J. Americo Gonzalez-Esparza

Three-dimensional nature of interaction regions: Pioneer, Voyager, and Ulysses solar cycle variations from 1 to 5 AU

We combined in-ecliptic observations of interaction regions from 1 to 5 AU by four spacecraft that traveled to Jupiter at different phases of the solar cycle: Pioneer 11 (declining phase of cycle 20), Voyager 1 and 2 (ascending phase of cycle 21), and Ulysses (just after solar maximum 22). We used this set of 97 interaction regions to study two different aspects of these events. (1) We analyzed the geometry of 38 stream interfaces, and found that the interaction regions detected by the three missions have different orientations. Some of these results might be associated with solar cycle variations such as the low-latitudinal inclination of the interaction regions detected by Ulysses and the high-latitudinal tilts of some interaction regions detected by Pioneer 11. Other results, such as the deviations with respect to the Parker spiral orientation, seem to be related to the persistent variations in the characteristics of the solar winds streams. (2) We studied the bulk speeds and the dynamic, magnetic, and thermal pressures of the fast and slow streams associated with 75 of these interaction regions. As a consequence of solar cycle variations, the bulk speed distributions of the fast and slow streams were different in the three missions. We found that the pressure ratios (dynamic, thermal, and magnetic) between fast and slow streams vary continuously. In about half of the interaction regions the dynamic pressure of the slow stream was higher than the dynamic pressure of the fast stream. We found similar variations in magnetic and thermal pressures. This implies that in many interaction regions the slow stream transfers momentum to the fast stream. The results presented here show that the solar wind streams associated with interaction regions vary at all the phases of the solar cycle, leading to interaction regions with different characteristics.

Two spacecraft observations of transient shocks and ejecta in the interplanetary medium

We compare Ulysses observations of 22 forward transient shocks (FTSs) and 11 ejecta during the first 19 months of its mission, with observations near Earth by IMP, in order to infer some properties of the propagation of these transient events in the interplanetary medium. We found that 13 of the 22 FTSs detected by Ulysses were also detected by IMP. The average of the mean radial transit speed of these 13 FTSs from 1 AU to Ulysses was about 504 km/s, which is slower than previous reports of transit speeds within 1 AU, suggesting shock deceleration beyond 1 AU. We found that whenever (in all cases) the two spacecraft detected the same FTS, the spacecraft were located within the same magnetic sector. During the period of the study we found 9 FTSs detected only by Ulysses and 10 FTSs detected only by IMP. For 16 of these shocks the two spacecraft were located within different magnetic sectors. The results suggest that magnetic sectors play a role in the propagation of transient shocks. Of the 11 ejecta detected by Ulysses, 7 of them also passed by IMP. The average of the mean radial transit speed of the 7 ejecta was about 407 km/s. In every case the radial width of the ejecta was larger at Ulysses than at IMP, showing a radial expansion with heliocentric distance. In the four events that we could estimate the shock-ejecta radial separation at 1 AU and Ulysses, we found that this radial distance was larger at Ulysses.

Estimates of ionosphere state over Mexico with TEC data

The ionosphere behaviour over Mexico was studied. We analysed variations of Total Electron Content (TEC) and critical frequency of F2-layer of the ionosphere (foF2). TEC values were extracted from data of local GNSS receivers and if missed then from global ionospheric maps. foF2 values were reconstructed using TEC measured over Mexico and equivalent slab thickness of the ionosphere measured in the adjacent to Mexico regions having ionosondes. Diurnal and seasonal patterns of TEC and foF2 behaviour over Mexico were revealed. The peculiarity of TEC behaviour during disturbances were studied. The presence of strong positive enhancements is a characteristic feature for Mexico that is confirmed by measurements of electron concentration at satellites CHAMP and DSMP.