Takamasa Tsubouchi, Wilken-Jon von Appen, T. Kanzow, L. de Steur
This study quantifies the overturning circulation in the Arctic Ocean, and associated heat transport (HT) and freshwater transport (FWT) from October 2004 to May 2010 based on hydrographic and current observations. Our main data source consists of 1,165 moored instrument records in the four Arctic main gateways: Davis Strait, Fram Strait, Bering Strait and the Barents Sea Opening. We employ a box inverse model to obtain mass and salt balanced velocity fields, which are then used to quantify the overturning circulation as well as HT and FWT. Atlantic Water is transformed into two different water masses in the Arctic Ocean at a rate of 3.9 Sv. Combined with 0.6 Sv Bering Strait inflow and 0.1 Sv surface freshwater flux, 1.8 Sv flows back to the south through Davis Strait and western Fram Strait as the upper limb of the overturning circulation, while 2.8 Sv returns southward through Fram Strait as the lower limb of the overturning. The Arctic Ocean imports heat of 180±57 TW (long-term mean ± standard deviation of monthly means) with a methodological uncertainty of 20 TW and exports FW of 156±91 mSv with an uncertainty of 61 mSv over the six years with a potential offset of ~30 mSv. The HT and FWT have large seasonalities ranging between 110-260 TW (maximum in winter) and 40-260 mSv (maximum in winter), respectively. The obtained overturning circulation and associated HT and FWT presented here are vital information to better understand the northern extent of the Atlantic Meridional Overturning Circulation.
{"title":"Temporal variability of the overturning circulation in the Arctic Ocean and the associated heat and freshwater transports during 2004-2010","authors":"Takamasa Tsubouchi, Wilken-Jon von Appen, T. Kanzow, L. de Steur","doi":"10.1175/jpo-d-23-0056.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0056.1","url":null,"abstract":"\u0000This study quantifies the overturning circulation in the Arctic Ocean, and associated heat transport (HT) and freshwater transport (FWT) from October 2004 to May 2010 based on hydrographic and current observations. Our main data source consists of 1,165 moored instrument records in the four Arctic main gateways: Davis Strait, Fram Strait, Bering Strait and the Barents Sea Opening. We employ a box inverse model to obtain mass and salt balanced velocity fields, which are then used to quantify the overturning circulation as well as HT and FWT. Atlantic Water is transformed into two different water masses in the Arctic Ocean at a rate of 3.9 Sv. Combined with 0.6 Sv Bering Strait inflow and 0.1 Sv surface freshwater flux, 1.8 Sv flows back to the south through Davis Strait and western Fram Strait as the upper limb of the overturning circulation, while 2.8 Sv returns southward through Fram Strait as the lower limb of the overturning. The Arctic Ocean imports heat of 180±57 TW (long-term mean ± standard deviation of monthly means) with a methodological uncertainty of 20 TW and exports FW of 156±91 mSv with an uncertainty of 61 mSv over the six years with a potential offset of ~30 mSv. The HT and FWT have large seasonalities ranging between 110-260 TW (maximum in winter) and 40-260 mSv (maximum in winter), respectively. The obtained overturning circulation and associated HT and FWT presented here are vital information to better understand the northern extent of the Atlantic Meridional Overturning Circulation.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46797551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that have been shown to interact and provide a route for kinetic energy (KE) dissipation of balanced oceanic flows. In this paper, we study these KE exchanges using an idealized model consisting of a two-dimensional geostrophically-balanced front undergoing strain-induced semigeostrophic frontogenesis and internal wave (IW) vertical modes. The front-IW KE exchanges are quantified separately during two frontogenetic stages: an exponential sharpening stage that is characterized by a low Rossby number and is driven by the imposed strain (i.e., mesoscale frontogenesis), followed by a superexponential sharpening stage that is characterized by an 𝒪 (1) Rossby number and is driven by the convergence of the secondary circulation (i.e., submesoscale frontogenesis). It is demonstrated that high-frequency IWs quickly escape the frontal zone and are very efficient at extracting KE from the imposed geostrophic strain field through the deformation shear production (DSP). Part of the extracted KE is then converted to wave potential energy. On the contrary, NIWs remain locked to the frontal zone and readily exchange energy with the ageostrophic frontal circulation. During the exponential stage, NIWs extract KE from the geostrophic strain through DSP and transfer it to the frontal secondary circulation via the ageostrophic shear production (AGSP) mechanism. During the superexponential stage, a newly identified mechanism, ‘convergence production’ (CP), plays an important role in the NIW KE budget. The CP transfers KE from the convergent ageostrophic secondary circulation to the NIWs and largely cancels out the KE loss due to the AGSP. This CP may explain previous findings of KE transfer enhancement from balanced motions to IWs in frontal regions of realistic ocean models. We provide analytical estimates for the aforementioned energy exchange mechanisms that match well the numerical results. This highlights that the strength of the exchanges strongly depends on the frontal Rossby and Richardson numbers.
