Observations and Modelling of Fronts and Frontogenesis

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hourly (once every 10-20 km at typical tow speeds), as were surface wind speed and direction (from an anemometer at 34.4 m height), dry and wet bulb air temperatures, and incident solar radiation. 11.3 Observations Sea surface temperature and salinity from ship-board CTD measurements during 16-28 January are displayed with contours of at (density) in Figure 11.2. The data range over 7 °C in temperature (T) and 1 ppt in salinity (S). Though temperature may vary by 1 °C at constant salinity, most of the data approximately obey a single identifiable T-S relation, with the exception of four points with T > 20.5 °C, S . 35.1 ppt, which occurred after the encounter of a strong front at the southern end of Tow 4. Salinity tends to compensate temperature, so the density variations are small, but relative temperature still tends to indicate relative density (warmer, more saline, water is typically less dense). Surface temperature, salinity, and at are displayed versus latitude in Figure 11.3. Scales have been chosen using the equation of state so that a unit distance change in temperature (salinity) at constant salinity (temperature) corresponds approximately to a unit distance change in at. Temperature and salinity tend to decrease toward higher latitudes. The corresponding density gradient is relatively
small, since the large-scale temperature and salinity gradients are density-compensating. Features with smaller horizontal scales also show compensation. A front near 300 N was crossed several times during 19-27 January and appears as a noisy step-like, partially compensated, feature. (Its apparent sharpness is exaggerated by a set of measurements taken during frontal transects at constant latitude.) The large temperature feature near 330 N is roughly 70% compensated by salinity. In contrast, the 2 °C front near 27° N has negligible salinity variation. There appears to be a density feature with roughly 300 km wavelength between 310 N and 34° N. For each of the tows, Figure 11.4 displays traces of 500 m horizontal averages of nominal 15 m (solid line) and 70 m (dashed line) thermistor temperature. These are respectively the shallowest and deepest depths at which thermistor measurements were made during all four tows. The dominant temperature features have horizontal wavelengths of 10 to 100 km, amplitudes of 0.2 to 1.0 °C, and no apparent preferred orientation with respect to the large-scale (climatological) temperature gradient. Satellite imagery of the Subtropical Frontal Zone in January and February 1980 (Van Woert, 1981, 1982), some of which is precisely simultaneous with the tows, shows a sea surface temperature field composed of highly distorted isotherms, such as result from advection of a
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: gravity waves. A maximum of 21 and
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 and 30: dominates the spectrum. At these wa
Page 31 and 32: typically iO-2iO3 °c m1-), and sin
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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