SCIENCE CHINA Technological Sciences © Science China Press and Springer-Verlag Berlin Heidelberg 2012 tech.scichina.com www.springerlink.com *Corresponding author (email: nbq@mail.iggcas.ac.cn)  RESEARCH PAPER  May 2012 Vol.55 No.5: 1189–1197 doi: 10.1007/s11431-012-4800-2 The first time observations of low-latitude ionospheric irregulari- ties by VHF radar in Hainan NING BaiQi 1, 2* , HU LianHuan 1, 2, 3 , LI GuoZhu 1, 2 , LIU LiBo 1, 2 & WAN WeiXing 1, 2 1 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 2 Beijing National Observatory of Space Environment, Beijing 102213, China; 3 Graduate University of Chinese Academy of Sciences, Beijing 100081, China Received December 12, 2011; February 10, 2012; published online March 26, 2012 Sanya VHF radar (18.4°N, 109.6°E, dip latitude 12.8°N) at Hainan Island is the first coherent backscatter radar for sounding low-latitude ionospheric irregularities in the mainland of China. In this paper, we present the first results of low-latitude iono- spheric E and F region irregularities using the radar data during the period from February 2009 to March 2010. The Doppler velocity of radar echoes from E region field aligned irregularities (FAIs) was about several tens of meters per second, while the Doppler spectral width was appreciably larger than the velocity, and could reach one hundred meters per second, indicating that the observed E region FAIs belonged to type 2 irregularities. The observations of range time intensity (RTI) maps of FAIs showed that E region irregularities most often occurred at night within the altitude range 85–115 km, and were rarely observed at afternoon hours. The percentage occurrence of E region FAIs maximized during spring months (Feb.–May) with a peak value over 80%. The heights at which the strongest echo related FAIs occurred were mainly around 100 km, lower than h’Es and the difference is mostly 10–20 km. December solstice seemed to be the minimum period of occurrence when the FAI ech- oes were commonly detected at a narrow altitude range 90–100 km. Moreover, simultaneous radar and GPS observations dur- ing spread F events in the pre-midnight hours of solar minimum revealed that significant GPS L band scintillations coincided with the appearance of F region plasma plume structures, which extended up to 450 km in altitude. low-latitude ionosphere, ionospheric irregularities, VHF radar Citation: Ning B Q, Hu L H, Li G Z, et al. The first time observations of low-latitude ionospheric irregularities by VHF radar in Hainan. Sci China Tech Sci, 2012, 55: 11891197, doi: 10.1007/s11431-012-4800-2 1 Introduction When a radio signal acts on the disturbed ionosphere, for example, the sporadic E (Es) or spread F structures, the re- ceived signal would show rapid fluctuations in amplitude and phase that is not consistent with the source strength or modulation. It is well known that ionospheric irregularity has the potential to affect satellite communication in a number of ways, from degradation of accuracy such as the range errors, to the loss of signal tracking. Since iono- spheric irregularity producing scintillation can cause con- siderable communication hazards for radio systems and is therefore of great practical interest, it is generally recog- nized that further research on the generation and evolution of different scale size ionospheric irregularities is required, especially using high power large aperture radar measure- ments to investigate the echo type and spectral characteris- tics of small scale irregularities in detail. Over the past several decades, the E region field-aligned irregularities (FAIs) in the equatorial electrojet (EEJ) and auroral electrojet regions have been extensively studied.