streams
associated with variations of the HSS SW sources during a few hours or days were also observed. This variability makes it
difficult to use the data of spacecraft STEREO-B for sufficiently accurate prediction of SW properties in the near-Earth space by the method of simple advanced ti me shift
due to heliolongitude difference between a spacecraft and the Earth even in solar activity minimum. 相似文献
12.
A. S. Kovtyukh 《Cosmic Research》2012,50(3):226-232
Satellite data on the position of maximum L m of the belt of relativistic electrons during strong storms, obtained at low altitudes (∼500 km) and at high altitudes (near the geomagnetic equator plane), are compared (L is the McIlwain parameter). Both at low and high altitudes the maximum of the storm belt of relativistic electrons is formed on the outer edge of the ring current. It is shown that the geomagnetic field can substantially deviate from dipole configuration not only at the geomagnetic trap periphery, but at its core as well (at L ∼ 2.5–3.5), and these deviations are nonlinear. Simultaneous measurements of the fluxes of relativistic electrons at low and high altitudes can serve for estimation of the real shape of magnetic field lines at L < 4 during geomagnetic disturbances. 相似文献
13.
On the basis of the long series of mass-spectrometer measurements conducted in rocket experiments during 1966–1992 period,
long-term changes in the structural parameters of the upper atmosphere within the 100–160 km height interval at equatorial,
middle, and high latitudes of the Northern Hemisphere of the Earth are quantitatively estimated. At all latitudes statistically
significant negative trends are revealed in the turbopause height, temperature of the neutral atmosphere, and atomic oxygen
concentration. Since the contribution to the obtained quantitative estimates of the trends caused by long-term solar-induced
factors does not exceed 15–20%, a conclusion is drawn on the anthropogenic nature of the changes having occurred in the upper
atmosphere. 相似文献
14.
Attitude control of spin-stabilized satellites by means of aerodynamic forces is investigated. A controller employing two rotatable control surfaces is proposed to control the roll-yaw motions of the spacecraft spin-axis. Optimal control theory is applied to synthesize a feedback control law for the control surface rotations which leads to asymptotically stable controller operation. The system response is interpreted in terms of performance criteria such as the maximum control surface excursions, the speed of response and the associated orbital energy loss due to drag. Even with a moderate size, the controller appears quite effective in maintaining the spacecraft attitude against external disturbances. 相似文献
15.
G. K. Garipov P. A. Klimov V. S. Morozenko M. I. Panasyuk B. A. Khrenov 《Cosmic Research》2011,49(5):391-398
Using a detector of near ultra-violet (UV) emission (wavelength range 300–400 nm) [1] onboard the Universitetsky-Tatiana satellite with an orbit height of 950 km and inclination of 81° we have detected and studied short UV flashes [2–5]. In this
paper the observed UV flashes are classified according to the type of their time profiles, and the times of emission intensity
rise and decay are investigated in every flash. Using the data on time profiles it turned out to be possible to estimate the
flash energy in the atmosphere even in case of saturation of a signal measuring channel at the maximum of emission. The energy
spectrum of observed flashes is estimated. Time and energy characteristics of the flashes are important for choosing a model
of development of electric discharges in the upper atmosphere that are responsible for observed emission. 相似文献
16.
The spatial dimensions and temporal dynamics of large scale disturbances of electron density in the ionospheric F-region during the preparatory phase of destructive earthquakes are estimated. The most appropriate data (as far as the moments of satellite passages are concerned) were selected out of more than 300 investigated cases. In order to demonstrate effects at different latitudes, the cases of high-latitude (Alaska), mid-latitude (Central Italy), and low-latitude (New Zealand) earthquakes were considered. Using the data of external vertical sounding of the ionosphere performed by the Alouette-1 and Interkosmos-19 satellites together with the data of vertical sounding of the ionosphere by ground-based instruments, we get for the first time with reasonable accuracy the spatial characteristics of precursors in the ionosphere. It is shown that seismic ionospheric disturbances are strongly time-dependent before the beginning of the main shock. Seismic ionospheric disturbances are generated weakly several days before the first shock, but at that moment the disturbed region is located not above the epicenter, but rather a little displaced from it. As the moment of the earthquake approaches, the disturbance covers more and more space; moreover, its value also increases. Several hours after the shock the disturbance migrates in the reverse order. Under some conditions, the disturbances may appear not only above epicenter regions. They can be transferred along the magnetic field lines into conjugate regions in the opposite hemisphere. 相似文献
17.
