Geoeffective Analysis of CMEs Under Current Sheet Magnetic Coordinates   总被引：1，自引：0，他引：1  

Xueshang Feng  Xinhua Zhao 《Astrophysics and Space Science》2006,305(1):37-47

Using 100 CME–ICME events during 1997.01–2002.11, based on the eruptive source locations of CMEs and solar magnetic field observations at the photosphere, a current sheet magnetic coordinate (CMC) system is established in order to statistically study the characteristics of the CME–ICME events and the corresponding geomagnetic storm intensity. The transit times of CMEs from the Sun to the Earth are also investigated, by taking into account of the angle between the CME eruption normal (defined as the vector from the Sun center to the CME eruption source) and the Sun-Earth line. Our preliminary conclusions are: 1. The distribution of the CME sources in our CMC system is obviously different from that in the ordinary heliographic coordinate system. The sources of CMEs are mainly centralized near the heliospheric current sheet (HCS), and the number of events decreases with the increment of the angular distance from the CME source to the HCS on the solar surface; 2. A large portion of the total events belong to the same–side events (referring to the CME source located on the same side of the HCS as the Earth), while only a small portion belong to the opposite–side events (the CME source located on the opposite side of the HCS as the Earth). 3. The intense geomagnetic storms are usually induced by the same–side events, while the opposite side events are commonly associated with relatively weak geomagnetic storms; 4. The angle between the CME normal and the Sun–Earth line is used to estimate the transit time of the CME in order to reflect the influence of propagation characteristic of the CME along the Sun–Earth direction. With our new prediction method in context of the CMC coordinate, the averaged absolute error for these 100 events is 10.33 hours and the resulting relative error is not larger than 30% for 91% of all the events.  相似文献   

Model of wind-generated ambient noise in stratified shallow water   总被引：1，自引：0，他引：1  

林建恒  高天赋 《中国海洋湖沼学报》2005,23(2):144-151

In order to build a rapid ocean ambient noise model adapted for a stratified shallow water, a hybrid model of normal mode method (for far field) and ray method (for near field) is suggested which combines the advantages of both methods. Since the near field of wind-generated noise is not sensitive to the sound speed profile, the sound speed profile is regarded as a constant; which makes the model rapid and accurate. The simulation results are in agreement with those of the wave model.  相似文献   

Propagation of solar flare-associated interplanetary shock waves in the heliospheric meridional plane   总被引：4，自引：0，他引：4  

Wei Fengsi  Murray Dryer 《Solar physics》1991,132(2):373-394

We have analyzed 149 flare-associated shock wave events based on interplanetary scintillation (IPS) observational data. All of the flare-associated shock waves tend to propagate toward the low latitude region near the solar equator for flares that are located in both the solar northern and southern hemispheres. Also, the fastest propagation directions tend toward the heliospheric current sheet near 1 AU. We suggest that this tendency is caused by the dynamic action of near-Sun magnetic forces on the ejected coronal plasma that traverses the helmet-like magnetic topologies near the Sun outward to the classical topology that is essentially parallel to the heliospheric current sheet.  相似文献   

地理信息系统中自然语言查询的分词处理与应用   总被引：4，自引：3，他引：1  

吴静  蔡砥  王铮 《地球信息科学学报》2005,7(3):67-71

随着地理信息系统应用的不断发展,本文提出了在地理信息系统中对基于受限自然语言的查询语句进行分词处理的方法--首字扩词分词法。该分词方法在汲取正向最大匹配分词方法的核心思想--长词优先原则。为了缩小匹配范围,提高匹配效率,该方法首先根据查询自然语言的首字对词汇库的记录进行筛选,得到以该首字开头的词汇库子集;然后再按照长词优先原则把原查询语句与词汇库子集进行匹配,切分查询语句。通过比较,该方法比正向最大匹配方法具有较小的时间复杂度。同时,采用DELPHI编程语言在计算机上得到了实现。  相似文献   

微波爆发区的日冕磁场研究     

周爱华  傅其骏 《天文学进展》1996,14(4):297-301

回顾了日冕磁的研究历史，介绍了我们首镒提出的日冕磁场的微波诊断方法及其应用的带来的启迪，提出进一步开展日冕磁场及其相关研究的建议。  相似文献   

The Influence of Coronal Background Structure with Nested and Closed Magnetic Fields on the Triggering of CME     

