Calm Zone Research Articles

The Sea-Breeze-Induced Coastal Calm Zone as Revealed by Satellite Data and Simulated by a Numerical Model

Abstract Meteorological satellite scanning radiometer data from a visual sensor during daylight hours are characteristically influenced by sunglint from the ocean surface as the sensor scans in the direction toward the sun (between the satellite subpoint and solar subpoint). When seas are calm in the region near the primary specular point (PSP), the sun's rays are either reflected directly into the spacecraft sensor yielding a high energy (bright) response, or away from the sensor yielding a low energy (dark) response. The particular effect depends on the proximity of the calm area to the PSP. This paper shows examples of bright and dark linear patterns adjacent to and tending to parallel coastlines. The patterns are interpreted to be sea-breeze-induced calm zones originating during periods of offshore flow when the pressure gradient causing the sea breeze is exactly counterbalanced by the larger-wale synoptic gradient. A two-dimensional planetary boundary layer (PBL) numerical model successfully simulate...

Velocity profile in "calming zone" of falling liquid films on inclined plates.

Falling liquid films on inclined plates have been experimentally studied with special attention to the "calming zone", where the surface is mirror-like in the range of Re from 2500 to 6000. Velocity profile by the hydrogen bubble method and film thickness by the pointer and gauge method were measured, and the film surface behavior was observed by laser beam reflection. Film flow in the calming zone is laminar with air drag at the air-liquid interface.

Thickness of liquid falling films in "calming zone" on inclined plates.

Thickness of liquid falling films in "calming zone" on inclined plates.

Atlantic Winds and Ocean Currents in Portuguese Nautical Documents of the Sixteenth Century

SynopsisThe idea that only after 1490 the European sailors had ‘come for the first time in recorded history to struggle with the limitations placed on sailing ships by the winds and currents of the open ocean’ does not correspond to reality. There is enough proof to show that much earlier, in the fifteenth century, the North-East Trades’ regularity, the wind variability in the zone directly north of them, and the Canaries Current were already known. When the fifteenth century ended, the Portuguese had already verified the symmetry of wind patterns in the Atlantic on both sides of the equatorial calm zone, which led them to apply the significant name of ‘ventos gerais’ to the trade winds of both hemispheres.Accurate knowledge of the wind and current systems was essential to good navigation and the Portuguese ratters of the sixteenth century, chiefly ‘carreira da India’ rutters, include an increasing amount of information on that subject, referring especially to zones in the passage from the North Atlantic to the South Atlantic. The report of a voyage (1503) proves that at that time the Portuguese already knew the Gulf of Guinea winds and currents sufficiently well. As a result of oceanic sailing, the traditional ratters, exclusively coastal, developed considerably, not only by adding data about latitudes and compass variations but also by the indication of winds and currents. There appeared also an even newer type of ratter, the ‘oceanic rutter‘, in which the safest and quickest routes, because of the changeability of winds and current patterns, are indicated.Information about elements concerning winds and currents which are included in the Portuguese ratters was revealed in printed matter after the end of the sixteenth century and this allowed some European scientists to study, because of the availability of better information, the causes of those physical phenomena, which had already been treated briefly in the sixteenth century by two nautical treatise writers, D. João de Castro and Father Fernando Oliveira.

Some Aspects on the Distribution of the Surface Winds within a Small Area

Intensive observations of the distribution of the surface winds in the city area of Tokyo were made four times a week from September, 1943 to August, 1945. Using these Data, wind characteristics were studied from a microclimatological viewpoint and the results were summarized as follows; (1) The greater the prevailing wind velocity, the smaller the deviation of the surface wind direction at each station from the avereage direction within an area. (2) In the condition of high wind velocity more than 5 m/s, the differences of the wind direction distribution between inland, coastal, upland, and lowland area in Tokyo were not significant statistically. (3) When the prevailing wind velocity was weak, the distribution of the stations having deviated wind direction showed some localization. Especially this was obvious in the coastal area. (4) Convergence zone or conflict zone of two winds flowing in right angle was shown as a calm zone because of relatively low velocity of the prevailing general wind. The position of this zone and a discontinuous line between the prevailing northerly winds and sea breezes showed a close relation to the topography, and to the distribution of land, sea and rivers in the area.