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1.
Donald E. Anderson Jr. 《Planetary and Space Science》1983,31(12):1517-1523
Time-dependent calculations of trace constituent distributions require as input the dissociating radiation field as a function of altitude and solar zenith angle. An isotropic, spherical, multiple scattering model of the radiation field has been developed to determine the radiation field at twilight. Comparison of the spherical model with a plane parallel model at twilight shows that: (1) for solar zenith angles less than 92°, plane parallel solutions for the source function are suitable if the initial deposition of solar energy is calculated for a spherical atmosphere; (2) for solar zenith angles greater than 92°, the plane parallel radiation field can be several orders of magnitude smaller than that calculated with the spherical model; (3) at altitudes above 40 km and at all solar zenith angles, the spherical model predicts 10–20% less radiation than the radiation field calculated with the plane parallel model. Calculations of the rate of photodissociation of NO2 in the troposphere and stratosphere show that the spherical model yields significantly higher values at solar zenith angles greater than 92°. 相似文献
2.
A thermal regime of the troposphere of Venus is mainly determined by the greenhouse effect. A closeness of the real temperature gradient to the adiabatic one indicates that turbulent heat fluxes are also essential. Additional problems arise as only about 11% of the solar radiation absorbed by the planet reaches the surface, and most of it is taken up in the clouds at altitudes of 60–70 km. The present study summarizes experimental data on atmospheric parameters related to turbulence and estimates turbulent fluxes and turbulence characteristics. These data confirm the author's hypothesis of an anomalous downward turbulent heat flux in the free atmosphere. A normal upward turbulent heat flux exists in the planetary boundary layer. 相似文献
3.
The production rate, ion density and electron density are calculated between longitudes 0° and 360° E due to incident radiation of wavelength range 1-102.57 nm in the dayside atmosphere of Mars. These calculations are made by using global analytical yield spectrum (AYS) model at solar zenith angle 80° between latitudes 50° and 70° N for spring equinox and medium solar activity condition. These conditions are appropriate for Mars Global Surveyor (MGS) Phase 2 aerobraking period during which both the accelerometer and the radio occultation data are used. The calculated results are compared with MGS radio occultation measurements carried out at different latitudes (64.7°-67.3° N) and longitudes (0°-360° E) in December 1998 between solar zenith angle 78° and 81°. This measurement shows primary and secondary ionization peaks, which are varying with longitudes. Our calculation suggests that first peak is produced by photoionization and photoelectron impact ionization processes due to absorption of solar EUV radiation (9-102.57 nm). The second peak is produced by photoelectron impact ionization of soft X-ray photon (1-9 nm). There is a good agreement between our calculation and measurement as far as the maximum and the minimum values of primary peak altitude/peak density of electrons are concerned. However, the calculated values of secondary peak density and peak altitude are higher than the measured values by a factor of 1.5-2.0 and 1.1, respectively. The secondary peak is brought into agreement with the measurement using low X-ray flux by a factor of 2 to 3 below 9 nm. The longitudinal distribution of calculated and measured peak density and peak altitude are fitted by least-square method with 0.95 confidence limits. 相似文献
4.
The total photoelectron and secondary electron fluxes are calculated at different times and altitudes along the trajectory of Mars Global Surveyor passing through the nightside and dayside martian ionosphere. These results are compared with the electron reflectometer experiment on board Mars Global Surveyor. The calculated electron spectra are in good agreement with this measurement. However, the combined fluxes of proton and hydrogen atom as calculated by E. Kallio and P. Janhunen (2001, J. Geophys. Res.106, 5617-5634) were found to be 1-2 orders of magnitude smaller than the measured spectra. We have also calculated ionization rates and ion and electron densities due to solar EUV, X-ray, and electron-proton-hydrogen atom impacting with atmospheric gases of Mars at solar zenith angles of 75°, 105°, and 127°. In the vicinity of the dayside ionization peak, it is found that the ion production rate caused by the precipitation of proton-hydrogen atom is larger than the X-ray impact ionization rate while at all altitudes, the photoionization rate is always greater than either of the two. Moreover, X-rays contribute greatly to the photoelectron impact ionization rate as compared to the photoion production rate. The calculated electron densities are compared with radio occultation measurements made by Mars Global Surveyor, Viking 1, and Mars 5 spacecraft at these solar zenith angles. The dayside ionosphere produced by proton-hydrogen atom is smaller by an order of magnitude than that produced by solar EUV radiation. X-rays play a significant role in the dayside ionosphere of Mars at the altitude range 100-120 km. Solar wind electrons and protons provide a substantial source for the nightside ionosphere. These calculations are carried out for a solar minimum period using solar wind electron flux, photon flux, neutral densities, and temperatures under nearly the same areophysical conditions as the measurements. 相似文献
5.
