首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 327 毫秒
1.
Long-term MGS drag density observations at 390 km reveal variations of the density with season LS (by a factor of 2) and solar activity index F10.7 (by a factor of 3 for F10.7 = 40-100). According to Forbes et al. (Forbes, J.M., Lemoine, F.G., Bruinsma, S.L., Smith, M.D., Zhang, X. [2008]. Geophys. Res. Lett. 35, L01201, doi:10.1029/2007GL031904), the variation with F10.7 reflects variations of the exospheric temperature from 192 to 284 K. However, the derived temperature range corresponds to variation of the density at 390 km by a factor of 8, far above the observed factor of 3. The recent thermospheric GCMs agree with the derived temperatures but do not prove their adequacy to the MGS densities at 390 km. A model used by Forbes et al. neglects effects of eddy diffusion, chemistry and escape on species densities above 138 km. We have made a 1D-model of neutral and ion composition at 80-400 km that treats selfconsistently chemistry and transport of species with F10.7, T∞, and [CO2]80 km as input parameters. Applying this model to the MGS densities at 390 km, we find variation of T∞ from 240 to 280 K for F10.7 = 40 and 100, respectively. The results are compared with other observations and models. Temperatures from some observations and the latest models disagree with the MGS densities at low and mean solar activity. Linear fits to the exospheric temperatures are T∞ = 122 + 2.17F10.7 for the observations, T∞ = 131 + 1.46F10.7 for the latest models, and T∞ = 233 + 0.54F10.7 for the MGS densities at 390 km. Maybe the observed MGS densities are overestimated near solar minimum when they are low and difficult to measure. Seasonal variations of Mars’ thermosphere corrected for the varying heliocentric distance are mostly due to the density variations in the lower and middle atmosphere and weakly affect thermospheric temperature. Nonthermal escape processes for H, D, H2, HD, and He are calculated for the solar minimum and maximum conditions.Another problem considered here refers to Mars global photochemistry in the lower and middle atmosphere. The models gave too low abundances of CO, smaller by an order of magnitude than those observed. Our current work shows that modifications in the boundary conditions proposed by Zahnle et al. (Zahnle, K., Haberle, R.M., Catling, D.C., Kasting, J.F. [2008]. J. Geophys. Res. 113, E11004, doi:10.1029/2008JE003160) are reasonable but do not help to solve the problem.  相似文献   

2.
The correlation coefficients of the linear regression of six solar indices versus 10.7 cm radio flux F 10.7 were analysed in solar cycles 21, 22 and 23. We also analysed the interconnection between these indices and F 10.7 with help of approximation by polynomials of second order. The indices we have studied in this paper are: the relative sunspot numbers – SSN, 530.3 nm coronal line flux – F 530, the total solar irradiance – TSI, Mg II 280 nm core-to-wing ratio UV-index, the Flare Index – FI and the counts of flares. In most cases the regressions of these solar indices vs. F 10.7 are close to the linear regression except the moments of time near the minimums and maximums of the 11-year activity. For the linear regressions, we found that correlation coefficients K corr(t) for the solar indices vs. F 10.7 and SSN dropped to their minimum values twice during each 11-year cycle.  相似文献   

3.
Nonthermal emission occurs in the cores of the 9.4- and 10.4-μm CO2 bands on Mars, and has been recently identified as a natural atmospheric laser. This paper presents observations of the total flux and center-to-limb dependence of this emission for Mars and Venus. The emission is believed to be excited by absorption of solar flux in the near-ir CO2 bands, followed by collisional transfer to the 00°1 state of CO2. A comparison is made between the observations and a detailed theoretical model based on this mechanism. It is found that the theoretical model successfully reproduces the observed center-to-limb dependence of this emission, to within the limits imposed by the spatial resolution of the observations. A comparison is also made between the observed fluxes and the predictions of the theoretical models. The observed flux from Mars agrees closely with the prediction of the model; the flux observed from Venus is 74% of the flux predicted by the model. This emission is utilized to obtain the kinetic temperatures of the Martian and Venusian mesospheres. For Mars near 70 km altitude, a rotational temperature analysis using five lines gives T = 135 ± 20°K. The frequency width of the emission is also analyzed to derive a temperature of 126 ± 6°K. In the case of the Venusian mesosphere near 109 km, the frequency width of the emission gives T = 204 ± 10°K.  相似文献   