{"title":"Kinetic energy exchanges between a two-dimensional front and internal waves","authors":"Subhajit Kar, R. Barkan","doi":"10.1175/jpo-d-22-0240.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0240.1","url":null,"abstract":"\u0000Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that have been shown to interact and provide a route for kinetic energy (KE) dissipation of balanced oceanic flows. In this paper, we study these KE exchanges using an idealized model consisting of a two-dimensional geostrophically-balanced front undergoing strain-induced semigeostrophic frontogenesis and internal wave (IW) vertical modes. The front-IW KE exchanges are quantified separately during two frontogenetic stages: an exponential sharpening stage that is characterized by a low Rossby number and is driven by the imposed strain (i.e., mesoscale frontogenesis), followed by a superexponential sharpening stage that is characterized by an 𝒪 (1) Rossby number and is driven by the convergence of the secondary circulation (i.e., submesoscale frontogenesis). It is demonstrated that high-frequency IWs quickly escape the frontal zone and are very efficient at extracting KE from the imposed geostrophic strain field through the deformation shear production (DSP). Part of the extracted KE is then converted to wave potential energy. On the contrary, NIWs remain locked to the frontal zone and readily exchange energy with the ageostrophic frontal circulation. During the exponential stage, NIWs extract KE from the geostrophic strain through DSP and transfer it to the frontal secondary circulation via the ageostrophic shear production (AGSP) mechanism. During the superexponential stage, a newly identified mechanism, ‘convergence production’ (CP), plays an important role in the NIW KE budget. The CP transfers KE from the convergent ageostrophic secondary circulation to the NIWs and largely cancels out the KE loss due to the AGSP. This CP may explain previous findings of KE transfer enhancement from balanced motions to IWs in frontal regions of realistic ocean models. We provide analytical estimates for the aforementioned energy exchange mechanisms that match well the numerical results. This highlights that the strength of the exchanges strongly depends on the frontal Rossby and Richardson numbers.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45642053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kai-Chieh Yang, S. Jan, Y. Yang, Ming‐Huei Chang, Joe Wang, Shih-Hong Wang, S. Ramp, D. B. Reeder, D. Ko
Observations from a Seaglider, two pressure sensor-equipped inverted echo sounders (PIESs), and a thermistor chain (T-chain) mooring were used to determine the waveform and timing of internal solitary waves (ISWs) over the continental slope east of Dongsha Atoll. The Korteweg-De Vries (KdV) and Dubreil-Jacotin-Long (DJL) equations supplemented the data from repeated profiling by the glider at a fixed position (depth ~1017 m) during 19–24 May 2019. The glider recorded pressure perturbations were used to compute the rarely-measured vertical velocity (w) with a static glider flight model. After removing the internal tide-caused vertical velocity, the w of the eight mode-1 ISWs ranged from −0.35 to 0.36 m s−1 with an uncertainty of ±0.005 m s−1 due to turbulent oscillations and measurement error. The horizontal velocity profiles, wave speeds, and amplitudes of the eight ISWs were further derived from the KdV and DJL equations using the glider-observed w and potential density profiles. The mean speed of the corresponding ISW from the PIES deployed at ~2000 m depth to the T-chain moored at 500 m depth and the 19°C isotherm displacement computed from the T-chain were used to validate the waveform derived from KdV and DJL. The validation suggests that the DJL equation provides reasonably representative wave speed and amplitude for the eight ISWs compared to the KdV equation. Stand-alone glider data provides near real-time hydrography and vertical velocities for mode-1 ISWs and is useful for characterizing the anatomy of ISWs and validating numerical simulations of these waves.
