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1.
An analysis of available observations of the April 7, 1968 occultation of BD ?17° 4388 by Neptune yields upper atmosphere temperatures of ～140°K near the 5 × 1014cm?3 level. The temperature structure of the atmosphere at these levels is complicated and nonisothermal. Diurnal temperature variations are certainly less than 10°K and may be absent. The average temperature decreases by less than 15°K between 0° and 55° latitude.  相似文献   

2.
Observations of the April 8, 1976 occultation of ? Gem by Mars made at the Agassiz Station of the Harvard College Observatory have been analyzed to yield temperature profiles of the Martian atmosphere for number densities between 1013 and 1015 cm?3. Pronounced wavelike structure is evident in both immersion and emersion profiles, with a peak-tto-peak variation of up to 50°K and a vertical scale of 20 km.  相似文献   

3.
A stellar occultation by Uranus and its rings was observed on August 15, 1980, from the European Southern Observatory (Chile), at the 3.6-m telescope equipped with an infrared (2.2 μm) photometer. The recording presents the best signal-to-noise ratio obtained since the discovery of the Uranian rings in March 1977. The nine rings were observed, and the profiles of rings α, β, and ? were resolved, the ring α exhibiting a double structure. Strong diffraction peaks are visible in the γ ring profile suggesting an opaque ring with very sharp edges. A broad and faint structure extends outward from the η ring, on a radial scale of about 55 km. Apart from the ring occultations, unexplained sharp and deep events were recorded, and no interpretation is possible until future observations are made. Furthermore, the stellar light curve during the immersion of the star behind the planet provides (via an inversion computation) the temperature profile of the upper atmosphere of Uranus. The temperature is close to 145 ± 10°K at the 3 × 10?2-mbar pressure level and is nearly constant (155 ± 15°K) in the pressure interval from 10?2 to 10?3 mbar. The thermal inversion is as strong as the inversion on Neptune but is located at higher altitudes. This high stratospheric temperature is consistent with the upper limit of the brightness temperature at 8 μm only if CH4 follows its saturation law.  相似文献   

4.
《Icarus》1987,69(3):499-505
The 1 May 1982 occultation of KME 15 by Uranus and its rings was observed at λ = 2.2 μm using the 1.9-m telescope of the Mount Stromlo Observatory. From model fits to the immersion and emersion ring profiles, accurate midtimes for rings 6, 5, 4, α, β, η, γ, σ, and ϵ, and ring widths, equivalent widths, and normal optical depths for all but ring 6 were obtained. The recently discovered ring 1986 U1R is not detectable in the data, setting an upper limit on the product of ring width and normal optical depth of ≤0.4 km at λ = 2.2 μm. From the immersion and emersion atmosphere occultations, vertical temperature profiles were obtained by numerical inversion. Both profiles show mean temperatures near 130°K and a local maximum near the 8-μbar pressure level.  相似文献   

5.
《Icarus》1987,69(1):176-184
The 22 April 1982 stellar occultation of KME 14 by Uranus was observed from Tenerife, Canary Islands, using the Teide Observatory 1.5-m telescope. From model fits to the immersion and emersion ring profiles, we obtained (1) midtimes of the ring events with a typical uncertainty of 0.01 sec; (2) ring widths for rings 4, α, β, γ, δ, and ϵ with a typical uncertainty of a few tenths of a kilometer; and (3) equivalent widths and normal optical depths of all nine rings. The immersion planetary occultation was clouded out, but emersion was successfully observed, and the stratospheric temperature profile was obtained by numerical inversion. The profile shows a temperature maximum near the 8-μbar pressure level, characterized by T(8 μbar) = 141°K and T(8 μbar)–T(13 μbar) = 5°K for the sampled suboccultation latitude of −11°.9. Both the mean temperature and the temperature variations are consistent with the latitude-dependent atmospheric structure found by B. Sicardy et al. (1985, Icarus 64, 88–106) from widely separated observations of the same event.  相似文献   

