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401.
Svetlana S. Kostrova Hanno Meyer Francisco Fernandoy Martin Werner Pavel E. Tarasov 《水文研究》2020,34(1):51-67
The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high-resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope-based palaeoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to −4‰) and δD (up to −40‰) values characterize summer air masses, and lighter isotope composition (−41‰ for δ18O and −322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, and no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p <.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p < 0.01; n = 55) for δD. Secondary fractionation processes (e.g., contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west, that is, the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the European Centre/Hamburg version 5 (ECHAM5)-wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p <.01; n = 55) and air temperature (r2 = 0.99; p <.01; n = 71). However, the ECHAM5-wiso model fails to capture observed variations in d excess (r2 = 0.14; p < 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer. 相似文献
402.
Pavel Spurný Hans Betlem Jaap van't Leven Peter Jenniskens 《Meteoritics & planetary science》2000,35(2):243-249
Abstract— Precise atmospheric trajectories including dynamic and photometric data on thirteen of the brightest Leonid fireballs have been determined from the double‐station photographic observations of Leonid meteors during the ground‐based expedition to China in 1998 November. the expedition was organized as a collaboration between the dutch and chinese academy of sciences and was supported by the leonid multi‐instrument aircraft campaign (mac) program (jenniskens and butow, 1999). All data presented here were taken at Xinglong Observatory and at a remote station, Lin Ting Kou near Beijing, on the night of 1998 November 16/17. At the Xinglong station, photographic cameras were accompanied by an all‐sky television camera equipped with an image intensifier and 15 mm fish‐eye objective in order to obtain precise timings for all observed meteors up to magnitude +2. Whereas beginning heights of photographed meteors are all lower than 130 km, those observed by the all‐sky television system are at ~160 km, and for three brightest events, even > 180 km. Such high beginnings for meteors have never before been observed. We also obtained a precise dynamic single‐body solution for the Leonid meteor 98003, including the ablation coefficient, which is an important material and structural quantity (0.16 s2 km?2). From this and from known photometry, we derived a density of this meteoroid of 0.7 g/cm3. Also, all PE coefficients indicate that these Leonid meteors belonged to the fireball group IIIB, which is typical for the most fragile and weak interplanetary bodies. From a photometric study of the meteor lightcurves, we found two typical shapes of light curves for these Leonid meteors. 相似文献
403.
Pavel SPURNÝ Hans BETLEM Klaas JOBSE Pavel KOTEN Jaap van't LEVEN 《Meteoritics & planetary science》2000,35(5):1109-1115
Abstract— In this paper, we study the extremely high beginning parts of atmospheric trajectories of seven Leonid meteors recorded by sensitive TV systems equipped with image intensifiers up to apparent magnitude +6.5. For all seven cases, we observed comet‐like diffuse structures with sizes on the order of kilometers that developed quickly during the meteoroids' descent through the atmosphere. For the brightest event with a maximum absolute magnitude of ?12.5, we observed an arc similar to a solar protuberance and producing a jet detectable several kilometers sideways from the brightest parts of the meteor head, and moving with a velocity over 100 km/s. These jets are common features for the seven studied meteors. Precise position in trajectory, velocity, and brightness at each point is available for all seven meteors, because of double‐station records on 85 km base‐line. When these meteoroids reached 130 km height, their diffuse structures of the radiation quickly transformed to the usual meteor appearance resembling moving droplets, and meteor trains started to develop. These meteor phenomena above 130 km were not recognized before our observations, and they cannot be explained by standard ablation theory. 相似文献
404.
Alessia M. Rodriguez y Baena Juan Carlos Miquel Pere Masqu Pavel P. Povinec Jerome La Rosa 《Marine Chemistry》2006,100(3-4):269
234Th is a particle-reactive radionuclide widely used to trace biogeochemical oceanic processes occurring over short timescales. During the last few years, small-volume techniques based on the co-precipitation of 234Th with MnO2 coupled with beta-counting have been developed as an alternative to large volume gamma-spectrometric techniques. Here a procedure has been developed to enhance quantitative measurement of 234Th in MnO2 precipitates. The main objectives were to obtain a purified Th fraction for beta-counting and to determine the chemical recovery of 234Th using Th spikes and alpha-spectrometry as an alternative to ICP-MS based methods. Two variations of the procedure are presented. In the first “1 spike” method a 230Th tracer is added to the sample prior to precipitation of MnO2, and UTEVA® extraction chromatography is used to obtain a NdF3(Th) purified source that can be used for both beta-counting of 234Th and alpha-spectrometry of 230Th. In the “2 spike” method a 230Th spike is added and the MnO2(Th) precipitate is directly beta-counted for 234Th and subsequently spiked with 228Th or 229Th prior to UTEVA® purification and alpha-spectrometry. The results confirm the need to process small-volume seawater samples for 234Th measurement in presence of a yield tracer, and show that both the 1 spike and 2 spike methods allow an accurate and precise determination of 234Th (relative percent difference, RPD, between expected and mean measured value < 1%; CV between replicate samples < 3%). Our work also suggests that, although the combined analytical uncertainty on total 234Th measurements accomplished with both versions of the NdF3 procedure is promising (6% for 2-L samples), the precision of the 234Th flux estimation will ultimately depend on the degree of disequilibrium between 234Th and 238U. 相似文献
405.
