TY  - JOUR
A1  - Park, Jaeheung
A1  - Lühr, Hermann
A1  - Stolle, Claudia
A1  - Rodriguez-Zuluaga, Juan
A1  - Knudsen, David J.
A1  - Burchill, Johnathan K.
A1  - Kwak, Young-Sil
T1  - Statistical survey of nighttime midlatitude magnetic fluctuations: Their source location and Poynting flux as derived from the Swarm constellation
JF  - Journal of geophysical research : Space physics
N2  - This is the first statistical survey of field fluctuations related with medium-scale traveling ionospheric disturbances (MSTIDs), which considers magnetic field, electric field, and plasma density variations at the same time. Midlatitude electric fluctuations (MEFs) and midlatitude magnetic fluctuations (MMFs) observed in the nighttime topside ionosphere have generally been attributed to MSTIDs. Although the topic has been studied for several decades, statistical studies of the Poynting flux related with MEF/MMF/MSTID have not yet been conducted. In this study we make use of electric/magnetic field and plasma density observations by the European Space Agency's Swarm constellation to address the statistical behavior of the Poynting flux. We have found that (1) the Poynting flux is directed mainly from the summer to winter hemisphere, (2) its magnitude is larger before midnight than thereafter, and (3) the magnitude is not well correlated with fluctuation level of in situ plasma density. These results are discussed in the context of previous studies.
Y1  - 2016
U6  - https://doi.org/10.1002/2016JA023408
SN  - 2169-9380
SN  - 2169-9402
VL  - 121
SP  - 11235
EP  - 11248
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Xiong, Chao
A1  - Stolle, Claudia
A1  - Lühr, Hermann
T1  - The Swarm satellite loss of GPS signal and its relation to ionospheric plasma irregularities
JF  - Space Weather: The International Journal of Research and Applications
N2  - In this study we investigated conditions for loss of GPS signals observed by the Swarm satellites during a 2 year period, from December 2013 to November 2015. Our result shows that the Swarm satellites encountered most of the total loss of GPS signal at the ionization anomaly crests, between +/- 5 degrees and +/- 20 degrees magnetic latitude, forming two bands along the magnetic equator, and these low-latitude events mainly appear around postsunset hours from 19: 00 to 22: 00 local time. By further checking the in situ electron density measurements of Swarm, we found that practically, all the total loss of GPS signal events at low latitudes are related to equatorial plasma irregularities (EPIs) that show absolute density depletions larger than 10 x 10(11) m(-3); then, the Swarm satellites encountered for up to 95% loss of GPS signal for at least one channel and up to 45% tracked less than four GPS satellites (making precise orbit determination impossible). For those EPIs with density depletions less than 10 x 10(11) m(-3), the chance of tracked GPS signals less than four reduces to only 1.0%. Swarm also observed total loss of all GPS signal at high latitudes, mainly around local noon, and these events are related to large spatial density gradients due to polar patches or increased geomagnetic/auroral activities. We further found that the loss of GPS signals were less frequent after appropriate settings of the Swarm GPS receivers had been updated. However, the more recent period of the mission, e.g., after the GPS receiver settings have been updated, also coincides with less severe electron density depletions due to the declining solar cycle, making GPS loss events less likely. We conclude that both lower electron density gradients and appropriate GPS receiver settings reduce the probability for Swarm satellites loss of GPS signals.
Y1  - 2016
U6  - https://doi.org/10.1002/2016SW001439
SN  - 1542-7390
VL  - 14
SP  - 563
EP  - 577
PB  - American Geophysical Union
CY  - Washington
ER  -