P. Pant 《Astrophysics and Space Science》1993,209(2):297-306
Sudden phase anomalies (SPA's) observed in the phase of GBR 16 kHz VLF signals during the years 1977 to 1983 have been analysed in the light of their associated solar X-ray fluxes in the 0.5–4 Å and 1–8 Å bands. An attempt has been made to investigate the solar zenith angle () dependence of the integrated solar X-ray flux for producing SPA's. It is deduced from the observations for < 81° that the phase deviation increases linearly as a whole with increasing solar X-ray fluxes in these two bands. The threshold X-ray flux needed to produce a detectable SPA effect has been estimated to be 1.6 × 10–4 ergcm–2 s–1 and 1.8 × 10–3 ergcm–2 s–1 in the 0.5–4 Å and 1–8 Å bands, respectively. For both bands the average cross section for all atmospheric constituents at a height of 70 km is almost equal to the absorption cross section for the 3 Å X-ray emission. 相似文献
6.
To evalute the effect of the non-uniform surface on the radiation field, the upwelling radiation at the top of the atmosphere bounded by the checkerboard type of terrain is computed using the modified doubling method. The terrain is composed of the square Lambert surfaces with two different albedoes. The dimension of the each square is assumed to be 0.5–6 km. The radiance of the terrain is discussed with respect to the atmospheric effect. The observational site is located at altitude 30 km. The corresponding projected point on the ground is located at the center of a square. The solar and observational direction is located in the plane parallel to the checkerboard squares. The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecules, where the model aerosol is of the oceanic or the water soluble types.Numerical simulation exhibits the extraordinary effect near the edge of each squares. The radiance of the terrain depends upon the difference of albedoes and size of squares. It increases with the increase of the dimension of the square. It decreases with the optical thickness. At large optical thickness, the variation of radiation with zenith direction depends upon the aerosol characteristics. It shows little dependence on the solar zenith angle if less than 20°. 相似文献
7.
The absorption spectrum and thermal radiation fluxes are calculated for the lower atmosphere of Venus in the far-wing approximation based on the theory of the collisional broadening of spectral lines. The results are in good agreement with the available experimental data. An outgoing thermal radiation flux is about 2.6 W/m2 near the planetary surface. This indicates that free convection significantly contributes to the thermal balance of the lower troposphere. The fluxes obtained in this study were compared to those calculated on the basis of empirical models of the spectral line profile. It was shown that the far wings of the CO2 lines considerably affect the radiative transfer in the transparency windows. This effect becomes weaker when the contribution of the absorption of minor constituents, primarily water vapor, increases. The profiles of absorption lines of minor constituents do not influence the thermal radiation fluxes.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 214–226.Original Russian Text Copyright © 2005 by Afanasenko, Rodin. 相似文献
8.
Frank E. Barmore 《Planetary and Space Science》1977,25(2):185-191
Ground based high resolution (R ～ 120,000) spectra of the zenith day sky near 6300 Å were obtained with a PEPSIOS. When compared with the solar spectrum taken with the same spectrometer, the 6300.3 Å line of atomic oxygen was clearly present in emission. The apparent emission rate averaged 6 to 8 kR for solar zenith angles of 50 to 60 deg and decreased smoothly to about 1 kR as the solar zenith angle increased to 95 deg. The average emission line is somewhat different in width than the thermal line width expected with the Jacchia (1971) model for a 250 km altitude. 相似文献
9.