6.
《Icarus》1987,71(1):91-102
The occultation of KME 17 by Uranus and its rings was observed with the 1.8-m telescope at SAAO through a K filter with an InSb detector on 25 March 1983. Immersion of the nine main rings and the emersion of rings, 5, 4, α, and β were recorded in the nonchopping mode. A diffracted square-well model was fitted to the data, and the midtime, width, and equivalent depth were determined for each profile. The profile model also includes the diameter of the occulted star as a free parameter, and an average of the narrow ring results yields 0.096 ± 0.005 milliarcsec for the angular diameter of KME 17, under the assumption of a fully darkened disk. The immersion and emersion atmospheric events give mean temperatures of 166 ± 15 and 149 ± 15°K within the pressure altitude range 1–10 μbar. Photometry in the JHKL bands for KME 17 and other stars previously occulted by the Uranian rings is presented.  相似文献   

7.
We analyze the angular structure of the 21-cm interstellar neutral hydrogen emission at six and seven declinations in the northern (published previously) and southern polar caps of the Galaxy (Galactic latitudes from ?40° to ?90°), respectively, with an extent of 90° in right ascension. The RATAN-600 radio telescope has a beam width averaged over these regions of 2.′0×30′. One-dimensional power spectra for the angular distribution of interstellar neutral hydrogen emission were computed in each 6.3-km s?1-wide spectral channel by using the standard Fast Fourier Transform (FFT) code and were smoothed over 1h in right ascension. The Galactic latitude dependence of the mean parameters for the sky distribution of H I line emission at high latitudes was found to correspond to the distribution of gas in the form of a flat layer only in the northern region, while in the southern cap, the gas distribution is much less regular. In addition, the mean H I radial velocities are negative everywhere (?3.7±3.0 km s?1 in the north and ?6.0±2.4 km s?1 in the south). The power spectra of the angular fluctuations in the range of angular periods from 10′ to 6° appear as power laws. However, the spectral indices change greatly over the sky: from ?3 to ?1.2; on average, as the Galactic latitude increases and the H I column density decreases, the fluctuation spectrum of the interstellar gas emission becomes flatter. In the northern polar region, this behavior is much more pronounced, which probably stems from the fact that the gas column density in the south is generally a factor of 2 or 3 higher than that in the north. Therefore, the spectra are, on average, also steeper in the south, but the dependence on Galactic latitude is weaker. Using simulations, we show that the observed power-law spectrum of the H I emission distribution can be obtained in terms of not only a turbulent, but also a cloud model of interstellar gas if we use our previous spectra of the diameters and masses of H I clouds.  相似文献   

8.
We present 20-μm photometry of Uranus and Neptune which confirms the presence of a temperature inversion in the lower stratospheres in both planets. We find the brightness temperature difference between 17.8 and 19.6 μm to be 0.8 ± 0.5°K for Uranus and 1.8 ± 0.6°K for Neptune. These results indicate that the temperature inversions on both planets are weaker than previously thought. Comparison to model atmospheres by J. Appleby [Ph.D. thesis, SUNY at Stony Brook 1980] indicates that the temperature inversions can be understood as arising from heating by the absorption of sunlight by CH4 and aerosols. However, the stratospheric CH4 mixing ratio on Neptune must be higher than that at the temperature minimum.  相似文献   

9.
Employing the synoptic maps of the photospheric magnetic fields from the beginning of solar cycle 21 to the end of 23, we first build up a time – longitude stackplot at each latitude between ±35°. On each stackplot there are many tilted magnetic structures clearly reflecting the rotation rates, and we adopt a cross-correlation technique to explore the rotation rates from these tilted structures. Our new method avoids artificially choosing magnetic tracers, and it is convenient for investigating the rotation rates of the positive and negative fields by omitting one kind of field on the stackplots. We have obtained the following results. i) The rotation rates of the positive and negative fields (or the leader and follower polarities, depending on the hemispheres and solar cycles) between latitudes ±35° during solar cycles 21–23 are derived. The reversal times of the leader and follower polarities are usually not consistent with the years of the solar minimum, nevertheless, at latitudes ±16°, the reversal times are almost simultaneous with them. ii) The rotation rates of the three solar cycles averaged over each cycle are calculated separately for the positive, negative and total fields. The latitude profiles of rotation of the positive and negative fields exhibit equatorial symmetries with each other, and those of the total fields lie between them. iii) The differences in rotation rates between the leader and follower polarities are obtained. They are very small near the equator, and increase as latitude increases. In the latitude range of 5° – 20°, these differences reach 0.05 deg day−1, and the mean difference for solar cycle 22 is somewhat smaller than cycles 21 and 23 in these latitude regions. Then, the differences reduce again at latitudes higher than 20°.  相似文献   

