Previous studies have proposed that both the thermospheric neutral wind and the equatorial electrojet(EEJ)near sunset play important roles in the pre-reversal enhancement(PRE)mechanism.In this study,we have used obser...Previous studies have proposed that both the thermospheric neutral wind and the equatorial electrojet(EEJ)near sunset play important roles in the pre-reversal enhancement(PRE)mechanism.In this study,we have used observations made in the equatorial region of Southeast Asia during March–April and September–October in 2010–2013 to investigate influences of the eastward neutral wind and the EEJ on the PRE’s strength.Our analysis employs data collected by the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE)satellite to determine the zonal(east-west direction)neutral wind at an altitude of~250 km(bottomside F region)at longitudes of 90°–130°E in the dusk sector.Three ionosondes,at Chumphon(dip lat.:3.0°N)in Thailand,at Bac Lieu(dip lat.:1.7°N)in Vietnam,and at Cebu(dip lat.:3.0°N)in Philippines,provided the data we have used to derive the PRE strength.Data from two magnetometers—at Phuket(dip lat.:0.1°S)in Thailand and at Kototabang(dip lat.:10.3°S)in Indonesia—were used to estimate the EEJ strength.Our study is focused particularly on days with magnetically quiet conditions.We have found that the eastward neutral wind and the EEJ are both closely correlated with the PRE;their cross-correlation coefficients with it are,respectively,0.42 and 0.47.Their relationship with each other is weaker:the cross-correlation coefficient between the eastward neutral wind and the EEJ is just 0.26.Our findings suggest that both the eastward neutral wind and the EEJ near sunset are involved in the PRE mechanism.Based on the weak relationship between these two parameters,however,they appear to be significantly independent of each other.Thus,the wind and the EEJ are likely to be influencing the PRE magnitude independently,their effects balancing each other.展开更多
In this study,we present a comprehensive evaluation of the magnetic field measurements from the Vector Field Magnetometer(VFM)aboard the recently launched Macao Science Satellite-1(MSS-1).One-year data from November 2...In this study,we present a comprehensive evaluation of the magnetic field measurements from the Vector Field Magnetometer(VFM)aboard the recently launched Macao Science Satellite-1(MSS-1).One-year data from November 2,2023,to November 1,2024,are considered.The MSS-1 flies with a low inclination(41°)and is designed to provide high-resolution magnetic field measurements,especially for monitoring the evolution of the South Atlantic Anomaly.Earlier studies confirmed the possibility of using MSS-1A data to model the Earth’s main magnetic field(e.g.,Jiang Y et al.,2024).Therefore,in this study we focus on the magnetic signatures related to the external field,which are primarily associated with magnetospheric and ionospheric currents.The global distributions of the magnetic residuals from MSS-1A show a pattern consistent with that derived from the European Space Agency’s Swarm A satellite.A statistical survey of the conjugated observations(withΔt<5 min andΔR<150 km)between the two satellites showed that the difference between their magnetic residuals is within±3 nanoteslas.By separating the magnetic residuals at the noon and midnight hours,we see that the MSS-1A data can effectively capture features of the magnetospheric and ionospheric currents,such as the magnetospheric ring current and ionospheric equatorial electrojet.Moreover,the magnetic residuals from MSS-1A show a diamagnetic effect caused by post-sunset equatorial plasma bubbles,which also suggests that the MSS-1A data have the potential to reveal the ionospheric structures.The comprehensive evaluations performed within this study demonstrate that the MSS-1A provides high-quality magnetic field data reaching the level of the Swarm satellite,which enables a deeper understanding of the modeling of Earth’s magnetic field as well as monitoring of the magnetic environment.展开更多
To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes t...To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.展开更多
This study aims at discussing longitudinal effects on the variability of the vertical E × B drift velocity at low latitudes, specifically over African sector. To this effect, observations from ground-based magnet...This study aims at discussing longitudinal effects on the variability of the vertical E × B drift velocity at low latitudes, specifically over African sector. To this effect, observations from ground-based magnetometers and the Ion Velocity Meter experiment onboard C/NOFS satellite are analyzed in conjunction with equatorial electric field and neutral wind model estimates under geomagnetically quiet conditions in the years 2012-2013. Notwithstanding the limitation in data over Africa, the combination of ground-based and in-situ observations confirmed the existence of longitudinal differences in the E × B between the Atlantic, Western and Eastern African sectors. This was well reproduced by the equatorial electric field model (EEFM) which showed that during noon, the peak of the equatorial electric field (EEF) was the lowest in the Atlantic sector, with an increasing trend towards the Eastern longitude. The Horizontal Wind Model 14 (HWM14) showed that the eastward zonal (poleward meridional) wind velocity was the lowest (highest) in the Eastern sector. Furthermore, the zonal (meridional) wind increased (decreased) from the Eastern to the Atlantic sector. These results highlight the contribution of the neutral wind velocity in driving the longitudinal difference in the vertical drift velocity over Africa.展开更多
