Long-Term and Short-Term Variations of Sea Level in Eastern Canada: A Review

This is a review of sea level data performed at three selected stations (Québec-Lauzon, Harrington Harbour,and Halifax) in eastern Canada in order to investigate the seasonal trends and other long-term and short-term changes which occurred since the beginning of the 20th century. Stations situated in riverine or estuarine regions (e.g., Québec-Lauzon) are significantly affected by freshwater flow in their annual cycle of sea level changes and exhibit a definite maximum in spring and minimum in autumn-winter. Other stations situated in the eastern half of the Gulf of St. Lawrence (e.g., Harrington Harbour) or near the open Atlantic coast (Halifax) mainly follow the general cycle of subarctic regions, with lows in spring-summer and highs in autumn-winter. Such seasonal variations appear to be related to the atmospheric pressure and baroclinic current variations. Secular trends in mean sea level in eastern Canadian waterbodies show a mean rise of about 2.56 mm/yr -1 due to tectonic motions, that is, land subsidence. At several stations in eastern Canada, evidence is found for the influence of the nodal tide (18.6 years), the sunspot cycle (10.8 years), the lunar perigee (8.47 years), the pole tide (14.5 months), the annual cycle (12 months), and semiannual tidal cycle (6 months) in sea level records. Beside long-term oscillations with periods of more than one year, evidence is found for high energetic semidiurnal and diurnal tides where they contribute largely (from 90-95%) to short term variability of sea level. In the residual signal (variations of sea level--tidal variations), short-term variations between 2 to 30 days can be attributed to meterological forcing (atmospheric pressure and winds), longitudinal seiches (2-10 h), atmospheric tides (12 h and 24 h) and inertial oscillations (16-18 h). A regressive model showed that the water discharge from the St. Lawrence River contributes 29% to the monthly residual sea level at Québec-Lauzon. The atmospheric pressure and winds contribute respectively 8.1% and 8.9% at this station. They contribute 52.1% and 7.7% at Harrington Harbour and 41.8% and 14.3% at Halifax. The regression coefficients of residual sea level on atmospheric pressure are respectively estimated to be -1.507 cm. ( hPa ) -1 ( - 0.345 cm. ( hPa ) -1 ), -0.776 cm. ( hPa ) -1 ( - 0.112 cm. ( hPa ) -1 ) and -0.825 cm. ( hPa ) -1 ( - 0.008 cm. ( hPa ) -1 ) at the three stations. Compared to the coefficient of the inverted barometer, estimated to be -1 cm. ( hPa ) -1 , these effects of the atmospheric pressure on sea level variations seem to be amplified at Que´bec-Lauzon by the wind effects (and water discharge) while they are reduced at Harrington Harbour and Halifax.     

Accuracy of tsunami travel‐time charts

Abstract

The tsunami travel‐time charts that are presently in use by the Tsunami Warning Center were constructed originally in 1948 based on the hydrographic data available in the mid 1940s. Even the revised charts of 1971 made use of essentially the same data. It is shown here that the travel times deduced by these charts could be in error by as much as two hours in some cases. Even worse, the compiled travel times as deduced from these charts are generally greater than the observed travel times, which is a dangerous situation from a tsunami warning point of view.     

Variations of the age of tides in the global oceans

Abstract

Earlier studies on the age of tide dealt mostly with the age of the semi‐diurnal tide in the Atlantic and Pacific Oceans. In these studies, the variations of the age of tide were determined making use of recorded tidal data up to and including the 1960s. In the present study, all available tidal data till the mid 1980s are utilized and the computations were done for the four global oceans: Atlantic, Pacific, Indian, and Arctic. Also, in addition to the age of the semi‐diurnal tide, the age of the parallax and the age of the diurnal tide were determined. The distribution patterns for the positive and negative ages for the semi‐diurnal tide, parallax, and diurnal tide were related whenever possible with the tidal amphidromic point locations and the amplitude ratios S₂/M₂, N₂/M₂, and O₁/K₁.     

Influence of delta growth on paleo‐tidal flow: Fraser River delta,British Columbia—Part 2: Tidal model

Abstract

The paleo‐tidal flows in the waters in the vicinity of Point Roberts and the Fraser River delta were numerically simulated through the development of a coarse grid model (2 km mesh size) and a fine grid model (2/3 km mesh size). The basic hydrodynamic equations, the numerical grid layout, and the finite‐difference forms are given. Special attention was given to transferring the boundary grid data generated from coarse grid model to the boundaries of the fine grid model. Diagrams are presented to show that the fine grid model yields much superior results in the sense of providing a greater amount of detail, in the current patterns and the eddy structure, than is provided by the coarse grid model, in the application to estimating sedimentary patterns.     

