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1.
Robert M. Haberle 《Icarus》1979,39(2):184-191
The large horizontal heating gradients that exist near the edge of the Martian polar caps during spring are shown to be capable of exciting large oscillations in the diurnal tide. To a lesser extent, the daily mass cycling between cap and atmosphere can also contribute. The calculations which demonstrate this are based on classical tidal theory as applied to the cylindrical coordinate system. This is done to facilitate the representation of the heating function. Results are presented for the horizontal surface winds only. They indicate a circulation at the cap edge somewhat analogous to the smaller scale terrestrial sea breeze. The amplitude of the zonal component is largest and is increased from 1 to 10 m sec?1 by the modeled influence of the polar cap. When coupled with the basic flow these cap-edge tides can produce strong surface winds during spring. Such a mechanism may contribute to the ability of the south polar cap winds to generate the local dust storms observed near the cap edge at this season.  相似文献   

2.
An investigation of the Martian polar cap winds and their response to a variety of factors is carried out by a series of numerical experiments based on a zonally symmetric primitive equation model. These factors are the seasonal thermal forcing, mass exchange between polar caps and atmosphere, large-scale topography, and polar cap size. The thermal forcing sets up a circulation whose surface winds adjust to achieve angular momentum balance, with low-latitude easterlies and high-latitude westerlies. The maximum westerlies occur roughly where the horizontal temperature gradients are largest. This pattern changes when cap and atmosphere exchange mass. Corriolis forces acting on the net outflow or inflow produce easterlies at the surface during spring (outflow) and westerlies during winter (inflow). Topography appears to have a small effect, but cap size does play a role, the circulation intensity increasing with cap size. Peak surface winds occur when outflow or inflow is a maximum and are 20 m sec?1 during spring and 30 m sec?1 during winter for the northern hemisphere. The model results show that surface winds near the edge of a retreating polar cap are substantially enhanced, a result which is consistent with the Viking observations of local dust storm activity near the edge of the south polar cap during spring. The results also indicate that the surficial wind indicators near the south pole are formed during spring and those near the north pole during winter. The implication is that the high-latitude dune fields in the northern hemisphere are formed at a time when the terrain is being covered with frost. It is therefore suggested that the saltating particles are “snowflakes” which have formed by the mechanism proposed by Pollack etal. The model results for the winter simulation, which have formed by the mechanism transport by large-scale eddies, compare favorably with general circulation model (GCM) calculations. This suggests that the eddy transports may be less important than those associated with the net mass flow, and that 2-D climate modeling may be more succesful for Mars than Earth.  相似文献   

3.
P.C Thomas  P Gierasch  D.S Miller  B Cantor 《Icarus》2003,162(2):242-258
Variable surface albedo features on Mars are likely caused by the entrainment and deposition of dust by the wind. Most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface. Some of the largest variable features, here termed mesoscale linear streaks, are up to 400 km in length and repeatedly occur in one of the smoothest regions of Mars: Amazonis Planitia. Their orientations and apparent season of variability as observed by Viking and Mars Orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms. They provide an example of the ability of large-scale winds, without significant local enhancement, to initiate dust motion on Mars. The sizes and spacing of the linear streaks may be controlled by boundary layer rolls. The repetitive formation of these streaks, over a span of more than 11 Mars years, gives one measure of the stability of Mars’ eolian processes.  相似文献   

4.
J.E. Ainsworth  J.R. Herman 《Icarus》1977,30(2):314-319
An examination of the effect of assumptions in the interpretation of the Venera wind data is made as a rebuttal to the suggestion by A.T. Young that the 140 m/sec Venera 8 horizontal wind at 45 km may be either spurious or anomalous. The Venera measurements of wind speed along with the Mariner measurements of a lower region of strong turbulence are evidence for a wide band of variable high-speed retrograde horizontal winds which girdle Venus at the equator. In the prevalent interpretation of the Mariner 10 uv photographs, the region of the top of the visible cloud is characterized by variable high-speed retrograde horizontal winds which orbit Venus with an average period of 4 Earth days, and by many features indicating vertical convection. This interpretation, together with the possibility of atmospheric corotation due to frictional coupling, suggests that the Venera-Mariner band of winds at 45 km extends well beyond the top of the visible cloud, and that the upper region of strong turbulence detected by the Mariners may result in part from vertical convection currents carried along by high-speed horizontal winds. In an alternate interpretation of the Mariner 10 uv photographs Young suggests that the predominant motions may be traveling wavelike disturbances with a 4-day period rather than bulk motion of the atmosphere. For this case the upper region of strong turbulence is interpreted as due mostly to vertical wind shear resulting from a rapid decrease in wind speed within a relatively short distance above the Venera-Mariner band of high-speed winds.  相似文献   

