Study on the three dimensional solar wind structure using computer assisted tomography analysis

利用计算机辅助断层扫描分析三维太阳风结构的研究

基本信息

批准号：
07454115
负责人：
KOJIMA Masayoshi
金额：
$ 5.06万
依托单位：
NAGOYA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

Spacecraft observations of the solar wind have been confined to regions near the ecliptic plane except only one spacecraft of Ulysses, and there has been no direct measurement at solar distances inside 70 Rs where the solar wind is significantly accelerated. An interplanetary scintillation (IPS) method is a unique and useful means to measure global structure of the solar wind in regions near the Sun and at high latitudes where in situ measurements are difficult. However the IPS measurements are biased by a line-of-sight integration through a three-dimensional structured solar wind. So we have developed a method which uses a computer assisted tomography (CAT) technique to obtain unbiased longitudinal and latitudinal distributions of a speed and electron density fluctuations.The CAT analyzes have retrieved not only unbiased solar wind parameters but also high spacial resolution ;1. Fractional Electron Density FluctuationsWe found that the fractional electron density fluctuation level DELTAN/N in the high-speed wind grows with a heliocentric distance and becomes larger than that in the low-speed wind at distances beyond 0.3 AU ;2. Latitudinal StructureThe latitudinal solar wind speed structure in the solar activity minimum phase has a bimodal structure which consists of low-speed and high-speed regions separated with a sharp velocity gradient ;3. Radial distance dependence of velocityComparing two velocity distribution maps made at 0.1-0.3 AUand 0.3-IAU,we found that the high-speed wind is accelerated to its final speed within 0.1 AU and that the high-speed Wind increases its velocity slightly as approaching the sun, that is, in average from 743-804 km/s at 0.3-1 AU to 791-896 km/s at 0.1-0.3 AU.

除尤利西斯号航天器外，航天器对太阳风的观测仅限于黄道面附近的区域，而且在太阳距离70卢比以内、太阳风明显加速的地方还没有直接测量。行星际闪烁（IPS）方法是一种独特而有用的方法，可以测量近太阳区域和难以进行现场测量的高纬度地区太阳风的全球结构。然而，IPS 测量因三维结构太阳风的视线整合而产生偏差。因此，我们开发了一种使用计算机辅助断层扫描（CAT）技术来获得速度和电子密度涨落的无偏经纬度分布的方法。CAT分析不仅检索了无偏太阳风参数，而且还获得了高空间分辨率；1．分数电子密度涨落我们发现，高速风中的分数电子密度涨落水平DELTAN/N随着日心距离的增加而增长，并且在距离超过0.3 AU时变得比低速风中的更大；2．纬向结构太阳活动极小期的纬向太阳风速度结构具有双峰结构，由速度梯度较大的低速区和高速区组成；3．速度的径向距离依赖性比较0.1-0.3 AU和0.3-IAU的两个速度分布图，我们发现高速风在0.1 AU内加速到最终速度，并且高速风在接近0.3-IAU时其速度略有增加。太阳，即平均从 0.3-1 天文单位时的 743-804 公里/秒到 791-896 公里/秒0.1-0.3 个天文单位。