MAY 1934 MONTHLY WEATHER REVIEW 157
usual and that the proportion of organic matt,er was
considerably more than average. Minerals, loess, spores, plant-hairs, bits of decayed matter, glass, and trans-
parent crystals were readily isolated and detected. A flat beaker was placed on the roof of the solar radiation observatory a t noon of the l l t h , and taken
down 24 hours later. hlr. M. E. Jefferson, of the Bureau of Chemistry nnd Soils, kindly consented to make FL
petrographic analysis of the contents of this beaker and
his results are quoted herewith:
NOTE ON THE PETROLOGY OF THE DISTRICT OF COLUMBIA DUST
STORM OF MAY 11, 1934
In connection with the observations on the dust storm discussed
in the preceding paper, a sample of the dust was collected by Mr. I. F. Hand in an open beaker which was set out early on the 11th
and taken in on the 12th at noon when the dust had practically
disappeared from the air. The sample was examined under the petrographic microscope by immersion in the usual oils. Quartz and gypsum were present in amounts great enough to be readily identified, while calcite was found in very small amounts in the form of small size particles. Orthoclase and microcliiie were identified and apparently showed no alterations. Quartz and feldspar were found to be clear and unstained. Mica was present but appeared altered at the edges to such an extent that
identification was impracticable. It is apparently muscovite and biotite. There was considerable isotropic material in the sample, none of which, however, could be definitely classified. Conrhodid frag-
ments had indices ranging from 1.45 to 1.60 and a few flat irregular fragments had less than 1.43, usually low. The volcanic glass, hornblende, zircon, and tourmaline found by
Alexander (4 ) in the Buffalo dustfall were not identified as such
here. Measurement of the particle size gave the range of diameter or
length 0.001 mm to 0.13 mni with most of the mineral constituents in the range 0.005 to 0.04 nim. Winchell and Miller (5 ) found the range in the Madison dustfall to be 0.003 to 0.1 mm the quartz and feldspar in this case were stained with limonite and hematite. In the Buffalo storm Alexander reports lengths up to 0.05 mm.
There is considerable opaque material of rather large particle size (0.01 to 0.1 mm) which we have made no attempt to identify.
The organic material present in this dust storm is much greater
than that given by Alexander being at least 30 percent and consists
of spores, stellate plant hairs, and vegetable fibers. No attempt was made to classify the spores and plant hair present. In several tests diatoms were recognized.
Dr. Charles F. Brooks, Director, Blue Hill Meteoro- logical Observatory, Harvard University, Hyde Park,
Mass., transmits the followTing note from C. A. Chapman:
DUST FROM CIRCULAR GLASS PLATE 25 CM IN DIAMETER AT
MOUNT WASHINGTON, MAY 11 AFTER EXPOSURE ALL DAY
Amount of dust on the plate - 0.011 -grams. The dust is very fine and varies from 5-30 microns in diameter.
The average grain size is 10 microns. For the most part the individual particles are decidedly angular
and show no signa of frosting. The dust consists principally of quartz and feldspar which exist as clear colorless grains. Several spebies of diatoms are present but no attempt was made
to identify any of them. They occur as small, porous, plant-like forms. Other minerale identified as occurring in small amounts were sericite, green chlorite, iron oxides, and several aggregate masses
of very fine-grained amorphous material.
LITERATURE CITED
(1) Kimball, Herbert H., and Hand, Irving F.
(2) Hand, Irving F.
Investigation of the dust content of the atmosphere. Mo.Wea.Rev., 1924, v. 52, pp. 133-139. A Study of the Smoke Cloud over Wash- ington, D.C., on January 16, 1936. Mo.Wea.Rev., 1926, v.64, pp. 19-20. (3) Himball, Herbert H., and Hand, Irving F. Investigations of
Mo.Wea.Rev., 1925, the dust content of the atmosphere.
V. 53. DD. 243-246.
(4) Alexander, A. E. Petrology of the great dustfall of November 13,1933. Mo.Wea.Rev., 1934, v. 62, p. 15.
(5) Winchell and Miller. The dustfall of March 9, 1918. Amer. Jour.Sc., v. 46,1918, pp. 599-609.