使用Seaglider、两个配备压力传感器的倒置回声测深仪（PIES）和一个热敏电阻链（T链）系泊装置的观测结果来确定东沙环礁以东大陆坡上空内部孤立波（ISW）的波形和时间。Korteweg De Vries（KdV）和Dubreil Jacobin-Long（DJL）方程补充了2019年5月19日至24日期间滑翔机在固定位置（深度~1017 m）重复剖面的数据。滑翔机记录的压力扰动用于使用静态滑翔机飞行模型计算很少测量的垂直速度（w）。在去除内部潮汐引起的垂直速度后，由于湍流振荡和测量误差，八个模式-1 ISW的w范围为-0.35至0.36 m s−1，不确定度为±0.005 m s−1。使用滑翔机观测到的w和势密度剖面，从KdV和DJL方程进一步推导出了八个ISW的水平速度剖面、波速和振幅。从部署在约2000 m深度的PIES到系泊在500 m深度的T链的相应ISW的平均速度以及从T链计算的19°C等温线位移用于验证KdV和DJL得出的波形。验证表明，与KdV方程相比，DJL方程为八个ISW提供了合理的代表性波速和振幅。独立滑翔机数据为1型ISW提供了近乎实时的水文和垂直速度，有助于表征ISW的解剖结构和验证这些波的数值模拟。
{"title":"Anatomy of mode-1 internal solitary waves derived from Seaglider observations in the northern South China Sea","authors":"Kai-Chieh Yang, S. Jan, Y. Yang, Ming‐Huei Chang, Joe Wang, Shih-Hong Wang, S. Ramp, D. B. Reeder, D. Ko","doi":"10.1175/jpo-d-23-0039.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0039.1","url":null,"abstract":"\u0000Observations from a Seaglider, two pressure sensor-equipped inverted echo sounders (PIESs), and a thermistor chain (T-chain) mooring were used to determine the waveform and timing of internal solitary waves (ISWs) over the continental slope east of Dongsha Atoll. The Korteweg-De Vries (KdV) and Dubreil-Jacotin-Long (DJL) equations supplemented the data from repeated profiling by the glider at a fixed position (depth ~1017 m) during 19–24 May 2019. The glider recorded pressure perturbations were used to compute the rarely-measured vertical velocity (w) with a static glider flight model. After removing the internal tide-caused vertical velocity, the w of the eight mode-1 ISWs ranged from −0.35 to 0.36 m s−1 with an uncertainty of ±0.005 m s−1 due to turbulent oscillations and measurement error. The horizontal velocity profiles, wave speeds, and amplitudes of the eight ISWs were further derived from the KdV and DJL equations using the glider-observed w and potential density profiles. The mean speed of the corresponding ISW from the PIES deployed at ~2000 m depth to the T-chain moored at 500 m depth and the 19°C isotherm displacement computed from the T-chain were used to validate the waveform derived from KdV and DJL. The validation suggests that the DJL equation provides reasonably representative wave speed and amplitude for the eight ISWs compared to the KdV equation. Stand-alone glider data provides near real-time hydrography and vertical velocities for mode-1 ISWs and is useful for characterizing the anatomy of ISWs and validating numerical simulations of these waves.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49206337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ruijian Gou, Pusheng Li, Kevin N. Wiegand, Clark Pennelly, D. Kieke, P. Myers
Eddies generated off the west Greenland coast modulate the deep convection in the Labrador Sea, while there are still open questions related to their formation mechanisms. Using eleven-years (2008-2018) of output from a NEMO model configured with a 1/60° nest in the Labrador Sea, we present the patterns of baroclinic and barotropic instability off the west Greenland coast. We highlight the generation of Irminger Rings at Cape Desolation and boundary current eddies at the location of the OSNAP West section. In between these formation sites, eddy energy attenuation occurs along the West Greenland Current (WGC). Overall, baroclinic instability dominates in the upper 1000 m and is twice as strong as the barotropic instability. Seasonally, the instabilities are generally twice as strong in winter compared to summer. Inter-annually from 2008 to 2018, the instabilities generally show a strengthening trend, with values in 2018 two to three times as strong as those in 2008. We found that on an interannual timescale, the strengthening of WGC and the steepening of its velocity contours enhance the barotropic instability, and the intrusion of the upper Irminger Sea Intermediate Water (uISIW) on the Irminger Water enhances the baroclinic instability by increasing the horizontal density gradient. On a seasonal timescale, variability of the eddy momentum and density fluxes modulate the barotropic and baroclinic instability respectively. From observation-based datasets, we also found that the downstream eddy kinetic energy is highly correlated with the uISIW transports, suggesting that the amount of uISIW affects the eddy formation. Using a very high-resolution numerical model, our study provides new insight into the variability and mechanisms of eddy formation along the west Greenland coast.
