tokens: of them had a clear impact. RPC-LAP senses a large increase of plasma during each CME passage on September 11 and 19, with elevated plasma density after. We can differentiate the spiky CME signatures in Fig. 4 from the oscillations in September which correspond to seasonal effects. The spikes also do not manifest until approach into the 30 km orbits. By factoring in the CMEs studied by McKenna-Lawlor et al. ( 2016 ), we can remove two of the large spikes in the September data so they do not appear in Fig. 6 . Another possibility relates to excessive variations of the solar EUV radiation, since the current intensities collected by RPC-LAP sweeps depend on the illumination and ultimately on the solar EUV flux. Thus, a variation in EUV flux should be seen as a variation in the collected photoelectron current density by the probe and qualitatively follow each other. Until the end of 2014 August, the solar EUV flux variations match those of the RPC-LAP current measurements, with a slow increase of the photoelectron emission that can be linked directly to the increase in the flux, as the heliocentric distance between Rosetta and the Sun decreases. The 27-d periodicity in the EUV flux, due to the Sun's rotation (e.g. Woods Rottman 2002 ), has an impact on the photoelectron emission yield of the probes, resulting in the EUV flux and the I 1 current density being in qualitative agreement. After the end of 2014 August, this trend starts to be significantly altered, with the I 1 current density exhibiting large variations that do not correlate any more with the solar EUV flux variation. At the time of the transition into the HDR, the solar EUV flux variations stop driving the evolution of the I 1 currents. Thus, some other effects begin to take precedence on 2014 September 9, and the transition found in the RPC-LAP photocurrent measurements is probably not a temporally isolated artefact due to a sudden variation of the solar flux. On the temporal scale that we study in this paper, we see oscillations of the knee potential, as well as traces of this in the ion attraction current I 1 . These signals correspond to the envelopes of the 6.2-h longitudinal oscillations reported by Odelstad et al. ( 2015 ) and Edberg et al. ( 2015 ), and relate to repeated crossings of more active regions on the comet (with increased neutral outgassing). The envelopes correspond to latitudinal variations, where the Northern hemisphere of 67P is the more active one, and can be seen for electrons with RPC-IES as early as in August (Clark et al. 2015 ), but at a smaller energy and density compared to 2014 September. Although part of the reason for the spread seen at 27–29 km from the nucleus is the oversampling of the projections of active regions once Rosetta enters into the 30 km orbit, this does not explain the sudden change of magnitude upon approach to this orbit. Rosina's Double Focusing Mass Spectrometer (DFMS) measurements show increased density of O 2 following entry
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