共查询到20条相似文献,搜索用时 62 毫秒
1.
Jinghong Liu Yibin Yao Jizhang Sang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):402-412
The Global Positioning System (GPS) has been applied in meteorology to monitor the change of Precipitable Water Vapor (PWV) in atmosphere, transformed from Zenith Wet Delay (ZWD). A key factor in converting the ZWD into the PWV is the weighted mean temperature (), which has a direct impact on the accuracy of the transformation. A number of Bevis-type models, like and type models, have been developed by statistics approaches, and are not able to clearly depict the relationship between and the surface temperature, . A new model for , called weighted mean temperature norm model (abbreviated as norm model), is derived as a function of , the lapse rate of temperature, δ, the tropopause height, , and the radiosonde station height, . It is found that is better related to through an intermediate temperature. The small effects of lapse rate can be ignored and the tropopause height be obtained from an empirical model. Then the norm model is reduced to a simplified form, which causes fewer loss of accuracy and needs two inputs, and . In site-specific fittings, the norm model performs much better, with RMS values reduced averagely by 0.45 K and the Mean of Absolute Differences (MAD) values by 0.2 K. The norm model is also found more appropriate than the linear models to fit in a large area, not only with the RMS value reduced from 4.3 K to 3.80 K, correlation coefficient increased from 0.84 to 0.88, and MAD decreased from 3.24 K to 2.90 K, but also with the distribution of simplified model values to be more reasonable. The RMS and MAD values of the differences between reference and computed PWVs are reduced by on average 16.3% and 14.27%, respectively, when using the new norm models instead of the linear model. 相似文献
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Manuel Arriagada Carolina Cipagauta Alberto Foppiano 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
A simple semi-empirical model to determine the maximum electron concentration in the ionosphere (NmF2) for South American locations is used to calculate NmF2 for a northern hemisphere station in the same longitude sector. NmF2 is determined as the sum of two terms, one related to photochemical and diffusive processes and the other one to transport mechanisms. The model gives diurnal variations of NmF2 representative for winter, summer and equinox conditions, during intervals of high and low solar activity. Model NmF2 results are compared with ionosonde observations made at Toluca-México (19.3°N; 260°E). Differences between model results and observations are similar to those corresponding to comparisons with South American observations. It seems that further improvement of the model could be made by refining the latitude dependencies of coefficients used for the transport term. 相似文献
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A.P. Kropotkin V.I. Domrin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Dynamics of the magnetotail involves elementary processes of magnetic field merging (reconnection layer formation) occurring on medium spatial scales. Every such process features two different stages, a fast one and a subsequent slower one. The corresponding short time scale T1 is associated with disturbances propagating in the tail lobes. The longer time scale T2 is associated with plasma motions in the plasma sheet. A disturbance appearing in the magnetotail on the time scale T1 results in a loss of equilibrium in the plasma sheet. By means of theoretical argument and numerical simulation, it is shown that the relaxation process which follows on the time scale T2, produces extremely thin embedded current sheets, along with generation of fast plasma flows. The process provides an effective mechanism for transformation of magnetic energy accumulated in the magnetotail, into energy of plasma flows. The fast flows may drive turbulent motions on shorter spatial scales. In their turn, those motions can locally produce very thin current sheets; after that, nonlinear tearing process leads to generation of neutral lines, and reconnection. The latter produces new fast disturbances on the time scale T1 closing the feedback loop. 相似文献
