Seasonal variability of submesoscale vertical heat transport in the Kuroshio Extension
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摘要: 亚中尺度过程伴随着强烈的垂向速度，显著影响着海洋表面与海洋内部之间热量、浮力和质量等示踪物的垂向输运。基于(1/48)°的LLC4320模式结果，本文对黑潮延伸体海域亚中尺度垂向热量输运的季节变化进行了研究。研究结果表明，黑潮延伸体海域亚中尺度垂向热量输运具有明显的春冬强、夏秋弱的季节变化特征。上层海洋净亚中尺度垂向热通量变化与混合层深度变化趋势较为一致，在混合层上方整体呈现出向上的亚中尺度热量输运，混合层下方也存在很强的亚中尺度垂向热量输运，但呈现正负交替的变化特征，净亚中尺度垂向热量输运较小。垂向热通量波数频率协同谱分析表明，混合层下方的亚中尺度垂向热量输运可能是由线性内波引起的，但线性内波引起的向上与向下的垂向热量输运相互抵消，在季节平均后净垂向热量输运较小。Abstract: Submesoscale processes associated with strong vertical velocities play significant roles in the vertical transport of tracers between the ocean surface and the interior, including heat, buoyancy, and mass. Based on the results of the (1/48)° LLC4320 model, this study investigates the seasonal variations of submesoscale vertical heat transport in the Kuroshio Extension. The results show that submesoscale vertical heat transport in the Kuroshio Extension exhibits distinct seasonal variations, with strong transport in spring and winter, and weaker transport in summer and autumn. The variation of net submesoscale vertical heat flux in the upper ocean is consistent with the trend of mixed layer depth, which shows overall upward submesoscale heat transport above the mixed layer and strong alternating positive and negative submesoscale vertical heat transport below the mixed layer, resulting in relatively small net submesoscale vertical heat transport. Coherent spectral analysis of vertical heat flux wavenumber-frequency suggests that submesoscale vertical heat transport below the mixed layer may be caused by linear internal waves, but the upward and downward vertical heat transports induced by linear internal waves counteract each other, leading to a reduced net vertical heat transport after averaging over the season.
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Key words:
- Kuroshio Extension /
- submesoscale /
- vertical heat transport
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图 1 黑潮延伸体10 m层年平均温度的空间分布
R1、R2和R3是研究的子区域
Fig. 1 The spatial distribution of the annual average temperature at the 10-meter depth of the Kuroshio Extension
R1, R2, and R3 are the sub-areas of the study
图 2 黑潮延伸体区域2012年1月15日40 m深度动能谱
Fig. 2 Kinetic energy spectrum at a depth of 40 m in the Kuroshio Extension region on January 15, 2012
图 3 春（a）、夏（b）、秋（c）、冬（d）季节平均亚中尺度垂向热通量的空间分布
Fig. 3 Spatial distribution of seasonally averaged submesoscale vertical heat transport in spring (a), summer (b), autumn (c), and winter (d)
图 4 R1（a）、R2（b）和R3（c）区域平均亚中尺度垂向热通量及混合层深度随时间的变化情况
Fig. 4 The time series of submesoscale vertical heat flux and mixed layer depth averaged over regions R1 (a), R2 (b) and R3 (c)
图 5 R1 (a)、R2 (b)和R3 (c)区域季节平均垂向热通量随深度的变化情况
Fig. 5 Seasonal average vertical heat flux variation with depth in regions R1 (a), R2 (b), and R3 (c)
图 6 R1（a）、R2（b）和R3（c）区域平均亚中尺度垂向热通量随深度、时间的变化情况
黑色曲线为混合层深度
Fig. 6 Vertical and temporal variations of the means of submesoscale vertical heat flux in regions R1 (a), R2 (b), and R3 (c)
The black line representing the mixed layer depth
图 7 相对涡度在1月15日（a, c）和7月15日（b, d）的空间分布
a和b为40 m层，c和d为200 m层，均以行星涡度标准化