4.
Slitless spectrograms obtained during the eclipse of 10 June 1972 have been analyzed to determine the height distribution of the D3 He line intensity.For undisturbed regions the maximum of D3 line intensity is confirmed to exist at about 1700km above the limb. Besides the above mentioned maximum, in plages a considerable intensity may be observed at low heights (h < 1000 km).An analysis of these observations for h > 1000 km has been carried out within the low temperature mechanism of triplet helium emission taking into account the helium ionization by XUV radiation. The density dependence of the 23 S level population at different XUV flux values has been calculated. Our observations give N e 2 × 1010 cm–3 in the chromosphere at h = 2000 km. The probable coincidence of the H and He emission small filaments in the middle chromosphere is discussed.  相似文献   

5.
Analysis of observed spectrograms is based on comparison with synthetic spectra. The O2(b1Σ+g?X3Σ?g Atm. (1,1) band in high latitude auroras observed from the ground is found to be the strongest in the Δv = 0 sequence. It is enhanced with altitude relative to the N2 1P(2, 0)and N+2 M(2,0) bands, but the O2 Atm. (2, 2) band has an unexpected low intensity. The range of rotational temperatures of the O2 Atm. bands varies from approx. 200 to above 500 K which indicates that the altitude of the centroid of the emission region varies from about 100 km to the F-region. The highest temperature is found in the midday aurora associated with the magnetospheric cusp. Conspicuous relative variations between the intensities of N2 and O2 spectra are documented, but a satisfactory explanation of the variety is not given. Deviations of the observed O2 Atm. band intensities from the vibrational intensity distribution predicted by Franck-Condor factors indicate that the excitation of the O2 Atm. bands in aurora is not mainly due to particle impact on O2, and the contribution due to energy transfer from hot O(1D) atoms has to be found in future research.  相似文献   

6.
Additional analysis of the behavior of the international sunspot number (R) series and the solar radio flux density (F10.7 cm) series during two long (250–500 days) and distinct episodes of persistent ≈13-day variations (Crane, Solar Phys. 1998, 253, 177) is reported. The conclusion is that while the center-to-limb behavior of R does not change between solar minimum and solar maximum, F10.7 cm exhibits significantly less limb brightening at solar maximum than at solar minimum.  相似文献   

7.
Venus nightglow was observed at NASA IRTF using a high-resolution long-slit spectrograph CSHELL at LT = 21:30 and 4:00 on Venus. Variations of the O2 airglow at 1.27 μm and its rotational temperature are extracted from the observed spectra. The mean O2 nightglow is 0.57 MR at 21:30 at 35°S-35°N, and the temperature increases from 171 K near the equator to ∼200 K at ±35°. We have found a narrow window that covers the OH (1-0) P1(4.5) and (2-1) Q1(1.5) airglow lines. The detected line intensities are converted into the (1-0) and (2-1) band intensities of 7.2 ± 1.8 kR and <1.4 kR at 21:30 and 15.5 ± 2 kR and 4.7 ± 1 kR at 4:00. The f-component of the (1-0) P1(4.5) line has not been detected in either observation, possibly because of resonance quenching in CO2. The observed Earth’s OH (1-0) and (2-1) bands were 400 and 90 kR at 19:30 and 250 and 65 kR at 9:40, respectively. A photochemical model for the nighttime atmosphere at 80-130 km has been made. The model involves 61 reactions of 24 species, including odd hydrogen and chlorine chemistries, with fluxes of O, N, and H at 130 km as input parameters. To fit the OH vibrational distribution observed by VEX, quenching of OH (v > 3) in CO2 only to v ? 2 is assumed. According to the model, the nightside-mean O2 emission of 0.52 MR from the VEX and our observations requires an O flux of 2.9 × 1012 cm−2 s−1 which is 45% of the dayside production above 80 km. This makes questionable the nightside-mean O2 intensities of ∼1 MR from some observations. Bright nightglow patches are not ruled out; however, the mean nightglow is ∼0.5 MR as observed by VEX and supported by the model. The NO nightglow of 425 R needs an N flux of 1.2 × 109 cm−2 s−1, which is close to that from VTGCM at solar minimum. However, the dayside supply of N at solar maximum is half that required to explain the NO nightglow in the PV observations. The limited data on the OH nightglow variations from the VEX and our observations are in reasonable agreement with the model. The calculated intensities and peak altitudes of the O2, NO, and OH nightglow agree with the observations. Relationships for the nightglow intensities as functions of the O, N, and H fluxes are derived.  相似文献   

