基于一次走航观测分析南海北部大气波导特征

Analysis of Atmospheric Duct in the Northern South China Sea Based on an Underway Observation

关键词:  无线电探空  大气修正折射率  悬空波导  蒸发波导  陷获层

Key words:  radiosonde  modified refractivity  elevated duct  evaporation duct  trapping layer

摘要:

大气波导现象会显著影响雷达的探测性能，因此对大气波导层的准确诊断和预报具有重要的经济和军事价值。海上大气波导研究往往受限于观测条件，对关键海区波导特征缺少系统的了解。本研究基于2019年6月在南海北部进行的（无线电）探空观测数据，统计了该区域蒸发波导和悬空波导的发生特征，并对两类波导形成原因进行了初步分析。研究结论如下：（1）观测期间每次探空都有蒸发波导出现，平均层顶高度（波导层厚度）为50m，平均强度64.7M；（2）观测海域悬空波导出现概率约为90%，平均波导层顶高度为1004m，平均厚度为109m，平均强度为6.1M，陷获层内的折射率梯度约为-0.15M·m-1；（3）大气湿度垂直梯度均贡献了两种波导主要的折射率梯度，但温度层结对蒸发波导一般起抑制作用，而对悬空波导起促进作用。本研究进一步明确了南海大气波导的特征，为该区域电磁传播环境的模型构建提供了研究基础。

Abstract:

Atmospheric ducts significantly affect radar's performance. Accurately diagnosing and forecasting of atmospheric duct layers thus has considerable value in economic and military fields. The scarcity of routine observations hampers the understanding of atmospheric ducts over the sea. This study uses a one- month continuous radiosonde experiment in the northern South China Sea to diagnose the characteristics and discuss the mechanism of the atmospheric duct. The conclusions are as follows: (1) The evaporation ducts appeared every day during the experiment, with an average duct height of 50 m and an average intensity of 64.7 M. (2) The elevated ducts appeared in 90 % of the observation period, with an average duct height of 1 004 m, an average thickness of 109 m, and an average intensity of 6.1 M, with a nearly identical refractivity gradient within the trapping layer of about -0.15 M m-1. (3) The atmospheric humidity dominates the primary refractivity gradient of both types of the ducts, while the stratification of atmospheric temperature usually tends to suppress the evaporation ducts but contributes to the elevated ducts. This study has further confirmed the characteristics of atmospheric ducts in the South China Sea, supporting the simulation studies of electromagnetic propagation.