南海反气旋涡旋温度细结构特征分析

基于水下滑翔机观测资料,对南海北部一个反气旋涡旋的温度细结构进行了特征分析。温度细结构强度由温度的脉动值确定,并随着尺度的增加呈指数衰减。在垂直方向上,细结构强度随着深度的加深而减弱,细结构特征在海洋表层(0~100 m)和表层以下(>100 m)存在显著区别。表层内,垂向混合和水平混合对细结构强度均有贡献,细结构强度大。在表层以下,约100~400 m深度范围,因为水平混合减弱和双扩散作用,细结构主要表现为盐指现象导致的阶梯状结构。在水平方向上,表层内细结构强度随尺度的衰减在涡旋内部小于涡旋外部,且由于涡旋内部变形小于涡旋外部,细结构强度自涡旋中心向外逐渐增强,表层以下的盐指在涡旋内部更明显,其垂向范围大于涡旋外部。此外,细结构存在显著的日变化特征。表层内,因为夜间发展的对流混合会削弱细结构特征,相对白天而言,夜晚的细结构强度更弱,衰减速度也更快。由于温跃层深度的日变化特征,会使得表层以下也存在显著的日变化特征,并影响细结构强度变化,表现为白天弱而夜晚强的特征。

Characteristics of the Temperature Fine Structure of Anticyclonic Eddy in the South China Sea

Based on glider observations,the characteristics of the temperature fine structure of an anticyclonic eddy in the northern South China Sea are analyzed.The strength of temperature fine structure can be defined with the temperature fluctuation value which decays exponentially with the increase of scale.In terms of vertical distribution,the strength of the fine structure decreases with depth,and the fine structure feature in surface layer(0-100 m)and that below the surface layer(>100m)is different.In the surface layer,both vertical mixing and horizontal mixing contribute to the strength of fine structures,and fine structures exhibit greater strength.Below the surface layer,at the depth of about 100-400 m,the fine structure is mainly of a step-like structure,which is caused by salt finger phenomenon due to diffusion and weakened horizontal mixing.The horizontal strength of the fine structure in the surface layer weakens faster inside the eddy than outside the eddy.This is because the deformation inside the eddy is smaller than that outside the eddy,the strength of fine structure gradually increases from the center to the edge of the eddy.Below the surface layer,the salt finger is more obvious inside the eddy and its vertical range is larger.In addition,the fine structure has significant diurnal variation.In the surface layer,the strength of fine structures at night is weaker and decays faster than that in the daytime because the convective mixing developed at night and weakens the fine structures.Due to the diurnal variation of thermocline depth,diurnal variation characteristics below the surface layer are more significant and affects the change of fine structure strength,which is weak in daytime that at night.