Effects of Solar Illumination and Substorms on Auroral Electrojets Based on CHAMP Observations

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In this work, prominent longitudinal variation of polar electrojet (PEJ) and field‐aligned currents (FACs) are reported for the first time in different local times and hemispheres. Larger longitudinal differences exist mostly in the south than in the north with nearly opposite phase except for the nighttime. The most prominent longitudinal variation occurs around noontime. In the nighttime, the longitudinal changes of PEJ and upward FACs in both hemispheres are similar. The larger northern summer FACs and PEJ at noon occur more frequently around 0°–60° and 300°–360° magnetic longitude (MLon), while the larger southern summer currents occur around 120°–300° MLon. The summer‐winter hemispheric differences in PEJ and upward FACs disappear in the midnight sector. The northern FACs dominance exists around 0°–120° and 270°–360° MLon, except for winter when the northern dominance of upward FACs at night exist in nearly all longitudes. In local summer, PEJ shows northern dominance around 0°–60° and 270°–360° MLon, and southern dominance around 120°–240° MLon. In local winter, PEJ shows northern dominance around 180° MLon near midnight, while in most other local times, PEJ shows northern dominance around 270° MLon. These longitudinal, seasonal and hemispheric differences are discussed in terms of mixing effects of ionospheric conductance and merging electric field in different local time sectors.

Section: Statistical Resultssupporting

confidence: 92%

Magnetic Longitudinal and Local Time Variations of Polar Electrojet and Field‐Aligned Currents

Wang,

Lühr

2023

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“…This could be related to the hemispheric fluxtube‐integrated conductance (local conductance plus conductance at conjugate hemisphere). Pervious finding showed that the nighttime westward PEJ is inversely correlated with the fluxtube‐integrated conductance in conjugate hemispheres (Wang & Lühr, 2021). Unlike duskside, the local winter PEJ is located at a higher latitude than the summer PEJ, which is related to the weaker Em activity in local winter (see Figure S1 in Supporting Information ).…”

Section: Statistical Resultsmentioning

confidence: 99%

IMF B_y Effects on the Strength and Latitude of Polar Electrojets: CHAMP and Swarm Joint Observations

Wang,

Lühr

2024

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In this study, the impact of the interplanetary magnetic field (IMF) By component on the peak strength and position of polar electrojets (PEJs) is analyzed, based on 16 years of joint observations from Challenging Minisatellite Payload (CHAMP; 2000–2010) and Swarm (2014–2020) satellites, while focusing on the local time and hemispherical differences. With a more positive IMF By, the duskside eastward PEJ enhances significantly at June solstice in the Northern Hemisphere. Around midnight, the impact of IMF By on the PEJ is more significant in the winter hemisphere; the westward PEJ is stronger in the Northern (Southern) Hemisphere for a more positive (negative) IMF By. In 03–08 MLT, the impact of IMF By is similar in both the winter and summer hemispheres: for IMF By > 0 and By < 0, the PEJ in the dawn sector is stronger in the December and June solstices, respectively. Around noon, a more duskward (dawnward) IMF By component leads to a higher eastward (westward) PEJ in the northern (southern) summer hemisphere. The northern westward (eastward) PEJ peaks at higher latitudes than the southern PEJ for a negative (positive) IMF By.

“…Additionally, Holappa and Buzulukova (2022) studied the IMF B y effect on the energetic proton flux specifically in the dusk sector, focusing on the 12 to 24 MLT interval. In this work, the MLT of peak PEJ is used to define the events, following previous works (e.g., Wang & Lühr, 2023, 2024).…”

Section: Data and Processing Methodsmentioning

confidence: 99%

“…This article is a follow‐on work of our previous research (Wang & Lühr, 2023, 2024), wherein we employed a consistent 6‐hr MLT interval. The motivation for using such a broad MLT bin width is to ensure sufficient statistics in all MLT bins.…”

Section: Data and Processing Methodsmentioning

confidence: 99%

Interplanetary Magnetic Field B_y Effects on the Strength and Latitude of Field‐Aligned Currents in Different Magnetic Local Time Sectors

Wang,

Sun,

Lühr

2024

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In this work, IMF By effects on field‐aligned currents (FACs) are examined in different local time sectors, seasons, and hemispheres. At dusk and 09–14 MLT, when the eastward polar electrojet (PEJ) prevails, the northern FACp (poleward side FACs) are stronger when IMF By < 0 than when IMF By > 0. Conversely, at dawn, 21–02 MLT, and 09–14 MLT with westward PEJ, the northern FACp are stronger with IMF By > 0 compared to IMF By < 0. The southern FACp shows a reversed relationship with IMF By direction. The dependence of FACe (equatorward side FACs) on IMF By is weaker, except for the midday FACe, which shows opposite variations with respect to IMF By when compared to FACp. Stronger IMF By effect is observed in local summer in most of local times. The northern FACs are located at higher latitude for IMF By > 0 than for IMF By < 0 in local times with eastward PEJ, while the opposite trend is observed in other local times and in the Southern Hemisphere. The hemispheric difference in the peak latitude of FACs demonstrates an inverse relationship with its intensity, with stronger FACs located at lower latitudes. Overall, the local time and hemispheric differences in FACs strength and latitude are discussed in the context of interhemispheric field‐aligned currents linked to IMF By.