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Charles F. Brooks
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CHARLES F. BROOKS

Abstract

During the past four years the Gulf Stream has been subjected to investigation by sea-water thermographs on crossing ships. Details of temperature, including alternating masses of warmer and cooler water, diurnal ranges of temperature, and rapid changes in distribution, have been written on the thermograms to form an amazingly complex picture.

The thermograph is a mercury-in-steel bulb and capillary type, the thermal element being fixed in the intake pipe through which large volumes of water from several feet below the surface are continually pumped to the condensers.

An instrument of this sort installed in 1928 on the Peninsular & Occidental steamship Henry M. Flagler, one of the three Key West-to-Habana car ferries, provides the temperature record for one round trip daily while the ship is in operation. The south-bound trip gives a night profile and the northbound a daytime one. From night to day in sunny quiet weather the sea temperature at the surface rises 3° or 4° F. and at a depth of 6 feet about 2°. In windy weather the diurnal range is reduced by stirring to 1° or less.

The summer profile is characteristically warmer in the north than in the south, while the temperature of Key West Harbor stands out several degrees above the Gulf Stream. A band of cool water is almost always traversed within a mile of the Cuban shore, apparently where swell and current striking the steeply sloping bottom bring cool water to the surface. Similar cool water often occurs likewise at the margin of shoal water south of Key West. The winter profile is usually 2° or more warmer in the south than in the north portion of the straits. A narrow zone of probably upwelling water several degrees cooler than on either side usually divides the warmer water from the cooler. This boundary shifts many miles with wind and other effects that bring at one time more water direct from the Caribbean and at another time from the Gulf. Great variations sometimes occur in the course of a few hours.

Storms, chiefly through their stirring action, reduce the surface temperatures by 1° or more. Strong cold winds have an even greater effect than hurricanes, for they chill the water considerably as well as mix the warm surface layer with the cooler substrata.

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Charles F. Brooks
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Charles F. Brooks

Synopsis

The two severe storms that overtook Columbus on the return portion of his first voyage, when examined in the light of modern frontal theory, do not appear to have been simple circular storms, as previously thought, but disturbances marked by well developed fronts. The centers of both passed north of Columbus; he apparently experienced the warm sectors of both. The February storm seems to have had two cold fronts, and the March one a very sharp cold front. Storms of both kinds have been observed in the same portion of the Atlantic in recent years.

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Charles F. Brooks
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Charles F. Brooks
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Charles F. Brooks
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CHARLES F. BROOKS

Abstract

SYNOPSIS

This paper is largely a summary of water-surface temperature comparisons by the author on a winter-time West Indies cruise of The R. M. S. Empress of Britain. An attempt was made to determine the accuracy of observational methods under a great variety of conditions, including the most trying ones likely to be experienced. Temperatures obtained nearly simultaneously (1) from a low deck with a 2 or 4 quart tin bucket by quick dips forward of the ship's main outtakes and (2) aft in the propellor wash, and (3) in the discharge from faucets attached to the condenser intake pumps, were consistent always within 0.25° F., and differed, on the average, but 0.1°F. Reliable results are evidently procurable from the stern, where “surface” observations may, perhaps, most accurately and readily be made in cold windy weather. A record from the condenser intake pipe appears truly representative of the surface temperatures under virtually all conditions.

The condenser intake temperature recorded by engineers in the engine-room log of the Empress of Britain were found to average 0.5°F. above the temperatures accurately obtained in other way. This difference appears to arise from some heating of the water about the fixed thermometers in the pumps but mostly from errors of parallax in reading. The most serious deficiency in these observations is the absence of a record of the exact time when they were made. Hourly observations on the international ice patrol ships, Tampa and Modoc are apparently of the same order of accuracy as those on the Empress of Britain.

In comparison with the surface water temperature obtained with a tin bucket from a lower deck at about the same time, water surface temperatures procured by the author with a canvas bucket dropped from the bridge averaged 0.5° F. too low, and those by quartermasters with the same bucket averaged 1° F. too low. These errors were the combined result of the predip temperature of the canvas bucket, evaporative cooling of the partially filled canvas bucket after leaving the sea, temperature change of the thermometer if withdrawn for reading, and several unsystematic errors, such as occasional 5 or 10 degrees misreadings. On some other ships the average depression of the recorder canvas bucket temperatures below the condenser intake values was found to be 3°F. or more. In the Gulf Stream region north and northeast of Hatteras, winter observations from four ships gave canvas bucket temperatures averaging about 5° F. lower than the condenser intake. In cold gales over the Gulf Stream, departures in a group of 24 observations from 4 ships were so large as to have a median at 7 and upper extremes of 20 to 24°F.

An analysis of some observations made on the ice patrol ships show the same tendencies when the air was much colder than the sea. Thus, Lieut. Commander E. H. Smith's observations of surface temperature stood higher than the usual canvas bucket determination from the bridge by an average of 0.7° F. for cold water (10 cases) and 1.8°F. for warm (13 cases) on and about the Grand Banks.

Errors are closely related to the depression of wet bulb or air temperature below the water temperature. With air temperatures no more than 3°F. below the observed water temperatures the temperatures obtained with the canvas bucket are likely to be more than 1°F. in error in but 15 to 30 per cent of the cases. Water temperatures obtained under lower air temperatures, and especially when wind velocities are high, are likely to be too low by one-third to one-half the depression of the air temperature below the observed water temperature.

With due care, involving the use of dry, stiffened canvas or wooden or fiber buckets dropped from a low deck, heaved up rapidly and as quickly observed accurate temperatures are obtainable. The use of a thermograph, the thermal element of which projects into the condenser intake pipe, is recommended, however, as much the easiest method for procuring temperatures of the general surface layer accurately under all conditions of weather. Even in late spring and summer, when surface layers are warmed more than those at intake depths, the average difference between the surface and 5 meters depth (16.3 feet) has been found to average but 0.2° C. (0.36° F.). In the 66 observations on which this average was based the surface was 0.5°C. 0.9°F.) or more warmer than water at 5 meters but 12 times, and 1°C. (1.8°F.) or more warmer but three times. The greatest difference observed was 1.52°C. (2.7° F.).

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CHARLES F. BROOKS

Abstract

SYNOPSIS

Whereas in current practice in the United States, select is that form of precipitation which is not snow, rain, or hail, an attempt to make a detailed descriptive and genetic definition seems advisable, and 30 cases of sleet are analyzed as a basis:

Select, a rattling type of ice precipitation formed in the free air, has the following characteristics: Size, smallest dimensions of largest pieces less than 6 mm. (¼ inch); form, angular, irregular, or nearly spherical; structure, nonregular ice part or all of which is cloudy or bubbly (except in extremely small drops), not more than one clear layer.

A select particle may be (1) a snowflake partly melted and refrozen. (2) a frozen raindrop, or (3) a frozen combination of snowflake, and raindrop or liquid (not undercooled) cloud droplets.

A generalized vertical section of sleet weather shows select as occurring usually with a cloud from which snow is falling through a stratum of air having a temperature above freezing and into air with a temperature below freezing.

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CHARLES F. BROOKS

Abstract

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