5.
The Venus Express (VEX) mission has been in orbit to Venus for more than 4 years now. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet that can be used to sample the atmosphere at different altitudes. Day-side images in the ultraviolet range (380 nm) are used to study the dynamics of the upper cloud at 66–72 km while night-side images in the near infrared (1.74 μm) map the opacity of the lower cloud deck at 44–48 km. Here we present a long-term analysis of the global atmospheric dynamics at these levels using a large selection of orbits from the VIRTIS-M dataset covering 860 Earth days that extends our previous work (Sánchez-Lavega, A. et al. [2008]. Geophys. Res. Lett. 35, L13204) and allows studying the variability of the global circulation at the two altitude levels. The atmospheric superrotation is evident with equatorial to mid-latitudes westward velocities of 100 and 60 m s?1 in the upper and lower cloud layers. These zonal velocities are almost constant in latitude from the equator to 50°S. From 50°S to 90°S the zonal winds at both cloud layers decrease steadily to zero at the pole. Individual cloud tracked winds have errors of 3–10 m s?1 with a mean of 5 m s?1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s?1. The zonal winds in the upper cloud change with the local time in a way that can be interpreted in terms of a solar tide. The zonal winds in the lower cloud are stable at mid-latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the South polar vortex. While the upper cloud presents a net meridional motion consistent with the upper branch of a Hadley cell with peak velocity v = 10 m s?1 at 50°S, the lower cloud meridional motions are less organized with some cloud features moving with intense northwards and southwards motions up to v = ±15 m s?1 but, on average, with almost null global meridional motions at all latitudes. We also examine the long-term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions.  相似文献   

6.
Electric currents, generated by thermospheric winds, flow along the geomagnetic field lines linking the E-and F-regions. Their effects on the electric field distribution are investigated by solving the electrical and dynamical equations. The input data include appropriate models of the F-region tidal winds, the thermospheric pressure distribution and the E-and F-layer concentrations. At the magnetic equator, the calculated neutral air wind at 240 km height has a prevailling eastward component of 55 m sec-1 and the west-east and vertical ion drifts agree in their general form with incoherent scatter data from Jicamarca  相似文献   

7.
Recent observations of strong vertical thermospheric winds and the associated horizontal wind structures, using the 01(3P-1D)nm emission line, by ground-based Fabry-Perot interferometers in Northern Scandinavia have been described in an accompanying paper (Paper I). The high latitude thermosphere at a height of 200–300 km displays strong vertical winds (30–50m ms?1)of a persistent nature in the vicinity of the auroral oval even during relatively quiet geomagnetic conditions. During an auroral substorm, the vertical (upward) wind in the active region, including that invaded by a Westward Travelling Surge, may briefly(10–30 min)exceed 150 m s?1. Very large and rapid changes of horizontal wind structure (up to 500 m?1 in 30 min) usually accompany such large impulsive vertical winds. Magnetospheric energy and momentum sources generate large vertical winds of both a quasi-steady nature and of a strongly time-dependent nature. The thermospheric effects of these sources can be evaluated using the UCL three-dimensional, time-dependent thermospheric model. The auroral oval is, under average geomagnetic conditions, a stationary source of significant vertical winds (10–40 m s?1). In large convective events (directly driven by a strong momentum coupling from the solar wind) the magnitude may increase considerably. Auroral substorms and Westward Travelling Surges appear to be associated with total energy disposition rates of several tens to more than 100 erg cm?2s?1, over regions of a few hours local time, and typically 2–5° of geomagnetic latitude (approximately centred on magnetic midnight). Such deposition rates are needed to drive observed time-dependent vertical (upward) winds of the order of 100–200m s?1.The response of the vertical winds to significant energy inputs is very rapid, and initially the vertical lifting of the atmosphere absorbs a large fraction (30% or more) of the total substorm input. Regions of strong upward winds tend to be accompanied in space (and time) by regions of rather lower downward winds, and the equatorward propagation of thermospheric waves launched by auroral substorms is extremely complex.  相似文献   