Astronomy Letters - Globular clusters $$(GCs)$$ are among the oldest stellar systems in the early universe. We present galaxies formed with two different stellar populations, which depend on the... 相似文献
406.
Pavel Voráček 《Astrophysics and Space Science》1983,91(1):5-8
It is shown in this paper that it is possible to relativize the rotative motion of a rigid body in such a manner that, without any other than apparent kinematic superluminal velocities, an explanation can be given of the origin of the centrifugal, Coriolis and Euler forces, which is completely consistent with Mach's principle. 相似文献
407.
František Jiříček Pavel Tříska O. A. Maltseva E. E. Titova T. A. Yakhnina Reviewer S. Fischer 《Studia Geophysica et Geodaetica》1986,30(4):404-410
Summary The occurrence zone of the VLF chorus in the upper ionosphere appears at L-shells lower than plasmapause position Lpp; with increasing geomagnetic activity the spatial dimension of the zone diminishes, its upper boundary being shifted in correspondence with the plasmapause position, the lower remaining practically without change(L=2.0÷2.5). Calculations of propagation paths have shown that the similarity of the VLF chorus spectrum at different upper-ionospheric latitudes as well as the large spatial dimension of the zone of observation can be explained as special features in the propagation of VLF waves from an equatorial source, starting in the vicinity of the plasmapause with different initial normal angles.
a umauu u ana amu L-, u Lpp (Lpp — nu nana); uu aum amumu nmam a am, nu aua am mmmuu uu nu nana, a u mam namuu u(L=2.0÷2.5). am mamu naam, m n¶rt;u nm a au uma u, ma a nmam ama a¶rt;u, m m mu anmau m amua umua, an amu nana, uu au au.相似文献
408.
E. D. Poezd V. N. Oraevskij Vladimír Fiala Pavel Tříska Reviewer S. Fischer 《Studia Geophysica et Geodaetica》1987,31(2):197-212
Summary The conditions are studied under which ballistic effects of transmission of waves through opacity barriers can be observed in magnetospheric experiments on board satellites. The mechanism of this effect consists of the regeneration of the radiation beyond the barrier by resonance electrons, modulated by a quasimonochromatic wave incident and reflected from the barrier. Ballistic processes in continuously inhomogeneous plasma are studied. Detailed analysis has been carried out for a barrier with a parabolic density profile. Recommendations are presented as to experimental procedures in circumterrestrial space and data processing. The possibilities are studied of observing ballistic effects in the course of active space experiments with sources of intensive broadband turbulence such as beam of charged particles, injected into the magnetosphere.
¶rt;a u, nu m ¶rt; nmu num aum na m a¶rt;am aumuu m n¶rt;u a namu, au m mum auu uu a a au mau, n¶rt;uau auamu , na¶rt;a a a u maa m . am aumuu n na¶rt;¶rt; na. ma u n¶rt; ¶rt; aa naauu nu nmmu. a ¶rt;auu n n¶rt;u numa nmam u n am ¶rt;a. ¶rt;am m a¶rt;u aumuu m ¶rt; amu uu num umuau umu un mmmu, mauu, a nu a amu umu aum.相似文献
409.
Jaroslava Bošková František Jiříček Pavel Tříska Reviewer S. Fischer 《Studia Geophysica et Geodaetica》1982,26(4):373-380
un nmu a ¶rt;u ¶rt;am ¶rt; mm u a uuuu¶rt; a () a na. m nm, u , ¶rt;um a amm mmu nmua a m m na ¶rt; mum uaum um (2uamm m fH u na amm m fN. uam mm n au ¶rt; amm , ¶rt;mum amu¶rt; f
N
2
f
H
2
u f
H
2
f
N
2
. a m a n¶rt;um umnmau aamumu auauu amm n u nmu a¶rt;u. 相似文献
410.
Summary The stability of steady states, the evolution of the magnetic field and possible changes of the magnetic field under small changes of velocity are studied on a non-stationary solution of a kinematic dynamo model. 相似文献