Detection of Leonids meteoric dust in the upper atmosphere by polarization measurements of the twilight sky

A new method for the meteoric dust detection in the upper atmosphere based on the polarimetric observations of the twilight sky is proposed. Polarization measurements are effective for detection of the meteoric dust scattering on the background consisting basically of troposphere multiple scattering. The method is based on the observed and explained polarization properties of the sky background during different stages of twilight. It is used to detect the mesosphere dust after the Leonids maximum in 2002, estimate its altitude range and to investigate its evolution—slow decrease of the altitude. The polarization method takes into account the multiple scattering and sufficient contribution of moonlight scattering background and turns out to be more sensitive than existing analogs used in the present time.     

Localized structures of nanosize charged dust grains in Earth's middle atmosphere

The Earth's middle atmosphere at altitudes of 80-95 km exhibits layered phenomena known as noctilucent clouds and polar mesosphere summer echoes. These structures are believed to be associated with the presence of large quantities of charged dust or aerosol particles. The sign of the charge depends on the material composition of the latter as well as the environment. The grains are normally composed of ice together with possible metallic impurities. Particles of pure ice are always charged negatively, but if the metal content is sufficiently high, they can become positive. The characteristics of self-organized structures on the dust acoustic time scale depend strongly on the sign of the charge, and the structures can appear as either electron (ion) density humps or dips. Such a physical distinction can be used for the identification and diagnostics of noctilucent clouds and polar mesosphere summer echoes.     

The thermal history of interplanetary dust particles collected in the Earth's stratosphere

Abstract— Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse-heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short-duration heat pulses to perform the extractions is an improvement over the employment of a step-heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (～40 μm in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.     

Charged dust in the Earth's magnetosphere

We have considered the electrodynamic effects on small Al₂O₃ spherules dumped into the Earth's magnetosphere in large quantities during solid rocket propellant burns. The charges acquired by these grains in all regions of the terrestrial environment (plasmasphere, magnetosphere, and solar wind) are modest. Consequently electrodynamic effects are significant only at the lower end of the dust size spectrum (R _g0.1 m). In that case, the electrodynamic forces conspire with solar radiation pressure to eliminate the grains from the magnetosphere in a comparatively short time. Although not studied here in detail, we anticipate a similar fate for fine micrometeoroids entering the Earth's magnetosphere, with the electro-dynamic effects playing an even more important role.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

1998年德令哈狮子座流星雨目视观测及初步分析

根据中国－荷兰狮子座流星雨合观测1998年11月13日至18是日在紫金山天文台德令哈观测站观测所得的数据，以及同期中国其他地方的观测数据，分析了1998年狮子座流星雨的分布特征，提出此次地球所遭遇的流星群带呈3层结构。     

Extreme ultra-violet absorption cross-sections in the Earth's upper atmosphere

Relative absorption cross-sections between 180 Å and 304 Å, and between 584 Å and 304 Å are obtained for atomic oxygen in the upper atmosphere, by observing the attentuation of solar radiation using a satellite instrument.     

Vertical distribution of scattering hazes in Titan's upper atmosphere

Radial intensity scars of a Voyager 2 high phase angle image of Titan have been inverted to yield vertical extinction profiles at 1° intervals around the limb. A detached haze layer with peak particle number densities ～0.2 cm^?3 exists at all latitudes south of ～45°N, and at an altitude of 300–350 km. The optical depth 0.01 level lies at a radius of 2932 ± 5 km at the equator and at a radius of 2915 ± 10 km over the poles (altitudes of 357 ± 5 and 340 ± 10 km, respectively). In addition to the haze layer at 300–350 km, there is a small enhancement in the extinction at ～450 km which exists at all latitudes between 75°S and ～60°N.     

Vertical distribution of water vapor and mars model lower and middle atmosphere

Observations and model calculations of water vapor diffusion suggest that about half the amount of water vapor is distributed with constant mixing ratio in the Martian atmosphere, the other half is the excess water vapor in the lower troposphere. During 24 hr the total content of water vapor may vary by a factor of two. The eddy diffusion coefficient providing agreement between calculations and observations is K = (3–10) × 10⁶ cm² sec^?1 in the troposphere. An analytical expression is derived for condensate density in the stratosphere in terms of the temperature profile, the particle radius r, and K. The calculations agree with the Mars 5 measurements for r = 1.5 μm, condensate density 5 × 10^?12 g/cm³ in the layer maximum at 30 to 35 km, condensate column density 7 × 10^?6 cm^?2, K = (1?3) × 10⁶ cm² sec^?1, and the temperature profile T = 185 ? 0.05z ? 0.01z² at 20 to 40 km. Condensation conditions yield a temperature of 160°K at 60 km in the evening; the scale height for scattered radiation yields T = 110°k at 80 to 90 km. The Mars model atmosphere has been developed up to 125 km.     