The results of calculations of the multiply-scattered solar-induced radiation field in the troposphere and stratosphere are presented for direct application to photochemical models. The enhancement factors due to multiple scattering are given for the heights, solar zenith angles and wavelengths (between 800 and 300 nm) which play a role in the photodissociation of various atmospheric constituents. 相似文献
10.
Fine time variation of hard X-rays has been explained in terms of a spread in the angle of incidence of the source electrons in non-thermal thick-target model for bremsstrahlung generation. The electron energy and angular distributions have been calculated by combining small angle scatterings using analytical treatment with a large angle collision using Monte Carlo calculations as a function of column density. The incidence angles of electrons are taken as 0, 30, and 60°. Using the Bethe-Heitler cross section and the above calculated electron distributions, the bremsstrahlung flux for different photon energies as a function of column density has been studied. The computed X-ray pulse as a function of column density has been converted into time profile. It corresponds well with the observed fine time structure. The calculated spectra of X-rays at the peak and valley are also consistent with the observations. The variation of photon flux with time has also been computed for photon energies 20, 50, and 100 keV for 90 and 180° observation angles together with the changes in spectral shapes of photon energy spectrum at different times for 90 and 180° observation angles. 相似文献
11.
The upwelling radiation at the top of the atmosphere is computed over a circular lake which is located in the uniform Lambert surface, using a modified version of the doubling-adding method. The radiance over the lake is discussed with respect to the atmospheric effect. The radius of the lake is assumed to be 0.5, 1, and 3 km. The observational site is located at altitude 30 km. The zenith of the observational site is located in the plane which is determined by the zenith of the center of the lake and incident solar direction. The zenith angle of the observational site to the center of the lake is fixed to 6.28°. The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecule, where the model aerosol is of the oceanic or the water soluble types.Numerical simulation exhibits an extraordinary effect near the lake. The radiance of the lake against the surrounding depends upon the albedo of the surrounding surface. It increases with the increase of the size of the lake and decreases with the optical thickness. At large optical depth, the radiance depends upon the aerosol characteristics. It shows little dependence on the solar zenith angle if less than 60°. 相似文献
12.
The energy and angular distributions of electrons have been studied by combining small angle scatterings using analytical treatment with large angle collisions using Monte Caroo calculations as a function of column density for initially power-law electron distributions and incidence angles of 0, 30, and 60°. Using these distributions the X-ray and EUV line flux as a function of column density has been computed. The flux increases with increase in column density. At the initial column densities the contribution of non-thermal electrons for the production of line flux is negligible. However, it becomes significant at intermediate column densities at which the electron energy and angular distributions have non-Maxwellian nature. X-ray and EUV flux have also been calculated as a function of electron spectral index at a fixed column density. It falls steeply with increase in spectral index. The calculated flux is compared with the observations. 相似文献
13.
The structure and variations of open field regions (OFRs) are analyzed against the solar cycle for the time interval of 1970–1996. The cycle of the large-scale magnetic field (LSMF) begins in the vicinity of maximum Wolf numbers, i.e. during the polar field reversal. At the beginning of the LSMF cycle, the polar and mid-latitude magnetic field systems are connected by a narrow bridge, but later they evolve independently. The polar field at the latitudes above 60° has a completely open configuration and fills the whole area of the polar caps near the cycle minimum of local fields. At this time, essentially all of the open solar flux is from the polar caps. The mid-latitude open field regions (OFRs) occur at a latitude of 30–40° away from solar minimum and drift slowly towards the equator to form a typical 'butterfly diagram' at the periphery of the local field zone. This supports the concept of a single complex – 'large-scale magnetic field – active region – coronal hole'. The rotation characteristics of OFRs have been analyzed to reveal a near solid-body rotation, much more rigid than in the case of sunspots. The rotation characteristics are shown to depend on the phase of the solar cycle. 相似文献
14.
