加拿大海盆东南部锚定观测双扩散阶梯的时间演化研究

加拿大海盆上层,分布着高温高盐的大西洋水和相对低温低盐的盐跃层下部水,两水团之间形成一系列的双扩散阶梯。通过分析2005年8月-2011年8月期间的锚定潜标数据,对双扩散阶梯和这两种水团之间的相互作用进行研究。基于固定盐度范围的方法,在盐度廓线中识别阶梯结构,在盐度34.45~34.83范围内,获取18个阶梯结构,并研究阶梯的参数。发现双扩散阶梯的位温主要受与其接近的水团的影响,同时也受其相邻的阶梯生成或消亡的影响,大西洋水对其上方的双扩散阶梯和盐跃层下部水起到加热作用;而盐跃层下部水的深度变化主导着大西洋水和双扩散阶梯的深度变化。两个相邻的阶梯具有一致的位温和深度变化趋势。通过经验公式,估计大西洋水通过双扩散阶梯向上传输的热通量为0.05~0.6 W/m2,且由下至上呈现逐渐增大的趋势。最后,估算由双扩散造成的垂向涡扩散系数为3×10-6~3.3×10-5 m2/s,且由下至上呈现逐渐减小的趋势。

Temporal evolution of mooring-based observations of double diffusive staircases in the southeast Canada Basin

In the upper Canada Basin,double-diffusive staircases are located between the Atlantic Water (AW) and the Lower Halocline Water (LHW). The McLane Moored Profiler (MMP) data measured from August 2005 to August 2011 at subsurface mooring stations are analyzed to explore the relationship between double-diffusive staircases and these two water masses. In the fixed salinity interval between 34.45 and 34.83,eighteen staircases are identified. It is found that the potential temperature of staircases is affected by their adjacent water masses and also the formation and decay of their adjacent staircases. There is heart transfer from the AW to the overlying staircases and the LHW,and the depth variations of the staircases and the AW are determined by the depth of the LHW. The adjacent staircases show almost the same variation trend between its potential temperature and depth. Based on the empirical formula,the heat flux across the staircase is estimated to be 0.05 to 0.6 W/m². The vertical heat flux is found to gradually increase as the salinity decreases upward. In addition,the effective vertical diffusivity,which is caused by double-diffusive convection,is estimated to be about 3×10^-6 to 3.3×10^-5 m²/s,and it gradually decreases as the salinity decreases.