the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Nov 2021
Are drivers of northern lights in the ionosphere?
Abstract. Known as northern lights, auroral spirals are distinct features of substorm auroras composed of large-scale spirals (100s km Surges) mixed with smaller scale ones (10s km Folds, and 1 km Rays). Spiral patterns are generally interpreted in terms of the field line mapping of the upward field-aligned currents produced in the magnetosphere during the field line dipolarization. The field line mapping results in opposing spiral rotations of small- and large-scale auroras. Because of a rotational symmetry deformation and similarity in deformation speeds (6~8 km/s) of small- and large-scale spirals, it has been suggested that common physical processes may underlie the deforming processes. Internal processes in the polar ionosphere (ionospheric driver) will be proposed as the general dynamic for spiral auroras. The ionospheric driver rotated in the ionosphere to produce spirals that characteristically differ from the field line mapping scenario.
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Status: closed
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RC1: 'Comment on angeo-2021-66', Anonymous Referee #1, 11 Jan 2022
The manuscript by Osuke Saka on "Are drivers of northern lights in the ionosphere?" is about origin of auroral spirals. This question is still under the debate and, therefore, this topic is actual and interesting. The author presents a model for explanation of the auroral spirals of different spatial scales. An observation is also presented to support the model. I, however, find the manuscript quite unclear and requiring more work and explanation before it can be published in Annales Geophysicae. Please find below more detailed comments:
lines 15-16 and introduction, Could you please provide references that field-line mapping results in opposing spiral rotations of small and large scale auroras.
lines 18-19, If I understand correctly the model, the driver is still related to a dipolarization in the magnetosphere.
lines 20-21, 40-42, 65-67, 69-72, These sentences are unclear.
Introduction, could you please provide references on the classification of auroral spirals from 1 km to 100s of km size?
line 74, What are "the dynamical trajectories"? Which total energy do you mean?
lines 75-78, Why perpendicular velocities will be lost?
lines 102-104, Which formula is used to calculate electric fields and electrostatic potential?
line 110, Which formula is used to calculate plot in Figure 2?
line 120-123, please provide references for the numbers.
Figure 3, It is unclear how observations in Figure 3 are related to auroral spirals. More explanation is necessary.
line 135, it would be good to show the magnetic field observations from the geosynchronous orbit.
lines 137-138, I do not see motion of shear layers in this Figure.
lines 146-149, this statement contradict to the statement in lines 73-75.
lines 151-152, please provide a reference about the width of the flow channels.
line 158, the plot in Figure 3 is has also source, it should be mentioned here.
Citation: https://doi.org/10.5194/angeo-2021-66-RC1 - AC1: 'Reply on RC1', Osuke Saka, 27 Jan 2022
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RC2: 'Comment on angeo-2021-66', Anonymous Referee #2, 18 Jan 2022
This paper attempts to explain the formation of rotational motion seen in the aurora, from small-scales (curls, ~1 km) up to spirals (~100 km), using a single mechanism.
I must admit that I do not completely follow the proposed mechanism, but it seems to essentially use oppositely directed E x B drift in the ionosphere on either side of an auroral arc as a means of rotating the structure. While I agree that E x B drift is indeed usually oppositely directed on either side of arc, I do not think the proposed mechanism agrees with observations of auroral spirals forming. Figure 2 of the manuscript shows the formation of an auroral spiral whereby the outer “ends” of an arc rotate a full 180 degrees in the magnetic field-perpendicular plane. However, observations of auroral spirals show that they do not form like this. Overall the arc stays roughly E-W aligned, with the part of the arc at the centre of the spiral rotating as the spiral winds up (see for example Partamies et al., 2001, and Keiling et al., 2009). Auroral curls (also called rays in the submitted manuscript, although note that these are different, see Ivchenko et al., 2005) have an opposite rotation to auroral spirals (Trondsen and Cogger, 1998) which would seem to be inconsistent with the formation mechanism proposed. The fact that the mechanism does not reflect observations is a major flaw.
A comparatively minor issue is that the title is much too general, and does not accurately represent the content of the manuscript.
