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101.
Acoustic radiation is the signal of choice for exploring Earth??s oceans. Its potential application for the oceans of icy moons requires investigation. However acoustic technology needs to be treated with care for extra-terrestrial purposes. Instruments, calibrations, and predictive codes that have served well on Earth may require fundamental redesign for use on other worlds. However when such an assessment is achieved, acoustic signals open up the possibility of exploring volumes exceeding one million cubic kilometres in a few minutes. This paper begins at tutorial level for novice acousticians, illustrating the principles by which acoustics can be used to monitor the environment at great distances from the source, both by projecting out signals and by using natural signals of opportunity. It then progresses to calculations for a generic icy moon (which resembles, but does not model Europa), proceeding from tutorial calculations of ??flat world?? models to calculate the propagation times for pulses to circumpropagate around the entire moon. Given that a single emitted pulse can produce multiple arrivals from different propagation paths, the paper discusses how the structure of the received time history can be used to monitor changes in the temperature profile in the ocean, position of the water/ice layer and the asphericity of the moon during orbit. 相似文献
102.
MacQueen R. M. Blankner J. G. Elmore D. F. Lecinski A. R. White O. R. 《Solar physics》1998,182(1):97-105
A new instrument capable of 3-min time resolution full-disk and limb observations in the Hei 1083 nm spectral line has been
in operation at the High Altitude Observatory's Mauna Loa Solar Observatory (MLSO) since April 1996. We discuss instrument
capabilities and performance and present some initial observations of limb activity from the first year of instrument operation.
We compare limb Hei and Hα observations of quiescent and active prominences, comment on the role of Doppler shifts in interpreting
the Hei observations, and illustrate the use of disk/limb Hei observations of a CME-associated eruptive filament in mass-ejection
studies. 相似文献
103.
Petrology and geochemistry of feldspathic impact‐melt breccia Abar al' Uj 012, the first lunar meteorite from Saudi Arabia 下载免费PDF全文
Marianna Mészáros Beda A. Hofmann Pierre Lanari Randy L. Korotev Edwin Gnos Nicolas D. Greber Ingo Leya Richard C. Greenwood A. J. Timothy Jull Khalid Al‐Wagdani Ayman Mahjoub Abdulaziz A. Al‐Solami Siddiq N. Habibullah 《Meteoritics & planetary science》2016,51(10):1830-1848
Abar al' Uj (AaU) 012 is a clast‐rich, vesicular impact‐melt (IM) breccia, composed of lithic and mineral clasts set in a very fine‐grained and well‐crystallized matrix. It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside. Bulk composition (31.0 wt% Al2O3, 3.85 wt% FeO) is close to the mean of feldspathic lunar meteorites and Apollo FAN‐suite rocks. The low concentration of incompatible trace elements (0.39 ppm Th, 0.13 ppm U) reflects the absence of a significant KREEP component. Plagioclase is highly anorthitic with a mean of An96.9Ab3.0Or0.1. Bulk rock Mg# is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 ± 5.2 kyr. AaU 012 contains a ~1.4 × 1.5 mm2 exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias. Bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali‐suite rocks. The IM clast is mainly composed of clinopyroxenes, contains a significant amount of cristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast shows similarities in texture and modal mineral abundances with some Apollo pigeonite basalts, it has lower FeO and higher SiO2 than any mare basalt. It also has higher FeO and lower Al2O3 than rocks from the FAN‐ or Mg‐suite. Its lower Mg# (59) compared to Mg‐suite rocks also excludes a relationship with these types of lunar material. 相似文献
104.
Silva Adriana V.R. Lin R.P. de Pater Imke White Stephen M. Shibasaki K. Nakajima H. 《Solar physics》1998,183(2):389-405
We present a comprehensive analysis of the 17 August 1994 flare, the first flare imaged at millimeter (86 GHz) wavelengths. The temporal evolution of this flare displays a prominent impulsive peak shortly after 01:02 UT, observed in hard X-rays and at microwave frequencies, followed by a gradual decay phase. The gradual phase was also detected at 86 GHz. Soft X-ray images show a compact emitting region (20), which is resolved into two sources: a footpoint and a loop top source. Nonthermal emissions at microwave and hard X-ray wavelengths are analyzed and the accelerated electron spectrum is calculated. This energy spectrum derived from the microwave and hard X-ray observations suggests that these emissions were created by the same electron population. The millimeter emission during the gradual phase is thermal bremsstrahlung originating mostly from the top of the flaring loop. The soft X-rays and the millimeter flux density from the footpoint source are only consistent with the presence of a multi-temperature plasma at the footpoint. 相似文献
105.