Cassini/VIMS limb observations have been used to retrieve vertical profiles of hydrogen cyanide (HCN) from its 3 μm emission in the region from 600 to 1100 km altitude at daytime. While the daytime emission is large up to about 1100 km, it vanishes at nighttime at very low altitudes, suggesting that the daytime emission originates under non-LTE conditions. The spectrally integrated radiances around 3.0 μm shows a monotonically decrease with tangent altitude, and a slight increase with solar zenith angle in the 40-80° interval around 800 km.A sophisticated non-LTE model of HCN energy levels has been developed in order to retrieve the HCN abundance. The population of the HCN 0 00 1 energy level, that contributes mostly to the 3.0 μm limb radiance, has been shown to change significantly with the solar zenith angle (SZA) and HCN abundance. Also its population varies with the collisional rate coefficients, whose uncertainties induced errors in the retrieved HCN of about 10% at 600-800 km and about 5% above. HCN concentrations have been retrieved from a set of spectra profiles, covering a wide range of latitudes and solar zenith angles, by applying a line-by-line inversion code. The results show a significant atmospheric variability above ∼800 km with larger values for weaker solar illumination. The HCN shows a very good correlation with solar zenith angles, irrespective of latitude and local time, suggesting that HCN at these high altitudes is in or close to photochemical equilibrium. A comparison with UVS and UVIS measurements show that these are close to the lower limit (smaller SZAs) of the VIMS observations above 750 km. However, they are in reasonable agreement when combining the rather large UV measurement errors and the atmospheric variability observed in VIMS. A comparison of the mean profile derived here with the widely used profile reported by Yelle and Griffith (Yelle R.V., Griffith, C.A. [2003]. Icarus 166, 107-115) shows a good agreement for altitudes ranging from 850 to 1050 km, while below these altitudes our result exhibits higher concentrations. 相似文献
15.
M. N. Izakov 《Solar System Research》2010,44(6):475-486
The turbulent energy dissipation rate and the coefficients of turbulent diffusion and viscosity caused by breaking buoyancy
waves (BWs) have been calculated. From the comparison of these values with other data, the contribution of BWs to the generation
of turbulence has been determined. The comparison confirms the validity of the turbulence characteristics of the Venusian
troposphere previously calculated from experimental data. 相似文献
16.
A series of telescopes having approximately a 30° half opening angle and responding to neutrons in the energy range 50 MeV to 350 MeV has been flown to the top of the atmosphere on balloons released from an equatorial launching site at Kampala, Uganda, between 1967 and 1969. The aim of the experiment was to attempt to detect solar neutrons during periods of enhanced solar activity. No neutrons of solar origin were detected, but an upper limit of the order of 30 neutrons m–2 s–1 at the Earth has been placed on the continuous solar neutron flux in the above energy range, and a limit of four photons m–2 s–1 has also been placed on the corresponding -ray flux above 80 MeV. Limits have likewise been placed on the total emission from various flares. For a 1B flare the values were 23 × 104 neutrons m–2 and 6 × 104 photons m–2. 相似文献
17.
In this paper the origin and evolution of the Sun's open magnetic flux are considered for single magnetic bipoles as they are transported across the Sun. The effects of magnetic flux transport on the radial field at the surface of the Sun are modeled numerically by developing earlier work by Wang, Sheeley, and Lean (2000). The paper considers how the initial tilt of the bipole axis () and its latitude of emergence affect the variation and magnitude of the surface and open magnetic flux. The amount of open magnetic flux is estimated by constructing potential coronal fields. It is found that the open flux may evolve independently from the surface field for certain ranges of the tilt angle. For a given tilt angle, the lower the latitude of emergence, the higher the magnitude of the surface and open flux at the end of the simulation. In addition, three types of behavior are found for the open flux depending on the initial tilt angle of the bipole axis. When the tilt is such that ge2° the open flux is independent of the surface flux and initially increases before decaying away. In contrast, for tilt angles in the range –16°<<2° the open flux follows the surface flux and continually decays. Finally, for le–16° the open flux first decays and then increases in magnitude towards a second maximum before decaying away. This behavior of the open flux can be explained in terms of two competing effects produced by differential rotation. Firstly, differential rotation may increase or decrease the open flux by rotating the centers of each polarity of the bipole at different rates when the axis has tilt. Secondly, it decreases the open flux by increasing the length of the polarity inversion line where flux cancellation occurs. The results suggest that, in order to reproduce a realistic model of the Sun's open magnetic flux over a solar cycle, it is important to have accurate input data on the latitude of emergence of bipoles along with the variation of their tilt angles as the cycle progresses. 相似文献
18.