Hydrodynamic control of microphytoplankton bloom in a coastal sea

The influence of hydrodynamics on phytoplankton bloom occurrence/formation has not been adequately reported. Here, we document diurnal observations in the tropical Bay of Bengal’s mid-western shelf region which reveal microphytoplankton cell density maxima in association with neap tide many times more than what could be accounted for by solar insolation and nutrient levels. When in summer, phytoplankton cells were abundant and the cell density of Guinardia delicatula reached critical value by tide caused zonation, aggregation happened to an intense bloom. Mucilaginous exudates from the alga due to heat and silicate stress likely promoted and stable water column and weak winds left undisturbed, the transient bloom. The phytoplankton aggregates have implication as food resource in the benthic region implying higher fishery potential, in carbon dioxide sequestration (carbon burial) and in efforts towards improving remote sensing algorithms for chlorophyll in the coastal region.     

Ozone Profile Retrieval from Satellite Observation Using High Spectral Resolution Infrared Sounding Instrument

I. IntroductionOzone p1ays a very 1mportant ro1e in globa1 climate change. This is particularly true inthe stratosphere, where ultra--v1olet solar radiation is strongly absorbed by ozone, leading tosubstantlal change in the earths atmospheric thermal, physical and chemical structure. Al-though the troposphere contains only about l0% of the total atmospheric ozone, the varia-tlon of tropospheric ozone may have more significant cllmatic effect than stratospheric ozoneon the earth's surface temP…     

A numerical technique for simulation of cloud seeding experiments

Two numerical cloud seeding experiments, using historic rainfall for the Deccan plateau region in Maharashtra state, were performed adopting different simulation techniques. The data used consisted of 1-day total rainfall for the 5-year period 1951–55. A double-area cross-over design with area randomisation was adopted. The first experiment, EXP-TR, was based on the simulation technique of Twomey and Robertson which involves about 100 hr of Robotron EC-1040 computer time. The second experiment, EXP-MMM was based on a different simulation technique proposed in the present study. The results of EXP-TR and EXP-MMM have shown close agreement. The numerical simulation technique of EXP-MMM is more promising for the following two reasons: (i) the computational time is reduced by about an order of magnitude without compromising the scientific value of the results, and (ii) a direct estimate of the lower limit of the double ratio value which can be detected at 5% level of significance is defined. The results of the two numerical experiments suggested that, for the Deccan plateau region, 15 and 20% increases in rainfall due to seeding could be detected with 80% or more probability in 5 years.     

Mixing heights and ventilation coefficients for urban centres in India

Monthly mean afternoon (maximum) and early morning (minimum) mixing heights have been calculated for the winter, pre-monsoon, monsoon and post-monsoon seasons for eleven stations in India, with the assumption of a dry adiabatic lapse rate in the mixing layer. The morning mixing heights have been calculated by adding +5 °C to the surface minimum temperature except for the monsoon season for which a value of +3 °C has been utilized to account for the urban heat island effect. The spatial variation of mean maximum mixing heights over India has also been studied by isopleth analysis. The morning and afternoon ventilation coefficients have been calculated for the eleven stations under consideration. The spatial distribution of afternoon ventilation coefficients has also been studied. The optimum siting industries to minimize our pollution has been discussed.     

Measurements of cloud droplet size distributions in seeded warm cumulus clouds

Summary Aircraft observations were made on cloud droplet size distribution in 19 cases of seeded warm cumulus clouds in three meteorologically different regions. An examination of the data suggested the following: (i) In all the 5 cases at Bombay (maritime), and in 6 out of the 7 cases at Poona (modified maritime) the values of median volume diameter, maximum cloud droplet size and liquid water content showed increase after seeding as compared to what they were before. The increases noticed in the median volume diameter ranged up to 48% at Bombay and 478% at Poona. The liquid water content and the maximum droplet size respectively increased upward of 56% and 25% at Bombay and 60% and 31% at Poona. (ii) In 4 out of the 7 cloud cases at Rihand (continental), the values of the parameters referred to above showed increase. The median volume diameter increased up to 372%. The liquid water content and the maximum droplet size increased upward of 160% and 66% respectively. (iii) In the cloud cases wherein the values of the parameters decreased after seeding, the decreases noticed ranged up to 94%. (iv) More unstable conditions prevailed on the days when the seeded clouds showed visible rain than on the days when they did not.