## 3 Swarm and Ancillary Data
The selection of Swarm A and C orbital tracks for the analysis of winter solstice starts from Swarm A and C trajectories recorded on 17 December 2016, which both took place 40 min. after the largest M = 7.9 earthquake occurred close to the eastern coast of New Ireland island in Papua New Guinea (10:51 UTC, which is 20:51 local time (LOC)). Then, for each satellite (A/C), an additional 90 Swarm tracks from the preceding and subsequent days are selected (1 November 2016-30 January 2017). The threshold difference in the 90 adjoined tracks in the time unit, in relation to that on 17.12, is set to a maximum of 4.4 h, whereas the allowed difference in longitude is a maximum of 20\({}^{\circ}\). The range of latitudes of the 91 selected tracks is approximately between 25\({}^{\circ}\)N and 45\({}^{\circ}\)S (Figure 2a). This selection produced 91 track sections, shown in Figure 2a, and the same rule with reference Swarm A/C tracks is applied in a more quiet region of the African Plate to select a similar number of 1  
of tracks at very similar latitudes (Figure 2b). In order to keep Figure 2a transparent, the date labels are only shown for the eight selected days and are also presented in Figures 4-6, including the most significant disturbances within the selected period. In the third selected region, which is the junction of the Pacific Plate and the North American Plate located at completely different latitudes, the reference Swarm track is selected from the 17 th day of the middle month (Figure 2c). The longitude differences and time differences of the adjoined tracks in relation to the reference track are the same as for the primary region. The Swarm orbital track selections in the Papua New Guinea region for the other seasons of 2016 are prepared in exactly the same way, starting with the track within very similar latitudes on the 17 th day of the middle month, and adjoining remaining Swarm passes at close longitudes using the same longitude and time separation maxima. Additionally, the same rule is applied for the selection of the opposite daytime tracks that were investigated, aside from the above-mentioned nighttime or nearly nighttime passes. Neither the track selection in the summer solstice and vernal equinox nor the daytime tracks need to be plotted in the figures, as these tracks follow the same rule that can be seen in Figures 2a and 3a. They pass tectonic plate boundaries within very similar latitudes, similar longitudes, and similar times, dependent on the actual Swarm trajectory, but always refer to the selected half of the day. The selection of Swarm B tracks starts from the Swarm B trajectory recorded on 8 December 2016, approximately 30 min. before the largest M = 7.8 earthquake in the Solomon Islands region near Papua New Guinea, which occurred close to the western coast of San Cristobal Island (17:38 UTC--3:38 LOC). Then, an additional 90 Swarm tracks from the preceding and subsequent days (1 November 2016-30 January 2017) are selected. The range of latitudes of the 91 selected tracks is approximately the same as for the Swarm A/C pair. The allowed between-track differences in time and longitude with respect to a trajectory of 8.12 are also the same. The tracks of Swarm B are grouped in a slightly  
Figure 2: **(a)** Selection of descending (nighttime) Swarm A/C tracks over Papua New Guinea between 1 November 2016 and 30 January 2017. The tracks are selected to have the closest possible time of the day and longitude to the first selected track just after M = 7.9 mainshock. The red triangles denote earthquakes above M = 6.5. **(b)** Selection of Swarm A/C tracks at the same latitudes and local time in amore seismically quiet region. The red triangles denote earthquakes above M = 4.0. **(c)** Selection of Swarm A/C tracks at the high and middle latitudes. The red triangles denote earthquakes above M = 4.5.  
different way than Swarm A/C, as the orbit repetition cycles of Swarm B (Figure 3a) differ in comparison to those for Swarm A/C.