{"title":"Variability of eddy formation off the west Greenland coast from a 1/60° model","authors":"Ruijian Gou, Pusheng Li, Kevin N. Wiegand, Clark Pennelly, D. Kieke, P. Myers","doi":"10.1175/jpo-d-23-0004.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0004.1","url":null,"abstract":"\u0000Eddies generated off the west Greenland coast modulate the deep convection in the Labrador Sea, while there are still open questions related to their formation mechanisms. Using eleven-years (2008-2018) of output from a NEMO model configured with a 1/60° nest in the Labrador Sea, we present the patterns of baroclinic and barotropic instability off the west Greenland coast. We highlight the generation of Irminger Rings at Cape Desolation and boundary current eddies at the location of the OSNAP West section. In between these formation sites, eddy energy attenuation occurs along the West Greenland Current (WGC). Overall, baroclinic instability dominates in the upper 1000 m and is twice as strong as the barotropic instability. Seasonally, the instabilities are generally twice as strong in winter compared to summer. Inter-annually from 2008 to 2018, the instabilities generally show a strengthening trend, with values in 2018 two to three times as strong as those in 2008. We found that on an interannual timescale, the strengthening of WGC and the steepening of its velocity contours enhance the barotropic instability, and the intrusion of the upper Irminger Sea Intermediate Water (uISIW) on the Irminger Water enhances the baroclinic instability by increasing the horizontal density gradient. On a seasonal timescale, variability of the eddy momentum and density fluxes modulate the barotropic and baroclinic instability respectively. From observation-based datasets, we also found that the downstream eddy kinetic energy is highly correlated with the uISIW transports, suggesting that the amount of uISIW affects the eddy formation. Using a very high-resolution numerical model, our study provides new insight into the variability and mechanisms of eddy formation along the west Greenland coast.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46617990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. M. Santos-Ferreira, J. da Silva, B. St-Denis, D. Bourgault, L. Maas
The equatorial cold tongue in the Pacific Ocean has been intensely studied during the last decades as it plays an important role in air-sea interactions and climate issues. Recently, Warner et al. (2018) revealed gravity currents apparently originating in Tropical Instability Waves. Both phenomena have strong dissipation rates, and were considered to play a significant role in cascading energy from the mesoscale to smaller horizontal scales, as well as to vertical scales less than one meter. Here, we present Sentinel-3 satellite observations of Internal Solitary Waves (ISWs) in the Pacific cold tongue near the equator, in a zonal band stretching from 210°E to 265°E, away from any steep bottom topography. Within this band these waves propagate in multiple directions. Some of the waves’ characteristics, such as the distance between wave crests, crest lengths and time scales, are estimated from satellite observations. In total we identify 116 ISW trains during one full year (2020), with typical distances between crests of 1500 m and crest lengths of hundreds of km. These ISW trains appear to be generated by buoyant gravity currents having sharp fronts detectable in thermal infrared satellite images. A 2D numerical model confirms that resonantly generated nonlinear internal waves with amplitudes of O(10) m may be continuously initiated at the fronts of advancing gravity currents.
