Mixed layer depth variability over the global ocean
Mixed layer depth variability over the global ocean
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DOI：
10.1029/2000jc000736
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发表时间：
2003-03-13
影响因子：
3.6
通讯作者：
Hurlburt, HE
中科院分区：
文献类型：
--
作者：
Kara, AB;Rochford, PA;Hurlburt, HE
[1]利用最近发展起来的海军研究实验室(NRL)海洋混合层深度(NMLD)气候学，研究了全球海洋气候混合层深度(MLD)的空间和月变化。MLD场是利用1994年《世界海洋地图集》中的次表层温度和盐度数据建造的[Levtus等人，1994；Levtus和Boyer，1994]。为了最大限度地减少这些全球数据在MLD测定中的限制，引入了一个简单的混合方案来形成稳定的水柱。使用这些新的数据集，在采用基于密度的标准的最佳定义的基础上产生全球MLD特征，该标准具有固定的温差DeltaT=0.8摄氏度和可变的盐度。副热带太平洋和高纬度MLD具有很强的季节性，冬季北大西洋有很深的混合层，南极各月都有很浅的混合层。利用NMLD气候学的月平均MLD场和等温层深度(ILD)场，给出了年平均DeltaT场，为确定近似等于最佳MLD的ILD提供了判据。这使得能够在没有盐度数据的情况下确定MLD。使用两个系泊设备的日平均次表层温度和盐度证明了ILD和MLD之间的对应关系的有效性：一个是热带大气海洋阵列系泊在赤道西太平洋暖池，盐度分层很重要；另一个是伍兹霍尔海洋研究所系泊在阿拉伯海，那里盛行强烈逆转的季节性季风风。在西赤道太平洋暖池，使用年平均DeltaT值为0.3°C的ILD标准得到的结果与最优MLD相当，而较大的DeltaT值则产生高估的MLD。对WHOI系泊中ILD和MLD的分析表明，对ILD使用不正确的DeltaT准则可能会低估或高估最优MLD。最后，利用从NMLD气候学构造的空间年平均DeltaT值，可以通过全球海洋上任何位置的等效ILD，仅从次表层温度数据估计最佳MLD。
[1] The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ocean is examined using the recently developed Naval Research Laboratory (NRL) Ocean Mixed Layer Depth (NMLD) climatologies. The MLD fields are constructed using the subsurface temperature and salinity data from the World Ocean Atlas 1994 [Levitus et al., 1994; Levitus and Boyer, 1994]. To minimize the limitations of these global data in the MLD determination, a simple mixing scheme is introduced to form a stable water column. Using these new data sets, global MLD characteristics are produced on the basis of an optimal definition that employs a density-based criterion having a fixed temperature difference of DeltaT = 0.8degreesC and variable salinity. Strong seasonality of MLD is found in the subtropical Pacific Ocean and at high latitudes, as well as a very deep mixed layer in the North Atlantic Ocean in winter and a very shallow mixed layer in the Antarctic in all months. Using the climatological monthly MLD and isothermal layer depth (ILD) fields from the NMLD climatologies, an annual mean DeltaT field is presented, providing criteria for determining an ILD that is approximately equivalent to the optimal MLD. This enables MLD to be determined in cases where salinity data are not available. The validity of the correspondence between ILD and MLD is demonstrated using daily averaged subsurface temperature and salinity from two moorings: a Tropical Atmosphere Ocean array mooring in the western equatorial Pacific warm pool, where salinity stratification is important, and a Woods Hole Oceanographic Institute (WHOI) mooring in the Arabian Sea, where strongly reversing seasonal monsoon winds prevail. In the western equatorial Pacific warm pool the use of ILD criterion with an annual mean DeltaT value of 0.3degreesC yields comparable results with the optimal MLD, while large DeltaT values yield an overestimated MLD. An analysis of ILD and MLD in the WHOI mooring show that use of an incorrect DeltaT criterion for the ILD may underestimate or overestimate the optimal MLD. Finally, use of the spatial annual mean DeltaT values constructed from the NMLD climatologies can be used to estimate the optimal MLD from only subsurface temperature data via an equivalent ILD for any location over the global ocean.