The center-to-limb variations of four Ca i lines in the photospheric spectrum at λ6500     

P. Ambruoso  C. Marmolino  M. T. Gomez  G. Severino 《Solar physics》1992,141(1):35-49

We study the center-limb (CL) variation of the average profiles of four Ca i lines near 6500 and compare these observations with synthetic data obtained from several line formation models having different thermal structures, line parameters, LTE and non-LTE conditions, and micro and macroturbulence values, to assess the formation characteristics of our Ca i lines in the solar photosphere.Comparison of numerical results with observations indicates that non-LTE is indispensable to fit the CL variation of the central residual intensity for the line 6493, and anisotropic microturbulence is indispensable to improve the CL behavior of the equivalent widths for all lines. The Ca i line analysis favors a cool photospheric model, but this cannot be disentangled clearly from the effects of non-LTE and small-scale velocity fields on the grounds of the present line formation models.  相似文献   

The latitude of filament bands at the sunspot minimum and the activity level in the two following 11-year solar cycles     

V. I. Makarov  V. P. Mikhailutsa 《Solar physics》1992,137(2):385-394

The zonal structure of the distribution of filaments is considered. The mean latitudes of two filament bands are calculated in each solar hemisphere at the minima of the sunspot cycle in the period 1924–1986: middle latitude _{2, m} and low latitude _{1, m} . It is shown that the mean latitude of the filament band _{2, m} at the minimum -m of the cycle correlates, with = 0.94, with the maximum - M sunspot area S(M) and maximum Wolf number W(M) in the succeeding solar cycle M. It is shown that the mean latitude of the low-latitude filament band _{1, m} is linearly dependent on the mean latitude filament band _{2, m + 1} at the succeeding minimum. We found a correlation of the latitude of the low-latitude filament band _{1, m} with the maximum sunspot area in the M + 1 cycle. This enables us to predict the power of two succeeding 11-year solar cycles on the basis of the latitude of filament bands at the minimum of activity, 1985–1986: W(22) - 205 ± 10, W(23) - 210 ± 10. The importance of the relationships found for theory and applied aspects is emphasized. An attempt is made to interpret the relationships physically.  相似文献   

Hydrogen photoionization rates for chromospheric and prominence plasmas     

P. Rudawy  P. Heinzel 《Solar physics》1992,138(1):123-131

New values of hydrogen photoionization rates for subordinate continua arising from bound levels with the principal quantum number i = 2–5 have been evaluated numerically, using an extensive compilation of the observed photospheric radiation fields. These rates can be directly incorporated into the equations of statistical equilibrium as so-called fixed rates. We tabulate the photoionization rates and equivalent radiation temperatures for various heights above the photosphere, which is particularly useful for chromospheric and prominence non-LTE modeling. Finally, we compare our results with those previously obtained by other authors.  相似文献   

Hall effects on heat and mass transfer flow with variable suction and heat generation     

H. S. Takhar  P. C. Ram  S. S. Singh 《Astrophysics and Space Science》1992,191(1):101-106

A study of the combined buoyancy effects of thermal and mass diffusion on MHD convection flow in the presence of Hall currents with variable suction and heat generation has been carried out. Analytical expressions for the velocity and the temperature of the fluid are given. The effects of Hall currents, parameterm, and heat source parameter on the velocity are discussed.  相似文献   

Quiet-Sun emission and local sources at meter and decimeter wavelengths and their relationship with the coronal neutral sheet     

P. Lantos  C. E. Alissandrakis  D. Rigaud 《Solar physics》1992,137(2):225-256

We analysed multifrequency 2-dimensional maps of the solar corona obtained with the Nançay radioheliograph during two solar rotations in 1986. We discuss the emission of the quiet Sun, coronal holes and local sources and its association with chromospheric and coronal features as well as with large-scale magnetic fields. The brightness temperature of the quiet Sun was 5 to 5.5 × 10⁵ K at 164 MHz and 4.5 to 5 × 10⁵ K at 408 MHz. A coronal hole, also detected in the 10830 Å He i line, had a brightness temperature of 4.5 × 10⁵ at 164 and 2.5 × 10⁵ at 408 MHz. We give statistics of source brightness temperatures (on the average 8% above the background at 164 MHz and 14% at 408 MHz), as well as distributions in longitude and latitude. Although we found no significant center-to-limb effect in the brightness temperature, the sources were not visible far from the central meridian (apparently a refraction effect). The brightest sources at 164 MHz were near, but not directly above active regions and had characteristics of faint type I continua. At 408 MHz some sources were observed directly above active regions and one was unambiguously a type I continuum. The majority of the fainter sources showed no association with chromospheric features seen on H synoptic charts, including filaments. Most of them were detected at one frequency only. Sources identified at three frequencies (164, 327, and 408 MHz) were located in regions of enhanced large-scale magnetic field, some of them at the same location as decayed active regions visible one rotation before on synoptic H charts. Multifrequency sources are associated with maxima of the green line corona. The comparison with K-corona synoptic charts shows a striking association of the radio sources with dense coronal regions, associated with the coronal neutral sheet. Furthermore, we detected an enhanced brightness region which surrounds the local sources and is stable over at least one solar rotation. We call this feature a coronal plateau and we identify it with the radio counterpart of the coronal neutral sheet.  相似文献   

