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Diurnal evolution of the F region electron density local time gradient at low and middle latitudes resolved by the Swarm constellation
Author(s) -
Xiong Chao,
Zhou YunLiang,
Lühr Hermann,
Ma ShuYing
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023034
Subject(s) - electron density , daytime , sunrise , crest , physics , local time , sunset , electron , f region , ionosphere , plasma , density gradient , atmospheric sciences , latitude , electric field , atomic physics , geophysics , optics , astronomy , mathematics , statistics , quantum mechanics
In this study we have provided new insights into the local time gradient of F region electron density (Δ Ne ) derived from the lower pair of Swarm satellites flying side by side. Our result shows that the electron density ( Ne ) increase starts just at sunrise, around 06:00 LT, simultaneously at low and middle latitudes due to the increased photoionization. At equatorial latitudes the increase in electron density gets even steeper after 07:00 LT, and the steepest increase of electron density (about 3 · 10 10 m −3 within 6 min) occurs around 09:00 LT. We suggest that the upward vertical plasma drift in connection with the buildup of the equatorial fountain effect plays a major role. We also found that the local time variations of the equatorial ionization anomaly (EIA) crest electron density during daytime are similar to the respective evolutions at the equator, but about 1–2 h delayed. We relate this delay to the response time between the equatorial electric field and the buildup of the plasma fountain. At equinox months a fast decrease of the F region electron density is seen at the EIA trough region during the prereversal enhancement, while an increase is found meanwhile at crest regions. Afterward, a fast decrease of the EIA crest electron density occurs between 19:00 and 23:00 LT, with seasonal dependence. The local time gradient between Swarm A and C shows also prominent longitudinal wave‐4 pattern around August months, and the phase of DE3 in Δ Ne is found to be delayed by 6 h compared to that in Ne .