8.
The fractional convective flux πF c (x c /πF) is computed for the effective level x c = logτ c = 0.125, using bi-dimensional co-spectra for relative continuum-brightness fluctuations ΔI and radial velocity fluctuations ΔV measured for the C i 5052.16 spectral line. A more uncertain flux for x Fe ≈ - 0.9 is obtained for the Fe i 5049.83 line. Since the results (Figure 1) incorporate current uncertainties in RMS ΔI , RMS ΔV and RMS ΔT (x), where ΔT are photospheric temperature fluctuations, they must be considered qualitative until these uncertainties are appreciably reduced. The requirement that the fractional convective flux < 1, places restrictions on these uncertainties which suggest that current RMS ΔT (x)'s are too large. The results confirm the importance of overshoot at the top of the solar hydrogen convection zone and suggest a non-negligible fractional convective flux throughout the lower photosphere. Qualitatively, they do not agree with the predictions of the generally-used, local, mixing-length theory or those of Parsons' (1969) modified mixing-length theory. However, qualitative agreement with the predictions of the non-local, generalized mixing-length theory of Spiegel (1963) and with the non-local theory of Ulrich (1970) cannot be considered as observational confirmation of these theories.  相似文献   

9.
The relations between variations of far UV (FUV) emission in 115–210 nm waveband and L 121.6 nm and F10.7 are studied. The changes of FUV flux are found to lag changes of F10.7 - as a rule for 1 day. It is shown that such a difference may be caused by two factors: 1) differences between the rates of decrease of local sources' (active regions) brightness in FUV and 10.7 cm; 2) differences between limb-darkening curves for different wavelengths. One may expect the fluxes at different wavelengths to exhibit phase shifts of one relative to another. Cross-correlation analysis reveals no time-delay between emission fluxes within the FUV waveband, in spite of different laws for limb-brightening (darkening) for different spectral intervals. The absence of a phase delay can be caused by relatively small contribution of active regions to the flux of the whole Sun at these wavelengths. Thus the Lyman-alpha line intensity variation reflects variations of Solar FUV emission more precisely than F10.7. Therefore, using the L intensity for flux intensity calculations of other FUV wavelengths is preferable to using the F10.7 index.  相似文献   

10.
Hypervelocity microparticle impact experiments were performed with a 2 MV Van De Graaff dust accelerator. From measurements of the light intensity I and the total light energy E, the relations I=c1mv4.1 and E=c2mv3.2 were obtained, where m is the projectile mass, ν the projectile velocity and c1,c2 are constants, depending on projectile and target material. Using the measured values of the spectral distribution of the light emitted during impact, the temperature of the radiating material was estimated to be between 2500 and 5000 K depending on the projectile velocity. From an analysis of these measurements the angular distribution of secondary particle velocities as well as the relative mass distribution of these particles was determined. Approximately 90% of the detected ejecta mass (ν?1 km/sec) is found between 50° and 70° ejection angle. For ejection angles smaller than 20°, ejecta velocities of up to 30 km/sec were detected when the primary particle velocity was 4.8 km/sec. Using the dependence of the light intensity on pressure in the target chamber, an estimate of the total amount of material vaporized during impact could be derived. It was concluded that at 7.4 km/sec particle impact velocity at least 1.6% of the displaced projectile and crater material was vaporized.  相似文献   

11.
Calculations using a wide range of model ionospheres (with a peak at 300 km) show that the integrated electron content up to the height of the satellite could be up to four times the value deduced from Faraday rotation measurements. However, using a fixed mean field height of 400 km, the observed Faraday rotation gives the electron content up to a height hF of 2000 km with an accuracy of ±3 per cent. For observations at different magnetic and geographic latitudes, and geostationary satellites at different longitudes, the optimum value of hF varies by only ±200 km. Night-time increases in the height of the ionosphere have little effect on hF, but increase the mean field height to about 470 km. Using a fixed value of 420 km, with hF = 2000 km, gives an accuracy of ±5 per cent under most conditions.  相似文献   

12.
The study of the variation of equivalent width in a Rayleighscattering planetary atmosphere along the intensity equator and along the mirror meridian on whichμ =μ 0 shows that the equivalent widths decrease monotonically towards the poles, the limb and the terminator with the following characteristics: (i) the weakest lines exhibit the maximum change; (ii) theI e r component shows more change than theI e r component; (iii) the decrease towards the limb or the terminator is not as sharp as that towards the poles; (iv)I e r component shows more decrease towards the limb whileI e r component shows more decrease towards the terminator; and (v) the relationW (μ, φ;μ 0,φ 0)= W (μ 0,φ 0;μ, φ) holds for the total intensity. These results are qualitatively in agreement with the observations of absorption bands in the spectra of Venus, Jupiter and Saturn.  相似文献   