10.
We present new measurements of the velocity field in the neighborhood of the high-speed jet located at approx. 24° N latitude in the Jovian atmosphere. The maximum zonal velocity is found to be 182 ± 10 m s?1 located at 23.7 ±0.2° N and representing the largest velocity measured on the planet. The distinctive cloud markings found close to this latitude are discussed and possible dynamical consequences presented.  相似文献   

11.
Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the Earth or the Moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The best determined coefficients of the harmonic expansion of the gravitational potential are: J2 = (1.96 ± 10.01) × 10?3 ; C22 = ?(5.1 ± 0.2) × 10?5; and S22 = (3.4 ± 0.2) × 10?5. The other coefficients have not been well determined on an individual basis, but the ensemble yields a useful model for the gravity field for all longitudes in the vicinity of 23° South latitude which corresponds to the periapse position for the orbiter.The value obtained for the inverse mass of Mars (3 098 720 ± 70 M⊙?1) is in good agreement with prior determinations from Mariner flyby trajectories. The direction found for the rotational pole of Mars, referred to the mean equinox and equator of 1950.0, is characterized by α = 317°.3 ± 0°.2, δ = 52°.7 ± 0°.2. This result is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites, but differs by about 0°.5 from the previously accepted value. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (i) the dynamical flattening, f = (5.24 ± 0.02) × 10?3; (ii) the maximum principal moment of inertia, C = (0.375 ± 0.006) MR2; and (iii) the period of precession of Mars' pole, P ? (1.73 ± 0.03) × 105 yr, corresponding to a rate of 7.4 sec of arc per yr.  相似文献   

12.
During moderate magnetic storms, changes in the neutral composition suggest that energy is deposited in the auroral zones. This results in thermal expansion (enhancement in N2, Ar) and consequent redistribution of the lighter species O and He such that their densities decrease at high latitudes and increase at low latitudes. From measurements obtained by the ESRO 4 gas analyzer during a major storm in late February 1973 (Kp = 7+) these typical high latitude characteristics were observed in the southern hemisphere and at certain longitudes to extend toward mid and low latitudes as far as ?20° invariant latitude. Further examination of these data for latitudes across the equator up to +20° latitude, however, shows evidence for an enhancement zone in He and O which is clearly displaced into the northern hemisphere thus suggesting a pronounced spherical asymmetry. Ground based observations on the state of the ionosphere between ±50° latitude confirm this asymmetry and suggest that the center of this enhancement zone occurs at about +15° invariant latitude. Adopting a suitable energy distribution in both hemispheres the magnetic storm response in the neutral composition is simulated with a circulation model. From this analysis it is concluded that for some longitudes a difference of a factor of two or more between the heating rates of the northern and southern hemispheres is required to match the ESRO-4 data.  相似文献   

13.
《Icarus》1986,67(1):126-133
Stellar occultations by Neptune on 7 and 25 June 1985 were observed in the K band from Sutherland (SAAO) to search for conforming evidence of the ring-like “arc” reported by Hubbard et al. (W.B. Hubbard, A. Brahic, B. Sicardy, L.-R. Elicer, F. Roques, and F. Vilas (1986). Nature 319, 636–640). A binary star was occulted on 7 June 1985, and since both components were occulted by the planet, their relative positions could be precisely determined. A single sharp dip, of high signal-to-noise ratio, was observed in the post-emersion occultation trace. If this feature were caused by material near Neptune, its corresponding projected equatorial plane radius is either 62,600 ± 160 km or 63,760 ± 120 km, depending on which of the binary star pair was occulted. The equatorial radius, width, and optical depth of the 7 June feature are similar to those described by Hubbard et al. The absence of a corresponding post-emersion dip due to the occultation of the companion star suggests that the ring-like material is discontinuous over a scale of several thousand kilometers in ring circumference. No ring-like features were observed during pre-immersion. The 25 June 1985 occultation was also successfully observed, including atmospheric occultation profiles for both immersion and emersion. No evidence for ring-like material was found in the region probed by this occultation during post-emersion, which included the entire range of equatorial radii over which “arc” events have been previously reported.  相似文献   

