Left (Right) bearing
Regarding the morphology, filament threads are not randomly aligned with respect to the local PIL. They are lined up along the magnetic PIL. When viewed from above, some threads extend farther away from the spine of the filament, forming a structure called “barbs.” Similar to the ramps of an elevated highway, barbs can be divided into left-bearing and right-bearing types. (Chen 2014 APJ)
Left bearing Right bearing
根据编者自己的理解,所谓的Left bearing or Right bearing判定 只与暗条的barbs形态有关,与磁场无关.陈老师把这种判定比作高速路出口,barb作为出口,与暗条脊线夹角应该为锐角.那么基于这个假定,可以判断到底是left or right bearing.
(Chen 2014 APJ) Barbs are fine structures of solar filaments. Seen from above, each barb makes an acute angle with respect to one direction of the filament spine. When viewed along this direction, the barb is located either on the left side or the right side of the spine. On the basis of this difference, filaments can be classified into either the left-bearing or the right-bearing types (Martin et al. 1992).
Martin and McAllister studied the direction of loops within coronal arcades overlying filaments to learn whether arcades also possess chirality. For consistency with the filaments, they defined the skew of loops relative to the filament axis and the filament barbs. When viewed from above, right-skewed arcades have loops that form an angle with respect to the filament axis in the same direction as right bearing barbs while the angle of left-skewed arcades with respect to the filament or channel axis is similar to the angle of the left-bearing barbs. The invariable relationship found by Martin and McAllister is that only the inverse relation exists as illustrated in Figure 10(c), left-skewed arcades always lie above dextral filaments with right- bearing barbs; only right-skewed arcades exist over sinistral filaments with left- bearing barbs. When viewed from above, the angle of the overlying arcade can be nearly perpendicular to the barbs.
Martin和Mcallister研究暗条的上覆场,考虑其是否具有手性. 为了与暗条保持一致,其定义相对于暗条主轴和barb的上覆场环系的偏向(skew). 当从顶部往下看时,右偏的磁拱,其环系,相对于暗条主轴,与right bearing 的barb是同样方向的.而左偏的磁拱,则与left bearing的 barb同样方向.当然图10c展示了反相关关系的情况.即定义的左偏的磁拱,其环系,相对于暗条主轴,与right bearing的barb的方向相反.
上述的观点是在2014年以前大家通用的Martin的判定方法,即Left bearing 对应的正helicity,而Right bearing对应的负helicity.(Martin et al 1994)
Most filaments in the northern hemisphere have right-bearing barbs and are overlaid by left-skewed coronal arcades, which have negative magnetic helicity. However, most filaments in the southern hemisphere have left-bearing barbs and are overlaid by right-skewed coronal arcades, which have positive helicity (Martin 1998). This chirality pattern is consistent with the hemispheric rule for the magnetic helicity of active regions (Pevtsov et al. 1995; Bao & Zhang 1998) and hence provides strong constraints on the modeling of the magnetic structure of the filament channel, as well as its formation mechanism (see Mackay et al. 2010 for a review).
绝大多数的北半球暗条barbs是right-bearing且上覆场为left-skewed日冕磁拱,拥有负的磁螺度.而南半球则相反 (Martin 1998). 这一手性对应法则与活动区磁场螺度半球法则相一致 (Pevtsov et al. 1995; Bao & Zhang 1998) 因而为暗条通道的磁场结构模拟与形成机制提供了强的约束 (见Machay 2010).
那么什么是 Sinistral (Dextral)?
Judging from the direction of the internal magnetic field, filaments can be divided into sinistral and dextral types, where the internal magnetic field—when viewed from the positive polarity of the filament channel—is pointed to the left or right for the sinistral or dextral filaments. Such a chirality is directly related to the magnetic helicity, i.e., a sinistral filament has positive helicity, whereas a dextral filament has negative helicity. It was found that there is a one-to-one correspondence between left-bearing (right-bearing) filaments and the sinistral (dextral) chirality (Martin et al. 1992).
通过对内部磁场的方向的判定,暗条可以被分为sinistral和dextral两类, 从暗条的正极位置看,内部的磁场指向左边或者右边即为sinistral or dextral 暗条. 该手性与磁场螺度直接相关,即sinistral的暗条具有正的helicity, dextral的暗条具有负的helicity. Martin认为left-bearing (right-bearing)的暗条与sinistral (dextral)手性一一对应.
(编者按)这里有个疑问,手性与sinistral(dextral)是什么关系? 我们知道手性指的是罗绕方向,而上述sinistral或dextral是指的磁场偏向. 这里有个前提,就是磁力线是从正极性足点往上延伸的,因而如下图:
(Green 2007) one sign of α and Hr, or a dominant chirality (handedness) of the magnetic field, can be associated with most active regions (with positive α and Hr corresponding to right-handed chirality). If a helical field with uniform sign of α contains a flux rope with little or no writhe, the sign of the twist in the rope equals the sign of α and Hr.