{"title":"Internal Solitary Waves within the Cold Tongue of the Equatorial Pacific generated by buoyant gravity currents","authors":"A. M. Santos-Ferreira, J. da Silva, B. St-Denis, D. Bourgault, L. Maas","doi":"10.1175/jpo-d-22-0165.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0165.1","url":null,"abstract":"\u0000The equatorial cold tongue in the Pacific Ocean has been intensely studied during the last decades as it plays an important role in air-sea interactions and climate issues. Recently, Warner et al. (2018) revealed gravity currents apparently originating in Tropical Instability Waves. Both phenomena have strong dissipation rates, and were considered to play a significant role in cascading energy from the mesoscale to smaller horizontal scales, as well as to vertical scales less than one meter. Here, we present Sentinel-3 satellite observations of Internal Solitary Waves (ISWs) in the Pacific cold tongue near the equator, in a zonal band stretching from 210°E to 265°E, away from any steep bottom topography. Within this band these waves propagate in multiple directions. Some of the waves’ characteristics, such as the distance between wave crests, crest lengths and time scales, are estimated from satellite observations. In total we identify 116 ISW trains during one full year (2020), with typical distances between crests of 1500 m and crest lengths of hundreds of km. These ISW trains appear to be generated by buoyant gravity currents having sharp fronts detectable in thermal infrared satellite images. A 2D numerical model confirms that resonantly generated nonlinear internal waves with amplitudes of O(10) m may be continuously initiated at the fronts of advancing gravity currents.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46993780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhongbin Sun, Zhiwei Zhang, Cheng Li, D. Yuan, Qin‐Xi Yuan, Wenbo Lu, Yuelin Liu, Chun Zhou, Jing Wang, Ya Yang, Wei Zhao, Jiwei Tian
Full-depth ocean zonal currents in the tropical and extratropical northwestern Pacific (TNWP) are studied using current measurements from 17 deep-ocean moorings deployed along the 143°E meridian from the equator to 22°N during January 2016 through February 2017. Mean transports of the North Equatorial Current and North Equatorial Countercurrent are estimated to be 42.7 ± 7.1 Sv (1 Sv ≡ 106 m3 s−1) and 10.5 ± 5.3 Sv, respectively, both of which exhibit prominent annual cycles with opposite phases in this year. The observations suggest much larger vertical extents of several of the major subsurface currents than previously reported, including the Lower Equatorial Intermediate Current, Northern Intermediate Countercurrent, North Equatorial Subsurface Current, and North Equatorial Undercurrent (NEUC) from south to north. The Northern Subsurface Countercurrent and NEUC are found less steady than the other currents. Seasonal variations of these currents are also revealed in the study. In the deep ocean, the currents below 2000 m are reported for the first time. The observations confirm the striation patterns of meridionally-alternating zonal currents in the intermediate and deep layers. Further analyses suggest a superposition of at least the first four and two baroclinic modes to represent the mean equatorial and off-equatorial currents, respectively. Meanwhile, seasonal variations of the currents are generally dominated by the first baroclinic mode associated with the low-mode Rossby waves. Overall, the above observational results not only enhance the knowledge of full-depth current system in the TNWP but also provide a basis for future model validation and skill improvement.