HOW A COMMERCIAL PILOT MAY CONTRIBUTE TO A PROGRAM OF AIR-MASS
ANALYSIS BY OBSERVATIONS MADE DURING FLIGHT
By L. P. HARRISON
[Weather Bureau, Wmhington, D.C.]
The need for analyzing weather as a three-dimensional system rather than merely as a two-dimensional one, such as is exemplified by the customary synoptic charts, has,
among other things, brought about the regular daily use of airplane observations to heights of 17,000 feet or
over as a permanent adjunct of the weather service.
The planes now einployed in this service are few in cqm- parison with those in commercial use, hence there exists
the possibility of securing a valuable addition to the scheduled soundings by enlisting the aid of commercial
air pilots to record and make available meteorological observations made during their flights over the airways,
just as many years ago the aid of mariners was enlisted
for the collection of meteorological observations made on commercial vessels plying the trade routes of the Seven
Seas. In requesting the cooperation of pilots for the develop- ment of a program along this line, we should ask them to make their observations from the viewpoint which has
contributed most to modern meterology, viz, physical
weather analysis and air-mass analysis. However, before we may detail the character of the observations
desired, we must first make clear just what we mean by
these terms.
72827-34-2
The fundamental concept of this method of analysis is based on the realization that our weather is caused, in general, by the expenditure and transformation of stored
atmospheric energy (gravitational potential, and thermal) with the attendant interplay between air masses of
markedly contrasting temperatures which have come into juxtaposition after having moved away from different
respective regions over which they have recently been at rest, or wandering for a length of time sufficient to permit
the environments to bring them to a state in regard to
temperature, moisture content, and other features, more
or less t pica1 of these regions for the given time of year. The in (iy ividual air masses do not freely mis with one
another but tend to remain separate with more or less
sharply defined boundary surfaces, or surfaces of dis- continuity between them. Not infrequently, if not ordinarily, it is found that relatively thin transition
zones serve instead of distinctly marked surfaces of discontinuity. Usually, rather marked changes in the characteristics of the respective air masses are observable
as one crosses a surface of discontinuity, for the air masses on their travels tend to retain the characteristics
of temperature, moisture content, and other properties
which are normal for the regions from which they orig-
158 MONTHLY WEATHER REVIEW May 1934
inated. However, the varied physiographic and other conditions along the course over which the body of air
has traversed esert a profound modifying influence upon these characteristics, especially upon those in its lower
portion. The formation of any of the forms of moisture condensation within the air mass, or their precipitation through it, likewise produce therein important deviations
from the original distinguishing traits.
The surfaces of discontinuity we have already referred to are of great significance in air-mass analysis since,
besides delimiting the estent of the air masses and their subdivisions, they frequently represent the loci wherein
the transformation of energy, potential or latent, is initiated. If one were to make a series of airplnne ascents
periodically a t a given locality, carrying suitable mete-
orological instruments, he would discover the atmosphere to be stratified and would observe the heights of the sur-
faces of discontinuity between the strata to be gradually becoming greater or less. Moreover, he woulcl some-
times find that the distinctive meteorological qualities within each of the strata might be changing gradually as
the latter moved bodily along with the wind; however, this is not necessary since not infrequently the air masses closely approsimate to horizontal homogeneity in respect
to these qualities. Since the surfaces of discontinuity
are not level in general, some of them must intersect the surface of the earth. Where this occurs we have the
phenomenon known as a front, the passage of which over a place is attended ordinarily by well-marked changes
in conditions of temperature, wind, etc. With this very general statement of the immediate
causes of our weather, we do not commit ourselves too specifically as to the details of the mechanism of the cyclone and anticyclone, but leave to the future the
settlement of these questions. At this point we may indicate the position that air-
mass analysis holds among the principal steps leading up
to and including forecasting of the weather. This may
perhaps best be done by means of a synopsis such as the
following:
1. Weather obser0ation.-The observing of meteorolog-
ical phenomena and the noting of data representing them.
2. Physical weather ana.lysis.-A physical analysis of
the state of the atmosphere and the activities going on within it. (a ) Air-mass analysis. - Iden tifica tion and delinli tation of air masses, that is, analysis of the magnitudes and distribution of characteristic properties and other sig-
nificant meteorological elements of the air masses; class- ification of the air masses according to source-region and
principal modifications due to trajectory over land and water surfaces; and determination of the position, struc-
ture, nature, etc., of the various fronts and surfaces of
discontinuity (zones and layers of transition) or boun- daries of the air masses.
