Solar activity effects of the ionosphere: A brief review

Solar radiation, which varies over multiple temporal scales, modulates remarkably the evolution of the ionosphere. The solar activity dependence of the ionosphere is a key and fundamental issue in ionospheric physics, providing information essential to understanding the variations in the ionosphere and its processes. Selected recent studies on solar activity effects of the ionosphere are briefly reviewed in this report. This report focuses on (1) observations of solar irradiance at X-ray and extreme ultraviolet wavelengths and the outstanding problems of solar proxies, in the view of ionospheric studies, (2) new findings and improved representations of the features of the solar activity dependence of ionospheric key parameters and the corresponding physical processes, (3) possible phenomena in the ionosphere under extremely high and low solar activity conditions that are unique, as indicated by historical solar datasets and the deep solar minimum of solar cycle 23/24, and (4) statistical studies and model simulations of the ionosphere response to solar flares. The above-mentioned studies provide new clues for comprehensively explaining basic processes in the ionosphere and improving the prediction capability of ionospheric models and related applications.

First observation of mesospheric and thermospheric winds by a Fabry-Perot interferometer in China

A Fabry-Perot interferometer,funded by the Meridian Project in China,was deployed at the Xinglong station(40.2°N,117.4°E) of the National Astronomical Observatories in Hebei Province,China.The instrument has been operating since April 2010,measuring mesospheric and thermospheric winds.The first observational data of winds at three heights in the mesosphere and thermosphere were analyzed,demonstrating the capacity of this instrument to aid basic scientific research.The wavelengths of three airglow emissions were OH892.0,OI 557.7,and OI 630.0 nm,which corresponded to heights of 87,98,and 250 km,respectively.Three 38-day data sets of horizontal winds,from April 5,2010 to May 12,2010,show clear day-to-day variations at the same height.The minimum and maximum meridional winds at heights of 87,98,and 250 km were-16.5 to 8.7 m/s,-24.4 to 15.9 m/s,and-43.6 to 1.5 m/s.Measurements of zonal winds were-5.4 to 7.6 m/s,2.3 to 23.0 m/s,and-22.6 to 49.3 m/s.The average data from the observations was consistent with the data from HWM93.The wind data at heights of 87 and 98 km suggest a semi-diurnal oscillation,clearly consistent with HWM93 results.Conversely there was a clear discrepancy between the observations and the model at 250 km.In general,this Fabry-Perot interferometer is a useful ground-based instrument for measuring mesospheric and thermospheric winds at middle latitudes.

Sodium fluorescence Doppler lidar to measure atmospheric temperature in the mesopause region

A sodium fluorescence Doppler lidar system has been developed to measure environmental parameters of the middle and upper atmosphere. The lidar system mainly comprises a transmitter system,receiver system,data acquisition and control system and data analysis system. A narrowband 589 nm laser is used to excite sodium atoms in the mesopause region. Excitation of the sodium atoms results in resonance fluorescence,which is collected by the receiver. The temperatures in the mesopause region(about 75-105 km) can be derived by analyzing the Doppler-broadened width of the sodium fluorescence. Observations were made with the lidar system,and the number density of sodium atoms and atmospheric temperature profiles were extracted from the observation data. Comparisons of the lidar temperatures and TIMED/SABER temperatures show good agreement,illustrating the reliability of the sodium fluorescence Doppler lidar measurements.