Rich Pawlowicz

Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE

A standard part of any oceanic pressure gauge or current meter analysis is the separation of tidal from non-tidal components of the signal. The tidal signal can either be discarded, or its characteristics described in some fashion useful for further analysis. Although tidal signals can be removed by standard high or bandpass filtering techniques, their relatively deterministic character and large amplitude make special techniques more effective. In classical harmonic analysis, the tidal signal is modelled as the sum of a finite set of sinusoids at specific frequencies related to astronomical parameters. A set of programs has been written in MATLAB to (a) perform classical harmonic analysis for periods of about 1 year or shorter, (b) account for (some) unresolved constituents using nodal corrections, and (c) compute confidence intervals for the analyzed components.

The Circulation and Residence Time of the Strait of Georgia using a Simple Mixing-box Approach

Abstract New observations in the Strait of Georgia, British Columbia, Canada show that temperature and dissolved oxygen have a pronounced seasonal cycle, with a spatially varying phase. Phase lags in oscillating systems arise due to internal time scales which can be interpreted in fluid systems as residence times. Exploiting phase we construct a quantitative and internally consistent circulation scheme for this body of water after dividing it into four regions: the Fraser River plume, the surface waters down to 50 m, the intermediate waters down to 200 m, and the deep water. In this scheme the intermediate water, the largest region by volume, is continually renewed, and its characteristics change in response to continuous changes in the characteristics of source waters. The dependence of the estuarine circulation on variations in fresh inflow is weak. The deep water is volumetrically less important, but seasonal changes in the density of oceanic source waters can produce a variation in the overall circulation by driving an additional inflow which leads to both deep renewal and increased upwelling. In turn, this increased upwelling results in lower surface temperatures than might otherwise be expected. Intermediate water residence times are about 160 days. Deep water is renewed once per year in summer and is affected only by vertical diffusion during the rest of the year. Surface water residence times for the entire Strait are a few months at most, but the Fraser River plume has a freshwater residence time of approximately 1 day. In addition, we find that the residence time of oceanic source waters in the Strait is 1.7 years due to a substantial recirculation in Haro Strait. Other consequences of this scheme are consistent with independent estimates of horizontal transports, air‐sea heat fluxes, subsurface oxygen (O2) utilization, and primary production. Finally, analysis of the spatial phase variations suggests that the intermediate inflow enters the Strait as a boundary current along the slopes of the Fraser delta.

Three-Dimensional Observations of a Deep Convective Chimney in the Greenland Sea during Winter 1988/89

Abstract All available temperature data, including moored thermistor, hydrographic, and tomographic measurements, have been combined using least-squares inverse methods to study the evolution of the three-dimensional temperature field in the Greenland Sea during winter 1988/89. The data are adequate to resolve features with spatial scales of about 40 km and larger. A chimney structure reaching depths in excess of 1000 m is observed to the southwest of the gyre center during March 1989. The chimney has a spatial scale of about 50 km, near the limit of the spatial resolution of the data, and a timescale of about 10 days. The chimney structure breaks up and disappears in only 3–6 days. A one-dimensional vertical heat balance adequately describes changes in total heat content in the chimney region from autumn 1988 until the time of chimney breakup, when horizontal advection becomes important. A simple, one-dimensional mixed layer model is surprisingly successful in reproducing autumn to winter bulk temperatur...

Software simplifies air‐sea data estimates

The atmosphere and oceans interact at the ocean surface through boundary layers that are millimeters to many tens of meters thick. Processes at work in this relatively thin region are crucial in controlling the coupling between air and ocean and, as such, are important both in studies of the ocean or atmosphere in isolation, and in studies of the coupled system that investigate—for example—interannual climatic variability However, as a practical matter, attempts to generate flux estimates from particular observational data sets often involve a great deal of effort, since the relevant parameterizations are scattered throughout the literature; may have only limited applicability to certain locations and regimes; and are found using algorithms that are often complex and iterative. This can be especially frustrating when boundary layer theory is only peripheral to the main scientific or educational interest.