(b ) Dynamical weather analysis.- Analysis or diagnosis of the physical activities underlying given weather con-
ditions, that is, a study of present and past weather situa- tions to describe the nature of the activities, such as
precipitation, cloudiness, definite relative motions of adjacent air masses, etc., which are occurring in the given weather situation and to determine the physical causes
which are bringing and have brought these activities about.
In short, air-mass analysis is the determination of what air masses are present, how they are characterized, and where they are. Dynamical weather analysis is the
determination of what the air-masses are doing and why they are doing it.
This consists of two parts:
3. Jt7eather prediction.-Forecasting the state of the weather a t some future time on the basis of present and
past weather situa tions. (a) Synoptic projection.-The projection of the present
and past configurations of air masses, pressure systems, etc., into the future, allowing for the nature, magnitudes, and distribution of the air masses, forces, etc., which are
operating, and for any changes which may occur with
plnce and time as a result of the various factors involved. (b ) Dynamicnl weather projection. -The projection
from present and past configurations of air masses, pres- sure systems, weather conditions, activities, etc., into the
future, and then the indication or description of the meteorological activities such as precipitation, tempera-
ture changes, etc., which must most probably occur.
For the processes of identification and delimitation of air masses, we require the determination of all the import-
ant conservative or semi-conservative qualities or attri- butes to be found in the atmosphere, such as specific
humidity, potential temperature, equivalent potential temperature, and the like. These attributes of each
respective type of air mass permit us to put a labeling
tag, so to speak, upon each air mass and allow us to recognize a given air mass through the course of its vicissitudes. By means of continuous or periodic observa-
tions of the proper sort, we may note the progressive
changes which occur. In order to satisfactorily describe and understand the nature of these chnnges, it is neces-
sary for us to employ dynamically significant criteria. That is, it is not sufficient for us merely to study such
directly observable quantities as pressure, temperature, and relative humidity, but we must nlso study quantities which may be computed in terms of those just mentioned
and which have been deduced by means of mathematico- physical reasoning along the lines of dynnmical meteoro-
logy from a minimum of suitable premises. The import-
ance of this nppronch is seen in the fact that physical weather analysis on this basis N ill lead to a verification or
disproval of the premises underlying the derivation of the
relationships which are expressed numerically by the
quantities in question. Thus, the outcome of this mode
of attack will be a more nearly esact knowledge of the dynamics of the atsmosphere which is so essential to the
elevation of weather forecasting from the present semi-
physical methods to the desired mathematico-physical methods so successful in other fields. We may now return to the question of how a commercial
pilot may contribute to a program of air-mass analysis by
observations made during flight. Observations made from a commercial airplane with the ordinary equipment
carried thereon are of course limited in scope; however,
worthwhile results may be so obtained. The main objectives in such cooperative effort. would be:
1. The location of surfaces of discontinuities and fronts
in space and time, with description of conditions on both
sides of the discontinuities.
2. Determination of vertical motion in the atmosphere
when detectable, and observation of accompanying phenomena.
3. Observations of conditions during occurrence of various phenomena such as icing of airplanes, develop- ment of clouds from a three-dimensional aspect over a
period of time, etc. For every phenomenon reported by a pilot there should
always be given the following data:
(a ) Geographical position (with respect to known towns
or cities; or latitude and longitude).
(b ) Date.
(c) Time of day (and standard meridian time used).
MAY 1934 MONTHLY WEATHER REVIEW 159
(d) Altimeter reading, expressed as height above sea
level or above some specified point. (e) The barometric pressure a t which the altimeter would read zero altitude; place and time of take-off;
tem erature a t surface a t time of take-off. Temperature of the free air, read froni a strut thermometer, a t point of observation of phenomenon.
(g) General weather conditions a t time of observation,
including: Cloudiness-amount , kind, and heights of bases and tops of various cloud formations, if determined;
precipitation-kind, intensity, greatest and lowest heights
a t which observable. Some observations which are of assistance in attaining
the first objective, viz, the location of surfaces of discon- tinuity and fronts, follow:
1. Discontinuities in atmospheric turbidity, i.e., surjmes
across which marked changes in turbidity are obserrmb1e.- (a) Haze layers; (b ) dust layers; (c) tops and bases of
stratiform clouds; (d) top of fog, etc.; giving in each case the cause of the turbidity, its thickness, horizontal extent, visibility, and measure of turbidity expressed preferably
in some such scale of opalescent turbidity as Bergeron has given in his well-known work, tfber die Dreiclimen-
sional Verknupfende Wetteranalyse, I, Geofysiske Publik-
asjoner, vol. V, Oslo, 1930.
