landslide winds, that avalanche would be a better term than landslide
as applied to winds associated with fallen masses of earth or snow.
With the enormous amounts of accumulated tabulated matter, and numerous
studies bearing on isolated meteorological phenomena, it is a specially
important consideration that some students pay constant attention to
the investigations of the laws of storms. From such researches definite
advances in theoretical meteorology may be made and fixed laws
determined, which may be of practical utility with reference to the
better forecasting of the weather. In the United States Signal Office,
Professor Abbe has brought together the results of his studies and
investigations for the past thirty years, under the title, "Preparatory
studies for Deductive Methods in Storm and Weather Predictions." This
report will appear as an appendix to the annual report of the Chief
Signal Officer of the army. Professor Abbe finds that the source and
maintaining power of storms depend on the absorption by clouds of solar
heat, and in the liberation of heat in the cloud during the subsequent
precipitation, which, as he endeavors to show, principally influences
the movement of the storm-centre.
In this method one takes a chart showing current meteorological
conditions, and the permanent orographic features of the continent;
lines of equal density are also drawn for planes at several elevations
above sea-level. On these latter, and on the lines of the orographic
resistance, are based intermediate lines of flow, which show where
conditions are favorable to cooling and condensation. The amount of
condensation and its character, whether rain or snow, are estimated by
the help of the graphic diagram. Numbers are thus furnished that can be
entered on the chart and show at once the character of the new centre
of buoyancy, or the directions and velocity of progress of the centre
of the indraft and the consequent low barometer.
It is hoped that this work of Professor Abbe's may be, as he
anticipates, of great practical as well as theoretical value. Steps are
being taken to test the theoretical scheme by practical and exhaustive
applications to current work.
Tiesserenc de Bort has continued his work, of improving weather
forecasts for France, by studying the distribution of the great and
important centres of high pressures, which prevail generally over the
middle Atlantic ocean, and, at certain periods of the year, over Asia,
Europe, and North America. His studies have proceeded on the theory
that the displacements of centres of high pressure, whether in Asia,
over the Azores, near Bermuda, in North America, or in the Polar
regions, set up a series of secondary displacements, which necessarily
cause storm centres to follow certain routes. M. de Bort concludes that
a daily knowledge of the relation of these centres and their areas of
displacement will eventually enable skilled meteorologists to deduce
the position of unknown and secondary centres. He has endeavored to
reduce these various displacements to a series of types and has made
very considerable progress in this classification. Daily charts
covering many years of observations have been prepared, and these
separated, whenever the characteristics are sufficiently pronounced,
into corresponding types. This plan of forecasting necessitates
extended meteorological information daily, which France obtains not
only from Russia, Algeria, Italy and Great Britain, but, through the
coöperation of United States, from North America. The daily information
sent by the Signal Office shows, in addition to the general weather
over the United States and Canada, the conditions on the western half
of the North Atlantic ocean, as determined by observations made on the
great steamships, and furnished voluntarily by their officers to the
Signal Office through the Hydrographic Office and the New York Herald
weather bureau.
The study of thunder storms has received very elaborate and extensive
consideration. M. Ciro Ferari in Italy finds that almost invariably the
storms come from directions between north and northwest, the tendency
in northern Italy being directly from the west, and in the more
southern sections from the northwest. The velocities of storm movements
are much greater from the west than from the east, considerably more so
in the centre and south of Italy than in the north; and in the months,
largest in July.
The velocity of propagation increases with greater velocities of the
winds accompanying the storms, with also greater attendant electrical
intensity. The front line of propagation while more often curved, is
sometimes straight and sometimes zigzag, and appears to undergo a
series of successive transformations, more or less affected by the
topographical nature of the country passed over.
Ferari thinks their principal cause is to be found in high temperatures
coincident with high vapor pressures. Thunder storms, he considers, are
essentially local phenomena, superposed on the general atmospheric
phenomena. A principal general cause of thunder storms in Italy is the
existence of a deep depression in northwest Europe, with a secondary
depression in Italy dependent on the first. This secondary feeble area
remains for several days over upper Italy, and nearly always is
followed by thunder storms. Minimum relative humidity precedes, and
maximum follows a storm, while the vapor pressure conditions are
exactly reversed. Ferari notes, as one matter of interest, the passage
of fully developed thunder storms from France into Italy over mountains
4,000 metres (13,000 feet) in elevation.
Dr. Meyer, at Gottingen, has investigated the annual periodicity of
thunder storms, while Carl Prohaska has made a statistical study of
similar storms in the German and Austrian Alps. The latter writer
thinks they are most likely to occur when the barometer is beginning to
rise after a fall, thus resembling heavy down-pours of rain.