《Chinese Astronomy and Astrophysics》2007,31(2):128-136

The influence of coronal streamer background with nested and closed magnetic fields on the of the triggering of coronal mass ejections (CMEs) is investigated in the meridian plane. In the coronal streamers’ background magnetic structure there are three small-scale closed magnetic fields, of which the middle one has a direction opposite to that of the global dipolar field of coronal streamers. The trigger model of CMEs emerges from beneath this small-scale closed magnetic field and possesses a concentric circular structure with radius of a = 0.1R_s (R_s being the solar radius). The direction of the magnetic field in the front half of the CME trigger model is opposite to that of the small-scale closed field and is the same as that of the streamers’ global dipolar field. As revealed by numerical simulation, when the ratio of the plasma pressure at the center of the CME trigger model to the boundary pressure is m ≤ 2, then the emerging model can trigger CMEs. When m < 2, then it cannot. The error in this critical value of 2 is less than 1%.  相似文献   

The first CO(1-0) mapping of the globule IC 1396 W     

《New Astronomy》2007,12(2):111-116

Near-infrared observations indicate that three H₂ outflows and their driving sources are present in the globule IC 1396 W, where the existence of molecular outflows has also been suggested by some authors. We made the first CO(1-0) map of IC 1396 W, and found that its CO molecular cloud may consist of three physically distinct components with different velocities. We detected neither molecular outflows nor the dense cores associated with candidate driving sources. One possible reason is that CO(1-0) and its isotopes cannot trace high density gas, and another is that the beam of our observation is too large to observe them. The CO cloud may be one part of the natal molecular cloud of IC 1396 W, in the process of disrupting and blowing away. The CO cloud seems to be in the foreground of the H₂ outflows.  相似文献   

ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE——Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES          下载免费PDF全文

邹晓蕾  吴国雄  叶笃正 《Acta Meteorologica Sinica》1992,(4)

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate thevertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal meanflow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo-cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbationcaused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow isvery weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagatingwaves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up-wards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-Pcross-sections obtained from both observational data and simulated results also demonstrate that waves excited by theRocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,inaddition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by theTibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetratesthe tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wavepropagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains inthe Northern Hemisphere.  相似文献   

NUMERICAL SIMULATION OF THE MINDANAO EDDY AND TROPICAL CURRENTS OF PACIFIC OCEAN     

李荣凤  曾庆存  季仲贞 《中国海洋湖沼学报》1992,10(3):258-267

Results of numerical simulation of currents in the western North Tropical Pacific Ocean by using a barotropic primitive equation model with fine horizontal resolution agreed well with observations and showed that the Mindanao Cyclonic Eddy located north of the equator and east of Mindanao Island exists during most of the year with monthly (and large seasonal) variations in scope . strength and central location . In June , an anticyclonic eddy occurs northeast of Halmahera Island, strengthens to maximum in August , exists until October and then disappears . The observed large-scale circulation systems such as the North Equatorial Current . the Mindanao Current and the North Equatorial Countercurrent are all very well reproduced in the simulations.  相似文献   

Broadband Radio Bursts and Fine Structures during the Great Solar Event on 14 July 2000     

Wang  Shujuan  Yan  Yihua  Zhao  Ruizhen  Fu  Qijun  Tan  Chengming  Xu  Long  Wang  Shijin  Lin  Huaan 《Solar physics》2001,204(1-2):153-164

25 MHz–7.6 GHz global and detailed (fine structure – FS) radio spectra are presented, which were observed in the NOAA 9077 active region for the Bastille Day (14 July 2000) flare at 10:10–11:00 UT. Besides broadband radio bursts, high-resolution dynamic spectra reveal metric type II burst, decimetric type IV burst and various decimetric and microwave FSs, such as type III bursts, type U bursts, reverse-slope (RS)-drifting burst, fiber bursts, patch and drifting pulsation structure (DPS). The peak-flux-density spectrum of the radio bursts over the range 1.0–7.6 GHz globally appears as a U-shaped signature. Analyzing the features of backbone and herringbones of the type II burst, the speeds of shock and relevant energetic electron beams were estimated to be 1100 km s⁻¹ and 58 500 km s⁻¹, respectively. Also the time sequence of the radio emission is analyzed by comparing with the hard X-rays (HXRs) and the soft X-rays (SXRs) in this flare. After the maxima of the X-rays, the radio emission in the range 1.0–7.6 GHz reached maxima first at the higher frequency, then drifted to the lower frequency. This comparison suggested that the flare included three successive processes: firstly the X-rays rose and reached maxima at 10:10–10:23 UT, accompanied by fine structures only in the range 2.6–7.6 GHz; secondly the microwave radio emission reached maxima accompanied by many fine structures over the range 1.0–7.6 GHz at 10:23–10:34 UT; then a decimetric type IV burst and its associated FSs (fibers) in the range 1.0–2.0 GHz appeared after 10:40 UT.  相似文献