14.
《Icarus》1987,71(1):159-177
Observations of Mars at wavelengths of 2 and 6 cm were made using the VLA in its A configuration. The season on Mars was late spring in the Northern Hemisphere (Ls = 60°). The sub-Earth latitude was 25°N, so the geometry for viewing the north polar region was optimal. Whole-disk brightness temperatures were estimated to be 193.2 ± 1.0°K at 2 cm and 191.2 ± 0.6°K at 6 cm (formal errors only). Since measurements of the polarized flux were taken at the same time, whole-disk effective dielectric constants could be estimated and from these estimates of subsurface densities could be made. The results of these calculations yielded a whole-disk effective dielectric constant of 2.34 ± 0.05, which implied a subsurface density of 1.24 ± 0.11 g cm−3 at 2 cm. The same calculations at 6 cm yielded an effective density of 1.45 ± 0.10 g cm−3 and dielectric constant of 2.70 ± 0.10. From the mapped data these parameters were also estimated as a function of latitude between latitudes of 15°S and 60°N. In addition to the effective dielectric constant and subsurface density, the radio absorption length of the subsurface was estimated. The radio absorption length for most of these latitudes was about 15 wavelengths with formal errors on the order of 5 or 10 wavelengths. The estimation of the effective dielectric constant at most latitudes was between 2 and 3.5 with only slight differences between the two different wavelengths. These estimates of the dielectric constant lead to estimation of the subsurface densities as a function of latitude. Most calculations of the subsurface density yielded results between 1 and 2 g cm−3 with errors on the order of 0.5 g cm−3. These results seem to imply that the subsurface is not much different than the surface as observed by the Viking and Mariner missions. In line with this, a comparison of the correlation of the dielectric constant at each wavelength with the thermal inertia determined from infrared measurements of the surface temperature shows that the correlation at 2 cm is slightly stronger than the correlation at 6 cm. Since the 2-cm radiation comes from a region closer to the surface than the 6-cm radiation, this decrease in correlation with depth is consistent with the idea that the physical makeup of the subsurface is varying slowly in the near subsurface region.  相似文献   

15.
Two coherently related radio signals transmitted from Voyager 1 at wavelengths of 13 cm (S-band) and 3.6 cm (X-band) were used to probe the equatorial atmosphere of Titan. The measurements were conducted during the occultation of the spacecraft by the satellite on November 12, 1980. An analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of Titan. The resolution was approximately 3 × 103 and 5 × 103 electrons/cm3 near the evening and morning terminators, respectively. Abrupt signal changes observed at ingress and egress indicated a surface radius of 2575.0 ± 0.5 km, leading to a mean density of 1.881 ± 0.002 g cm?3 for the satellite. The nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in Titan's troposphere and stratosphere. No absorption was detected; the resolution was about 0.01 dB/km at the 13-cm wavelength. The gas refractivity data, which extend from the surface to about 200 km altitude, were interpreted in two different ways. In the first, it is assumed that N2 makes up essentially all of the atmosphere, but with very small amounts of CH4 and other hydrocarbons also present. This approach yielded a temperature and pressure at the surface of 94.0 ± 0.7°K and 1496 ± 20 mbar, respectively. The tropopause, which was detected near 42 km altitude, had a temperature of 71.4 ± 0.5°K and a pressure of about 130 mbar. Above the tropopause, the temperature increased with height, reaching 170 ± 15°K near the 200-km level. The maximum temperature lapse rate observed near the surface (1.38 ± 0.10°K/km) corresponds to the adiabatic value expected for a dry N2 atmosphere—indicating that methane saturation did not occur in tbis region. Above the 3.5-km altitude level the lapse rate dropped abruptly to 0.9 ± 0.1°K/km and then decreased slowly with increasing altitude, crossing zero at the tropopause. For the N2 atmospheric model, the lapse rate transition at the 3.5-km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate, and a higher stable region in radiative equilibrium. In the second interpretation of the refractivity data, it is assumed, instead, that the 3.5 km altitude level corresponds to the bottom of a CH4 cloud layer, and that N2 and CH4 are perfectly mixed below this level. These assumptions lead to an atmospheric model which below the clouds contains about 10% CH4 by number density. The temperature near the surface is about 95°K. Arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere.  相似文献   