2. Thermal discontinuities.-The airplane should carry
a strut thermometer to detect such discontinuities. Due
to various diaculties only inversions of temperature (i.e. increase of temperature with height) are easily detectable
by means of a strut thermometer. Fronts also may be
easily detectable thereby.
3. Humidity discontinuities.-Conimercial airplanes usually are not equipped to measure relative humidity.
4. n*ind discontinuities.-Marked shifts in wind direc- tion, and rapid changes in speed with change in height
or change in horizontal position are observable from
mechanical effects on the flight of the airplane or from
changes in the drift of the ship when the ground is visible. Squalls and wind-shift lines such as are en-
countered near cold fronts and in connection with thun- derstorms, come under this heading.
As for the second object,ive mentioned above, there may be observed:
1. Bumpiness.-Bumpiness map be reported on a scale of 0-5, such as was given by W. H. Pick and G. A.
Bull in Great Britain Meteorological Office Professional Notes No. 46, A Note on Bumpiness at Cranwell, Lincolnshire, 1927; 0 , no bumps; 1, slight bumps;
3, occasional bumps; 3, bumpy; 4, very bumpy; 5, escep- tionally bumpy. Horizontal extent, nature of the terrain
and accompanying phenoniena, if noticeable, should also be given.
2 . Marked upward and clownirard large sccrle currents.-
These are most pronounced in spring and suniiner and usually in connection with cumulus and cuinulo-nimbus clouds (thunderheads). Also with the squall-line attend-
ing cold fronts. Such currents are detectable by rapid
vertical cloud motions and by differences in clinibing or
gliding speeds from the norinal for the given flying condi- tions.
The third objective given above applies to miscellaneous phenomena, e.g.:
1. Icing of airplane.-Ice which accumulates on air- planes should be classified as (a) hard ice; (b ) rime;
(c) frost. Hard ice is essentially the saine as glaze; however, it may be either clear or opaque (whitish). The thickness, physical appearance, place of formation,
teinperature of am, visibility in cloud (or rain) where formation occurred, rapidity of formation, etc., should also be given.
2. Development of clouds.-The aviator can frequently observe details in regard to the growth or disappearance
of clouds not easily obtainable from ground observations. Such information may possibly be of value in the final
analysis of what processes actually cause condensation of
water vapor into clouds and subsequent precipitation. In conclusion, it would appear feasible to prepare
printed forms on which commercial pilots could indicate the pertinent phenomena observed during flights, and to develop a system whereby the pilot would turn in these
reports to local weather observers at airports who would then forward them to the proper headqiiarters where
studies would be made of the accumulated data. Such
a cooperative effort might conceivably be of inestiinable value in the long run to both parties concerned by virtue
of the enhancement of our knowledge of the atmosphere and the improvement in forecasts.
The synopsis of weather analysis given earlier in the paper represents the consensus of opinion of officials at the Central Office of the Weather Bureau.
A STATISTICAL ANALYSIS OF FOGS AT GREENSBORO, N.C., AIRPORT
By JOHN C, SCHOLL
[Angier, N.C., May 19341
During the 4-year period, August 1929 to July 1933, general conditions and changes favorable to fog are well inclusive, fog occurred a t the Greensboro Airport 381 known. However, many of these fogs unquestionably times. Of this number 4 began as dense and ended as occurred as a result of purely local changes, some of
light, 1 was dense from start to finish, 116 began as light which were probably very slight and seemingly insig- but were dense some time, while the remaining 260 were nificant. Consequently the results of this study are light all the time. The average number per month of not entirely representative of the conditions which exist
light and dense fogs for this period was 7.9 and 2.5, in any locality other than the Greensboro Airport. respectively. Figure 1 substantiates the general opinion that both Each of these 381 cases was, of course, the result of light and dense fogs are more prevalent in the winter either general or local meteorological changes. The months. It is believed that if data were available for a