Observations and Modelling of Fronts and Frontogenesis

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qualitative nature of the records noted in Section 11.3 (e.g., the single large feature in Tow 1 versus the myriad smaller features in Tows 2a, 2b). Each spectrum has a broad peak or plateau at low wavenumber, a break in slope near 10 km, and is approximately proportional to k1- between 10 km and 1 km. A minimum occurs between 1 km and 350 m wavelengths in three of the five spectra. A secondary peak appears near 350 m in these three spectra, followed by a decrease toward the Nyquist wavelength (200 m). The spectra appear to fall off slightly toward wavelengths larger than 50 km. In this region however the number of data points is small and the 95% confidence intervals large. The spectrum from Tow 3b is not shown. At the 95% confidence level, it is essentially indistinguishable from the Tow 3a spectrum. Because of the close time and space scales, we interpret this as a lack of independence between the two spectral estimates from Tow 3, and have only included the estimate from Tow 3a in the ensemble average. Figure 11.10 displays ensemble averaged horizontal wavenumber spectra of 15 m and 70 m temperature, band averaged to 5 bands per decade. We interpret the difference between the spectral levels at 15 m and 70 m in the bands above 0.1 cpkm as internal wave vertical displacements at 70 m. Since the average vertical temperature gradients are small at 15 m (less than l0 0C ma-; at 70 m they are 18
typically iO-2iO3 °c m1-), and since the vertical internal wave velocities must vanish at the surface, temperature variance from internal wave isotherm displacements will be small at 15 m. If the 70 m spectrum is composed of the sum of an internal wave vertical displacement spectrum that is uncorrelated with the 15 m spectrum and a spectrum (due to other processes) equal in variance to the 15 m spectrum at each wavenumber, the 70 m internal wave spectrum will be the difference of the power spectra at 70 m and 15 m. (Differencing the series leads to an overestimate of the internal wave variance, as incoherent parts not due to internal waves will contribute to the power spectrum of the differenced series.) Using average vertical temperature gradients at 70 m from entire tow means of surrounding thermistors to estimate displacements and the local buoyancy frequency, we obtain for Tows 2 and 4 the internal wave energy spectral estimates shown in Figure 11.11. The empirical Garrett-Munk prediction (Eq. Al2, Katz and Briscoe, 1979; Garrett and Munk, 1972), with Desaubies (1976) parameters r 320 m2 h1- and t = 4 x l0 cph cpm-, is plotted for comparison. The spectral levels are mostly within 2 to 3 times the predicted values, and the spectral slopes show excellent agreement. A large temperature inversion and small vertical gradients prevented reliable calculations for Tows 1 and 3. Even in Tows 2 and 4, average 19
Page 1 and 2: AN ABSTRACT OF THE THESIS OF Roger
Page 3 and 4: Observations and Modelling of Front
Page 5 and 6: To my parents, Hans and Nancy Samel
Page 7 and 8: This research was supported by ONR
Page 9 and 10: TABLE OF CONTENTS I. INTRODUCTION 1
Page 11 and 12: Figure LIST OF FIGURES (continued)
Page 13 and 14: OBSERVATIONS AND MODELLING OF FRONT
Page 15 and 16: II. TOWED THERMISTOR CHAIN OBSERVAT
Page 17 and 18: oriented multiple surface fronts up
Page 19 and 20: gravity waves. A maximum of 21 and
Page 21 and 22: small, since the large-scale temper
Page 23 and 24: front at about 18.5 °C. There is f
Page 25 and 26: given in the stable cases (downward
Page 27 and 28: temperatures for January and Februa
Page 29: dominates the spectrum. At these wa
Page 33 and 34: 11.5 Geostrophic turbulence We have
Page 35 and 36: energy of each of the longitudinal
Page 37 and 38: varying N and a flow isolated from
Page 39 and 40: adiabatic meridional displacements
Page 41 and 42: z0 34 32 V v 30 a -J 28 26 a) - 2b$
Page 43 and 44: U0 V L 0 L V 20 E 16 V 12 p ; t *,
Page 45 and 46: 30 E 50 -c a- I, 0 70 90 300 360 37
Page 47 and 48: 10 10° 10-2 1 0 -3.0 -2.0 -1.0 0.0
Page 49 and 50: 1 o 1 102 101 - 0 LU 00 x I.- - -1
Page 51 and 52: E (I) a. z 106 1 o5 102 101 100 1O
Page 53 and 54: Table 11.1 Tow start and finish pos
Page 55 and 56: Table 11.3 Climatological sea surfa
Page 57 and 58: Paulson, C. A., R. J. Baumann, L. M
Page 59 and 60: 111.1 Introduction In this chapter
Page 61 and 62: interior layers, on the horizontal
Page 63 and 64: polynomials in z.) The vertical mom
Page 65 and 66: hit + (hivi) = We, (8a) h2t + (h2v2
Page 67 and 68: Equations (la) and (2a) are dynamic
Page 69 and 70: subdivided into subdomains with dif
Page 71 and 72: mixed layer. As is the case with (2
Page 73 and 74: constant pressure c = 4.1x103 J K1-
Page 75 and 76: When (28) have been solved for the
Page 77 and 78: occur with the initial conditions w
Page 79 and 80: analytically. Let Al2 and A23 be th
Page 81 and 82:
Shortly after t = 8.1, the mixed la
Page 83 and 84:
that around the offshore front, exc
Page 85 and 86:
the reduced equations numerically.
Page 87 and 88:
(1) The upwelled horizontal profile
Page 89 and 90:
Figure 111.1 Model geometry. zO z z
Page 91 and 92:
* j 0. -20. >\ - -40. 0 > .0 0. 40.
Page 93 and 94:
4) 20. 10. 0. 20. 1 0. 0. 0 y/X 0.
Page 95 and 96:
BIBLIOGRAPHY Batchelor, G. K. , 195
Page 97 and 98:
Rhines, P. B., 1979: Geostrophic Tu
Page 99 and 100:
APPENDIX A: DYNAMICAL DERIVATION OF
Page 101 and 102:
In a manner exactly analogous to th
Page 103 and 104:
smoothness. The large vorticities t
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