In connection with Schmucher's theory on the origin of thunder storm
electricity, Dr. Less has been able to satisfactorily answer in the
affirmative an important point in the theory, as to whether the
vertical decrement of temperature is especially rapid. Less finds
evidences of very rapid decrement of temperature during thunder storms,
as shown by the examination of records of 120 stations for ten years.
Mohn and Hildebrandsson have also published a work on the thunder
storms of the Scandinavian peninsula. The rise in the barometer at the
beginning of rain, they agree with Mascart in attributing largely to
the formation of vapor and the evaporation of moisture from rain
falling through relatively dry air.
A. Croffins has discussed thunder storms at Hamberg from observations
for ten years. He believes that all such storms are due to the
mechanical interaction of at least two barometric depressions.
As a matter of interest bearing on the much discussed phenomena of
globular lightning, an incident is recounted by F. Roth, where a man
feeding a horse was struck by lightning and lost consciousness. The man
states that he felt no shock, but was suddenly enveloped in light and
that a ball of fire the size of his fist, traveled along the horse's
neck. This points to the fact that "ball" lightning is probably a
physiological phenomenon.
In view of the recent extended interest in the question as to whether
the climate of the United States is permanently changing, it should be
remarked that this question has lately been under consideration with
regard to Europe. Messrs. Ferrel, Richter, Lang, Bruchen and others
conclude, from an examination of all available data, that there is no
permanent climatic change in Europe. In connection with this discussion
in Europe, long series of vintage records, going back to the year 1400,
have been used. Apart from the ocean borders, extensive simultaneous
climatic changes occur over extended areas, which changes--as might be
expected--are more accentuated in the interior of the continents. These
changes involve barometric pressure, rainfall and temperature, which
all recur to that indefinite and complex phenomenon--the variation in
the amount of heat received by the earth. The idea is advanced that
these oscillations have somewhat the semblance of cycles, the period of
which is thirty-six years. It may easily be questioned, however, in
view of the fragmentary and heterogeneous character of the data on
which this assumption is based, whether the error in the observations
is not greater than the range of variation. Blanford, in one of his
discussions, has pointed out that the temperature or rainfall data in
India can be so arranged as to give a cycle with a period of almost any
number of years, but, unfortunately, the possible error of observation
is greater in value than the variations.
As to the United States, it is pertinent to remark that the Signal
Office is in possession of temperature observations in Philadelphia,
covering a continuous period of one hundred and thirty-two years. The
mean annual temperature for the past ten years is exactly the same as
for the entire period.
There have been criticisms in years past that the climatological
conditions of the United States have not received that care and
attention which their importance demanded. Much has been done to remedy
defects in this respect, although, as is well known here in Washington,
the general law which forbids the printing of any works without the
direct authority of Congress, has been an obvious bar to great activity
on the part of the Signal Office. Within the year the rainfall
conditions of twelve Western States and Territories have been published
with elaborate tables of data and fifteen large charts, which set forth
in considerable detail the rainfall conditions for that section of the
country. In addition the climatic characteristics of Oregon and
Washington have been graphically represented; and rainfall
maps,--unfortunately on a small scale,--have been prepared, showing for
each month, the average precipitation of the entire United States, as
determined from observations covering periods varying from fifteen to
eighteen years.
In Missouri, Professor Nipher has prepared normal rainfall charts for
that State, unfortunately on rather a small scale. In New York,
Professor Fuertes, and in Michigan, Sergeant Conger, of the Signal
Service, have commenced maps showing, by months, the normal
temperatures of their respective States on maps of fairly open scale.
Work of a similar character has been carried on in Pennsylvania under
the supervision of Professor Blodget, well known from his
climatological work. In other directions and in other ways, work of a
similar character is in progress.
Without doubt too much is anticipated from pending or projected
irrigation enterprises in the very arid regions of the West. These
unwarranted expectations must in part result from a failure on the part
of the investors to consider the general question of these enterprises,
in its varied aspects, with that scientific exactness so essential in
dealing theoretically with extended subjects of such great importance.
Everyone admits the correctness of the statement that the amount of
water which flows through drainage channels to the sea, cannot exceed
the amount which has evaporated from adjacent oceans and fallen as
precipitation on the land. Further it is not to be denied that the
quantity of water available in any way for irrigation must be only a
very moderate percentage of the total rainfall which occurs at
elevations _above_, and perhaps it may be stated _considerably above_,
that of the land to be benefited.
Elsewhere it might be appropriate to dwell in detail upon the
importance of cultivated land in serving as a reservoir which parts
slowly with the water fallen upon or diverted to it, and in avoiding
the quick and wasteful drainage which obtains in sections devoid of
extensive vegetation or cultivation; and also that water thus taken up
by cultivated lands must later evaporate and may again fall as rain on
other land. But the pertinence of meteorological investigations in
connection with irrigation and this annual address, relates much more
directly to important questions of the manner by, and extent to which,
precipitation over the catchment basins of the great central valleys
fails to return in direct and visible form, through the water courses,
to the Gulf of Mexico.