Tilting separation flows: a mechanism for intense vertical mixing in the coastal ocean

Observations of a front associated with boundary layer separation from a headland illustrate a mechanism by which horizontal density gradients create intense turbulence and vertical mixing, thus, contributing to water property modification in the coastal zone. Tidal current past an island separates from the coast, creating a shear zone between the primary flow and the slowly moving water in the lee of the island. The density structure on either side of the front may differ due to different origins or degrees of prior mixing. Consequently, there can be horizontal density gradients across the front. Boundary layer separation from the headland begins as a vertical vortex sheet on which instabilities grow to form a sequence of eddies. The presence of horizontal density gradients causes the shear layer to tilt. Tilting and stretching of the sheared flow generates intense circulation. Whirlpools and boils appear at the surface accompanied by vertical motions in which broad areas of upwelling alternate with narrow areas of downwelling. These mix the water throughout its depth; bubbles entrained at the surface reach depths of over 120 m. Such violent mixing weakens stratification associated with the estuarine circulation and aerates water masses passing through the area.

Effects of sea ice cover on acoustic ray travel times, with applications to the Greenland Sea tomography experiment

The travel‐time effects of a sea ice cover on an acoustic pulse are estimated using generalized ray theory. This expands upon the previous work done by Jin and Wadhams [Prog. Oceanogr. 22, 249–275 (1989)] by including the effects of frequency dispersion and different sets of ice parameters. Travel‐time changes due to single reflections are approximated by plane wave reflection theory, and compared to the generalized ray theory results. Statistical effects for multiple reflections, such as the ice thickness probability distribution function, Fresnel zone averaging, and shadowing are considered. Finally, the effects of ice‐induced travel‐time changes on tomographic inversions for water column oceanography are considered. The implications of this work on the 1988–89 Greenland Sea tomography experiment are considered in detail.

Diagnosing vertical mixing in a two-layer exchange flow

Most classification schemes and analyses of estuarine and exchange flows use only salinity as a tracer. Temperatures are generally ignored. However, a proper understanding of the effects of surface heating can explain observed seaward changes in the slope of temperature-salinity correlations. A theory is proposed relating changes in temperature and salinity with transport and mixing parameters in a two-layer exchange flow. Results show that along-channel changes in the slope of T-S correlations are virtually independent of vertical mixing but are directly related to horizontal layer transport. Changes in the layer salinities can be related to various ratios of horizontal and vertical transports. Combining these two features of the theory permits a diagnostic determination of Lagrangian transport and mixing from standard hydrographic observations of layer temperature and salinity and an estimate of the surface heat input. The theory is applied to observations made through the spring/neap tidal cycle of mixing in Haro Strait, British Columbia.

Metrological challenges for measurements of key climatological observables. Part 3: seawater pH

Water dissolves many substances with which it comes into contact, leading to a variety of aqueous solutions ranging from simple and dilute to complex and highly concentrated. Of the multiple chemical species present in these solutions, the hydrogen ion, H+, stands out in importance due to its relevance to a variety of chemical reactions and equilibria that take place in aquatic systems. This importance, and the fact that its presence can be assessed by reliable and inexpensive procedures, are the reasons why pH is perhaps the most measured chemical parameter. In this paper, while examining climatologically relevant ocean pH, we note fundamental problems in the definition of this key observable, and its lack of secure foundation on the International System of Units, the SI. The metrological history of seawater pH is reviewed, difficulties arising from its current definition and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent TEOS-10 seawater standard. It is concluded that the International Bureau of Weights and Measures (BIPM), in cooperation with the International Association for the Properties of Water and Steam (IAPWS), along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems.

Metrological challenges for measurements of key climatological observables Part 2: oceanic salinity

Salinity is a key variable in the modelling and observation of ocean circulation and ocean-atmosphere fluxes of heat and water. In this paper, we examine the climatological relevance of ocean salinity, noting fundamental deficiencies in the definition of this key observable, and its lack of a secure foundation in the International System of Units, the SI. The metrological history of salinity is reviewed, problems with its current definitions and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent seawater standard TEOS-10.

Seismic, satellite, and site observations of internal solitary waves in the NE South China Sea

Internal solitary waves (ISWs) in the NE South China Sea (SCS) are tidally generated at the Luzon Strait. Their propagation, evolution, and dissipation processes involve numerous issues still poorly understood. Here, a novel method of seismic oceanography capable of capturing oceanic finescale structures is used to study ISWs in the slope region of the NE SCS. Near-simultaneous observations of two ISWs were acquired using seismic and satellite imaging, and water column measurements. The vertical and horizontal length scales of the seismic observed ISWs are around 50 m and 1–2 km, respectively. Wave phase speeds calculated from seismic observations, satellite images, and water column data are consistent with each other. Observed waveforms and vertical velocities also correspond well with those estimated using KdV theory. These results suggest that the seismic method, a new option to oceanographers, can be further applied to resolve other important issues related to ISWs.