General Statement

This manuscript summarizes the particles and fields measurements and initial results returned by the BepiColombo Mercury mission during its first Venus flyby (VFB-1) on 15 October 2021. While nearly all aspects of such flybys are driven by requirements related to the spacecraft’s safety and timely arrival at their primary destinations, these events constitute special opportunities that have produced important “bonus” science on previous missions.  The manuscript is well-constructed and the writing is quite good.  All key aspects of the VFB-1 operations and instrument performance are well-documented. New science results from the initial analyses of these measurements indicate that Venus’ draped magnetic field tail extends at least ~ 48 Rv downstream of the planet and that the period for tail “flapping” is much broader than previously observed, at least ~ 3 to 7 min. Some minor suggestions are provided below, however, the manuscript reports important new observations of the solar wind interaction with Venus and significant new science results. Further, the BepiColombo VFB-1 data set is documented in detail for future scientific studies to follow. Accordingly, I recommend that the manuscript be published with only minor revisions.   

Specific Comments and Suggestions:

Lines 41-49: I think you should not spend too much time on history, but first surveys of the Venus magnetotail were carried out by the Venera 9 and 10 orbiters in 1975-1976 (for details see Verigin et al., Plasma analysis, JGR, August, 1978; Eroshenko et al., induced magnetic tail, Cosmic Research, 17, 17, 1979).  This is very near the time of Mariner 10 primarily magnetosheath flyby, but for the sake of completeness you might consider referencing Venera and 9 and 10’s historic contribution.

Section 2 “The Data”: The description of the BepiColombo mission and the impact of the stacked science spacecraft and SEP carrier cruise configuration may be too brief for Readers who are not already familiar with the mission. You do note the impact of the cruise configuration on the field-of-view of some individual particle instruments in  isolated sentences later in the text. However, I would recommend at least a brief overview of BepiColombo’s cruise configuration (e.g., MMO behind heat shielding; MPO MAG further from “SEP carrier module” but still seeing some stray B-field contamination) early in Section 2 to provide context for the instrumental considerations that follow.

Section 3.2: The smoothed magnetic field data and the limited number of cross-tail current sheet crossings may preclude this analysis, but did you examine the angular rotation of B as BC traversed the cross-tail current sheet,?  If you did, then were the rotations  < 180 deg and, if so, by how much? After the draped IMF flux tubes that make up the “induced” tail slip about the Venus ionosphere and move downstream, they start to “unkink” as the ionospheric plasma and pickup ions from the dayside and flank interaction regions are accelerated by the J x B (aka “magnetic sling-shot” effect – just like in a comet tail) in the cross-tail current sheet. This effect was observed very clearly in the Pioneer Venus Orbiter data with the magnetic field rotations across the current sheet decreasing (i.e. increasingly below 180 deg) as the downtail distance grew and the speed of the O+ in the cross-tail current sheet increased toward solar wind speeds (Slavin et al., JGR, 1989). Given that, as you point out, the BepiColombo VFB1 Tail encounters were further downtail than the PVO sampling a measurement of the magnetic field rotation across the current sheet crossings would be of great interest, if it is possible with these data?.

--------------- General comments:

The manuscript “Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby” by Volwerk et al. presents highly interesting and unique measurements from Venus’ long magnetotail made by the BepiColombo spacecraft.

The figures in the paper show the measured magnetic field, ion and electron measurements in a very clear and informative way. Moreover, the authors interpret the data and put the observation into a wider context by discussing and comparing observations with the previous plasma and field observations from the Venus magnetotail.

The paper is logically structured, and text is clearly written. In addition to the presentation of the data, the work is valuable also because it is foreseen that in the future the presented observations will motivate global modelling works.

Some more details should, however, be provided before the work is ready for publishing, please see below.

--------------- Individual scientific remarks:

* Please describe in more details what can be seen in Figure 11:

    - The authors state that the black arrows show the direction of the magnetic field, but they look rather like directions of the IMF.

    - Fig. 11d) and 11e): Colour bars are hardly visible. Is the yellow region a constant velocity surface? Does the mostly green colour region show the speed of the solar wind on the ecliptic plane?

* A brief piece of information. The analysed flyby is exciting also because the observations may include effects of an ICME. Interestingly, such a situation when an ICME hits Venus has been analysed, and also simulated, already when the VEX observations has been analysed (Dimmock et al., JGR, 2018).

--------------- Technical corrections/suggestions:

*  [Fig. 8] When the authors refer to the time range between purple, green, cyan and red lines show in Fig. 8, they use the term “box” although there are no purple, green, cyan and red boxes but just lines. This terminology could be clearer.

*  “ASPERA-4-IMA” is typically written as “ASPERA-4 IMA” and “ASPERA-4-ELS” as “ASPERA-4 ELS”.

*  [l. 223] Here “…magnetotail flapping in the near-Venus tail around ~ (1.5,0.1,0.5) RV …” the x position should probably be “(-1.5,0.1,0.5)” i.e. the X_VSO should be negative in order the position would be on the night side.

*  [l. 247-248] Similarly, this “… VEX near X ~ 1.5RV and BepiColombo near X ~ 15 RV,…” should probably read as “… VEX near X  ~ -1.5 RV and BepiColombo near X ~ -15RV,…”. Also, in Fig. 9. figure caption this “…near ~ (1.5,0.1,0.5) observed…” should probably read as “…near ~ (-1.5, 0.1, 0.5) observed…”

*  [l. 259] The value of F would be good to express in SI units, i.e. as “F = 20 nT”.

*  [l. 309] “thetime” -> “the time”

*  [Fig. 11 figure caption] “Ocotber” -> “October”

*  [l. 381] “as welll” -> “as well”