scholarly journals Decadal Variability of Upper-Ocean Heat Content Associated with Meridional Shifts of Western Boundary Current Extensions in the North Pacific

2017 ◽  
Vol 30 (16) ◽  
pp. 6247-6264 ◽  
Author(s):  
Bunmei Taguchi ◽  
Niklas Schneider ◽  
Masami Nonaka ◽  
Hideharu Sasaki
Keyword(s):  
North Pacific ◽  
Frontal Zone ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Temperature Anomalies ◽  
The North ◽  
Subarctic Frontal Zone ◽  
The North Pacific

Generation and propagation processes of upper-ocean heat content (OHC) in the North Pacific are investigated using oceanic subsurface observations and an eddy-resolving ocean general circulation model hindcast simulation. OHC anomalies are decomposed into physically distinct dynamical components (OHC ρ) due to temperature anomalies that are associated with density anomalies and spiciness components (OHC χ) due to temperature anomalies that are density compensating with salinity. Analysis of the observational and model data consistently shows that both dynamical and spiciness components contribute to interannual–decadal OHC variability, with the former (latter) component dominating in the subtropical (subpolar) North Pacific. OHC ρ variability represents heaving of thermocline, propagates westward, and intensifies along the Kuroshio Extension, consistent with jet-trapped Rossby waves, while OHC χ variability propagates eastward along the subarctic frontal zone, suggesting advection by mean eastward currents. OHC χ variability tightly corresponds in space to horizontal mean spiciness gradients. Meanwhile, area-averaged OHC χ anomalies in the western subarctic frontal zone closely correspond in time to meridional shifts of the subarctic frontal zone. Regression coefficient of the OHC χ time series on the frontal displacement anomalies quantitatively agree with the area-averaged mean spiciness gradient in the region, and suggest that OHC χ is generated via frontal variability in the subarctic frontal zone.

scholarly journals Seasonal Evolutions of Atmospheric Response to Decadal SST Anomalies in the North Pacific Subarctic Frontal Zone: Observations and a Coupled Model Simulation

2012 ◽  
Vol 25 (1) ◽  
pp. 111-139 ◽  
Author(s):  
Bunmei Taguchi ◽  
Hisashi Nakamura ◽  
Masami Nonaka ◽  
Nobumasa Komori ◽  
Akira Kuwano-Yoshida ◽  
...  
Keyword(s):  
North Pacific ◽  
Frontal Zone ◽  
Ocean Dynamics ◽  
The North ◽  
The Pacific ◽  
Decadal Scale ◽  
Anomaly Pattern ◽  
Subarctic Frontal Zone ◽  
The North Pacific ◽  
Sst Anomalies

Abstract Potential impacts of pronounced decadal-scale variations in the North Pacific sea surface temperature (SST) that tend to be confined to the subarctic frontal zone (SAFZ) upon seasonally varying atmospheric states are investigated, by using 48-yr observational data and a 120-yr simulation with an ocean–atmosphere coupled general circulation model (CGCM). SST fields based on in situ observations and the ocean component of the CGCM have horizontal resolutions of 2.0° and 0.5°, respectively, which can reasonably resolve frontal SST gradient across the SAFZ. Both the observations and CGCM simulation provide a consistent picture between SST anomalies in the SAFZ yielded by its decadal-scale meridional displacement and their association with atmospheric anomalies. Correlated with SST anomalies persistent in the SAFZ from fall to winter, a coherent decadal-scale signal in the wintertime atmospheric circulation over the North Pacific starts emerging in November and develops into an equivalent barotropic anomaly pattern similar to the Pacific–North American (PNA) pattern. The PNA-like signal with the weakened (enhanced) surface Aleutian low correlated with positive (negative) SST anomalies in the SAFZ becomes strongest and most robust in January, under the feedback forcing from synoptic-scale disturbances migrating along the Pacific storm track that shifts northward (southward) in accord with the oceanic SAFZ. This PNA-like signal, however, breaks down in February, which is suggestive of a particular sensitivity of that anomaly pattern to subtle differences in the background climatological-mean state. Despite its collapse in February, the PNA-like signal recurs the next January. This subseasonal evolution of the signal suggests that the PNA-like anomaly pattern may develop as a response to the persistent SST anomalies that are maintained mainly through ocean dynamics.

scholarly journals Mechanisms for the Maintenance of the Wintertime Basin-Scale Atmospheric Response to Decadal SST Variability in the North Pacific Subarctic Frontal Zone

