Abstract. A solar-flare-induced, high-latitude (peak at 70–75 ∘ geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77 ∘ GGlat near local noon detected northward geomagnetic deviations ( ΔB ) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, the subsolar crochet (seen at lower latitudes), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, the interplanetary magnetic field (IMF) BY is not the driver, with the BY values of only 0–1 nT out of a 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 h in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements, which were conducted over the same region as the most intense ΔB , show enhancements of electron density (and hence of ion-neutral density ratio) at these altitudes ( ∼100 km) at which strong background ion convection ( >100 m s −1 ) pre-existed in the direction of tidal-driven diurnal solar quiet (Sq0) flow. Therefore, this new zonal current can be related to this Sq0-like convection and the electron density enhancement, for example, by descending the E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore, the mechanism is still unclear compared to the subsolar crochet that is maintained by a transient redistribution of the electron density. The signature is sometimes seen in the auroral electrojet (AE = AU − AL) index. A quick survey for X-class flares during solar cycle 23 and 24 shows clear increases in AU for about half the > X2 flares during non-substorm time, despite the unfavourable latitudinal coverage of the AE stations for detecting this new crochet. Although some of these AU increases could be the auroral crochet signature, the high-latitude crochet can be a rather common feature for X flares. We found a new type of the solar flare effect on the dayside ionospheric current at high latitudes but equatorward of the cusp during quiet periods. The effect is also seen in the AU index for nearly half of the > X2-class solar flares. A case study suggests that the new crochet is related to the Sq0 (tidal-driven part) current.

中文翻译：

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高纬度钩针编织：太阳耀斑引起的磁干扰独立于低纬度钩针编织

摘要。研究了由太阳耀斑引起的高纬度（峰值在 70-75 ∘ 地理纬度 – GGlat）电离层电流系统。就在 2017 年 9 月 6 日 X9.3 耀斑之后，位于当地中午附近 68-77 ∘ GGlat 的磁站检测到北向地磁偏差 (ΔB) 超过 3 小时，峰值幅度 >200 nT，没有任何伴随的亚暴活动。从它的位置来看，这种太阳耀斑效应或钩针不同于以前研究过的，即太阳下钩针（在低纬度地区可见）、极光钩针（在阳光下需要极光电喷射）或尖头钩针（仅在低纬度地区可见）尖）。新的钩针编织比太阳下的钩针编织更强烈，持续时间更长。持续时间长，与高太阳X射线通量（超过M3级耀斑水平）的时期相匹配。与尖头钩针不同的是，行星际磁场 (IMF) BY 不是驱动因素，在 3 nT 的总磁场中，BY 值只有 0-1 nT。等效电离层电流在有限的纬度范围内向东流动，但在当地时间（LT）延长了至少 8 小时，在地磁封闭区上形成了极冠赤道方向的纬向电流区。在与最强 ΔB 相同的区域进行的 EISCAT 雷达测量显示，在这些高度（约 100 公里）处电子密度（以及因此离子-中性密度比）的增强，在该高度，强背景离子对流（>100 毫秒） -1 ) 预先存在于潮汐驱动的昼夜太阳安静 (Sq0) 流方向。因此，这种新的带状电流可能与这种类似 Sq0 的对流和电子密度增强有关，例如，通过降低 E 区高度。然而，我们还没有发现为什么在有限的纬度范围内发现了新的钩针，因此，与通过电子密度的瞬时重新分布维持的太阳下钩针相比，其机制仍不清楚。有时会在极光电射流 (AE = AU − AL) 指数中看到这种特征。对太阳活动周期 23 和 24 期间 X 级耀斑的快速调查显示，在非亚暴时期，大约一半 > X2 耀斑的 AU 明显增加，尽管用于检测这种新钩针的 AE 站的纬度覆盖率不利。尽管其中一些 AU 增加可能是极光钩针编织的特征，但高纬度钩针编织可能是 X 耀斑的一个相当常见的特征。我们发现了一种新型的太阳耀斑对高纬度地区日侧电离层电流的影响，但在安静时期的风尖赤道附近。在 AU 指数中也可以看到近一半 > X2 级太阳耀斑的影响。一项案例研究表明，新钩针与 Sq0（潮汐驱动部分）电流有关。