International Field Year For The Great Lakes Research Articles

Modelling the circulation and exchange of Kingston Basin and Lake Ontario with FVCOM

An unstructured grid, finite-volume, 3-dimensional primitive equation, sigma-coordinate terrain following ocean model (FVCOM) has been applied to Lake Ontario to investigate its monthly climatological circulation with a focus on Kingston Basin. Kingston Basin, in the northeastern end of Lake Ontario, sits between the main body of the lake and the outflowing St. Lawrence River and is adjacent to the Bay of Quinte Area of Concern designated by the International Joint Commission. The focus of this study is to use the unstructured model FVCOM to model the mean circulation in the Basin. Results showed that the FVCOM model can take up to 3 years to spin-up from rest for a wind-forced, almost fully enclosed lake model. The model accurately reproduced the current flow field within the main body of the lake and compared favourably to the flow field observed during the International Field Year for the Great Lakes (IFYGL) in Kingston Basin. Transport streamfunction results show that the structure of the flow into Kingston Basin from the main body of the lake changes throughout the year.

A Model for Entrainment into a Cloud-Topped Marine Boundary Layer. Part I: Model Description and Application to a Cold-Air Outbreak Episode

Abstract A model is presented for the growth and evolution of a cloud-topped marine boundary layer. In this model the entrainment rate is determined from the turbulence kinetic energy (TKE) budget. It is assumed that the TKE budget can be partitioned according to whether each process produces TKE or converts it into potential energy, and that dissipation is proportional to production. This leads to an entrainment relationship which is considerably different than used in previous cloud-topped models. This model is used to study an episode of cold-air outbreak over Lake Ontario during the International Field Year for the Great Lakes (IFYGL). The model reproduces changes in potential temperature and dew point as the air crossed the lake and the associated time variation of these parameters at the down-wind shore with an accuracy of better than 1°C. Model and measured soundings closely match, especially with respect to the presence and location of such features as cloud layers. Depth of the mixed layer also w...

A Model for Entrainment into a Cloud-Topped Marine Boundary Layer. Pad II: Discussion of Model Behavior and Comparison with Other Models

Abstract The model for the cloud-topped marine boundary layer presented by Stage and Businger (1981) is discussed and compared with previous models. Our model gives a considerably different interpretation of the energetics of the layer and indicates that a much higher fraction (20%) of the layer turbulence kinetic energy production is available to drive entrainment than previously supposed. In a test case, the Lilly (1968) minimum entrainment model gives entrainment rates similar to ours; however, this model is based on physically unrealistic assumptions about layer energetics. It is noted that two soundings from the International Field Year for the Great Lakes (IFYGL) exhibit behavior not allowed by Deardorff’s (1976) model. In these cases our model gives a good fit to the data and Deardorff’s model predicted a boundary layer much deeper than observed. The depth of the layer of radiative cooling at cloud top is shown to be important only if it is a significant fraction of the mixed-layer depth zB. Layer ...

An ecological model of Lake Ontario

An ecological model of the epilimnion, hypolimnion and sediment of Lake Ontario is described. The model is based on realistic process equations posed by experimentalists over the past several decades and it simulates observations made of several phytoplankton and zooplankton groups; components of the phosphorus, nitrogen, silicon and carbon cycles; dissolved oxygen; and particulate sediment and pore water dynamics during the International Field Year for the Great Lakes (IFYGL). Model output is aggregated into a carbon flow diagram to illustrate the importance of detritus and herbivorous zooplankton in the ecology of Lake Ontario. The model serves as a synthesis tool for analysis of the large ecosystem.

Low‐frequency current fluctuations in Lake Ontario, winter 1972–1973 (IFYGL)

An analysis is presented of the low‐frequency (ω ≲ 0.6 cycles per day) current fluctuations in Lake Ontario, using measurements made at 15 and 75 m during the 1972–1973 winter. The data, collected as part of the International Field Year for the Great Lakes (IFYGL), were obtained at nine stations: one near midlake and the other eight spaced around the lake, about 50 km apart and 12 km from shore. Let U denote the alongshore velocity (positive leaving the shore to the right) and V the cross‐shore velocity (positive offshore). It is found that (1) the standard deviation of V is approximately constant; (2) the standard deviation of U, which is about 2.4 times greater than that of V, may be depth independent and is less at the southern shore stations than at the shallower northern stations where the flow appears to be directly wind driven; (3) the velocity fluctuations are roughly aligned with the local orientation of the coastline; (4) the U fluctuations show much better mutual correlation than the V fluctuations, having an alongshore coherence length of about 250 km (nearly half the basin perimeter); (5) the U signal shows high coherence for periods of about 10–25 and 4–5 days; and (6) the computation of lagged correlations shows the U fluctuations to propagate in a counterclockwise sense from the northern shore at a rate of about 42 km d−1 (0.5 m s−1), which implies a period of about 13 days for a complete circuit around the lake. These results provide additional evidence for the existence of topographic Rossby waves (shelf waves) in Lake Ontario, the calculated period being consistent with results of previous studies which used data from the summer and fall of 1972.

