Search for: All records

Abstract We present an investigation of the F‐region electron temperature to an intense geomagnetic storm that occurred on 5 August 2011. The investigation is based on the incoherent scatter radar measurements at Arecibo Observatory, Puerto Rico (18.3°N, 66.7°W). The electron temperature exhibits a rapid and intensive enhancement after the commencement of the geomagnetic storm. The electron temperature increases by ∼800 K within an hour, which is seldomly reported at Arecibo. At the same time, a depletion of the electron density is also observed. The daytime perturbations of electron density and temperature are anticorrelated with the correlation coefficient, which is −0.88 and −0.91 on the day and the following day of the geomagnetic storm, respectively. According to the Global Ultraviolet Imager measurements, the ratio of atomic oxygen to molecular nitrogen concentration () decreases dramatically during the storm. Our analysis suggests that the enhancement of the electron temperature is due to the depletion of the electron density, which is likely associated with the decrease of . The reduction of maybe caused by a prompt upward plasma motion after the commencement of the geomagnetic storm. 

Abstract 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 incrementalT_iare 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⁺. 

Abstract Using data collected from the Arecibo incoherent scatter radar during 5–10 February 2016, we present a study on the quarterdiurnal tide (QDT) from 250 to 360 km. A sudden stratospheric warming (SSW) event occurred on 8 February coincided with our observation. The maximum amplitude of the QDT, at ~37 m/s, is comparable with the diurnal tide and much larger than the semidiurnal tide. The QDT is largely evanescent. Our results manifest that theFregion QDT could be as important as the diurnal and semidiurnal tides. The tidal waves show large variability before and after the commencement of the SSW. Our analysis indicates that the enhancement of the QDT is most likely due to the effect of the SSW. Nonlinear interaction of the diurnal tide with the terdiurnal tide is found to play a significant role in amplifying the QDT during the SSW event.