References
Ivchenko et al., 2005, GRL, 32, doi:10.1029/2005GL022650
Keiling et al., 2009, Ann. Geophys., 27, 11, doi:10.5194/angeo-27-4317-2009
Partamies et al., 2001, JGR, 106, A12, doi:10.1029/2001JA900093
Trondsen and Cogger, 1998, JGR, 103, A5, doi:10.1029/98JA00619Citation: https://doi.org/10.5194/angeo-2021-66-RC2 - AC2: 'Reply on RC2', Osuke Saka, 27 Jan 2022
Status: closed
-
RC1: 'Comment on angeo-2021-66', Anonymous Referee #1, 11 Jan 2022
The manuscript by Osuke Saka on "Are drivers of northern lights in the ionosphere?" is about origin of auroral spirals. This question is still under the debate and, therefore, this topic is actual and interesting. The author presents a model for explanation of the auroral spirals of different spatial scales. An observation is also presented to support the model. I, however, find the manuscript quite unclear and requiring more work and explanation before it can be published in Annales Geophysicae. Please find below more detailed comments:
lines 15-16 and introduction, Could you please provide references that field-line mapping results in opposing spiral rotations of small and large scale auroras.
lines 18-19, If I understand correctly the model, the driver is still related to a dipolarization in the magnetosphere.
lines 20-21, 40-42, 65-67, 69-72, These sentences are unclear.
Introduction, could you please provide references on the classification of auroral spirals from 1 km to 100s of km size?
line 74, What are "the dynamical trajectories"? Which total energy do you mean?
lines 75-78, Why perpendicular velocities will be lost?
lines 102-104, Which formula is used to calculate electric fields and electrostatic potential?
line 110, Which formula is used to calculate plot in Figure 2?
line 120-123, please provide references for the numbers.
Figure 3, It is unclear how observations in Figure 3 are related to auroral spirals. More explanation is necessary.
line 135, it would be good to show the magnetic field observations from the geosynchronous orbit.
lines 137-138, I do not see motion of shear layers in this Figure.
lines 146-149, this statement contradict to the statement in lines 73-75.
lines 151-152, please provide a reference about the width of the flow channels.
line 158, the plot in Figure 3 is has also source, it should be mentioned here.
Citation: https://doi.org/10.5194/angeo-2021-66-RC1 - AC1: 'Reply on RC1', Osuke Saka, 27 Jan 2022
-
RC2: 'Comment on angeo-2021-66', Anonymous Referee #2, 18 Jan 2022
This paper attempts to explain the formation of rotational motion seen in the aurora, from small-scales (curls, ~1 km) up to spirals (~100 km), using a single mechanism.
I must admit that I do not completely follow the proposed mechanism, but it seems to essentially use oppositely directed E x B drift in the ionosphere on either side of an auroral arc as a means of rotating the structure. While I agree that E x B drift is indeed usually oppositely directed on either side of arc, I do not think the proposed mechanism agrees with observations of auroral spirals forming. Figure 2 of the manuscript shows the formation of an auroral spiral whereby the outer “ends” of an arc rotate a full 180 degrees in the magnetic field-perpendicular plane. However, observations of auroral spirals show that they do not form like this. Overall the arc stays roughly E-W aligned, with the part of the arc at the centre of the spiral rotating as the spiral winds up (see for example Partamies et al., 2001, and Keiling et al., 2009). Auroral curls (also called rays in the submitted manuscript, although note that these are different, see Ivchenko et al., 2005) have an opposite rotation to auroral spirals (Trondsen and Cogger, 1998) which would seem to be inconsistent with the formation mechanism proposed. The fact that the mechanism does not reflect observations is a major flaw.
A comparatively minor issue is that the title is much too general, and does not accurately represent the content of the manuscript.
References
Ivchenko et al., 2005, GRL, 32, doi:10.1029/2005GL022650
Keiling et al., 2009, Ann. Geophys., 27, 11, doi:10.5194/angeo-27-4317-2009
Partamies et al., 2001, JGR, 106, A12, doi:10.1029/2001JA900093
Trondsen and Cogger, 1998, JGR, 103, A5, doi:10.1029/98JA00619Citation: https://doi.org/10.5194/angeo-2021-66-RC2 - AC2: 'Reply on RC2', Osuke Saka, 27 Jan 2022
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