Inertial Current in Lake Ontario, Winter 1972–73 (IFYGL)

Abstract Nearly four months of continuous current and temperature data, taking during the 1972–73 winter depths of about 15 and 75 m in Lake Ontario, have been analyzed for evidence of inertial oscillations. The data, collected as part of the International Field Year for the Great Lakes (IFYGL), were obtained at nine stations: one near midlake, about 40 km from shore, and in about 140 m of water; the other eight spaced around the lake, about 50 km apart, 12 km from shore and in 100 m of water. Inertial currents occurred in episodes lasting less than 5 days and had speeds less than 15 cm s−1. At the midlake and easternmost stations, the inertial currents accounted for as much as 10% (on average) of the total current variance. Some inertial events in midlake had no counterpart nearer shore. In contrast, a lakewide episode of inertial currents was induced by a storm during a two to three week period of vertical stratification. The average hodographs during the stratified period, calculated from bandpassed sh...

A model for computing small-scale wind variations over a water surface

Based on the primitive equations, a one-level model is described for computing surface winds under the meso-scale influences of orography, friction and heating. The effects of atmospheric stability and land-water contrasts are examined in detail. Results of testing the model with data collected during the International Field Year for the Great Lakes (IFYGL) in 1972 are given. The model is able to simulate land and lake breezes as well as meso-scale effects due to gradients in surface water temperature. Compared to simple methods of computing surface winds, use of the model reduces the vector error in estimates of surface winds by about 1.25 m s−1 on the average.

Analysis of Vorticity and Divergence Fields and Other Meteorological Parameters over Lake Ontario during IFYGL

Abstract Surface wind data obtained from the United States and Canadian International Field Year for the Great Lakes (IFYGL) buoy network are used to estimate the vorticity and divergence feeds over Like Ontario. Hourly values of these variables are computed for the period May–October 1972. Lakewide temperature,, relative humidity and wind speed for the same period of time are also analyzed for their spectral characteristics. Distinct land-lake breeze circulations are observed on calm days in summer, when the flow is divergent and anticyclonic during the day and convergent and cyclonic at night. The six-month averaged daily values show similar but weaker diurnal variations. The changes from land-to-lake and lake-to-land breeze occur at about 0800 and 1800 local time, respectively. The six-month average of the divergent field is zero and that of the vorticity field is cyclonic with a value of 3.5×10−6 s−1. Spectral characteristics are also investigated by analyzing the six-month time series. In addition to...

Intermittent ‘full’ upwelling in Lake Ontario

A strong enough longshore impulse leaving the coast to the left (looking downwind) generates ‘Full’ upwelling in which the thermocline comes to intersect the free surface. This problem is beyond the scope of linearized (small displacement) theory, but it may be treated as a simple geostrophic adjustment problem in which the wind stress is supposed to be exerted impulsively on a two-layer fluid. A minimum impulse is found to be necessary for a full upwelling to develop from hydrostatic equilibrium, the magnitude of which is close to the product of top layer depth and propagation velocity of long waves on the thermocline. When the upwelling-favoring wind impulse is greater than the minimum, the upwelled front moves offshore by a distance proportional directly to the extra impulse (above the minimum) and inversely to top layer depth times Coriolis parameter. Upwelling episodes observed in Lake Ontario during the International Field Year for the Great Lakes (IFYGL) and feasibility studies before IFYGL show a frontal behavior in good quantitative agreement with the simple theoretical model. The offshore component of the impulsively exerted wind leaves the position of the front unaffected. However, a sustained offshore wind increases somewhat the offshore displacement due to a prior longshore impulse. The effect is relatively weak, and an offshore wind alone rarely produces full upwelling. A sustained longshore wind acting on an already upwelled thermocline generates considerable negative potential vorticity. Adjustment following such a ‘second’ longshore impulse produces a more complex thermocline shape and under certain conditions a frontal countercurrent. In a closed basin, full upwelling following a wind stress impulse occurs over only a portion of the shoreline. Given quiescent conditions, the upwelled front may be expected to propagate alongshore, somewhat as an internal Kelvin wave. Observations in October 1972 in Lake Ontario show frontal motions resembling internal Kelvin waves. However, only one half of the wave propagates, that half in which particle velocities have the same direction as the wave propagation velocity. Furthermore, the propagating warm zone is much narrower than the cold upwelled zone which developed under a succession of previous wind impulses.

