Several effects of a baroclinic current on the cross‐stream propagation of inertial‐internal waves†

Several effects of a baroclinic current on inertial‐internal waves at constant frequency are investigated, primarily through use of the method of characteristics. The special case of waves propagating transverse to a baroclinic current is considered. When the slope of an isopycnal is of the same order of magnitude as the slope of the characteristics, appreciable asymmetries are induced in the characteristics, the phase and group velocities, and the solution itself. These asymmetric effects are especially significant for waves at the low frequency end of the passband for free waves. Also, modifications occur to the passband, resulting in anomalously high and low frequency bands. The effective local inertial frequency, σ_f = [f(f+v_x )]^1/2, separates the normal and anomalously low frequency bands. Hence, the low frequency limit of the normal frequency band increases or decreases depending upon whether the horizontal shear in the mean flow is cyclonic or anticyclonic. In the anomalous frequency bands, the slopes of both characteristics have the same sign, causing various refraction and reflection phenomena. If the absolute value of the slope, s, of an isopycnal exceeds its critical value, s_c = effective local inertial frequency/Väisälä‐Brunt frequency, the anomalously low frequency band extends to imaginary frequencies. If s ? 0, the reflection of waves from a boundary is modified, the effective wavelength is increased, and the lines of constant phase are tilted from the vertical. For the general solution, discontinuities in the first‐order partial derivatives of the velocity field occur across certain characteristics. The nonseparable normal modes do not exhibit these discontinuous derivatives, but they only satisfy one of the two pairs of kinematic boundary conditions in rectangular regions.     

Contribution Of Spray Irrigation Of Wastewater To Groundwater Contamination In The Karst Of Southeastern Minnesota,USA

A vegetable- and meat-canning facility located in the karst of southeastern Minnesota disposes ≈2.85×10⁵ m³ yr^?1 of wastewater by spray irrigation of an 83.7-ha field located atop the local groundwater divide. Cannery effluent contains high levels of chloride and nitrogen (organic and ammonia), in excess of 7000 mg/l and 400 mg/l, respectively. Nitrate-nitrogen concentrations are generally < 5 mg/l. Agricultural, domestic, and municipal sources of chloride and nitrate are common in the region, and water supplies frequently exceed the drinking-water limit for nitrate-nitrogen of 10 mg/l. Fifty-two area wells and thirteen surface-water locations were sampled and analyzed for five ionic species, including: chloride (Cl), nitrate-nitrogen (NO₃-N), sulfate (SO₄), nitrite-nitrogen (NO₂-N), and phosphate (PO₄). Two distinct chloride plumes flowing outward from the groundwater divide were identified, and 65% of the wells sampled had nitrate-nitrogen concentrations in excess of 10 mg/l. The data were divided into two groups: one group of samples from wells located near the canning facility and another group from outside that area. A correlation coefficient of R²= 0.004 for Cl vs. NO₃-N in the vicinity of the irrigation fields indicates essentially no relationship between the source of Cl and NO₃. In areas of agricultural and domestic activities located away from the cannery, an R² of 0.54 suggests that Cl and NO₃ have common sources in these areas.     

Three-dimensional perspectives of the Florida current: transport, potential vorticity, and related dynamical properties

The Florida Current flows through the Straits of Florida, which starts as a zonal channel and turns to become a meridional channel. The spatial structure of the Florida Current and its transport, potential vorticity, and related dynamical properties are investigated using a three-dimensional, baroclinic, primitive equation model with a mesoscale-admitting (5.6 km) horizontal resolution and 25 vertical (sigma: terrain-following) levels. At 83°W, the Florida Current fills only a portion of the channel; however, due to the interaction with the shoaling bottom topography (from a maximum depth of over 2000 m at 83°W to less than 800 m at 27°N) and the narrowing Straits of Florida (from a maximum width of about 170 km at 83°W to about 110 km at 27°N), the Florida Current fills the entire channel at 27°N, and the potential vorticity distribution is altered. The specified transport of 28.6 Sverdrup (1 Sv = 10⁶ m³ s⁻¹) from the Loop Current at the western boundary and the inflow from the Old Bahama Channel of 1.9 Sv converge into the meridional channel. With an additional inflow of 1.2 Sv from the Northwest Providence Channel, the simulated total transport of 31.8 Sv at 27°N is comparable to the STACS (Subtropical Atlantic Climate Studies) mean transport of 31.7 Sv. Both vertically and laterally integrated subsectional transports are examined at transects 83°W, 82°W, 81°W, 25°N, 26°N, and 27°N. The potential vorticity increases (decreases) on the cyclonic (anticyclonic) side of the Florida Current at 27°N compared to 83°W. The downstream variation of static stability, relative vorticity, and Froude number is also examined. While the vertical shear is strong only on the northern side at 83°W it is comparable on the both western and eastern sides downstream at 27°N, reaching to the bottom of the meridional channel. Large values of the Froude number exist only in the upper 300 m of the zonal channel, but they reach to the bottom of the meridional channel.     

