Reviewer’s report on the manuscript by Prykryl et al. titled “Multi-instrument observations of polar cap patches and traveling ionospheric disturbances generated by solar wind Alfvén waves coupling to the dayside magnetosphere” (manuscript #: angeo-2022-14)

In this manuscript, the authors try to show a close relationship between the solar wind Alfvén waves and the polar cap patches / traveling ionospheric disturbances, using multiple events based on the observation by the RISR IS radar, ground-based magnetometers, GNSS receivers, and SuperDARN radars. The topic itself is scientifically interesting, although several points should be improved. I consider that the following points should be addressed and revised before the manuscript is ready for publication in the Annales Geophysicae journal.

Overall comments:

1. Interpretation of the data. The authors demonstrate that the TIDs are generated only by the Joule Heating due to the dayside ionospheric currents. These days it is not a generally accepted idea. The TIDs are highly correlated with the lower atmospheric disturbances (e.g., Frissell et al., 2016). I am also surprised to see that the manuscript includes minimal discussion. The authors should add the discussion section, cite the related papers such as those mentioned in this report, and discuss the differences between the current events and the previous studies.
   
   
   
   

Recent progress of the TID studies using the SuperDARN is summarized in the review paper by Nishitani et al. (2019). I recommend that the authors check this paper.

2. Definition of the LSTID / MSTID. The manuscript states that the LSTIDs have greater than 10000 km. I am not certain how the authors can distinguish between LSTIDs and MSTIDs in Figure 9. The authors need to add a more detailed description. In addition, I am not sure whether the LSTIDs observed by the SuperDARN radar and pointed out in the text are actually LSTIDs. Lines 261-262 state, “Figs. 9a-d show TIDs observed in the detrended vertical vTEC and the radar ground-scatter power focused and defocused by TIDs moving equatorward.” The LSTID wavelength greater than 1000 km cannot produce focusing / defocusing of the radar waves. LSTIDs are supposed to be observed in the Doppler velocities of the ground scatter data. For example, Hayashi et al. (2010) showed that the SuperDARN Doppler velocities changes in the ground scatter data are consistent with the GNSS TEC data in the framework of the propagation of atmospheric gravity waves.

3. Lines 144-145 say, “Fig. 3 shows the ionospheric currents (EICs) mapped in geographic coordinates….” It is strange that later in the manuscript, Figures 16-18 are plotted in AACGM (geomagnetic coordinates). I do not understand why the authors plot the same (e.g., EIC) data in different coordinates in one manuscript. It will cause serious confusion among the readers. I strongly recommend plotting the data in the same coordinate system.
   
   
   
   

Individual comments:

Lines 128-129 and Figure 2: Please describe the RISR-C and RISR-N field of views (beam positions). Otherwise, the readers cannot understand what the authors mean.

Lines 138-140: “The first few patches (enhancements in Ne) that were observed by RISR-N between 16:00 and 17:00 UT were not detected by RISR-C (Fig. 2a). This implies that the cusp was in the RISR-C FoV since polar patches are known to be produced by flow channels in the cusp.” I do not understand these sentences. Maybe something is wrong. Please check.

Lines 146-147: “The GPS ionospheric pierce points (IPPs) at 110 km shown as circles scaled by the CHAIN GPS phase variation values, σΦ, are discussed in Section 3.3.3.” – I wonder why the authors set the pierce points at 110 km. Obviously, the electron density is higher in the F-region than in the E-region, and so is the amplitude of scintillations. By the way, I cannot find section 3.3.3.

Line 185: “were” – is it “which were”?

Figure 9 and Lines 266-267 (as well as other corresponding lines): Are the ground scatter ranges plotted the same way as the ionospheric scatter? If so, it will cause a severe misunderstanding among the readers. If the ground scatter comes from a 1-hop propagation mode, then the focusing / defocusing point should be the mid-point between the radar and the backscatter region (for 2+ hops the geometry becomes more complicated). It is not appropriate to plot the SuperDARN echo data with the range set to the backscatter point, together with the GNSS TEC data with the same range.

