JULY, 1901. MONTHLY WEATHER REVIEW. 297
made. I n the dry sections cotton, while holding its own remarkably well, beginning to suffer for moisture; picking began in some of the southern counties about the 15th, and by the close of the month a number oE bales had been ginned and marketed.-N. R. Taglor. =h.-The mean temperature was 75.4', or 4.7' above normal: the highest was 115', at Hite on the loth, and the lowest, 47", at Soldier Summit on the 4th. The average precipitation.was 0.41, or 0.19 be- low normal; the greatest monthly amount, 1.76, occurred at Frisco, while none fell at Corinne and Kelton. One of the warmest. if not the warmest, months since the settlement
of the State.-L. H. Afurdoch.
Vi@nfa.-The mean temperature was 75.6', or 1.3' above normal; the hi hest was 106', at Stephens City on the lst, and the lowest, 47', atsurkes Garden on the 9th. The average precipitation was 4.94, or 0.42 above normal; the greatest monthly amount, 9.83, occurred at Alexandria, and the least, 2.44, at Callaville.
The month, as a whole, was quite favorable for crop growth and work. Extremely high temperatures prevailed during the first and last da s of the month, but no crop damage resulted. There werealso a numler of heavy, washing rains and some freshet water in small streams. These were productive of some harm to lowland corn and tobacco, but not sufficient to materially affect the general situation.- Edward A. Evans.
Wishington.-The mean temperature was 6!?.5', or 3.5' below normal! the highest was 106', at Pasco on the 30th, and the lowest, 30°, at Sno ualmie Falls on the 12th. The average precipitation was 0.5i, or 0.078elow normal; the greatest month1 amount, 2.48, occurred at Ilwaco, while none fell at Ellensburg, Lateside, and Pasco. Although rather cool for corn and several kinds of vegetables, the month was the best possible for the heading out and filling of spring wheat. I t was also very favorable for haying, and ideal for fall wheat harvesting.-@. N. Salisbwy.
Wbst Vivgin&.-The mean temperature was 77.4', or 3.7' above nor-
mal; the hi 'hest was 104' at Magnolia and New Martinsville on the 1st. and theqowest, 47', at hhilippi on the 9th. The avera e precipi- tation was 3.16, or 1.63 below normal; the greatest month& amount, 6.41, occurred at Josiah, and the least, 0.69, at Parkersborg. Fine harvest weather during the month; wheat cutting com leted by the fourth week, and wheat mostly in stack and thrashing %e n, but yield not meeting expectations, there not being more than h a r t 0 two-thirds cro . Clover and r e cutting mostly over by second week, with fair yiel&. Durin the ttird week grass and oat cutting in gen- eral progress, and by t!& last of the month, these crops had been mostlysaved in fine condition, with a good crop of hay and a fair yield of oats. Crops of all kinds continued to improve until the fourth week, when the intense heat and drought began to have an injurious effect, especially on corn, gardens, and potatoes. Apples continued to fall, and the rospect was for not more than half a crop; peaches plentiful, but smaly and of inferior quality.-E. C. Vim. Wisconsin.-The mean temperature was 75.3', or 6.5" above normal; the highest was lll', at Brodhead on the 21st, and the lowest, 33', at City Point on the 7th. The average precipitation was 429, or 2.23 above normal; the Ereatest monthly amount, 9.17, occurred at Florence, and the least, 0.86, at Racine. The month was characterized by a severe and protracted drought over the southern section of the State, which, together with the exces- sive heat, caused much damage to corn, tobacco, and other crops. In the central and northern ortions the rainfall was amDle, and in some localities excessive. I n tge central and northern sections a large hay crop was secured in excellent condition, and other crops are satisfac- tor -W. iK. Wilson. $lmning.-The mean temperature was 71.3", or 4.4' above normal; the ighest was ]lo0, at Fort Bitter Creek on the 14th and 16th, and the lowest, 23', at Daniel on the 5th. The average precipitation was 0.70, or 0.39 below normal; the greatest monthly amount, 2.87, occurred at Casper, while none fell at Embar and Hyattville, and but a trace at Lander and Fort Washakie.- W. 6. Palmar.
- -
SPECML (YONTRIBUTIONS.
THE THUNDERSTORM ; A NEW EXPLANATION OF ONE
OF ITS PHENOMENA.
BY BYRON MCFARLAND. A. B., dated Monroe City, lo., June i T , 1901.
The daily weather maps issued by the United States Weathei
Bureau show that areas of high pressure, and areas of low
pressure-or highs and lows-are continually passing acrose
the continent in a more or less easterly direction. Thunder. storms occur usually in these lows and are therefore called secondary storms, being small, local storms in a large, 01
general, storm area. These storms furnish the chief supply
of rain during the summer months. There can be little doubt but that thunderstorms are composed of rising air and de- scending air; the air currents blow both to and from the
thunderstorm-both up and down in it. A peculiar feature
of the thuuderstorm is the coolness of the air within it. At
the storm's arrival the temperature may drop from loo to 3OC
F., or even more.
