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[MTT37-09] Study of Conditions for Occurrence of Plasma Bubbles Reaching Mid-Latitudes Based on GNSS observations at the American Longitudinal Sector
Keywords:ionosphere, GNSS, GPS, plasma bubble
Plasma bubbles, which are characterized by localized decreases in ionospheric electron density, originate at the magnetic equator and expand toward higher latitudes. Recent observations of Total Electron Content (TEC) using the Global Navigation Satellite System (GNSS) have revealed that plasma bubbles can reach mid- and high-latitudes. However, the specific conditions under which plasma bubbles extend to mid- and high-latitudes remain unclear.
This study aims to clarify the conditions under which plasma bubbles reach mid-latitudes. We focused on the American longitudinal sector (geographic longitude: 230–330 deg.), where GNSS data covering a wide latitudinal range from the magnetic equator are available. We analyzed TEC data obtained over an 11-year period from 2012 to 2022 by GNSS receivers in this region. Plasma bubbles were detected using the Rate of TEC Index (ROTI), an indicator of electron density irregularities in the plasma bubbles.
As a result, 48 cases of plasma bubbles reaching magnetic latitudes of 30 deg. or higher were identified, among which 13 cases extended beyond 35 deg. It is known that plasma bubble occurrence depends on the strength of the eastward electric field at the magnetic equator. To investigate this relationship for the plasma bubbles reaching mid-latitudes, we examined the correlation between the maximum magnetic latitude and poleward propagation speed of plasma bubbles and the F-region height and its upward velocity at the magnetic equator. However, no clear correlation was observed among these variables. This result suggests that while the eastward electric field and F-region height at the magnetic equator are important factors in determining the plasma bubble occurrence, they do not directly determine the maximum latitude that the bubbles can reach.
Furthermore, when plasma bubbles reached mid-latitudes, the TEC integrated along the geomagnetic field in both northern and southern hemispheres at mid-latitudes were found to be higher than those observed on the day without plasma bubbles reaching mid-latitudes. This result suggests that whether the electron density inside the plasma bubble, which originates at the equator, becomes comparable to the surrounding background electron density plays a key role in determining the maximum latitude that the bubble can reach. Additionally, the increase in the integrated electron density in both hemispheres at mid-latitudes may be one of the key conditions for plasma bubbles to extend to mid-latitudes.
This study aims to clarify the conditions under which plasma bubbles reach mid-latitudes. We focused on the American longitudinal sector (geographic longitude: 230–330 deg.), where GNSS data covering a wide latitudinal range from the magnetic equator are available. We analyzed TEC data obtained over an 11-year period from 2012 to 2022 by GNSS receivers in this region. Plasma bubbles were detected using the Rate of TEC Index (ROTI), an indicator of electron density irregularities in the plasma bubbles.
As a result, 48 cases of plasma bubbles reaching magnetic latitudes of 30 deg. or higher were identified, among which 13 cases extended beyond 35 deg. It is known that plasma bubble occurrence depends on the strength of the eastward electric field at the magnetic equator. To investigate this relationship for the plasma bubbles reaching mid-latitudes, we examined the correlation between the maximum magnetic latitude and poleward propagation speed of plasma bubbles and the F-region height and its upward velocity at the magnetic equator. However, no clear correlation was observed among these variables. This result suggests that while the eastward electric field and F-region height at the magnetic equator are important factors in determining the plasma bubble occurrence, they do not directly determine the maximum latitude that the bubbles can reach.
Furthermore, when plasma bubbles reached mid-latitudes, the TEC integrated along the geomagnetic field in both northern and southern hemispheres at mid-latitudes were found to be higher than those observed on the day without plasma bubbles reaching mid-latitudes. This result suggests that whether the electron density inside the plasma bubble, which originates at the equator, becomes comparable to the surrounding background electron density plays a key role in determining the maximum latitude that the bubble can reach. Additionally, the increase in the integrated electron density in both hemispheres at mid-latitudes may be one of the key conditions for plasma bubbles to extend to mid-latitudes.