{"title":"Mooring measurements of full-depth zonal currents along 143°E meridian in the northwestern Pacific Ocean","authors":"Zhongbin Sun, Zhiwei Zhang, Cheng Li, D. Yuan, Qin‐Xi Yuan, Wenbo Lu, Yuelin Liu, Chun Zhou, Jing Wang, Ya Yang, Wei Zhao, Jiwei Tian","doi":"10.1175/jpo-d-22-0210.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0210.1","url":null,"abstract":"\u0000Full-depth ocean zonal currents in the tropical and extratropical northwestern Pacific (TNWP) are studied using current measurements from 17 deep-ocean moorings deployed along the 143°E meridian from the equator to 22°N during January 2016 through February 2017. Mean transports of the North Equatorial Current and North Equatorial Countercurrent are estimated to be 42.7 ± 7.1 Sv (1 Sv ≡ 106 m3 s−1) and 10.5 ± 5.3 Sv, respectively, both of which exhibit prominent annual cycles with opposite phases in this year. The observations suggest much larger vertical extents of several of the major subsurface currents than previously reported, including the Lower Equatorial Intermediate Current, Northern Intermediate Countercurrent, North Equatorial Subsurface Current, and North Equatorial Undercurrent (NEUC) from south to north. The Northern Subsurface Countercurrent and NEUC are found less steady than the other currents. Seasonal variations of these currents are also revealed in the study. In the deep ocean, the currents below 2000 m are reported for the first time. The observations confirm the striation patterns of meridionally-alternating zonal currents in the intermediate and deep layers. Further analyses suggest a superposition of at least the first four and two baroclinic modes to represent the mean equatorial and off-equatorial currents, respectively. Meanwhile, seasonal variations of the currents are generally dominated by the first baroclinic mode associated with the low-mode Rossby waves. Overall, the above observational results not only enhance the knowledge of full-depth current system in the TNWP but also provide a basis for future model validation and skill improvement.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44284577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhuoqun Wang, Yonggang Liu, Xunqiang Yin, Ming Zhang, Jian Zhang, F. Qiao
We investigate the mechanisms with which the sea surface temperature (SST) in the tropical Pacific responds to the perturbation of an exponential form to the background vertical mixing of the upper ocean. For a surface value of 0.005 m2 s−1 and a scale depth of 10 m (as typically used in the so-called non-breaking wave parameterization), it is found that only ocean temperature within the equatorial eastern Pacific (EEP) is directly impacted; surface cooling and thermocline warming anomalies are produced. These signals propagate poleward as coastal Kelvin waves and then westwards as equatorial Rossby waves. The surface cooling is severely damped while the thermocline warming is able to reach the western coast. This warm anomaly is brought up to the surface by equatorial upwelling more strongly around 110°W than at other places. In the coupled model, such equatorial warming induces an El Niño-like large-scale warming through Bjerknes feedback. Increasing the surface value of vertical mixing by a factor of 10 does not increase the equatorial surface warming while increasing the scale depth to 20m does. Increasing the scale depth generates thermocline warming also in the subtropical region, which then propagates to the equatorial thermocline and enhances the warming there. Moreover, the off-equatorial cooling is enhanced, which makes the final warming anomaly narrower meridionally compared to an El Niño pattern.