Some of the facts known about thunderstorms are as fol-
lows: (a) from some distance in front the air blows toward the storm, turns upward as it approaches it, and finally entere
the main cloud. (b ) On the ground below the margin of the
cloud the air blows from the cloud ; this forms the " squall "
or strong cool wind that usually precedes the main storm
proper. (e) I n the center of the storm, the air is more nearly
calm than a t the border-especially its front border. (d ) The air pressure is greater in the center of the storm than
just in front of the margin of the cloud, i. e., the barometer rises slightly, and generally suddenly, during the passage of
the cloud. (e ) The air in the ('squall " is Considerably cooler
than the surrounding air.
To account for these phenomena of pressure a d of air cur-
rents (a-e) three explanations have been offered: (1) The rain drops falling through the air, push it down and out, thus
producing the rise of the barometer and the L L squall " below.
(2) The warm moist air rising into a region of decreased air
pressure, becomes cloud and expands, and in thus pushing
aside the surrounding upper air it presses downward with more than its weight, causing a t once the slight'rise in the
barometer a t the ground and the outruehing squall. The ascending air produces therefore a sort of recoil comparable
to the c L kick " of a gun, aud this recoil is what "kicks " out
the squall below. (3) The rising air above overflows into the iieighboring air, and this additional weight produces the
increased pressure and the squall below.
(1) The first of these explanations has undoubtedly some
foundation in fact, for falling bodies will produce descending currents and lateral winds below. But the fact that the in-
tensity of the squall is not always pro.portiona1 to the inten-
sity of the rainfall shows that the theory is only a partial explanation of the phenomena in question. (2) The second-
named theory is even less tenable. That cloudy air in as-
cending cools more slowly, and hence expands more rapidly than dry air, is quite true; but this expanding air can not
"kick " a constant squall out of the bottom. I will admit
that should a large mass of warm, cloudy air be in some way
carried up to the center of the convectional column and there
suddenly turned loose, it would expand and increase tempo-
rarily the pressure down at the ground. But the thuader- storm is a continuous process of some duration. The follow-
ing statements appear to- me as being in this connection
unquestionably true, viz, (1) the pressure at the ground
could not be increased without the pressure above being also and even first increased ; (2) the increased pressure a t the
ground could not be maintained (as it in fact is) unless the
increased pressure above be maintained; and (3) if the in-
creased pressure above be maintained, convection would
cease, and the thunderstorm would be brought a t once to an snd.
In my judgment, the only condition under which air can
:ontinue to rise for hours into the upper part of the storm is
the presence there, not of increased, but of relatively decreased
air pressure. The idea that the rising and expanding air above :an maintain a constant downward recoil or kick" sufficient
JULY, 1901
~
to produce the squall, and a t the same time not interfere with
the incoming currents above, seems hard to understand. For
it could not “kick” at all unless its pressure be increased;
and if its pressure be increased, it would ‘&kick” in all direc-
tions, and would (‘kick” back the incoming currents and pre- vent them from entering tho storm area a t all. The surround-
ing.air could not enter until the high pressure had given way
to’lower pressure; but when this takes place, the high pressure
on the ground would also give way to lower pressure, and the squall would cease. But, in fact, both the inflowing currents
above and the outrushing squall below blow with comparative
uniformity, thus showing that there are some sort of constant barometric conditions established, which insure a low pressure
above and a relatively high pressure below.
(3) The “convectional overturn ”.theory has the same weak-
ness that the “kick” theory has, because (u) the upper air could not ‘L overflow ” until its pressure be greater than that of the surrounding air ; (b ) if the overflowing air above has
relatively greater pressure, it will produce greater pressure be- low also, unless the column is abnormally warm or light, and
we should have the anomaly of air rising into relatively higher
pressure and settling in lower pressure.
The explanation which I wish to suggest is based on the well-known coolness of the air in the squall. Under uniform
pressure, the density of the air decreases 1/491 of that a t 32O F.