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W.F. El-Taibany A.A. Mamun Kh.H. El-Shorbagy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Nonlinear propagation of fast and slow magnetosonic perturbation modes in an ultra-cold, degenerate (extremely dense) electron–positron (EP) plasma (containing non-relativistic, ultra-cold, degenerate electron and positron fluids) has been investigated by the reductive perturbation method. It is shown that due to the property of being equal mass of the plasma species (me=mp, where me and mp are electron and positron mass, respectively), the degenerate EP plasma system supports the K-dV solitons which are associated with either fast or slow magnetosonic perturbation modes. It is also found that the basic features of the electromagnetic solitary structures, which are found to exist in such a degenerate EP plasma, are significantly modified by the effects of degenerate electron and positron pressures. The applications of the results in an EP plasma medium, which occurs in compact astrophysical objects, particularly in white dwarfs, have been briefly discussed. 相似文献
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Fridrich Valach Josef Bochníček Pavel Hejda Miloš Revallo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The paper deals with the relation of the southern orientation of the north–south component Bz of the interplanetary magnetic field to geomagnetic activity (GA) and subsequently a method is suggested of using the found facts to forecast potentially dangerous high GA. We have found that on a day with very high GA hourly averages of Bz with a negative sign occur at least 16 times in typical cases. Since it is very difficult to estimate the orientation of Bz in the immediate vicinity of the Earth one day or even a few days in advance, we have suggested using a neural-network model, which assumes the worse of the possibilities to forecast the danger of high GA – the dominant southern orientation of the interplanetary magnetic field. The input quantities of the proposed model were information about X-ray flares, type II and IV radio bursts as well as information about coronal mass ejections (CME). In comparing the GA forecasts with observations, we obtain values of the Hanssen–Kuiper skill score ranging from 0.463 to 0.727, which are usual values for similar forecasts of space weather. The proposed model provides forecasts of potentially dangerous high geomagnetic activity should the interplanetary CME (ICME), the originator of geomagnetic storms, hit the Earth under the most unfavorable configuration of cosmic magnetic fields. We cannot know in advance whether the unfavorable configuration is going to occur or not; we just know that it will occur with the probability of 31%. 相似文献
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Emirant Bertillas Amabayo Jurua Edward Pierre J. Cilliers John Bosco Habarulema 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
This study presents results on the investigation of the diurnal, monthly and seasonal variability of Total Electron Content (TEC), phase (σΦ) and amplitude (S4) scintillation indices over Ugandan (Low latitude) region. Scintillation Network Decision Aid (SCINDA) data was obtained from Makerere (0.34°N, 32.57°E) station, Uganda for two years (2011 and 2012). Data from two dual frequency GPS receivers at Mbarara (0.60°S, 30.74°E) and Entebbe (0.04°N, 32.44°E) was used to study TEC climatology during the same period of scintillation study. The results show that peak TEC values were recorded during the months of October–November, and the lowest values during the months of July–August. The diurnal peak of TEC occurs between 10:00 and 14:00 UT hours. Seasonally, the ascending and descending phases of TEC were observed during the equinoxes (March and September) and solstice (June and December), respectively. The scintillations observed during the study were classified as weak (0.1≤S4,σΦ≤0.3) and strong (0.3<S4,σΦ≤1.0). The diurnal scintillation pattern showed peaks between 17:00 and 22:00 UT hour, while the seasonal pattern follows the TEC pattern mentioned above. Amplitude scintillation was more dominant than phase scintillation during the two years of the study. Scintillation peaks occur during the months of March–April and September–October, while the least scintillations occur during the months of June–July. Therefore, the contribution of this study is filling the gap in the current documentation of amplitude scintillation without phase scintillation over the Ugandan region. The scintillations observed have been attributed to wave-like structures which have periods of about 2–3 h, in the range of that of large scale travelling ionospheric disturbances (LSTIDs). 相似文献
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WenBin Shen Jinsheng Ning Dingbo Chao Jinnan Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We propose a test of the gravitational time dilation in general relativity by long term clock comparison between two stations separated in height. The geopotential difference between the two National time keeping centers in China, Lintong (A) and Beijing (B) is around 4000 geopotential unit, which corresponds to the height difference of 400 m. Two clocks CA and CB are fixed at stations A and B, respectively, which are synchronized at beginning by a portable clock C in a short time period with go-back synchronization approach. After one month, the clock C is again transported between A and B , comparing the records of the keeping time by clocks CA and CB, respectively. Calculations show that, after one month, the difference of the time durations between the clocks CA and CB is around 121 ns, if general relativity is correct. 相似文献
