Northwest pacific heat balance analysed using In-situ, model and satellite data

다국어 초록 (Multilingual Abstract)

Heat balance within an ocean mixed layer is important since it describes whether ocean-atmosphere and ocean-climate interactions occur locally or remotely. In paticular, a knowledge of heat balance will improve our understanding of the causes of variations in sea surface temperature and air-sea heat exchange. In this study, the heat balance mechanism is analysed on a seasonal scale. The study region is the Northwest Pacific where the role of the strong Kuroshio Extension geostrophic current on the heat balance has not been quantified previously. A combination of in-situ, model, and satellite data is used for the period October 1992 to September 1995.
Components of the heat balance are determined as follows. The horizontal geostrophic heat advection is obtained using current velocities from satellite altimetry and a Gaussian jet model. The errors in the monthly and spatial mean values of the zonal and meridional geostrophic heat advection reach respectively 150 % (46 W m^(-2)) and 300 % (61 W m^(-2)) of the signal. Although these errors are substantial, such evaluations of the signal and error level have not been achieved before. A validation of the velocity from the jet model is performed for the first time in the Northwest Pacific. The r.m.s. error is 17 cm s^(-1) or 46 % of the signal. The entrainment heat advection is estimated rigorously on a climatological monthly scale. This term is neglected in the heat budget since its maximum magnitude of 30 W m^(-2) is at least a factor of three smaller than those of the other balance terms. The heat storage rate is computed using mixed layer temperatures from satellite infrared imagery and mixed layer depths from subsurface temperature records. The horizontal Ekman heat advection is derived using ECMWF model wind speeds.
The seasonal heat advection by the Kuroshio Extension is insignificant in the basin-scale heat balance. It is less than 10 % of the heat storage rate. The horizontal Ekman heat advection is also observed to be insignificant. It is concluded that the heat balance is achieved locally.
Monthly net surface heat fluxes are derived from the sum of the heat balance terms. Errors in these fluxes are estimated thoroughly. First, systematic and random errors in the basic fields are determined by validation. Then formulae are given and used on how these errors propagate into the flux error through mathematical operations such as product or spatial and temporal average. A value of 30 W m^(-2) is obtained for the error in the three-year mean net surface heat flux over the basin. This is smaller in percentage terms than that achieved by the best bulk-formulae method. However, this error still exceeds lOW m^(-2) required by climate studies. Horizontal heat advection (Ekman plus geostrophic) contributes 21 W m^(-2) to the error in the three-year mean net surface heat flux.

목차 (Table of Contents)

