Ionospheric Day-to-Day Variability Around the Whole Heliosphere Interval in 2008

Abstract

Ionospheric F2 peak electron densities (NmF2) measured at ten ionosonde stations have been analyzed to investigate ionospheric day-to-day variability around the Whole Heliosphere Interval (WHI) in 2008 (Day of Year (DOY) 50 -140). The ionosonde data showed that there was significant global day-to-day variability in NmF2. This variability had 5-, 7-, 9-, 11-, 13.5-, and 16 -21-day periodicities. At middle latitudes, the ionosphere appeared to respond directly to the solar-wind and interplanetary-magnetic-field (IMF) induced geomagnetic-activity forcing, with the day-to-day variability having the same periods as those in the solar-wind/IMF and geomagnetic activity. At the geomagnetic Equator, the ionosphere had a strong 7-day periodicity, corresponding to the same periodicity in the IMF B z component. In the equatorial anomaly region, the ionosphere showed more complicated day-to-day variability, dominated by the 9-day periodicity. In addition, there were also peri- odicities of 11 days and 16 -21 days in the ionosonde data at some stations. The ionosonde data were compared with the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) simulations that were driven by the observed solar-wind and IMF data during the WHI. The CMIT simulations showed similar ionospheric daily variability seen in the data. They captured the positive and negative responses of the ionosphere at middle latitudes during the first corotating interaction region (CIR) event in the WHI. The response of the model to the second CIR event, however, was relatively weak.

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

“…The ionosphere and thermosphere respond most strongly to negative IMF B Z , where the periodicity in B Z was mostly around 27, and 13.5 days, with a significant peak at seven days. Wang et al (2011) found that the periodicities in B TOT and B Z for three Carrington rotations centered around CR 2068/WHI were similar to those for the entire year. Most of the parameters in Figure 11 share the nine-day periodicity of the solar wind, including the peak electron density in the F region (NmF2) at all latitudes studied by Wang et al (2011).…”

“…showed that the geomagnetic indices of the auroral electroject (AE) and the disturbed (Dst) equatorial current were larger for the first HSS than for the second. Wang et al (2011) showed that Kp and the ionospheric-storm responses were larger for the first HSS than for the second. Indeed, increased responses for negative IMF GSM B Z can be seen in the larger responses in the geospace parameters in Figure 11 between the red vertical lines marking the HCS crossings.…”

“…Woods et al, 2009;Solomon et al, 2010Solomon et al, , 2011Araujo-Pradere et al, 2011;Emery et al, 2011;Gibson et al, 2011;Haberreiter, 2011;Lei et al, 2011;Wang et al, 2011;White et al, 2011) • Cosmic-ray modulation? Jian, Russell, and Luhmann, 2011) • Morphology of heliosphere?…”

“…(Leamon and McIntosh, 2009;Gibson et al, 2011;Zhao and Fisk, 2011) • What can we learn about plasma/neutral and density boundaries? Emmert, Lean, and Picone, 2010;Gibson et al, 2009Gibson et al, , 2011McIntosh and De Pontieu, 2009;de Toma, 2010;Lei et al, 2011;Wang et al, 2011;Vásquez et al, 2011) • How about magnetic boundaries (current sheets/sector boundaries, magnetopauses)? (Petrie, Canou, and Amari, 2011;Riley et al, 2011;Zhao and Fisk, 2011) • Is there evidence for interchange reconnections at coronal-hole boundaries?…”

“…Lepping et al, 2010;Maris and Maris, 2010;Riley et al, 2011;Webb et al, 2011) • How do they interact with planetary magnetospheres and geospace? (Araujo-Pradere et al, 2011;Emery et al, 2011;Jackman and Arridge, 2011;Lei et al, 2011;Wang et al, 2011) To properly address these questions, the dates of WHI needed to occur near solar minimum, and multi-point heliospheric measurements would have to include out-of-the-Ecliptic observations provided by the Ulysses mission. Fortunately, Ulysses was in an ideal location, and the STEREO mission provided two additional measurements points near the solar Ecliptic plane.…”