Figure 4 caption: There is no description of the SuperDARN convection map.

References:

Frissell NA, Baker JBH, Ruohoniemi JM, Greenwald RA, Gerrard AJ, Miller ES, West ML (2016) Sources and characteristics of medium-scale traveling ionospheric disturbances observed by high-frequency radars in the North American sector. J Geophys Res Space Physics 121:3722–3739. https://doi.org/10.1002/2015JA022168

Hayashi H, Nishitani N, Ogawa T, Otsuka Y, Tsugawa T, Hosokawa K, Saito A (2010) Large-scale traveling ionospheric disturbance observed by SuperDARN Hokkaido HF radar and GPS networks on 15 December 2006. J Geophys Res 115:A06309. https://doi.org/10.1029/2009JA014297

Nishitani, N., Ruohoniemi, J.M., Lester, M. et al. Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars. Prog Earth Planet Sci 6, 27 (2019). https://doi.org/10.1186/s40645-019-0270-5

Review of “Multi-instrument observations of polar cap patches and traveling ionospheric disturbances generated by solar wind Alfven waves coupling to the dayside magnetosphere” by Prikryl, Gillies, Themens, Weygard, Thomas and Chakraborty

The paper is well written, contains interesting new results and should be published in Annales Geophysicae after suitable revision.

Main Comments

There are two distinct parts to solar wind high speed streams. At the leading edge where the high speed stream interacts with the upstream slow speed stream, a “corotating interaction region” or CIR (GRL 3, 3, 137-140, 1976; JGR 100, A11, 21717-21733, 1995) forms.  CIRs have both high magnetic fields and high plasma densities, higher than the following high speed stream proper.  The Alfven wave amplitudes are also higher inside the CIR due to the compression (GRL, 22, 23, 3397-3400, 1995). It will be interesting for the AG readership to know where your effects are strongest, associated with the CIR or the high speed stream proper.  Also since the plasma densities inside the CIR are high, can this play a role in magnetic reconnection and the tongues of ionization?

Introduction Section.  I doubt that Jim Dungey (1961) intended to imply that the interplanetary magnetic field remained southward and there occurred a steady state of energy input into the magnetosphere. This statement should be reworded a bit to remove this implication. Short duration (~30 min to 1 hr) southward magnetic fields causes substorms (PSS, 12, 273-282, 1964; JGR, 77, 16, 2970, 1972; JGR, 78, 4, 617-629, 1973). Longer duration (hrs) southward fields cause magnetic storms (JGR, 99, A4, 5771-5792, 1994; JGR 113, A05221, doi:10.1029/2007JA012744, 2008).  Southward component interplanetary fields associated with Alfven waves in either CIRs or high speed streams have been shown to do the same, cause substorms and DP2 events (JGR, 73, 11, 5549-5559, 1958; JGR, 95, A3, 2241-2252, 1990; JGR 100, A11, 21717-21733, 1995; JASTP 66, 167-176, 2004). In the JGR 2000 paper it was noted that southward IMFs with durations less than 15 min were not geoeffective. Can you please mention (roughly) the duration of the southward components of the Alfven waves? The ionospheric currents that you mention most certainly must be DP2 currents.  Please quote and discuss.

Line 52.  It should be noted that spacecraft observations of the polar cap and auroral zone noted auroral patches during HILDCAA intervals ( southward component of Alfven waves in solar wind high speed streams causing reconnection).    Please see p235-243 in AGU mon. 167, 2006; Substorms 7: Proceedings of the 7^th International Conference on Substorms, edited by N. Ganushkina and T.I. Pulkkinen, 1, 67, 2004.  These papers should be quoted.

Line 113.  The reference to the HCS discovery should be quoted here. It is JGR 83, 717, 1978.