• Acknowledgements = 4
• Abstract = 6
• Contents = 7
• List of figures = 11
• List of tables = 18
• Chapter 1. Introduction = 19
• 1.1. Outline = 19
• 1.2. Climate and oceans = 20
• 1.3. Importance of mixed layer heat balance = 28
• 1.4. Mid-latitude Northwest Pacific = 32
• 1.5. Research objectives = 43
• 1.5.1. Understanding the heat balance mechanism = 43
• 1.5.2. Improving a present estimate of net surface heat flux = 49
• 1.6. Thesis outline = 51
• Chapter 2. Methodology and data = 52
• 2.1. Outline = 52
• 2.2. Equation for mixed layer beat balance = 52
• 2.3. Data description = 61
• 2.3.1. Temperature-depth profile = 61
• 2.3.2. Sea surface temperature from satellite infrared imagery = 62
• 2.3.3. Sea surface height records from satellite altimetry = 65
• 2.3.4. Wind speeds from the ECMWF numerical model = 68
• 2.3.5. Time frame of this study = 70
• 2.3.6. Common grid space and spatial interpolation = 70
• 2.4. Fundamentals of error estimate = 72
• 2.4.1. Principles = 72
• 2.4.2. Error reduction: the case of Gaussian interpolation = 76
• Chapter 3. Heat storage rate = 78
• 3.1. Outline = 78
• 3.2. Mixed layer depth = 79
• 3.2.1. Computation using temperature-depth profiles = 80
• 3.2.2. Treatment of non-ideal profiles = 89
• 3.2.3. Sensitivity of the depths to the choice of computation algorithm = 96
• 3.2.4. Error estimate = 98
• 3.3. Temporal change in the mixed layer temperature = 103
• 3.3.1. Evaluation = 103
• 3.3.2. Error estimate = 105
• 3.4. Heat storage rate = 108
• 3.4.1. Evaluation = 108
• 3.4.2. Error estimate = 109
• 3.5. Summary = 112
• Chapter 4. Horizontal geostrophic heat advection = 115
• 4.1. Outline = 115
• 4.2. Absolute geostrophic velocities across satellite ground tracks = 116
• 4.2.1. Problems in the hydrographic method for velocity determination = 116
• 4.2.2. Employing satellite altimetry = 117
• 4.2.3. Employing Kelly and Gille's method = 118
• 4.2.4. Improvements in Kelly and Gille's method = 122
• 4.2.4.1. Determination of the jet axis position = 122
• 4.2.4.2. Choice of pre-smoothing filter details = 125
• 4.2.5. Validation of the altimeter cross-track velocity = 131
• 4.3. Zonal and meridional velocities = 133
• 4.3.1. Principles = 134
• 4.3.2. Determination of flow direction = 136
• 4.3.3. Errors before the interpolation = 140
• 4.3.4. Errors in the interpolated velocities = 144
• 4.3.4.1. Random error estimate: formulation = 144
• 4.3.4.2. Random error estimate: evaluation = 145
• 4.4. Spatial change in the mixed layer temperature = 149
• 4.4.1. Evaluation = 149
• 4.4.2. Error estimate = 151
• 4.5. Horizontal geostrophic heat advection = 153
• 4.6. Summary = 164
• Chapter 5. Horizontal Ekman and entrainment heat advection = 167
• 5.1. Horizontal Ekman heat advection = 167
• 5.1.1. Outline = 167
• 5.1.2. Horizontal Ekman volume advection = 168
• 5.1.2.1. Formulation = 168
• 5.1.2.2. Evaluation = 169
• 5.1.2.3. Error estimate: principles = 173
• 5.1.2.4 Error estimate: in the ERA vector wind = 174
• 5.1.2.5. Error estimate: in the OA vector wind = 179
• 5.1.2.6. Error estimate: in the Ekoman volume advection = 180
• 5.1.3. Spatial change in the mixed layer temperature = 182
• 5.1.4. Ekman heat advection = 182
• 5.1.4.1. Evaluation = 182
• 5.1.4.2. Error estimate = 184
• 5.1.5 Summary = 186
• 5.2. Entrainment heat advection = 187
• 5.2.1. Outline = 187
• 5.2.2. Entrainment mass advection = 187
• 5.2.2.1. Temporal mixed layer depth term = 188
• 5.2.2.2. Lateral induction = 190
• 5.2.2.3. Vertical velocity: theory = 191
• 5.2.2.4. Vertical velocity: evaluation = 193
• 5.2.2.5. Comparison of the three components = 195
• 5.2.3. Temperature difference across a mixed layer base = 195
• 5.2.3.1. Theory = 197
• 5.2.3.2. Evaluation: for temporal mixed layer depth term = 204
• 5.2.3.3. Evaluation: for lateral induction and vertical velocity = 205
• 5.2.4. Entrainment heat advection = 214
• 5.2.5. On non-zero annual mean beat storage rate = 217
• 5.2.6. Summary = 219
• Chapter 6. Overall heat balance = 222
• 6.1. Outline = 222
• 6.2. Heat balance mechanism = 223
• 6.2.1. Using contemporaneous data = 223
• 6.2.1.1. On a seasonal scale = 224
• 6.2.1.2. On an interannual time scale = 235
• 6.2.2. Importance of the Kuroshio Extension in heat balance = 238
• 6.2.2.1. Verification of the methodology = 239
• 6.2.2.2. Results = 240
• 6.3. Net surface beat flux error estimate = 249
• 6.3.1. Comparison of net surface heat flux from different methods = 249
• 6.3.2. Direct estimate of errors = 257
• 6.3.3. Discussions of the error estimate = 265
• 6.3.3.1. Can the systematic error be removed? = 265
• 6.3.3.2. Allowance in the error etsimate = 268
• 6.3.9.3. Comparison with previous error estimates = 270
• 6.4. Summary of this chapter and conclusions of the thesis = 275
• Chapter 7. Future work = 278
• Appendix = 286
• References = 297