Numerical simulations of mesoscale variability in the Straits of Florida

The circulation in the Straits of Florida is dominated by the throughflow of the Florida Current, as modified by tidal flows, responses to atmospheric cold front and extratropical cyclone (easterly wave and tropical cyclone) passages in winter (summer), and intrinsic mesoscale variability due to instabilities of the Florida Current front and jet system. Monthly meanders of the Florida Current, persistent oceanic fronts associated with the Florida Current’s baroclinic jet, and frontal eddies shed weekly by the Florida Current are the primary mesoscale features. A limited area model (Princeton Ocean Model: POM) is implemented to cover the Straits of Florida with a curvilinear grid that resolves the mesoscale structure, especially where the baroclinic flow is locked to steep topography in a 90 degree bend of the Straits. Florida Current cyclonic frontal eddies are spawned spontaneously, grow as they translate downstream, interact with shelf waters, and exhibit the same space-time attributes that characterize their observed counterparts, as evidenced by satellite imagery, shipboard synoptic mapping, coastal HF radar, and moored time series. Here, a deeper understanding is attempted for the frontal eddy kinematics and dynamics by examining, for example, their sensitivity to model parameter values, synoptic versus monthly atmospheric forcing, and other determinants of the flow. The mean flow shears are concentrated along the shelfbreak, where these frontal eddies are trapped, favoring the formation of the eddies by mean flow instabilities. In particular, it is found that the Florida Current frontal eddies exist independent of the wind-forcing considered (i.e., no winds, monthly winds, and synoptic (but not mesoscale) winds); however, they are modulated by the synoptic wind-forcing. Nevertheless, intriguingly, the frontal eddies have the same weekly time scale as the weather cycle.     

Review: “Jacob’s Zoo”—how using Jacob’s method for aquifer testing leads to more intuitive understanding of aquifer characteristics

The interpretation of aquifer responses to pumping tests is an important tool for assessing aquifer geometry and properties, which are critical in the assessment of water resources or in environmental remediation. However, the responses of aquifers, measured by time-drawdown relationships in monitoring wells, are nonunique solutions that are affected by many factors. Jacob’s Zoo is a collection of graphical interpretations that allows students and practitioners to develop an intuitive feel for how natural hydrogeological systems work, and develop a set of skills that provide a better understanding of aquifer properties far beyond interpretation of pumping tests. Jacob’s Zoo, based on the work of Jacob (1950), fosters a deeper understanding, although few practitioners realize the full utility of the method. Jacob CE (1950) Flow of groundwater, In: Rouse H (ed) Engineering Hydraulics, Wiley, New York. P 321–386.

     

Performance of a nowcast/forecast system for Prince William Sound,Alaska

A coastal ocean extended Prince William Sound nowcast/forecast system (EPWS/NFS) has been running semi-automatically for an extended domain of Prince William Sound (PWS), Alaska for 2 years. To determine the performance of this modeling system, an assessment is conducted. EPWS/NFS and PWS/NFS (viz., its predecessor) nowcasts are compared with observed time series of sea surface temperature (SST) and coastal sea level (CSL) at a few stations, and to velocity profiles from a moored ADCP. With the extension of the model domain to include the continental shelf outside PWS and forced by an operational global ocean model (Global-Navy Coastal Ocean Model (Global-NCOM)) and a 2D tidal model at the open boundary, EPWS/NFS has achieved significant improvement over PWS/NFS, which covered only PWS per se, for most of the predicted variables in this study. In both magnitude and phase, EPWS/NFS accurately predicts the coastal tide fluctuations, as well as M2 tidal currents in Central Sound, although significant errors in coastal tides exist during some spring and neap tide cycles. Other than for the tidal motions, EPWS/NFS generally produces less energetic CSL and velocity variations than those observed. In comparison, although PWS/NFS well predicts the coastal tides, it suffers from the absence of low-frequency CSL variations, as well as misprediction of M2 tidal currents in Central Sound. For 40 h low-passed PWS/NFS and EPWS/NFS velocities, significant phase error occurs during the model–date comparison period, while EPWS/NFS nowcasts generally produce less root-mean-square-error (rmse) and smaller correlations with the observations than PWS/NFS does. Both observations and EPWS/NFS have similar vertical profiles of baroclinic velocity standard deviations, but some substantial discrepancies occur in the velocity direction. Also, in the Central Sound, EPWS/NFS predicts well the SST seasonal cycle and a major cooling event during the summer 2005. However, for periods shorter than 1 week, both PWS/NFS and EPWS/NFS SST underestimated the observed fluctuations by an order of magnitude.     

