Statistical patterns of high‐latitude convection obtained from Goose Bay HF radar observations
Statistical patterns of high‐latitude convection obtained from Goose Bay HF radar observations
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DOI：
10.1029/96ja01584
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发表时间：
1996-10
影响因子：
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通讯作者：
J. Ruohoniemi;R. Greenwald
中科院分区：
文献类型：
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作者：
J. Ruohoniemi;R. Greenwald
我们得到了描述北半球高纬度地区电离层对流的星际磁场(IMF)统计相关性的模式。用位于拉布拉多鹅湾的高频相干后向散射雷达对1987年9月至1993年6月期间的等离子体运动进行了观测。测量覆盖的区域从65°Λ向极地延伸到约85°Λ的工作极限。导出了静电势的分布，并将其表示为球谐函数的级数展开式。这些模式是首次从对电离层对流的直接地面观测中得出的，这种模式在完整性和详细程度上接近于最近的卫星研究中得出的模式[Rich和Hairston，1994；Wemer，1995]。给出了GSMy-z平面内三个IMF量级区间内对流与IMF角的关系。除了主要向北移动的IMF外，对流主要是两个单体的对流。黄昏细胞在空间范围和位势变化方面都较大，IMF by的影响在细胞的整体形状和MLT的整体图案方向上是明显的；因为By+(由−)黄昏(黎明)细胞更圆(新月形)，图案更倾向于早期MLT。对夜间对流的副效应是明显的，并且是半球反对称的，就像众所周知的白天效应一样。对于日益向北移动的IMF来说，白天的对流轨迹变得越来越扭曲，通过三单体环流演变为四单体环流。额外的细胞出现在正午经线的两边，并导致向阳流动。与卫星研究结果的总体一致性是好的，并且在与Wemer[1995]的比较中扩展到相当细微的细节。这与磁力计测量得出的统计模式有很大不同，后者往往显示出黎明而不是黄昏细胞的主导地位。
We have derived patterns that describe the statistical interplanetary magnetic field (IMF) dependencies of ionospheric convection in the high-latitude region of the northern hemisphere. The observations of plasma motion were made with the HF coherent backscatter radar located at Goose Bay, Labrador, over the period September 1987 to June 1993. The area covered by the measurements extended poleward of 65°Λ to a working limit of about 85°Λ. Distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics. The patterns are the first derived from direct ground-based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies [Rich and Hairston, 1994; Weimer, 1995]. We show the dependence of the convection on IMF angle in the GSM y–z plane for three intervals of IMF magnitude in this plane. Except for predominantly northward IMF, the convection is primarily two-cell. The dusk cell is larger in terms of both spatial extent and potential variation/The effect of IMF By is apparent in the global shaping of the cells and the orientation of the overall pattern in MLT; for By + (By−) the dusk (dawn) cell is more round (crescent-shaped) and the pattern more rotated toward earlier MLTs. The By effect on the nightside convection is pronounced and is hemispherically antisymmetric, like the well-known day side By effect. For IMF increasingly northward, the convection trajectories on the dayside become increasingly distorted, evolving through a three-cell to a four-cell circulation. The additional cells appear on either side of the noon meridian and result in sunward flow. The overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with Weimer [1995]. There are significant differences with the statistical patterns derived from magnetometer measurements, which tend to show domination by the dawn rather than the dusk cell.