This paper describes a scenario for magnetosphere-ionosphere coupling during magnetotail dipolarisations.  The scenario describes the anticipated ionospheric response to transient magnetospheric induction electric fields: differing horizontal ion and electron motions, charge accumulation, potential changes, and the acceleration of charges up and down field lines.  The conclusion is that the ionosphere plays an active role in magnetosphere-ionosphere coupling.

My main criticism of the paper is that it does not place itself within the context of the relevant literature.  It is well-known that the magnetosphere and ionosphere couple through electric fields, horizontal ionospheric Hall and Pedersen currents and vertical field-aligned currents.  It is well-known that the ionospheric currents are a result of differing ion and electron mobility in the E region.  It is also well-known that ionospheric plasma is a source of current-carriers for downwards FACs and that ionospheric outflow in response to M-I coupling is an important contributor to magnetospheric dynamics.  However, none of the related literature is discussed in the paper, so it is not clear if the proposed model is consistent or inconsistent with well-established ideas, or whether it contributes anything new to our understanding of M-I coupling.  Any revision of the paper would need to discuss the past literature in much more depth and explain what is new in the current paper.

I would also say that the title of the paper is rather too broad for its contents.

This manuscript extends the theory of Saka [2019] to account for field-aligned particle transport and field-aligned current. The work uses simple derivations to show the basic physics lying behind what people usually take for granted about ionosphere-magnetosphere coupling. This is a nice small piece of work for understanding this coupling. I will recommend the manuscript to be accepted after the author address the following comments:

- Line 44: the electric field inside the dipolarization front is typically 5 mV/m instead of 1 mV/m. See e.g., Figure 7e of Runov+ [2011 (the paper cited here)] and Figure 4c of Liu+ [2014 (2013JA019395)].

- Line 69: ‘generator’: I do not understand why this is a generator. A ‘generator’ means j dot E < 0. Please describe in details where and how this j dot E < 0 occurs.

- Line 134: caried -> carried.

- Lines 173-176: the author mentions edges of the ionosphere. How can the ionosphere have edges? I think the author means the edges of the ionospheric footprint of a flow channel.

- Lines 173-176, and Lines 194-196: The author writes southward/northward, clearly thinking of only the northern hemisphere. Equatorward/poleward are more appropriate.

- Line 174: upward ions could not provide enough current density: This statement comes form nowhere. The author did not estimate the upward current density from ions. Please compute this too.

- Line 179-185: The author writes that this paper reports a new ionospheric process. However, this process is first reported in Saka 2019 instead of this paper. This paper only extends the description of this process to include field-aligned particle transport and currents.