8.
Observations of vertical and horizontal thermospheric winds, using the OI (3P-1D) 630 nm emission line, by ground-based Fabry-Perot interferometers in Northern Scandinavia and in Svalbard (Spitzbergen) have identified sources of strong vertical winds in the high latitude thermosphere. Observations from Svalbard (78.2N 15.6E) indicate a systematic diurnal pattern of strong downward winds in the period 06.00 U.T. to about 18.00 U.T., with strong upward winds between 20.00 U.T. and 05.00 U.T. Typical velocities of 30 m s?1 downward and 50 m s?1 upward occur, and there is day to day variability in the magnitude (30–80 m s?1) and phase (+/- 3 h) in the basically diurnal variation. Strong and persistent downward winds may also occur for periods of several hours in the afternoon and evening parts of the auroral oval, associated with the eastward auroral electrojet (northward electric fields and westward ion drifts and winds), during periods of strong geomagnetic disturbances. Average downward values of 30–50 m s?1 have been observed for periods of 4–6 h at times of large and long-lasting positive bay disturbances in this region. It would appear that the strong vertical winds of the polar cap and disturbed dusk auroral oval are not in the main associated with propagating wave-like features of the wind field. A further identified source is strongly time-dependent and generates very rapid upward vertical motions for periods of 15–30 min as a result of intense local heating in the magnetic midnight region of the auroral oval during the expansion phase of geomagnetic disturbances, and accompanying intense magnetic and auroral disturbances. In the last events, the height-integrated vertical wind (associated with a mean altitude of about 240 km) may exceed 100–150 m s?1. These disturbances also invariably cause major time-dependent changes of the horizontal wind field with, for example, horizontal wind changes exceeding 500 m s?1 within 30 min. The changes of vertical winds and the horizontal wind field are highly correlated, and respond directly to the local geomagnetic energy input. In contrast to the behaviour observed in the polar cap or in the disturbed afternoon auroral oval, the ‘expansion phase’ source, which corresponds to the classical ‘auroral substorm’, generates strong time-dependent wind features which may propagate globally. This source thus directly generates one class of thermospheric gravity waves. In this first paper we will consider the experimental evidence for vertical winds. In a second paper we will use a three-dimensional time-dependent model to identify the respective roles of geomagnetic energy and momentum in the creation of both classes of vertical wind sources, and consider their propagation and effects on global thermospheric dynamics.  相似文献   

9.
Abstract– We present initial results from hydrocode modeling of impacts on Al‐1100 foils, undertaken to aid the interstellar preliminary examination (ISPE) phase for the NASA Stardust mission interstellar dust collector tray. We used Ansys’ AUTODYN to model impacts of micrometer‐scale, and smaller projectiles onto Stardust foil (100 μm thick Al‐1100) at velocities up to 300 km s?1. It is thought that impacts onto the interstellar dust collector foils may have been made by a combination of interstellar dust particles (ISP), interplanetary dust particles (IDP) on comet, and asteroid derived orbits, β micrometeoroids, nanometer dust in the solar wind, and spacecraft derived secondary ejecta. The characteristic velocity of the potential impactors thus ranges from <<1 to a few km s?1 (secondary ejecta), approximately 4–25 km s?1 for ISP and IDP, up to hundreds of km s?1 for the nanoscale dust reported by Meyer‐Vernet et al. (2009) . There are currently no extensive experimental calibrations for the higher velocity conditions, and the main focus of this work was therefore to use hydrocode models to investigate the morphometry of impact craters, as a means to determine an approximate impactor speed, and thus origin. The model was validated against existing experimental data for impact speeds up to approximately 30 km s?1 for particles ranging in density from 2.4 kg m?3 (glass) to 7.8 kg m?3 (iron). Interpolation equations are given to predict the crater depth and diameter for a solid impactor with any diameter between 100 nm and 4 μm and density between 2.4 and 7.8 kg m?3.  相似文献   

10.
Vertical winds have been observed by optical Doppler measurements of the 557.7 nm emission in the aurora, using a Fabry-Perot spectrometer. Both upward and downward winds were observed, of 15 m s?1 magnitude. The upward winds were associated with westward overhead currents, and with low altitude aurora (～ 110 km) as determined by the auroral temperature, while a high altitude aurora (～ 135 km) and eastward currents were associated with the downward wind. The Lorentz force of these currents has the wrong direction to act as a direct forcing mechanism. It is concluded that Joule heating is directly responsible for the upward winds, while the divergence of horizontal winds is responsible for the downward winds.  相似文献   

