The "fip effect" and the Origins of Solar Energetic Par ticles and of the Solar Wind
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- 3. The FIP-Dependence of CIR and FSW Abundances
- 4. Discussion
Z FIP [eV] Photosphere 1 SEPs 2 CIRs 3 Interstream Solar Wind 4 Coronal Hole Solar Wind 4 H 1 13.6 1.74×10 6 * (≈1.6±0.2)×10 6 (1.81±0.24)×10 6 – – He 2 24.6 1.6×10 5 91000±5000 159000±10000 90000±30000 75000±20000 C 6 11.3 550±76 * 420±10 890±36 680±70 680±70 N 7 14.5 126±35 * 128±8 140±14 78±5 114±21 O 8 13.6 1000±161 * 1000±10 1000±37 1000 1000 Ne 10 21.6 210 157±10 170±16 140±30 140±30 Na 11 5.1 3.68 10.4±1.1 – 9.0±1.5 5.1±1.4 Mg 12 7.6 65.6 178±4 140±14 147±50 106±50 Al 13 6.0 5.39 15.7±1.6 – 11.9±3 8.1±0.4 Si 14 8.2 63.7 151±4 100±12 140±50 101±40 P 15 10.5 0.529±0.046 * 0.65±0.17 – 1.4±0.4 – S 16 10.4 25.1±2.9 * 25±2 50±8 50±15 50±15 Cl 17 13.0 0.329 0.24±0.1 – – – Ar 18 15.8 5.9 4.3±0.4 – 3.1±0.8 3.1±0.4 K 19 4.3 0.224±0.046 * 0.55±0.15 – – – Ca 20 6.1 3.85 11±1 – 8.1±1.5 5.3±1.0 Ti 22 6.8 0.157 0.34±0.1 – – – Cr 24 6.8 0.834 2.1±0.3 – 2.0±0.3 1.5±0.3 Fe 26 7.9 57.6±8.0 * 131±6 97±11 122±50 88±50 Ni 28 7.6 3.12 6.4±0.6 – 6.5±2.5 – Zn 30 9.4 0.083 0.11±0.04 – – – The FIP Effect and Origin of SEPs and the Solar Wind D. V. Reames 6 tor of 1.2) behave more like ions in the SSW source but more like neutral atoms in the SEPs. 3. The FIP-Dependence of CIR and FSW Abundances Corotating interaction regions (CIRs) are formed when FSW streams overtake and collide with SSW emitted in that direction earlier in the solar rotation. Two shock waves may be formed, generally beyond 1 AU; the forward shock propagates outward into the SSW and the reverse shock propagates sunward into the FSW. Ions are accelerated mainly from the FSW at the reverse shock which is usually stronger (e.g. Richardson et al. 1993; Mason and Sanderson 1999; Richardson 2004). Using the data in Table 1, we compare the FIP effect of the CIR and FSW populations in Figure 2. Figure 2. The CIR/photospheric and FSW/photospheric abundances, normalized at O, are shown as a function of FIP. C and S behave like the low-FIP ions Mg, Si, and Fe, especially in the CIR population. With the exception of He, the FIP patterns in Figure 2 are in reasonable agree- ment. However, variations of He/O are known in the solar wind as functions of time and The FIP Effect and Origin of SEPs and the Solar Wind D. V. Reames 7 of solar-wind speed (Collier et al. 1996; Bochsler 2007; Rakowsky and Laming 2012). Nevertheless, C and S clearly behave like low-FIP ions, Mg, Si, and Fe, especially in the CIR population, unlike the behavior of the SEPs where C and S behave like N, O, and Ne. There is some evidence that C/O increases with the speed of the high-speed stream (Richardson et al. 1993; Mason et al. 1997), but this could reflect changes in the seed population that may prefer residual suprathermal SEP ions at the weaker shocks at lower stream speeds. 4. Discussion Brooks, Ugarte and Warren (2016; Abbo et al. 2016) have made a full-sun map of FIP bias based upon the S/Si abundance ratio. This map shows a large FIP bias in active re- gions. Based upon our forgoing analysis, S/Si should certainly show regions of appropri- ate FIP bias for SEPs, but certainly not for the SSW, since S and Si are both low-FIP ele- ments for the solar wind. Thus S/Si should be unaltered in the source of the SSW. The S/Si map shows the source of the FIP pattern seen by SEPs to be in active regions. The SEP FIP pattern suggests a source that is cooler, in some sense, than that of the SSW, so that C, S, and P are less likely to be ionized so they behave more like neutral atoms. The model of Laming (2015, 2017) explains the FIP effect in terms of the ponderomotive force of Alfvén waves on ions in the chromosphere and the low corona. This force can differ on closed and open magnetic loops since on closed loops the wavelength can resonate with the loop length. The fractionation is concentrated at the top of the chromosphere where H is becoming ionized if the waves causing the ponderomotive force are in resonance with a coronal loop above (see Figure 8 of Laming 2015). In this case back diffusion of any small neutral fraction restricts fractionation, Download 236.69 Kb. Do'stlaringiz bilan baham: |
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