We investigate the behavior of mean values of the solar wind’s and interplanetary magnetic field’s (IMF) parameters and their
absolute and relative variations during the magnetic storms generated by various types of the solar wind. In this paper, which
is a continuation of paper [1], we, on the basis of the OMNI data archive for the period of 1976–2000, have analyzed 798 geomagnetic
storms with D
st
≤ −50 nT and their interplanetary sources: corotating interaction regions CIR, compression regions Sheath before the interplanetary
CMEs; magnetic clouds MC; “Pistons” Ejecta, and an uncertain type of a source. For the analysis the double superposed epoch
analysis method was used, in which the instants of the magnetic storm onset and the minimum of the D
st
index were taken as reference times. It is shown that the set of interplanetary sources of magnetic storms can be sub-divided
into two basic groups according to their slowly and fast varying characteristics: (1) ICME (MC and Ejecta) and (2) CIR and
Sheath. The mean values, the absolute and relative variations in MC and Ejecta for all parameters appeared to be either mean
or lower than the mean value (the mean values of the electric field E
y
and of the B
z
component of IMF are higher in absolute value), while in CIR and Sheath they are higher than the mean value. High values
of the relative density variation sN/〈N〉 are observed in MC. At the same time, the high values for relative variations of the velocity, B
z
component, and IMF magnitude are observed in Sheath and CIR. No noticeable distinctions in the relationships between considered
parameters for moderate and strong magnetic storms were observed. 相似文献
18.
Analysis and implementation of in-plane stationkeeping of continuously perturbed Walker constellations 总被引:1,自引:0,他引:1
Jean A. Kchichian 《Acta Astronautica》2009,65(11-12):1650-1667
The stationkeeping of symmetric Walker constellations is analyzed by considering the perturbations arising from a high order and degree Earth gravity field and the solar radiation pressure. These perturbations act differently on each group of spacecraft flying in a given orbital plane, causing a differential drift effect that would disrupt the initial symmetry of the constellation. The analysis is based on the consideration of a fictitious set of rotating reference frames that move with the spacecraft in the mean sense, but drift at a rate equal to the average drift rate experienced by all the vehicles over an extended period. The frames are also allowed to experience the J2-precession such that each vehicle is allowed to drift in 3D relative to its frame. A two-impulse rendezvous maneuver is then constructed to bring each vehicle to the center of its frame as soon as a given tolerance deadband is about to be violated. This paper illustrates the computations associated with the stationkeeping of a generic Walker constellation by maneuvering each leading spacecraft within an orbit plane and calculating the associated velocity changes required for controlling the in-plane motions in an exacting sense, at least for the first series of maneuvers. The analysis can be easily extended to lower flying constellations, which experience additional perturbations due to drag. 相似文献
19.
We investigate the relative occurrence rate for various types of the solar wind and their geoeffectiveness for magnetic storms
with Dst < —50 nT. Both integrated effect for the entire time 1976–2000 and variations during this period of 2.5 cycles of solar activity
are studied As raw data for the analysis we have used the catalog of large-scale types of the solar wind for the period 1976-2000
(see ftp://ftp.iki.rssi.ru/omni/) created by us with the use of the OMNI database (http://omni.web.gsgc.nasa.gov) [1] and
described in detail in [2]. The average annual numbers of different type of events are as follows: 124 ±81 for the heliospheric
current sheet (HCS), 8 ±6 for magnetic clouds (MC), 99 ±38 for Ejecta, 46 ±19 for Sheath before Ejecta, 6 ±5 for Sheath before
MC, and 63 ±15 for CIR. The measurements that allowed one to determine a source in the solar wind were available only for
58% of moderate and strong magnetic storms (with index Dst < —50 nT) during the period 1976–2000. Magnetic clouds (MC) are shown to be the most geoeffective (~61%). The CIR events and
Ejecta with Sheath region are three times less geoeffective (~20–21 %). Variations of occurrence rate and geoeffectiveness
of various types of the solar wind in the solar cycle are discussed. 相似文献