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Effect of Temperature and Vertical Drift on Helium Ion Concentration Over Arecibo During Solar Maximum
Author(s) -
Gong Yun,
Lv Xiedong,
Zhou Qihou,
Ma Qingjin,
Scott Mark,
Zhang Shaodong
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027144
Subject(s) - altitude (triangle) , atmospheric sciences , solstice , equinox , daytime , ion , environmental science , helium , lapse rate , physics , atomic physics , ionosphere , latitude , geophysics , astronomy , geometry , quantum mechanics , mathematics
We present an analysis of helium ion (He + ) fraction in an altitude range from about 400 km to around 700 km and its relationship to the ion temperature ( T i ) and the vertical ion drift under solar maximum conditions. The data were obtained from the Arecibo incoherent scatter radar during 27 September to 1 October 2014 and 16–20 December 2014. The large He + fraction (>10%) lasts 15 hr per day during the winter solstice, which is 3 times larger than during fall equinox. This difference is caused by the more persistent downward ion drift in the winter. The incremental He + fraction and incremental T i are well anticorrelated, and the anticorrelation is more prominent during the daytime. These characteristics are associated with whether O + and He + are in diffusive equilibrium. During nighttime, we show that the vertical ion flow is downward causing the He + layer peak altitude to move to an altitude of 500 km from above 650 km. According to our analysis, He + fraction has to be larger than two thirds for diffusive equilibrium to occur above the He + peak height. Therefore, above the He + peak altitude, O + and He + cannot be in diffusive equilibrium with He + being the minor species. The vertical ion flow plays an important role in determining the diurnal variation and seasonal difference of He + distribution and whether He + is in a diffusive equilibrium with O + .