Exchange processes over a Middle Atlantic bight shelfbreak canyon

A synoptic oceanographic study was conducted in August 1978 at the Middle Atlantic shelfbreak along the shelf-slope front and over the Wilmington Canyon. Four masses (surface, cold pool, shelf, and slope waters) were identified from nutrients and hydrographic variables. Also identified were two pycnocline mixing regimes; one between cold pool and slope waters across the inverted thermocline at the bottom of the cold bool protruding off the shelf, and the other directly across the summer thermocline between slope and shelf waters seaward of the cold pool. These two distinct mixing regimes appear to provide some of the common means for water exchange across the shelf-slope front. The associated mixing may be promoted by the circulation and mixing anomalies induced over canyon topographies. Physical data suggested a cyclonic flow pattern over the Wilmington Canyon, with warm slope water moving up its axis and cold pool water moving off its southwest flank. The above water masses were best identified chemically on the basis of oxygen saturation due to the high apparent photosynthesis at the shelf-slope front. This high primary productivity at the front seems linked to the cold pool and its nutrient supplies.     

Report on INSMAP'90: The second international symposium on Marine Positioning

Abstract

INSMAP'90, the second in a series of quadrennial international symposia on marine positioning, was held October 15–19, 1990. INSMAP is organized by the Marine Geodesy Committee of the Marine Technology Society (MTS) with the co‐sponsorship of over 25 organizations of the United States and other countries, including the University of Miami's Rosenstiel School of Marine and Atmospheric Science, which hosted the meeting. INSMAP'90 focused attention on special problems associated with positioning in the marine environment, providing a timely forum and opportunity for in‐depth discussions and exchange of ideas, identified immediate and future requirements and applications, and enhanced interdisciplinary and interagency collaboration. Over 100 scientists and students attended; countries represented included Australia, Canada, China, Egypt, France, Germany, Great Britain, Indonesia, Italy, Japan, Monaco, New Zealand, Norway, Portugal, Sweden, the United States, and Venezuela. During the week, more than 60 papers were presented, there were five symposium‐wide lectures, five workshops (each with several lectures), and a tour of the U.S. Naval Observatory Alternate Time Service and VLBI/GPS facility, where all the exhibitors set up their demonstrations. Most of the papers and addresses are available in a single hard‐bound volume from the MTS.     

Several effects of baroclinic currents on the three‐dimensional propagation of inertial‐internal waves†

A ray theory is applied to the problem of three‐dimensional propagation of inertial‐internal waves in the presence of a mean baroclinic current which does not vary in the downstream coordinate. As time increases, the Doppler‐shifted wave frequency, or intrinsic frequency, tends to a limiting value determined by the horizontal and vertical variations of the mean current and density fields. The limiting value of the intrinsic frequency determines critical surfaces where energy is transferred to the mean motion. Also, the group velocity tends to the mean current velocity, and the phase velocity tends to be oriented towards or away from the core of the mean current, depending upon whether the wave is either initially propagating with a wave number component antiparallel or parallel to the mean current.     

Holocene landscape evolution and the development of models for human interaction with the environment: An example from the mississippi headwaters region

Integration of a record of Holocene landscape evolution with the cultural record from a multicomponent archaeological site in northern Minnesota has fostered the development of a regional model of human interaction with the changing physical environment. Excavation of 21-CA-169 near Nushka Lake revealed two components, an aceramic Archaic zone where processing of large mammals was the major activity and an upper zone with artifacts suggestive of wild rice processing. Seasonal occupation of the lower zone occurred during a period of falling regional lake levels resulting from natural stream network evolution. The upper zone represents human occupation in a physical and biological setting that was quite different than during earlier occupation. Integration of the geomorphic history of the region along with an interpretation of the types of cultural activities occurring on the changing landscape have provided a model to understand land use and to predict the location of other sites. © 1993 John Wiley & Sons, Inc.