11.
An automated cloud tracking algorithm is applied to Cassini Imaging Science Subsystem high-resolution apoapsis images of Saturn from 2005 and 2007 and moderate resolution images from 2011 and 2012 to define the near-global distribution of zonal winds and eddy momentum fluxes at the middle troposphere cloud level and in the upper troposphere haze. Improvements in the tracking algorithm combined with the greater feature contrast in the northern hemisphere during the approach to spring equinox allow for better rejection of erroneous wind vectors, a more objective assessment at any latitude of the quality of the mean zonal wind, and a population of winds comparable in size to that available for the much higher contrast atmosphere of Jupiter. Zonal winds at cloud level changed little between 2005 and 2007 at all latitudes sampled. Upper troposphere zonal winds derived from methane band images are ～10 m s?1 weaker than cloud level winds in the cores of eastward jets and ～5 m s?1 stronger on either side of the jet core, i.e., eastward jets appear to broaden with increasing altitude. In westward jet regions winds are approximately the same at both altitudes. Lateral eddy momentum fluxes are directed into eastward jet cores, including the strong equatorial jet, and away from westward jet cores and weaken with increasing altitude on the flanks of the eastward jets, consistent with the upward broadening of these jets. The conversion rate of eddy to mean zonal kinetic energy at the visible cloud level is larger in eastward jet regions (5.2 × 10?5 m2 s?3) and smaller in westward jet regions (1.6 × 10?5 m2 s?3) than the global mean value (4.1 × 10?5 m2 s?3). Overall the results are consistent with theories that suggest that the jets and the overturning meridional circulation at cloud level on Saturn are maintained at least in part by eddies due to instabilities of the large-scale flow near and/or below the cloud level.  相似文献   

12.
High vertical resolution scans of the Venus limb made by the Pioneer Venus Orbiter Cloud Photopolarimeter at 365 nm and 690 nm wavelengths are used to investigate the level of the haze top, and haze particle properties and scale height. Haze particle vertical optical depth 0.01 occurs at altitude 80 to 85 km based on knowledge of instrument pointing. The lowest haze tops were observed close to subsolar longitudes but the data set supports a longitude dependence no more than a temporal variation. Single scattering computations for a spherical shell atmosphere show good agreement with observed intensities for particles smaller than 0.3 μm radius and refractive index less than 1.7, consistent with, but not limited to, concentrated sulfuric acid. Particle scale height in the 0.5 to 2 mbar pressure regions varies between 1 and 3 km over the season (12 of 92 days), latitude (15–45°N), and local time (0900–1800) ranges of the observations. Detached layers of haze are sometimes present. An average particle scale height of 2.2 km at 84 km altitude yields an eddy diffusion coefficient of 1.3 × 105 cm2 sec?1.  相似文献   

13.
We find that faint sodium emission originating in the middle Jupiter magnetosphere has two distinct kinematical components. The “normal” signature of atoms on bound orbits with large apojoves seems always to be present, and we suggest these atoms are an extension of the bright, near-Io sodium cloud. The “fast” signature, with speeds up to at least 100 km sec?1, is seen only occasionally, and we suggest it is due to an interaction of the near-Io sodium cloud with the corotating, heavy-ion plasma. Both elastic and charge-exchange collisions seem consistent with the observed kinematical and temporal signatures. Elastic collisions seem marginally more capable of producing the high observed sodium atom speeds. We predict observable occurences of the fast component in the hours following passage of the Io sodium cloud through the plasma centrifugal symmetry surface if Io is at a favorable orbital longitude. Between 10 and 20 RJ we find an atomic sodium density ～10?2 cm?3. If the photoionization lifetime applies, an Io source of at least 1026 sodium atoms sec? is required to maintain this remote sodium population.  相似文献   