2017 ◽  
Vol 31 (1) ◽  
pp. 297-315 ◽  
Author(s):  
Satoru Okajima ◽  
Hisashi Nakamura ◽  
Kazuaki Nishii ◽  
Takafumi Miyasaka ◽  
Akira Kuwano-Yoshida ◽  
...  
Keyword(s):  
North Pacific ◽  
Frontal Zone ◽  
Atmospheric Response ◽  
The North ◽  
Model Response ◽  
Basin Scale ◽  
Sst Anomaly ◽  
Subarctic Frontal Zone ◽  
The North Pacific ◽  
Sst Anomalies

Abstract Mechanisms for the maintenance of a large-scale wintertime atmospheric response to warm sea surface temperature (SST) anomalies associated with decadal-scale poleward displacement of the North Pacific subarctic frontal zone (SAFZ) are investigated through the following two ensemble experiments with an atmospheric general circulation model (AGCM): one with climatological-mean SST and the other with positive SST anomalies along the SAFZ prescribed on top of the climatological-mean SST. As actually observed, the simulated January ensemble response over the North Pacific is anticyclonic throughout the depth of the troposphere, although its amplitude is smaller. This response is maintained through energy conversion from the ensemble climatological-mean circulation realized under the climatological SST as well as feedback from anomalous transient eddy activity, suggesting that the response may have characteristics as a preferred mode of variability (or “dynamical mode”). Conversions of both available potential energy and kinetic energy from the climatological-mean state are important for the observed anomaly, while the latter is less pronounced for the model response. Net transient feedback forcing is also important for both the observed anomaly and simulated response. These results imply that a moderate-resolution (~1°) AGCM may be able to simulate a basin-scale atmospheric response to the SAFZ SST anomaly through synoptic- and basin-scale dynamical processes. Weaker PNA-like internal variability in the model may lead to the weaker response, suggesting that misrepresentation of intrinsic atmospheric variability can affect the model response to the SST anomaly.

PDO-Related Heat and Temperature Budget Changes in a Model of the North Pacific

2007 ◽  
Vol 20 (10) ◽  
pp. 2092-2108 ◽  
Author(s):  
Jordan T. Dawe ◽  
Lu Anne Thompson
Keyword(s):  
Heat Flux ◽  
North Pacific ◽  
Heat Budget ◽  
Heat Content ◽  
Ocean Dynamics ◽  
Upper Ocean ◽  
The North ◽  
Atmospheric Heat ◽  
The Kuroshio ◽  
The North Pacific

Abstract Heat and temperature budget changes in a ⅓° model of the North Pacific driven by an idealized Pacific decadal oscillation (PDO) atmospheric forcing are diagnosed to determine the roles of atmospheric heat flux and ocean dynamics in upper-ocean heat content and mixed layer temperature (MLT) changes. Changes in MLT and heat content during the transition between negative and positive PDOs are driven primarily by atmospheric heat fluxes, with contributions from ageostrophic advection and entrainment. Once the new PDO state is established, atmospheric heat flux in the central North Pacific works to mitigate the MLT change while vertical entrainment and ageostrophic advection act to enhance it. Upper-ocean heat content is affected in a similar matter, except that vertical processes are not important in the heat budget balance. At the same time, changes in wind stress curl cause the subtropical gyre to spin up and the subpolar gyre boundary to migrate southward. These circulation changes cause a large increase in the geostrophic advective heat flux in the Kuroshio region. This increase results in more heat flux to the atmosphere, demonstrating an active role for ocean dynamics in the upper-ocean heat budget. Eddy heat flux divergence along the Kuroshio Extension doubles after the transition, due to stronger eddy activity related to increased Kuroshio transport.

scholarly journals Dominant Modes of Upper Ocean Heat Content in the North Indian Ocean

Climate ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 71 ◽  
Author(s):  
Meer Ali ◽  
Neetu Singh ◽  
Manchikanti Kumar ◽  
Yangxing Zheng ◽  
Mark Bourassa ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Thermal Energy ◽  
Heat Content ◽  
North Indian Ocean ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Modes Of Variability ◽  
The North ◽  
Ocean Atmosphere Interaction

