Storms Hurricanes And Typhoons

The solution of the question--How far and in what manner are storms

connected with atmospheric waves?--must be extremely interesting to

every one engaged in either the naval or merchant service. As we have in

the former chapters directed attention to their connexion, our great

object here will be to endeavour to mark out such a line of observation

as appears most capable of throwing light, not only on the most

desiderata as connected with storms, but also their connexion

or non-connexion with atmospheric waves. We shall accordingly

arrange this portion of the instructions under the following

heads:--_Desiderata_; _Localities_; _Margins_; _Preceding and Succeeding

Accumulations of Pressure._

_Desiderata._--The most important desiderata appertaining to the subject

of storms, are certainly their origin and termination. Of these initial

and terminal points in the course of great storms we absolutely know

nothing, unless _the white appearance of a round form_ observed by Mr.

Seymour on board the Judith and Esther, in lat. 17° 19' north and long.

52° 10' west (see Col. Reid's 'Law of Storms,' 1st edit. p. 65), may be

regarded as the commencement of the Antigua hurricane of August 2, 1837.

This vessel was the most eastern of those from which observations had

been obtained; and it is the absence of contemporaneous observations to

the eastward of the 50th meridian that leaves the question as to the

origin of the West Indian revolving storms unsolved. Not one of Mr.

Redfield's storm routes extends eastward of the 50th meridian; this at

once marks out, so far as storms are concerned, the entire space

included between the 20th and 50th meridians, the equator and the 60th

parallel, as a most suitable area for observations, under particular

circumstances hereafter to be noticed, with especial reference either to

the commencement or termination of storms, or the prolongation of Mr.

Redfield's storm paths.

_Localities._--The three principal localities of storms are as

follows:--I. The western portion of the basin of the North Atlantic; II.

The China Sea and Bay of Bengal; and III. The Indian Ocean, more

particularly in the neighbourhood of Mauritius. The first two have

already been marked out as areas for the three-hourly observations; to

the latter, the remark as to extra observations under the head of

Desiderata will apply.

_Margins._--Mr. Redfield has shown that on some occasions storms have

been preceded by an unusual pressure of the atmosphere; the barometer

has stood remarkably _high_, and it has hence been inferred that there

has existed _around_ the gale an accumulation of air forming a margin;

barometers placed under this margin indicating a much greater pressure

than the mean of the respective localities. With regard to the West

Indian and American hurricanes--any considerable increase of pressure,

especially within the space marked out to the eastward of the 50th

meridian, will demand immediate attention. Upon the barometer ranging

_very high_ within this space, three-hourly observations should be

immediately resorted to; and if possible, _hourly_ readings taken, and

this is the more important the nearer the vessel may be to the 50th

meridian. Each observation of the barometer should be accompanied by an

observation of the wind--its direction should be most carefully noted,

and the force estimated according to the scale in page 21, or by the

anemometer. It would be as well _at the time_ to project the barometric

readings in a curve even of a rough character, that the extent of fall

after the mercury had passed its maximum might be readily discernible by

the eye. A paper ruled in squares, the vertical lines representing the

commencement of hours, and the horizontal tenths of an inch, would be

quite sufficient for this purpose. The _force_ of the wind should be

noted at, or as near to the time of the passage of the maximum as

possible. During the fall of the mercury particular attention should be

paid to the manner in which the wind changes, should any change be

observed; and should the wind continue blowing steadily in _one_

direction, but gradually _increasing_ in force, then such increments of

force should be most carefully noted. During the fall of the barometer,

should the changes of the wind and its increasing force indicate the

neighbourhood of a revolving storm, (independent of the obvious reasons

for avoiding the focus of the storm,) it would contribute as much to

increase our knowledge of these dangerous vortices to keep as near as

possible to their margins as to approach their centres. The recess from

the centre towards the margin of the storm, will probably be rendered

apparent by the _rising_ of the mercury; and so far as the observations

may be considered valuable for elucidating the connexion of atmospheric

waves with rotatory storms (other motives being balanced), it might be

desirable to keep the ship near the margin--provided she is not carried

beyond the influence of the winds which characterize the latter half of

the storm--until the barometer has nearly attained its usual elevation.

By this means some notion might be formed of the general direction of

the line of barometric pressure preceding or succeeding a storm.

Should a gale be observed commencing without its having been preceded by

an unusual elevation of the mercurial column, and consequently no

additional observation have been made; when the force of the wind is

noted in the usual observations at or above 5, then the three-hourly

series should be resorted to, and the same care taken in noting the

direction, changes, and force of the wind as pointed out in the

preceding paragraph.

The foregoing remarks relate especially to the central and western

portions of the North Atlantic; they will however equally apply to the

remaining localities of storms. Under any circumstances, and in any

locality, a _high_ barometer not less than a low one should demand

particular attention, and if possible, _hourly_ readings taken some time

before and after the passage of the maximum: this will be referred to

more particularly under the next head.

_Preceding and Succeeding Accumulations of Pressure._--Mr. Redfield has

shown in his Memoir of the Cuba Hurricane of October, 1844, that two

associated storms were immediately preceded by a barometric wave, or

accumulation of pressure, the barometer rising above the usual or annual

mean. We have just referred to the importance of _hourly_ observations

on occasions of the readings being _high_ as capable of illustrating the

marginal phænomena of storms, and in connexion with these accumulations

of pressure in advance of storms we would reiterate the suggestion.

These strips of accumulated pressure are doubtless crests of atmospheric

waves rolling forwards. In some cases a ship in its progress may cut

them transversely in a direction at right angles to their _length_, in

others very obliquely; but in all cases, whatever section may be given

by the curve representing the observations, too much attention cannot be

bestowed on the barometer, the wet and dry bulb thermometer, the

direction and force of the wind, the state of the sky, and the

appearance of the ocean during the ship's passage _through_ such an

accumulation of pressure. When the barometer attains its mean altitude,

and is rapidly rising above it in any locality, then _hourly_

observations of the instruments and phænomena above noticed should be

commenced and continued until after the mercury had attained its highest

point and had sunk again to its mean state. In such observations

particular attention should be paid to the direction and force of the

wind preceding the barometric maximum--and the same phænomena succeeding

it, and particular notice should be taken of the time when, and amount

of any change either in the direction or force of the wind. It is by

such observations as these, carried on with great care and made at every

accessible portion of the oceanic surface, that we may be able to

ascertain the continuity of these atmospheric waves, to determine

somewhat respecting their length, to show the character of their

connexion with the rotatory storm, and to deduce the direction and rate

of their progress.