Dynamical response of horizontal temperature fields in the mid-latitude thermocline to the decadal variation of wind stress curl 風系の数十年変動に起因する中緯度温度躍層における水平温度場の力学的応答

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Author

    • 中村, 啓彦 ナカムラ, ヒロヒコ

Bibliographic Information

Title

Dynamical response of horizontal temperature fields in the mid-latitude thermocline to the decadal variation of wind stress curl

Other Title

風系の数十年変動に起因する中緯度温度躍層における水平温度場の力学的応答

Author

中村, 啓彦

Author(Another name)

ナカムラ, ヒロヒコ

University

北海道大学

Types of degree

博士 (理学)

Grant ID

甲第3713号

Degree year

1995-09-29

Note and Description

博士論文

資料形態 : テキストデータ プレーンテキスト

コレクション : 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文

A major objective of this paper is to propose the mechanism that generates the variability in thermohaline structures, which was actually observed at intermediate depths of the North Atlantic subtropical-subpolar gyres, with interdecadal time scales. The observed variability is first compared with the climatological mean thermohaline structures and related to the observed variability in the wind stress curl over the North Atlantic. This data analysis yields two hypotheses: 1) a primary cause of the observed variability in thermohaline structures was the weakened wind stress cur,, and 2) the thermohaline variability caused by a uniform change in the wind stress curl was different between the western and eastern portions in both subtropical and subpolar gyres. In order to test these hypotheses, a four-level model, which is driven by wind stresses and surface buoyancy flux, is constructed with thermohaline structures represented by a temperature field. The model is used to examine responses of the subtropical-subpolar thermohaline field to a sudden and uniform change in wind stress curl. The model demonstratet that the uniformly weakened wind stress curl generates the thermohaline change with different tendencies between the western and eastem domains in both subtropical and subpolar gyres, similar to the observed pattern. The thermohaline change with different tendencies between the western and eastern domains is not related to a previous linear theory, which is associated with the local Ekman pumping and the long baroclinic Rossby wave. ln this study, the responses of the subtropical-subpolar thermohaline field are examined on the basis of a non-linear theory, which is associated with nonlinear advection in addition to above two mechanisms. The model solutions are analyzed using an analytical method: ie., the characteristic curves associated with both a linear wave propagation and nonlinear advection effects. The mechanism which generates the thermohaline change wi th different tendencies between the western and eastern domains is summarized as follows: the 1st baroclinic velocity field is weakened by the vertical shift of the temperature field in both subtropical and subpolar gyres. This process almost corresponds to the linear response. The weakened 1st baroclinic velocity field forms temperature anomalies in the thermocline, which have different tendencies between the western and eastern domains in both subtropical and subpolar gyres. The formation areas of temperature anomalies are related to the mean horizontal temperature structures, which are maintained by the wind stresses and surface buoyancy flux. The propagation of temperature anomalies along the characteristics generates the horizontal shift of temperature field.

Table of Contents

  1. Contents
  2. 1 Introduction
  3. 2 Observational evidences in the North Atlantic
  4. 2.1 Spatial pattern of the variation in the temperature and salinity structures
  5. 2.2 Temporal and spatial variability of the wind stress curl
  6. 2.3 Summary of observational evidences
  7. 3 Description of the numerical model
  8. 3.1 The model and governing equations
  9. 3.2 Outline of the numerical experiments
  10. 4 Preliminary considerations
  11. 4.1 Dynamics based on the planetary geostrophic equations
  12. 4.2 The basic equations for the analytical method
  13. 4.3 Dynamics at the eastern/western boundaries
  14. 5 Results of numerical experiments
  15. 5.1 The comparison of the North Atlantic with the model results
  16. 5.2 The comparison of EX1 with EX2
  17. 5.3 The steady state of Γ and θ fields
  18. 5.4 The immediate response of Γ and θ fields
  19. 5.5 The long-term response of Γ field
  20. 5.6 The long-term response of θ field
  21. 5.7 The variation of the meridional circulation
  22. 6 Discussion
  23. 7 Summary and conclusion
  24. Abstract
8access

Codes

  • NII Article ID (NAID)
    500002043723
  • NII Author ID (NRID)
    • 8000002607723
  • DOI(NDL)
  • Text Lang
    • eng
  • NDLBibID
    • 000000291383
  • Source
    • Institutional Repository
    • NDL ONLINE
    • NDL Digital Collections
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