for every degree Fahrenheit above the freezing point of water. We will suppose the distance from the thundercloud to the
ground to be 1,300 feet (it may be more), and suppose, also, that the air between the cloud and ground is, on an average,
150 F. cooler than the surrounding air (i t is often consider-
ably more). It may easily be found that the differeuce in
weight of these two columns of air (each 1,300 feet high)
would ba about 0.04 inch of niercury, that is to say, placed side by side, the cool column would support 0.04 inch more
mercury than the warm column would. Evidently, if the
air be much cooler (say 35O F.), and if the height of the cool column be several thousand feet, the diflerence in weight
would be much more marked. The presence of this cool
column of air, then, extending from the cloud to the ground,
will account for the higher air pressure below. But not only
this, it will account, also, for the permanent low above. If
a series of isobars be drawn in a vertical plane section through
the thunderstorm, the isobaric surfaces will crowd together in the cool column and be farther apart in the surrounding re-
gion of warm air. The higher pressure below will suffice to produce the squall, and the lower pressure above will permit
convection to go on undisturbed. The rise in barometer during the passage of a thunderstorm is usually very slight. I have often noted, in well defined
storms, a rise of not more than 0.03 inch. I n very violent
storms, however, the rise may be considerably more, as much
as 0.15 or even 0.26 of an inch. But it is a notable fact that
in these violent storms, the drop in temperature is very marked. This is just what we should expect if the ‘‘ cold air ” theory
is true. I have yet to hear of a thunderstorm accompanied by a typical squall in which the air of the squall was warmer
than the surrounding air. The “cool air” theory will undoubtedly suffice, provided only the cool air column is present. And as indications that
the column of cool air does exist, we mention the following:
(1 ) The internal air of the squall is considerably cooler on the ground. (2) The fact that the so-called wind cloud is usually much lower than the other convectional clouds which
arg fed from air of like temperature and humidity, shows that the rising air meets with relatively cooler air below the mar-
gin of the cloud. There are, of course, several things to be remembered in
applying this “ cool air ” theory. Confessedly there are still
a good many ‘‘ unknowns ” in the thunderstorm ; but the fol-
lowing will evidently modify and determine the violence of
the squall. (1) The average difference of temperature be-
tween the cool column and the surrounding air. (2) The height of the cool column. (3) The diameter of the cool
column. (4) The progressive motion of the storm itself.
No one of these four will alone determine the violence of the
squall. I n general, the intensity of the squall will vary directly with the relative coolness of the column, its height,
and its diameter. But these factors may vary considerably
among themselves, and there can be no narrow, cast-iron rules
laid down. We should expect to find the squall strongest
when these factors combine and weakest when they are weak. The progressive motion of the storm will affect the squall
somewhat, making it apparently stronger in front than
behind.
As to the origin of the cold air of the squall there is some diversity of opinion. By some it is thought that the cool-
ness of the air is due to cold rain falling through it. In many cases this seems a sufficient explanation. Thunderclouds probably often extend above the snow line. The melting of this snow, the warming of the cold water in its descent, and
the resulting evaporation of some of it, might well keep the
air through which it falls several degrees cooler than the out-
side air. The amount of air that rises into the thunder
cloud is apparently several times greater than that which blows out from it below. The falling snow and rain cool a
comparatively small amount of air beneath the clouds.
Cool squalls in the absence of rain are thought to be caused by the settling of overlying masses of air that are intrinsi-
cally and abnormally cold. This is entirely probable. It is
generally supposed that thunderstorms, especially those ac- companied by tornadoes, are overlaid by layers of cold air.
But it is more probable, I think, that many of the wind
clouds, unaccompanied by rain, are the last remnants of former thunderstorms, or are the products of actions that were too feeble to produce a thunderstorm.
It seems pretty certain that the circulation of air in an active or “typical ” thunderstorm is as about as follows: The
air from around rises toward the cloud ; the inner layer of
this ascending air meeting with the falling snow or rain is
cooled, and also pushed down by the rain drops ; both cooling
and pushing cause it to be turned downward. And as it is more and more cooled (i. e., relatively), and continually beaten down by the falling rain, it settles more and more
rapidly, and on reaching the ground becomes the cool out-
rushing squall. The presence and the appearance of the so-
called “ wind cloud ” that generally just precedes the rain
cloud, seems to indicate this. It is a long light-colored fleecy
cloud that suggests a huge roll of wool. A cloud formed a t the level where the rising air turns to descend would have
an appearance like this.
A METBOROLOGIUAL BALLOON ASUBNSION AT STRAS- BUR<), GERMANY.
By A. LAWBEHOE ROTOR, Dlreot r of the Blue Ell1 Obeervatory, dated Aug. 7.1901.
Through the courtesy of Professor Hergesell, the President of the International Aeronautical Committee, the writer (who is the American member of the Committee) partici-
pated in the eighteenth series of balloon ascents on July 4, 1901, when balloons were diepatched from Paris, Berlin,
Strashurg, Munich, Vienna, and St. Petersburg. The manned ascension from Strasburg was made by Professor Hergesell
and the writer in the new cotton balloon “Girbaden,” of
1,300 cubic meters, belonging to the Aeronautical Society of
the upper Rhine. On this occasion this balloon was filled
with coal gas and had a lift at starting represented by six-
teen sacks of ballast weighing together about 300 kilograms.