TY  - JOUR
A1  - Yamazaki, Yosuke
A1  - Stolle, Claudia
A1  - Matzka, Jürgen
A1  - Liu, Huixin
A1  - Tao, Chihiro
T1  - Interannual variability of the daytime equatorial ionospheric electric field
JF  - Journal of geophysical research : Space physics
N2  - Understanding the variability of the ionosphere is important for the prediction of space weather and climate. Recent studies have shown that forcing from the lower atmosphere plays a significant role for the short-term (day-to-day) variability of the low-latitude ionosphere. The present study aims to assess the importance of atmospheric forcing for the variability of the daytime equatorial ionospheric electric field on the interannual (year-to-year) time scale. Magnetic field measurements from Huancayo (12.05 degrees S, 75.33 degrees W) are used to augment the equatorial vertical plasma drift velocity (V-Z) measurements from the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere radar during 2001-2016. V-Z can be regarded as a measure of the zonal electric field. After removing the seasonal variation of similar to 10m/s, midday values of V-Z show an interannual variation of similar to 2m/s with an oscillation period of 2-3years. No evidence of solar cycle influence is found. The Ground-to-topside Atmosphere-Ionosphere model for Aeronomy, which takes into account realistic atmospheric variability below 30km, reproduces the pattern of the observed interannual variation without having to include variable forcing from the magnetosphere. The results indicate that lower atmospheric forcing plays a dominant role for the observed interannual variability of V-Z at 1200 local time.
KW  - interannual variability
KW  - plasma drifts
KW  - equatorial electrojet (EEJ)
KW  - vertical coupling
KW  - JULIA
KW  - GAIA
Y1  - 2018
U6  - https://doi.org/10.1029/2017JA025165
SN  - 2169-9380
SN  - 2169-9402
VL  - 123
IS  - 5
SP  - 4241
EP  - 4256
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Sobhkhiz-Miandehi, Sahar
A1  - Yamazaki, Yosuke
A1  - Arras, Christina
A1  - Miyoshi, Yasunobu
A1  - Shinagawa, Hiroyuki
T1  - Comparison of the tidal signatures in sporadic E and vertical ion convergence rate, using FORMOSAT-3/COSMIC radio occultation observations and GAIA model
JF  - Earth, planets and space : EPS
N2  - Sporadic E or Es is a transient phenomenon where thin layers of enhanced electron density appear in the ionospheric E region (90-120 km altitude). The neutral wind shear caused by atmospheric tides can lead ions to converge vertically at E-region heights and form the Es layer. This research aims to determine the role of atmospheric solar and lunar tides in Es occurrence. For this purpose, radio occultation data of FORMOSAT-3/COSMIC have been used, which provide complete global coverage of Es events. Moreover, GAIA model simulations have been employed to evaluate the vertical ion convergence induced by solar tides. The results show both migrating and non-migrating solar tidal signatures and the semidiurnal migrating lunar tidal signature mainly in low and mid-latitude Es occurrence. The seasonal variation of the migrating solar tidal components of Es is in good agreement with those in the vertical ion convergence derived from GAIA at higher altitudes. Furthermore, some non-migrating components of solar tides, including semidiurnal westward wavenumbers 1 and 3 and diurnal eastward wavenumbers 2 and 3, also significantly affect the Es occurrence rate.
KW  - Sporadic E
KW  - Es
KW  - wind shear
KW  - solar tide
KW  - lunar tide
KW  - GAIA
KW  - radio occultation
Y1  - 2022
U6  - https://doi.org/10.1186/s40623-022-01637-y
SN  - 1880-5981
VL  - 74
IS  - 1
PB  - Springer
CY  - Heidelberg
ER  -