官厅水库夏季叶绿素a浓度短时分布特征

分析官厅水库夏季(8月份)叶绿素a浓度短时变化特征,对于水库水体富营养化研究具有重要意义。利用以分钟为步长的水温、水深及叶绿素a浓度实测数据及气象数据,对叶绿素a浓度垂向及昼夜变化特征进行了分析。结果表明:叶绿素a浓度最高值是表层浓度的1.5~2倍,其出现位置与温度跃层位置基本一致。叶绿素a浓度具有昼夜周期性变化特征。白昼,温度跃层以上叶绿素a浓度随水深增加逐渐增加,在温度跃层以下,随水深增加逐渐降低;夜间,温跃层以上叶绿素a浓度基本稳定不变,在温度跃层以下与白昼变化趋势相同。表层水体叶绿素a浓度夜间大于白天,且与光照及表层水温呈负相关。水库叶绿素a浓度短时分布特征主要与温度分层以及限制性营养盐磷的释放有关。

基于稳定分布噪声的分数低阶自适应时频分布

信号中的α稳定分布噪声会使自适应时频分布方法失效。针对该问题,利用分数低阶统计量理论,提出一种改进的分数低阶自适应时频分布。为了实现带噪信号的实时在线处理及长时间信号的时频分布分析,给出一种分数低阶短时自适应时频分布。仿真结果表明,2种方法都能在含有α稳定分布噪声和高斯噪声的环境下进行有效的时频分布分析。

Some properties of field-aligned electron events in high-altitude polar regions

Using data from the Cluster spacecraft from January 2003 to December 2004, we perform a statistical study on some properties of the field-aligned electron(FAE) events and interplanetary magnetic field(IMF) By dependence of FAE events with different durations in high-altitude polar regions. A total of 1335 FAE events were observed by the C3 spacecraft. More down-flowing events were observed in the Southern Hemisphere, and more up-flowing events were observed in the Northern Hemisphere. It proves that down-flowing events mainly originate from magnetosphere or solar wind and up-flowing events are mainly derived from ionosphere. Short-lifetime events showed a morning concentration in the magnetic local time distribution, and long-lifetime events were concentrated both before and after noon. For the IMF By dependence of the FAE events, short-lifetime events were much affected by IMF By and resulted in a morning concentration, while the long-lifetime events were almost unaffected by IMF By. With further analysis, we determined that the short-lifetime and long-lifetime events had different sources.