基金supported by the program of Follow-up Research Guidance of Japan Student Services Organization(JASSO)in 2019the Indonesian Ministry of Research and Technology and National Research and Innovative Agency(Kementerian RISTEK-BRIN)through the program of Pusat Unggulan Iptek(PUI)in 2019+4 种基金the Space Science Center of LAPAN through a research grant program in 2020support from JSPS KAKENHI Grants 18H01270,18H04446,and 17KK0095JRPs-LEAD with DFGpartially supported by JSPS KAKENHI Grant Number 20H00197supported by the Program Management Unit for Human Resources&Institutional Development,Research and Innovation(grant number B05F630018)。
文摘Previous studies have proposed that both the thermospheric neutral wind and the equatorial electrojet(EEJ)near sunset play important roles in the pre-reversal enhancement(PRE)mechanism.In this study,we have used observations made in the equatorial region of Southeast Asia during March–April and September–October in 2010–2013 to investigate influences of the eastward neutral wind and the EEJ on the PRE’s strength.Our analysis employs data collected by the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE)satellite to determine the zonal(east-west direction)neutral wind at an altitude of~250 km(bottomside F region)at longitudes of 90°–130°E in the dusk sector.Three ionosondes,at Chumphon(dip lat.:3.0°N)in Thailand,at Bac Lieu(dip lat.:1.7°N)in Vietnam,and at Cebu(dip lat.:3.0°N)in Philippines,provided the data we have used to derive the PRE strength.Data from two magnetometers—at Phuket(dip lat.:0.1°S)in Thailand and at Kototabang(dip lat.:10.3°S)in Indonesia—were used to estimate the EEJ strength.Our study is focused particularly on days with magnetically quiet conditions.We have found that the eastward neutral wind and the EEJ are both closely correlated with the PRE;their cross-correlation coefficients with it are,respectively,0.42 and 0.47.Their relationship with each other is weaker:the cross-correlation coefficient between the eastward neutral wind and the EEJ is just 0.26.Our findings suggest that both the eastward neutral wind and the EEJ near sunset are involved in the PRE mechanism.Based on the weak relationship between these two parameters,however,they appear to be significantly independent of each other.Thus,the wind and the EEJ are likely to be influencing the PRE magnitude independently,their effects balancing each other.
基金supported by the National Natural Science Foundation of China(Grant Nos.42474200 and 42174186)Chao Xiong is supported by the Dragon 6 cooperation 2024-2028(Project No.95437).
文摘In this study,we present a comprehensive evaluation of the magnetic field measurements from the Vector Field Magnetometer(VFM)aboard the recently launched Macao Science Satellite-1(MSS-1).One-year data from November 2,2023,to November 1,2024,are considered.The MSS-1 flies with a low inclination(41°)and is designed to provide high-resolution magnetic field measurements,especially for monitoring the evolution of the South Atlantic Anomaly.Earlier studies confirmed the possibility of using MSS-1A data to model the Earth’s main magnetic field(e.g.,Jiang Y et al.,2024).Therefore,in this study we focus on the magnetic signatures related to the external field,which are primarily associated with magnetospheric and ionospheric currents.The global distributions of the magnetic residuals from MSS-1A show a pattern consistent with that derived from the European Space Agency’s Swarm A satellite.A statistical survey of the conjugated observations(withΔt<5 min andΔR<150 km)between the two satellites showed that the difference between their magnetic residuals is within±3 nanoteslas.By separating the magnetic residuals at the noon and midnight hours,we see that the MSS-1A data can effectively capture features of the magnetospheric and ionospheric currents,such as the magnetospheric ring current and ionospheric equatorial electrojet.Moreover,the magnetic residuals from MSS-1A show a diamagnetic effect caused by post-sunset equatorial plasma bubbles,which also suggests that the MSS-1A data have the potential to reveal the ionospheric structures.The comprehensive evaluations performed within this study demonstrate that the MSS-1A provides high-quality magnetic field data reaching the level of the Swarm satellite,which enables a deeper understanding of the modeling of Earth’s magnetic field as well as monitoring of the magnetic environment.
基金supported by the Inter-university Upper atmosphere Global Observation NETwork(IUGONET)projectfunded by the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan,the National Institute of Polar Research through General Collaboration Projects(Grant no.23-14)JSPS KAKENHI(Grant no.11020535)
文摘To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.
文摘This study aims at discussing longitudinal effects on the variability of the vertical E × B drift velocity at low latitudes, specifically over African sector. To this effect, observations from ground-based magnetometers and the Ion Velocity Meter experiment onboard C/NOFS satellite are analyzed in conjunction with equatorial electric field and neutral wind model estimates under geomagnetically quiet conditions in the years 2012-2013. Notwithstanding the limitation in data over Africa, the combination of ground-based and in-situ observations confirmed the existence of longitudinal differences in the E × B between the Atlantic, Western and Eastern African sectors. This was well reproduced by the equatorial electric field model (EEFM) which showed that during noon, the peak of the equatorial electric field (EEF) was the lowest in the Atlantic sector, with an increasing trend towards the Eastern longitude. The Horizontal Wind Model 14 (HWM14) showed that the eastward zonal (poleward meridional) wind velocity was the lowest (highest) in the Eastern sector. Furthermore, the zonal (meridional) wind increased (decreased) from the Eastern to the Atlantic sector. These results highlight the contribution of the neutral wind velocity in driving the longitudinal difference in the vertical drift velocity over Africa.