The inter-relation of rainfall and river outflows is one of peculiar
interest, in connection with the important matter of irrigation now
under consideration in this country.
Probably more attention has been paid to this subject in the valley of
the Seine, by Belgrand and Chateaublanc, than in any other portion of
the globe. One of the curious outcomes of Chateaublanc's observations,
is one bearing on the maximum value of the floods in the Seine for the
cold season, from October to May, by which he says that the reading of
the river gauge at Port Royal is equal to 12.7 minus the number of
decimetres of rainfall which has fallen on an average throughout the
catchment basin during the preceding year. This curiously shows that
the intensity of the winter floods of the Seine is inversely
proportional to the quantity of rain of the _preceding_ year.
Sometime since, John Murray, Esq., in the Scottish Geographic Magazine,
treated generally the question of rainfall and river outflows. The
annual rainfall of the globe was estimated to be 29,350 cubic miles, of
which 2,343, falling on inland drainage areas, such as the Sahara
desert, etc., evaporate. The total annual discharge of rivers was
estimated at 7,270 cubic miles. In the case of European drainage areas
between a third and a fourth of the rainfall reaches the sea through
the rivers. The Nile delivers only one thirty-seventh of the rainfall
of its catchment basin, while tropical rivers in general deliver
one-fifth.
The Saale river of Germany, from late data based on 45 rainfall
stations in its catchment basin, during the years 1883 to 1886,
discharged 30 per cent. of its rainfall.
During the past year Professor Russell, of the Signal Office, has
determined carefully the rainfall and river outflow over the most
important part of the United States, the entire catchment basin of the
Mississippi river and its tributaries. This work was done as
preliminary to formulating rules for forecasting the stage of the water
several days in advance on the more important of the western rivers in
the United States. The river outflows at various places on the
Mississippi and Missouri and Ohio rivers, were tabulated from data
given in the reports of the Mississippi and Missouri River Commissions.
The tables were largely derived from the results of the measurement of
current velocities. As gauge readings were taken at the time of
discharge or outflow measurements, the discharges or outflows can be
told approximately at other times when only the river gauge readings
are known. The results for the outflow of rivers derived from
measurements made under the supervision of these commissions, are of a
high order of accuracy, and it is not probable that the results deduced
from the gauge readings are much in error. Of 1881 and 1882, during
which years measurements were made, 1881 was a year of great flood in
the Missouri river, while the Mississippi river was not flooded. The
year 1882, on the other hand, was marked by a great flood in the lower
Mississippi river, with a stage in the Missouri much above the average.
The rainfall in the six great valleys of the Mississippi, during the
entire years 1881 and 1882, was charted from all observations
available, and its amount in cubic miles of water calculated with the
aid of a planimeter.
In connection with this investigation, and as a matter of value in
showing the forces which are in operation to affect the river outflow,
the fictitious or possible evaporation of the six great valleys
referred to were calculated, in cubic miles of water, from July, 1887,
to July, 1888, and also the average amounts of water in the air as
vapor, and the amount required to saturate the air in the same valleys
during the same period.
During the year 1882, the year of great flood in the lower Mississippi
valley, the outflow at Red River Landing, La., was 202.7 cubic miles,
of which the upper Mississippi river above St. Louis furnished 16 per
cent., the Ohio 43, and the whole Missouri above Omaha, 4 per cent. The
upper Missouri valley (that is, from the mouth of the Yellowstone up to
the sources), and the middle Missouri valley (from the mouth of the
Platte to the Yellowstone), each furnished only about 2 per cent. of
the entire amount of the water which passed Red River Landing. The
lower Mississippi valley, including the Arkansas, etc., furnished 32
per cent.
During March, April and May, 1882, the time of highest stage of the
water of the lower Mississippi, the outflow at Red River Landing and
through the Atchafalaya measured 82.7 cubic miles. During this time
there flowed through the upper Mississippi river above St. Louis, 14
per cent. of the amount; through the Ohio, 38 per cent., and through
the Missouri 6 per cent.; while the rivers of the lower Mississippi
valley contributed 41 percent. The water that passed Omaha was 1.92
cubic miles, or 2 per cent. of the flow of the whole Mississippi during
the same time. The water which flowed from the upper and middle
Missouri valleys during March, April and May, 1882, was for each
valley, probably only 1 per cent. of the water that flowed through the
lower Mississippi river. The flood of the lower Mississippi was
undoubtedly due to the great discharge of the Ohio, supplemented by
heavy river inflow below the mouth of the Ohio, and the unusually heavy
rainfall in the lower Mississippi valley.
The ratios of river outflow to rainfall over the catchment basins, as
derived by Professor Russell from the two years' observations, 1881 and
1882, were as follows:
Upper and Middle Missouri valleys, about 335,000 square miles, 13 per
cent.
