A quantitative study of ionospheric density gradients at midlatitudes
A quantitative study of ionospheric density gradients at midlatitudes
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DOI：
10.1029/2000ja000397
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发表时间：
2001-10
影响因子：
--
通讯作者：
H. Vo;J. Foster
中科院分区：
文献类型：
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作者：
H. Vo;J. Foster
位于美国东北部磁纬度的亚极光电离层由于磁层扰动电场的空间天气效应而受到严重的 F 区电离层密度结构的影响。依赖于跨电离层传播的通信和导航系统必须能够补偿与中纬度电离层槽和风暴时间扰动效应相关的总电子含量 (TEC) 急剧变化 (>10X) 的影响。 Millstone Hill 非相干散射雷达数据库已用于研究 TEC 的空间范围和时间演化以及中纬度和亚极光纬度的密度高度/纬度结构，作为太阳周期、当地时间和地磁活动水平的函数。超过11,000次雷达高程扫描覆盖>20°的纬度和150至750公里之间的高度，已被用于识别在跨越20年和两个太阳周期的各种情况下电离层槽赤道边缘附近的密度梯度特征。在 Millstone Hill 扫描的 ∼35% 中可以识别出明显的密度梯度，我们提出了这些最陡 TEC 梯度的平均幅度和位置的统计特征。在某些情况下（尤其是中午附近），海槽的赤道边缘位于我们观测视野的极地，与海槽以外的现象相关的梯度有助于我们的统计。在大多数日子里，波谷出现在 1600 到 2000 磁当地时间 (MLT) 之间的雷达扫描中。较大的 TEC 梯度出现在太阳活动极大期以及背景 TEC 较高时。最陡的梯度出现在高 TEC 环境中（太阳活动极大期且邻近风暴增强密度 (SED) 区域），此时产生槽的过程最强（高 Kp）。高梯度值出现在阳光照射区域，TEC 梯度最大值（∼10 TEC/deg 纬度，1 TEC 单位 = 10 16 el m -2 ）出现在正午电离层中。新英格兰上空 1600 MLT 时 Kp 100 的平均太阳最大 TEC 梯度为 3-4 TEC/deg，TEC 梯度为 ∼50 TEC/deg。
The subauroral ionosphere, at the magnetic latitudes which characterize the northeastern United States, is subject to severe F region ionospheric density structuring due to the space weather effects of magnetospheric disturbance electric fields. Communications and navigation systems relying on transionospheric propagation must be able to compensate for the effects of the sharp changes (>10X) in total electron content (TEC) associated with the ionospheric trough and storm time disturbance effects at midlatitudes. The Millstone Hill incoherent scatter radar database has been used to investigate the spatial extent and temporal evolution of TEC and density altitude/latitude structure at middle and subauroral latitudes as a function of solar cycle, local time, and level of geomagnetic activity. More than 11,000 radar elevation scans covering >20° of latitude and altitudes between 150 and 750 km have been used to identify the characteristics of the density gradient near the equatorward edge of the ionospheric trough in a variety of circumstances spanning 20 years and two solar cycles. Pronounced density gradients can be identified in ∼35% of the Millstone Hill scans, and we present a statistical characterization of average magnitude and location for these steepest TEC gradients. In some cases (especially near noon) the equatorward edge of the trough lies poleward of our observational field of view, and gradients associated with phenomena other than the trough contribute to our statistics. On most days the trough appears in the radar scans between 1600 and 2000 magnetic local time (MLT). Larger TEC gradients occur at solar maximum and when the background TEC is higher. The steepest gradients occur in an environment of high TEC (at solar maximum and adjacent to regions of storm-enhanced density (SED)), when the processes which generate the trough are strongest (high Kp). High gradient values occur in the sunlit sector, with maximum values of TEC gradient (∼10 TEC/deg latitude, with 1 TEC unit = 10 16 el m -2 ) found in the postnoon ionosphere. Mean solar maximum TEC gradient at 1600 MLT is 3-4 TEC/deg for Kp 100 over New England and TEC gradients of ∼50 TEC/deg.