Global distribution of helium in the upper atmosphere during solar minimum

Helium in the Earth's thermosphere traces the dynamical systems that redistribute energy and mass. Measurements of the global helium distribution in the thermosphere, using Atmosphere Explorer satellite C. (AE-C), show a gradual seasonal change in the number density of helium for all latitudes. The enhancement in helium over the winter pole (the helium bulge) changes in magnitude slowly as seasons progress. The bulge builds and recedes following the progression of winter North to South and back again. This progression of the winter helium enhancement is presented in this paper using latitudinal profiles of helium number density for each month during the year. The absolute magnitude of the winter helium enhancement in the auroral regions is affected by auroral heating at low altitudes. The reduction in the winter helium bulge at low altitudes shown in AE-C data can be traced to this localized heating. The gradual variation in helium concentration measured at many latitudes for all seasons of the year implies that global thermospheric wind systems change gradually with the seasons.     

Momentum of meteoroids and its effect on the Earth's atmosphere

Recent studies have attributed certain properties of the Earth's atmosphere to excess orbita angular momentum of impinging meteoroids. A realistic analysis of meteor observations does not support the existence of this excess.     

Matching cometary ejection processes to the Leonids 1998–2001 using a hybrid numerical model

A new scheme for simulating meteor showers is introduced, based on a hybridization of current numerical modelling techniques. It involves an iterative method that generates particles which hit a real-scale Earth, removing the spatial and temporal blurring common to other modelling techniques. The scheme is applied to the activity profile of the Leonids 2001 using three different models of meteoroid ejection velocity and then applied to the Leonids 1998–2000 using the most favourable models. It is shown that to reproduce the observed meteor activity profiles there must be a strong concentration of ejection around perihelion. The modelling also implies that meteoroid density must be towards the higher end of the currently acceptable range, although the derived limits are not independent of the ejection velocity model. We also find that the extreme narrowness of Leonid activity peaks is not easily reproduced with outgassing over the entire day side of the comet but it is fitted well by outgassing in a restricted direction as one would expect from an outgassing jet. In addition, we show that double-peaked features, corresponding to a semihollow meteoroid streamlet, can arise in a meteor shower activity profile from outgassing during a single perihelion passage of the parent comet. It is suggested that this process caused the double-peaked feature in the first maxima of the 2001 Leonids.     

Thermal structure of the Martian atmosphere during the dissipation of the dust storm of 1971

The secular variation of the thermal structure of the Martian atmosphere during the dissipation phase of the 1971 dust storm is examined, using temperatures obtained by the infrared spectroscopy investigation on Mariner 9. For the latitude range ?20° to ?30°, the mean temperature at the 2mbar level is found to decrease from approximately 220 K in mid-December 1971 to about 190 K by June 1972 while for the 0.3mbar level a decrease from 203 K to 160 K is observed. Over the same period, the amplitude of the diurnal temperature wave also decreased. Assuming a simplified radiative heating model, the dust optical depth is found to decrease approximately exponentially with an e-folding time of about 60 days at both the 0.3 and 2mbar levels. Stokes-Cunningham settling alone cannot account for this behavior. Sedimentation models which include both gravitational settling and vertical mixing are developed in an effort to explain the time evolution of the dust. Within the framework of a model which assumes an effective vertical diffusivity K independent of height, a mean dust particle diameter of ～2 μm is inferred. To provide the necessary vertical mixing, K ? 10⁷ cm²sec^?1 is required in the lower atmosphere.     

Effect of charging of aerosols in the lower atmosphere of Mars during the dust storm of 2001

Aerosols are very important in the Martian climate system. Aerosols get charged by the attachment of ions in the atmosphere. Charging of aerosols reduces the conductivity of the atmosphere as the very mobile ions are lost during the ion-aerosol attachment. During a dust storm the dust opacity increases and more ion-aerosol attachment process occurs and consequently conductivity reduces further. It was found that with the background aerosols (dust opacity ∼0.2), the conductivity close to the surface of Mars was reduced by a factor of 5, but during the dust storm (opacity ∼5) of 2001 the conductivity decreased by about 2 orders of magnitude.     

On the presence of cosmic dust in the upper atmosphere

The activity of Librids on 4 April 1973 was detected by the rise of the twilight luminosity. The ratio of circumzenithal luminosity in the antisolar to solar azimuth also increases in the presence of cosmic dust in the upper atmosphere.     

Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulations

We perform Monte Carlo simulations of cosmic ray-induced hard X-ray radiation from the Earth's atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range 25–300 keV is mainly determined by Compton scatterings and photoabsorption, and is almost insensitive to the incident cosmic ray spectrum. We provide a fitting formula for the hard X-ray surface brightness of the atmosphere as would be measured by a satellite-borne instrument, as a function of energy, solar modulation level, geomagnetic cut-off rigidity and zenith angle. A recent measurement by the INTEGRAL observatory of the atmospheric hard X-ray flux during the occultation of the cosmic X-ray background by the Earth agrees with our prediction within 10 per cent. This suggests that Earth observations could be used for in-orbit calibration of future hard X-ray telescopes. We also demonstrate that the hard X-ray spectra generated by cosmic rays in the crusts of the Moon, Mars and Mercury should be significantly different from that emitted by the Earth's atmosphere.     

Fragmentation of Leonids in space and a model of spatial distribution of meteoroids within the Leonid stream

The contribution presents an analysis of the Leonids 1999 HDTV Leonid MAC data. The observed grouping of the Leonids over a random level is explained by progressive fragmentation of meteoroids in space. The observed data are compared with a spatial distribution model. Possible fragmentation processes of meteoroids in space are presented and discussed.