An IFYGL Carbon Budget for Lake Ontario

A carbon budget was produced for each month of the International Field Year for the Great Lakes (IFYGL) year (April 1972 to March 1973) to determine the importance of the various sources and sinks of carbon. Major sources were found to be CO 2 which was fixed in organic matter during primary production and inorganic carbon in tributary streams, especially the Niagara River. The major sinks were found to be inorganic carbon outflow at the St. Lawrence River and net CO 2 gas exchange between the inorganic carbon pool and the atmosphere. Inflow and outflow of organic matter in rivers, sedimentation of organic and inorganic matter, ground water transport, and municipal and industrial perturbations accounted in total for less than 10% of the annual budget. The lake had an inventory of approximately 4.0 × 10 10 kg of inorganic carbon and approximately an order of magnitude less organic carbon. The riverborne flux of inorganic carbon of 0.5 × 10 10 was 13% of the lake's inventory, assuming complete mixing; a minimum mean residence time of 8 years can be calculated from that inventory. The seasonal cycle inherent in the fixation of carbon in primary production was primarily balanced by a complementary seasonal cycle in the air-lake CO 2 gas exchange system. The lake acts as a sink for CO 2 gas in the warm months when primary productivity is highest and as a source of CO 2 in the colder part of the year. The IFYGL year had higher than normal rates of water flow, but this does not appear to have perturbed the inorganic carbon system. A comparison of IFYGL carbon budget results with corresponding estimates calculated for a typical year from historical data shows no major differences.

IFYGL Shipboard Visual Wave Observations vs. Wave Measurements

Data used for this study were collected in Lake Ontario during 1972, the International Field Year for the Great Lakes (IFYGL). Shipboard meteorological observations, which include visual estimates of wave height and wave period, are made in the Great Lakes by over 100 ships from the United States and Canada. Data collected from these ship reports cover a wide range of lake conditions and hence provide a useful basis for climatological studies of surface waves in the Great Lakes. The objective of this paper is to present an assessment of the reliability of these ship reports. Records from deep water wave gauges were compared with shipboard observations made within 50 km of the gauges. The results show that visually estimated wave heights, H vo, and wave periods T vo, are correlated with the recorded significant wave heights, H s, and average zero-crossing wave periods, T z, respectively by H s = (0.25 + 0.6 H vo) meters and T z = (2.0 + 0.2 T vo) seconds. Visual observations appear to substantially underestimate the steepness of the waves. Long-term distributions for wave heights and wave periods follow the log-normal distribution quite closely. These results are generally similar to those of oceanic studies.

Distribution of Macrobenthic Species in Lake Ontario in Relation to Sources of Pollution and Sediment Parameters

Bottom samples were collected in Lake Ontario during the International Field Year for the Great Lakes (IFYGL) in November 1972. Samples were collected in triplicate at 55 stations located throughout the lake. Sand prevailed at the shallow areas but silt dominated the intermediate and deep-water areas. Total carbon and total Kjeldahl nitrogen content of the sediment increased with increased depth, but no trend was evident in the total phosphorus content. Oligochaetes and the amphipod Pontoporeia affinis accounted for 92% of all organisms collected. The former group dominated the shallow areas while the latter dominated the intermediate and deep-water zones. Stylodrilus heringianus and Limnodrilus hoffmeisteri were the most widely distributed species, being collected at 51 of the 55 stations. Several approaches were used to evaluate trophic conditions in the lake - the indicator species approach, the oligochaete-density index, a modified “Goodnight-Whitley” index, and the Brinkhurst % L. hoffmeisteri index. The indicator species approach proved to be the most sensitive index because inconsistencies arose when the other indices were applied. The most obviously eutrophic areas were near the mouth of the Niagara River and off Toronto. These areas were characterized by high oligochaete densities dominated by either L. hoffmeisteri or T. tubifex. Mesotrophic conditions were evident along the southern shoreline from the mouth of the Niagara River to Rochester, New York. Stylodrilus heringianus, L. hoffmeisteri, T. tubifex, and P. affinis were significantly related to some of the measured sediment parameters in either the intermediate or deep-water areas.

IFYGL radar network to measure Ontario watershed rainfall

Rainfall over Lake Ontario and its basin will be measured more accurately than ever before by a special radar system which, together with a back‐up rain‐gage network, is now in full operation for the International Field Year for the Great Lakes (IFYGL).U.S. radars located at Buffalo and Oswego, New York, will be tied in with a Canadian radar near Toronto (Woodbridge, Ontario) to cover the entire lake watershed. The Buffalo radar is operated by the National Weather Service of NOAA and has been specially instrumented to undertake this project. At the other end of the lake, a new radar has been erected about eight miles south of Oswego, and is operated by State University of New York at Oswego under contract to NOAA.

IFYGL

The Third Workshop on the International Field Year for the Great Lakes (IFYGL), was held at the U.S. National Academy of Sciences, Washington, D.C., from January 18–21, 1972.The purpose of the Washington Workshop was twofold: (1) to assess the status of projects and scheduling in IFYGL and to evaluate the significance of any apparent problems in the program; and (2) to update and validate the 1972 Technical Plan for the data collection phase of the Field Year.