Fig. 7 The spatial distributions of relative vorticity on January 15th (a, c) and July 15th (b, d)
a and b are at the 40 m level, c and d are at the 200 m level, all normalized by planetary vorticity
图 8 垂向热通量在1月15日（a, c）和7月15日（b, d）的空间分布
a和b为40 m层，c和d为200 m层
Fig. 8 Spatial distribution of vertical heat flux at depths of 40 m (a, b) and 200 m (c, d) on January 15th (a, c) and July 15th (b, d)
a and b are at the 40 m level, c and d are at the 200 m level
图 9 水平浮力梯度在1月15日（a, c）和7月15日（b, d）的空间分布
a和b为40 m层，c和d为200 m层
Fig. 9 Spatial distribution of horizontal buoyancy gradient on January 15th (a, c) and July 15th (b, d)
a and b are at the 40 m level, c and d are at the 200 m lever
图 10 冬季R1（a、d）、R2（b、e）和R3（c、f）区域在40 m（a、b、c）和200 m（d、e、f）深垂向热通量的波数频率协同谱
蓝色实线分别为第一斜压模态的内波频散曲线（左）和第十斜压模态的内波频散曲线（右），蓝色虚线为M2内潮频率，黑色实线为惯性频率f，黑色虚线分别代表7 d和50 km所在的频率和波数。其中蓝色实线之间的区域为线性内波影响区，空间尺度小于50 km，处于第十斜压模态的内波频散曲线与7 d频率之间的为亚中尺度影响区，空间尺度大于50 km，时间频率大于7 d的为中尺度影响区
Fig. 10 Wavenumber-frequency co-spectra of vertical heat flux at depths of 40 m (a, b, c) and 200 m (d, e, f) in regions R1(a, d), R2(b, e), and R3(c, f) during winter
The solid blue lines represent the dispersion curves of the first baroclinic mode (left) and the tenth baroclinic mode (right) of internal waves. The blue dashed lines represent the M2 internal tide frequency, the solid black line represents the inertial frequency f, and the black dashed lines represent the frequencies and wavenumbers corresponding to 7 days and 50 km. The area between the solid blue lines is designated as the linear internal gravity wave influence zone. The region with a spatial scale less than 50 km, situated between the internal wave dispersion curve of the tenth baroclinic mode and a frequency of 7 days, is defined as the submesoscale influence zone. The region with a spatial scale greater than 50 km and a temporal frequency greater than 7 days is defined as the mesoscale influence zone
图 11 夏季R1（a、d）、R2（b、e）和R3（c、f）区域在40 m（a、b、c）和200 m（d、e、f）深垂向热通量的波数频率协同谱
蓝色实线分别为第一斜压模态的内波频散曲线（左）和第十斜压模态的内波频散曲线（右），蓝色虚线为M2内潮频率，黑色实线为惯性频率f，黑色虚线分别代表7 d和50 km所在的频率和波数。其中蓝色实线之间的区域定为线性内波影响区，空间尺度小于50 km，处于第十斜压模态的内波频散曲线与7 d频率之间的为亚中尺度影响区，空间尺度大于50 km，时间频率大于7 d的为中尺度影响区
Fig. 11 Wavenumber-frequency co-spectra of vertical heat flux at depths of 40 m (a, b, c) and 200 m (d, e, f) in regions R1(a, d), R2(b, e), and R3(c, f) during summer
The solid blue lines represent the dispersion curves of the first baroclinic mode (left) and the tenth baroclinic mode (right) of internal waves. The blue dashed lines represent the M2 internal tide frequency, the solid black line represents the inertial frequency f, and the black dashed lines represent the frequencies and wavenumbers corresponding to 7 days and 50 km. The area between the solid blue lines is designated as the linear internal gravity wave influence zone. The region with a spatial scale less than 50 km, situated between the internal wave dispersion curve of the tenth baroclinic mode and a frequency of 7 days, is defined as the submesoscale influence zone. The region with a spatial scale greater than 50 km and a temporal frequency greater than 7 days is defined as the mesoscale influence zone
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