Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract：利用全天时钠层荧光激光雷达和GPS电离层探测仪, 在2009年7月22日武汉日全食期间, 开展钠层与电离层的联合观测试验. 观测结果表明, 钠层密度半高全宽在日全食过程中稍有变窄, 而日全食过后增宽, 钠层峰值高度在日全食过程中稍有降低, 日全食过后高度略增, 钠层变化特性表现出快速的日出日落过程. 电离层电子总含量和天空背景光噪声也随日全食期间太阳辐照的变化而呈现出明显下降和上升的波动特征. 所不同的是, 钠层原子的这种半宽度起伏变化要比电离层的变化迟缓得多, 这可能是由于钠层受到日全食辐照扰动后, 会产生一系列复杂的光化学反应及动力输运过程, 再复合成钠原子被激光雷达探测到, 有一个滞后过程, 这也正好与理论模拟的结果相符.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Sodium lidar is recognized as a useful tool to investigate gravity wave (GW) which influences the circulation, structure and composition of middle and upper atmosphere notably. For further understanding GW and their characteristics, more sufficient observational data within global models, especially those at low latitude are extremely expected. Meanwhile, long-term observations are also quite helpful for the GW analysis. As one part of Meridian Project, the observational Na lidar system at Hainan (19. 50 degrees N, 109. 1 degrees E) employed the double wavelengths laser beam, which is consists of three channels for Mie scattering, Rayleigh scattering and broadband sodium fluorescence. A pulsed Nd:YAG laser was rebuilt to trigger off two green laser beams simultaneously, one of which was 532 nm and used to excite the Mie and Rayleigh scattering, and the other laser beam pumped by a pulsed dye laser was about 589 nm and with 30 mJ per pulse. Resonant fluorescence from the sodium layer was received by a Cassegrain telescope with a primary mirror of 1000 mm diameter. The lidar profiles are stored automatically in a computer. The temporal and spatial resolution was about 167s and 96 m, respectively. Seasonal variations of the GW activity and their spectra at Hainan were studied with comparison to the previous reports and the predictions of theories of GW saturation and dissipation. The seasonal variations of GW activity and characteristics spectra at Hainan are mainly presented as follows: (1) The mean RMS atmospheric density perturbation over Hainan are 5. 63 %, which at solstice are obviously larger than that near the equinox. And the GW activity in winter is still active, which are quite different from those reports at the middle latitude area. (2) Due to the linear theory, the m spectra were calculated which show power law shapes and their range of variation were between -2. 14 and -3. 56 with an annual mean value of -2. 93. The calculated omega spectra were between -1. 22 and -2. 36 with an annual mean value of -1. 80, respectively. (3) The amplitudes of atmospheric density perturbation spectra at m = 2 pi/8km, 2 pi/4km, 2 pi/2km, 2 pi/1km and omega = 2 pi/60min, 2 pi/40min, 2 pi/25min all exhibit large nightly variability as well as large seasonal variations, with the maxima occurring near the solstice. While in winter, their amplitudes indicated that the GW activity is still active, which are consistent with the RMS atmospheric density perturbation annual variations. (4) The seasonal variation regularity of the GW activity at Hainan and the possible GW source there were discussed. It is concluded that the reaction of the Qinghai-Tibet plateau with the convection and the equatorial undercurrent may be the main reason of the GW behaviors at Hainan. The seasonal variation of GW activity at Hainan were measured based on 3 year's observation. The RMS atmosphere perturbation, the vertical wave number spectral amplitudes at 2 pi/8km 2 pi/4km 2 pi/2km and 2 pi/1km and omega spectra with those frequencies at 2 pi/60min, 2 pi/40min, 2 pi/25min all show that the semiannual maxima occur near the solstices, while the GW activity in winter is still active, which is quite different from the middle latitude area. The vertical wave number spectra and frequency spectra were also calculated which were fitted well with the theoretical value. It is concluded that the fact of the Qinghai-Tibet plateau's topography, intense convection of South China Sea and the equatorial undercurrent could be the main reason of the GW's behaviors at Hainan.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： In the noncoherent Doppler wind lidar system, the laser line width and frequency stability are two important factors influencing the accuracy of measurement results. The injection seeding technique method was used to obtain narrow linewidth of 532 nm lidar. The iodine filters as receiv frequency discriminators and lock the transmitter laser frequency. Using VB language writing instrument control program based on PID algorithm, the frequency of seed laser locked in iodine molecular absorption lines, which was 1109 line of high reflection on the edge. The frequency stability was better then �.5 MHz for 4 h, the long-term frequency stability as 3.55�0-9. Design the continuous light velocity measuring system, which concluded the cure about Doppler frequency shift and actual speed of chopped wave plate, the velocity error was less than 0.4 m/s. This also shows that the laser velocity measuring system can be calibrated on the lock the frequency of the whole system. This experiment also provides guidance significance for the construction of wind lidar. � 2015, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved.
Peer Review Status:Awaiting Review
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