Geoscience

Latitude and Longitude Variations of the Ionosphere Stratification Structure

The variation features of the 3D space structure of the ionosphere electron density and their generation mechanisms were of one forefront area of international research in recent years. Compared with the vertical structure of the ionosphere at medium latitude, the height variations of the ionosphere at low latitude areas are more complicated because of the influence of the fountain effect caused by the latitudinal electric field. Zhao Biqiang, Associate Professor and his colleagues of the Division of Geomagnetism and Space Physics Key Laboratory, Institute of Geology and Geophysics, CAS, used roughly the 2.5 million ionospheric profiles acquired by the occultation inversion technology of the U.S. COSMIC constellation observing system to study the stratification structure of the ionosphere. By striking the gradient height variations of electronic density profile and counting the occurrence rate of double-layer structures, they, for the first time, disclosed the latitude and longitude variations of the ionosphere stratification structure. The features of these variations are as following: 1) The stratification structure is mainly concentrated in the low latitude areas, and the occurrence maximum of low-latitude ionosphere stratification structure appears at magnetic latitude 7-8° for Northern/Southern Hemisphere during summer months; 2) The longitude variation of the ionosphere stratification structure in summer is similar to the WN4 structure of many parameters’ changes modulated by DE3 tidal ionosphere; 3) The maximum local time of the occurrence of stratification structure is 10:00-12:00 after the sunrise, which is consistent with the statistical results measured on the ground. The consistency between satellite measurements and the statistical results of ground observations proves the considerable reliability of the occultation inversion technology in the reflection of the fine structure of the ionosphere. The research results were recently published in Geophysical Research Letters(Zhao et al. Global characteristics of occurrence of an additional layer in the ionosphere observed by COSMIC/FORMOSAT‐3. Geophys. Res. Lett.，2011，38，L02101，doi:10.1029/2010GL045744).

Inland Aridification of Asia Dates Back to 25 Million Years

The research group led by An Zhisheng, Member of CAS, Institute of Earth Environment, CAS, conducted a four-year systematic research of magnetostratigraphy, sedimentology and geochemistry on the 654 m core obtained from Zhuanglang area located at the western region of the Chinese Loess Plateau. The results show that the Zhuanglang core is mainly composed of high-resolution eolian red clay sequence, and it records the continuous magnetic change sequences ranging from 25.6 to 4.8 Ma, which extends the emergence of red clay in China from the early Miocene back into the late Oligocene. It shows that as early as the late Oligocene period, the environment of Asian monsoon and deserts suitable for the formation of red clay had taken shape in northern China, and the differentiation and evolution of Asian monsoon-arid environment may be closely related with the uplift of the Qinghai-Tibet Plateau in the late Oligocene. This article was published in the recent issue of Science China (Qiang Xiaoke, et al, 2011. New eolian red clay sequence on the western Chinese Loess Plateau linked to onset of Asian desertification about 25 Ma ago. SCIENCE CHINA Earth Sciences, 54(1), 136-144.)