Lower Missouri valley, about 210,000 square miles, 12 per cent.
Entire Missouri valley, about 545,000 square miles, nearly 13 per cent.
The upper Mississippi valley, about 172,000 square miles, 33 per cent.
Ohio valley, about 212,000 square miles, 40 per cent.
Lower Mississippi valley, about 343,000 square miles, about 27 per
cent.
The above percentages, while showing the averages for two entire years,
and so of decided value, are not to be depended upon for special years
or months. For instance: in the Ohio valley in 1881, the outflow was 33
per cent., while in 1882 it was 50 per cent., and as the rainfall in
1882 was 180 cubic miles against 151 cubic miles in 1881, it appears
evident that a much greater proportional quantity of water reaches the
rivers during seasons of heavy rainfalls than when the precipitation is
moderate or scanty.
Evaporation is also a very potent cause in diminishing river outflow,
and as this depends largely on the temperature of the air and the
velocity of the wind, any marked deviation of these meteorological
elements from the normal, must exercise an important influence on the
ratio of outflow to rainfall.
In connection with Professor Russell's work it is desirable to note
that Professor F. E. Nipher has lately made a report on the Missouri
rainfall based on observations for the ten years ending December, 1887,
in which he points out as an interesting coincidence that the average
annual discharge of the Missouri river closely corresponds in amount to
the rainfall which falls over the State of Missouri. From Professor
Nipher's figures it appears that the discharge of the Missouri river in
the ten years ending 1887, was greatest in 1881 and next greatest in
1882, so that the averages deduced from Professor Russell's report of
the outflow of the Missouri are too large, and should be somewhat
reduced to conform to the average conditions. In different years the
average of the discharge in the outflow of the Missouri varies largely,
as is evidenced by the fact reported by Professor Nipher, that the
discharge in 1879 was only 56 per cent. of the outflow in 1881.
In New South Wales, under the supervision of H. C. Russell, Esq.,
government astronomer, the question of rainfall and river discharge has
also received careful attention, especially in connection with
evaporation. The observations at Lake George are important, owing to
the shallowness of the lake (particularly at the margin); its
considerable surface area (eighty square miles), its moderate elevation
(2,200 feet), and the fact that it is quite surrounded by high lands.
Observations of the fluctuations of this lake have been made from 1885
to 1888, inclusive. In the latter year the evaporation was enormous,
being 47.7 inches against a rainfall of 23.9 and an in-drainage of 5.3
inches, so that the total loss in depth was 18.5 inches for the year.
It appears that the evaporation in different years on this lake varies
as much as 50 per centum of the minimum amount. According to Russell
the amount of evaporation depends largely on the state of the soil,
going on much faster from a wet surface of the ground than from water;
with dry ground the conditions are reversed. In 1887, the outflow from
the basin of Lake George, the drainage from which is not subject to
loss by long river channels, was only 3.12 per centum of the rainfall.
In the Darling river, above Bourke, says Russell, the rainfall is
measured by 219 gauges. The average river discharge, deduced from
observations covering seven years, is only 1.45 per centum of the
rainfall, and in the wettest year known the discharge amounted only to
2.33 per centum of the rainfall, and has been as low as 0.09 per centum
in a very dry year. In the Murray basin the average discharge relative
to the rainfall is estimated to be about 27 per centum from a record of
seven years, and has risen as high as 36 per centum in a flood year.
In connection with the regimen of rivers, it appears a proper occasion
to again refute the popular opinion that the spring and summer floods
of the Missouri and Mississippi valleys result from the melting of the
winter snows. This is an erroneous impression which I have combatted
since 1873, when my duties required a study of the floods of the entire
Mississippi catchment basin. It is only within the last two years,
however, that the meteorological data has been in such condition that
the opinion put forth by me could be verified, namely: that the floods
of the late spring and early summer owe their origin almost entirely to
the heavy rains immediately before and during the flood period.
Occasionally a very heavy fall of snow precedes extended general rains;
but in this case the snow is lately fallen and is not the winter
precipitation.
Referring to the Missouri valley, the section of the country where the
winter snowfall has been thought to exercise a dominating influence in
floods, it has elsewhere been shown by me that about one-third of the
annual precipitation falls over that valley during the months of May
and June. In either of the months named the average precipitation over
the Missouri valley is greater than the entire average precipitation
for the winter months of December, January and February.
Woiekoff thinks that the anomalies of temperatures shown in forest
regions, particularly in Brazil--with its abnormally low temperatures,
are due to heavy forests promoting evaporation, and by causing the
prevalence of accompanying fogs thus prevent more intense insolation.
He considers this an argument for the maintenance of forests to sustain
humidity and distribute rain over adjacent cultivated land, as well as
to maintain the fertility of the soil, which diminishes rapidly by
washing away of the soil after deforestation.