13.
The photometric UBV observations of AS 338 that we began after its outburst in 1983 are presented. They were accompanied by yearly spectroscopic observations and by occasional estimations of the star’s infrared JHKL magnitudes. In June 1993, the star’s optical spectrum was extended to the ultraviolet via IUE observations of AS 338. Collectively, the above observations make it possible to trace the evolution of stellar activity over a period of 15 years in various spectral ranges. In particular, a short-time return of the hot component of AS 338 to the state when He II lines reappeared in the star’s spectrum was noted in 1993. At this time, a blend of the C IV λλ5802 and 5812 lines, which is typical of Wolf-Rayet spectra, was detected in it. In June 1993, the temperature of the hot component was T h ≈ 8.8 × 104 K, and the ratio of its bolometric flux to that of the red giant was F h, bol/F g, bol ≈ 1.0. In August, its temperature increased to ～1.0×105 K, while the bolometric flux dropped by a factor of ～1.5(F h, bol/F g, bol ≈ 0.7). In the B-V, U diagram, the points referring to this so-called quiescent state form a separate group shifted in B-V from all the remaining ones located in a horizontal strip with $\Delta U \approx 3\mathop .\limits^m 5$ and $\Delta (B - V) \approx 0\mathop .\limits^m 4$ . This allows us to diagnose the state of the hot component without spectroscopic observations of the star. In October 1993, the hot component flared up again. The main brightness rise took no more than 19 days. The outburst occurred shortly before eclipse egress of the hot component, whose duration was ～0.01P orb. In December 1993, F h, bol/F g, bol≤1.5 at maximum light. During the recurrent, even stronger outburst in April 1995, F h, bol/F g, bol≤3.4. The Hαline during outbursts has a P Cyg profile and broad wings stretching to velocities of ±1500 km s?1. The color temperature of the active hot component at short optical wavelengths and in the ultraviolet lies in the range of effective temperatures for hot supergiants. Nevertheless, it always produces an H II region in the circumstellar envelope that is larger in size than this binary system.  相似文献   

14.
The impact light flash produced by electrostatically accelerated iron particles with diameters meters ranging from 5 to 0.05 μm and velocities lying between 1 km/sec and 30 km/sec has been investigated by means of photomultipliers. As target materials mainly gold and tungsten were used. The pulse of the multiplier was registered directly and after electronic integration. The pulse height of the multiplier signal, the amplitude of the integrated signal as well as its rise time were found to be unique functions of the mass and velocity of the impacting particle. For the pulse height of the differential signal the relation I = c1 × m1.25 × v5 was obtained, and for the integrated signal the relation I = c2 × m1.25 × v3.8, with only c1 and C2 depending on the target material. The rise time of the integrated signal follows the relation T = 2.2 × 102 × v?0.4 using gold as target, and in the case of tungsten material follows the relation T = 9.8 × 102 × v?1.2, where v is expressed in km/sec and T in μsec. Using the spectral distribution of the light intensity, measured by means of calibrated photomultipliers, the total amount of light energy emitted in the visible range could be calculated. As a result we obtained that for v = 4 km/sec and m = 10?11 g about 3 × 10?4 of the kinetic energy of the particle was converted into light energy. The variation of the impact flash intensity with the target material and the measured spectral distribution allowed the temperature of the crater after the impact to be estimated as between 2000 and 3000 K.  相似文献   

15.
Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m?2 for H >; 43 km and ～45 W m?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω0, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω0) is <10?3 for 0.49 and 0.7 μm. The parameter (1 ? ω0) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω0) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10?8 normalized to S2 molecules is the absorber. The upper limits of the mixing ratio for Cl2, Br2, and NO2 are 4 × 10?8, 2 × 10?11, and 4 × 10?10, respectively. The CO2 and H2O bands are confidently identified in the observed spectra. The mean value of the H2O mixing ratio is 3 × 10?5 < FH2O < 10?4 in the undercloud atmosphere. The H2O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from FH2O = 2 × 10?5 near the surface to a 10 to 20 times higher value in the clouds.  相似文献   