A Monte Carlo model designed to compute both the input and output radiation fields from spherical-shell cometary atmospheres has been developed. The code is an improved version of that by H. Salo (1988, Icarus76, 253-269); it includes the computation of the full Stokes vector and can compute both the input fluxes impinging on the nucleus surface and the output radiation. This will have specific applications for the near-nucleus photometry, polarimetry, and imaging data collection planned in the near future from space probes. After carrying out some validation tests of the code, we consider here the effects of including the full 4×4 scattering matrix in the calculations of the radiative flux impinging on cometary nuclei. As input to the code we used realistic phase matrices derived by fitting the observed behavior of the linear polarization as a function of phase angle. The observed single scattering linear polarization phase curves of comets are fairly well represented by a mixture of magnesium-rich olivine particles and small carbonaceous particles. The input matrix of the code is thus given by the phase matrix for olivine as obtained in the laboratory plus a variable scattering fraction phase matrix for absorbing carbonaceous particles. These fractions are 3.5% for Comet Halley and 6% for Comet Hale-Bopp, the comet with the highest percentage of all those observed.The errors in the total input flux impinging on the nucleus surface caused by neglecting polarization are found to be within 10% for the full range of solar zenith angles. Additional tests on the resulting linear polarization of the light emerging from cometary nuclei in near-nucleus observation conditions at a variety of coma optical thicknesses show that the polarization phase curves do not experience any significant changes for optical thicknesses τ?0.25 and Halley-like surface albedo, except near 90° phase angle. 相似文献
19.
The coronal magnetic field (CMF) during Carrington rotation 1870 is inferred by using the so-called 'potential model' with the photospheric magnetic field observed at Kitt Peak. Magnetic field lines starting at areas restricted (90deg; ± 30deg; in longitude and 0deg; ± 20deg; in latitude) in both the photosphere and the source surface of 2.5 solar radii are traced to examine fine geometrical structures of the CMF. We found a well-ordered planar magnetic structure (PMS) near 90° Carrington longitude in the corona. The PMS consists of magnetic flux of negative polarity emanating from several small areas in the photosphere. The magnetic flux expands into a wide longitudinal angle in the source surface making a planar magnetic structure. 相似文献
20.
S. T. Lindgren 《Solar physics》1968,5(3):382-409
McMath plage region 8818 passed over the visible solar disk on May 17–31, 1967. It was very active from its first appearance on the Eastern limb, several times producing bright optical flares and hard X-ray emission, accompanied by intense type II, type IV and centimeter radio bursts. Nevertheless, no solar particles could be detected near the earth until the evening of May 23, when three bright flares were observed in close succession at 25°–28° E. During the following build-up of the solar particle flux over 36 hours, the galactic cosmic ray flux > 1 GeV decreased gradually by about 5%. The flux of solar particles decreased in two steps on May 25, both accompanied by decreases in the equatorial geomagnetic field. These field depressions are attributed to storm plasma ejected from the parent flare of the May 23 particle event. The propagation of solar particles from May 23 on thus appears to be strongly affected by storm plasma from the parent flare of the May 23 event, without any indications of solar particles being trapped in that plasma.A later particle event early on May 28 was also associated with a bright flare in McMath region 8818, at 33° W. This event displayed a rapid build-up, with electrons arriving first, and an exponential decay. A smooth proton peak, 20 min wide, was detected on May 30 closely associated with an SSC attributed to plasma ejection from the parent flare of the May 28 event.Between the geomagnetic storms beginning on May 25 and May 30 an anomalous daily variation was observed in the cosmic ray flux >1 GeV, the time of maximum falling 7–10 hours earlier than normal. Storm time increases in the flux of galactic cosmic rays were seen on May 26 when the equatorial geomagnetic field was depressed by more than 400 . Low latitude auroras were also observed during that time.On leave from the University of Uppsala, Sweden. 相似文献