14.
We consider the problem of dust grain survival in the disk winds from T Tauri and Herbig Ae stars. For our analysis, we have chosen a disk wind model in which the gas component of the wind is heated through ambipolar diffusion to a temperature of ～104 K. We show that the heating of dust grains through their collisions with gas atoms is inefficient compared to their heating by stellar radiation and, hence, the grains survive even in the hot wind component. As a result, the disk wind can be opaque to the ultraviolet and optical stellar radiation and is capable of absorbing an appreciable fraction of it. Calculations show that the fraction of the wind-absorbed radiation for T Tauri stars can be from 20 to 40% of the total stellar luminosity at an accretion rate ? a = 10?8-10?6 M ⊙yr?1. This means that the disk winds from T Tauri stars can play the same role as the puffed-up inner rim in current accretion disk models. In Herbig Ae stars, the inner layers of the disk wind (r ≤ 0.5 AU) are dust-free, since the dust in this region sublimates under the effect of stellar radiation. Therefore, the fraction of the radiation absorbed by the disk wind in this case is considerably smaller and can be comparable to the effect from the puffed-up inner rim only at an accretion rate of the order of or higher than 10?6 M ⊙yr?1. Since the disk wind is structurally inhomogeneous, its optical depth toward the observer can be variable, which should be reflected in the photometric activity of young stars. For the same reason, moving shadows from gas and dust streams with a spiral-like shape can be observed in high-angular-resolution circumstellar disk images.  相似文献   

15.
《Icarus》1987,70(3):442-468
The predictions of an analytical steady thermally forced viscous model for the zonally averaged global circulation of the Martian atmosphere are compared to observations of atmospheric temperatures and eolian feature directions. The temperature of the winter polar atmosphere is a sensitive indicator of the value of the mean eddy diffusivity v of the atmosphere. For global dust storm season, the observed large warming of the atmosphere over the winter (north) pole during the 1977b storm as well as the distribution and azimuths of Type I(b) dust streaks can be well reproduced if v = 107−108cm2sec−1. Observed northeasterly surface winds at high northern latitudes could be produced by plausible fluxes of CO2 from the northern polar cap. The thermal structure at southern latitudes during this storm is satisfactorily produced, but a major discrepancy exists between observations and predictions of the temperature structure at middle northern latitudes. By comparing these results with those from previous inviscid models of the zonal mean circulation on Mars, we suggest v > 107cm2sec−1 at heights above 30 km and v ⪡ 107cm2sec−1 at lower altitudes may yield a meridional circulation which produces the dynamical warming necessary to account for the observed thermal structure at 0.6 mbar at all latitudes. For late southern summer when the dust content of the atmosphere has decreased to levels characteristic of much of the Martian year, the lack of dynamical warming of the winter pole implies v ≤ 106cm2sec−1. In addition, the predicted surface wind azimuths at this season agree well with the observed azimuths of Type I(d) dust streaks, which are observed to form at this season. The observed latitudinal concentration of the streaks is not explained by the model and may require additional processes which have not been included.  相似文献   

16.
Xun Zhu  Darrell F. Strobel 《Icarus》2005,176(2):331-350
Titan's atmospheric winds, like those on Venus, exhibit superrotation at high altitudes. Titan general circulation models have yielded conflicting results on whether prograde winds in excess of 100 m s−1 at the 1 mbar level are possible based on known physical processes that drive wind systems. A comprehensive two-dimensional (2D) model for Titan's stratosphere was constructed to systematically explore the physical mechanisms that produce and maintain stratospheric wind systems. To ensure conservation of angular momentum in the limit of no net exchange of atmospheric angular momentum with the solid satellite and no external sources and sinks, the zonal momentum equation was solved in flux form for total angular momentum. The relationships among thermal wind balance, meridional circulation, and zonal wind were examined with numerical experiments over a range of values for fundamental input parameters, including planetary rotation rate, radius, internal friction due to wave stresses, and net radiative drive. The magnitude of mid-latitude jets is most sensitive to a single parameter, the planetary rotation rate and results from the conversion of planetary angular momentum to relative angular momentum by the meridional circulation, whereas the strength of meridional circulation is mainly determined by the magnitude of the radiative drive. For Titan's slowly rotating atmosphere, the meridional temperature gradient is vanishingly small, even when the radiative drive is enhanced beyond reasonable magnitudes, and can be inferred from zonal winds in gradient/thermal wind balance. In our 2D model large equatorial superrotation in Titan's stratosphere can be only produced through internal drag forcing by eddy momentum fluxes, which redistribute angular momentum within the atmosphere, while still conserving the total angular momentum of the atmosphere with time. We cannot identify any waves, such as gravitational or thermal tides, that are sufficiently capable of generating the required eddy forcing of >50 m s−1 Titan-day−1 to maintain peak prograde winds in excess of 100 m s−1 at the 1 mbar level.  相似文献   