{"title":"The Effect of an Exponentially Decaying Upper-ocean Vertical Mixing on the Pacific Tropical Sea Surface Temperature","authors":"Zhuoqun Wang, Yonggang Liu, Xunqiang Yin, Ming Zhang, Jian Zhang, F. Qiao","doi":"10.1175/jpo-d-23-0026.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0026.1","url":null,"abstract":"\u0000We investigate the mechanisms with which the sea surface temperature (SST) in the tropical Pacific responds to the perturbation of an exponential form to the background vertical mixing of the upper ocean. For a surface value of 0.005 m2 s−1 and a scale depth of 10 m (as typically used in the so-called non-breaking wave parameterization), it is found that only ocean temperature within the equatorial eastern Pacific (EEP) is directly impacted; surface cooling and thermocline warming anomalies are produced. These signals propagate poleward as coastal Kelvin waves and then westwards as equatorial Rossby waves. The surface cooling is severely damped while the thermocline warming is able to reach the western coast. This warm anomaly is brought up to the surface by equatorial upwelling more strongly around 110°W than at other places. In the coupled model, such equatorial warming induces an El Niño-like large-scale warming through Bjerknes feedback. Increasing the surface value of vertical mixing by a factor of 10 does not increase the equatorial surface warming while increasing the scale depth to 20m does. Increasing the scale depth generates thermocline warming also in the subtropical region, which then propagates to the equatorial thermocline and enhances the warming there. Moreover, the off-equatorial cooling is enhanced, which makes the final warming anomaly narrower meridionally compared to an El Niño pattern.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44505928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The short-period current fluctuations (topographic wave fluctuations, TWFs) on the southern rim slope of the abyssal Japan Sea were investigated using current meter datasets from closely spaced mooring arrays. The TWFs occurred almost continuously throughout the year with short periods in a narrow band (1.5–5-d), showing a seasonal modulation in their amplitude. The TWFs were attributable to alternate passage of cyclonic and anti-cyclonic eddies on the rim slope, which propagated eastward at a speed of 0.15–0.23 m s−1. In addition, the TWFs showed a bottom-intensified characteristic, along with the two-layer structure consisting of an almost barotropic lower layer and a marginally baroclinic upper layer. The lowest topographic Rossby mode, which is a normal mode of the topographic Rossby waves prescribed by the two ridges on the rim slope, was considered as a cause of the TWFs because of its eastward-propagating eddy train structure along the rim slope and the eigenperiod (3–5-d) near the TWF-band. In addition, the local time-dependent Sverdrup balance was considered as a mechanism of the TWF generation, since the TWFs significantly correlated with the wind stress curl variations over the observation area with time lags. That is, the current fluctuations near the eigenperiod were selectively amplified via the resonance between the lowest topographic Rossby mode and the Ekman pumping variations induced by the TWF-band wind stress curl. We concluded that the observed TWFs were a manifestation of the wind-induced lowest topographic Rossby mode prescribed by the bottom topography.
利用紧密间隔系泊阵列的流计数据，研究了日本深海南缘斜坡上的短周期流波动(地形波波动，TWFs)。twf全年几乎连续发生，周期短，频带窄(1.5 ~ 5 d)，振幅有季节性变化。气旋和反气旋涡旋在边缘斜坡上交替通过，以0.15 ~ 0.23 m s−1的速度向东传播。此外，twf还表现出底部强化的特征，低层几乎为正压，上层为偏斜压的两层结构。最低的地形罗斯比模态是由边缘斜坡上的两个脊所规定的地形罗斯比波的正态模态，由于其沿边缘斜坡向东传播的涡列结构和在twf波段附近的特征周期(3-5-d)，被认为是twf产生的原因。此外，局地时变Sverdrup平衡被认为是TWF产生的一种机制，因为TWF与观测区域的风应力旋度变化具有显著的时滞相关性。即，通过最低地形罗斯比模态与twf波段风应力旋度引起的Ekman泵送变化之间的共振，选择性地放大了特征周期附近的电流波动。我们认为，观测到的twf是由底部地形规定的风致最低地形罗斯比模态的表现。