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L.H. Chao W.H. Bian K.L. Huang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Using the bulge data from AGN image decomposition with ground-based observations, we calculate the ratios of the central supermassive black hole mass(SMBH) to the Bulge mass (Mbh/Mbulge) in a sample of X-ray selected AGNs, including 15 Narrow-line Seyfert 1 galaxies (NLS1s) and 18 broad-line Seyfert 1 galaxies (BLS1s). We found that the mean value of log(Mbh/Mbulge) is -3.81±0.11 for 15 NLS1s, and -2.91±0.13 for 18 BLS1s, showing the lower Mbh/Mbulge in NLS1s relative to BLS1s. The calculation shows that the Bulge mass from the host image decomposition in NLS1s is statistically smaller than that from Hubble-type correction method, and a linear mass relation is suggested for NLS1s and a nonlinear mass relation for BLS1s. The studying of host galaxies with ground-based observations strongly limited by the atmospheric seeing. We need to do the decomposition of host images for NLS1s with Hubble Space Telescope observation in the future. 相似文献
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B. Tellili Y. Elmahroug C. Souga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The interaction of galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the lunar surface produces secondary radiations as neutrons. The study of the production and attenuation of these neutrons in the lunar soil is very important to estimate the annual ambient dose equivalent on the lunar surface and for lunar nuclear spectroscopy. Also, understanding the attenuation of fast neutrons in lunar soils can help in measuring of the lunar neutron density profile and to measure the neutron flux on the lunar surface. In this paper, the attenuation of fast neutrons in different lunar soils is investigated. The macroscopic effective removal cross section (ΣR) of fast neutrons was theoretically calculated from the mass removal cross-section values (ΣR/ρ) for various elements in soils. The obtained values of (ΣR) were discussed according to the density. The results show that the attenuation of fast neutrons is more important in the landing sites of Apollo 12 and Luna 16 than the other landing sites of Apollo and Luna missions. 相似文献
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Maria S. Pulinets Elizaveta E. Antonova Maria O. Riazantseva Svetlana S. Znatkova Igor P. Kirpichev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Crossings of the magnetopause near the subsolar point are analyzed using data of THEMIS mission. Variations of the magnetic field near magnetopause measured by one of THEMIS satellites are studied and compared with simultaneous measurements in the solar wind by another THEMIS satellite. The time delay of the solar wind arrival at the subsolar point of the magnetopause is taken into account. 30 and 90 s averaging of the magnetic field in the magnetosheath is produced. The results of averaging are compared with the results of measurements in the solar wind before the bow shock and foreshock. It is shown, that Bx component of the magnetic field near magnetopause is near to zero, which supports the possibility to consider the magnetopause as the tangential discontinuity. Comparatively good correlation of By component in the solar wind and near the magnetopause is observed. The correlation of Bz component near the magnetopause and IMF is practically absent, the sign of the Bz near the subsolar point does not coincide with the sign of IMF Bz in ∼30% cases. 相似文献
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On the effects of each term of the geopotential perturbation along the time I: Quasi-circular orbits
Diogo M. Sanchez Antonio F.B.A. Prado Tadashi Yokoyama 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