Edwin GNOS Silvio LORENZETTI Otto EUGSTER A. J. Timothy JULL Beda A. HOFMANN Ali Al‐KATHIRI Manuel EGGIMANN 《Meteoritics & planetary science》2009,44(3):375-387
Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five 14C measurements on stones of variable size and weathering grade yielded 14C from 3.8 to 49.9 dpm/kg. Three samples give a 14C/ 10Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the 4He and 40Ar gas retention ages of 0.29 ± 0.10 and that of the 3He and 21Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost 4He and 40Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm?3would have been at least 75 cm. 相似文献
106.
107.
108.
M. R. Kundu V. V. Grechnev S. M. White E. J. Schmahl N. S. Meshalkina L. K. Kashapova 《Solar physics》2009,260(1):135-156
We investigate accelerated electron energy spectra for different sources in a large flare using simultaneous observations
obtained with two instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) at hard X-rays. This flare is one of the few in which emission up to energies exceeding 200 keV
can be imaged in hard X-rays. Furthermore, we can investigate the spectra of individual sources up to this energy. We discuss
and compare the HXR and microwave spectra and morphology. Although the event overall appears to correspond to the standard
scenario with magnetic reconnection under an eruptive filament, several of its features do not seem to be consistent with
popular flare models. In particular we find that (1) microwave emissions might be optically thick at high frequencies despite
a low peak frequency in the total flux radio spectrum, presumably due to the inhomogeneity of the emitting source; (2) magnetic
fields in high-frequency radio sources might be stronger than sometimes assumed; (3) sources spread over a very large volume
can show matching evolution in their hard X-ray spectra that may provide a challenge to acceleration models. Our results emphasize
the importance of studies of sunspot-associated flares and total flux measurements of radio bursts in the millimeter range. 相似文献
109.
Calculations of the trapping of heavy noble gases within multiple guest clathrates under Mars-like conditions show that a substantial fraction of the martian Xe, perhaps even the vast majority, could be in clathrates. In addition, the Xe/Kr ratio in the clathrates would probably be much higher than in the atmosphere, so the formation or dissociation of a relatively small amount of clathrate could measurably change the atmospheric ratio. Relatively crude (factor of 2) measurements of the seasonal variability in that ratio by in situ spacecraft would be sensitive to ∼10% of the seasonal atmospheric CO2 variability being a result of clathrates, rather than pure CO2 frost. In addition, sequestration of Xe in clathrates remains a viable mechanism for explaining the variable Xe/Kr ratios seen in different suites of martian meteorites. 相似文献
110.
Building upon our previous work, in which we analyzed smoothed and subsampled velocity data from the Michelson Doppler Imager (MDI), we extend our analysis to unsmoothed, full-resolution MDI data. We also present results from the Helioseismic and Magnetic Imager (HMI), in both full resolution and processed to be a proxy for the low-resolution MDI data. We find that the systematic errors that we saw previously, namely peaks in both the high-latitude rotation rate and the normalized residuals of odd \(a\)-coefficients, are almost entirely absent in the two full-resolution analyses. Furthermore, we find that both systematic errors seem to depend almost entirely on how the input images are apodized, rather than on resolution or smoothing. Using the full-resolution HMI data, we confirm our previous findings regarding the effect of using asymmetric profiles on mode parameters, and also find that they occasionally result in more stable fits. We also confirm our previous findings regarding discrepancies between 360-day and 72-day analyses. We further investigate a six-month period previously seen in \(f\)-mode frequency shifts using the low-resolution datasets, this time accounting for solar-cycle dependence using magnetic-field data. Both HMI and MDI saw prominent six-month signals in the frequency shifts, but we were surprised to discover that the strongest signal at that frequency occurred in the mode coverage for the low-resolution proxy. Finally, a comparison of mode parameters from HMI and MDI shows that the frequencies and \(a\)-coefficients agree closely, encouraging the concatenation of the two datasets. 相似文献