{"title":"Local topographic Rossby modes observed in the abyssal Japan Sea","authors":"T. Senjyu","doi":"10.1175/jpo-d-22-0209.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0209.1","url":null,"abstract":"\u0000The short-period current fluctuations (topographic wave fluctuations, TWFs) on the southern rim slope of the abyssal Japan Sea were investigated using current meter datasets from closely spaced mooring arrays. The TWFs occurred almost continuously throughout the year with short periods in a narrow band (1.5–5-d), showing a seasonal modulation in their amplitude. The TWFs were attributable to alternate passage of cyclonic and anti-cyclonic eddies on the rim slope, which propagated eastward at a speed of 0.15–0.23 m s−1. In addition, the TWFs showed a bottom-intensified characteristic, along with the two-layer structure consisting of an almost barotropic lower layer and a marginally baroclinic upper layer. The lowest topographic Rossby mode, which is a normal mode of the topographic Rossby waves prescribed by the two ridges on the rim slope, was considered as a cause of the TWFs because of its eastward-propagating eddy train structure along the rim slope and the eigenperiod (3–5-d) near the TWF-band. In addition, the local time-dependent Sverdrup balance was considered as a mechanism of the TWF generation, since the TWFs significantly correlated with the wind stress curl variations over the observation area with time lags. That is, the current fluctuations near the eigenperiod were selectively amplified via the resonance between the lowest topographic Rossby mode and the Ekman pumping variations induced by the TWF-band wind stress curl. We concluded that the observed TWFs were a manifestation of the wind-induced lowest topographic Rossby mode prescribed by the bottom topography.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"1 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64643513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The evolution of wind-generated near-inertial waves (NIWs) is known to be influenced by the mesoscale eddy field, yet it remains a challenge to disentangle the effects of this interaction in observations. Here, the model of Young and Ben Jelloul (YBJ), which describes NIW evolution in the presence of slowly evolving mesoscale eddies, is compared to observations from a mooring array in the Northeast Atlantic Ocean. The model captures the evolution of both the observed NIW amplitude and phase much more accurately than a slab mixed layer model. The YBJ model allows for the identification of specific physical processes that drive the observed evolution. It reveals that differences in the NIW amplitude across the mooring array are caused by the refractive concentration of NIWs into anticyclones. Advection and wave dispersion also make important contributions to the observed wave evolution. Stimulated generation, a process by which mesoscale kinetic energy acts as a source of NIW potential energy, is estimated to be 20 μWm−2 in the region of the mooring array, which is two orders of magnitude smaller than the global average input to mesoscale kinetic energy and likely not an important contribution to the mesoscale kinetic energy budget in this region. Overall, the results show that the YBJ model is a quantitatively useful tool to interpret observations of NIWs.
{"title":"Interpreting Observed Interactions between Near-Inertial Waves and Mesoscale Eddies","authors":"Scott Conn, J. Fitzgerald, J. Callies","doi":"10.1175/jpo-d-23-0139.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0139.1","url":null,"abstract":"The evolution of wind-generated near-inertial waves (NIWs) is known to be influenced by the mesoscale eddy field, yet it remains a challenge to disentangle the effects of this interaction in observations. Here, the model of Young and Ben Jelloul (YBJ), which describes NIW evolution in the presence of slowly evolving mesoscale eddies, is compared to observations from a mooring array in the Northeast Atlantic Ocean. The model captures the evolution of both the observed NIW amplitude and phase much more accurately than a slab mixed layer model. The YBJ model allows for the identification of specific physical processes that drive the observed evolution. It reveals that differences in the NIW amplitude across the mooring array are caused by the refractive concentration of NIWs into anticyclones. Advection and wave dispersion also make important contributions to the observed wave evolution. Stimulated generation, a process by which mesoscale kinetic energy acts as a source of NIW potential energy, is estimated to be 20 μWm−2 in the region of the mooring array, which is two orders of magnitude smaller than the global average input to mesoscale kinetic energy and likely not an important contribution to the mesoscale kinetic energy budget in this region. Overall, the results show that the YBJ model is a quantitatively useful tool to interpret observations of NIWs.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"70 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139351946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：