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Abstract The polarFregion ionosphere frequently exhibits sporadic variability (e.g., Meek, 1949,https://doi.org/10.1029/JZ054i004p00339; Hill, 1963,https://doi.org/10.1175/1520‐0469(1963)020<0492:SEOLII>2.0.CO;2). Recent satellite data analysis (Noja et al., 2013,https://doi.org/10.1002/rds.20033; Chartier et al., 2018,https://doi.org/10.1002/2017JA024811) showed that the high‐latitudeFregion ionosphere exhibits sporadic enhancements more frequently in January than in July in both the northern and southern hemispheres. The same pattern has been seen in statistics of the degradation and total loss of GPS service onboard low‐Earth orbit satellites (Xiong et al. 2018,https://doi.org/10.5194/angeo‐36‐679‐2018). Here, we confirm the existence of this annual pattern using ground GPS‐based images of TEC from the MIDAS algorithm. Images covering January and July 2014 confirm that the high‐latitude (>70 MLAT)Fregion exhibits a substantially larger range of values in January than in July in both the northern and southern hemispheres. The range of TEC values observed in the polar caps is 38–57 TECU (north‐south) in January versus 25–37 TECU in July. First‐principle modeling using SAMI3 reproduces this pattern, and indicates that it is caused by an asymmetry in plasma levels (30% higher in January than in July across both polar caps), as well as 17% longer O+plasma lifetimes in northern hemisphere winter, compared to southern hemisphere winter.
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Traveling Ionosphere Disturbance Signatures on Ground‐Based Observations of the O( 1 D ) Nightglow Inferred From 1‐D Modeling
Abstract This paper reports our simulations of the volume emission rate of the O(1D) redline nightglow perturbed by waves traveling across the thermosphere at around 250 km altitude. Waves perturb the electronic and neutral background densities and temperatures in the region and modify the O(1D) layer intensity as it is captured by ground‐based nightglow instruments. The changes in the integrated volume emission rate are calculated for various vertical wavelengths of the perturbations. We demonstrate that, as the solar activity intensifies, the vertical scales of most likely observable TID waves become larger. For high solar activity, we demonstrate that only waves presenting vertical wavelengths larger than 360 km are likely to be observed. The variation of the range of likely observable vertical wavelengths with the solar cycle offers a plausible explanation for the low occurrence rate of TID in measurements of the redline nightglow during high solar activity periods. We have compared our results with those of Negale et al. (2018;https://doi.org/10.1029/2017JA024876) and Paulino et al (2018;https://doi.org/10.5194/angeo-36-265-2018) to verify that observed vertical wavelengths distribute around 140–210 km, in good correspondence with our predicted threshold wavelength160 km for very low solar cycle period.
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- PAR ID:
- 10450828
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 124
- Issue:
- 11
- ISSN:
- 2169-9380
- Page Range / eLocation ID:
- p. 9348-9363
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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