16.
H. C. Spruit 《Solar physics》1976,50(2):269-295
  相似文献   

17.
《Planetary and Space Science》1987,35(10):1317-1321
In this study a method is outlined which is capable of giving neutral temperatures and height changes in the aurora when the molecular emissions originate from the E-region.Absolute spectrometric measurements of N2+ 1NG and O2+ 1NG bands and the auroral green line are performed in a nightside aurora. Rotational temperatures and band intensities are deduced by a least-squares fit of synthetic spectra to observations. There is a close correlation between the variations in rotational temperatures and the relative intensity ratio of N2+ 1NG(0,3) and O2+ 1NG(1,0) bands. The change in the relative intensity ratio is similar to the intensity variation predicted by the changing N2 and O2 densities from 120 to 150 km, obtained from the MSIS 83 model atmosphere, and the derived neutral temperature variations are consistent with a similar change in emission height of the aurora. Therefore the changing temperature is most likely due to a changing emission height of the aurora, and no local heating can be inferred.  相似文献   

18.
We have studied the excitation of the Cameron bands of carbon monoxide (a3π → X1Σ+) by electron impact on CO and CO2. This investigation was prompted by a recent study of the Martian airglow by Conway (1981) who concluded that the cross section for the dissociative excitation of the Cameron bands is seven times larger than the laboratory value reported by Ajello (1971a) and by a perplexing inconsistency between the optical cross section and CO(a3π) time-of-flight experiments. We have found now that three factors have contributed to these discrepancies: (1) spectral contamination of the (1,4) Cameron band used by Ajello to normalize the entire Cameron band cross section, (2) major revisions in the magnitude of the CO(a3π) radiative lifetime, and (3) new insights into the effects of the CO(a3π) velocity distribution on the field of view of the emission experiments. The new results largely reconcile the TOF and emission measurements, but they also suggest that the calculated photoelectron fluxes in the Martian atmosphere may be too large by a factor of 3.  相似文献   

19.
We observed a cluster of extremely bright penumbral grains located at the inner limb‐side penumbra of the leading sunspot in active region NOAA 10892. The penumbral grains in the cluster showed a typical peak intensity of 1.58 times the intensity I0 of the granulation surrounding the sunspot. The brightest specimen even reached values of 1.8–2.0 I0, thus, exceeding the temperatures of the brightest granules in the immediate surroundings of the sunspot. We find that the observed sample of extremely bright penumbral grains is an intermittent phenomenon, that disappears on time scales of hours. Horizontal flow maps indicating proper motions reveal that the cluster leaves a distinct imprint on the penumbral flow field. We find that the divergence line co‐located with the cluster is displaced from the middle penumbra closer towards the umbra and that the radial outflow velocities are significantly increased to speeds in excess of 2 km s–1. The extremely bright penumbral grains, which are located at the inner limb‐side penumbra, are also discernible in offband Hα images down to Hα ± 0.045 nm. We interpret the observations in the context of the moving flux tube model arguing that hotter than normal material is rapidly ascending along the inner footpoint of the embedded flux tube, i.e., the ascending hot material is the cause of the extremely bright penumbral grains. This study is based on speckle‐reconstructed broad‐band images taken at 600 nm and chromospheric Hα observations obtained with two‐dimensional spectroscopy. All data were taken with adaptive optics under very good seeing conditions at the Dunn Solar Telescope, National Solar Observatory/Sacramento Peak, New Mexico on 2006 June 10. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
We present radiometrically calibrated spectrophotometric images of Mars taken at the NASA Infrared Telescope Facility (IRTF) near and during the 1995 and 1999 oppositions. Absolute intensity and radiance factor (rF = I/F) values have been calculated for approximately 95% of the surface over all longitudes between −70° to 90° latitude in the 1.5- to 4.1-μm spectral region at a spectral resolution (Δλ/λ) of 1.5%. Values of radiance factor range from rF = 0.4 to 0.6 at 2.2 μm for the bright regions such as Moab and Arabia to rF = 0.12 to 0.3 at 2.2 μm around the dark regions Syrtis Major and Acidalia Planitia. Variations are seen due to seasonal dust and/or condensate cloud cover and viewing geometry. Our results are generally consistent with the few reported previous radiance factor determinations for Mars. These data are unique among ground-based data in their relatively high spatial resolution (?200 km/pixel at the sub-Earth point) and coverage combined with their spectral resolution and coverage. These radiometrically calibrated observations can be used as input to studies focusing on spectral unmixing of surface and atmospheric components, radiative transfer modeling of disk and limb radiances, and photometric modeling of the martian phase function.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号