16.
An analysis of the Mariner 10 dual frequency radio occultation recordings has yielded new information on the radius and atmosphere of Mercury. The ingress measurements which were conducted near 1.1° North latitude and 67.4° East longitude on the night side of the planet, gave a value for the radius of 2439.5 ± 1 km. Egress near 67.6° North latitide and 258.4° East longitude in the sunlit side yielded a radius of 2439.0 ± 1 km. The atmospheric measurements showed the electron density to be less than 103 cm?3 on both sides of the planet. From the latter result one may infer an upper limit to the dayside surface gas density of 106 molecules per cm3.  相似文献   

17.
B.L. Ulich  E.K. Conklin 《Icarus》1976,27(2):183-189
We have measured the 3.33 mm wavelength disk brightness temperatures of Ganymede (136 ± 21°K), Callisto (95 ± 17°K), Ceres (137 ± 25°K), Uranus (125 ± 9°K), and Neptune (126 ± 9°K). Our observations of Ganymede are consistent with the radiation from a blackbody in solar equilibrium, whereas Callisto's microwave spectrum indicates a surface similar to that of the Moon. The disk temperature for Ceres agrees with that expected from a rapidly rotating blackbody. The millimeter temperatures of Uranus and Neptune greatly exceed solar equilibrium values, implying atmospheres with large temperature gradients.  相似文献   

18.
《Icarus》1987,72(3):635-646
The occultation of a bright (K∼6) infrared star by Neptune revealed a central flash at two stations and provided accurate measurements of the limb position at these and several additional stations. We have fitted this data ensemble with a general model of an oblate atmosphere to deduce the oblateness e and equatorial radius a0 of Neptune at the 1-μbar pressure level, and the position angle pn of the projected spin axis. The results are e=0.0209±0.0014, a0=25269±10 km, pn=20.1°±1°. Parameters derived from fitting to the limb data alone are in excellent agreement with parameters derived from fitting to central flash data alone (E. Lellouch, W.B. Hubbard, B. Sicardy, F. Vilas, and P. Bouchet, 1986, Nature 324, 227–231), and the principal remaining source of uncertainty appears to be the Neptune-centered declination of the Earth at the time of occultation. As an alternative to the methane absorption model proposed by Lellouch et al., we explain an observed reduction in the central flash intensity by a decrease in temperature from 150 to 135°K as the pressure rises from 1 to 400 μbar. Implications of the oblateness results for Neptune interior models are briefly discussed.  相似文献   

19.
Nitric oxide is formed in the atmosphere through the ionization and dissociation of molecular nitrogen by galactic cosmic rays. One NO molecule is formed for each ion pair produced by cosmic ray ionization.The height-integrated input (day and night) to the lower stratosphere is of the order of 6 × 107 NO molecules cm?2/sec in the auroral zone (geomagnetic latitude Φ ? 60°) during the minimum of the sunspot cycle and 4 × 107 NO molecules cm?2/sec in the subauroral belt and auroral region (Φ? 45°) at the maximum of solar activity. The tropical production is less than 10?7 NO molecules cm?2/sec above 17 km and at the equator the production is only 3 × 106NO molecules cm?2/sec.  相似文献   

20.
The spectrum of Saturn was measured from 80 to 350 cm?1 (29 to 125 μm) with ≈6-cm?1 resolution using a Michelson interferometer aboard NASA's Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm?1, Saturn's brightness temperature rises slowly, reaching ≈111°K at 100 cm?1. The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH3 that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH3 is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum (ν > 230 cm?1) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν1.5. This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition.  相似文献   

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