The thermal energy needed for the development of hurricanes and monsoons as well as any prolonged marine weather event comes from layers in the upper oceans, not just from the thin layer represented by sea surface temperature alone. Ocean layers have different modes of thermal energy variability because of the different time scales of ocean–atmosphere interaction. Although many previous studies have focused on the influence of upper ocean heat content (OHC) on tropical cyclones and monsoons, no study thus far—particularly in the North Indian Ocean (NIO)—has specifically concluded the types of dominant modes in different layers of the ocean. In this study, we examined the dominant modes of variability of OHC of seven layers in the NIO during 1998–2014. We conclude that the thermal variability in the top 50 m of the ocean had statistically significant semiannual and annual modes of variability, while the deeper layers had the annual mode alone. Time series of OHC for the top four layers were analyzed separately for the NIO, Arabian Sea, and Bay of Bengal. For the surface to 50 m layer, the lowest and the highest values of OHC were present in January and May every year, respectively, which was mainly caused by the solar radiation cycle.

Exploratory Analysis of Upper-Ocean Heat Content and Sea Surface Temperature Underlying Tropical Cyclone Rapid Intensification in the Western North Pacific

2020 ◽  
Vol 33 (3) ◽  
pp. 1031-1050 ◽  
Author(s):  
Cheng-Hsiang Chih ◽  
Chun-Chieh Wu
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Pacific ◽  
Western North Pacific ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Sea Surface ◽  
Upper Ocean ◽  
Rapid Intensification ◽  
Upper Ocean Heat Content

AbstractThe statistical relationships between tropical cyclones (TCs) with rapid intensification (RI) and upper-ocean heat content (UOHC) and sea surface temperature (SST) from 1998 to 2016 in the western North Pacific are examined. RI is computed based on four best track datasets in the International Best Track Archive for Climate Stewardship (IBTrACS). The statistical analysis shows that the UOHC and SST are higher in the RI duration than in non-RI duration. However, TCs with high UOHC/SST do not necessarily experience RI. In addition, the UOHC and SST are lower in the storm inner-core region due to storm-induced ocean cooling, and the UOHC reduces more significantly than the SST along the passages of TCs in the lower-latitude regions. Moreover, most of the RI (non-RI) duration is associated with the higher (lower) UOHC, but this is not the case for the SST pattern. Meanwhile, the TC intensification rate during the RI period does not appear to be sensitive to the SST, but shows statistically significant differences in the UOHC. In addition, there is a statistically significant increasing trend in the UOHC underlying TCs from 1998 to 2016. It is also noted that the percentages of the TCs with RI show different polynomial and linear trends based on different calculations of the RI events and RI durations. Finally, it is shown that there is no statistically significant difference in the UOHC, SST, and the percentage of RI among the five categories of ENSO events (i.e., strong El Niño, weak El Niño, neutral, weak La Niña, and strong La Niña).

Decadal North Pacific Bred Vectors in a Coupled GCM

2007 ◽  
Vol 20 (23) ◽  
pp. 5744-5764 ◽  
Author(s):  
Yury Vikhliaev ◽  
Ben Kirtman ◽  
Paul Schopf
Keyword(s):  
Time Scales ◽  
North Pacific ◽  
Low Frequency ◽  
Heat Content ◽  
Ocean Basin ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Coupled Gcm ◽  
Bred Vectors

Abstract A number of recent studies done with simple numerical models suggest that the decadal variability in the extratropical North Pacific Ocean is a result of the excitation of low-frequency ocean basin modes. To test this assumption, low-frequency North Pacific variability was examined using a state-of-the-art coupled general circulation model (CGCM). Earlier studies had shown that slowly varying dynamical modes in a CGCM can be effectively isolated using the breeding technique. In this study, the breeding method was applied to the Center for Ocean-Land-Atmosphere Studies (COLA) anomaly coupled GCM (ACGCM), and it was found that several types of slow modes can be isolated depending on the parameters of the breeding cycle. Tropical bred vector SST and upper-ocean heat content are dominated by the ENSO, which is consistent with the results obtained earlier using other CGCMs. Extratropical bred vector upper-ocean heat content is dominated by oceanic instability localized east of Japan, varying on seasonal-to-interannual time scales, and decadal modes with the large-scale pattern over the central and eastern extratropical North Pacific. Similar to ocean basin modes, the decadal modes have a signature of westward-propagating long baroclinic Rossby waves, but do not exhibit the global imprint typical for global basin modes. The relationship between the decadal bred vectors and the background anomalies is consistent with linear damped dynamics. Presumably, the growth of the decadal bred vectors is due to the atmospheric stochastic forcing, but the existence of extratropical instability on decadal time scales still needs to be verified.

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