Review of Conditions for the Formation and Maintenance of Filaments Paper by Sara F. Martin, 1998 Review presented by Samuel Tun October 13,

Introduction and overview The paper reviews the 1. the filament environment 2. dynamic conditions related to the formation of filaments, and 3. Additional clues from the features of filaments and their surroundings Typical thickness, height, and length are 5000 km, km, and km, respectively (Stix, Ch. 9). Filaments and prominences are the same phenomenon. Here’s a movie of an erupting one showing that. All movies kindly provided by Dr. C. Denker, BBSO / NJIT

Conditions of the Filament environment Filaments and photospheric B-fields filaments occur along boundaries of opposite polarity line of sight magnetic fields, or neutral lines filaments occur along boundaries of opposite polarity line of sight magnetic fields, or neutral lines Figure 1, Martin 1998

above condition applies to quiescent and active region filaments, and of all scales (temporal and spatial) above condition applies to quiescent and active region filaments, and of all scales (temporal and spatial) temporal and spatial scales hold the relation big and slowly evolving, small and quickly evolving temporal and spatial scales hold the relation big and slowly evolving, small and quickly evolving

although the boundary containing large-scale filaments can be all within one bipolar region, about twice as many filaments form between ARs than within them. Filaments can form between ARs of different ages. although the boundary containing large-scale filaments can be all within one bipolar region, about twice as many filaments form between ARs than within them. Filaments can form between ARs of different ages. the above preference points to a possible quadrupolar magnetic configuration. Models abound, and evidence from magnetograms seems to indicate that this is so. the above preference points to a possible quadrupolar magnetic configuration. Models abound, and evidence from magnetograms seems to indicate that this is so. Overlying arcades seems all filaments have overlying arcades seems all filaments have overlying arcades Figure 2, Martin 1998

overlying coronal loops connect regions of opposite polarity unless they have different helicities. overlying coronal loops connect regions of opposite polarity unless they have different helicities. northern hemisphere dominated by regions of negative helicity, while the reverse is true for the southern one northern hemisphere dominated by regions of negative helicity, while the reverse is true for the southern one arcades are a necessary but insufficient condition for filaments arcades are a necessary but insufficient condition for filaments The Filament Channel  In medium to strong fields, filaments form only where there are no fibril bridges across the neutral line (across polarity inversion, region of maximum magnetic shear). From

examples of fibril alignment (channel formation) preceding filament formation are presented examples of fibril alignment (channel formation) preceding filament formation are presented some channels remain filament-less, and the mechanism for fibril alignment is yet to be determined. some channels remain filament-less, and the mechanism for fibril alignment is yet to be determined. Figure 11, Martin 1998

photospheric magnetograms show field is aligned along the filament channel. However, this is confirmed only for strong fields and of rough spatial resolution due to instrumental limitations. photospheric magnetograms show field is aligned along the filament channel. However, this is confirmed only for strong fields and of rough spatial resolution due to instrumental limitations. There is a permeating "background of mixed-polarity, small-scale fields" in quiet Sun. However, filament formation in ARs occurs between the greater plage areas, indicating that the formation of the channels depends on the large-scale AR magnetic fields There is a permeating "background of mixed-polarity, small-scale fields" in quiet Sun. However, filament formation in ARs occurs between the greater plage areas, indicating that the formation of the channels depends on the large-scale AR magnetic fields From

barbs have mass flows in different directions, ending in points of "minority polarity“ barbs have mass flows in different directions, ending in points of "minority polarity“ almost complete absence of barbs in ARs almost complete absence of barbs in ARs Figure 5, Martin 1998

Dynamic conditions for the formation of filaments Convergence of B-fields and canceling magnetic flux, the movie.

there is evidence that in order for filaments to form one must have merging areas of opposite polarities (flux convergence) there is evidence that in order for filaments to form one must have merging areas of opposite polarities (flux convergence) opposite fields cancel, but the mechanism is still debated opposite fields cancel, but the mechanism is still debated Figure 7, Martin 1998

Changing fine structure  high-resolution spectra show a constant movement in the fine structure, and the highest resolution images show thread lifetimes of about 10 minutes  mass usually moves along the observable threads, indicating field alignment with threads

vector magnetograms give evidence that, in AR, filaments form in regions of maximum magnetic shear (low and parallel to polarity inversion line) vector magnetograms give evidence that, in AR, filaments form in regions of maximum magnetic shear (low and parallel to polarity inversion line) some threads of large filaments appear to be inclined to the filament axis, demonstrating that there are fields pointing in those large angles some threads of large filaments appear to be inclined to the filament axis, demonstrating that there are fields pointing in those large angles

Field direction from plasma flows BBSO images were used to show that mass flows at different optical depths move in different directions in the filament and barbs BBSO images were used to show that mass flows at different optical depths move in different directions in the filament and barbs  Detection of counter streaming can compliment magnetograms in determining the filament magnetic fields Figure 9, Martin 1998

Discussion-pieces of prominence puzzle in broader context Chirality patterns in channels, filaments, and overlying arcades coronal loop chirality is defined such that left- skewed arcades always lie over dextral filaments. coronal loop chirality is defined such that left- skewed arcades always lie over dextral filaments. Figure 10, Martin 1998

 dextral chirality dominates in Northern hemisphere, while the inverse is true for the South.This preference is sometimes violated, but chirality relationships (dextral with right bearing barbs) always hold. Confirmation of inverse magnetic component filaments there exists a component of B-field perpendicular to the field of the coronal loops above the filament. This had previously been modeled as an x-type neutral point there exists a component of B-field perpendicular to the field of the coronal loops above the filament. This had previously been modeled as an x-type neutral point Martin argues that since the footpoints of all the barbs in her figure 5 were found to be in the minority polarity, that their magnetic fields have a large component opposite that of the overlying loops Martin argues that since the footpoints of all the barbs in her figure 5 were found to be in the minority polarity, that their magnetic fields have a large component opposite that of the overlying loops

Barbs to fibril relations barbs and fibril pattern is aligned as viewed from above, but they are not so if viewed along the filament axis barbs and fibril pattern is aligned as viewed from above, but they are not so if viewed along the filament axis on positive side barbs reach down into minority polarity “plagettes”, while fibrils have upward reaching components going into the corona...separate fields on positive side barbs reach down into minority polarity “plagettes”, while fibrils have upward reaching components going into the corona...separate fields channel-filament relation indicates that the channel magnetic field will dictate the filament properties channel-filament relation indicates that the channel magnetic field will dictate the filament properties The Cavity  Martin suggested that the cavity exists because the fields of the filaments and the overlying arcades have different helicities (already saw these do not interconnect)

Summary and conclusions 1. Filaments exist between fields of opposite polarity at sides and ends 2.a. all filaments have overlying arcade of coronal loops b. arcade is skewed with respect to polarity boundary b. arcade is skewed with respect to polarity boundary 3.a. filament channel exists below, and fibrils aligned b. no fibrils cross the neutral line b. no fibrils cross the neutral line c. magnetic field of the channel has inverse component c. magnetic field of the channel has inverse component 4. Opposing magnetic flux move towards each other so as to bring the regions unto an overlap 5. Converging magnetic fields cancel 6. Barbs require continuous mass supply 7. Minority polarity fields must exist nearby 8. Chirality relations exist and must be satisfied by any model Reference (paper discussed) Martin, S.F., 1998: Conditions for the Formation and Maintenance of Filaments, Solar Physics 182,