17.
William K. Hartmann 《Icarus》1978,33(2):380-387
Mariner 9 high-resolution photos and topographic information were used to make a topographic analysis of “blue” and “red” cloud positions reported over a 66-year period in Lowell Observatory records. A sample of 77 “blue” cloud sites lay preferentially at the highest Martian elevations; 60% centered precisely on the seven major volcanic mountain peaks (unknown when the clouds were observed); another 16% lay on substantial slopes or contacts between cratered terrain and lower plains. The median altitude of blue cloud sites was 2.1 km above the global topographic median. These results agree with other evidence that most Earth-detected blue clouds are orographic uplift clouds, composed of condensates. Over half of 131 sporadic yellowish or red clouds were associated with blue clouds or volcanoes, and thus probably did not represent dust storm phenomena, contrary to a commonly held belief. Of 88 “possible dust clouds” (chosen by additional criteria), about two-thirds occur at borders between light and dark areas, in the light regions. These sites may have thin veneers of dust, and current depositional or denudational activity. Median altitude of “possible dust cloud” sites was 0.5 km below the global topographic median. Major dust storms begin in a few “core areas,” two of which associate with major basins Hellas and Isidis, probable reservoirs of mobile dust; but exact topographic control and causes of dust storms are unclear.  相似文献   

18.
The Venera 8 descent module measured pressure, temperature, winds and illumination as a function of altitude in its landing on July 22, 1972, just beyond the terminator in the illuminated hemisphere of Venus. The surface temperature and pressure is 741 ± 7°K and 93 ± 1.5kgcm?2, consistent with early Venera observations and showing either no diurnal variation or insignificant diurnal variation in temperature and pressure in the vicinity of the morning terminator. The atmosphere is adiabatic down to the surface. The horizontal wind speed is low near the surface, about 35m/sec between 20 and 40km altitude, and increasing rapidly above 48km altitude to 100–140m/sec, consistent with the 4-day retrograde rotation of the ultraviolet clouds. The illumination at the center of the day hemisphere of Venus is calculated to be about 1% of the solar flux at the top of the atmosphere, consistent with greenhouse models and high enough to permit photography of the Venus surface by future missions. The attenuation below 35km altitude is explained by Rayleigh scattering with no atmospheric aerosols; above 35km there must be substantial extinction of incident light.  相似文献   

19.
Calculations of the steady-state photoelectron energy and angular distribution in the altitude region between 120 and 1000 km are presented. The distribution is found to be isotropic at all altitudes below 250 km, while above this altitude anisotropies in both pitch angle and energy are found. The isotropy found in the angular distribution below 250 km implies that photoelectron transport below 250 km is insignificant, while the angular anisotropy found above this altitude implies a net photoelectron current in the upward direction. The energy anisotropy above 500 km arises from the selective backscattering of the low energy photoelectron population of the upward flux component by Coulomb collisions with the ambient ions. The total photoelectron flux attains its maximum value between about 40 and 70 km above the altitude at which the photoelectron production rate is maximum. The displacement of the maximum of the equilibrium flux is attributed to an increasing (with altitude) photoelectron lifetime. Photoelectrons at altitudes above that where the flux is maximum are on the average more energetic than those below that altitude. The flux of photoelectrons escaping to the protonosphere at dawn was found to be 2.6 × 108 cm?2 sec?1, while the escaping flux at noon was found to be 1.5 × 108 cm?2 sec?1. The corresponding escaping energy fluxes are: 4.4 × 109 eV cm?2 sec?1 and 2.7 × 109 eV cm?2 sec?1.  相似文献   

20.
In this work, the bolide is studied as an atmospheric event causing significant release of meteoritic dust into the stratosphere. Ground-based pictures taken by eyewitnesses and images from the Japan geostationary satellite MTSAT-2 are used as a database. The analysis of the ground-based pictures allows the altitude of the main burst to be estimated as 22.9 ± 1.6 km. It is shown that the top of the cloud formed due to the main burst rose to 11 km for about 60–80 s due to convection, which provides an estimate of the maximum vertical velocity of 130–180 m/s. According to calculations, the upper part of the trail is affected by a strong wind drift and is located at an altitude of >53 km, in the mesosphere. The MTSAT-2 data show that the mesospheric part of the trail traveled southwestward, while the stratospheric part, northeastward, with velocities higher than 100 km/h.  相似文献   

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