Some observations on migration within and from the former USSR in the 1990s     

Cole JP  Filatotchev IV 《Post-Soviet geography》1992,33(7):432-453

"Patterns of population distribution revealed from 1989 census data are used to assess how future population movements could be affected by current political, social, and economic changes. Much migration in the USSR has reflected central planning decisions as much as the spontaneous decisions of individuals. To the extent that the influence of the command economy diminishes and a market economy emerges, major new directions of migration flows can be expected. The return of ethnic 'expatriates' to home republics can be expected to increase, as can economic migration to areas with favorably perceived economic prospects, and migration to Central and Western Europe."  相似文献   

改进的能量守恒方法及其在CHAMP重力场恢复中的应用(英文)   总被引：1，自引：0，他引：1  

XU Tianhe HE Kaifei Xi’an Research Institute of Surveying  Mapping  Middle Yanta Road  Xi’an  China. 《地球空间信息科学学报》2008,11(3):168-173

An efficient method for gravity field determination from CHAMP orbits and accelerometer data is referred to as the energy balance approach. A new CHAMP gravity field recovery strategy based on the improved energy balance approach IS developed in this paper. The method simultaneously solves the spherical harmonic coefficients, daily Integration constant, scale and bias parameters. Two 60 degree and order gravitational potential models, XISM-CHAMPO1S from the classical energy balance approach, and XISM-CHAMPO2S from the improved energy balance, are determined using about one year＇s worth of CHAMP kinematic orbits from TUM and accelerometer data from GFZ. Comparisons among XISM-CHAMPO1S, XISM-CHAMPO2S, EIGEN-CGO3C, EIGEN-CHAMPO3S, EIGEN2, ENIGNIS and EGM96 are made. The results show that the XISM-CHAMPO2S model is more accurate than EGM96, EIGENIS, EIGEN2 and XISM-CHAMPO1S at the same degree and order, and has almost the same accuracy as EIGEN-CHAMPO3S.  相似文献   

GPS单点测速的误差分析及精度评价 (英文)     

Fuhong Wang  Xiaohong Zhang  Jingsong Huang 《地球空间信息科学学报》2008,11(2):133-138

Error sources which decrease the accuracy of GPS in absolute velocity determination have been changed since SA was turned off. Firstly, quantities of all kinds of error sources that influence velocity determination are analyzed. The potential accuracy of GPS absolute velocity determination is derived from both theory and field GPS data simulation. After that, two tests were carried out to evaluate the performance of GPS absolute velocity determination in the case of a static and an airborne GPS receiver and INS （Inertial Navigation System） instrument in kinematic mode. In static mode, the receiver velocity has been estimated to be several mm/s with the carrier-phase derived Doppler measurements, and several cm/s with the receiver generated Doppler measurements. In kinematic mode, GPS absolute velocity estimates are compared with the synchronized measurements from the high accuracy INS. The root mean square statistics of the velocity discrepancies between GPS and INS come up to dm/s. Moreover, it has a strong correlation with the acceleration or jerk of the aircraft.  相似文献   

根据多卫星高度计海面高数据推算南中国海及菲律宾海域重力异常(英文)   总被引：1，自引：0，他引：1  

Isaac Dadzie  Jiancheng Li  Yonghai Chu 《地球空间信息科学学报》2008,11(3):174-179

t Gravity anomalies on a2.5 ×2.5 arc-minute grid in a non-tidal system were derived over the South China and Philippine Seas from multi-satellite altimetry data. North and east components of deflections of the vertical were computed from altimeter-derived sea surface heights at crossover locations, and gridded onto a 2.5 × 2.5 arc-minute resolution grid. EGM96-derived components of deflections of the vertical and gravity anomalies gridded into 2.5 × 2.5 arc-minute resolutions were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Inverse Vening Meinesz formula via the 1D-FFT technique to predict the gravity anomalies over the South China and Philippine Seas from the gridded altimeter-derived components of deflections of the vertical. Statistical comparisons between the altimeter-derived and the shipboard gravity anomalies showed that there is a root-mean-square agreement of 5.7 mgals between them.  相似文献   

基于交互多模型的水下目标跟踪方法(英文)   总被引：1，自引：0，他引：1  

Weiming Xu  Yanchun Liu  Xiaodong Yin 《地球空间信息科学学报》2008,11(3):186-190

According to the requirements of real-time performance and reliability in underwater maneuvering target tracking as well as clarifying motion features of the underwater target, an interacting multiple model algorithm based on fuzzy logic inference （FIMM） is proposed. Maneuvering patterns of the target are represented by model sets, including the constant velocity model （CA）, the Singer mode~, and the nearly constant speed horizontal-turn model （HT） in FIMM technology. The simulation results show that compared to conventional IMM, the reliability and real-time performance of underwater target tracking can be improved by FIMM algorithm.  相似文献