This paper provides a useful new method to determine minimum and maximum range of values for the degree and order of the geopotential coefficients required for simulations of orbits of satellites around the Earth. The method consists in a time integration of the perturbing acceleration coming from each harmonic of the geopotential during a time interval T. More precisely, this integral represents the total velocity contribution of a specific harmonic during the period T . Therefore, for a pre-fixed minimum contribution, for instance 1×10-8 m/s during the period of time T, any harmonic whose contribution is below this value can, safely, be neglected. This fact includes some constraints in the degree and order of the terms which are present in the geopotential formula, saving computational efforts compared to the integration of the full model. The advantage of this method is the consideration of other perturbations in the dynamics (we consider the perturbations of the Sun, the Moon, and the direct solar radiation pressure with eclipses), since these forces affect the value of the perturbation of the geopotential, because these perturbations depend on the trajectory of the spacecraft, that is dependent on the dynamical model used. In this paper, we work with quasi-circular orbits and we present several simulations showing the bounds for the maximum degree and order (M) that should be used in the geopotential for different situations, e. g., for a satellite near 500 km of altitude (like the GRACE satellites at the beginning of their mission) we found 35?M?198 for T=1 day. We analyzed the individual contribution of the second order harmonic (J2) and we use its behavior as a parameter to determine the lower limit of the number of terms of the geopotential model. In order to test the accuracy of our truncated model, we calculate the mean squared error between this truncated model and the “full” model, using the CBERS (China-Brazil Earth Resources Satellite) satellite in this test. 相似文献
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Huynh Anh Nguyen Le Soojong Pak Myungshin Im Minjin Kim Chae Kyung Sim Luis C. Ho 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We present medium resolution near-infrared host galaxy spectra of low redshift quasars, PG 0844+349 (z = 0.064), PG 1226+023 (z = 0.158), and PG 1426+015 (z = 0.086). The observations were done by using the Infrared Camera and Spectrograph (IRCS) at the Subaru 8.2 m telescope. The full width at half maximum of the point spread function was about 0.3 arcsec by operations of an adaptive optics system, which can effectively resolve the quasar spectra from the host galaxy spectra. We spent up to several hours per target and developed data reduction methods to reduce the systematic noises of the telluric emissions and absorptions. From the obtained spectra, we identified absorption features of Mg I (1.503 μm), Si I (1.589 μm) and CO (6-3) (1.619 μm), and measured the velocity dispersions of PG 0844+349 to be 132 ± 110 km s−1 and PG 1426+015 to be 264 ± 215 km s−1. By using an MBH–σ relation of elliptical galaxies, we derived the black hole (BH) mass of PG 0844+349, log(MBH/M⊙)=7.7±5.5 and PG 1426+015,log(MBH/M⊙)=9.0±7.5. These values are consistent with the BH mass values from broad emission lines with an assumption of a virial factor of 5.5. 相似文献
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Leo Hebert III Brian A. Tinsley Limin Zhou 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Small changes in extended winter (November–March) 500 hPa vorticity area index (VAI) values for the 60–80°N latitude band are shown to be positively correlated with changes in a proxy for the high latitude ionosphere-to-surface current density Jz. 相似文献
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Merged series of normalized water leaving radiances obtained from multiple satellite missions for the Mediterranean Sea 总被引:1,自引:0,他引:1
Frédéric Mélin Giuseppe Zibordi Samuel Djavidnia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Merging time series of ocean color-derived products provided by independent satellite missions supports related biogeochemical and environmental applications by combining temporally overlapping data sets and by increasing data coverage. The creation of a merged series of normalized water leaving radiances LWN, the primary ocean color product, is presented for the Mediterranean Sea using the SeaWiFS and MODIS data records. The merging relies on an optically-based technique that combines the available LWN signal in a spectrally consistent way. Validation statistics indicate uncertainties associated with the merged LWN decreasing from 23% at 412 nm to 12% in the 500- to 555-nm spectral range. The inter-comparison of the sensor-specific products, conducted at the scale of the basin for daily-to-monthly time scales, indicates an overall consistency. The level of differences varies with the wavelength considered and shows a marked seasonal cycle, with differences that tend to be higher in winter. The merged series is remarkably consistent with the sensor-specific data, with average absolute percent differences lower than 10% for all wavelengths below 555 nm. The benefit of merging in terms of sampling frequency over the basin is also illustrated. A merged series of LWN data based on the two considered missions provides valid data over 36% of the basin area on a daily basis. 相似文献